Physiological Effects of Exsufflation with Negative Pressure (E.W.N.P.)

Abstract

The effects of Exsufflation With Negative Pressure (E.W.N.P.), a mechanical method of eliminating retained secretions, were studied in respect to cardiovascular function, diaphragmatic motion, and intragastric pressure. The physiological effects of E.W.N.P. were studied in 17 patients with bronchopulmonary disease with special reference to changes induced on the circulation. Although inspiratory pressures of 40 mm. Hg. were employed to inflate the lungs, the use of a negative lung deflating pressure of 40 mm. Hg. during the expiratory cycle resulted in comparatively low mean ventilatory pressures and, consequently, only slight rises in peripheral venous pressure, i.e., 5.8 cm. H2O. In contrast, a much higher venous pressure rise took place during the patients' natural vigorous cough, i.e., 16.1 cm. H2O. Small changes in arterial blood pressure also occurred during E.W.N.P., viz., an average increase of 8 mm. Hg. in systolic and 4 mm. Hg. in diastolic pressure in 22 subjects. Changes in the electrical axis of the heart due to nearly maximal lung inflation and deflation were similar to those induced by the deepest possible voluntary inspiration and expiration. Elimination of mucopurulent secretions by E.W.N.P. postoperatively seemed a somewhat safer procedure than the use of the patients' natural cough since intra-abdominal pressure was lower with this procedure: with E.W.N.P., the rise in intragastric pressure averaged 26 mm. Hg. in comparison to a rise of 85 mm. Hg. during the patient's cough. The reduction in pain at the wound site during the use of E.W.N.P. as compared to voluntary cough further suggested its value as a safety factor in respect to healing of abdominal wounds in the postoperative state. An average rise of 8 mm. Hg. systolic and 4 mm. Hg. diastolic in arterial blood pressure took place in 22 subjects. The change in electrical axis of the heart during the positive and negative pressure cycles were similar to those induced by the deepest possible voluntary inspiration and expiration. In 17 patients with bronchopulmonary disease and poliomyelitis an average venous pressure rise of 58 mm. H2O over the control level occurred during E.W.N.P. as compared to that of 161 mm. H2O in 12 of these subjects during their own natural cough. The relatively slight rise in blood pressure and venous pressure during E.W.N.P. was related to the low mean mask pressure found in this type of pressure breathing. Higher rises occurred in subjects who resisted inspiratory inflation by the apparatus. In conscious patients, cooperation with the technique of E.W.N.P. is an essential factor in the effective use of this apparatus.