Computer gated positive expiratory pressure method

The computer gated positive expiratory pressure method alters pressure in a patient breathing pathway in a respiratory ventilator during specified periods of a patient's heart cycle. Heartbeats of a patient are detected in patient cardiac cycles, and an electrical heartbeat signal is generated in response to the heartbeats. In a presently preferred embodiment, the electrical heartbeat signal is squared to amplify the signal. A variable moment following a detected heartbeat is determined, and positive ventilation pressure in the patient breathing pathway is altered commencing at the variable moment following a detected heartbeat, for a variable time interval during selected cardiac cycles.

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 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 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 
pump 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 in 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 
synchronized with diasrole. 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 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 this, his recorded data show that pulmonary 
artery pressure was waxing and waning precisely opposite to the blood 
pressure. A plausible explanation is an increase in pulmonary artery 
pressure is simply a reflection of an increase in pulmonary vascular 
resistance which causes a decrement in left ventricular filling and thus 
decrease in systemic blood pressure secondary to a decrease in cardiac 
output. If the slight oscillations in the systemic blood pressure reflect 
oscillations in cardiac output, then Pinchak's study would support Pinsky 
and Carlson's work, suggesting that positive airway pressure is least 
detrimental during diastole. 
SUMMARY OF THE INVENTION 
The invention concerns a computer-gated, positive expiratory pressure 
system for supplementing positive end-expiratory pressure (PEEP) systems. 
The output of a cardiogram machine is amplified and squared, or an LED of 
a cardiogram machine is optically monitored, to determine an R-wave, or 
the beginning of electrical systole. A signal is fed to a multiplier where 
the R-R wave signal (period) is multiplied representing the duration of 
the R-R wave with a variable interval set by a physician. The resultant 
product (R-R wave times variable interval) is used to trigger a solenoid 
operated 3-way valve. The 3-way valve is normally closed to pass a 
positive pressure to a standard PEEP valve which functions normally. When 
triggered, the 3-way valve opens to allow a relatively low pressure to 
pass to the PEEP valve such that the PEEP valve creates a low pressure to 
the patient. 
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.

DETAILED DESCRIPTION OF THE INVENTION 
The computer-gated, positive expiratory pressure system is shown in FIG. 1 
in its environment, connected to a therapeutic device such as a PEEP 
system. A patient 10 is shown using a respirator or ventilator 12 via a 
standard expiratory (PEEP) valve 14. The PEEP valve 14 opens and closes to 
allow low and high pressures to the patient 10. In accordance with the 
present 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 FIGS. 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 pneumatically connected to a low relative 
pressure 28, while a third end is connected to the PEEP valve 14 via which 
the patient 10 received the positive pressure breaths. 
Under normal operation of the ventilator 12, the PEEP valve 14 is operated 
to allow alternate low and high positive pressure breaths (approximately 
0.4 psi) from the ventilator 12 to pass directly to the patient 10. 
However, in response to the output of microcomputer 18, the solenoid 22 is 
energized to yield at output 30, 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 low pressure is 
received by the patient 10 from the ventilator 12. The resultant low 
pressure, in accordance with the present invention, occurs just prior to a 
predicted heart beat to insure 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 FIG. 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. 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 attending physician between 15 and 400 
microseconds, for instance, by typical analog controls. The variable 
interval signal from 20 and the period signal from calculator 36 are used 
to generate a product in multiplier 38. The resultant product is used as a 
signal to energize the solenoid 32, to control 3-way valve 24. 
In a normal state, 3-way 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.times.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 
pulse to the solenoid is controlled by a second timer (not shown). 
FIG. 3 reveals a second embodiment for determining or sensing heart beats. 
A photodetector 40 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 FIG. 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 (e.g. C 64 Commodore Computer) may be adapted and software 
developed to monitor and determine beat period, with a programmable 
variable interval for use by the physician.