Air flow control apparatus and method for an automatic blood pressure gauge
First Claim
1. Apparatus suitable for use in an automatic blood pressure gauge having a cuff which contains a pressurizing fluid, comprising:
- pressure measuring means, coupled to the cuff, for measuring an instantaneous pressure level of the pressurizing fluid in the cuff at a plurality of instants corresponding to starting points of a respective plurality of time periods to produce a pressure signal;
valve means, coupled to the cuff and having an aperture which may be changed in response to an applied control signal, for venting the pressurizing fluid from the cuff at a flow rate determined by said control signal; and
flow control means, communicating with said pressure measuring means so as to be responsive to the pressure signal, for generating successive predictive values for the control signal applied to the valve means at respective ones of the instants corresponding to the starting points of the plurality of time periods, to produce a reduction in the instantaneous pressure level of the pressurizing fluid in the cuff during a time interval which includes the plurality of time periods, and at a rate which approximates a predetermined desired rate of pressure reduction;
and wherein said flow control means includes a table of possible predictive values for the control signal, each value in said table being associated with a respective value of the pressure signal; and
means for indexing the table of possible predictive values using the pressure signal to obtain a next predictive value of the control signal to be used during a corresponding next one of the plurality of time periods.
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Accused Products
Abstract
A deflation control system for the pressurized cuff of an automatic blood pressure gauge uses a pressure sensor to control solenoid valves. The solenoid valves are responsive to respective pulse signals having variable duty cycles to change their time-apertures and, thus, their flow rates. The duty cycles of the pulse signals are controlled to maintain a desired constant rate of pressure reduction in the cuff. A microprocessor generates a control value which determines the duty cycles of the pulse signals. This value is proportional to the initial volume of fluid in the cuff and to a predictive term which is provided from a table that is indexed by cuff pressure. This value is then augmented by a feedback term, generated by a feedback control loop to ensure an accurate deflation rate. The gain of the feedback loop is selected so that the feedback correction signals do not interfere with pulse signals modulating the pressure signal. The feedback term is normalized by the initial volume measurement. In addition, any new valve setting is applied in small steps over a time interval to further ensure smooth changes in the flow rate.
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Citations
21 Claims
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1. Apparatus suitable for use in an automatic blood pressure gauge having a cuff which contains a pressurizing fluid, comprising:
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pressure measuring means, coupled to the cuff, for measuring an instantaneous pressure level of the pressurizing fluid in the cuff at a plurality of instants corresponding to starting points of a respective plurality of time periods to produce a pressure signal; valve means, coupled to the cuff and having an aperture which may be changed in response to an applied control signal, for venting the pressurizing fluid from the cuff at a flow rate determined by said control signal; and flow control means, communicating with said pressure measuring means so as to be responsive to the pressure signal, for generating successive predictive values for the control signal applied to the valve means at respective ones of the instants corresponding to the starting points of the plurality of time periods, to produce a reduction in the instantaneous pressure level of the pressurizing fluid in the cuff during a time interval which includes the plurality of time periods, and at a rate which approximates a predetermined desired rate of pressure reduction; and wherein said flow control means includes a table of possible predictive values for the control signal, each value in said table being associated with a respective value of the pressure signal; and means for indexing the table of possible predictive values using the pressure signal to obtain a next predictive value of the control signal to be used during a corresponding next one of the plurality of time periods. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Apparatus suitable for use in an automatic blood pressure gauge having a cuff which contains a pressurizing fluid, comprising:
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pressure measuring means, coupled to the cuff, for measuring an instantaneous pressure level of the pressurizing fluid in the cuff at a plurality of instants corresponding to starting points of a respective plurality of time periods to produce a pressure signal; valve means, coupled to the cuff and having an aperture which may be changed in response to an applied control signal, for venting the pressurizing fluid from the cuff at a flow rate determined by said control signal; volume determining means coupled to the pressure measuring means and responsive to the pressure signal produced thereby for determining an initial volume of the pressurizing fluid in the cuff and; flow control means, communicating with said pressure measuring means so as to be responsive to the pressure signal, and communicating with said volume determining means so as to be responsive to the determined initial volume for generating successive predictive values for the control signal applied to the valve means at respective ones of the instants corresponding to the starting points of the plurality of time periods, to produce a reduction in the instantaneous pressure level of the pressurizing fluid in the cuff during a time interval which includes the plurality of time periods, and at a rate which approximates a predetermined desired rate of pressure reduction. - View Dependent Claims (11, 12)
