Sequential Cardiac Responses during the Respiratory Cycle: Patterns of Change in Systolic Intervals

¹ Cardiology Division, Medical Service, Lemuel Shattuck Hospital and the Department of Medicine, Tufts University School of Medicine, Boston
² Research Associate, Cardiology Division, Lemuel Shattuck Hospital
³ Chief, Cardiology Division, Lemuel Shattuck Hospital; Associate Professor of Medicine, Tufts University School of Medicine; Lecturer in Medicine, Boston University School of Medicine

Left ventricular systolic intervals were measured at the extremes and the midpoint of normal inspiration and expiration. Pre-ejection period (PEP) left ventricular ejection time (LVET), PEP/LVET and electromechanical systole of the left ventricle (LV-EMS) all showed the expected maximal changes at the respiratory extremes, but te greatest part of these changes occurred during the earlier part of inspiration and expiration—ie, there were sharp reversals after peak inspiration (I₁) and the nadir of expiration (E_N), so that most of the changes had already occurred by mid-inspiration and mid-expiration. By contrast, most variations in the duration of electromechanical systole of the right ventricle (RV-EMS), and consequently in the splitting interval of the second heart sound (II_A-II_P interval), took place just before and after I₁—ie, in late inspiration and early expiration. These patterns of change in time intervals and of respiratory splitting of S₁₁ can be explained by respiratory changes in hemodynamics reported both in intact subjects and experimental preparations.