Use of the systolic time intervals in clinical pharmacology.

Measurement of the systolic time intervals is a method of assessing left ventricular function in terms of the timing of well defined events in the cardiac cycle. It can be performed non-invasively, so has considerable advantages over cardiac catheterization in that normal subjects can be studied, and repeated measurements made, either in the basal state, or after interventions. It is thus attractive for the study of drugs with an action on the cardiovascular system. The technique has been in use for a number of years, and has been used extensively to investigate clinical left ventricular disease. It has been the subject of several reviews (Weissler, Harris Harris, 1974; Lewis, Rittgers, Forrester & Boudoulas, 1977). The ability to express left ventricular function in terms of single numbers has advantages when the effects of drugs or other interventions are being compared, but it must be stressed that this simplicity is only apparent, and may conceal complex underlying changes in circulatory state. Furthermore, although left ventricular disease and drug administration have similar effects on the systolic time intervals, there is much evidence to suggest that the mechanisms responsible are widely different and not comparable in these simple terms.