A comparison of artificial ventilation and spontaneous respiration with particular reference to ventilation-bloodflow relationships.

IT was suggested by Lucas and Milne (1955) that artificial ventilation by intermittent positive pressure (I.P.P.) is "inefficient" in that a larger ventilation is required to maintain the gaseous composition of the arterial blood than that required during spontaneous breathing. It has also been suggested by Howell and Peckett (1957) and by Butler and Smith (1957) that the distribution of air within the lungs is abnormal during I.P.P. We have investigated certain aspects of pulmonary physiology during spontaneous and artificial ventilation. Our main aims have been to determine, first, to what extent the altered distribution of ventilation within the lungs produces a "deadspace effect" due to the relative overventilation of some parts of the lungs: and, secondly, to what extent the altered distribution causes a "shunt effect" due to the relative underventilation of parts of the lungs. We have made use of the "ideal" alveolar air concept and the analysis of ventilation-bloodflow relationships described by Riley and Cournand (1949).

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