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Reflex control of vascular capacitance during hypoxia, hypercapnia, or hypoxic hypercapnia
C F Rothe1, A D Flanagan, R Maass-Moreno
1Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46223.
Canadian Journal of Physiology and Pharmacology
|March 1, 1990
Summary
Cardiovascular reflexes are essential for regulating venous tone during changes in blood oxygen and carbon dioxide levels. Without these reflexes, hypoxia and hypercapnia have minimal direct impact on vascular capacitance.
Area of Science:
- Cardiovascular Physiology
- Respiratory Physiology
Background:
- Venous tone significantly influences circulatory dynamics.
- The role of cardiovascular reflexes in mediating responses to altered blood gases is not fully understood.
Purpose of the Study:
- To investigate the necessity of intact cardiovascular reflexes for changes in venous tone induced by hypoxia and hypercapnia.
Main Methods:
- Mongrel dogs were used, with anesthesia and paralysis.
- Cardiac output and central blood volume measured via indocyanine green dilution.
- Mean circulatory filling pressure estimated using central venous pressure during cardiac fibrillation.
Main Results:
- Intact reflexes led to increased mean circulatory filling pressure and cardiac output during hypoxia, hypercapnia, or both.
- Hypoxia, but not normoxic hypercapnia, increased arterial pressure and maintained total peripheral resistance with intact reflexes.
- With reflexes blocked, gas mixtures decreased peripheral resistance and arterial pressure, with minimal changes in mean circulatory filling pressure or cardiac output.
Conclusions:
- Hypoxia, hypercapnia, and combined hypoxic hypercapnia have minimal direct effects on vascular capacitance.
- Intact cardiovascular reflexes are crucial for the significant increase in mean circulatory filling pressure observed under altered blood gas conditions.