U.S. patent application number 11/225744 was filed with the patent office on 2007-03-15 for self-compensating blood pressure bleed valve.
This patent application is currently assigned to Welch Allyn, Inc.. Invention is credited to Allan I. Krauter, Richard W. Newman.
Application Number | 20070060825 11/225744 |
Document ID | / |
Family ID | 37856222 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070060825 |
Kind Code |
A1 |
Newman; Richard W. ; et
al. |
March 15, 2007 |
Self-compensating blood pressure bleed valve
Abstract
A bleed flow valve for venting air from a blood pressure cuff
includes a valve body having an axially extending central bore. The
central bore has a transition section, a fluid inlet port opening
into the central bore upstream of the transition section and a
fluid outlet port opening into the central bore downstream of the
transition section. A piston is disposed within the central bore of
the valve body and is axially translatable within the central bore
of the valve body. An annular orifice is defined between an outer
circumferential surface on the piston and the transition section of
the central bore. The bleed valve is self-compensating as the
pressure within the cuff decreases in that the piston self adjusts
axially within the central bore to adjust the area of the annular
orifice so as to maintain a relatively constant cuff pressure
change rate throughout the deflation process.
Inventors: |
Newman; Richard W.; (Auburn,
NY) ; Krauter; Allan I.; (Skaneateles, NY) |
Correspondence
Address: |
WALL MARJAMA & BILINSKI
250 SOUTH CLINTON STREET
SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
Welch Allyn, Inc.
Skaneateles Falls
NY
|
Family ID: |
37856222 |
Appl. No.: |
11/225744 |
Filed: |
September 13, 2005 |
Current U.S.
Class: |
600/498 |
Current CPC
Class: |
A61B 5/0235
20130101 |
Class at
Publication: |
600/498 |
International
Class: |
A61B 5/02 20060101
A61B005/02 |
Claims
1. A bleed valve for controlling the pressure change rate in a
reservoir of fluid under pressure when venting fluid therefrom
through said valve, said valve comprising: a valve body having a
central bore extending axially therethrough, the central bore
having a transition section transitioning from a relatively larger
diameter upstream of the transition section to a relatively smaller
diameter downstream of the transition section, a fluid inlet port
opening through said valve body into the central bore upstream of
the transition section, and a fluid outlet port opening through
said value body into the central bore downstream of the transition
section; a piston disposed within the central bore of said valve
body, said piston having an outer circumferential surface facing
the transition section of the central bore thereby establishing an
annular orifice defining a flow area between the outer
circumferential surface on said piston and the transition section
of the central bore, said piston being axially translatable within
the central bore of said valve body; a biasing device operatively
associated with said piston for exerting a force on said piston,
said biasing device acting to translate said piston in an upstream
direction in opposition to a fluid pressure force on said piston
acting to translate said piston in a downstream direction, whereby
said piston self adjusts axially within the central bore to vary
the flow area defined by the annular orifice so as to maintain a
relatively constant pressure change rate in said reservoir.
2. A bleed valve as recited in claim 1 wherein said biasing device
comprises a spring member and a preload device, said preload device
for compressing said spring member to establish an initial preload
force of said spring on said piston, said spring acting to
translate said piston in an upstream direction.
3. A bleed valve as recited in claim 2 wherein: said spring member
comprises a compressible coil spring disposed about a downstream
portion of said piston; and said preload device comprises a closure
member disposed within the central bore downstream of and abutting
said spring member, said closure member being selectively axially
positioned so as to adjust the preload force on said piston.
4. A bleed valve as recited in claim 1 wherein the transition
section comprises a step transition from the relatively larger
diameter to the relatively smaller diameter.
5. A bleed valve as recited in claim 4 wherein a portion of the
outer circumferential surface of the piston faces the step
transition section and has a tapered surface.
6. A bleed valve as recited in claim 1 wherein the transition
section comprises a tapered surface facing the outer
circumferential surface of said piston.
7. A bleed valve as recited in claim 6 wherein said piston has a
circumferential ridge extending thereabout.
8. A bleed valve as recited in claim 7 wherein the circumferential
ridge has a tapered outer circumferential surface.
9. A bleed valve as recited in claim 1 further comprising a first
closure member closing a first end of said valve body and a second
closure member closing a second end of said valve body.
10. A bleed valve as recited in claim 9 further comprising a low
pressure stop supported by said first closure member, said low
pressure stop being selectively axially translatable.
11. A bleed valve as recited in claim 10 wherein said first closure
member comprises an end cap.
12. A bleed valve as recited in claim 9 further comprising a high
pressure stop supported by said second closure member, said high
pressure stop being selectively axially translatable.
13. A bleed valve as recited in claim 12 wherein said second
closure member comprises an end plug.
14. A bleed valve as recited in claim 12 wherein said high pressure
stop limits translation of said piston so as to prevent the outer
circumferential surface of said piston from contacting the
transition section of the central bore.
15. A bleed valve for controlling the rate of change of pressure in
an inflated blood pressure cuff when venting air from the blood
pressure cuff to deflate the blood pressure cuff, said valve
comprising: an axially elongated valve body having a first end and
a second end and having a central bore extending axially
therethrough, the central bore having a first generally cylindrical
cavity, a second generally cylindrical cavity, and third cavity
disposed between the first and second cavities, said third cavity
having a transition section; a first closure member closing the
first end of said valve body; a second closure member closing the
second end of said valve body; a piston disposed within the central
bore of said valve body, said piston having a generally cylindrical
body including an outer circumferential surface on said valve body
facing the transition section of the central bore thereby
establishing an annular orifice defining a flow area between the
outer circumferential surface on said piston and the transition
section of the central bore, said piston being axially translatable
within the central bore of said valve body; a first port opening
through said valve body into said first cavity upstream of said
transition section, said first port pneumatically coupled to the
blood pressure cuff; a second port opening through said valve body
into said third cavity downstream of said transition section, said
second port being a vent; and a biasing device operatively
associated with said piston for exerting a force on said piston
acting to translate said piston in an upstream direction in
opposition to a fluid pressure force on said piston acting to
translate said piston in a downstream direction, whereby said
piston self adjusts axially within the central bore to vary the
flow area defined by the annular orifice so as to maintain a
relatively constant cuff pressure change rate.
16. A bleed valve as recited in claim 15 wherein said third cavity
of the central bore of said valve body has a tapered transition
section.
17. A bleed valve as recited in claim 15 wherein said piston has a
tapered outer circumferential surface facing the transition section
of the central bore.
18. A bleed valve as recited in claim 15 wherein said biasing
device comprises a spring member and a preload device, said preload
device for compressing said spring member to establish an initial
force of said spring on said piston, said spring acting to
translate said piston in an upstream direction.
19. A bleed valve as recited in claim 15 further comprising a low
pressure stop supported by said first closure member, said low
pressure stop being selectively axially translatable.
20. A bleed valve as recited in claim 15 further comprising a high
pressure stop supported by said second closure member, said high
pressure stop being selectively axially translatable.
