Spirometric device

A spirometric device for connection to the respiratory piping system of a patient and wherein a delivery pickup system is situatable on an exhalation branch of the system. The signals transmitted by a pressure pickup included in the device and situated on the respiratory system and those transmitted by the delivery pickup are led to a computing and measuring assembly which integrates the delivery signals while correcting these as a function of the pressure variations and/or of the errors caused by the gas contained in the respiratory system.

The present invention relates to a spirometric device incorporating 
pressure correction, applicable in particular to controlled delivery 
respirators, that is to say to an apparatus allowing a patient to be 
induced to breathe artificially. The spirometric device measures the 
volume or the delivery of gas exhaled, referred to as "current volume," 
the same substantially corresponding to the respiratory capacity, referred 
to as the "effective" capacity hereinafter, since it corresponds to the 
quantity of gas the lungs may actually exhale and which is evidently 
smaller than the true capacity, the lungs not emptying altogether during 
each breathing cycle up to the point of collapse. 
In the prior art a variety of artificial respiratory techniques have been 
employed without yielding complete satisfaction; the following patents 
will be cited by way of example: 
U.S. Pat. No. 3,006,336 filed on July 26, 1957. In accordance with this 
patent, the device to nullify the pressure loss in the spirometer which 
impedes the exhalation of the patient, by means of a piston controlled in 
such manner as to keep the pressure constant in the chamber of the 
spirometer. 
The prior art moreover comprises many devices for measuring volumes of 
volumetric flows incorporating pressure correction, making use of a 
pressure correction by application of Boyle's law, and in particular U.S. 
Pat. Nos. 3,759,249 and 3,799,149 which, respectively, relate to a 
respiratory analysis device incorporating a mass spectrometer and a 
metabolic analyzer wherein a calculator introduces a pressure correction 
by application of Boyle's law. 
The fact that the pressure is controlled and measured is disclosed in U.S. 
Pat. No. 3,414,896 filed on Jan. 5, 1965. 
Practically all the known devices operate on an approximate pressure 
measurement and do not allow for the variations of this pressure, which 
are frequently substantial during one and the same cycle. 
According to the present invention there is provided a spirometric device 
for connection to a respiratory piping system of a patient and comprising 
a delivery pickup system for location on an exhalation branch of the 
system and responsive to signals transmitted thereby, a pressure pickup 
situated on said system and responsive to signals transmitted thereby, and 
pressure pickup signals being fed to a computing and measuring assembly 
for integrating the delivery signals and correcting these as a function of 
pressure variations, said pressure pickup being followed by two circuits 
in parallel for detecting the maximum pressure and the minimum pressure 
and by a first subtracting device for delivering an analogical signal 
proportional to the difference of said two extreme pressures. 
With the device of the present invention, the measurement is rendered more 
precise while making allowance for the maximum pressure and the minimum 
pressure as well as for the overpressures or negative pressures occurring 
during the respiratory cycle. 
Moreover, the solution offered by the present invention is very 
uncomplicated and, as compared to other solutions such as the mechanical 
solution of U.S. Pat. No. 3,006,336, offers the advantages of electronics 
which are now well known.

The corresponding elements of the different figures are marked by the same 
references. In these figures, it is assumed that there is a negative 
pressure. If there is no negative pressure, it is sufficient to replace 
the indices 2 by the indices 0. 
It is appropriate to recall, with reference to FIG. 1, that a conventional 
artificial respiration apparatus essentially comprises a Y-shaped pipe 
whereof one branch is connected to the patient P, a second one to a source 
of gas under pressure (bottle or tank and compressor, in particular) via a 
valve EV1 which is commonly electrical in recent equipment, and the third 
to the surrounding atmosphere via a valve EV2, which is equally electrical 
in the greater number of cases, followed or not by a spirometer S. 
It is known that when the patient requires artificial respiration, that is 
to say if it is thought that he is partly or wholly unable to ensure his 
own breathing spontaneously, so that upon inhalation (EV2 being closed and 
EV1 being open) the patient should be subjected to a slight overpressure 
as compared to atmospheric pressure, this overpressure being increased the 
more difficult the patient's own breathing. The volume inhaled is thus at 
a pressure differing from the atmospheric pressure prevailing externally, 
which corresponds to a gaseous mass greater than that of an identical 
volume at atmospheric pressure. Moreover upon exhalation (EV1 being 
closed, and EV2 being open), the pressure is re-established progressively 
and the pressure of the air varies as it is being discharged through the 
spirometer, that is to say that the initial overpressure diminishes until 
it is zero, so that the spirometer measures a volume under a pressure 
varying in the course of the operation. 
