Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Patent
1992-01-24
1994-05-03
Wiecking, David A.
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
12820424, 12820423, A61M 1600
Patent
active
053077954
DESCRIPTION:
BRIEF SUMMARY
This invention relates to improvements in or relating to medical ventilators and, in particular, concerns improvements in the control of the operation of medical ventilators.
There are two basic types of known medical ventilators.
A first known kind of medical ventilator, termed a constant volume flow generator, operates with respiratory fresh gas at relatively high pressure and therefore functions as a flow generator capable of providing a set flow of respiratory fresh gas such that the volume of respiratory gas supplied to a patient during a breathing cycle remains approximately constant irrespective of changes in the pulmonary characteristics, i.e. resistance of the airways and pulmonary compliance, which constitute a load to the ventilator. This type of ventilator is not versatile for all age groups of patients and suffers from high lung pressures.
A second known kind of medical ventilator operates with a relatively low generated pressure and functions as a pressure generator which is not capable of maintaining constant the volume of the ventilating respiratory gas supplied to the patient during a breathing cycle in the face of changes in the pulmonary characteristics. This pressure generator type of ventilator is highly versatile and can be used safely for any patient age groups.
Because known medical ventilators of the second kind are preset to maintain pressure conditions which are constant once set, changes in the condition of the lungs of a patient connected to such a ventilator, after the initial pressure conditions have been set to suite the initial condition of the patient's lungs, can cause considerable changes in physiological respiratory parameters, such as the volume of gas delivered to the patient's lungs during the breathing cycle or the concentration of carbon dioxide in the expired gas at the end of the expiration phase of the breathing cycle, the so-called end tidal carbon dioxide concentration.
It is an object of the present invention to provide an improved medical ventilator of the pressure generator kind and a method of operating such a ventilator to regulate automatically a selected physiological parameter of the patient's respiration, even though the pulmonary characteristics change over time.
Accordingly, in one aspect, the present invention provides a medical ventilator comprising means for initially setting the pressure of respiratory fresh gas supplied to a patient to obtain a desired value of a respiratory parameter to be controlled, means for measuring the value of the respiratory parameter during subsequent operation of the ventilator, means for detecting in the measured value of the respiratory parameter any change from the desired value, and means for adjusting the setting means in dependent upon the change in the measured value of the respiratory parameter in order to vary the pressure of respiratory fresh gas supplied by the ventilator so as to maintain the respiratory parameter at the desired value.
In another aspect, the invention provides a method of operating a medical ventilator in which the pressure of respiratory fresh gas supplied to a patient is variable, comprising initially setting the pressure of the respiratory fresh gas to obtain a desired value of a respiratory parameter to be controlled, measuring the respiratory parameter during subsequent operation of the ventilator, detecting in the measured respiratory parameter any change from the desired value, and adjusting the pressure of the respiratory fresh gas supplied by the ventilator in dependence upon the change in the respiratory parameter so as to maintain the respiratory parameter at the desired value.
In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic representation of one medical ventilator embodying the present invention; and
FIG. 2 is a diagrammatic representation of another medical ventilator embodying the invention.
Referring firstly to FIG. 1, one
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Chakrabarti Mihir K.
Whitwam James G.
Caduceus Limited
Lewis Aaron J.
Wiecking David A.
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