21. A bleed valve as recited in claim 15 further comprising a vent
control valve operatively associated with said second port of said
bleed valve, said vent control valve being selectively positioned
in a first position wherein bleed flow can not vent through said
second port of said bleed valve to atmospheric pressure and a
second position wherein bleed flow can vent through said second
port of said bleed valve.
22. A bleed valve as recited in claim 15 wherein said piston self
adjusts axially within the central bore to vary the flow area
defined by the annular orifice so as to maintain a relatively
constant cuff pressure change rate substantially independently of
the size of the blood pressure cuff.
23. A bleed valve as recited in claim 15 further comprising a vent
control valve having: a vent control valve body having a cavity
therein, said vent control valve body having a first port opening
to the cavity and in flow communication with said blood pressure
cuff, a second port opening to the cavity and in flow communication
with said second port of said bleed valve, and a third port opening
to the cavity and venting to atmospheric pressure; and a member
operatively associated with said vent control valve body, said
member selectively positioned in a first position wherein neither
of the first port nor the second port of said vent control valve is
in flow communication with the third port of said vent control
valve, in a second position wherein only the second port of said
vent control valve is in flow communication with the third port of
said vent control valve, and a third position wherein only the
first port of said vent control valve is in flow communication with
the third port of said vent control valve.
24. A method for venting air from an inflated blood pressure cuff
through a bleed valve at a relatively constant cuff pressure change
rate comprising the steps of: providing an annular orifice between
an upstream cavity and a downstream cavity in said bleed valve, the
annular orifice providing a flow path having a variable flow area
between the upstream cavity and the downstream cavity; passing air
under pressure from the blood pressure cuff to the upstream cavity;
venting air from the downstream cavity; and automatically varying
the flow area of the flow path between the upstream cavity and the
downstream cavity in response to a change in the pressure of the
air within the upstream cavity so as to maintain said relatively
constant cuff pressure change rate.
25. A method as recited in claim 24 further comprising the step of
preventing an increase in the flow area of the flow path between
the upstream cavity and the downstream cavity in response to a
decrease in the pressure of the air within the upstream cavity to a
predetermined maximum flow area at a predetermined relatively low
pressure.
26. A method as recited in claim 24 further comprising the step of
preventing a decrease in the flow area of the flow path between the
upstream cavity and the downstream cavity in response to an
increase in the pressure of the air within the upstream cavity to a
predetermined minimum flow area at a predetermined relatively high
pressure.
27. A method as recited in claim 24 wherein the step of varying the
flow area of the flow path between the upstream cavity and the
downstream cavity in response to a change in the pressure of the
air within the upstream cavity comprises increasing the flow area
in response to a decrease in the pressure of the air within the
upstream cavity and decreasing the flow area in response to an
increase in the pressure of the air within the upstream cavity.
28. A method as recited in claim 27 further comprising the step of:
exerting a biasing force on a piston, said biasing force acting to
translate the piston in an upstream direction in opposition to a
fluid pressure force on the piston, the fluid pressure force acting
to translate the piston in a downstream direction, whereby the
piston self adjusts axially within the central bore to adjust the
annular orifice so as to maintain said relatively constant cuff
pressure change rate.
29. A method as recited in claim 28 further comprising the step of:
establishing an initial biasing force on the piston acting to
translate the piston in an upstream direction, whereby a desired
pressure change rate is preset.
30. A method as recited in claim 28 further comprising the step of:
adjusting the biasing force on the piston acting to translate the
piston in an upstream direction, whereby a desired pressure change
rate may be selectively set.
31. A method as recited in claim 28 further comprising the step of:
adjusting the biasing force on the piston acting to translate the
piston in an upstream direction in response to substantially large
changes in cuff size, whereby a desired pressure change rate may be
selectively set.
32. A method as recited in claim 28 further comprising the step of:
adjusting the biasing force on the piston acting to translate the
piston in an upstream direction in response to a heart rate of a
patient, whereby a desired pressure change rate may be selectively
set.
33. A method as recited in claim 24 wherein the step of providing
an annular orifice between an upstream cavity and a downstream
cavity in said bleed valve comprises providing a valve body having
a central bore extending axially therethrough and having a
transition section and an axially translatable piston disposed
within the central bore of the valve body, the piston having an
outer circumferential surface facing the transition section of the
central bore thereby defining the annular orifice.
34. A method as recited in claim 33 wherein the step of providing
an annular orifice between an upstream cavity and a downstream
cavity in said bleed valve further comprises providing a valve body
having a central bore having a tapered transition section.
35. A method as recited in claim 33 wherein the step of providing
an annular orifice between an upstream cavity and a downstream
cavity in said bleed valve further comprises providing a piston
having a tapered outer circumferential surface facing the
transition section of the central bore.
36. A method as recited in claim 33 further comprising the step of:
exerting a biasing force on the piston acting to translate the
piston in an upstream direction in opposition to a fluid pressure
force on said piston acting to translate said piston in a
downstream direction, whereby said piston self adjusts axially
within the central bore to adjust the annular orifice so as to
maintain a relatively constant cuff pressure change rate.
37. A method as recited in claim 24 wherein automatically varying
the flow area of the flow path between the upstream cavity and the
downstream cavity in response to a change in the pressure of the
air within the upstream cavity so as to maintain said relatively
constant cuff pressure change rate comprises automatically varying
the flow area of the flow path between the upstream cavity and the
downstream cavity in response to a change in the pressure of the
air within the upstream cavity so as to maintain said relatively
constant cuff pressure change rate substantially independently of
blood pressure cuff size.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the field of
blood pressure measurement devices and, more particularly, to a
nearly constant flow rate bleed valve for use in either manual or
automatic blood pressure measurement devices.
[0002] Blood pressure measurement devices, also referred to as
sphygmomanometers, of the type commonly used to measure arterial
blood pressure include an inflatable sleeve, commonly referred to
as a cuff, adapted to fit around a limb, e.g. an arm or leg, of a
patient. The cuff includes an interior chamber that is in fluid
communication with a device for selectively inflating the interior
chamber of the cuff with pressurized air. A gage is operatively
connected in fluid communication with the interior chamber of the
cuff for monitoring the air pressure within the cuff. A bleed valve
is also operatively connected in fluid communication with the
interior chamber to permit selective depressuring of the interior
chamber when it is desired to deflate the cuff.
[0003] In conventional manual sphygmomanometers, the interior
chamber of the cuff is connected through a length of flexible
tubing to a pneumatic bulb. In operation, the cuff is fitted, e.g.
wrapped, about the arm of the patient and, once so positioned; the
cuff is inflated by squeezing the pneumatic bulb to force air
through the tubing into the interior chamber of the cuff. Once the
interior chamber of the cuff has been inflated to a desired level,
as indicated on the pressure gage, the cuff is deflated by opening
the bleed valve to allow the pressurized air within the interior
chamber of the cuff to vent to atmosphere. A stethoscope is
positioned under the cuff and over the patient's artery to monitor
the patient's arterial pulses as the cuff deflates, thereby
allowing the systolic and diastolic blood pressures to be
determined by listening for the Korotkoff sounds. It can also be
done oscillometrically by detecting the minute changes in the cuff
pressure due to flow through the brachial artery.
