RESUMO
BACKGROUND AND PURPOSE: Cerebrovascular reactivity (CR) is an ideal biomarker to detect cerebrovascular damage. CR can be quantified by measuring changes in cerebral blood flow velocity (CBFV) resulting from a CO2 vasodilatory stimulus, often using the breath-holding index (BHI). In this method, transcranial Doppler (TCD) ultrasound is used to measure CBFV changes in the middle cerebral artery (MCA) during a breath-hold maneuver. Despite its convenience, BHI has high variability. Changing body position may contribute to potential variability. It is important to determine if CR differs with body position. The aims of this study were, first, to propose an alternative, more robust index to evaluate CR using a breath-hold maneuver; second, investigate the effect of body position on CR measured with conventional (BHI) and a new proposed index. METHODS: Ten healthy young volunteers held their breath for 30 seconds on a tilt table. CR was calculated at five different angles using two indices: the conventional BHI, and the breath-hold acceleration index (BHAI), a new index obtained by linear regression of the most linear portion of the mean velocity change during the breath-hold maneuver. The regression represents acceleration (change in blood flow velocity per unit of time) sampled at each cardiac cycle. RESULTS: The mean coefficient of variation was 43.7% lower in BHAI in comparison with BHI. Neither index was statistically significant between body positions (P > .05). CONCLUSIONS: BHAI has less variability in comparison with the conventional standard BHI. Additionally, neither index showed statistical significance in CR based on change in body position.
