Certain effects of positive pressure respiration on the circulatory and respiratory systems

Abstract Experimental studies were carried out on dogs anesthetized with pentobarbital sodium to determine the effect of long periods of pressure breathing alone and when combined with acute hemorrhage or trauma of the hind limbs. The following results were obtained: 1. 1. Continuous positive pressure respiration with a pressure of 20 cm. of water. 2. a. Five of nine animals survived three hours of continuous positive pressure respiration, but, in the case of the other four, fatal apnea developed. 3. b. The apnea caused by a continuous positive respiratory pressure of 20 cm. of water was not affected by large doses of atropine but was abolished by bilateral vagotomy. 4. c. Continuous positive pressure respiration had a variable effect on the femoral arterial pressure and on the heart rate. It slowed and deepened the respirations. It elevated the jugular venous pressure, the renal venous pressure, the pulmonary arterial pressure, and the pulmonary venous pressure. It decreased the diameter of the heart and thoracic inferior vena cava but increased the diameter of the abdominal vena cava. It dilated the tracheobronchial tree. 5. d. Three of eight animals survived two hours of continuous positive pressure respiration after a hemorrhage of 30 c.c. per kilogram of body weight in five minutes, but in the case of the other five animals either apnea or circulatory failures developed. 6. e. Three hours of continuous positive pressure respiration did not cause either pneumothorax or mediastinal emphysema in a single case, but in all of a group of five animals acute parenchymal and subpleural emphysema developed. 7. 2. Intermittent positive pressure respiration with a pressure of 20 cm. of water. 8. a. All of a group of five animals withstood three hours of intermittent positive pressure respiration without difficulty. 9. b. Intermittent positive pressure respiration produced considerable fluctuation of the femoral arterial pressure with a decrease of the mean pressure. It elevated the jugular venous pressure, the pulmonary venous pressure, the renal venous pressure, and the pulmonary arterial pressure. It decreased the diameter of the heart and thoracic inferior vena cava but increased the diameter of the abdominal vena cava and the tracheobronchial tree. It slowed and deepened the respirations but had no consistent effect on the heart rate. 10. c. Three of five animals survived, without difficulty, two and a half hours of intermittent positive pressure respiration following a hemorrhage of 30 c.c. per kilogram of body weight in five minutes. In the case of the other two, eirculatory failure developed and the animals were given 10 c.c. of blood per kilogram of body weight with such improvement that they were then able to complete the experiment. 11. d. Splenectomized animals were unable to withstaud even a small hemorrhage (10 to 20 c.c. per kilogram of body weight) during intermittent positive pressure respiration. 12. e. Trauma to the hind limbs during intermittent positive pressure respiration proved fatal to all four animals. It was demonstrated that the pressure breathing was a definite factor in hastening their death. 13. f. Three hours of intermittent positive pressure respiration with a pressure of 15 cm. of water did not cause either pneumothorax or mediastinal emphysema in a single case, but in all of a group of three animals acute parenchymal and subpleural emphysema developed.