Abstract: The present invention relates to the use of the arterial pressure waveform recorded invasively or non-invasively, to distinguish between compensatory vasoconstriction with low cardiac output on the one hand from vasodilation from more severe organ damage on the other, as a cause of hypotension in acute emergencies. The waveforms may be subjected to harmonic analysis and the moduli of their harmonic components compared whereby a hypotensive individual can be confirmed to have the higher (second and above) greater than the first harmonic is considered as having vasoconstriction as a cause of hypotension.

Abstract: A method is disclosed for determining the aortic flow velocity waveform non-invasively. A calibrated ascending aorta pressure waveform can be derived from peripheral measurements, for example at the radial artery, and calibrated from conventional syphgmomanometry, for example at the brachial artery. From the calibrated ascending aorta pressure waveform the flow velocity waveform in the ascending aorta can be determined, by using the Fourier transform of the pressure waveform and the age-related phase and modulus values. The method can also be used for invasively measured pressure waveforms to provide a flow waveform.

Abstract: Disclosed is an improved arrangement for allowing more accurate automatic calibration for a system in which blood pressure pulses are derived for remote sites from a calibrated measurement and a waveform measurement, when these are made at different sites. Where a calibrated measurement is made, say, at the brachial artery (11), and a waveform recorded at the radial artery (12), a waveform is derived for the calibrated site using a known transfer function, this drived waveform is then calibrated by the measurements already made, and the calibrated waveform for any remote site, for example the ascending aorta (14), can be derived using a known transfer function.