AU598255B2

AU598255B2 - Computer gated positive expiratory pressure system

Info

Publication number: AU598255B2
Application number: AU72316/87A
Authority: AU
Inventors: Charles C. Cummings; Robert I. Prince
Original assignee: Puritan Bennett Corp
Current assignee: Puritan Bennett Corp
Priority date: 1986-03-31
Filing date: 1987-03-27
Publication date: 1990-06-21
Anticipated expiration: 2007-03-27
Also published as: DK162257B; EP0273041A1; AU7231687A; SE8703727L; NL8720165A; CA1302505C; JPH0488952U; DK504687D0; DE3790137T1; GB2194892A; CH672991A5; DK504687A; JPH06125Y2; SE8703727D0; SE459214B; EP0273041A4; WO1987006040A1; GB8722069D0; JPS63503207A; GB2194892B

Description

AU-AI-72316/87 P P T WORLD INTELLECTUAL PROPERTY ORGANIZATION P C TJ International Bureau T E Y (P T INTERNATIONAL APPLICATION PUBLI H D D H T CPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 87/ 06040 G06F 15/42 Al (43) International Publication Date: 8 October 1987 (08.10.87) (21) International Application Number: PCT/US87/00644 (74) Agent: FINCH, Walter, 1501-03, Fidelity Bldg., Baltimore, MD 21201 (US).

(22) International Filing Date: 27 March 1987 (27.03.87) (81) Designated States: AT, AT (European patent), AU, BB, (31) Priority Application Number: 845,942 BE (European patent), BG, BR, CH, CH (European patent), DE, DE (European patent), DK, FI, FR (Eu- (32) Priority Date: 31 March 1986 (31.03.86) ropean patent), GB, GB (European patent), HU, IT (European patent), JP, KP, KR, LK. LU, LU (Euro- (33) Priority Country: US pean patent), MC, MG, MW, NL, NL (European patent), NO, RO, SD, SE, SE (European patent), SU.

(71) Applicant: PURITAN-BENNETT CORPORATION [US/US]; 9401 Indian Creek Parkway, Overland Park, Published KS 66225-5905 With international search report.

(72) Inventors: CUMMINGS, Charles, C. 291 West Greenwood Avenue, Lansdowne, PA 19050 PRINCE, Robert, I. ;4912 S.W. 83rd Terrace, Gainesville, FL J 2 NOV 1p7 32067 V98

AUSTRALIAN

2 0 OCT 1987 This document contains the amendments made undbr PATENT OFFICE Section 49 and is correct for printing.

(54) Title: COMPUTER GATED POSITIVE EXPIRATORY PRESSURE SYSTEM (57)Abstract The use of Positive-End-Expiratory Pressure (PEEP) systems result in decreased cardiac output and decreased regional blood flow because the heart is surrounded by higher than usual pressure (elevated intrathoracic pressure). The in- ,entiQn lowers intrathoracic pressure selectively during a imall portion of the heart cycle when it causes its greatest detrianent. The invention lowers thoracic pressurq by providing a low pressure source to the PEEP valve Included in the invention are a sensing .means (L6)'for.sensing sequential heart beats of a patient, together with a computing means (18), which is connected to the sensing means for computing a ,period between the sequential heart beats. In addition, a valve means (24) is connected electrically to the computing means (18) and pneumatically to ventilator means (12) for con- ,trolling the ventilator means with the valve imeans (14) being positioned to cease supply of positive pressure in response to the computed period.

1 TITLE OF THE INVENTION Computer Gated Positive Expiratory Pressure System

BACKGROUND

When breathing normally, one's diaphragm is dropped to increase one's thoracic cavity, thus creating a negative pressure in the thoracic cavity, relative to atmospheric pressure. Air is driven by the atmospheric pressure into the negative-pressure thoracic cavity.

Many patients, such as victims of accidents suffering from shock, trauma or heart attack, may require a respirator or ventilator to aid breathing. Prior respirators used intermittent, positive pressure breaths to increase the pressure within a patient's lungs until filled. Air is expelled passively by the natural stiffness of the lungs.

Such respirators drive a positive pressure breath into the lungs which are already at atmospheric pressure.

