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Hypoxic vasoconstriction in pulmonary arterioles and venules
S C Hillier1, J A Graham, C C Hanger
1Department of Anesthesia, Indiana University School of Medicine, Indianapolis 46202, USA.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|April 1, 1997
Summary
Pulmonary microvessels constrict during hypoxia, challenging previous assumptions. This active response suggests a role in matching ventilation and blood flow within the lungs.
Area of Science:
- Pulmonary Physiology
- Vascular Biology
- Respiratory Medicine
Background:
- Pulmonary microvessels (less than 70 micrometers) have incomplete muscular media.
- It was hypothesized that these thin-walled vessels do not contribute to the hypoxic pressor response.
Purpose of the Study:
- To test the hypothesis that pulmonary microvessels do not participate in the hypoxic pressor response.
- To investigate the active role of pulmonary microvessels in response to hypoxia.
Main Methods:
- Isolated canine lung lobes were pump-perfused under controlled microvascular pressures.
- A videomicroscope with computerized image enhancement measured subpleural arteriole and venule diameters.
- Vessel diameter changes were assessed during normoxia and hypoxia, with and without nitric oxide administration.
Main Results:
- Hypoxia induced a 25% average reduction in microvessel diameters, despite constant vascular pressure.
- The hypoxic constriction was reversible upon the addition of nitric oxide.
- Fluorescent microspheres showed no redistribution of lobar blood flow, indicating the constriction was an active process.
Conclusions:
- Pulmonary microvessels actively constrict in response to hypoxia.
- This active constriction suggests a mechanism for intra-acinar ventilation-perfusion matching.
- The findings challenge the traditional view of thin-walled pulmonary vessels' role in hypoxic responses.