U.S. patent number 3,875,626 [Application Number 05/423,789] was granted by the patent office on 1975-04-08 for device for measuring the tidal gas volume in a lung ventilator.
This patent grant is currently assigned to Jungner Instrument AB. Invention is credited to Sven Olofsson, Goran Sjoberg, Jan Tysk.
United States Patent |
3,875,626 |
Tysk , et al. |
April 8, 1975 |
Device for measuring the tidal gas volume in a lung ventilator
Abstract
A device in a lung ventilator for measuring the tidal volume for
exhaled gas volume, comprising a rigid container divided in two
separate compartments by a flexible, substantially freely movable,
internal partition wall so that the sum of the volumes of the two
compartments is always constant and independent of the position of
the partition wall. One compartment is connected to a conduit
leading to the respiratory ways of the patient during the
exhalation phase of the ventilation cycle of the ventilator so as
to receive the gas being exhaled by the patient and to the ambient
atmosphere during the inhalation phase of the ventilation cycle.
The other compartment in the container is connected to a device for
injecting a predetermined constant gas flow into this other
compartment. The injection of this constant gas flow is started at
the end of the exhalation phase of the ventilator, when the
communication between the first compartment in the container and
the conduit leading to the respiratory ways of the patient is
interrupted, and is automatically interrupted when said first
compartment has attained its smallest possible volume, that is when
it has been emptied of all exhaled gas. The device for injecting
the constant gas flow in the second compartment of the container is
preferably controlled from a pressure transducer sensing the gas
pressure in said second compartment. The duration of the constant
gas flow injected in the second compartment of the container is
measured; this duration being directly proportional to the gas
volume exhaled by the patient during the preceding exhalation
phase.
Inventors: |
Tysk; Jan (Ekero,
SW), Sjoberg; Goran (Kungsangen, SW),
Olofsson; Sven (Skalby, SW) |
Assignee: |
Jungner Instrument AB (Solna,
SW)
|
Family
ID: |
20301850 |
Appl.
No.: |
05/423,789 |
Filed: |
December 11, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Dec 12, 1972 [SW] |
|
|
16188/72 |
|
Current U.S.
Class: |
600/541;
73/223 |
Current CPC
Class: |
A61B
5/093 (20130101); G01F 17/00 (20130101) |
Current International
Class: |
A61B
5/093 (20060101); A61B 5/08 (20060101); G01F
17/00 (20060101); A61b 005/08 () |
Field of
Search: |
;128/2.08,2.07
;73/23,223 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Dunne; G. F.
Attorney, Agent or Firm: Waters, Roditi, Schwartz &
Nissen
Claims
What we claim is:
1. A device in a lung ventilator for measuring the gas volume
exhaled by a patient, comprising a rigid container provided with an
internal freely movable partition wall dividing the interior of the
container into a first and a second compartment in such a way that
the sum of the volumes of said first and second compartments is
constant and independent of the position of said partition wall and
any change of the position of said partition wall results in
equally large but opposite changes in the volumes of said first and
second compartments; valve means for putting said first compartment
into communication with a gas conduit leading to the respiratory
ways of the patient during the exhalation phase of the ventilation
cycle of the ventilator and in communication with the ambient
atmosphere during the inhalation phase of the ventilation cycle;
means for producing a predetermined constant gas flow and injecting
this constant gas flow into said second compartment; means for
activating said gas flow producing means to start the injection of
said constant gas flow into said second compartment when at the end
of the exhalation phase the communication between said first
compartment and said conduit leading to the respiratory ways of the
patient is interrupted; pressure transducer means responsive to the
gas pressure in said second compartment for actuating said gas flow
producing means to interrupt the injection of said constant gas
flow into said second compartment and instead putting said second
compartment into communication with the ambient atmosphere when
said first compartment attains its smallest possible volume and the
pressure in said second compartment thus rises momentarily; and
time measuring means for measuring the duration of said constant
gas flow.
2. A device as claimed in claim 1, wherein said pressure transducer
means provides an electric output signal representing the gas
pressure in said second compartment and said time measuring means
is controlled by said electric output signal so as to start its
time measuring process in response to the pressure rise caused by
the starting of said constant gas flow and to interrupt its time
measuring process in response to the pressure rise produced when
said second compartment attains its maximum possible volume.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device in lung ventilators for measuring
the so called tidal volume, that is the gas volume exhaled by the
patient.