The pressure in the lungs is increased above atmospheric pressure, contrary to normal occurrence, which inhibits the heart's ability to pump blood. During normal respiration, negative thoracic pressure is developed upon inspiration of air, which aids in filling the heart with blood. The resultant pressure gradient (the relatively positive pressure in the periphery and X A 4 'L i

I

i

I

2 negative pressure in the thorax) helps to fill the heart as it opens, subsequent to the heart's squeezing or pumping motion. If however, the pressure in the thoracic chamber is increased, as with respirators, the amount of blood returning or entering the heart is decreased. The heart also must squeeze against a higher pressure. A lower cardiac output results.

The common technique for improving arterial oxygen tension is the use of Positive-End-Expiratory Pressure (PEEP), where a low level of positive pressure is maintained in the airway between positive pressure breaths. PEEP uses a standard switch. A pressure signal applied to the valve controls the high or low pressure states of the valve. The low PEEP state is generated when the valve is fully open. A partial closing of the valve creates high intrathoracic pressure between breaths, as some air from the tidal volume is not allowed to escape. However, at 10 centimeters of water pressure of PEEP, cardiac output drops significantly.

Intravenous fluids are used to increase intravascular volume in an effort to minimize this fall in cardiac output. The patient may already have compromised cardiac function, minimizing or negating the advantages of the intravascular volume increase. Additionally, patients 040 0 0 :0 4 0 3 requiring respirators typically lack adequate kidney function and cannot process the added fluids. If too much intravenous fluid is used, relative to the patient's ability (aided or not) to process the fluid, the fluid may enter the patient's lungs.

Positive inotropic agents are used to increase the squeeze of the heart to punp more blood. Obviously, the heart works harder than normal resulting in possible heart attacks or arrhythmias. Often, physicians will prescribe a combination of increased intravenous fluids and positive inotropic agents with PEEP.

Several investigators have evaluated the effect of cardiac cycle-specified, increases irt thoracic pressure on cardiac output. They synchronized high frequency jet ventilation to various phases of the R-R interval.

Carlson and Pinsky found that the cardiac depressant effect of positive pressure ventilation is minimized if the positive pressure pulsations are syrchronized with diastole. Otto and Tyson, however, found no significant changes in cardiac output while synchronizing positive pressure pulsations to various portions of the cardiac cycle.

Pinchak described the best frequency in high frequency jet ventilation. He also noticed rhythmic l l S* 4 oscillations in pulmonary artery pressure (PAP) and also rhythmic changes in systemic blood pressure. A possible explanation for these oscillations is that the jet pulsations move in and out of synchrony with the heart rate. In evaluating his data it appears that when jet airway pressure peak occurred during early systole there was a high pulmonary artery pressure, and a low systemic blood pressure. While Pinchak does not comment on thi-, his recorded data show that pulmonary artery pressure was waxing and waning precisely opposite the blood pressure. A plausible explanation is an increase in pulmonary artery pressure is simply a 4 4 reflection of an increase in pulmonary vascular resistance whic.h causes a decrement in left ventricular 9o *o filling and thus decrease in systemic blood pressure 0*00 secondary to a decrease in cardiac output. If the 0 slight oscillations in the systemic blood pressure reflect oscillations in cardiac output, then Pinchak's o1 study would support Pinsky and Carlson's work, suggesting °e o B 0 *that positive airway pressure is least detrimental during diastole.

According to one aspect of the present invention there is provided a computer gated positive expiratory pressure 1 system for controlling pressure breaths to a patient, 2 comprising: 3 a sensing means for sensing sequential heart beats of a 4 patient; a computing means, connected to the sensing means, for 6 computing a period between the sequential heart beats; 7 a ventilator means including a PEEP valve; 8 a valve means connected electrically to the computing 9 means and pneumatically to the PEEP valve of the ventilator means for controlling the ventilator means, the valve means 11 being arranged to cease positive pressure breaths in 12 response to the computed period.

13 According to another aspect of the present invention 14 there is provided a computer gated positive expiratory pressure system for controlling pressure breaths to a 16 patient including: 17 a therapeutic device, such as a ventilator including a 18 PEEP valve; 19 a valve means through which a fluid may flow to control the PEEP valve; 21 a sensing means for sensing a patient's sequential .CIS 22 heart beats and generating beat signals; 23 a computing means, connected to receive the sensed tiff 24 beat signals, for computing a period between sequential beat signals, and for generating a period signal; C 26 a variable means for generating a variable interval 27 signal; 28 a combining means, connected to receive and combine the iii 29 period signal and the variable interval signal, and connected to the valve means,for controlling the valve means 31 in response to the combined pariod signal and variable 32 interval signal.

