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 (Qs/Qt). 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.
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