The effect of the overpressure on the volume, in the case in which it is 
itself negligible, may be ignored, but it must normally be taken into 
account. 
The present invention offers a solution to this problem by means of a 
pickup K measuring the pressure in the Y pipe, with data transmitted to a 
measuring and computing unit M which, equally receiving the data from the 
spirometer S, and instantaneously applies the required corrections to the 
measurements of this latter. If the index 0 is attributed to the 
atmospheric conditions and the index 1 to the maximum overpressure 
conditions (which may possibly vary from one respiratory cycle to another) 
M thus no longer integrates the volumes passing into the spirometer, but 
these volumes are corrected to atmospheric pressure. 
As will be apparent from the two examples of embodiment described below, 
two solutions are offered, the one being approximative, wherein the 
delivery is integrated for multiplication by the pressure variation 
##EQU1## 
the other being more precise, wherein the flow corrected for atmospheric 
pressure is integrated at each instant 
##EQU2## 
P being the momentary pressure measured by the pickup K, the momentary 
elementary volume dV or the momentary delivery dV/dt being measured by 
Boyle's law, which is applicable for perfect gases or for real gases for 
low pressure variations, which is the most common case in spirometry, is 
applied in the present case, but it would be possible to integrate while 
applying another law in extreme cases, that is to say if the pressure 
variations were to be very substantial. This is possible, for example, 
when victims of dives to great depths are being revived in a pressurized 
chamber. 
Allowance should equally be made for the fact that, on modern equipment, 
not only is the operation performed under overpressure upon inhaling, but 
equally under negative pressure upon exhaling (index 2); 
##EQU3## 
is thus integrated in M. Corrections may also be made if the spirometer 
itself causes a pressure loss damping the pressure variations in the 
course of time. 
What is more, it is appropriate to recall that the volume of the ducts is 
not negligible as a rule and that it must be taken into account since the 
datum of importance to the doctor is the quantity of gas discharged by the 
lungs. This information may be available without correction at the mouth 
of the sick person by measuring the delivery and pressure at the same, but 
this localization of the measurements is inappropriate because of the 
fouling caused by the condensations of water vapour or the excretions of 
the patient, which falsifies the measurements. This explains why, at this 
time, the trend is to position the pickups, particularly those intended 
for the rate of flow, sufficiently far from the mouth of the sick person, 
so that the result thereof is an increase in length and volume of the 
pipes which must be taken into account. 
Consequently, it is appropriate to reduce the volume at atmospheric 
pressure corresponding to the gaseous mass which, itself, corresponds to 
the difference between those contained in the pipe between P1 and Po. 
The delivery pickup S (FIGS. 1 and 2) transmits the flow datum in liters to 
the unit M during the exhalation periods of each cycle, for example by 
transmitting a number of pulses proportional to the speed of passage in 
the pickup and thus proportional to the rate of flow. For example, this 
may be obtained with a capacitative type turbine pickup. 
In integrator 2, the integration as a function of time for each cycle 
yields the so-called "current volume" volume. In integrator 3, it yields 
the so-called "minute volume" for each minute. These data correspond to 
the total volume delivered by the respirator (at varying pressure during a 
cycle). 
The capacity of the pipes being Co notwithstanding the pressure P, a volume 
##EQU4## 
that is to say 
##EQU5## 
if there is no negative pressure upon exhalation, and 
##EQU6## 
that is to say 
##EQU7## 
if the contrary is the case, flows within the delivery pickup apart from 
the respiratory volume. 
(The volume Co of the gas in the pipes is actually Co (P/Po) upon changing 
from the pressure P to the pressure Po). 
The pressure pickup K supplies the unit M at 4 with a pressure measurement 
whereof the maximum P1 is marked at 5 and the minimum (Po or P2 depending 
on whether there is negative pressure or not) is marked at 6, and the 
difference is established in 7. 
This pressure change is transmitted to the corrector devices 8 and 9 which, 
respectively receiving the "minute volume" and the "current volume" from 3 
and from 2, supply the corrected "minute volume" and the "current volume," 
with allowance for the pressure variations and for the correction 
.DELTA.C. The indication is made at 10 and 11, respectively. 