33 Preferably the valve means comprises a 3-way valve and 34 said ventilator or therapeutic device includes a gated PEEP valve. When triggered, the 3-way valve opens to allow a 36 relatively low pressure to pass to the PEEP valve such that 7 the PEEP valve creates a pressure which is relatively low c ,ompared to that in the patients lungs.

I

6 Thus, PEEP is removed for a variable time ratio immediately before a next heart beat. The PEEP valve is controlled by computer gating a 3-way valve to create pressure drops, allowing the heart to fill.

Once the heart fills, PEEP is resumed without any detrimental effects. Respiration of the patient is coordinated with the patient's heart-beat to maximize cardiac output. Additionally pressure can be replaced immediately after drop out in an effort to improve emptying of the heart.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic of the present invention in its environment.

Figure 2 is a block diagram of the Figure 1 microcomputer contents, as connected to a 3-way valve.

Figure 3 reveals a second embodiment for detecting a heart beat interval.

DETAILED DESCRIPTION OF THE INVENTION The computer-gated, positive expiratory pressure system is shown in Figure 1 in its environment, connected to a therapeutic device such as a PEEP ventilator system. A patient 10 is shown using a respirator or ventilator 12 ~P through a standard expiratory (PEEP) valve 14. The PEEP valve 14 opens 'ad clos'Js to allow Iow'8nd' ligh pt siJres to oo o i i, 7 the patient 10. In accordance with the present I invention, the patient 10 is also connected to a cardiogram machine (EKG) 16. Successive heart beats are detected by the EKG 16 and a signal representing each beat is output to a microcomputer 18, the details of which are discussed regarding Figures 2 and 3. A variable interval is generated by generator 20 as a second input to the microcomputer 18, the value of the interval being set by the attending physician. The microcomputer 18 combines the variable interval signal from 20 and a value representing the period between successive heart beats from EKG 16 and generates a controlling output to a solenoid 22 of a 3-way valve 24.

The 3-way valve 24 is connected by a first end to a positive pressure source 26. A second valve end is preumatically connected to a low relative pressure 28, while a third end is connected to t'he PEEP valve 14 through which the patient 10 received the positive pressure breaths.

Under rormal operation of the ventilator 12, the PEEP valve 14 is operated to allow alternate low and high positive pressure breaths (approximately .4 psi) from the ventilator 12 to pass directly to the patient LL 10. However, in response to the output of microcomputer 8, the s le 2 2is energiz yid at ou't ct t t a a «.611 41.t t -ao U~o- I 8 a negative pressure from the low relative pressure source 28. The negative pressure output at 30 opens the PEEP valve 14. Because the PEEP valve 14 is fully opened, a relatively low pressure is received by the patient from the ventilator 12. The resultant relatively low pressure, in accordance with the present invention, occurs just prior to a predicted heart beat to ensure the heart, when filling, does not work against high pressures.

PEEP systems per se too often generate high pressures when the heart beats, inhibiting heart filling and decreasing cardiac .output.

In Figure 2, the details of microcomputer 18 are evident. The output of EKG 16 is run through an operational amplifier 32 to a timer 34 which squares the amplified EKG signal to develop a series of electrical pulses corresponding to successive heart beats. The electrical pulses of timer 34 are received by memory/calculator 36 which determines a period representing the interval between successive heart beats (R-R waves) This period is used to predict a next heart beat so a low pressure is delivered to the patient slightly before and during this next heart beat. The variable interval generator 20 is set by the SAUMattending physician between 15 and 400 microseconds, or instane, Iy typil caV anolog conrols The S ?t 9 variable interval signal from 20 and the period signal from calculator 36 are used to generate a produce in multiplier 38. The resultant product (R-R wave period times variable interval) is used as a signal to energize the solenoid 32, to control 3-way valve 24.

In a normal state, 3-wa.y valve 24 connects the positive pressure 26 to the output 30, putting PEEP valve 14 in a partially closed position. Thus, the ventilator 12 can generate a high, positive pressure breath to the patient 10. However, assume the EKG 16 detects a heart beat each second. The EKG signal is amplified at 32, squared by timer 34, and the period of one second calculated in memory 36. If the variable interval generator is set by the physician for 0.8 second, multiplier 38 forms a product of the period and variable interval (1.0 x 0.8) equal to 0.8 seconds. Thus, 0.2 second before the next predicted, heart beat (0.8 second from the last heart beat) solenoid 22 is energized. The 3-way valve 24 now opens output 30 to the vacuum 28, Accordingly, a resultant negative pressure fully opens the PEEP valve 14 and a low pressure reaches the patient.