[0004] Electronic oscillometric blood pressure measurement devices
that utilize an inflatable cuff are also known in the art. Such
devices generally employ one or more pressure sensing devices, such
as a transducer, to monitor the pressure within the interior
chamber of the cuff, as well as the minute changes in the cuff
pressure due to flow in the patient's artery, as the cuff deflates.
Electronic circuitry is provided that processes the signals from
the pressure sensing devices and determines the systolic and
diastolic blood pressures. A motor driven pump is usually provided
to inflate the cuff. However, the inflation can be done by a
pneumatic bulb. Typically, a digital display is provided for
displaying the systolic and diastolic blood pressures.
[0005] To obtain accurate measurements, it is necessary to deflate
the inflated cuff at a relatively constant rate in the range of
about 2 to about 3 millimeters mercury (2-3 mmHg) per second or
about 2 to about 3 millimeters mercury (2-3 mmHg) per heartbeat.
Maintaining a relatively constant bleed flow rate has been a
problem when using many prior art sphygmomanometers, particularly
when used by untrained personnel. In prior art sphygmomanometers,
the bleed commonly comprises a fixed orifice vent valve, that is a
valve which vents the interior chamber of the inflated cuff through
a fixed area port. With a fixed area port, the vent flow rate
varies as a function of the pressure differential across the port
at any given time in the venting process. As the pressure within
the interior chamber will continuously decrease during the
deflation process, the pressure differential, that is the
difference between the air pressure within the interior chamber of
the cuff and ambient pressure, will also continuously decrease.
Therefore, as the pressure differential across the vent port is
continuously decreasing, the vent flow rate will not remain
relatively constant during the deflation process, but rather will
continuously decrease. U.S. Pat. No. 4,690,171, for example,
discloses a bleed valve having a fixed air bleed orifice assembly
for metering the vent flow to slowly deflate the cuff and a
separate opening for rapid deflation of the cuff.
[0006] Constant-rate deflation valves using a flexible valve member
to vary the effective vent port area are known in the art for use
in connection with sphygmomanometers. For example, U.S. Pat. No.
5,833,620 discloses a constant rate deflator including a
ventilation adjusting shaft that has a recess formed on one end
thereof, and a ventilation valve having a hole formed at the center
thereof and a projection having almost the same shape as that of
the recess in the ventilation adjusting shaft. The ventilation
valve is made of a flexible material, such as rubber, whereby the
width of the clearance between the projection from the ventilation
valve and the valve recess increases as the pressure of the air
venting through the valve decreases such that the flow rate through
the clearance remains relatively constant. U.S. Pat. No. 5,143,077
also discloses a constant rate discharge valve for a
sphygmomanometer utilizing a flexible valve body to move a valve
stem to control vent port size in response to the pressure of the
fluid venting therethrough.
[0007] For proper functioning in controlling the rate of vent flow,
such constant-rate valves rely upon a predictable response of the
flexible valve member to changes in pressure differential across
the flexible member. Over repeated flexing, the potential exists
for such flexible members to lose some degree of flexibility and
even to crack or otherwise fail from fatigue after repetitive
flexure under pressure.
SUMMARY OF THE INVENTION
[0008] It is an object of one aspect of the invention to provide a
self-compensating bleed valve exhibiting a relatively constant
bleed flow rate.
[0009] It is an object of one aspect of the invention to provide a
relatively constant flow rate bleed valve that does not employ any
flexible diaphragm to adjust the flow area of vent port in response
to varying pressure differential across the vent port.
[0010] It is an object of one aspect of the invention to provide a
bleed flow valve for use in connection with deflating a blood
pressure cuff.
[0011] It is an object of one aspect of the invention to provide a
method of deflating a blood pressure cuff.
[0012] In one aspect of the invention, a bleed flow valve is
provided for controlling the pressure change rate in a reservoir of
fluid under pressure when venting fluid therefrom through the
valve. The bleed valve includes a valve body having a central bore
extending axially therethrough. The central bore has a transition
section, a fluid inlet port opening into the central bore upstream
of the transition section and a fluid outlet port opening into the
central bore downstream of the transition section. The transition
section may be provided by a step change from a larger diameter
upstream cavity to a smaller diameter downstream cavity or by an
inwardly tapered surface extending between a larger diameter
upstream cavity and a smaller diameter downstream cavity. A piston
is disposed within the central bore of the valve body and is
axially translatable within the central bore of the valve body. The
piston includes an outer circumferential surface facing the
transition section of the central bore. An annular orifice is
defined between the outer circumferential surface on the piston and
the transition section of the central bore. A biasing device
operatively associated with the piston exerts a force on the piston
acting to translate the piston in an upstream direction in
opposition to a fluid pressure force on the piston acting to
translate the piston in a downstream direction. In this manner, the
bleed valve of the invention is self-compensating as the pressure
within the reservoir decreases in that the piston self adjusts
axially within the central bore to adjust the area of the annular
orifice so as to maintain a relatively constant pressure change
rate in reservoir pressure throughout the venting process.
[0013] In one embodiment, the biasing device comprises a spring
member and a preload device for compressing the spring member to
establish an initial preload force on the piston acting to
translate the piston in an upstream direction. The spring member
may be a compressible coil spring disposed about a downstream
portion of the piston. The preload device may be a closure member
disposed within the central bore downstream of and abutting the
spring member, the closure member being selectively axially
positioned so as to adjust the preload force on the piston.
[0014] In an embodiment, the outer circumferential surface on the
piston may be a tapered outer circumferential surface. In another
embodiment, the outer circumferential surface may be provided on a
circumferential ridge extending about the piston. In another
embodiment, a circumferential ridge having an tapered outer
circumferential surface may be provided on the piston.
[0015] In an embodiment, a first proximal closure member closes the
first end of the valve body and a second distal closure member
closes the second end of the valve body. Further, a low pressure
stop that is selectively axially translatable may be supported by
the first closure member and a high pressure stop that is
selectively axially translatable may be supported by the second
closure member.
[0016] In a further aspect of the invention, a bleed flow valve is
provided for controlling the pressure change rate experienced by a
flow of air under pressure venting from a blood pressure cuff. The
valve includes an axially elongated valve body having a first end,
a second end, and a central bore extending axially therethrough.
