B. Bromberger-Barnea

Effects of changes in abdominal pressure on left ventricular performance and regional blood flow.

Many clinical conditions are associated with an increase in abdominal pressure. While the effects on venous return have been studied in the past little attention has been given to the effect of abdominal pressure on left-sided hemodynamic events. The effects of acute changes in abdominal pressure (Pab) on left ventricular (LV) hemodynamics and outflow distribution were evaluated in ten open-chest dogs, which had undergone right heart bypass to eliminate the influence of changes in Pab on systemic venous return. Pressures were measured in the left atrium (Pab), aorta (Pab), and stomach (Pab). Electromagnetic flow probes were positioned around the ascending aorta (Qaa), descending aorta (Qaa) and the innominate or subclavian artery (Qin) to reflect total cardiac output and the respective regional caudad and cephalad blood flows. Compressing the abdomen to increase acutely Pab (9.2 ± 0.6 torr) also significantly increased Pao (7.8 ± 1.2 torr), Pla (1.7 ± 0.4 torr), and Qin (15.2 ± 4.5%), while Qaa (-9.5 ± 2.0%) and Qda (-26.3 ± 7.0%) significantly decreased. Opposite findings were obtained immediately after release of abdominal compression. Thus, an acute increase in Pab with a constant pulmonary artery inflow increased the after-load imposed on the left ventricle and redistributed LV output, with a reduction in flow to the abdomen. Part of the fall in Qaa and increase in Pla could be attributed to passive elevation of the diaphragm by the increase in Pab, i.e., heart-lung-diaphragm interdependence. We conclude that acute changes in Pab may significantly effect left-sided hemodynamic events through changes in LV afterload, regional distribution of cardiac output, and diaphragmatic position. These findings have important clinical implications for understanding hemodynamic events under numerous conditions associated with changes in Pab.

A re-evaluation of the hemodynamic consequences of intermittent positive pressure ventilation

The hemodynamic effects of intermittent positive pressure ventilation (IPPV) have generally been considered straightforward, being dominated by the inspiratory reduction in systemic venous return. Paradoxically, there is considerable debate regarding the effects of PEEP. We have studied both right ventricular (RV) and left ventricular (LV) performance during a single IPPV respiratory cycle in dogs with intact circulatory systems or the right heart bypassed in open and closed chest conditions. We have found that the “reverse pulsus paradoxus” during inspiration reflects both transmission of the increased intrathoracic pressure to the thoracic aorta and an increase in LV stroke volume (SV). This inspiratory increase in LVSV has been found to be influenced by, but not dependent on: (a) respiratory variations in RVSV; (b) variations in functional residual capacity or tidal volume altering pulmonary venous return and the degree of physical compression of the heart by the lungs; (c) an inspiratory decrease in RV volume, increasing LV diastolic compliance and, thus, probably improving pulmonary venous return; (d) a decreased transmural aortic diastole pressure reflecting an effective decrease in LV afterload produced by both the general increase in intrathoracic pressure and the direct compression of the heart; and (e) variations in the pulmonary vascular volume as indicated by changes in the transmural LV end-diastolic pressure. An understanding of IPPV during a single respiratory cycle facilitates an appreciation of the steady state hemodynamic effects of IPPV with or without PEEP. Our results imply that measurements made only at endexpiration, ignoring inspiratory events, may have serious limitations. Furthermore, they suggest that IPPV with PEEP should be evaluated as a form of LV assist in LV failure.

Ventilatory responses to peripheral nerve stimulation at different times in the respiratory cycle

Abstract Discrete stimulation (40–500 msec duration) of the femoral nerve in the dog and the carotid sinus nerve of the cat was achieved at different moments during the respiratory cycle. Changes in tidal volume, respiratory rate and now pattern were measured. The response to stimulation varied according to the time in the cycle that the stimulus was given. Tidal volume and expiratory peak flow rate were usually reduced after stimulation in early inspiration but increased by the same stimulus in late inspiration or early expiration. Respiratory rate generally increased whatever time the stimulus was given. The pattern of response was broadly similar for the two nerves but there were important differences in detail.

Ventilation-Perfusion Changes During Thoracotomy

Eleven patients were studied during pulmonary lobectomy and during occlusion of one main bronchus to determine ventilation-perfusion abnormalities, blood gas exchange, and the extent of metabolic acidosis. Anesthesia consisted of intravenous agents plus 100 per cent oxygen. On opening the thorax there was a decrease of pH and blood buffer base. The fraction of the lungs which was ventilated but not perfused increased at this time, but returned to control levels when the bronchus to the operated side was occluded. The perfused but unventilated fraction of the lung rose to a lesser degree on thoracotomy, and rose somewhat further on occlusion of the bronchus. The effective (ventilated and perfused) fraction of the lung diminished on thoracotomy, but increased (P > 0.05) on occlusion of the bronchus to the operated side. By increasing minute ventilation it was possible to maintain normal blood gas concentrations when only one lung was ventilated.

Effects of Antimony on Myocardial Performance in Isolated and Intact Canine Hearts

Abstract The effects of sodium antimony and potassium antimony on contractility, coronary blood flow, and electrocardiogram were studied in isolated perfused dog hearts as well as in intact open-chested dogs. The isolated heart preparation used was a spontaneously beating dog heart perfused with blood from a donor animal. Myocardial contractility was measured by strain gauge arches sutured to the myocardial surface. Coronary vasomotor effects were investigated by observing changes in the amplitude of the perfusion pressure at constant flow. Antimony in doses of 10 to 15 mg/kg of body weight injected as a single dose into the coronary circulation of the isolated heart produced a progressive decrease in myocardial contractile force which was not reversible. The same dose injected intravenously was fatal in intact open-chested dogs. Antimony decreased the perfusion pressure at constant flow in the isolated heart, which indicates decreased coronary vasomotor tone. In the normally perfused heart this decreased...

Perfusion of lung periphery: effects of local exposures to ozone and pressure

Following ozone (O3) exposure, airways reactivity increases. We investigated the possibility that exposure to O3 causes a decrease in pulmonary perfusion, and that this decrease is associated with the increase in reactivity. Perfusion was measured with radiolabeled microspheres. A wedged bronchoscope was used to isolate sublobar segments in the middle and lower lobes of anesthetized dogs. Isolated segments were exposed to either O3 or an elevated alveolar pressure. Although increased alveolar pressure decreased microsphere density, exposure to 1 ppm O3 did not. Collateral system resistance rose significantly following exposure to O3 and to high pressure. These studies do not support the hypothesis that pulmonary perfusion is decreased following O3 exposure and is associated with subsequent increases in reactivity.