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Autoregulatory response and CO2 reactivity of the basilar artery
Cheol Wan Park1, Mathias Sturzenegger, Colleen M Douville
1Cerebrovascular Laboratory, Department of Neurological Surgery, University of Washington School of Medicine, Harborview Medical Center, Seattle 98104-2499, USA. cwpark@ghil.com
Insights
Transcranial Doppler assessed cerebrovascular control in the basilar artery (BA) and middle cerebral artery (MCA). Autoregulation and CO2 reactivity were found to be similar in both arteries in healthy volunteers.
Area of Science:
- Neuroscience
- Cerebrovascular Physiology
- Medical Imaging
Background:
- Transcranial Doppler (TCD) is widely used to assess cerebrovascular control mechanisms.
- Previous studies have established normal autoregulatory response (AR) and CO2 reactivity (CR) for the middle cerebral artery (MCA).
- Limited data exist on these indices for the basilar artery (BA).
Purpose of the Study:
- To measure AR and CR in the BA of healthy volunteers.
- To establish normal values for BA autoregulation and CO2 reactivity.
- To compare BA measurements with simultaneous MCA measurements.
Main Methods:
- Sixteen healthy subjects underwent simultaneous TCD monitoring of the BA and MCA.
- Mean arterial blood pressure (MABP) and end-tidal PaCO2 (ETCO2) were manipulated.
- Autoregulation was assessed using the thigh cuff method and graded by the dynamic autoregulatory index (ARI).
- CO2 reactivity (CR) was measured as the percentage change in velocity per mm Hg ETCO2.
Main Results:
- Mean autoregulatory index (ARI) for the BA was 4.62±1.26, compared to 4.77±1.23 for the MCA (P=0.598).
- Mean CO2 reactivity (CR) for the BA was 2.54±0.39%/mm Hg ETCO2, compared to 2.51±0.29%/mm Hg ETCO2 for the MCA (P=0.686).
- No significant differences were found between the BA and MCA for either ARI or CR.
Conclusions:
- The autoregulatory response (AR) and CO2 reactivity (CR) in the basilar artery (BA) are comparable to those in the middle cerebral artery (MCA).
- These findings provide normal reference values for BA cerebrovascular control.
- TCD can reliably assess cerebrovascular function in both the BA and MCA.
Background And Purpose:
Transcranial Doppler has been extensively used to measure cerebrovascular control mechanisms, including autoregulation in humans and in patients with cerebrovascular diseases. There have been sufficient reports on the measurement of normal autoregulatory response (AR) and CO2 reactivity (CR) of the middle cerebral artery (MCA) but few reports of these indices for the basilar artery (BA). We measured AR and CR in the BA in healthy volunteers to determine normal values and compared them with simultaneous measurements made in the MCA.
Methods:
Sixteen normal subjects were enrolled. Time-averaged mean velocities of maximum blood flow in the BA and MCA were continuously and simultaneously monitored by using transcranial Doppler along with continuous measurement of mean arterial blood pressure (MABP). Values were obtained during rest, alterations of end-tidal PaCO2 (ETCO2), and acute decrease and recovery of MABP. AR was evaluated by using the thigh cuff method and graded by the standard dynamic autoregulatory index (ARI), with values between 0 and 9. CR was measured as percentage change in time-averaged mean velocity per mm Hg ETCO2.
Results:
The mean age of 16 subjects was 27.38+/-8.50 years. Average baseline values for MABP and ETCO2 were 82.29+/-7.10 and 42.75+/-3.77 mm Hg, respectively. Mean ARI was 4.62+/-1.26 for the BA and was 4.77+/-1.23 for the MCA (n=15) (P=0.598). Average CR was 2.54+/-0.39%/mm Hg ETCO2 for the BA and 2.51+/-0.29%/mm Hg ETCO2 for the MCA (n=16) (P=0.686).
Conclusions:
Our study demonstrates that ARI and CR values for the BA are similar to those for the MCA.