Method and apparatus for producing a central pressure waveform in an oscillometric blood pressure system

A method for estimating forward and reflected components of the aortic blood pressure waveform from an aortic pressure waveform obtained from a blood pressure cuff, said method comprising the steps of:

• a. inflating a blood pressure cuff on a brachial artery of an arm to a pressure at least as great as the diastolic pressure;
• b. holding the molar amount of fluid in the blood pressure cuff constant;
• c. sensing a sequence of cuff pressure waveforms associated with the brachial artery that result from at least one cardiac ejection cycle;
• d. determining the portion of the aortic pressure waveform, P, that occurs during diastole;
• e. finding two parameters, γ and PRes fitting an exponential decay to the diastolic portion of the waveform P, to determine an exponentially decaying pressure, PDecay;
• f. assuming a form of the incident waveform emanating from the heart, PIncident;
• g. calculating a reflected wave, PIliac, from PIncident and a predetermined model of reflection from the distal aorta;
• h. calculating a pressure wave PValve representing a further reflection of the reflected wave PIliac from the aortic valve, wherein the further reflection substantially only occurs during diastole;
• i. calculating the parameters, α and β, that best fit an equation of the form PEst=PRes+α PIncident+β(PIliac+PValve)+PDecay to the measured aortic pressure waveform P;
• and
• j. calculating the incident wave according to α×PIncident and the reflected wave according to β×PIliac.