Ventilator

Abstract: A ventilator (1) to be connected to the airways of a human or an animal comprises several functional units, where each functional unit is controlled and/or supervised by a separate microprocessor. At least one of the functional units comprises an analog control unit (11), whereby the microprocessor only compensates for the coarseness in the regulating function of the analog control unit (11) to increase the accuracy. This makes the ventilator (1) expeditious, accurate and safe.

Description: The invention relates to a ventilator to be connected to the airways of a human or of an animal for supplying and emitting respiratory gas to and from the airways, respectively, according to a predetermined pattern, which is dependent on at least one parameter, said ventilator comprising an analog control unit, which, depending on the parameter, regulates the supplying and/or the emitting of the respiratory gas so that a predetermined pattern is largely maintained. The invention also relates to a ventilator, which comprises several functional units, which makes it possible for the ventilator to let the supplying and or emitting of respiratory gas to follow a predetermined pattern and a microprocessor, which controls and/or supervises at least one of the functional units. A known ventilator (Servo Ventilator 900C, Gebrauchsanweisung publ. No. AG 11884, oct 88) comprises an expiration section with an expiration valve, which opens and closes by means of an electromagnet. Thereby, a desired pressure can be maintained in the expiration section of the ventilator. The electromagnet is controlled by an analog control unit, which, depending on the existing air pressure, controls the position of the expiration valve. The advantage with the analog control unit is that it quickly adjusts to the desired regulation level, but it is not very accurate when it comes to maintaining a constant desired pressure. Another known ventilator (7200 Series Microprocessor Ventilator, Puritan Bennett, form No. AA-213, May 83) has a microprocessor that controls and supervises practically all functions of the ventilator. For example, the pressure in the expiration section may be maintained with high accuracy at the desired value. On the other hand, the complexity of the system slows down a desired change of the pressure in the expiration unit as the microprocessor moves towards the new position of equilibrium at a slow pace. Further, the ventilator is extremely vulnerable. If the microprocessor would cease to function for any reason, also the functional units of the ventilator will cease to operate, and the result may be disastrous for a patient connected to the ventilator. It would therefore be desirable with a ventilator where the desired values, such as flow or pressure, can be obtained quickly and maintained with high accuracy, and also have increased safety for the patient. This is achieved in accordance with the invention in that the ventilator according to page 1, first paragraph further comprises a digital control unit which, depending on the parameter and the regulation of the analog control unit, compensates for the coarseness in the regulating function of the analog control unit so that the predetermined pattern is maintained almost in its entirety. Hereby, the advantages of the rapid analog adjustment and the accurate digital adjustment are combined. Since the digital unit only compensates for the fault of the regulation of the analog unit, the ventilator will be fairly insensitive to failures in the digital unit. Should the digital unit break down, the function of the ventilator would not be inferior to a system controlled by only an analog control unit. The digital control unit preferably comprises a microprocessor. Alternatively, for the ventilator according to page 1, second paragraph, the problem is solved in that a further microprocessor controls and/or supervises at least one of the other functional units. This decreases the risk of having the entire ventilator break down if a microprocessor ceases to function. By distributing the tasks of the microprocessors correctly, it is possible to maintain the essential life supporting functions even if a microprocessor ceases to function, and the patient will not be exposed to any danger. Further, each microprocessor can be specialized for its function and thereby be able to individually work faster than a central microprocessor, whereby the speed of the system also increases. For optimal function, the microprocessors should exchange information with each other, and this may be done digitally, analogously or both. The essential is to prevent erroneous signals from a broken-down microprocessor to disturb a functioning microprocessor. This may, for example, be done by having the functioning microprocessor ignore the information from the broken-down microprocessor if it falls outside a specific interval that is dependent on other information in the microprocessor. By combining the two alternative solutions, a much safer ventilator is provided, which is fast