BPSHAPE-WK4 - A COMPUTER-PROGRAM THAT IMPLEMENTS A PHYSIOLOGICAL MODEL FOR ANALYZING THE SHAPE OF BLOOD-PRESSURE WAVE-FORMS

We describe the theory and computer implementation of a newly-derived mathematical model for analyzing the shape of blood pressure waveforms . Input to the program consists of an ECG signal, plus a single contin uous channel of peripheral blood pressure, which is often obtained inv asively from an indwelling catheter during intensive-care monitoring o r non-invasively from a tonometer. Output from the program includes a set of parameter estimates, made for every heart beat. Parameters of t he model can be interpreted in terms of the capacitance of large arter ies, the capacitance of peripheral arteries, the inertance of blood fl ow, the peripheral resistance, and arterial pressure due to basal vasc ular tone. Aortic flow due to contraction of the left ventricle is rep resented by a forcing function in the form of a descending ramp, the a rea under which represents the stroke volume. Differential equations d escribing the model are solved by the method of Laplace transforms, pe rmitting rapid parameter estimation by the Levenberg-Marquardt algorit hm. Parameter estimates and their confidence intervals are given in si x examples, which are chosen to represent a variety of pressure wavefo rms that are observed during intensive-care monitoring. The examples d emonstrate that some of the parameters may fluctuate markedly from bea t to beat. Our program will find application in projects that are inte nded to correlate the details of the blood pressure waveform with othe r physiological variables, pathological conditions, and the effects of interventions.