Hemodynamic responses to breathing 100% oxygen for an average of 30 min were studied in eight healthy male volunteers. Cardiac output and related determinations were performed with central injections of a radioactive indicator and calculated by the method of Stewart and Hamilton. Arterial blood gas analyses were performed in each phase of the study. Slight but statistically significant decreases in cardiac index and heart rate were observed during oxygen breathing. There was no change in the central blood volume, but a masked increase in pulmonary blood volume may have occurred. Statistically significant increases in peripheral vascular resistance, mean arterial pressure, and both systolic and diastolic arterial pressures occurred during oxygen breathing and persisted at least 40 min after oxygen was discontinued. Submitted on May 1, 1961
A B T R A C T The effect of steady-state increases in systemic arterial pressure on the duration of left ventricular ejection time was studied in 11 normal male subjects. Methoxamine, a pressor amine of predominantly vasoconstrictor activity but lacking significant inotropic effect, was administered intravenously resulting in an average increase in mean arterial pressure of 27 mm Hg. Heart rate was held constant by high right atrial pacing, and there was no significant change in cardiac output. During methoxamine infusion, when stroke volume, heart rate, and inotropic state were held constant, left ventricular ejection time increased as mean arterial pressure increased. There was a highly significant correlation between the increase in mean systolic blood pressure and the prolongation of left ventricular ejection time (r = 0.870). In one subject, an increase in mean systolic pressure of 75 mm Hg prolonged left ventricular ejection time 55 msec, producing paradoxical splitting of the second heart sound. The prolongation of left ventricular ejection time during infusion was not blocked by the prior intravenous administration of atropine sulfate or propranolol hydrochloride, thus ruling out both vagal inhibition of the left ventricle and reflex withdrawal of sympathetic tone as its cause. In three subjects, left ventricular end diastolic pressure was mea-A partial report of this work appeared in abstract form. 1966. J. Clin. Res. 14: 261.Dr. Paley's present adress is the Mt. Zion Hospital, San Francisco, Calif.
A B S T R A C T A study was performed in five normal men in whom left ventricular volume was measured by thermodilution in the supine and 600 head-up postures. in the control state, and then during steady-state response to isoproterenol. The mean rate of circumferential shortening of the left ventricle was calculated for each of the postures in both inotropic states and was found to remain constant in the control state at 12.5 ±0.6 cm/sec in the supine posture and 13.3 +0.5 cm/sec in the tilted posture. Similarly, mean rate of circumferential shortening remained constant in response to the positive inotropic effect of isoproterenol at 20.9 ±0.5 cm/sec in the supine position and 20.7 ±0.5 cm/sec in the tilted pos-
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.