Patient ventilator disconnect alarm

Normal breathing cycles of a ventilator cause an alarm controller circuit to emit a periodic pulse which resets a timer circuit thereby maintaining an alarm device in an "off" condition. Patient disconnect is sensed by an alarm trigger circuit which sends an inhibit pulse to the controller circuit inhibiting the timer circuit reset pulse. This causes the timer to "time out" thereby turning on an alarm actuator circuit which causes an audible and/or visual alarm condition.

BACKGROUND OF THE INVENTION 
This invention relates to alarm devices. More specificaly it relates to 
patient disconnect alarms for ventilators. 
Prior art patient disconnect alarms for ventilators merely monitored 
pressure in a ventilator circuit, eg., at the patient manifold, and if the 
pressure did not exceed a preset pressure limit an alarm would sound after 
a time delay. 
This system has a serious drawback in that any restriction at the end of 
the patient circuit, eg., a tracheotomy tube, can cause circuit pressure 
to increase even with the patient disconnected, thus causing the monitor 
to falsely indicate that the patient is connected. If the pressure drop 
created by a bacterial filter and/or a humidifier is added to that of a 
tracheotomy tube it becomes relatively easy for a pressure monitor to 
falsely indicate that a patient is connected to the ventilator. 
Also, if the pressure sensor is connected to the patient manifold, bacteria 
can enter the sensing tube, thus causing sterility and cross-contamination 
problems.

SUMMARY OF THE INVENTION 
In accordance with the invention there is provided a fluidic patient 
disconnect alarm controller apparatus for ventilators utilizing a 
pressurized source of gas, eg., oxygen, for operating the fluidic 
circuity. The apparatus comprises a patient disconnect alarm controller 
circuit having a first input port for sensing a periodic pressure signal 
from the ventilator, and providing a timer reset signal at a first output 
port thereof; and a second input port for sensing an alarm trigger circuit 
inhibit signal from a fluidic alarm trigger circuit and providing an 
inhibit signal at a second output port thereof. 
The fluidic alarm trigger circuit is provided with an input port for 
sensing the pressure of a breathing gas, eg. oxygen, at the patient outlet 
of the ventilator, an output port providing an alarm controller inhibit 
signal in response to a sensed pressure loss in the breathing hose 
representing a patient disconnect, and means coupling the inhibit signal 
to the second input port of the alarm controller circuit. 
A timer circuit is provided having an input port coupled to the first 
output port of the alarm controller circuit, and an output port providing 
a timed output pressure signal. 
An alarm actuating circuit is provided having an input port coupled to the 
output port of the timer circuit and an output port providing an output 
pressure signal to an alarm means. 
The alarm means is coupled to the output port of the alarm actuating 
circuit. 
Preferably the fluidic alarm trigger circuit has at least one input port 
for receiving a pressure reference signal, corresponding to a 
predetermined minimum patient breathing hose gas pressure. 
More preferably the alarm trigger circuit consists of a six-stage fluidic 
circuit having three proportional amplifiers connected in series with each 
other and with three serially connected fluidic flip flops. The trigger 
circuit provides means for connecting the inputs of one of the fluidic 
amplifier to a PEEP (positive-end expiratory pressure) signal and the 
patient breathing hose signal source. Also provided are means for 
connecting inputs of another one of the fluidic amplifiers to a pressure 
limit signal source and an adjustable positive-end expiratory pressure 
signal. The trigger circuit also provides for means connecting the outputs 
of one of the flip flops to the fluidic alarm controller circuit as a 
source of the alarm signal and to the atmosphere. The trigger circuit can 
provide an output in response to a small differential pressure at its 
inputs. 
Preferably the timer circuit comprises a fluidic capacitance, coupled to a 
variable fluidic resistance in communication with ambient atmosphere for 
timed discharge of the fluidic charge of the capacitance. 
