Loring B. Rowell

Human Splanchnic and Forearm Vasoconstrictor Responses to Reductions of Right Atrial and Aortic Pressures

Regional vascular responses to gradual reductions in right atrial pressure and aortic pressure were investigated in nine men. In each study, lower body negative pressure was applied in a ramp of −1 mm Hg/min for 40–50 minutes. During the range from control to −20 mm Hg, right atrial pressure (4 studies) fell from 4.2 mm Hg to −0.6 mm Hg; heart rate was slightly reduced (2 beats/min), and aortic mean pressure and pulse pressure (6 studies) were unchanged. The maximal rate of rise of aortic pressure showed no consistent trends. Forearm blood flow (30 studies) fell with the onset of lower body negative pressure and reached 67% of the control value by −20 mm Hg. Splanchnic blood flow (14 studies) was significantly reduced by −7 mm Hg and fell to 89% of control by −20 mm Hg. During the range from −20 to −50 mm Hg, right atrial pressure continued to fall. Aortic mean pressure fell slightly or was unchanged in four subjects and fell dramatically at −35 mm Hg in two subjects. Aortic pulse pressure began to fall at about −20 mm Hg and fell linearly thereafter. Heart rate paralleled aortic pulse pressure (r= −0.86 to −0.93). Forearm blood flow fell to 55% and splanchnic blood flow fell to 65% of control at −50 mm Hg. Thus, significant vasoconstriction occurred without measurable change in arterial blood pressure. We concluded that low-pressure baroreceptors, presumably in the cardiopulmonary region, initiate splanchnic and forearm vasoconstriction with more pronounced vasoconstriction occurring in the forearm.

Stability of heterogeneity of myocardial blood flow in normal awake baboons

Regional myocardial blood flow has been thought to be relatively uniform, in accord with the singular function of myocardial cells. However, considerable spatial heterogeneity has been observed in the hearts of anesthetized animals and in isolated hearts. Studies were undertaken in a total of 13 baboons. Eleven were awake, healthy animals sitting in chairs at rest or feeding, some performed mild leg exercise (wheel turning), and others were subjected to whole body heating; two were anesthetized, methodological controls. Microspheres (15 +/- 3 micron diameter, 0.5 X 10(6)/kg body weight) were injected via a catheter into the apex of the left ventricle while arterial blood was sampled at a constant rate for calculating cardiac output. Microspheres with different labels were injected at six intervals of 20 minutes to several hours. On sacrifice, the hearts were sectioned into 204 locatable pieces (left ventricle, 168; right ventricle, 27; and atria, 9). Average resting myocardial flow was 2.1 +/- 0.2 ml/g per min (mean +/- SD, n = 11). Left and right ventricles and atria comprised 70 +/- 2% (n = 13), 20 +/- 2%, and 10 +/- 2% respectively of the total heart mass while receiving 80 +/- 3%, 16 +/- 2%, and 4 +/- 2% of the total myocardial flow. Thus, mean left ventricular flow was 114 +/- 5% of the average for the whole heart, right ventricular flow was 81 +/- 13%, and atrial flow was 41 +/- 13%. Myocardial flow heterogeneity was marked; in left ventricle, regional flows ranged from one-third to two times the mean, the relative dispersion (= standard deviation/mean) of regional flows, corrected for methodological scatter and temporal variation, was 0.33 +/- 0.06 (n = 67) in the whole heart, 0.26 +/- 0.07 in left ventricle, 0.32 +/- 0.11 in right ventricle, and 0.22 +/- 0.19 in the atria. The pattern of regional flows in each heart tended to remain stable with time. In each piece averaged over time, the relative dispersion due to temporal heterogeneity was 0.11 +/- 0.03 (n = 2040) in the whole heart, 0.09 +/- 0.03 in the left ventricle, 0.15 +/- 0.05 in the right ventricle, and 0.23 +/- 0.06 in the atria. The conclusion is that the degree of spatial heterogeneity of local myocardial flows in conscious primates is similar to that of anesthetized animals and isolated hearts, and is much greater than that due to temporal fluctuations.

