Time domain analysis of the arterial pulse in clinical medicine

The arterial pulse at any site is created by an impulse generated by the left ventricle as it ejects blood into the aorta, together with multiple impulses travelling in the opposite direction from reflecting sites in the peripheral circulation. The compound wave at any site depends on the pattern of ventricular ejection, the properties of large arteries, particularly their stiffness (which determines rate of propagation) and the distance to and impedance mismatch at reflecting sites. Physicians are familiar with waveform analysis in the time domain, as in the electrocardiogram (ECG) where the principal features are explicable on the basis of atrial depolarisation followed by ventricular depolarisation, then repolarisation. Effects of cardiac functional and structural disease can be inferred from the ECG. It is more difficult to make similar interpretations from the pulse waveform and clinicians usually use this only to count heart rate, extremes of the pressure pulse to express systolic and diastolic pressure, and (sometimes) time from wave foot to incisural notch to measure time of systole and diastole. More information can be gleaned from the shape of the arterial pressure wave through consideration of the factors which create it--on stiffening of large arteries with age, effects of drugs on smallest arteries, and changes in such arterial properties on left ventricular load and function. Such is a major challenge to future physicians. It is aided by better and more accurate methods for measuring flow and diameter as well as pressure waveforms, and by appropriate use of other analytic techniques such as analysis of the pulse in the frequency domain.