John P. Meehan

The use of psychosocial stimuli to induce prolonged systolic hypertension in mice.

&NA; The increase in systolic pressure with age, which is observed in some but not all human populations, is believed to be a response to repeated symbolic stimuli arising from the social environment. An attempt was made to simulate these conditions in experimental animals by playing on their inborn drives for territory, survival, and reproduction. Meaningful stimuli were presented to CBA mice in a series of long‐term experiments. The methods involved (1) mixing of animals previously maintained in different boxes, (2) aggregation in small boxes, (3) subjecting groups to threat from a predator, and (4) inducing conflict for territory by placing equal numbers of males and females in an interconnected box system. In the experimental situations involving the most severe psychosocial stimulation, the mean arterial blood pressure rose from 126 mm. Hg to the range 150–160; it was sustained at these higher levels for 6–9 months. Those aggregated from birth showed less pressure elevation (to the range 140–150). Blood pressures in females were in the same range as those of males that had been aggregated from birth, but castrates showed minimal effects. Ether anesthesia did not abolish a sustained pressure rise, but the persistently elevated pressure of threatened animals returned to the normal range when reserpine was given. The study demonstrated that social groupings of nonprimates can be used in the experimental approach to the role of psychosocial stimuli and the early environment in the etiology of human hypertension.

Impaired atrial receptor responses in dogs with heart failure due to tricuspid insufficiency and pulmonary artery stenosis.

In a study of the effects of heart failure on the responses of cardiac receptors, ten dogs were subjected to tricuspid avulsion and pulmonary artery stenosis. One case of spontaneous heart failure was included in the series, and the electrical spike responses of atrial receptors to progressive changes in atrial stretch induced by infusion and hemorrhage were contrasted with those in normal control dogs. In the control dogs, the number of spikes per cycle increased very sharply with moderate, i.e., 5–10 cm H2O, venous pressure increments before reaching a maximum at 20 cm H2O. In the experimental dogs, the firing rate failed to increase to the same extent despite large increases in pressure. The resulting sets of curves exhibited a sharp dichotomy. This evidence for the impaired response of elements of the subendocardial receptor network is compatible with a decrease in the sensitivity of feedback mechanisms responsible for the regulation of sodium and water metabolism.

Hemodynamic findings in heart block with slow ventricular rates

Abstract Six patients with acquired heart block and ventricular rates below 40 per minute were catheterized. Pertinent hemodynamic findings were: (1) elevated right atrial and right ventricular systolic pressure; (2) atrial systolic waves transmitted to both the right ventricle and main pulmonary artery successively; (3) giant atrial a waves occurring at the time of simultaneous atrioventricular systoles, but not when this occurred in or near early diastole of the preceding ventricular beat; (4) systolic pulmonary hypertension; (5) reduced mean brachial artery pressure, but elevated mean pulmonary artery pressure; (6) increased total vascular resistance of both the pulmonic and systemic circulations; (7) reduced oxygen consumption; (8) reduced cardiac index; and (9) increase of stroke index to 28 per cent or less above normal in four of the six patients. The injection of Isuprel via a catheter directly into the main pulmonary artery in two patients resulted in: (1) more rapid ventricular rate; (2) conversion to a sinus rhythm in one; (3) unaltered stroke volume; (4) increased cardiac output; (5) unaltered oxygen consumption; (6) decreased arteriovenous oxygen difference; and (7) decreased total vascular resistance in both the pulmonic and systemic circulations.

Evidence for retrograde transpulmonary propagation of the V (or regurgitant) wave in mitral insufficiency

Abstract 1. (1) Seven patients with mitral insufficiency and giant V waves in the wedged pulmonary artery position have been studied. 2. (2) The systolic peak of the V (or regurgitant) wave approximated the systolic peak of the right and main pulmonary artery pressure curves. 3. (3) Pulmonary arteriolar resistance was found to be normal or reduced. 4. (4) A consideration of the hemodynamic data favors the concept that in mitral insufficiency a retrograde transmission of the V wave may occur and that it results from an increase in the tone of the pulmonary vascular system without an increase in the pulmonary vascular resistance.

An Implantable Blood Pressure and Flow Transmitter

A miniature totally implantable FM/FM telemetry system has been developed to simultaneously measure blood pressure and blood flow, thus providing an appreciation of the hemodynamics of the circulation to the entire body or to a particular organ. Developed for work with animal subjects, the telemetry systems transmission time is controlled by an RF signal that permits an operating life of several months.

An Interferometric Blood Flow Measurement Technique - A Brief Analysis

An ultrasonic interferometric technique of measuring blood flow with an extravascular probe is presented and analyzed. The difference in phase between pulses of ultrasonic energy transmitted simultaneously from a pair of barium titanate crystals diagonally through the vessel and received by the same pair of crystals is employed as the basic measurement of blood flow velocity. It is shown that the sensitivity is influenced mainly by variability in the internal diameter of the vessel and the zero-flow baseline voltage position is influenced principally by variations in the level of energy reflected from the vessel surfaces. Baseline stability is enhanced by the use of an asymmetrical probe which minimizes the variable reflection components. This measurement technique is currently being employed in long term telemetry implants in which flow measurements have been satisfactorily performed for periods in excess of three months duration.

The effect of respiration on the arterial pulse in left ventricular failure

Abstract An anomalous effect of respiration on the arterial pulse has been found in several patients with severe left heart failure. In contrast to the behavior of the pulse in normals in which the pulse beat becomes stronger in expiration, in these cases the strong beats occurred in inspiration. In two of the cardiac patients the pattern reverted to normal with clinical improvement.