U.S. patent number 3,695,263 [Application Number 05/006,845] was granted by the patent office on 1972-10-03 for closed circuit medical respirators.
This patent grant is currently assigned to Pye Limited. Invention is credited to Barry John Kipling.
United States Patent |
3,695,263 |
Kipling |
October 3, 1972 |
CLOSED CIRCUIT MEDICAL RESPIRATORS
Abstract
A closed circuit medical respirator provided with a face mask
for applying patient gas to a patient and for transmitting exhaled
gas to the respirator. A closed path extends from the face mask to
a gas purifier, a bellows and back to the face mask. Appropriate
drive means are connected with the bellows for causing flow of gas
to and from the patient so as to create a positive pressure in the
path during one part of the respiratory cycle and a negative
pressure during the other part. A gas flow sensor is provided in
the path and is connected to a controller for operating the drive
means of the bellows. Changeover switches connected with a
multi-vibrator are provided for connection with the controller and
inspiratory and expiratory valves so as to alternately operate the
flow of gas in accordance with the required respiratory cycle.
Inventors: |
Kipling; Barry John (Cambridge,
EN) |
Assignee: |
Pye Limited (Cambridge,
EN)
|
Family
ID: |
9789904 |
Appl.
No.: |
05/006,845 |
Filed: |
January 29, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Jan 30, 1969 [GB] |
|
|
5,110/69 |
|
Current U.S.
Class: |
128/204.24 |
Current CPC
Class: |
A61M
16/00 (20130101); A61M 16/0009 (20140204); A61M
2016/0024 (20130101); A61M 16/0075 (20130101) |
Current International
Class: |
A61M
16/00 (20060101); A61m 016/00 () |
Field of
Search: |
;128/145.6,145R,145.7,145.5,DIG.17,146,146.4,146.5,142-142.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Mitchell; J. B.
Claims
What is claimed is:
1. A closed circuit medical respirator comprising a face mask for
applying patient gas to a patient, an expiratory valve within said
face mask and having an inlet port and an outlet port, a gas
purifier having an inlet and an outlet connected on the inlet side
thereof to the outlet port of said expiratory valve, a gas
container connected to the outlet of said gas purifier, said
container being connected to said inlet port of said expiratory
valve to thereby complete a closed path, a source of patient gas to
replenish losses in the system connected to said path, sensor which
produces an outlet signal in response to a predetermined fluidic
property connected with said path at a point between said
expiratory valve and said gas purifier, a bias control means
connected to said sensor, a source of driving gas connected to said
bias control, a controller connected to and operated by the output
signal of said sensor, a driving means linked to said container for
driving same, a source of driving gas connected to said controller
so as to be passed therethrough and connected to said driving
means, a pneumatic timing circuit operated by a source of driving
gas connected thereto, and a pair of changeover valves connected to
said timing circuit and operated thereby so as to alternately
provide a source of driving gas to the driving means operating the
flow of gas from said container in accordance with the required
respiratory cycle, said sensor operating to vary the amount of
driving gas allowed to pass through said controller as determined
by the phase of the respiratory cycle.
2. The closed circuit medical respirator according to claim 1
wherein said container comprises an expandable bellows.
3. The closed circuit medical respirator according to claim 2
further comprising a first non-return valve located in said closed
path between the outlet port of said expiratory valve and the inlet
of said gas purifier, a second non-return valve located in said
closed path between the outlet of said gas purifier and said
bellows, and a third non-return valve located in said closed path
between said bellows and the inlet port of said expiratory valve,
said non-return valves being provided so as to prevent circulation
of gas in the wrong direction.
4. The closed circuit medical respirator according to claim 3
wherein said source of patient gas for replenishing losses is
substantially at atmospheric pressure and is connected directly to
said path at a point between said second non-return valve and the
outlet of said gas purifier.
5. The closed circuit medical respirator according to claim 3
further comprising an inspiratory valve having the source of
patient gas for replacing losses connected thereto, said
inspiratory valve being connected to said closed path at a point
between said second non-return valve and the outlet of said gas
purifier.
6. The closed circuit medical respirator according to claim 5
further comprising a first actuating cylinder for said expiratory
valve and a second actuating cylinder for said inspiratory valve,
said actuating cylinders being connected through one of said
changeover valves to a source of driving gas so as to be
alternately energized in accordance with the required respiratory
cycle.
7. The closed circuit medical respirator according to claim 6
further comprising an amplifier connected between the output of
said sensor and said controller.
8. The closed circuit medical respirator according to claim 7
wherein said sensor is a differential pressure operated valve.