2. Description of the Prior Art
It is a very important and well known requirement in connection
with lung ventilators that the gas volume exhaled by the patient
can be measured as accurately as possible, as this gas volume
corresponds exactly to the volume of gas actually supplied to the
patient, provided that no leaks exist in the exhalation pipe from
the patient to the measuring device. Devices of various designs for
measuring the exhaled gas volume in lung ventilators are known in
the prior art. These prior art devices can in the main be regarded
as belonging to two different types, namely on the one hand
continuously operating meters as for instance various types of
rotor meters, and on the other hand intermittently operating
meters, in which the exhaled gas from one or possibly several
successive exhalation phases is collected in an expansible or
inflatable container, as for instance a gas bell or a bellows, the
expansion of which is measured for determining the volume of the
exhaled gas and which is subsequently emptied before its next
filling with exhaled gas. However, all prior art devices have as a
common disadvantage that they are comparatively complicated and
thus expensive and sensitive to disturbances and/or that they have
an unsatisfactory measuring accuracy, in particular for small tidal
volumes.
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide an improved
device for measuring the exhaled gas volume in lung
ventilators.
For this object the invention provides a device for measuring the
exhaled gas volume in a lung ventilator, which comprises a rigid
container provided with an internal, freely movable partition wall
dividing the interior of the container in first and second separate
compartments in such a manner that the sum of the volumes of said
first and second compartments remains constant and independent of
the actual position of the partition wall and that any change in
the position of the partition wall results in equally large but
opposite changes in the volumes of said first and second
compartments, valve means for putting said first compartment in
communication with a conduit leading to the respiratory ways of the
patient during the exhalation phase of the ventilation cycle of the
lung ventilator and in communication with the ambient atmosphere
during the inhalation phase of the ventilation cycle, means for
injecting a predetermined constant gas flow into said second
compartment, means for activating said gas flow injecting means to
start said constant gas flow when at the end of the exhalation
phase the communication between said first compartment and said
conduit leading to the respiratory ways of the patient is
interrupted, pressure transducer means responsive to the gas
pressure in said second compartment for initiating said gas flow
injecting means to interrupt said constant gas flow and instead put
said second compartment in communication with the ambient
atmosphere when said first compartment attains its minimum value
and as a result thereof the pressure in said second compartment
rises momentarily, and means for measuring the duration of said
constant gas flow.
In a preferred embodiment of the invention the pressure transducer
means responsive to the gas pressure in the second compartment of
the container are designed to produce an electric signal
representing said gas pressure and the time measuring means are
responsive to this electric signal so as to start the time
measuring process in response to the pressure rise resulting from
the starting of the constant gas flow and to interrupt the time
measuring process in response to the pressure rise appearing when
said second compartment of the container attains its maximum
volume.
The device according to the invention has a comparatively simple
structural design and is therefore inexpensive and reliable.
Further, the device according to the invention makes it possible to
measure large tidal volumes, as the expansible compartment, in
which the exhaled gas is collected, is emptied positively during
the following inhalation phase, and has at the same time a good
accuracy also for small tidal volumes, as the volume measurement
can be based on an electronic time measurement. Further, the
accuracy of the device according to the invention is not dependent
on any accurate tolerances in the design of the container and its
internal partition wall or the accuracy of the movements of the
partition wall as is the case in many prior art devices, where the
measurement is based on observation of the movements of the
partition wall.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be further described with
reference to the accompanying drawings, which illustrate by way of
example some embodiments of a device according to the invention. In
the drawings:
FIG. 1 illustrates schematically a first embodiment of a device
according to the invention;
FIG. 2 illustrates schematically a second embodiment of a device
according to the invention;
FIG. 3 is a diagram illustrating the pressure as a function of time
during the emptying of the inflatable compartment used for
collecting the exhaled gas in the device illustrated in FIG. 2;
and
FIG. 4 is a diagram illustrating the time derivative of the
pressure signal in FIG. 3.
In FIGS. 1 and 2 electric signal connections are indicated by solid
lines provided with arrows indicating the direction of signal
transfer. In FIG. 1 as well as FIG. 2 only the device according to
the invention is shown, whereas all other parts of the lung
ventilator, with which the devices according to the invention is
associated, are omitted, as these other parts of the lung
ventilator can be of any conventional type already well known in
the art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The device according to the invention illustrated schematically and
by way of example in FIG. 1 comprises a rigid container 1, the
interior of which is divided in two separate compartments 2 and 3
by a flexible, substantially freely inflatable bag 4, which thus
forms a partition wall between the two compartments 2 and 3. It is
appreciated that the sum of the volumes of the two compartments 2
and 3 is always constant and that any change in the volume of one
of these compartments results in an equally large but opposite
change in the volume of the other compartment.
