James P. Henry

Evidence of the Atrial Location of Receptors Influencing Urine Flow

Receptors believed responsible for the diuresis of negative pressure breathing have been located by observing the effect on urine flow of a stepwise engorgement of the intrathoracic vascular bed. Distension of the pulmonary arterial tree (injection of plastic beads) and of the entire pulmonary circulation (snares on the pulmonary veins) were without effect. A diuresis was however elicited by expansion of a balloon in the left atrium. It is concluded that stretch receptors in the left atrium and terminal pulmonary veins are instrumental in a mechanism linking changes in the actively circulating blood volume with homeostatic responses of the kidney.

A model of psychosocial hypertension showing reversibility and progression of cardiovascular complications.

The sequence of pathophysiological changes that can result from the stimulating effects of a sustained disturbance of the social environment was studied in ten colonies of socially deprived mice. Sixteen formerly isolated males were placed with 16 normal females in population cages consisting of seven intercommunicating boxes. Six of these socially disturbed 32-member colonies were terminated after periods of interaction ranging from 2 days to 9 months. The remaining four were terminated a month or more after the males had been returned to individual isolation. Indirect blood pressure measurements, body and heart weights, and sections of hearts and aortas were studied in the males. Following the shorter exposures, blood pressure reverted to normal in a few days. Exposures of 6 months or more were associated with unchanged body weights and sustained increases in heart weight and blood pressure readings. In addition, there was a significant development of aortic arteriosclerosis and myocardial fibrosis. These changes persisted despite prolonged return to isolation.

Changes in Central Venous Pressure after Moderate Hemorrhage and Transfusion in Man

Changes in central venous pressure were recorded continuously before, during and for 40 to 50 minutes after hemorrhage and transfusion in the amounts of 6.5 cc. per Kg. and 8.1 cc. per Kg. The pressures obtained 15 to 20 minutes after onset of blood volume changes were independent of the rate of hemorrhage or transfusion. In the average subject of 70 Kg., ΔP/ΔV for zero time was 0.7 cm. of water pressure change per 100 cc. volume change. Recovery from hemorrhage was imperceptible during the one hour observation period, but recovery from transfusion was slightly faster.

[Homeostasis of extraarterial blood circulation; volume regulation as an independent physiologic parameter].

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The Effect of Moderate Changes in Blood Volume on Left and Right Atrial Pressures

The blood volume of 15 dogs was progressively increased an estimated 30 per cent by repeated blood infusions and decreased 30 per cent by stepwise hemorrhage. The pressures in the venous system, both atria and the pulmonary artery, rose and fell in unison with these moderate changes in blood volume and the new levels remained stable for at least 10 to 20 minutes. Although the right ventricle anatomically separates the systemic venous bed from the pulmonary circulation, small hemorrhages and transfusions have so little effect on its activity that, from the point of view of pressure volume relationships, the systemic veins and the left atrium are parts of the same functional unit.

Plasma Renin Activity in Psychosocial Hypertension of CBA Mice

We studied plasma renin activity (PRA) in male full-color brown Agouti (CBA) mice subjected to varying degrees of psychosocial stress induced by manipulation of their housing patterns. Blood samples were obtained from unanesthetized mice by retro-orbital puncture; blood pressure (BP) was measured by tail plethysmography. At 4 months of age, PRA was lower in mice isolated since weaning (isolates) than in mice housed together in standard cages (boxed sibs). Isolation of boxed sibs for 7 days also decreased PRA. PRA did not change in isolates during a 10-month period. In contrast, PRA and BP changed markedly after 4-month-old isolates were placed in an interconnected box system [population cage (PC)] which increased social interaction and competition; values at all times were greater than those of isolated controls. PRA increased rapidly during the first 1-2 days, declined from these high values over the next 3 weeks to values similar to those of boxed sibs (but higher than control isolates), and then rose again progressively during the next 5-6 months. BP was elevated within 1 week (particularly in subordinate mice), then rose slowly throughout the experiment. During the first 2 months, PRA and BP were inversely correlated; no significant correlation existed after 2 months. Hematocrit tended to be lower in PC mice from 7 days on. Blood urea was increased in 10-month-old PC mice. Increased PRA and BP also occurred in boxed sibs placed in PC for 3-10 weeks. The pattern of PRA changes in these mice is analogous to that observed in certain forms of human essential hypertension and is further evidence that psychosocial hypertension in CBA mice may be an appropriate model for the study of essential hypertension.

A Medical Massage Suit for Continuous Wear

1 Presented at the First Annual Meeting of the American College of Angiology, June 4, 1955, Atlantic City, New Jersey. 2 Aero Medical Laboratory, Wright Air Development Center, Air Research and Development Command, Wright-Patterson Air Force Base, Ohio. 3 Present address: 118 S.E. Riverside Street, Evansville 8, Indiana. 4 Present address: Cornell TTniversity Medical College, New York, N. Y. During World War II, pilots in fighter aircraft discovered that the muscle cramps and fatigue of long missions were relieved by any aerial maneuver abrupt enough to activate their antigravity suits (g-suits). These protective devices compress the pilot’s legs and abdomen with air-bladders that automatically inflate when a high-speed aircraft changes direction of flight. Circulatory effects demonstrated in the laboratory explained this effect of the g-suit in preventing muscular ache. In particular, venous pressure at the ankle was reduced to half the

Psychosocial stress induces high blood pressure in a population of mammals on a low-salt diet

The relative importance of salt intake and psychosocial stimulation in the development of high blood pressure has been studied in colonies of CBA/USC mice. Approximately 50 males were observed for 3-4 months in five population cages which successfully induced chronic psychosocial interaction, resulting in chronic hypertension. Under these conditions, progressive arteriosclerosis develops together with myocardial hypertrophy, increased catecholamine synthesis and increased angiotensin sensitivity. Previous work indicates that this condition shows the characteristics of renin dependent human hypertension. A special grain based diet was used which included 0.014% sodium. This resulted in the ingestion of the equivalent of 40 mmol/l sodium or 3.0 g NaCl in a 70-kg man. This, and an even more stringent synthetic diet containing less than 0.01% NaCl, i.e. less than 2 g NaCl per day in man, were contrasted with the standard chow which contains 0.4% sodium. Over 4 months of social interaction the psychosocial stimulation proved to be the critical factor and, despite the low-salt intake, blood pressure rose to the same levels as those of control groups on a normal diet containing 1% salt. Hypertension occurs in the absence of kidney failure as assessed by blood urea. Plasma renin levels on the low-salt grain based diet were double those on standard chow, showing that the diet was sufficiently low in salt to activate the renin-angiotensin system.

Inhibition of Angiotensin - Converting Enzyme in CBA Mice with Psychosocial Hypertension

Captopril (SQ 14,225) was acutely administered to control mice and to mice which had developed hypertension as a result of being caged in a manner which facilitates social interactions and competition. Systolic blood pressure was measured four hours after captopril administration, and blood was taken for measurement of plasma renin activity (PRA) several days later. Captopril produced no effect on normotensive control mice living in isolation nor did it reduce the blood pressure of the hypertensive mice on days 1, 7, and 14 following their placement in the special caging, despite the fact that their PRA was significantly elevated at these times. In contrast, by 1.5 months after placement in the cages and continuing for the next 5.5 months, captopril abolished the hypertension; PRA was normal during this period. We conclude that the increased PRA existing during the early stage of this psychosocial model of hypertension is not a significant direct contributor to the hypertension, whereas the renin-angiotensin system may be essential for the maintenance of the hypertension beyond the early stage.