Should the heart rate vary, the difference between predicted and actual heart beats will be detected and pulse timing corrected. The time duration of the ulse to the solenoid is controlled by a second timer 1 not sho o 1 m t at I -a I I 11.1 .1.1 l' 1-1 I Figure 3 reveals a second embodiment for determining or sensing heart beats. A photodetector is used to detect the blinking LED 42 which is typically part of a cardiogram machine. The photodetector 40, turning on and off with the flash of the LED 42, requires no timer or wave squarer, and thus is input directly to the amplifier 32 for subsequent processing in the manner of the Figure 2 embodiment.

Other modifications are apparent to those skilled in the art which do not depart from the spirit of the present invention, the scope being defined by the appended claims. For instance, rather than use a microcomputer, a microprocessor C 64 Commadore Computer) may be adapted and software developed to monitor and determine beat period, with a programmable variable interval for use by the physician.

Claims

2. A system as in claim 1, including: a low p:cessure source means, pneumatically connected to the valve means, for generating a relatively low pressure to the ventilator means through the valve means.
3. A system as in claim 2, including a positive pressure means, the valve means comprising a 3-way valve having first, second and third ends, the first end connected Spneumatically to the ventilator means, the second end connected to the low pr4bsure source means, and the third end connected to a positive pressure means.
4. A system as in claim 3, the 3-way valve having a solenoid electrically connected to the computing means for positioning the 3-way valve. I 5. A system as in any of claims 1 to 4, including a t variable interval means, connected to the computing means, for generating a variable interval signal to the computing means.
6. A system as in claim 5, the computing means having a multiplier means, connected to the sensing means and the variable interval means, for generating a product signal based on the computed period times the variable interval signal.
7. A system as in any of claims 1 to 6, the ventilator P means having said PEEP valve pneumatically connected to the 2 -12 first end of the valve means, said PEEP valve being opened by the valve means pneumatic connection of the relative low pressure source means to the ventilator means, and the PEEP valve being closed by the valve means pneumatic connection of the positive pressure means to the ventilator means;
8. A computer gated positive expiratory pressure system for controlling pressure breaths to a patient including: a therapeutic device, such as a ventilator including a PEEP valve; a valve means through which a fluid may flow to control the PEEP valve; a sensing means for sensing a patient's sequential heart beats and generating beat signals; Sa computing means, connected to receive the sensed beat signals, for computing a period between sequential beat r signals, and for generating a period signal; ,a variable means for generating .a variable interval signal; a combining means, connected to receive and combine the period signal and the variable interval signal, and connected to the'valve means,for controlling the valve means in response to the combined period signal and variable interval signal.
9. A system as in claim 8 including a low pressure source means, pneumaically connected to the valve means, for creating a relative negative pressure when the valve means is opened. A system as in claim 9, including a positive pressure means,, the valve means 'comprising a 3-way valve having three S- end means; a first end means for connection to the therapeutic device, a second end means for connection to the low pressure source means, and a third end means for connection to the positive pressure means.
11. A system as in claim 10, the 3-way valve having a solenoid electrically connected to the computing means for positioning the 3-way valve. S2. A system as in any of claims 8 to 11, the computing S328,ar«pe.029,72316cl, 1 .y r IT I ct t I' -13 means comprising a multiplying means, connected to the sensing means and the variable means, for generating a product signal based on the computed period times the variable interval signal.
13. A system as in any of claims 8 to 12 further comprising an amplifying means connected to the sensing means, for amplifying the beat signals generated by the sensing means.
14. A system as in claims 12 and 13, the computing means including a timing means, connected to the amplifying means, for squaring the signals from the amplifying means, and for generating pulses to the multiplying means. A system as in claim 13 or 14, the sensing means comprising a photodetector means for detecting light signals produced in response to a patient's heart beat, the photodetector means generating an output to the amplifying means. Dated this 28th day of March, 1990 DAVIES COLLISON Patent Attorneys for PURITAN-BENNET CORPORATION L1~ I I I St S S *1 St