A Computer Analysis of Pulmonary Function in Surgical Patients

Abstract A small analogue computer for studying the mechanics of ventilation in preoperative and postoperative patients has been designed. We found that more air was moved per minute and that respiratory rate was increased in the postoperative period. Most important was the finding that the increase in work per minute was proportionately greater than the amount of air moved. This finding implies an inherent decrease in efficiency with increased ventilation and airway obstruction or increased stiffness of the lungs postoperatively. There was a decrease in dynamic compliance but tidal volume remained unchanged during the postoperative period, emphasizing the importance of changes in compliance and work/ventilation ratio. In patients who developed respiratory difficulties postoperatively, a high work/ventilation ratio was noted preoperatively; these values rose to very high levels during the immediate postoperative period.