The effect of hypercapnia on regional cerebral blood flow regulation during progressive lower-body negative pressure

Purpose Previous work indicates that dynamic cerebral blood flow (CBF) regulation is impaired during hypercapnia; however, less is known about the impact of resting hypercapnia on regional CBF regulation during hypovolemia. Furthermore, there is disparity within the literature on whether differences...

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Bibliographic Details
Published in:European journal of applied physiology 2021, Vol.121 (1), p.339-349
Main Authors: Thrall, Scott F., Tymko, Michael M., Green, Chanelle L. M., Wynnyk, Kristi I., Brandt, Rachelle A., Day, Trevor A.
Format: Article
Language:English
Subjects:
Biomedical and Life Sciences
Biomedicine
Birth control
Blood flow
Blood pressure
Body mass index
Carbon dioxide
Cerebral blood flow
Conductance
Doppler effect
EKG
Ethics
Heart rate
Human Physiology
Hypercapnia
Hyperventilation
Metabolism
Occupational Medicine/Industrial Medicine
Original Article
Physiology
Software
Sports Medicine
Ultrasound
Veins & arteries
Velocity
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Summary:Purpose Previous work indicates that dynamic cerebral blood flow (CBF) regulation is impaired during hypercapnia; however, less is known about the impact of resting hypercapnia on regional CBF regulation during hypovolemia. Furthermore, there is disparity within the literature on whether differences between anterior and posterior CBF regulation exist during physiological stressors. We hypothesized: (a) lower-body negative pressure (LBNP)-induced reductions in cerebral blood velocity (surrogate for CBF) would be more pronounced during hypercapnia, indicating impaired CBF regulation; and (b) the anterior and posterior cerebral circulations will exhibit similar responses to LBNP. Methods In 12 healthy participants (6 females), heart rate (electrocardiogram), mean arterial pressure (MAP; finger photoplethosmography), partial pressure of end-tidal carbon dioxide (P ET CO 2 ), middle cerebral artery blood velocity (MCAv) and posterior cerebral artery blood velocity (PCAv; transcranial Doppler ultrasound) were measured. Cerebrovascular conductance (CVC) was calculated as MCAv or PCAv indexed to MAP. Two randomized incremental LBNP protocols were conducted (− 20, − 40, − 60 and − 80 mmHg; three-minute stages), during coached normocapnia (i.e., room air), and inspired 5% hypercapnia (~ + 7 mmHg P ET CO 2 in normoxia). Results The main findings were: (a) static CBF regulation in the MCA and PCA was similar during normocapnic and hypercapnic LBNP trials, (b) MCA and PCA CBV and CVC responded similarly to LBNP during normocapnia, but (c) PCAv and PCA CVC were reduced to a greater extent at − 60 mmHg LBNP ( P  = 0.029; P  
ISSN:1439-6319
1439-6327
DOI:10.1007/s00421-020-04506-2