Studies on the respiration and circulation of the cat: IV. The heart output during respiratory obstruction

THE RESPONSE TO RESPIRATORY RESISTANCE : A COMPARISON OF THE EFFECTS PRODUCED BY PARTIAL OBSTRUCTION IN THE INSPIRATORY AND EXPIRATORY PHASES OF RESPIRATION

1. A study has been made of the effects of resistance to respiration in the inspiratory and expiratory phases. 2. Resistance to inspiration caused an increase in respiratory rate, a decrease in tidal air, and in most instances a severe limitation of the minute volume of pulmonary ventilation. Anoxemia and acidosis accompanied these changes. 3. When resistance was removed the respiratory rate continued to be rapid, but the tidal air and minute volume increased. As a result of this there was a fall in pCO₂, a rise in pH, and in some cases a complete disappearance of anoxemia. 3. Resistance to expiration slowed the respiratory rate and produced a constant decrease in the minute volume of pulmonary ventilation. Anoxemia and carbon dioxide retention occurred, but were less pronounced than in the inspiratory experiments. Release of resistance to expiration resulted in a return of all functions to their normal, or approximately normal, levels. 4. A difference in the gross pulmonary pathology found at autopsy in these two types of experiments has been described, and an attempt has been made to correlate changes in function with changes in structure. 5. No direct evidence has been supplied for the liability to fatigue of the respiratory center.

Hemodynamic effects of continuous positive and negative pressure breathing in normal man

Alterations in cardiac output, central blood volume, and arterial and central venous pressures were studied in 36 young men subjected to continuous negative or continuous positive pressure breathing. Negative pressure breathing increased cardiac output, stroke volume, and, to a lesser extent, central blood volume. Positive pressure, without overbreathing, decreased both cardiac output and central blood volume, but hyperventilation reversed these effects. On the basis of these observations, it is concluded that decreased intrathoracic pressure is important in maintaining or increasing the blood available to the heart in man, particularly during circulatory stress.

The right ventricle and critical illness: a review of anatomy, physiology, and clinical evaluation of its function

This paper reviews right ventricular anatomy and physiology in the critically ill patient. The role of right ventricular function during acute pulmonary artery hypertension and the effect of acute myocardial injury upon right ventricular performance are examined. Clinical methods of assessing right ventricular function at the bedside in acutely ill patients are critically reviewed.

The association of lung distention, PEEP and biventricular failure

Although positive and expiratory pressure (PEEP) is known to depress the cardiac output, the mechanism remains debated. Two series of experiments were designed to explore this mechanism. In the first study, the application of 15 cm H(2)O of PEEP to nine anesthetized, ventilated dogs led to a reduction of cardiac index from (mean +/- one standard error of the mean) 2.71 L/min .m (2) +/- 0.35 to 2.19 L/min m(2) +/- 0.22 (p < .05) and a drop in mean arterial pressure (MAP) from 117 mm Hg +/- 8 to 91 mm Hg +/- 11 (p < .01). The mean net (vascular minus pleural pressure) pulmonary artery pressure (MPAP) rose from 15.3 mm Hg +/- 1.2 to 20.6 mm Hg +/- 1.8 (p < .02). The mean net central venous pressure (CVP) rose from 5.2 mm Hg +/- 0.9 to 8.4 mm Hg +/- 0.9 (p < .05) and the net pulmonary arterial wedge pressure (PAWP) rose from 6.7 mm Hg +/- 0.7 to 9.5 mm Hg +/- 0.9 (p < .01). There was a nonsignificant rise in the mean net left atrial pressure (LAP). As PEEP was raised in increments from 0 to 20 cm H(2)O, both LAP and PAWP increased. The rise in PAWP was always greater than the increase in LAP. The difference between PAWP and LAP was strongly correlated with the increase in MPAP (r = 0.98). This relationship was useful in correcting the PAWP during PEEP. The problem of cardiac depression was evaluated in a second series of eight dogs. These animals underwent complete chest wall excision to eliminate any possible direct effects of increased pleural pressure on the heart and great vessels. The absence of the chest wall permitted hyperexpansion of the lungs, particularly with positive end expiratory pressure. At 15 cm H(2)O of PEEP, the mean cardiac index fell in these animals from 2.36 L/min. m(2) +/- 0.26 to 1.47 L/min.m(2) +/- 0.18 (p < .01) and the MAP fell from 105 mm Hg +/- 16.2 to 68 mm Hg +/- 4.8 (p < .001). The CVP rose from a mean of 5.5 mm Hg +/- 0.4 to 8.3 mm Hg +/- 0.6 (p < .01) and the LAP rose from 6.3 mm Hg +/- 0.8 to 8.0 mm Hg +/- 1.1 (p < .05). The MPAP rose from 18.0 mm Hg +/- 0.6 to 23.3 mm Hg +/- 1.6 (p < .01). Comparison of Group I and II showed a significantly greater depression of the cardiac output and MAP in the open-chested animals. At the same time LAP was significantly higher. These data strongly suggest that PEEP and particularly pulmonary hyperinflation induce biventricular failure.