9. A closed circuit medical respirator comprising a flexible
bellows forming a gas container for receiving and supplying gas to
a patient, means for coupling said container to a patient, a
driving means connected to said container for operating the flow of
gas therefrom, said driving means comprising a piston within a
cylinder connected to the container, a sensing means connected
between said coupling means and said container, said sensing means
having adjustable bias means applied thereto and output means
controllable by the level of said bias, controller means for
controlling said driving means so that the difference between the
flow of gas as determined by said driving means and a flow of gas
from said patient is substantially constant, a piston rod connected
between said piston and said bellows so that movement of the piston
within the cylinder produces a change of volume within the bellows
thereby controlling the flow of gas to and from the patient, and a
source of driving gas connected to the cylinder for operating same,
said output means of said sensing means being connected to said
controller means so as to control the pressure of gas passing
therethrough, said sensing means being arranged to detect said
difference between flow rates and said difference being controlled
by the bias applied to the sensor.
10. The closed circuit medical respirator according to claim 9
further comprising first and second changeover valves connected to
said expiratory and said inspiratory valves and to said means for
controlling said driving means and said cylinder respectively for
controlling movement of the piston within the cylinder in alternate
directions in accordance with the respective periods of the
respiratory cycle, and a fluid operated multi-vibrator having a
source of driving gas connected thereto, said multi-vibrator being
connected to said first and second changeover switches.
11. The closed circuit medical respirator according to claim 10
wherein said means for controlling said driving means comprises a
controller device connected between said sensing means and said
piston carrying cylinder, a source of driving gas and means
connected between said source of driving gas and said controller
for passing driving gas therethrough to the cylinder, whereby said
sensor controls the amount of driving gas passed by said controller
to said cylinder.
12. The closed circuit medical respirator according to claim 11
further comprising an amplifier connected between the output of
said sensing means and said controller for amplifying the output
signal to the controller so that said controller controls the
pressure of the drive gas fed to the cylinder.
13. The closed circuit medical respirator according to claim 12
wherein said means for coupling said supply of gas to a patient is
a face mask having housed therein a respiratory valve controlled by
alternate operation of said multi-vibrator so that the respiratory
valve allows patient gas to flow from the bellows via one part of
the closed circuit to the face mask during each inspiratory period
of the respiratory cycle and from the face mask back to the bellows
via the other part of the closed circuit during each expiratory
period.
Description
The present invention relates to medical respirators having closed
circuit operation.
Medical respirators are frequently used on "closed circuit" and
when so used, gas exhaled by a patient is purified and returned to
the input of the machine to be retransmitted to the patient. To
replace any loss that may occur due to leakage and/or absorption by
the patient over a period of time it is customary to introduce a
small bleed of patient gas into the closed circuit formed by
patient and respirator, the bleed frequently being inserted in the
return path so that additional gas may augment that from the
patient during an expiratory period. The gas may be passed to and
from the patient by, for example, the variation in volume of a
driven bellows, or by other similar means, a reservoir being
provided in the circuit to allow for the differences in volume of
the circuit during a respiratory cycle. With such circuits it is
difficult to obtain any negative pressure to extract all gas from
the patient or to provide any resistance to the flow of gas from
the patient during an expiration period, either of which may be
desirable in certain circumstances.
The invention provides a respirator that follows a flow rate/time
curve, during the expiratory period of a respiratory cycle to give
more natural rhythm to the breathing of the patient.
The invention also provides a gas circuit for a respirator which,
on closed circuit, requires a minimum volume of reservoir and
provides negative or positive resistance to gas flow during the
expiratory period as required.
The various features and advantages of the present invention will
be apparent from the following description of an exemplary
embodiment thereof, taken in conjunction with the accompanying
drawings in which:
FIG. 1 is a block diagram of part of the closed gas circuit of a
respirator embodying the invention, and
FIG. 2 shows the parts of FIG. 1 included in a block schematic
diagram of the patient and drive gas circuits of a pneumatically
operated respirator.
Referring now to FIG. 1, a pipe line 6 forms a gas connection
between a patient (not shown) and a bellows P, the bellows being
operated by a mechanical link T driven by a driving element U/V.
Power for operating the driving element is supplied from line 7 via
a controller 8 and thence by line 9. A sensor 10, having a bias or
operating point (i.e. the input level at which an output signal is
available) which may be varied and having an output proportional to
the difference in input pressure in lines 6 and a regulating
pressure determined by the bias is connected to line 6 and may have
a connection from the power supply as shown by broken line 11. A
line 12 carries any output signal from the sensor 10 to an
amplifier 13 supplied with power over line 7A, the output from the
amplifier being applied via line 14 to the controller 8.
In operation, gas in line 6 causes the sensor 10 to produce an
output signal which is enlarged by amplifier 13 and passed to the
controller 8 so as to apply power from the supply to the driving
element U/V which then controls the operation of the bellows P in
such a manner that the bellows movement assists, follows, or
resists the flow of gas in line 6 according to the adjustment of
the bias of sensor 10. If gas is being received by the bellows P
from the patient via pipeline 6 and the bias of sensor 10 is
adjusted so that no output is immediately produced, movement of the
bellows P will create a positive resistance to the flow of gas from
the patient. On the other hand, if an output signal is produced by
the sensor 10 during a period when no gas is being passed from the
patient, the bellows P will be driven by the driving element U/V to
lead gas from the patient and a negative resistance to gas flow
will be produced, i.e. negative pressure is established, tending to
draw gas from the patient. Further, the bias adjustment may be set
to zero in which case the movement of the bellows will follow the
natural expulsion rate curve of gas from the patient.
