PHYSIOLOGICAL VARIATIONS OF THE CARDIAC OUTPUT IN MAN

Abstract

X. A study was made of the cardiovascular and metabolic changes occurring in 5 normal human subjects over a temp. range of 0[degree] to 45[degree] C. The pulse rate rises progressively with increasing temp., the changes below room temp. being slight. The blood pressure undergoes a change of only about 10% throughout this range with only slight variations in the pulse pressure. The metabolism declines with increasing temp., to a minimum, at about 30[degree], after which it again rises slowly. The nature of these changes in the metabolism and their probable causation is discussed. The cardiac output is constant over the temp. range of 0[degree] to about 28[degree]. At temperatures over 28[degree] the cardiac output gradually increases with increasing temp., giving at 45[degree] a value (for the average sized individual) 1.3 liters above the value at normal room temp. These effects of temp. on the cardiac output are explained as being the resultants of 2 diverse phenomena. The constancy of the cardiac output with moderate degrees of cold is analogous to its constancy with slight muscular activity. The increase at higher temp. represents the peripheral dilatation occurring under these conditions. The effect of baths (as compared to air as the environmental medium) and the possible differences to be encountered in pathological cases are also discussed. The bearing of the present results and those obtained on other animals on the theory of the calorigenic function of epinephrine is indicated. XI. The pulse rate, blood pressure, O consumption, and cardiac output of 3 normal, young individuals were determined in the sleeping and waking states throughout the course of the night. If one compares the values of the above-named functions during sleep with those obtained a few min. later, after awakening the subject, one finds that only the pulse rate rises as a result of awakening the subject. This is attributed to the lability of the pulse and its stimulation by the optic and acoustic stimuli which are active when the subject is awake. The sleeping state per se is not associated with a decrease in the blood pressure, O consumption, or cardiac output, as compared to the waking state under completely relaxed conditions at the same hr. of the night. These functions assume sub-basal values (i.e., lower than the minimum values obtained under optimum conditions of rest during the day) after 5 or 6 hrs. of sleep. The observed changes in the cardiovascular and metabolic functions during sleep are either incidental to the prolonged bodily rest associated with this state or are a manifestation of cyclic changes in the organism of the nature of a diurnal rhythm.