Comparing cerebral blood flow velocity and cerebral blood flow measures between transcranial Doppler ultrasound and phase contrast magnetic resonance imaging during hypercapnia and hypocapnia (1183.2)

Abstract

To test the hypothesis that middle cerebral artery (MCA) diameter remains stable across physiologic stimuli, the cross‐sectional area (CSA) of the MCA was assessed using high‐field magnetic resonance imaging (MRI) (3T, T2 images) during hypercapnia (HC) and hypocapnia (HO). Estimates of cerebral blood flow velocity (CBV) collected with transcranial Doppler (TCD) ultrasound and phase contrast (PC) MRI were also compared with subsequent calculation of cerebrovascular reactivity (CVR). End‐tidal carbon dioxide (ETCO2) levels were manipulated through hyperventilation (30 breaths/min) and inhalation of 6% CO2 gas. The CSA increased from 5.5 ± 0.9 to 6.4 ± 1.2 mm2 (p<0.001; n=16) during HC and decreased from 5.7 ± 1.0 to 5.1 ± 0.8 mm2 (p<0.001; n=14) during HO. During HC CBV increased from 68 ± 9 to 85 ± 15 cm/s (p=0.003, n=7) measured with TCD and from 64 ± 10 to 85 ± 15 cm/s (p=0.002, n=7) measured with PC, while there was a decrease from 69 ± 8 to 55 ± 16 cm/s (p = 0.02, n=7) with TCD and from 61 ± 8 to 51 ± 8 cm/s (p = 0.02, n=7) during HO. Cerebrovascular reactivity during HC was 2.42 ± 3.98 cm/s/mmHg for TCD and 2.87 ± 1.63 cm/s/mmHg for PC (p = 0.70). Cerebrovascular reactivity during HO was ‐1.67 ± 1.37 cm/s/mmHg for TCD and ‐0.92 ± 1.17 cm/s/mmHg for PC (p = 0.11). Therefore, CSA of the MCA is not constant across this range of ETCO2. Further, TCD and PC provide similar estimates of absolute CBV and CVR during HO and HC. Grant Funding Source: Supported by the Canadian Institutes of Health Research