C. The composition of the trigger mechanism

1. The concept and the purpose

It detects the beginning of the spontaneous-respiration, it makes the beginning of this and the mechanical ventilation synchronize and it improves the efficiency of the ventilation and the comfort of the patient.

2. The component

(1) It is composed by the sensor and (2) signal conditioning type (3) breathing circuit.

3. The control system (The controlling mechanism and the operation theory)

Theoretically, it made the float rigger which makes current velocity and a flow rate an index main constituent. It saw and the best method was chosen from the technology background and the ventilation mode in the times because the method was best but the proposition to secure a physically stable sensitive sensor, being small, being light-weight and being cheap could not be solved. In turn of them specified by it

1) The classic times (The 1940-1950s)

The resuscitator this time is called "Controller" and doesn't have a trigger mechanism. It became the method which drives a piston and Belleau through the cam, the gear by the rotary force of the electric motor. It becomes the structure to prescribe by these mechanisms in the intake time and the expiration time, too. Moreover, it was difficult for the inertia weight of mechanical itself to do disaster and to drive according to the beginning of the intake effort of the patient. (Bang, Beaver, Spiropulsator, Barnet, and so on)

2) The pressure switch, the new Mattick control system (1950 pieces of the second half-the 1960s)

The switch which detects an airway pressure change in the new Mattick circuit-system and changes the flow of gas which was controlled, that the flow of gas was mechanical is used (Bird mark Assister of 4, Bennett PR-2, MRT CV-2000, Blease Plumoflator 等).

3) The pressure switch, the electric circuit method (1960 pieces of the second half-the 1980s)

The electrical switch is necessary in 入 in the airway pressure change and signals an electric-control circuit. It is used in Volume Assister of Bennett MA-1, New Port E-100, the -3000th prize CV.

4) The flow rate switch, the electric-control method (The 1980s -)

It takes the flow of intake gas in the physical phenomenon and it signals an electric-control circuit. It was used with the SIMV machine of Ohmeda CPU-1, the -2nd prize Bear.

5) Flow rate sensor ー, the electric-control method (1981-)

It is measuring an intake capacity continuously with flow rate sensor ー and it signals an electric-control circuit if becoming above the constant value. It is used in Engstrom Erica, Elvira (the SIMV machine-PSV compatible machine).

6) The pressure sensor, the electric circuit method (1980 -)

The method which begins intake in the pressure change in the trigger period by which the change of the airway pressure changed into the electronic signal continuously and it used for the various control circuit but was limited with the pressure sensor Bennett 7200, Bear-5, Bird 6400, Bird Most of 8400, the -300th prize Servo present typical PSV compatible machines belong to this group.

7) Multi- mode of processing of sensor's being compound (The 1990s -)

At the recent resuscitator (the equipment which has PSV and the other ironhand type ventilation mode), in each circuit part, it is measuring but these information is judged by the complex-condition using MPU in the pressure and the current velocity, the flow rate. Also, there is a machine which changes a trigger condition by the mode, too. Bennett At 7200, to be general is a pressure trigger formula but at the time of Flow by, a flow rate trigger is used. Servo-300 can choose a pressure trigger and the pressure/flow rate trigger. The ventilation setting changes a trigger condition at the pressure/the flow rate. In Drager Evita, the pressure trigger is used for usual ventilation but uses a complex-condition for ASB and BIPAP. A 0.2-mbar negative pressure and the intake flow rate of 40 ml are used. The flow rate condition of 1-15LPM (variable), too, can be taken account of. However, the complex-condition is unfinished and are groping about the best method by it.

8) The trigger inside the premature baby, in the newborn baby (PTV,Patient Triggered Ventilation) (The 1990s -)

The PTV feature began with Siemens Servo-300 but the equipment of each Inc. is equipped with it one after another. Drager BabyLog, Infrasonic Infant Star, VIP Bird, SLE-2000, BearCub II are a representative. The trigger formula is in the condition of acceleration sensor ー and hundred flowers 繚乱 inside the pressure, the flow rate, in the diaphragm. The method the sensor technology, too, is immature about the sensing by such a nano-domain and also for where it is the optimal, too, is a groping step. To converge on the constant method, the time will be necessary.

4. The decorative element

1) The time constant of breathing circuit

The circuit time constant of breathing circuit is fixed by the compliance and the tube resistance of breathing circuit. It is easy to absorb a change by the intake effort when the compliance is high. Also, the time constant increases and to be behind in the phase becomes big and moreover it increases delay to the detection. The increase of the tube resistance has a big influence on the trigger sensitivity in addition to influencing a time constant. In the pressure trigger formula, it is favorable but it is disadvantageous to the flow rate trigger formula.

2) The detection method and the part of the intake effort

(1) The output inside the resuscitator

Because the pressure change detection method in this place undergoes influence by the heating humidifier, the sensitivity, the driver reaction time are dull. It was made a machine in front of 1 generation by the frequently-used in the current velocity, the flow rate trigger formula.

(2) The Y peace part

A pressure change detection method in this part is used in the boiling when the trouble that breathing circuit is blockaded supports a high circuit for the infant when wanting to improve sensitivity on the mechanism when wanting to make have the leak revision feature of breathing circuit. But, Proximal Airway Pressure Tube becomes necessary, being extra. of the sensitivity which is high in the flow rate, the current velocity change detection method in the part The quick response can look forward to it but in addition to that there is an agreement which makes sensor unit itself light-weight, being small, there is a problem of the price and the quality control, the maintenance of the reliability, the sterilization and so on, too.

(3) The exhalation-valve eve

A pressure change detection method in this place is most often used with the machine for the adult. To undergo the other side where breathing circuit becomes simple, influence by the time constant of breathing circuit is a fault.

(4) The other part

The method which detects the change of the esophageal-pressure as the substitution of the cavitas pleuralis internal pressure, the method, equal "GA" which detects the movement of the parapet are contrived but don't become popular in point of the certainty, the handiness.

3) The existence of the various continuous flow

of intake gas in breathing circuit in of the prevention of the regressiveness infection in of the cohesion for circuit Uchimizu The gas which was named a rinse flow, a purge flow, a bias flow, a constant flow in the separation of expiration gas, the reduction of the work volume to the trigger, the precision securing, the equal "WO" purpose of the sensor, being various is flowing. These continuous flows influence sensitivity, a response even if they are current velocity, a flow rate trigger formula in addition to the pressure trigger formula.

4) The sensitivity and the response of the trigger mechanism

Generally, the quickness is desirable for the response of the resuscitator but the response is related closely to the time constant of the servo loop of the resuscitator. If seeing from the resuscitator, breathing circuit and the lung are the load which has capacity and principal vibration. Even if it is an expiratory-phase, for the purpose, the maintenance of PEEP and the rinse style, intake gas is output. At the latest resuscitator, the improvement of the response is pursued and the time constant becomes small consequently. When using a silicone rubber tube for breathing circuit, there is a case that the time constant of the servo loop of the resuscitator and the time constant of the load (breathing circuit and the lung) approach and that the resonance causes the oscillation (the vibration) of the circuit. Because the circuit vibration is noise in this case, when making the "DURA" boiling sensitivity to have been high, Auto-cycle and the malfunction occur. As the measure, the time constant of breathing circuit must be changed. In other words, it considers the change of the length and the material, the diameter. There is a purpose to make a trigger signal rise from the noise ingredient in the complex-condition which is used for Evita and Servo-300. In the past, a concept, the noise countermeasure of the ambiguous patient circuit, is established in new Bennett840, being clear. The noise ingredient least-izes that it is effectively removed by filtering algorithm and the malfunction of the trigger mechanism.