The central bore has a first generally cylindrical cavity, a second
generally cylindrical cavity, and third cavity disposed between the
first and second cavities with the third cavity having a tapered
transition section. A first closure member closes the first end of
the valve body and a second closure member closes the second end of
the valve body. A piston is disposed within the central bore of the
valve body. The piston has a generally cylindrical configuration
and includes a tapered outer circumferential surface facing the
tapered transition section of the central bore, thereby defining an
annular orifice between the tapered outer circumferential surface
on the piston and the tapered transition section of the central
bore. The piston is axially translatable within the central bore of
the valve body. A first port, which opens through the valve body
into the first cavity upstream of the tapered outer circumferential
surface on the piston, is pneumatically coupled to the blood
pressure cuff. A second port, which opens through the valve body
into the second cavity downstream of the tapered outer
circumferential surface on the piston, provides a vent hole. A
biasing device operatively associated with the piston exerts a
force on the piston acting to translate the piston in an upstream
direction in opposition to a fluid pressure force on the piston
acting to translate the piston in a downstream direction. In this
manner, the bleed valve of the invention is self-compensating as
the pressure within the reservoir decreases in that the piston self
adjusts axially within the central bore to adjust the area of the
annular orifice so as to maintain a relatively constant cuff
pressure change rate throughout the venting process. The piston
self adjusts axially within the central bore to vary the flow area
defined by the annular orifice so as to maintain a relatively
constant cuff pressure change rate substantially independently of
the size of the blood pressure cuff.
[0017] In one embodiment, the biasing device comprises a spring
member and a preload device for compressing the spring member to
establish an initial preload force on the piston acting to
translate the piston in an upstream direction. The spring member
may be a compressible coil spring disposed about a downstream
portion of the piston. The preload device may be a closure member
disposed within the central bore downstream of and abutting the
spring member, the closure member being selectively axially
positioned so as to adjust the preload force on the piston.
Advantageously, the first closure member may be an end cap and the
second end closure may be an end plug. Further, a low pressure stop
that is selectively axially translatable may be supported by the
first closure member and a high pressure stop that is selectively
axially translatable may be supported by the second closure
member.
[0018] In one embodiment, a selectively positioned vent control
valve is operatively associated with the bleed valve to provide for
selectively closing the second port of the bleed valve or opening
the second port of the bleed valve to vent to atmosphere pressure.
Advantageously, the vent control valve may include a valve body
having a cavity therein having a first port opening to the cavity
and in flow communication with the blood pressure cuff, a second
port opening to the cavity and in flow communication with the
second port of the bleed valve, and a third port opening to the
cavity and venting to atmospheric pressure. A selectively
positionable member is operatively associated with the valve body.
The member is selectively positioned in a first position wherein
neither of the first port or the second port of the vent control
valve is in flow communication with the third port of the vent
control valve, in a second position wherein only the second port of
the vent control valve is in vent communication with the third port
of the flow control valve, and a third position wherein only the
first port of the vent control valve is in flow communication with
the third port of the vent control valve.
[0019] In a further aspect of the invention, a method is provided
for venting an inflated blood pressure cuff through a bleed valve
at a relatively constant cuff pressure change rate. The method
includes the steps of: providing an annular orifice having a
variable flow area between an upstream cavity and a downstream
cavity; passing air under pressure from the blood pressure cuff to
the upstream cavity; venting air from the downstream cavity; and
varying the flow area of the flow path between the upstream cavity
and the downstream cavity in response to a change in the pressure
of the air within the upstream cavity so as to maintain a
relatively constant cuff pressure change rate. Further, the method
may include the step of preventing an increase in the flow area of
the flow path between the upstream cavity and the downstream cavity
in response to a decrease in the pressure of the air within the
upstream cavity to a predetermined maximum flow area at a
predetermined relatively low pressure. The method may also include
the step of preventing a decrease in the flow area of the flow path
between the upstream cavity and the downstream cavity in response
to a change in the pressure of the air within the upstream cavity
to a predetermined minimum flow area at a predetermined relatively
high pressure.
[0020] The method may include the step of exerting a biasing force
on the piston acting to translate the piston in an upstream
direction in opposition to a fluid pressure force on the piston
acting to translate the piston in a downstream direction, whereby
the piston self adjusts axially within the central bore to adjust
the annular orifice so as to maintain a relatively constant cuff
pressure change rate. The method may include the step of
establishing an initial biasing force on the piston acting to
translate the piston in an upstream direction, whereby a desired
cuff pressure change rate is preset. The method may include the
step of adjusting the biasing force on the piston acting to
translate the piston in an upstream direction, whereby a desired
cuff pressure change rate may be selectively set. The biasing force
may be adjusted in response to a change cuff size from that for
which the biasing force was preset; or in response to heart rate of
the patient being significantly different from the normal heart
rate for which the biasing force was preset.
[0021] In another aspect, a method is provided for automatically
varying the flow area of the flow path between the upstream cavity
and the downstream cavity in response to a change in the pressure
of the air within the upstream cavity so as to maintain said
relatively constant cuff pressure change rate substantially
independently of blood pressure cuff size.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a sectional elevation view of a particular
embodiment of a bleed flow valve in accordance with the present
invention;
[0023] FIG. 2 is an exploded elevation view, partly in section, of
the end cap and low pressure stop assembly of the bleed flow valve
of FIG. 1;
[0024] FIG. 3 is an exploded elevation view, partly in section, of
the end plug and high pressure stop assembly of the bleed flow
valve of FIG. 1;
[0025] FIG. 4 is a cross-section view taken along line 4-4 of FIG.
3;
[0026] FIG. 5 is an exploded side elevation view, partly in
section, of the valve body and piston of the bleed flow valve of
FIG. 1;
[0027] FIG. 6 is a cross-section view taken along line 6-6 of FIG.
5;
[0028] FIG. 7 is an enlarged side elevation view of the conical
transition section of the valve body of the bleed flow valve of
FIG. 1 illustrating the piston in a first operational position and
a second operational position; and
[0029] FIGS. 8A, 8B and 8C are elevation views, partly in section,
of the bleed flow valve of FIG. 1 connected in operative
association with a three position vent control valve, with the vent
control valve in its first, second and third positions
respectively.
DETAILED DESCRIPTION
[0030] Referring now to FIGS. 1 through 6, the bleed valve 10
includes an axially elongated body 30 defining a centrally disposed
and axially elongated central bore 32, closed at one end by a first
end fitting supporting a low pressure stop 42, and closed at its
other end by a second end fitting supporting a high pressure stop
52. A first set of threads 31 is provided on the exterior surface
of the body 30 at one end thereof and a second set of threads 33 is
provided on the surface of the bore 32 at the other end of the body
30 of the bleed valve 10. As will be discussed in further detail
hereinafter, the central bore 32 of the body 30 has a central
cavity 35 disposed between a pair of axially spaced, larger
diameter end cavities 37 and 39.
[0031] In the embodiment shown, the first end fitting comprises an
end cap 40 provided with a set of threads 41 on an internal end
bore 43 that are compatible with the first set of threads 31 on
body 30 whereby the end cap 40 may be releaseably mounted to the
body 30 by screwing the set of threads 41 onto the set of threads
31. A circumferential seal 91, for example an O-ring seal, is
disposed in the bore 43 of the end cap 40 intermediate the body 30
and the end cap 40 and is supported in a circumferential groove 92.
The circumferential groove 92 may be formed in the exterior surface
of the body 30, as shown in the depicted embodiment, or formed in
the surface of the bore 43 in the end cap 40.
