To the Editor.
—We read with interest the excellent article by Bough and associates in the October Archives (138:1476-1480, 1978) and also the editorial by Mazzaferri and Lewis (138:1470-1471, 1978) in the same issue. Their results very closely match ours,1 and we would in principle agree with their conclusions regarding the usefulness of the systolic time intervals (STIs) in serial follow-up examinations. However, as Bough et al have correctly pointed out, there is a problem in that there are considerable individual variations of the STIs that tend to obscure true drug effects. While this does not affect retrospective analysis of follow-up data, dayto-day evaluation of results may be quite difficult unless one can estimate the magnitude of spontaneous variations. We have, therefore, examined ten healthy male volunteers aged 19 to 28 years (mean, 24.3 years) in whom the STIs were measured six times over a nine-month period under identical