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

, , 690-694. 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 (ao) with a fall in alveolar to arterial oxygen gradient (A—ado) 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 ao, A—ado 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 (Vo) 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.