Effects of volume control, pressure control, and pressure-regulated volume control on cardiopulmonary parameters in a normal rat lung.

The purpose of this study was to investigate the differences in diaphragm shortening and cardiopulmonary parameters at varying tidal volumes during volume control (VC), pressure control (PC), and pressure-regulated volume control (PRVC). A miniaturized ultrasonic sensor attached to the inferior surface of the upper costal surface of the right hemidiaphragm of 16 Sprague-Dawley rats provided a direct assessment of diaphragm shortening. Within each control mode of mechanical ventilation, the tidal volume was increased from 3 to 12 ml in increments of 3 ml. There were no differences in cardiac output, mean arterial pressure, central venous pressure, peak inspiratory pressure, or end-tidal CO2 among the three modes of mechanical ventilation. At equivalent tidal volumes, diaphragm shortening was less during PRVC than during VC or PC. This finding suggests that differences in diaphragm shortening may be caused by shorter resting (end-expiratory) diaphragm muscle length. The cardiopulmonary data obtained in this study provide new information for clinicians to consider when using various modes of ventilation, particularly PRVC.