No significant change of extracranial conduit vessel diameter during cerebral vasomotor reactivity test with moderately‐altered end‐tidal CO2
Abstract
Cerebral vasomotor reactivity (CVMR) is often assessed using transcranial Doppler (TCD) to measure the cerebral blood flow velocity (CBFV) in the middle cerebral artery (MCA). Recently the validity of this technique has been questioned because of the assumption that MCA diameter does not change. The goal of this work was to test if the extracranial cerebral arteries, i.e. internal carotid and vertebral arteries (ICA and VA), have a significant diameter change during moderate alteration of end‐tidal carbon dioxide (ETCO2). Fifteen healthy subjects (6 males; age: 32±10 yrs) were enrolled. The CBFV at the MCA was continuously recorded with TCD during an 8‐min CVMR test, i.e. 2‐min resting ventilation, 2‐min inspiration of 5% CO2, 21% O2, balance nitrogen, 2‐min recovery, and 2‐min mild hyperventilation. 8 min protocol was repeated on the same subjects, to allow measurement of ICA diameter during one run and VA during the other using high‐frequency ultrasound. CVMR is expressed as the percent change in MCA's CBFV per mmHg change in ETCO2, as quantified by the slope of this relationship. The time‐averaged diameter during each static stage was measured offline with echo‐tracking software. All results presented as Mean ± SD. The experimental protocol resulted in a moderated change of ETCO2 (mmHg) during 5% CO2 inspiration (+6.9±2.0) and mild hyperventilation (−14.8±5.8) relative to the baseline values (34.6±2.7). Both hypercapnic and hypocapnic stages showed no significant changes (relative to the baseline) in blood pressure, heart rate, diameters of ICA (5.23±0.83 and 5.21±0.71, vs. baseline 5.22 ±0.83 mm; P = 0.88 and 0.86) and VA (3.91±0.69 and 3.91±0.72, vs. baseline 3.87±0.65 mm; P = 0.40 and 0.55), except for a slight increase (+7±8 bpm, P 2, as no significant change of the conduit vessel diameter is likely to occur. However, future work is necessary to confirm that flow changes in the extracranial arteries are reflective of relative changes in TCD values.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Apr 01, 2019
- Source ID
- 10.1096/fasebj.2019.33.1_supplement.528.12
Entities
People
- Allan Knox
- Jie Liu
- Jorge M Serrador
- Thuy Tien Cao Le
Organizations
- California Lutheran University
- Rutgers University
- United States Department of Defense