Responses of Systemic Arterial Pressure and Heart Rate to Increased Intrapulmonary Pressure in Anesthetized Dogs

Abstract

Conclusions

Effects of varying pulmonary inflation pressure upon heart rate and arterial blood pressure were observed in anesthetized dogs. Mechanical, sympathetic and parasympathetic factors are believed to be involved in the responses observed as in the Valsalva phoenomenon. A high inflation pressure caused paradoxical bradycardia in phase 2, and a lack of arterial pressure overshoot in phase 4. From the evidences available, the bradycardia in phase 2 is interpreted as due to reflex vagal activity plus an active suppression of the sympathetic reflex. The lack of arterial pressure overshoot in phase 4 is considered to be the result of the mechanical effect of muscle relaxation due to anesthesia associated with peripheral blood pooling.

When a low pulmonary inflation pressure was employed under mild to moderate anesthesia, and when the mechanical factor caused by anesthesia was eliminated, the responses observed were quite similar to the Valsalva phenomenon in man. The preparation used in this experiment appears to provide a useful tool for the study of the cardiovascular sympathetic and parasympathetic reflex activities under various experimental hemodynamic states with or without pharmacological interventions.