In FIG. 2, the closed patient gas circuit comprises a patient (not
shown) connected to port S of an expiratory valve R associated with
a face mash FM, line 6 connected to a second port of valve R, a
non-return valve NR3, a gas purifier 15, a non-return valve NR1,
port P1, bellows P, port P3, non-return valve NR2, line 3 and a
third port of expiratory valve R. Patient gas to charge the system
and make up losses is applied to a port N which, if the gas is
substantially at atmospheric pressure, may be connected directly
with the junction of non-return valve NR1 and purifier 15. With
patient gas supplied at above atmospheric pressure, inspiratory
valve R2 may be used as shown or it may be replaced by a spring
loaded valve. The purpose of the non-return valves NR1, 2 and 3 is
to prevent gas circulation in the wrong direction and valve NR3 is
essential when patient gas is supplied at pressure and when
expiratory valve R is of the type that does not at any time prevent
gas flow from bellows to patient.
Driving gas for the pneumatically operated and timed respirator
shown in the example is applied to ports C, L2, L3, 16 and 17; 7:
the gas at these various ports not necessarily being of equal
pressure. Conveniently, the driving gas is compressed air. Driving
gas from port 16 passes via line 7A to pneumatic ampifier 13 and
from port 17 to an adjustable pressure regulator PR4 and thence by
line 11 to a pressure sensor 10, which may be a valve operated by
differential pressure, whose input port 10A is connected to line 6
between valves R and NR3.
A pneumatic timing circuit 18, conveniently of the fluid
multi-vibrator type operates changeover valves CO2 and CO3
alternately in accordance with the required respiratory cycle, the
feeds to ports V1 and V2 of a double-acting bellows driving
cylinder V being alternately energized, via ports E3 and D2, from
inlet ports L3 and L2 respectively. The feed to the actuating
cylinders Z and Z2 of valves R and R2 are simultaneously
alternately de-energized by these same changeover valves. The feed
to port V2 is direct from port D2 of valve CO2, but that to port V1
from port E3 of valve CO3 is taken via line 7 to the input of the
controller 8 and thence by line 9 to port V1 of the cylinder V.
Sensor 10 in this embodiment comprises a differential pressure
operated valve which, when pressure at its port 10A has a
predetermined relationship with that set by regulator PR4 the bias
control, produces an output signal in line 12 which is then applied
to the input of amplifier 13, which may also be a pressure
differential operated valve. The output from amplifier 13 is passed
over line 14 to open the controller 8, also a pressure controlled
valve, an so permit driving gas from port L3 to drive the piston U
of cylinder V in a direction that expands the bellows P, the piston
and bellows being linked by the piston rod T.
FIG. 2 shows the position at the commencement of the expiratory
stroke, with solid lines indicating a gas passage then available
within valves CO2 and CO3. The broken lines within the valves show
the available gas passages in the alternative positions of the
valves. Valve R and the piston of actuating cylinder Z are in their
upper position connecting port S to line 6 (port Z being vented to
atmosphere via ports D3 and F3). Valve R2 and the piston of
cylinder Z2 are in their lower position because driving gas is
supplied to the cylinder Z2 from inlet L2 via port E2; so
connecting patient gas from port N to the closed circuit. Piston U
of cylinder V is free to move downwards, since port V2 is vented to
atmosphere via ports D2 and F2 of valve CO2. Driving gas from port
L3 is applied to controller 8 via port E3 and line 7, and the drive
to the piston U via line 9 and port V1 will be controlled as
previously described by the sensor 10.
As during the first portion of the expiratory period gas flow from
a patient is high, the signal from sensor 10 will be large, thereby
opening controller 8 towards its full extent and thereby expanding
the bellows rapidly. At a later period in the expiratory period the
gas flow from the patient is at a lower level resulting in a
smaller signal from the sensor 10, a smaller amount of opening of
controller 8 and a slower expansion of the bellows. The natural
variation of tidal volume (the amount of patient gas passed to the
patient during an expiratory period) with time is thus followed by
the respirator to produce a more natural rhythm of the respiratory
cycle.
If desired another sensor, with associated pressure regulator,
amplifier and controller, may be similarly arranged to control the
inspiratory period in a more natural manner, the other sensor input
then being connected to line 3 and the other controller being
inserted in the line between ports D2 and V2.
The sensor 10, amplifier 13 or controller 8 may be such that there
is a non-linear relationship between the input signal applied to
the sensor and the movement of the bellows.
The sensor 10 is not restricted to a type operated by pressure
differential but may be operated by other means, e.g. rate of flow
of gas. In such a case a restriction may be placed in the line 6
with the two inlet ports of a differential pressure sensor
connected to a line 6, one on each side of the restriction. Bias,
mechanical or pneumatic, may be applied to the sensor and/or
controller to provide the previously mentioned lag or lead of the
bellows movement and correction operation of the system.
* * * * *