[0032] Additionally, the end cap 40 has a central bore 45 in its
end surface which extends to and opens into the bore 43 of the cap
40. The low pressure stop 42 has a head 44, a shaft 46 extending
from the head 44, and a tip 48 that extends axially from the shaft
46 into the bore 32 of the body 30. A circumferential seal 93, for
example an O-ring seal supported in a circumferential groove 94, is
disposed in the central bore 45 of the end cap 40 to seal the
clearance between the surface of the bore 45 in the end cap 40 and
the shaft 46 of the low pressure stop 42. The circumferential
groove 94 may be formed in the surface of the low pressure stop 42,
as shown in the depicted embodiment, or formed in the surface of
the central bore 45. The tip 48 has threads 47 by means of which
the low pressure stop 42 may be threaded into threads 49 provided
in the surface of the passage between the central bore 45 and the
end bore 43 of the end cap 40. Advantageously, the low pressure
stop 42 may be selectively axially adjustable within the central
bore 45 by screwing or turning the head 44 of the low pressure stop
42 either clockwise or counter clockwise thereby selectively
positioning the tip 48 of the low pressure stop 42 within end
chamber 37 of the bore 32 of the body 30.
[0033] In the embodiment shown, the second end fitting comprises an
end plug 50 provided with a set of threads 51 on its outer surface
that are compatible with the second set of threads 33 on body 30
whereby the end plug 50 may be releaseably mounted to the body 30
by screwing the set of threads 51 into the second set of threads 33
on the body 30. Referring now in particular to FIGS. 3 and 4, the
end plug 50 has a body 54 having a tip 58 that extends axially
therefrom and a central bore 55 that extends axially through the
body 54 and tip 58, the portion of the bore 55 extending through
the body 54 being provided with threads 53. The tip 58 of the end
plug 50 may have a plurality of circumferentially spaced, axially
extending slits 68 provided therein for providing air communication
passages between the upper portion of central bore 55 and central
bore 32. The high pressure stop 52 has a tip 56 that extends
axially inwardly into the bore 55 of the end plug 50. The tip 56 of
the high pressure stop has threads 57 compatible with the threads
53 on the central bore 55 through the end plug 50 whereby the high
pressure stop 52 may be threaded into the end plug 50.
Advantageously, the high pressure stop 52 may be selectively
axially adjustable within the central bore 55 by turning the head
98 at the end of the body 54 of the high pressure stop 52 either
clockwise or counter clockwise thereby selectively positioning the
end face 59 of tip 56 of the high pressure stop 52 within the bore
55 of the end plug 50.
[0034] As noted hereinbefore, the axially elongated bore 32 of the
body 30 of the valve 10 includes a central chamber 35 disposed
between a pair of axially spaced, relatively larger diameter,
generally cylindrical, end cavities 37 and 39, as best seen in FIG.
5. The central cavity 35 includes a relatively smaller diameter
cylindrical section 63 and a conical section 65 that forms a
transition between the relatively larger diameter end section 37
and the relatively smaller diameter section 63 of the central
cavity 35. A first port 60 extends through the body 30 to open into
the end cavity 37. A second port 62 extends through the body 30 to
open into section 63 of the central cavity 35. The conical
transition section 65 of the central cavity 35 lies intermediate
the first port 60 and the second port 62 and tapers inwardly from
cavity 37 to section 63 of the central cavity 35 at a angle of
approximately ten degrees relative to the axis of the bore 32
through the valve body 30. However, one skilled in the art will
understand that other angles of taper may be used without departing
from the teachings of the invention.
[0035] Referring now to FIGS. 5 and 6 in particular, the valve 10
further includes a piston 70 adapted to be disposed within the
axially elongated bore 32 of the body 30 and operatively associated
with the body 30 for axial translation within the axially elongated
bore 32. The piston 70 includes a head 72, which may have one or
more holes 99 passing therethrough to reduce the overall weight of
the piston 70, and a shaft 76. The generally cylindrical shaft 76
extends axially from a distal end of the head 72 of the piston 70
and into the bore 55 in the tip 58 of the end cap 50. The head 72
includes a plurality of guide members 74 extending radially
outwardly from a proximal end of the head 72. In this manner, the
piston 70 is supported at its opposite ends with the guide members
74 bearing on the inner wall of cavity 37 of the central bore 32 at
its proximal end and with the shaft 76 bearing on the inner wall of
the tip 58 of the end cap 50 at its distal end. The wide spacing
between these bearing surfaces ensures stability in translation of
the piston 70 within the central bore 32 of the body 30 of the
valve 10 and decreased sensitivity to variation in tolerances which
could otherwise result in rocking. Further, the circumferentially
spaced slits 68 in the tip 58 of the high pressure stop serve as
vent channels for venting flow as the piston translates within the
bore 32, thereby preventing pressure build-up that could otherwise
hinder proper translation of the piston. The flow passages 88
between the circumferentially spaced guide members 74 of the piston
70 ensure that the entire cavity 37 of the valve body has the same
air pressure.
[0036] A spring member 80 is disposed about the shaft 76 between
the distal end of the body 72 and the end face 78 of the tip 58 of
the end cap 50 which serves as a stop for the spring member 80. The
spring member 80 may be a resilient compression coil spring, such
as shown in the depicted embodiment, or other type of resilient
member capable of compression and expansion.
[0037] Referring again now to FIG. 1, the first port 60, which
opens to cavity 37 of the central bore 32 in the body 30 of the
bleed valve 10, is adapted to receive fluid flow from a conduit 100
that is in flow communication with a volume of fluid under
pressure, for example a blood pressure measurement cuff (not
shown). A fitting 102 may be provided, either as a separate
component or as an integral part of the valve body 32, as a means
for connecting the conduit 100 to the first port 60. In the
depicted embodiment, the conduit 100 comprises a tube connected to
a blood pressure cuff or blood pressure gage of a blood pressure
measurement device (not shown), and the fitting 102 comprises a
conventional threaded fitting of the type commonly employed with
blood pressure tubing. The fitting 102 has a threaded stem which is
screwed into threads provided in the port 60 and a tapered nipple
extending outwardly therefrom and adapted to be received in sealing
engagement into the conduit 100. The second port 62, which opens to
the relatively smaller diameter cylindrical section 63 of the
central cavity 35, serves as a vent port through which fluid
flowing into the bleed valve 10 through the first port 60 may be
vented to a low pressure, typically ambient pressure, environment
exterior of the valve 10.
[0038] In operation, the first port 60 lies upstream of the conical
transition section 65 of the central cavity 35 with respect to
fluid flow through the central bore 32 of the valve 10 and the
second port 62 lies downstream of the conical transition section 65
of the central cavity 35 with respect to fluid flow through the
central bore 32 of the valve body 30. In accord with one aspect of
the invention, a circumferential ridge 75 is provided on the piston
72 as a means of throttling fluid flow through the central bore 32
of the valve body 30. In the embodiment depicted in FIG. 7, the
circumferential ridge 75 has a radially outward surface 77
extending about the circumference thereof that is axially tapered
inwardly from its upstream end to its downstream end at an angle of
approximately ten degrees relative to the axis of the bore 32
through the valve body 30. However, one skilled in the art will
understand that other angles of taper may be used without departing
from the teachings of the invention. Those skilled in the art will
also understand that the outer surface of circumferential ridge is
not limited to a tapered surface, but rather may take other shapes,
including for example planar, arcuate or any other desired shape,
that in operative association with the valve body provides an
annular orifice defining a flow area that is variable with axial
translation of the piston 70.
