Augmentation of cardiac function by elevation of intrathoracic pressure

Abstract

We studied the cardiovascular effects of increasing intrathoracic pressure in an acute pentobarbital-anesthetized canine model of acute ventricular failure induced by large doses of propranolol. Left ventricular (LV) function curves were generated by volume loading from LV filling pressures of 5-20 Torr. The animals were ventilated by using intermittent positive-pressure ventilation with large tidal volumes (30 ml/kg). Chest and abdominal pneumatic binders were used to increase intrathoracic pressure. When compared with the control state, acute ventricular failure was associated with a decrease in the slope of the LV function curves (P less than 0.01). After binding the increase in intrathoracic pressure (1.1 +/- 1.6 to 12.1 +/- 2.4 Torr, P less than 0.01) was associated with an improvement in both right ventricular and LV function. Our study demonstrates that in this model of acute ventricular failure, increasing intrathoracic pressure improves cardiac function. We postulate that this observed improvement with increased intrathoracic pressure is due to reduced LV wall stress in a manner analogous to that seen with arterial vasodilator therapy in congestive heart failure.

Cardiorespiratory Interactions: The Relationship Between Mechanical Ventilation and Hemodynamics

“…Adjunct therapies that may affect cardiorespiratory interactions are considered as well. [3][4][5][6] Cardiorespiratory Economics…”

“…[3][4][5][6] The right ventricle receives blood from beyond the thorax (ie, from the superior vena cava and inferior vena cava) and pumps it within the thorax. As such, the flow of blood to the right ventricle is sensitive to alterations in mean intrathoracic pressure for several physiologic reasons.…”

“…Left ventricular afterload is dependent on left ventricular myocardial wall tension, 5 which is affected by the difference between the left ventricular systolic pressure and mean intrathoracic pressure. 5,6 The physiologic effects of PPV on left ventricular wall tension are complex, as the systemic arterial system has both intrathoracic and extratho- racic components. When mean intrathoracic pressure is increased, the pressure is rapidly transmitted to the intrathoracic arterial system.…”

“…5,6 A reflexive decrease in aortic pressure occurs along with a compensatory reduction in left ventricular pressure. When aortic pressure reflexively returns to baseline, left ventricular systolic pressure decreases.…”

Acute and chronic effects of continuous positive airway pressure therapy on left ventricular systolic and diastolic function in patients with obstructive sleep apnea and congestive heart failure

“…Increased right ventricular afterload can increase right ventricular volume and result in a leftward shift of the septum, adversely affecting left ventricular filling (50). However, increased intrathoracic pressure with acute CPAP therapy may directly decrease left ventricular transmural pressure and left ventricular afterload, potentially counteracting or minimizing the negative left ventricular preload effects on left ventricular systolic function (52,53). Ultimately, the hemodynamic effect of acute CPAP therapy may depend on the individual's specific preload and afterload states (18).…”