Changes in left ventricular contractility with the phase of respiration.
The end-systolic wall stress (sigma(es))-velocity of circumferential fiber shortening (V(cfsc)) relation was defined during the respiratory cycle, in order to obtain a totally noninvasive measure of left ventricular contractility. Eight young, healthy subjects were studied with echocardiography and calibrated carotid pulse tracings, while performing slow paced breathing. Left ventricular sigma(es) vs. V(efsc) relation was determined by fitting linear regression line to data points obtained at different times during the respiratory cycle. Data are given as mean+/-1SD. Left ventricular sigma(es) and V(efsc) exhibited small but significant changes during the respiratory cycle: sigma(es) was highest in late inspiration (56.9+/-4.8 g/cm2) and lowest in late expiration (49.2+/-3.7 g/cm2); inversely, V(cfsc) was lowest during late inspiration (1.18+/-0.17 circ/s) and highest during late expiration (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 was 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 then expiration, suggesting that contractility was reduced during the expiratory phase. The reduced expiratory contractility might reflect increased vagal influence on the ventricular myocardium.
Karlocai
K
K
Department of Cardiology, National Koranyi Institute, Semmelweis Medical University, Budapest, Hungary.
Jokkel
G
G
Kollai
M
M
D000328:Adult; D004562:Electrocardiography; D006352:Heart Ventricles / Q000166:cytology / Q000294:innervation; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009206:Myocardium / Q000166:cytology; D012119:Respiration; D013314:Stress, Mechanical; D013318:Stroke Volume / Q000502:physiology; D013599:Systole / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology; D016276:Ventricular Function; D016277:Ventricular Function, Left / Q000502:physiology*