[0039] The circumferential ridge 75 is disposed within the conical
transition section 65 of the central cavity 35 and translates
axially within the conical transition section 65 as the piston
translates. In cooperation, the tapered wall 67, best seen in FIG.
7, of the valve body 30 within the conical transition section 65
and the tapered surface 77 of the circumferential ridge 75 on the
piston 72 form an annular orifice 85 therebetween. As the piston 70
translates axially within the central bore 32 of the valve body 30
under the influence of varying pressure in the cavity 37, the flow
area provided through the annular orifice 85 will change, becoming
smaller as the piston 72 translates axially toward the high
pressure stop 52 and becoming larger as the piston 72 translates
axially toward the low pressure stop 42. All throttling of the flow
occurs at this orifice which is always positioned between the
bearing surfaces of the piston within the valve body.
[0040] When the valve 10 is connected to a blood pressure
measurement device, or other reservoir of pressurized fluid,
typically air, fluid flow will enter the cavity 37 through the
first port 60 and establish a pressure within the cavity 37 that
will be approximately equal to the cuff pressure. The fluid flow
entering through the first port 60 will fill the cavity 37 and
exert a force on the end face 71 of the piston 72 that will act
against the force exerted by the coil spring 80 on the piston 72.
The force exerted by the fluid pressure within the cavity 37 upon
the piston 72 will cause the piston to translate axially towards
the high pressure stop 52. As the piston translates toward the high
pressure stop 52, as illustrated by position A in FIG. 7, the
annular orifice 85 established between the tapered surface 77 of
the circumferential ridge 75 on the piston 72 and the tapered wall
67 of the valve body 30 will narrow, thereby resulting in a
decrease in the flow area through the annular orifice 85. As the
pressure within the cavity increases with an increase in cuff
pressure, the piston 72 will continue to translate axially toward
the high pressure stop 52 until either an equilibrium of the
respective forces due to air pressure and the spring pressure
occurs or the end face 79 of the piston shaft 76 abuts against the
end face 59 on the tip 56 of the high pressure stop 52. The high
pressure stop 52 can be adjusted by turning the head 58 of the high
pressure stop 52 counter-clockwise or clockwise to selectively
position the end face 59 of the tip 56 of the high pressure stop
within the cavity 39, thereby selectively limiting the travel of
the piston 72 to ensure that the flow area provided by the annular
orifice 85 does not decrease below a desired lower limit. In this
manner, the high pressure stop 52 can be set to ensure that bleed
flow can not be completely shut off, thereby protecting against the
cuff being inflated to an excessive pressure.
[0041] Conversely, as the pressure within the cavity 37 decreases,
for example during deflation of the cuff, the piston translates
toward the low pressure stop 42, as illustrated by position B in
FIG. 7. The annular orifice 85 established between the tapered
surface 77 of the circumferential ridge 75 on the piston 72 and the
tapered wall 67 of the valve body 30 will enlarge, thereby
resulting in an increase in the flow area through the annular
orifice 85. As the pressure within the cavity decreases with a
decrease in cuff pressure, the piston 72 will continue to translate
axially toward the low pressure stop 42 until an equilibrium of the
respective forces due to air pressure and the spring pressure
occurs or the end face 71 of the piston 72 contacts against the end
of the tip 48 of the low pressure stop 42. The low pressure stop 42
can be adjusted by turning the head 44 of the low pressure stop 42
counter-clockwise or clockwise to selectively position the end of
the tip 48 of the low pressure stop within the cavity 37, thereby
selectively limiting the travel of the piston 72 to ensure that the
flow area provided by the annular orifice 85 does not increase
above a desired upper limit. With the high and low pressure stops
properly adjusted, the tapered surface 77 on the circumferential
ridge 75 on the piston 72 and the tapered wall 67 of the valve body
30 will never contact thereby ensuring no wear of the piston or
valve in the throttling region. Further, because these surfaces
will not contact, flow will always be able pass through the orifice
85 to "clean" this region and preclude potential build-up of dust
or other debris in this region.
[0042] The flow rate of fluid flow passing through the annular
orifice 85 will change as a function of the flow area provided by
the annular orifice 85. When the pressure within the cavity 37 is
high, the flow area provided by the annular orifice 85 is
relatively small. Conversely, when the pressure within the cavity
37 is low, the flow area provided by the annular orifice 85 is
relatively large. As the pressure within the cavity 37 decreases
during fluid passage through the annular orifice from the cavity 37
into section 63 of the central cavity 35 and out the vent port 62,
the flow area at the annular orifice 85 increases, thereby
resulting in an increase in the bleed flow rate and thereby also
tending to maintain a constant cuff pressure decrease rate.
Therefore, the bleed flow valve 10 is self-compensating in that the
flow area changes inversely with the pressure within the cavity 37
and therefore inversely to the cuff pressure or pressure within
whatever reservoir to which the first port 60 is connected. The
self-compensating characteristic of the bleed flow valve 10 of the
invention enables the cuff or reservoir bleed pressure change rate
to effectively be maintained at a relatively constant value over a
major portion of the pressure bleeding process.
[0043] In normal operation, the pressure change rate is controlled
by the equilibrium balancing between the opposing air pressure and
spring forces on the piston. The low pressure stop 42 and the high
pressure stop 52 do not control the cuff pressure change rate
during normal operation, but rather serve to provide limits on the
minimum cuff pressure change rate and maximum cuff pressure change
rate. The spring member 80 and its preload are selected to provide
a desired spring characteristic that will ensure a cuff pressure
change rate within a specified range of desired cuff pressure
change rates. End plug 50 serves to preload the spring 80. The
preload on the spring 80 may be adjusted as desired simply by
turning the end plug 50 clockwise or counterclockwise. The preload
on the spring 80, in conjunction with the spring geometry and the
taper angles, determine the operational characteristic of the valve
10, that is the bleed pressure change rate of the cuff. The desired
cuff pressure change rate can be set at the factory to the
recommend rate or can be set or adjust by a skilled medical
practitioner by adjusting the preload on the spring 80 as
previously discussed.
[0044] The self-compensating characteristic of the bleed flow valve
10 of the invention offers a distinct advantage when used in
connection with blood pressure measurement devices, such as
manually operated sphygmomanometers and automated electronic blood
pressure monitors. By proper positioning of the low pressure stop
42 and the high pressure stop 52, and by proper adjustment of the
preload on the spring 80, the bleed pressure change rate during
deflation of the blood pressure cuff may be constrained within
desired minimum and maximum limits, or near the desired 2-3 mm Hg
per second rate. In traditional manually operated
sphygmomanometers, the user must continually adjust the valve as
the pressure decreases to attempt to maintain a relatively constant
cuff pressure change rate. Conventionally, automated electronic
blood pressure monitors are provided with pressure transducers and
an electronic circuitry that automatically controls and adjusts a
bleed valve as pressure decreases so as to maintain a relatively
constant pressure drop rate. The required pressure transducers,
electronic circuitry and electronically-controlled bleed valve are
expensive.
