Influence of Respiration on Venous Return in Pulmonary Emphysema

Abstract

The influence of respiration on the flow of blood from the abdominal vena cava into the thorax was studied in 15 patients with pulmonary emphysema and in 10 control subjects without thoracic disease or heart failure. In control subjects, during quiet breathing blood flowed into the thorax throughout the respiratory cycle at a rate which was greatest during inspiration. Simultaneously the transmural pressure of the abdominal vena cava fell and transmural right atrial pressure increased. The same pattern of flow was observed in nine of the patients with emphysema. In the other six patients, however, flow was greatly reduced or completely arrested during inspiration, with simultaneous increase in transmural caval pressure and reduction in transmural atrial pressure. This inspiratory obstruction at the thoracic inlet was associated with gross hyperinflation of the lungs and a low diaphragmatic position. It probably was not the result of the high negative and positive intrathoracic pressures that develop during inspiration and expiration, respectively, in such subjects. It is possible that this phenomenon may account for the peripheral edema that occurs in patients who have emphysema without associated pulmonary hypertension or cardiomegaly.