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Thresholds for hypoxic cerebral vasodilation in volunteers
A K Gupta1, D K Menon, M Czosnyka
1Department of Anesthesia, University of Cambridge, Addenbrooke's Hospital, United Kingdom.
Anesthesia and Analgesia
|October 10, 1997
Summary
This study found that healthy volunteers show cerebral blood vessel dilation at a peripheral oxygen saturation (Spo2) of 90% using noninvasive transcranial Doppler sonography. This threshold for hypoxic cerebral vasodilatation is higher than previously reported.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
- Medical Technology
Background:
- Limited human data exists on hypoxemia's effects on cerebral vasculature, often relying on invasive methods.
- Noninvasive bedside techniques are needed to measure hypoxic vasodilatation thresholds in individual patients, especially those with impaired intracranial compliance.
Purpose of the Study:
- To identify thresholds of hypoxic cerebral vasodilatation in healthy volunteers using noninvasive measurement techniques.
- To assess the clinical utility of noninvasive methods for detecting cerebral blood vessel responses to reduced oxygen levels.
Main Methods:
- Thirteen healthy volunteers underwent transcranial Doppler sonography.
- Measurements included middle cerebral artery maximal flow velocity (MCA FVx), mean arterial blood pressure, peripheral oxygen saturation (Spo2), and end-tidal CO2.
- Graded reduction of Spo2 to 85% at normocapnia, with flow velocity and cerebrovascular resistance (CVRe) indexed against Spo2.
Main Results:
- No significant change in mean arterial pressure was observed down to 85% Spo2.
- Heart rate increased from 65 to 82 bpm during desaturation.
- Cerebral vasodilatation, indicated by increased MCA FVx and decreased CVRe, occurred when Spo2 dropped below 90%.
Conclusions:
- Hypoxemic cerebral vasodilatation can be measured noninvasively in humans.
- The threshold for this response in healthy volunteers is approximately 90% Spo2, which is higher than previously suggested.
- These findings are crucial for understanding adequate cerebral perfusion in various pathological conditions.