Influence of posture and abdominal pressure on the hemodynamic effects of Mueller's Maneuver

Abstract

Respiratory distress due to airway obstruction is usually associated with decreased mean intrathoracic pressure, which increases the afterload of the left ventricle. In normal subjects, Mueller's maneuver has been used to study left ventricular volume responses to controlled decreases in intrathoracic pressure. However, reported left ventricular responses have not been uniform. Using first-pass radionuclide ventriculography (RVG), we explored sources of variability, including experimental technique, posture, abdominal pressure, and heart rate in the cardiocirculatory response to Mueller's maneuver (pleural pressure change, −40 to −55 cm H 2O) in normal male volunteers. Individual responses to Mueller's maneuver were highly variable. In seven subjects, compared with the supine posture, the upright posture was associated with increased baseline heart rate and decreased baseline left ventricular end-diastolic volume (LVEDV). During Mueller's maneuver in both postures there was a significant increase in heart rate but no significant change in LVEDV, left ventricular end-systolic volume (LVESV), or left ventricular ejection fraction. In a separate group of seven subjects, Mueller's maneuver was performed in two different ways. The change in mouth pressure was the same, but in one maneuver, abdominal pressure was kept constant and in the other, it was increased. Left ventricular afterload, expressed as arterial minus pleural pressure increased by 36 torr when abdominal pressure increased and increased by 24 torr when abdominal pressure did not change ( P < .01). However, there was no associated difference in the left ventricular responses to Mueller's maneuver. In seven patients, pairs of RVGs were performed serially with no other intevention. For both ejection fraction and LVEDV, there were no significant differences between the first and second RVGs. The range of repeat measurements was far less than that associated with Mueller's maneuver. Although there were no differences in the reponses of LVEDV to Mueller's maneuver for the groups as a whole, when the data were pooled, LVEDV was found to be inversely correlated with change in heart rate during the maneuver (y = 1.1× + 20.8; r = .44; P < .04). We conclude that, in normals, (1)individualleft ventricular responses to Mueller's maneuver are highly variable, (2) little of this variability is inherent in making serial measurements using our techniques, (3) an important source of variability of the left ventricular volume response is the change in heart rate during the maneuver, and (4) neither changes in posture nor changes in abdominal pressure in the range studied are significant determinants of the left ventricular volume response to Mueller's maneuver.