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Noninvasive ventilation using noninvasive bilevel positive airway pressure (Bi-PAP) has been shown to be an effective means of improving oxygenation and respiratory status in patients with obstructive pulmonary disease (COPD) and acute congestive heart failure (CHF). However, it is uncertain what effects this positive airway pressure has on the haemodynamic condition of these patients. This study examines the acute changes in basic circulatory parameters with the initiation of Bi-PAP. Noninvasive measurements of the heart rate, systolic and diastolic arterial pressure, cardiac index, total peripheral resistance, ventricular ejection time, and total diastolic time were determined by impedance cardiography before and after the institution of Bi-PAP (pressures 15/5) in a group of healthy volunteers. In a collateral study, the same measurements were made in COPD patients in whom Bi-PAP was initiated for therapeutic reasons. Changes in the haemodynamic parameters were analysed using a paired t-test (p < 0.05). In the 12 healthy volunteers studied there were no significant differences in any of the haemodynamic parameters measured (average cardiac index: 2.75 +/- 0.78) over a period of 15 minutes after the placement of Bi-PAP. Similar results for most haemodynamic parameters were found in the 7 COPD patients with imminent respiratory failure (average respiratory rate 24.8 +/- 3.2) when Bi-PAP was utilized with the exception of significant but small increases in the cardiac index, stroke volume and oxygen saturation (p<0.05). While Bi-PAP is frequently used in the treatment of patients with acute respiratory failure, little is known about its effect on haemodynamics. This study suggests that the effects of the initiation of Bi-PAP on the general circulation and cardiac output may be of minor relevance.

We investigated the effects of three anesthetics on the size of myocardial infarction and on blood flow distribution within the myocardial wall. Myocardial infarcts were induced in 34 dogs by ligating a coronary artery for 90 minutes, and permitting reflow for 90 minutes. The anesthetics used were fentanyl, Na-pentobarbital, and halothane. Under halothane the mean blood pressure (BP) during coronary artery ligation was 113 +/- 2/82 +/- 2 mm Hg and the heart rate (HR) was 135 +/- 2/min. Under fentanyl, the BP was 143 +/- 3/91 +/- 2 mm Hg and HR 99 +/- 3/min. Under Na-pentobarbital, BP was 141 +/- 2/104 +/- 2 mm Hg and HR 146 +/- 2/min. A higher mean BP combined with a slower HR, as seen under fentanyl, was associated with the smallest infarct (24 +/- 8%). Low BP and higher HR, as seen under halothane, was associated with the largest infarct (51 +/- 5%). Na-pentobarbital, with a higher BP but also a faster HR, resulted in an infarct size of 32 +/- 5%. We conclude that a higher mean BP combined with a slower HR might favor the preservation of a larger mass of vulnerable myocardial tissue in a totally occluded coronary artery.

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