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Pulmonary hypoxic vasoconstriction: how strong? How fast?

D W Sheehan1, R A Klocke, L E Farhi

  • 1Department of Physiology, School of Medicine and Biomedical Sciences, State University of New York, Buffalo 14214.

Respiration Physiology
|March 1, 1992
PubMed
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This study introduces a minimally invasive method to measure regional blood flow in sheep using methane clearance. The technique reveals hypoxic vasoconstriction is more potent during eucapnic hypoxia.

Area of Science:

  • Physiology
  • Respiratory Physiology
  • Cardiovascular Physiology

Background:

  • Studying regional blood flow in conscious animals typically requires invasive methods like open-chest surgery.
  • Existing techniques for measuring regional perfusion often involve flow probes or tracer infusions, which can be complicated.
  • Accurate assessment of regional blood flow is crucial for understanding physiological responses, particularly in the respiratory and cardiovascular systems.

Purpose of the Study:

  • To develop and validate a minimally invasive technique for continuously measuring regional blood flow in conscious sheep.
  • To assess the influence of different hypoxic conditions (eucapnic vs. hypocapnic) on pulmonary vasoconstriction.
  • To investigate the time course of hypoxic vasoconstriction and its implications for existing literature.
Keywords:
NASA Discipline Regulatory PhysiologyNon-NASA Center

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Main Methods:

  • Developed a technique using regional methane clearance to quantify regional perfusion in conscious sheep.
  • Utilized tracheal intubation with a dual-lumen catheter to isolate gas exchange in the right apical lobe (RAL) for measurement.
  • Measured methane elimination from the isolated lung region (RAL) and the control lung (CL) by entraining expirates in constant flows.
  • Validated the technique by comparing results with regional oxygen uptake measurements.

Main Results:

  • The developed technique provides continuous and minimally invasive measurements of regional blood flow.
  • Results from the methane clearance method showed excellent agreement with regional oxygen uptake.
  • Hypoxic vasoconstriction was found to be significantly more potent and stable during eucapnic hypoxia compared to hypocapnic hypoxia.
  • The observed time course of vasoconstriction suggests that previous studies might have been conducted before reaching a steady state.

Conclusions:

  • The novel methane clearance technique offers a reliable and less invasive alternative for studying regional blood flow in conscious sheep.
  • Eucapnic hypoxia induces a more pronounced and sustained pulmonary vasoconstrictive response than hypocapnic hypoxia.
  • The findings highlight the importance of achieving steady-state conditions when investigating hypoxic pulmonary vasoconstriction to ensure accurate data interpretation.