Coronary circulatory effects of increased intrathoracic pressure in intact dogs

Effect of abruptly increased intrathoracic pressure on coronary blood flow velocity in patients

To assess the effects of abruptly increased intrathoracic pressure on coronary blood flow, arterial pressure, heart rate, and intracoronary Doppler blood flow velocity were measured continuously during cough(s) and again during the four phases of the Valsalva maneuver in 14 patients. Coughing significantly increased the systolic pressure (137 +/- 25 to 176 +/- 30 mm Hg), diastolic pressure (72 +/- 10 to 84 +/- 18 mm Hg), and arterial pulse pressure (65 +/- 27 to 92 +/- 35 mm Hg), with no change in heart rate. The mean coronary flow velocity decreased (17 +/- 10 to 14 +/- 12 cm/sec, p less than 0.03). During the Valsalva maneuver, despite marked reduction in the mean arterial pressure during phase III (96 +/- 12 to 68 +/- 14 mm Hg, p less than 0.05), the reduction of coronary blood flow velocity did not achieve statistical significance. These data demonstrate that neither type of abrupt physiologic increase in intrathoracic pressure enhances coronary blood flow. Coughing does not improve coronary perfusion pressures or flow velocity, despite marked increases in arterial diastolic pressure. The Valsalva maneuver, for the most part, does not significantly alter coronary blood flow velocity.

Effects of transient increase in intrathoracic pressure on hemodynamic determinants of myocardial oxygen supply and demand

Effects of transient increases in intrathoracic pressure on hemodynamic indexes of myocardial oxygen supply and demand were evaluated in 21 patients with ischemic heart disease. Left ventricular, ascending aortic, and right atrial pressures and electrocardiogram (ECG) were recorded while a Valsalva maneuver was performed during ischemia. Myocardial oxygen demand was assessed from the tension time index (TTI) and cardiac size and potential myocardial oxygen supply were assessed from a diastolic pressure time index (DPTI) and relative changes in supply/demand ratio from DPTI/TTI. During an asymptomatic interval an abrupt but small transient decrease in TTI and cardiac size occurred during phase II (p less than 0.05) of the Valsalva maneuver. DPTI did not change significantly and DPTI/TTI increased (p less than 0.05). When Valsalva maneuver was initiated during angina, 16 patients reported prompt and complete relief of angina, and left ventricular end-diastolic pressure declined following the maneuver. Relief of ischemia occurred uniformly during the latter part of straining (phase II) coincident with the peak reduction in TTI, cardiac size, and increase in DPTI/TTI. These data indicate that a transient increase in intrathoracic pressure results in a decrease in hemodynamic determinants of myocardial oxygen demand and an increase in the myocardial oxygen supply:demand ratio.

Effects of the Valsalva maneuver on myocardial ischemia in patients with coronary artery disease

The influence of the Valsalva maneuver (VM) on myocardial ischemia was evaluated in 24 patients with coronary heart disease. Clinical and hemodynamic responses to the VM were studied during acute ischemia manifested by angina pectoris with transient left ventricular (LV) dysfunction and compared with responses during nonischemic intervals. In the absence of evidence for acute ischemia (angina and increased LV end-diastolic pressure), six patients had abnormal hemodynamic responses to the VM. Five had lack of systolic pressure overshoot and in one, systolic pressure did not decline during straining. When the VM was performed during an ischemic episode, 14 patients had abnormal responses (12 with lack of overshoot in phase IV and two with lack of systolic pressure decline in phase II). In 18 patients a prompt decline in LV end-diastolic pressure occurred with the disappearance of angina during the VM. These changes uniformly occurred during the latter part of straining (VM phase II) as cardiac size and systolic pressure declined. No adverse effects occurred when a VM was performed during acute ischemia. Our observations suggest that the VM abruptly reduces determinants of cardiac oxygen demand, relieving acute ischemia without harmful effects.

Instantaneous blood flow responses to positive end-expiratory pressure with spontaneous ventilation

Variable hemodynamic responses to positive end-expiratory pressure (PEEP) with spontaneous ventilation have been reported. To clarify these responses, 15 awake patients were studied using a catheter-tip velocity transducer to record phasic aortic root blood flow continuously before, during and after PEEP (10 cm H2O) applied with a face mask. Central blood volume and effective ventricular filling pressures were measured. Phasic pulmonary artery blood flow was also simultaneously recorded in three of these patients. PEEP produced an acute aortic blood flow reduction, detected within one respiratory cycle. Stroke volume decreased 12%, and since heart rate was unchanged, cardiac output also declined (p less than 0.05). Inspiratory-to-expiratory aortic flow changes were less during PEEP. In contrast, inspiratory-to-expiratory pulmonary artery flow alterations were exaggerated due to a marked flow decline during expiration. Central blood volume and effective left ventricular filling pressure decreased 9% and 19%, respectively (p less than 0.05 in all patients). The decrease in pulmonary artery flow was associated with a decrease in central blood volume in the three patients in whom pulmonary flow was measured. PEEP promptly reduces cardiac output during spontaneous ventilation, related to a decrease in pulmonary flow in expiration.

The effect of positive end expiratory pressure after three types of open heart surgery

It has previously been shown that patients who have undergone mitral valve replacement (MVR) tolerate a positive end expiratory pressure (PEEP) of 1.0 kPa better than patients who have had aortic valve replacement (AVR). the difference was explained by the fact that the mitral patients had pre-existing pulmonary vascular disease. In the present study the effect of PEEP up to 2.0 kPa is investigated in three types of operations: aortocoronary bypass graft (ACBG), mitral valve replacement, and aortic valve replacement; there were five patients in each group. We found that our mitral patients tolerated PEEP better than the two other groups, and that tolerance was not correlated to a higher pulmonary vascular resistance, but rather to a higher level of pulmonary capillary wedge pressure. The influence of PEEP varies in different types of patients and the effect is still difficult to predict.