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13. A method of deflating a cuff of an automatic blood pressure gauge in a controllable manner, the cuff containing a pressurizing fluid, the method comprising the steps of:
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a) measuring an instantaneous pressure level of the pressurizing fluid in the cuff at a plurality of instants corresponding to starting points of a respective plurality of time periods to produce a pressure signal; b) determining an initial volume of the pressurizing fluid in the cuff; c) generating, at the instants corresponding to the starting points of the plurality of time periods, a respective plurality of successive predictive values for a control signal responsive to the measured pressure levels, wherein the successive predictive values of the control signal determine a rate at which the measured pressure levels are decreasing in the cuff during the respective time periods, so as to reduce the pressure of the pressurizing fluid in the cuff at a rate which approximates a predetermined desired rate of pressure reduction; and d) controllably venting the pressurizing fluid from the cuff in response to the control signal. - View Dependent Claims (14, 15, 16, 17, 18)
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19. Apparatus for measuring the initial volume of pressurizing fluid in a cuff of a blood pressure gauge, comprising:
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pump means coupled to the cuff for inflating the cuff with the pressurizing fluid; pressure measuring means coupled to the cuff for measuring an instantaneous pressure of the pressurizing fluid in the cuff to generate a pressure signal; inflation rate determining means coupled to the pressure measuring means and responsive to the pressure signal for calculating, from the pressure signal, an inflation rate signal representing a rate at which the instantaneous pressure of the pressurizing fluid in the cuff is increasing as the cuff is inflated by the pump means; flow rate determining means coupled to the pressure measuring means and responsive to the pressure signal, for generating a flow rate signal, representing an instantaneous rate of flow of the pressurizing fluid into the cuff; and means coupled to both the inflation rate and flow rate determining means and responsive to both the inflation rate and flow rate signals, for dividing the flow rate signal by the inflation rate signal to produce a value representing the instantaneous volume of the pressurizing fluid in the cuff.
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20. Apparatus for measuring the initial volume of pressurizing fluid in a cuff of a blood pressure gauge, comprising:
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pump means coupled to the cuff for inflating the cuff with the pressurizing fluid; pressure measuring means coupled to the cuff for measuring an instantaneous pressure of the pressurizing fluid in the cuff to generate a pressure signal; inflation rate determining means coupled to the pressure measuring means and responsive to the pressure signal for calculating, from the pressure signal, an inflation rate signal representing a rate at which the instantaneous pressure of the pressurizing fluid in the cuff is increasing as the cuff is inflated by the pump means; flow rate determining means, coupled to the pump means, for providing a flow rate signal, representing a flow rate for the pressurizing fluid provided by the pump means to the cuff; and means coupled to both the inflation rate determining and flow rate indicator means and responsive to both the inflation rate and flow rate signals, for dividing the flow rate signal by the inflation rate signal to produce a value representing the instantaneous volume of the pressurizing fluid in the cuff.
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21. Apparatus suitable for use in an automatic blood pressure gauge having a cuff which contains a pressurizing fluid the apparatus, comprising:
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pressure measuring means, coupled to the cuff, for measuring instantaneous pressure levels of the pressurizing fluid in the cuff to provide a pressure signal; valve means, coupled to the cuff and having an aperture which may be changed in response to a control signal, for venting the pressurizing fluid from the cuff at a rate determined by the control signal; and feedback control means coupled to the pressure measuring means and responsive to the pressure signal for generating said control signal to control the venting of the pressurizing fluid from the cuff to maintain a desired rate of pressure reduction, said feedback control means including; deflation rate determining means, coupled to receive said pressure signal, for calculating a deflation rate signal representing an instantaneous rate of pressure reduction in the cuff; differencing means coupled to the deflation rate determining means and responsive to the deflation rate signal for calculating a difference between the deflation rate signal and the desired rate of pressure reduction to produce a deflation rate difference signal; and means coupled to the differencing means and responsive to the difference signal for multiplying the deflation rate difference signal by a value representing an initial volume of the pressurizing fluid in the cuff to generate said control signal.
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Specification