Physiological Effects of Mechanical Exsufflation on Experimental Obstructive Breathing in Human Subjects 1

Abstract

The increased physical effort necessary to breathe through a constricted orifice results in an instantaneous and uncomfortable sensation of dyspnea. The immediate sensation of difficulty in breathing is aroused by proprioceptive reflexes. The duration of inspiration and expiration becomes markedly prolonged, (1, 2) and in spite of the increased work entailed, the peak volume flow rates diminish. The minute ventilation has been shown by Cain and Otis (1) to decrease. Haldane and Priestley (3) and others (1, 4) also noted that hypoxia and retention of carbon dioxide develops due to the prolonged duration of the respiratory cycle and reduced alveolar ventilation, resulting from obstructed breathing. Furthermore, a lower or more negative intrapleural pressure develops during the inspiratory phase when breathing against a resistance. The pathological consequences of obstructed breathing, namely pulmonary congestion, have been demonstrated in animals by Moore and Binger (4, 5) and Barach and his associates (6)(7)(8).During the initial studies on the physiological effects of exsufflation, the principle of which is described in Methods, it was noted that the physical effort required to breathe against a resistance introduced at the mouth was markedly diminished (9, 10). Since exsufflation appeared subjectively to relieve dyspnea it was of interest to study its physiological effect on experimentally produced obstructed breathing in normal human subjects. METHODSTwo mechanical methods of simulating a cough in man were originally devised by Barach and his coworkers (9-11) as a means of eliminating secretions in patients who are unable to cough effectively. One of these methods, exsufflation, i.e., rapid movement of air from the lungs, is accomplished by enclosing the body of the patient in a conventional tank respirator. A negative intra-tank pressure of 40 mm. Hg, developed over a two-second period by a motor blower unit attached to the respirator, is followed by a rapid return to atmospheric pressure in 0.06 seconds by means of a swift-opening

The Effect of Mechanical Exsufflation on Respiratory Gas Exchange in Chronic Pulmonary Emphysema

“…This might be explained by the ability of the exsufflator both to overcome obstruction to breathing (9) and to ventilate the alveoli more effectively.…”

The Resistance of Endotracheal Connectors

“…According to Macintosh and Mushin (1947), in an adult breathing 8 litres per minute quietly, the maximum flow rate of air during normal inspiration reaches 25 litres per minute, and they use this latter rate to measure experimentally the resistance of endotracheal connectors. This figure may be on the low side, however, as Proctor and Hardy (1949) found an average peak inspiratory velocity (in normal patients) of 35 litres per minute; similarly Cherniack et al (1952) give a figure of 35.5 litres per minute, and Mead and Whittenberger (1953) 30-50 litres per minute for quiet breathing.…”

Management of Respiratory Paralysis using a "Mechanical Cough" Respirator

“…This device has proved useful in the treatment of cases with chronic bronchial infection, and has been applied successfully to patients with respiratory paralysis undergoing artificial respiration in tank respirators. Cherniack et al (1952) have also demonstrated physiological advantages of this effect, particularly in obstructed breathing.…”