Preferably a gate valve is coupled between the alarm controller circuit and 
the timer circuit, the gate valve comprising, a diaphragm switch having a 
sealed chamber provided with first and second ports coupled respectively 
to the source of the controller circuit timer signal and the timer circuit 
input port, the diaphragm permitting both communication between the first 
and second ports and sealing of the first and second ports, the diaphragm 
actuated for sealing by a third input port coupled to the second output 
port of the alarm controller circuit. 
Preferably the alarm actuating circuit comprises a gate valve comprising a 
diaphragm switch having a sealed chamber provided with a first and second 
ports coupled respectively to a source of alarm actuating fluidic pressure 
source gas and the alarm means, the diaphragm permitting both 
communication between the first and second ports and sealing of the first 
and second ports, the diaphragm actuated for sealing by a third input port 
coupled to the source of the timed output pressure signal of the timer 
circuit. 
Preferably a pressure regulator circuit is coupled upstream of the fluidic 
capacitance, the pressure regulator circuit comprising, a diaphragm switch 
having a sealed chamber provided with a first port in fluidic 
communication with the fluidic capacitance of the timer circuit and a 
second port in fluidic communication with ambient atmosphere, the 
diaphragm permitting both communication between the first and second ports 
and sealing of the first and second ports, the diaphragm actuated for 
sealing by a third input port coupled to a variable fluidic pressure 
source. It is the purpose of the regulator to provide a relatively 
constant time delay period, regardless of patient breathing rates. 
Preferably the periodic pressure signal to the first input port of the 
alarm controller circuit from the ventilator apparatus is transmitted by a 
signal delay circuit which comprises a diaphragm switch having a sealed 
chamber provided with a first port in fluidic communication with the 
ventilator inspiratory valve controlling means and a second port coupled 
to the first input port of the alarm controller circuit, the diaphragm 
permitting both communication between the first and second ports and 
sealing of the first and second ports, the diaphragm actuated for sealing 
by a third input port in fluidic communication with ventilator expiratory 
valve controlling means. 
The invention also provides a manually operable pressure switch (e.g. 
manual override) fluidically connected to the first input port of the gate 
valve coupled between the alarm controller circuit and the timer circuit, 
the pressure switch allowing fluidic pressure to override the diaphragm 
when the diaphragm is actuated closed by the alarm controller circuit 
inhibit signal. 
Broadly in the operation of the Patient Ventilator Disconnect Alarm of this 
invention, (See FIG. 1) the fluidic alarm controller circuit 10 senses a 
periodic pressure signal from the ventilator apparatus inhalation valve 
driver 11 and in the absence of an inhibiting signal provides a timer 
reset signal. This timer reset signal fluidically charges a capacitance in 
the timer circuit 12 which maintains a pressure signal on the alarm 
actuating circuit 13 preventing it from actuating the alarm means 14. A 
variable resistance in the timer circuit 12 allows for a predetermined 
timed discharge e.g., 15 to 30 seconds, of the fluidic charge of the 
capacitance which in the absence of a timer reset pressure signal, allows 
the timer to "time out", e.g., discharge its fluidic charge. 
When the timer circuit 12 pressure signal drops below that maintained at 
the alarm actuating circuit 13, the circuit 13 is activated causing the 
alarm means 14 to indicate a patient disconnect. The alarm may be an 
audible and/or visual signal. 
The timer inhibit signal is provided by the fluidic alarm trigger circuit 
16 which senses the pressure of the oxygen at the patient outlet of this 
ventilator 17 and compares it with a reference signal 18. An alarm trigger 
signal e.g., a timer reset inhibiting signal, is sent in response to a 
sensed pressure loss in the breathing hose representing that the patient 
is disconnected. The reference signal 18 also compensates for the use of 
PEEP which would otherwise negate the use of the alarm. 
Upon correction of the disconnect condition, the alarm maybe reset by means 
of a manual override 19 of the timer inhibit signal. 
As shown in FIG. 2 the pressure in the patient circuit is monitored during 
the time interval shown at A in diagrams I and II. This interval 
represents the oxygen pressure decay time between the ending of the 
inspiration period and the beginning of the exhalation period. 
