The Effects of Intermittent Positive Pressure Breathing on Intrathoracic Pressure, Pulmonary Mechanics, and the Work of Breathing1,2,3

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Abstract
Intrathoracic pressure during intermittent positive pressure breathing (IPPB) at identical mask pressures varied widely depending on the degree of relaxation of the subject. In the completely relaxed subject, intrathoracic pressure remained positive in relation to the end-expiratory point throughout inspiration. In contrast to spontaneous breathing, pulmonary compliance varied inversely with flow rate in normal subjects. In patients with obstructive disease, decrease of compliance with flow rate was of similar magnitude to that occurring during unassisted breathing. Tidal volume varied inversely with flow rate. Inspiratory viscous resistance diminished slightly in normal subjects, and by 17 to 48% of control values in patients with obstructive disease during IPPB. In the completely relaxed subject, the work of breathing during inspiration approaches zero. Values for total thoracic and chest wall work and compliance determined during IPPB are similar to those previously reported in the literature. This method is a relatively simple one for assessing chest wall mechanics.

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