The compartment 3 inside the bag 4 can by means of a valve device 5
be put into communication alternatively with a pipe conduit 6
leading to the respiratory ways of the patient or with the ambient
atmosphere. As schematically indicated with an electric signal
connection 7, the valve device 5 is controlled from the control
unit of the lung ventilator in such a manner that the interior 3 of
the bag 4 communicates with the pipe conduit 6 leading to the
respiratory ways of the patient during the exhalation phase of the
ventilation cycle of the ventilator, whereas it communicates with
the ambient atmosphere during the inhalation phase of the
ventilation cycle.
The compartment 2 in the container 1 outside the bag 4 can through
a valve device 8 be connected either to a device 9 for injecting a
predetermined, constant gas flow into the compartment 2 or to the
ambient atmosphere. The device 9 can be of any suitable
conventional design, for instance consisting of a pressurized gas
source with predetermined constant pressure and a restriction
determining the rate of the gas flow. The valve device 8 is
normally in the position, in which the compartment 2 in the
container 1 is communicating with the ambient atmosphere, but is
operated from the control unit of the lung ventilator in such a
manner that at the end of the exhalation phase of the ventilation
cycle the valve device interrupts the communication between the
ambient atmosphere and the compartment 2 and instead opens the
communication between the compartment 2 and the device 9 so that a
constant gas flow from the device 9 is injected into the
compartment 2. The valve device 8 is returned to its normal
position in response to a control signal from a pressure transducer
10 connected to the compartment 2 in the container 1, as will be
described more in detail in the following.
Further, the device comprises a time measuring device 11, which is
started by the control unit of the lung ventilator at the end of
the exhalation phase of a ventilation cycle and is stopped again in
response to the signal from the pressure transducer 10 at the same
time as the constant gas flow from the device 9 into the
compartment 2 of the container 1 is interrupted.
The device illustrated in FIG. 1 operates in the following manner.
During the exhalation phase of a ventilation cycle of the
ventilator the two valve devices 5 and 8 are in positions opposite
to those illustrated in the drawing, wherefore the compartment 3
inside the bag 4 communicates with the pipe conduit 6 leading to
the respiratory ways of the patient, whereas the compartment 2
outside the bag 4 communicates with the ambient atmosphere. The gas
volume exhaled by the patient flows consequently into the interior
3 of the bag 4, which is thus inflated to a corresponding degree at
the same time as the volume of the compartment 2 is reduced. At the
end of the exhalation phase the two valve devices 5 and 8 are
returned in response to the control unit of the ventilator to the
positions illustrated in the drawing, whereby the interior 3 of the
bag 4 is put into direct communication with the ambient atmosphere,
whereas the compartment 2 outside the bag 4 is connected to the
device 9, which starts to inject a constant gas flow into the
compartment 2. At the same time the time measuring device 11 is
also started. Under the effect of the constant gas flow injected
into the compartment 2 outside the bag 4 from the device 9 the bag
4 is emptied through the valve device 5 to the ambient atmosphere.
It is appreciated that the rate of emptying the bag 4 will be
constant and directly proportional to the rate of the gas flow from
the device 9, wherefore the time for a complete emptying of the bag
4, that is until the compartment 3 within the bag 4 attains its
smallest possible volume, will be directly proportional to the gas
volume exhaled by the patient during the preceding exhalation
phase, as this gas volume was collected in the bag 4.
When the bag 4 has been completely emptied as described above and
thus the compartment 3 has attained its smallest possible volume,
the pressure in the compartment 3 will rise steeply due to the gas
flow from the device 9. This steep and large pressure rise is
sensed by the pressure transducer 10, which produces a
corresponding output signal, which on the one hand stops the time
measuring device 11 and on the other hand returns the valve device
8 to its other position so that the gas flow from the device 9 into
the compartment 2 of the container 1 is interrupted and the
compartment 2 is instead put into communication with the ambient
atmosphere.
From the above description of the operation of the device it is
appreciated that the time interval measured by the time measuring
device 11 will be directly proportional to the gas volume which is
expelled from the interior 3 of the bag 4 and thus to the gas
volume exhaled by the patient during the preceding exhalation
phase. A direct measure of this gas volume is obtained by
multiplying the time measured by the time measuring device 11 and
the rate of the constant gas flow from the device 9.
