Effect of acute standing and prolonged upright activity on left ventricular hemodynamics, systolic and diastolic intervals, and QT-QS 2 relationship

Abstract

It is generally accepted that upright posture decreases preload and afterload, which could alter left ventricular (LV) performance. It is not known if changes occurring with acute standing persist after prolonged ambulatory activity (amb-act). In seven normal subjects echocardiographic end-diastolic and end-systolic diameters, percent shortening of the internal diameter (%Δ d) and end-systolic wall stress (ES-WS), radionuclide diastolic volume and ejection fraction, preejection period over left ventricular ejection time ( PEP LVET ), and diastolic time and QT-QS 2 were measured supine, within 1 to 2 minutes after standing and after prolonged (60 minutes) amb-act. In addition, serial measurements were performed in PEP LVET for 105 minutes at 15-minute intervals. With acute standing, end-diastolic diameter, diastolic volume, and ES-WS decreased ( p < 0.01); heart rate and PEP LVET increased ( p < 0.01); while %Δ d and ejection fraction remained unchanged. There was an inverse correlation between change in PEP LVET and diastolic diameter ( r = −0.59), but no correlation between PEP LVET and ES-WS. The diastolic time per beat and per minute decreased (375 ± 115 msec from 519 ± 176 msec [ p < 0.01] and 31.3 ± 4.2 sec/min from 33.7 ± 4.5 sec/min [ p < 0.01]). The QT-QS 2 increased when compared to supine (−7 ± 7.6 msec from −22 ± 7.7 msec [ p < 0.005]), but the QT-QS 2 relationship remained normal (QT ≤ QS 2). All the dynamic changes that occurred with acute standing tended to persist during prolonged amb-act.