and accurate. A ventilator in accordance with the invention is described in more detail in connection with the figure. The figure shows a simplified diagram of a ventilator 1 according to the invention. The ventilator 1 comprises an inspiration section 2, an expiration section 3 and a setting/supervising section 4. Air and possible additional gases enter the inspiration section 2 under high pressure through the gas inlets 5a, 5b, 5c and pass through an inspiration unit 6, in which the respiratory gas is mixed to correct proportion and its pressure and flow adjusted by means of a set of valves. In the inspiration unit 6, there is also a bacteria filter, a pressure transducer, a flow transducer, an oxygen transducer, a safety valve, etc. There are therefore several functions that need to be maintained, e.g., keeping the mixture of gases constant. This is achieved by a functional unit, which comprises valves at the gas inlets 5a, 5b, 5c. Another functional unit may supervise the mixture of gases and sound an alarm if the mixture gets out of proportion. Thereby, the safety for the patient may be optimized. In this embodiment, the inspiration unit 6 with its functional units is controlled by a control device 7, which provides instructions for the inspiration unit 6 via a conductor 101 and which receives information from the inspiration unit 6 via a conductor 102. The conductor 102 also provides the information to the setting/supervising section 4, which will be described in more detail below. From the inspiration unit 6, the respiratory gas is led through a tube 8 to the airways of a patient. In the expiration section 3, the respiratory gas is led away from the airways of the patient through the tube 8 and out to the surrounding area. On its way out, the respiratory gas will pass a pressure- and flow transducer 9 and a valve arrangement 10. By letting the valve arrangement 10 keep the tube more or less closed, a desired pressure can be maintained in the expiration section 3. Measured values of pressure and flow are transferred through a conductor 103 to an analog linearizer 11, a digital compensator 12 and to a servo unit in the valve arrangement 10. The conductor 103 also leads to the setting/supervising section 4, which is described in more detail below. The analog linearizer 11 is connected with the digital compensator 12 via a conductor 104, with the valve arrangement 10 via a conductor 105 and with the setting/supervising section 4, which is described in more detail below. The setting/supervising section 4 comprises a setting/display unit 13, a supervising unit 14 and a reference signal generator 15. A data bus 107 connects the setting/display unit 13, the supervising unit 14, the reference signal generator 15 and the digital compensator 12 with each other. These connections may also be analog. The setting/display unit 13 can also send information to the analog linearizer 11 via a conductor 108 and to the control device 7 via a conductor 109 and receive information from the supervising unit 14 via a conductor 111. The supervising unit 14 can further, via the conductor 102, as mentioned above, receive information from the inspiration unit 6 and may also receive information from the pressure-and flow transducer 9 via the conductor 103 and from the analog linearizer 11 via a conductor 112. The reference signal generator 15 may via a lead 106 send signals to the valve arrangement 10. Finally, the control device 7, the supervising unit 14 and the reference signal generator 15 are connected with a data bus 110. This data bus 110 may also be replaced by analog connections. When a patient is connected to the ventilator 1, a suitable pattern is set on the setting/display unit 13, which pattern is tracked by the ventilator and adapted to the patient. The set values are transferred to a microprocessor in the setting-/display unit 13, where they can be transferred further in digital form via the data bus 107. Some of the set values are also transferred in analog shape through the conductors 108 and 109 to the analog linearizer 11 and the control device 7, respectively. The reference signal generator 15, which comprises a microprocessor, calculates, based on the settings made, the breathing curve to be tracked by the inspiration section 2 and transfers this information to a microprocessor in the control device 7 via the data bus 110. The control device 7 also comprises an analog control unit, which has been provided information via the conductor 109. It is the task of the microprocessor to compensate for any fault in the regulation of the analog control unit. The control of the valve arrangement 10 in the expiration section 3 takes place in a similar way. The reference signal generator 15 sends a signal to the valve arrangement 10. The signal is compared with the actual pressure obtained from the pressure- and flow transducer 9. To speed up the control of the valve arrangement 10, a digitally compensated signal is also sent from the analog linearizer 11 to the valve arrangement 10. The digitally compensated