The device according to the invention illustrated in FIG. 1 has
obviously a gas consumption - from the device 9 - which is equal to
the gas volume exhaled by the patient. This comparatively large gas
consumption may be a disadvantage, particularly if the lung
ventilator is driven from its own compressor. FIG. 2 in the
drawings shows schematically a device according to the invention,
which constitutes an improvement in this respect and which is also
simplified in some other respects.
The device according to the invention shown in FIG. 2 comprises
also a rigid container 12, the interior of which is divided in two
separate compartments 13 and 14 by a flexible, substantially freely
movable diaphragm 15, which can move between the two extreme
positions indicated with dotted lines.
The compartment 14 can be put into communication with the pipe
conduit 17 leading to the respiratory ways of the patient through a
valve 16 operated from the control unit of the lung ventilator and
with the ambient atmosphere through a biased check valve 18. The
valve 16 is operated from the control unit of the ventilator in
such a manner that it is closed during the inhalation phase and
open during the exhalation phase of the ventilation cycle of the
ventilator. Consequently, the gas volume exhaled by the patient
during the exhalation phase flows into the compartment 14 of the
container 12 resulting in an increase of the volume of the
compartment 14 and a corresponding reduction of the volume of the
compartment 13. The biassing of the check valve 18 is such that the
valve does not open under the influence of the pressure arising in
the compartment 14 during the exhalation phase but only for a
predetermined higher pressure.
The compartment 13 in the container 12 communicates with the
ambient atmosphere through an ejector device 19, which is connected
to a device 20 producing a drive gas flow for the ejector 19 having
a predetermined constant flow rate and pressure, whereby the
ejector device 19 will under the influence of this drive gas flow
inject a predetermined constant gas flow into the compartment 13 of
the container 12. The major portion of this gas flow is of course
taken from the ambient atmosphere. By proper design of the ejector
device 19 it is possible to achieve that at least 90 percent of the
gas flow injected into the compartment 13 is taken from the ambient
atmosphere. It is appreciated that in the absence of a drive gas
flow from the device 20 to the ejector device 19 the compartment 13
of the container 12 is communicating directly with the ambient
atmosphere through the ejector device. The device 20 can be of any
suitable conventional type and for instance consist of a source of
pressurized gas with predetermined constant pressure and a
restriction for determining the rate of the gas flow; the drive gas
flow to the ejector 19 being started and interrupted respectively
by means of any suitable valve device.
The device 20 is started to supply the necessary drive gas flow to
the ejector 19, whereby a constant gas flow is injected into the
compartment 13 of the container 12, by actuation from the control
unit of the ventilator at the end of the exhalation phase
simultaneously with the closing of the valve 16. The injection of
the constant gas flow in the compartment 13 results in a very rapid
increase of the pressure in the compartment 13 up to the opening
pressure for the check valve 18, as shown at the time t.sub.1 in
the pressure diagram in FIG. 3. This pressure rise is sensed by the
pressure transducer 21 connected to the compartment 13. The
pressure signal from the pressure transducer 21 is preferably
differentiated so that a corresponding signal pulse A is produced,
as shown in the diagram in FIG. 4. This signal pulse starts a time
measuring device 22.
After the opening of the check valve 18 at the time t.sub.1, the
constant gas flow from the ejector 19 into the compartment 13 will
cause a corresponding emptying of the compartment 14 to the ambient
atmosphere through the check valve 18. When the compartment 14 is
completely emptied, that is has attained its smallest possible
volume, the pressure in the compartment 13 will once again rise
steeply, as illustrated at the time t.sub.2 in the pressure diagram
in FIG. 3. Also this pressure rise is sensed by the pressure
transducer 21 and its differentiated pressure signal will
consequently display a signal pulse B, as shown in the diagram in
FIG. 4. In response to this signal pulse B the time measuring
device 22 is stopped and the device 20 is actuated to interrupt the
drive gas flow to the ejector 19. Consequently, the injection of a
constant gas flow into the compartment 13 of the container 12 is
interrupted and this compartment 13 is instead put into direct and
free communication with the ambient atmosphere through the
non-operating ejector 19.
It is realized that also in this case the time interval .DELTA.t in
FIGS. 3 and 4 as measured by the time measuring device 22 will be
directly proportional to the gas volume expelled from the
compartment 14 to the ambient atmosphere and thus also directly
proportional to the gas volume exhaled by the patient during the
preceding exhalation phase.
* * * * *