Abstract
Background.
Both CO2 inhalation followed by hyperventilation and breath‐holding have been utilized to measure cerebral vasomotor reactivity (VMR) but their correlation has been poorly studied and understood.
Methods.
A retrospective study was conducted in 143 subjects (62.6 ± 15.8 years old, 64% men) with transcranial Doppler ultrasonography measurement of mean flow velocity (MFV) at baseline, after 30 seconds of breath‐holding, and after CO2 inhalation followed by hyperventilation, in the left and right middle cerebral artery. Breath‐holding index (BHI) was calculated as the percentage of MFV increase from baseline per second of apnea. CO2 inhalation/hyperventilation index (CO2/HV) was calculated as the percentage of MFV difference between CO2 inhalation and hyperventilation.
Results.
There were 75 carotid arteries with >70% stenosis or occlusion, and 18 middle cerebral arteries with >50% stenosis or occlusion. The mean BHI was 0.93 ± 0.7 and 0.89 ± 0.6, whereas the mean CO2/HV was 61 ± 26% and 60 ± 26%, respectively, on the right and left sides. The correlation between BHI and CO2/HV was moderate on the right (r = 0.33; p < 0.01) and left sides (r = 0.38; p < 0.01). Multivariate linear regression analysis indicated that age (p = 0.01) and history of stroke (p = 0.007) were associated independently with an impaired VMR on the right as measured by CO2/HV. No predictors for impaired VMR by CO2/HV on the left and by BHI on either side were found.
Conclusions.
CO2/HV and BHI are only moderately correlated. Further studies are necessary to determine which method more accurately predicts clinical morbidity. © 2012 Wiley Periodicals, Inc. J Clin Ultrasound 2012; Published online in Wiley Online Library