[0045] The bleed valve 10 of the present invention may
advantageously be employed in operative association with an on/off
vent valve, particularly in blood pressure measurement
applications. For example, a conventional thumb screw valve, such
as commonly included in association with the inflation bulb on
manual blood pressure sphygmomanometers, may be operatively
associated with the vent port 62 of the bleed valve 10 for enabling
the user to selectively open or close the vent port 62. When
inflating the blood pressure cuff, the user would position the
thumb screw vent valve in a fully closed position. When the cuff
has been inflated to the desired pressure level, the user would
simply reposition the thumb screw valve to its fully open position
and the bleed valve 10 would control the rate of deflation of the
cuff as hereinbefore described to maintain a relatively constant
cuff pressure change rate throughout the deflation process.
[0046] However, in blood pressure measurement applications, it may
be desirable, for example for patient comfort, to rapidly deflate
the cuff once the diastolic blood pressure measurement has been
completed. Referring now to FIGS. 8A, 8B and 8C, the bleed valve 10
is coupled in operative association with a vent control valve 120
that is selectively positioned by the user amongst a first
position, illustrated in FIG. 8A, wherein the vent port 62 of the
bleed valve 10 is closed for inflation of the blood pressure cuff,
a second position, illustrated in FIG. 8B, wherein venting of the
cuff during deflation is controlled through the bleed valve 10, and
a third position, illustrated in FIG. 8C, wherein the cuff is
rapidly deflated directly through the vent control valve 120.
[0047] In the exemplary embodiment depicted in FIGS. 8A, 8B and 8C,
the vent control valve 120 includes an axially elongated body 122
having an axially aligned central bore 124 extending therethrough
and an axially elongated plunger rod 126 disposed within the
central bore 124. The plunger rod 126 is adapted to be axially
translatable within the central bore 124 among the aforementioned
first, second and third positions. The valve body 122 is provided
with a first port 121 at a proximal end of valve body, a second
port 123 at a distal end of the valve body, and a third port 125
intermediate the first and second ports. Each of the ports 121, 123
and 125 extends generally radially through the valve body 122 to
open into the central bore 124 thereby establishing a flow path
through the wall of the valve body. The first port 121 is coupled
to the conduit 100 via branch conduit 101. Thus, port 60 of the
bleed valve 10 and the first port 121 of the vent control valve 120
are directly connected to the conduit 100, which in the depicted
embodiment comprises a tube connected to a blood pressure cuff (not
shown). The second port 123 of the vent control valve 120 is
connected via conduit 104 directly to the second port 62, i.e. the
vent port, of the bleed valve 10. The third port 125 of the vent
control valve 120 serves as a vent port for venting the central
bore 124 of the vent control valve 120 to a low pressure
environment, typically to atmospheric pressure. Generally, the
third port 125 may simply be open directly to the atmosphere.
[0048] The central bore 124 is sealed at the proximal and distal
ends of the valve body 120 by means of seals 128 and 129,
respectively. The seals 128 and 129 seal the gap between the
axially translatable plunger rod 126 and wall of the valve body 120
defining the central bore 124. Each of the seals 128 and 129 may
constitute an O-ring of conventional sealing material carried in
circumferential glands provided in the wall bounding the central
bore 124. Additionally, a pair of axially spaced ring seals 130 and
132 is carried in corresponding circumferential grooves on the
plunger rod 126. As with the seals 128 and 129, the ring seals 130
and 132 also seal the gap between the axially translatable plunger
rod 126 and wall of the valve body 120 defining the central bore
124. Therefore, three sealed cavities are established within the
central bore 124 of the valve body 122 irrespective of the position
of the plunger rod 126 within the central bore 124. A first cavity
133 is formed between the proximal seal ring 128 and the ring seal
130, a second cavity 135 is formed between the axially spaced seal
rings 130 and 132, and a third cavity is formed between the ring
seal 132 and the distal seal ring 129.
[0049] Referring now to FIG. 8A in particular, with the plunger rod
126 positioned as depicted in the first position within the valve
body 122, the first port 121 opens to the first cavity 133, the
second port 123 opens to the third cavity 137 and the third port
125 opens to the second cavity 135. Thus, in the first position,
the vent port 62 of the bleed valve 10 is effectively closed in
that the vent port 62 is coupled in flow communication through the
conduit 104 and the second port 123 with the sealed cavity 137.
Similarly, conduit 100 from the cuff is coupled in flow
communication through branch conduit 101 and the first port 121
with the sealed cavity 133. The third port 125 opens to the sealed
cavity 135. Therefore, the first position constitutes the "off" or
closed position for the vent control valve 120 in that the vent
port 62 of the bleed valve 10 is not in flow communication with the
third port 125, i.e. the vent port, of the vent control valve 120.
The vent control valve 120 is selectively positioned in this first
position whenever it is desired to inflate the blood pressure
cuff.
[0050] Referring now to FIG. 8B in particular, with the plunger rod
126 positioned as depicted in the second position within the valve
body 122, the first port 121 again opens to the first cavity 133,
the third port 125 again opens to the second cavity 135, but the
second port 123 now also opens to the second cavity 135. Thus, in
the second position, the vent port 62 of the bleed valve 10 is
coupled in flow communication with the third port 125 of the valve
body 122 through the conduit 104, the second port 123 and the
second cavity 135. Conduit 100 from the cuff remains coupled in
flow communication through branch conduit 101 and the first port
121 with the sealed cavity 133. Therefore, the second position
constitutes the "on" or first open position for the vent control
valve 120 in that the vent port 62 of the bleed valve 10 is now in
flow communication with the third port 125, i.e. the vent port, of
the vent control valve 120. The vent control valve 120 is
selectively positioned in this second position whenever it is
desired to deflate the blood pressure cuff in a controlled manner
through the bleed valve 10.
[0051] Referring now to FIG. 8C in particular, with the plunger rod
126 positioned as depicted in the third position within the valve
body 122, the first port 121 again opens to the first cavity 133,
the second port 123 again opens to the second cavity 135, but the
third port 125 now also opens to the first cavity 133. Thus, in the
third position, the first port 121 of the valve body 10 is now
coupled in flow communication with the third port 125 of the valve
body 122 through the first cavity 133. Conduit 100 from the cuff is
thus coupled in flow communication through branch conduit 101, the
first port 121, and the sealed cavity 133 directly with the third
port 125 of the vent control valve 120. Therefore, the third
position constitutes the rapid deflate or dump position for the
vent control valve 120 in that the conduit 100 from the blood
pressure cuff is now in direct flow communication with the third
port 125, i.e. the vent port, of the vent control valve 120. The
vent control valve 120 is selectively positioned in this third
position whenever it is desired to bypass the bleed valve 10
entirely and rapidly deflate the blood pressure cuff.
