Circulatory effects of administering a pneumothorax equal to the functional residual capacity to dogs are reported. Cardiac output dropped 20% immediately and 20% more during the next 5 hours. Mean systemic blood pressure rose from 135 to 152 between 1 and 3 hours after pneumothorax. Pulmonary artery pressure was unaffected for 3 hours, but rose from 14 to 19 mm Hg after that period, probably because of hypoxia occurring at that time. Peripheral vascular resistance rose in every case to a mean of twice prepneumothorax values. This appeared to be a reflex phenomenon. A series of control experiments revealed no significant change in any of the above values.
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Simmons et al. (1958) studied this question.
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