Measuring cerebrovascular reactivity in a hemodialysis cohort

Introduction Cerebrovascular reactivity (CVR) can inform about cerebral vascular health and provide prognostic information on risk cerebral ischemic injury. Use of transcranial Doppler ultrasound (TCD) is a non-invasive and inexpensive method to measure CVR and often uses a stimulus of increase in arterial partial pressure of carbon dioxide (pCO₂). We evaluate re-breathing and breath-hold to measure CVR in a medically complex hemodialysis cohort who are at risk for cerebral hypoperfusion due to circulatory stress of hemodialysis. Methods CVR was measured using both a 30 s breath-hold and a re-breathing period. We used percent change in mean flow velocity of the middle cerebral artery, measured with TCD over the change in end-tidal CO₂ to calculate CVR. Paired T-test was used to compare the parameters of CVR and Pearson correlation to evaluate relevant risk factors for lower CVR. Results 16 participants completed both CVR measurements, with mean (SD) age of 64.2 (11.2) years. CVR measured from each technique was similar 3.4 (2.9) %/mmHg (breath-hold) vs 2.7 (1.6) %/mmHg, (re-breathing) p = 0.37. Older age and history of stroke were associated with lower CVR when measured with re-breathing but not with breath-hold technique. Conclusions Re-breathing to increase pCO₂ and measure CVR is well-tolerated by a frail older medically complex patient population and may be a way to measure cerebrovascular health.