When the patient is connected to the ventilator the oxygen pressure decay 
period A is gradual, as contrasted with the sharp decay shown when the 
patient is disconnected from the ventilator. Typically, if the oxygen 
pressure signal exceeds 4-5 cm. H.sub.2 O during the monitoring period 
(A), no timer inhibit signal will be sent by the fluidic alarm trigger 
circuit. 
The signal delay circuit 15 serves to delay the beginning of the monitoring 
of the time interval A slightly (interval B FIG. 2). Otherwise, compliant 
items in the patient circuit such as humidifiers mock the appearance of a 
patient. 
An advantage of the apparatus of this invention is that by sensing patient 
pressure at the ventilator outlet, upstream of a bacterial filter and 
humidifier, the sensing means e.g., tube is in the clean port of the 
circuit, and sanitation is not a problem. 
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
An embodiment of the invention is depicted in FIG. 3 wherein the alarm 
controller circuit 10 comprises an Inhibited OR gate 21, having a 
ventilator signal input 22 and an alarm signal input 23. Fluidic conduits 
24a and 24b connect a timer circuit reset output signal to the timer 
circuit 12 fluidic capacitance 26 via a gate valve 27. 
The gate valve 27 comprises a diaphragm switch 28 having a sealed chamber 
29, which provides fluidic communication between the conduit parts 24a and 
24b. Diaphragm 28 is actuated for sealing of conduit parts 24a and 24b by 
the "normally on" signal output 31 of the Inhibited OR gate 21. A one way 
valve 32 is provided to prevent fluidic back flow from a manual override 
19. 
An adjustable orifice, e.g., variable resistance 33 allows for the timed 
discharge of the fluidic charge of the capacitance 26 to the atmosphere. 
The capacitance 26 maintains a timed output pressure signal 34 at the 
alarm actuating circuit 13 preventing actuation of the alarm means shown 
generally at 14. The alarm actuating circuit 13 comprises a gate valve 
having a diaphragm switch 37 and a sealed chamber 38, which provides 
fluidic communication between a regulated oxygen signal (alarm actuating 
fluidic pressure source) 39 and an alarm means actuating signal 41. 
Diaphragm 37 is actuated for sealing conduits 39 and 41 by the timer 
circuit output pressure signal 34. 
The alarm signal input 23 to the Inhibited OR 21 is provided by the fluidic 
alarm trigger circuit 16. The preferred form of circuit 16 is shown as 
comprising a six-stage fluidic device incorporating three proportional 
amplifiers 44a, 44b, and 44c, connected in series with each other and in 
series with three serially connected flip flops 46a, 46b, and 46c. Each of 
the six circuits has its supply input coupled along the conduit 47 to the 
regulated oxygen signal 48. Also each of circuits 44a, 44b, 44c, 46a, 46b 
and 46 c have their control inputs coupled to the respective outputs of 
the preceding stage. The control inputs of the first proportional 
amplifier 44a are coupled respectively to the output of a PEEP circuit 49 
and a patient reference line (patient manifold) 51. 
An additional input to the alarm trigger circuit 16 includes a regulated 
oxygen signal 18 coupled with the Orifice 52 to supply a reference oxygen 
signal to proportional amplifier 44b. Reference 44b is additionally 
supplied with a regulated signal from the PEEP circuit 49 via adjustable 
orifice 53. 
The ventilator signal input 22 to the Inhibited OR 21 is preferably 
supplied via a signal delay circuit 15. The circuit 15 comprises a 
diaphragm switch 56 having a sealed chamber 57, which provides fluidic 
communication between the inspiratory side of the ventilator OR/NOR 
circuit signal 58 e.g., ventilator inspiratory valve controlling means, 
and input signal 22 to the Inhibited OR 21. Diaphragm 56 is actuated for 
sealing of fluidic OR/NOR expiratory signal 58 and the input signal 22 by 
the expiratory side of the Ventilator OR/NOR circuit signal, 59 e.g., 
ventilator inspiratory valve controlling means. The switching delay 
characteristics of circuit 15 is sufficient to delay the monitoring time 
interval A, for a period B (see FIG. 2). 