[0052] Referring to FIGS. 1 and 3, in particular, in the embodiment
of the bleed valve 10 shown, a pair of seals, depicted as O-rings
95 and 97 carried in circumferential glands respectively on the end
plug 50 and the high pressure stop 52, are provided to seal the
cavity 39 thereby preventing leakage through the threaded
connections between the end plug 50 and the distal end of the bleed
valve body 30 and between the high pressure stop 52 and the end
plug 50. With the seals 95 and 97 so disposed, all of the vented
air must pass through the vent control valve 120. However, it is to
be understood that the seals 95 and 97 are not needed if the bleed
valve 10 is not operatively associated with a vent valve 120 to
control the venting of air through the bleed valve 10.
[0053] In the embodiment of the bleed valve 10 of the invention
depicted in FIGS. 1 through 7, the central bore 32 includes a
conical transition section 65 that tapers inwardly from a
relatively larger diameter cavity 37 upstream of the transition
section to a relatively smaller diameter cavity 35 downstream of
the transition section. The circumferential ridge 75 on the piston
70 in operative association with this conical transition section
provides an annular orifice 85 that defines a flow area that varies
in response to axial translation of the piston 70. It is to be
understood that the invention is not limited to that particular
embodiment. Rather, those skilled in the art will understand that
other respective configurations of the outer circumferential
surface of the piston 70 and the transition section in the central
bore 30 may effectively cooperate to provide an annular orifice
defining a flow area that varies in response to axial translation
of the piston 70 within the central bore 32 of the valve body
30.
[0054] For example, referring now to FIG. 9, an alternate
embodiment of the invention is depicted wherein the central bore 32
within the valve body 30 of the bleed valve includes a step
transition from a relatively larger diameter section 37 and a
relatively smaller diameter section 35 and the piston 70 has a
tapered surface 77 that extends between and tapers inwardly from
the larger diameter piston head 72 to the smaller diameter piston
shaft 76. In this embodiment, the annular orifice 85 is established
between the tapering surface 77 on the piston 70 and the radially
inner corner 88 provided by the step transition in the central bore
32. The annular orifice 85 so provided defines a flow area that
will vary upon axial translation of the piston 70. The flow area
defined by the annular orifice 85 will increase in area as the
piston 70 translates axially in the direction indicated by arrow A,
being biased in that direction by the spring 80 as the pressure in
the blood pressure cuff, or other pressure reservoir, decreases as
air vents therefrom. Conversely, the flow area defined by the
annular orifice 85 will decrease in area as the piston translates
axially in the direction indicated by arrow B, being biased in that
direction as the pressure in cavity 37 increases in response to an
increase in the pressure within the blood pressure cuff or other
pressure reservoir. Therefore, the embodiment depicted in FIG. 9
will also operate in accord with the invention to automatically
vary the flow area defined by the annular orifice 85 in response to
a change in pressure of the air within the upstream cavity so as to
maintain a relatively constant pressure change rate throughout the
venting process.
[0055] As noted before, the bleed valve 10 is particularly useful
in blood pressure measurement applications. For example, in a
typical blood pressure measurement procedure, the user, whether a
physician, nurse, EMT, other trained professional, or the patient,
first connects the measurement cuff to the pump of an automated
electronic measurement apparatus or the inflation bulb of a manual
sphygmomanometer, if not already connected, and then wraps the cuff
about the patient's arm as in conventional practice. The user then
closes the vent port 62, for example by closing a thumb screw or,
if the bleed valve 10 is connected to a vent control valve, such as
the plunger type vent control valve 120, position the vent control
valve in its closed (first) position. With the vent port 62 closed,
the cuff is inflated with the pump or the sphygmomanometer bulb to
a pressure somewhat above, for example approximately 30 millimeters
Hg, the expected systolic pressure. Once the cuff is inflated to
the desired pressure, the user opens the vent port 62, either by
opening a thumb screw or, if the bleed valve 10 is connected to a
vent control valve, such as the plunger type vent control valve
120, positions the vent control valve in its open (second)
position. With the vent port 62 now open to atmospheric pressure,
the cuff will deflate through the bleed valve 10 in a controlled
manner at the desired pressure decrease rate, for example at the
American Heart Association recommended rate of approximately 2-3 mm
Hg per heartbeat. As the bleed valve 10 is self-compensating for
cuff pressure, the piston 70 will self-adjust the area of the
orifice 85 within the bleed valve 10 to maintain the rate of
decrease in cuff pressure relatively constant as the cuff deflates
through the bleed valve 10. Once the diastolic blood pressure
reading has been obtained the cuff will continue to deflate at the
controlled rate. However, if the bleed valve 10 is coupled to a
vent control valve having a third position, such as the vent
control valve 120, wherein the bleed valve 10 can be bypassed to
permit a direct venting of the cuff to atmosphere, the user may
selectively reposition the vent control valve to its rapid deflate
position and proceed to rapidly deflate the cuff.
[0056] It is contemplated that the bleed valve 10 will be
factory-calibrated during manufacturing to provide a relatively
constant pressure decrease rate at the aforementioned AHA recommend
rate for adult blood pressure measurement when a typical adult cuff
is used. The pressure decrease rate, as well as other operational
characteristics of the bleed valve 10, are determined by the spring
constant of the spring 80, by the preload on the spring, by the
specific valve geometry (for example the taper angle for the
conical transition section 65), and by the effective
cross-sectional piston and valve orifice areas at the annular
orifice 85. Those skilled in the art will recognize that the
particular dimensions, spring selection, spring preload and other
design factors may be selected to provide the desired operational
characteristics. For the range of cuff sizes needed, that is from
neonate cuffs to large adult cuffs, a proper selection of the
spring, orifice area and piston area provide relative independence
of the cuff pressure decrease rate relative to the cuff size
range.
[0057] Since the bleed valve 10 operates in response to the
pressure differential across the orifice, and not in response to
the volume of air in the cuff, the operation of the bleed valve 10
provides a cuff pressure decrease rate that is theoretically
dependent on cuff size. However, with proper selection of bleed
valve components, this dependence has been found to be sufficiently
small, so that the bleed valve 10 may be used with various size
cuffs. Nevertheless, depending upon cuff size or the preference of
the user, the bleed valve 10 may require field adjustment to
provide a pressure change rate somewhat different than the
factory-calibrated pressure change rate. For example, if the bleed
valve is employed with a non-adult cuff or the adult patient has a
heart beat elevated well above about sixty beats per minute, it may
be desirable to adjust the rate of pressure decrease during
deflation of the cuff through the bleed valve 10. The rate of
pressure decrease may be adjusted by changing the preload on the
spring 80. To do so, the user merely turns the end fitting
clockwise or counter-clockwise as appropriate to further compress
the spring 80 to increase the preload on the spring 80 or to lessen
the compression of the spring 80 to decrease the preload on the
spring 80.
[0058] While the present invention has been particularly shown and
described with reference to the exemplary embodiments as
illustrated in the drawing, it will be understood by one skilled in
the art that various changes in detail and design may be effected
therein without departing from the spirit and scope of the
invention as defined by the claims.
* * * * *