BACKGROUND AND PURPOSECerebrovascular 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 CO(2)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.METHODSTen 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.RESULTSThe mean coefficient of variation
was 43.7% lower in BHAI in comparison with BHI. Neither index was statistically significant
between body positions (P > .05).CONCLUSIONSBHAI has less variability in comparison
with the conventional standard BHI. Additionally, neither index showed statistical
significance in CR based on change in body position.
