The response of patients with respiratory failure and cardiopulmonary disease to different levels of constant volume ventilation.

The purpose of this study was to determine the effect of increasing the tidal volume on pulmonary ventilation-perfusion relations in patients with respiratory failure caused by cardiopulmonary disease. The frequent occurrence of an increased physiologic dead space (2, 3) and of increased physiologic shunting (3) in patients undergoing prolonged artificial ventilation has previously been described. These changes in ventilation-perfusion ratios mean that very large tidal volumes and high percentages of inspired oxygen are often required to maintain life during prolonged intermittent positive pressure ventilation. The aim of our study was to measure the consequences of changing the tidal volume, but not the respiratory frequency, of patients with respiratory failure secondary to either acute intrapulmonary infection or chronic pulmonary emphysema.