signal is obtained in that the analog linearizer 11 first linearizes the flow value from the pressure- and flow transducer 9. This linearization is sent to the digital compensator 12 that comprises a microprocessor where a compensation is calculated and sent back to the analog linearizer 11 and added to its linearizing signal. The digitally compensated signal is also transferred to the supervising unit 14. The digital compensator 12 hereby compensates for, among other things, the mixture of the gas (viscosity), the pressure of the surrounding area and the signal from the analog linearizer 11. The supervising unit 14 has mainly two tasks; one is to provide the setting-/display unit 13 with the actual measured values in the ventilator and the other is to sound an alarm as soon as the measured values differ too much from the set values. A microprocessor in combination with analog back-up systems makes the supervising safe and accurate. The ventilator 1 in this embodiment comprises five microprocessors in all. They are, as described above, located in the setting-/display unit 13, in the reference signal generator 15, in the control unit 7, in the digital compensator 12 and in the supervising unit 14. The microprocessors basically operate independently of each other but do exchange information for an optimal function. As mentioned previously, the exchange of information may be purely digital, purely analog or a combination of both. It is possible to have one or several of the microprocessors out of order without severe damage to the function of the ventilator 1. If, for example, the microprocessor in the setting-/display unit 13 ceases to function, the worst that can happen is that the compensation in the control device 7 and the digital compensator 12 becomes a bit less accurate. This can happen because the microprocessor may transmit completely wrong signals when it has ceased to function. But, as the settings made also have been provided analogously through the setting of the potentiometers, the coarse regulation of the analog control will not be affected. The supervising unit 14, however, will sound an alarm, which means that a microprocessor has ceased to function and the ventilator can then be replaced and repaired at a suitable time. Reference list 1 ventilator 2 inspiration section 3 expiration section 4 setting-/supervising section 5a, 5b, 5c gas inlets 6 inspiration unit 7 control device 8 tube 9 pressure- and flow transducer 10 valve arrangement 11 analog linearizer 12 digital compensator 13 setting-/display unit 14 supervising unit 15 reference signal generator 101 - 106 conductors 108 - 109 conductors 111 - 112 conductors 107, 110 data buses

Claims: Ventilator (1) to be connected to the airways of a human or of an animal for supplying and emitting respiratory gas to and from the airways, respectively, according to a predetermined pattern, which is dependent on at least one parameter, said ventilator comprising an analog control unit (11), which, depending on the parameter, regulates the supplying and/or the emitting of the respiratory gas so that the predetermined pattern is largely maintained, characterized in that a digital control unit (12), depending on the parameter and the regulation of the analog control unit (11), compensates for the coarseness in the regulating function of the analog control unit (11) so that the predetermined pattern is almost completely maintained. Ventilator according to claim 1, characterized in that the digital control unit (12) comprises a microprocessor. Ventilator according to claim 1 or 2, characterized in that the ventilator 1 further comprises several analog control units. Ventilator according to claim 3, characterized in that for each analog control unit there is a separate microprocessor, which compensates for the coarseness in the regulating function of each analog control unit, respectively. Ventilator (1) to be connected to the airways of a human or of an animal for supplying and emitting respiratory gas to and from the airways respectively, which ventilator comprises several functional units, which makes it possible for the ventilator to allow the supplying and/or emitting of a respiratory gas to follow a predetermined pattern and a microprocessor, which controls at least one of the functional units, characterized in that a further microprocessor controls and/or supervises at least one of the other functional units. Ventilator according to claim 5, characterized in that at least one of the functional units comprises an analog control unit (11). Ventilator according to claim 6, characterized in that a microprocessor (12) compensates for the coarseness in the regulating function of the analog control unit (11).

Inventors: CEWERS GOERAN, DAHLSTROEM BO, OLSSON SVEN-GUNNAR DR, RYDGREN GOERAN, CEWERS, GOERAN, DAHLSTROEM, BO, OLSSON, SVEN-GUNNAR, DR., RYDGREN, GOERAN, Cewers, Göran, Dahlström, Bo, Rydgren, Göran
Applicants: SIEMENS AG, SIEMENS ELEMA AB, SIEMENS AKTIENGESELLSCHAFT
Application year: 1991
Main classification: A61M16
IPC codes: A61M16