Effect of Orthostatic Stress on Systolic Time intervals in Rabbits

K. Singh

Department of Physiology

PGIMS, Rohtak – 124 001

Abstract : Systolic time intervals (STI) are sensitive indices of myocardial function. The present study was conducted to evaluate the effect of orthostatic stress on STI before and after 70° head up tilt (HUT) in rabbits. Electrocardiogram (ECG), phonocardiogram and carotid arterial pulse were recorded simultaneously on four channel polyrite (INCO). Within 1 second of tilt there was a significant rise (P<0.001) in electromechanical systole (QS2), left ventricular ejection time (LVET), pre-ejection period (PEP), and ratio of PEP/LVET (P<0.01), however, there was no change in heart rate and mean arterial blood pressure insignificantly. QT/QS2 ratio and ejection fraction (EF) were also elevated (P<0.05) on tilt. After 20 seconds of HUT, QS2 showed reduction (P<0.001), LVET elevation (P<0.001), PEP and ratio of PEP/LVET reduction (P<0.001) from control level. QT/QS2 and EF declined gradually towards basal values. These changes in STI (raised LVET, reduced PEP and PEP/LVET ratio) and increased QT/SQ2 ratio and EF pointed towards rise in contractility of heart.

Key words : systolic time intervals                    ejection fraction               QT/QS2