Disparities Between Aortic and Peripheral Pulse Pressures Induced by Upright Exercise and Vasomotor Changes in Man

Blood pressures were recorded simultaneously from the aortic arch and radial artery using two manometric systems with identical static and dynamic sensitivities. Measurements were made in four normal young men at rest and upright exercise requiring 29, 49, 78, and 100% of maximal oxygen uptake. Average radial arterial pressure rose from 133/66 mm Hg at rest to 236/58 mm Hg at maximal exercise. At the same time, average aortic pressures were 112/68 and 154/70 mm Hg, respectively. From rest to maximal exercise, pulse pressures at central and peripheral sites increased by factors of 1.95 and 2.60, respectively. Inducing reactive hyperemia in the arm abolished peripheral amplification. This amplification also diminished with time during prolonged heavy exercise. Mean pressures were nearly identical at the two sites at any oxygen uptake; mean pressures rose from 87 to 104 mm Hg from mild to maximal exercise. We conclude that estimates of stress on aortic and cerebral vessel walls and central baroreceptors would be grossly overestimated by use of peripheral pulse pressures.

Human Cardiovascular Adjustments to Rapid Changes in Skin Temperature during Exercise

In 11 normal men, central circulatory responses were measured while skin temperature was changed in a square-wave pattern during uninterrupted exercise (26% to 64% maximal oxygen consumption). Skin temperature was changed at 30-minute intervals, beginning at 32°C. On raising it to 38.2°C at low oxygen consumption (V˙o2), cardiac output increased 2.5 liters/min, and central blood volume, aortic mean pressure, and stroke volume fell (7%, 7%, and 11%, respectively). Right atrial mean pressure fell 2.2 and 2.3 mm Hg during control and heating periods, respectively. All variables returned to control levels when skin temperature was reduced toward 26.9°C. Raising it to 40°C reproduced these changes with a more clear-cut drop in right atrial mean pressure. Results indicated reduced peripheral venous tone and cutaneous pooling of blood during heating and rapid reversal on cooling. On raising skin temperature to 38.7°C at high V˙o2, cardiac output increased 19% (3.1 liters/min), stroke volume decreased 14%, and central blood volume rose slightly. Aortic mean pressure fell during the control period and was maintained or rose during heating periods. On cooling, central blood volume and stroke volume rose, cardiac output remained elevated, and aortic mean pressure fell. Increases in cardiac output during heating were related to skin temperature and not to V˙o2 or body temperature. At high V˙o2, circulatory adjustments favor metabolic rather than thermoregulatory demands.

Skeletal muscle lipids: I. Analytical method and composition of monkey gastrocnemius and soleus muscles

Abstract 1. 1. In order to effectivey explore the physiologic role of lipids in skeletal muscle, a method of analysis is needed to permit the separation and subsequent detailed examinatin of the lipid components. Such a method is described for the quantitative determination of the major and minor classes of lipids present in monkey skeletal muscle. Since the various lipid classes are quantitatively isolated, radioactivity in the lipid components is also easily determined. 2. 2. About one-third of the lipid is neutral lipid and two-thirds phospholipid. The neutral lipid is primarily triglyceride and cholesterol. More than 50% of the phospholipid is lecithin and about 25% is phosphatidylethanolamine. Appreciable quantities of phosphatidylinositol and “polyglycerophosphatide” are also present. The plasmalogen/lipid-phosphorus molar ratio is considerably greater than that reported for muscles of other species. 3. 3. The method was applied to an analysis of monkey gastrocnemius and soleus muscles. The lipid composition of a bilateral pair of muscles is found to be sufficiently similar to permit physiological investigation in which one of the bilateral pair serves as a control as the other undergoes contraction. While the functionally different soleus and gastrocnemius muscles are found to have similar lipid compositions, certain definite differences in the nature of their lipids are uncovered.

NEURAL CONTROL OF MUSCLE BLOOD FLOW: IMPORTANCE DURING DYNAMIC EXERCISE

1. The present review examines the control of muscle vascular conductance by the sympathetic nervous system during exercise.

Cardiovascular responses to heat stress and blood volume displacements during exercise in man

SummarySubjects exercised in the upright position at approximately 50% of maximal oxygen consumption in four situations: in 25‡ C air, in 45‡ C air [mean skin temperature (

Physiological Significance of Maximal Oxygen Intake in "Pure" Mitral Stenosis

\bar T