Relationship between the fall in blood pressure in the standing position and diaphragmatic muscle thickness: proof of concept study.

Abstract

The diaphragm is an important muscle of respiration, and regulates the intrathoracic pressure. Blood pressure is regulated by the baroreceptor reflex system, and is also affected by intrathoracic pressure. We examined the relationship between the diaphragmatic muscle thickness and the degree of drop in blood pressure in the standing position. We prospectively studied 15 healthy subjects. The diaphragmatic muscle thickness was measured using a B-mode ultrasonic imaging device. The blood pressure before and after standing was measured by a head-up tilt test. The diastolic blood pressure difference during expiration and inspiration showed a significant correlation with the diaphragmatic muscle thickness (r = 0.578, P = 0.024 and r = 0.518, P = 0.048, respectively). The diaphragmatic muscle thickness was related to the fall in diastolic blood pressure in the standing position. This indicates that adequate diaphragmatic muscle thickness helps to maintain intrathoracic pressure and prevents excessive drop in blood pressure in the standing position.