Positive expiratory pressure plateau breathing in spontaneously breathing patients with myocardial infarction and pulmonary oedema.

Kerr, F., Ewing, D. J., Irving, J. B., Sudlow, M. F., and Kirby, B. J. (1974).Thorax, 29, 690-694. Positive expiratory pressure plateau breathing in spontaneously breathing patients with myocardial infarction and pulmonary oedema. The respiratory effects of breathing with a positive expiratory pressure plateau (PEPP) was studied in 24 spontaneously breathing, alert, nonsedated patients with pulmonary oedema following myocardial infarction. When 20 patients breathed room air with PEPP a small rise in arterial oxygen tension (Pao2) with a fall in alveolar to arterial oxygen gradient (A—ado2) occurred. Arterial carbon dioxide tension did not change significantly. When PEPP was used in six patients after breathing 100% oxygen for 20 minutes there was no significant change in Pao2, A—ado2 or anatomical shunt (Q̇s/Q̇t). Expired air collection in a further six of the patients demonstrated that although PEPP produced an increase in tidal volume (Vt), alveolar ventilation (Va) fell slightly as a result of a decrease in respiratory rate, and oxygen consumption (Vo2) did not change. In 10 normal subjects functional residual capacity (FRC), measured continuously in a whole-body volume displacement plethysmograph, decreased by a small amount when these subjects breathed with PEPP. Positive expiratory pressure plateau breathing in spontaneously breathing conscious patients with pulmonary oedema produced a small improvement in ventilation/perfusion matching not by an increase in FRC but by an increase in Vt. The increase in Vt probably altered the ventilation/perfusion relationships by a redistribution of inspired gas.