CHANGES IN LEFT-VENTRICULAR CONTRACTILITY WITH THE PHASE OF RESPIRATION

The end-systolic wall stress (sigma(es))-velocity of circumferential f iber shortening (V-cfsc) relation was defined during the respiratory c ycle, in order to obtain a totally noninvasive measure of left ventric ular contractility. Eight young, healthy subjects were studied with ec hocardiography and calibrated carotid pulse tracings, while performing slow paced breathing. Left ventricular sigma(es) vs. V-cfsc relation was determined by fitting linear regression line to data points obtain ed at different times during the respiratory cycle. Data are given as mean +/- 1SD. Left ventricular sigma(es) and V-cfsc exhibited small bu t significant changes during the respiratory cycle: sigma(es) was high est in late inspiration (56.9 +/- 4.8 g/cm(2)) and lowest in late expi ration (49.2 +/- 3.7 g/cm(2)); inversely, V-cfsc was lowest during lat e inspiration (1.18 +/- 0.17 circ/s) and highest during late expiratio n (1.34 +/- 0.20 circ/s). The relation was significant in each subject (r = -0.64 +/- 0.13) and remained inverse and significant, when it wa s determined separately for inspiration and expiration (r = -0.61 +/- 0.17 and -0.68 +/- 0.12, respectively). At identical end-systolic wall stress, the velocity of shortening was greater during inspiration the n expiration, suggesting that contractility was reduced during the exp iratory phase. The reduced expiratory contractility might reflect incr eased vagal influence on the ventricular myocardium. (C) 1998 Elsevier Science B.V. All rights reserved.