By way of example, this device has been simplified since it does not 
perform the integration 
##EQU8## 
in which V.sub.1.sup.2 represents the volume passing into the pickup 
between 1 and 2, that is to say during the exhalation period. By contrast 
(FIG. 4) if the momentary pressure P is transmitted from 4 to an 
instantaneous corrector 12 upflow of the integrators 2 and 3, the 
integration is then performed as stated above and the computing 
calculators 2 and 3 deliver 
##EQU9## 
the correctors 8 and 9 provide only the correction applicable to .DELTA.C 
in this case. 
With reference to FIG. 3, the manner in which circuits performing these 
operations may be designed, will be understood. If the .DELTA.C correction 
is applied for the current volume, the correction n.DELTA.C will have to 
be applied for the minute volume, n being the number of respiratory cycles 
per minute. The measurement of n is not illustrated in diagrams 2 and 4, 
but an example of embodiment thereof will be given in FIG. 4. 
Numerous solutions are actually possible: n is the number of pressure 
cycles and may thus be counted in K (every time P = Po if there is no 
negative pressure, or half the number of times when P = Po or P2 are a 
minimum), or in S every time the delivery becomes nought (inhalation), 
this solution having the merit of being easy to apply. It is also possible 
to count the closings and openings of EV1 or EV2; or else to establish the 
quotient of the "minute volume" and of the "current volume," etc. 
FIG. 3 illustrates an example of embodiment of the fundamental layout of 
FIG. 2. 
With reference to FIG. 3, the greater number of the circuit elements are 
identical and the transposition lies within the sphere of one versed in 
the art. The spirometer is constructed by means of a turbine 20 followed 
by a capacitative pickup 21 and by a voltage comparator 22. The form of 
the signals transmitted has been illustrated diagrammatically in the 
figure. 
The comparator 22 acts, on the one hand, on a monostable circuit 23 of the 
constant amplitude pulse type and, on the other hand, on a detector 24 
comprising an RC circuit pulse blocked for zero resetting. The signals of 
the monostable circuit 23 are transmitted, on the one hand, to an RC 
circuit areal integrator 25 over a minute, followed by a d.c. amplifier 26 
which thus delivers an analogical signal proportional to the "minute 
volume." The signals of the monostable circuit 23 are transmitted, on the 
other hand, to the RC circuit areal integrator 27 over a cycle, equally 
followed by a d.c. amplifier 28 transmitting an analogical signal 
proportional to the "current volume." The integrator 27 acting over one 
cycle is equally acted upon by the detector 24 which resets the integrator 
27 to zero for each cycle and triggers the monostable circuit 29 of the 
constant amplitude pulse type, followed by an areal integrator 30 acting 
over one minute, which consequently transmits a signal proportional to n, 
the respiratory frequency per minute. 
Moreover, the analogical pressure pickup K is followed by a d.c. amplifier 
31 followed by a filter 32 separating the crests P1 and in parallel by a 
filter 33 separating the troughs (or negative crests) P2 (or Po). 
P2 is inverted in 34 which renders it possible, on the one hand, to summate 
P1 - P2 in the amplifier 35 from the signals issuing from 32 and 34 and, 
on the other hand, to establish n(P1 - P2) in the amplifier 36 from the 
signals issuing from 30; the amplifiers 35 and 36 thus deliver analogical 
signals proportional, respectively, to .DELTA.C.sub.1.sup.2 and .DELTA.Cl 
min. The signals issuing from the summating amplifiers 35 and 36 are 
adjusted by means of the potentiometers 37 and 38, respectively, to allow 
for the true volume of the pipes which may evidently vary according to the 
conditions of application. The d.c. amplifiers 39 and 40 respectively, 
will thus receive analogical signals corresponding to .DELTA.C.sub.1.sup.2 
and .DELTA.Cl min. originating from 37 and 38 and analogical signals 
corresponding to V.sub.1.sup.2 and V.sub.1 min. originating from 28 and 
26. They correct the volumes and deliver corrected volume signals 
V.sub.1.sup.2 - .DELTA.C.sub.1.sup.2 and V 1 min - .DELTA.C l min. These 
amplifiers 39 and 40 are followed, respectively, by output amplifiers 41, 
42; the indication may be made by any adequate means, either by analogical 
indications such as graduated galvanometers 43 and 44, or by digital 
indications, for example of the "nixies" type. 
It will be observed that, in the block diagram of FIG. 3, only the 
correction of .DELTA. C has been illustrated, to simplify matters, since 
the correction of .DELTA.p is negligible as compared to that of .DELTA.C 
in many cases.