Pressure Breathing: Functional Circulatory Changes in the Dog

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Abstract
Observations were made on two series of dogs breathing air at 17 and 26 mm Hg positive pressure. In one series (8 dogs) the animals had the benefit of counterpressure while the other group (10 dogs) did not. Systolic blood pressure decreased in each group while breathing against 17 mm Hg positive pressure, but to a greater extent in the group without counterpressure. While breathing against 26 mm Hg positive pressure, there was essentially no difference between the two groups. Changes in diastolic blood pressure followed a pattern similar to the changes in systolic pressure. Pulse pressure was essentially maintained. Venous pressure increased markedly during pressure breathing. This increase in the group with counterpressure more nearly approximated the simultaneous increase in intratracheal pressure. Intracranial pressure was elevated during pressure breathing. This increase was greatest and maintained in the group with counter-pressure. Heart rate increased during pressure breathing, especially in the group with counterpressure, and slightly decreased in the group without counterpressure. A period of apnea occurred at the onset of pressure breathing in the group without counterpressure while respiration rate remained essentially unchanged in the group with counterpressure. Hematocrit determinations indicated hemoconcentration during pressure breathing. Submitted on June 27, 1955

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