In a preferred embodiment of the invention a pressure regulator circuit 61 
is fluidically coupled upstream of the fluidic capacitance 26. The 
pressure regulator circuit 61 comprises a diaphragm switch 62 having a 
sealed chamber 63, which provides a fluidic communication between the 
fluidic capacitance 26 via conduit 64 and the atmosphere via conduit 66. 
Diaphragm 62 is actuated for sealing of conduits 64 and 66 by port 67 
which is coupled to a variable fluidic pressure source 68, e.g., oxygen. 
The alarm means shown generally at 14 is depicted as an audible alarm, 
though it is understood that a combination visual and audible alarm is 
within the scope of this invention. It is also understood that single or 
multiple alarms may be used. 
The alarm means 14 comprises a pair of audible whistles 71a and 71b which 
are activated by a pair of conventional alarm drivers 72a and 72b. It is a 
feature of the alarm means 14 that an oscillator valve may be incorporated 
to create an intermittant alarm. One such oscillator valve is shown at 73. 
It comprises a diaphragm switch 74 having a sealed chamber 76, which 
provides fluidic communication between the alarm means actuating signal 41 
and the alarm driver 72a and 72b actuating signal 77. Diaphragm 74 is 
actuated for sealing signals 41 and 77 by an oxygen flow interuptor signal 
78. 
FNT Diaphragm amplifiers #128, Fred Knapp Engineering Co., Racine, Wisc. 
A provision of alarm 71b and driver 72b is that they may be actuated as an 
alarm for other function of the ventilator by means of ventilator signal 
79. 
When the reason for a patient disconnect has been corrected, the alarm may 
be reset, e.g., the capacitance 26 fluidically changed, by means of the 
manual override 19. This override generates sufficient pressure to 
overcome the inhibit signal output 31 and allow fluidic communication 
within chamber 29. fluidic communication between the OR/NOR exspiratory 
signal 58 and input 22 of the Inhibited OR gate 21. The diaphragm switch 
56 causes a 40 millisecond delay approximately in the input signal 22 and 
in the absence of an inhibit signal input 23, a timer reset pulse is sent 
out via 24a and 24b to charge the fluidic capacitance 26. The fluidic 
charge in the capacitance 26 maintains an output pressure signal 34 on the 
alarm actuating circuit 13. Signal 34 has a preset time period set by the 
variable resistance 33 as it discharges the fluidic charge of the 
capacitance 26 to the atmospheric. If at the end of the time period the 
capacitance 26 has not been recharged, the capacitance 26 "times out" and 
the output pressure signal 34 ceases, causing the actuation of circuit 13. 
Recharging capacitance 26 before it "times out" maintains output signal 
34, inhibiting the alarm circuit 13. 
The maximum pressure in the capacitance 26 is limited to 20-30 cm H.sub.2 O 
by the pressure regulator circuit 61. This makes the capacitance 26 
discharge less dependent upon the cycling rate of the ventilator. The 
reference pressure of 20-30 cm H.sub.2 O is provided by the variable 
fluidic pressure source 68 by adjustment of the variable resistance 69. 
An alarm signal input 23 to the Inhibited OR gate 21 from the alarm trigger 
circuit 16 inhibits the timer circuit reset output signal to the 
capacitance 26 causing the capacitance 26 to "time out" thus causing the 
alarm means 70 to be actuated. 
The alarm trigger circuit 16 monitors a patient circuit input 51 and 
compares it with a regulated oxygen reference signal 48 and a PEEP signal 
49. The restricted orifice 52 sets the swithcing level of circuit 16 at 
about 4 to 6 cm H.sub.2 O. A patient circuit input 51 greater than 8 cm 
H.sub.2 O prevents an alarm signal and the fluidic charge is vented to 
atmosphere at 42. 
A patient circuit input 51 less than 4 to 6 cm H.sub.2 O switches the 
signal from vent 42 to an alarm signal input 23 to the Inhibited OR gate 
21. An inhibit signal output 31 from gate 21, seals the chamber 29 causing 
the capacitance 26 to "time out" and hence cause the alarm means 14 to be 
actuated.