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Cerebrovascular Responses to Trigeminal Nerve Stimulation in Humans
Author(s) -
Ahmed Amar,
Edwards Louisa,
Braz Igor Dutra,
Fisher James P
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.706.1
Subject(s) - heart rate , anesthesia , medicine , vasoconstriction , reflex , blood pressure , transcranial doppler , middle cerebral artery , stimulation , cardiology , ischemia
The mammalian diving reflex, evoked by cold water face immersion, is characterized by peripheral vasoconstriction, an increase in blood pressure (BP) and a concomitant reduction in heart rate (HR). Trigeminal nerve stimulation (TGS) partly mediates these reflex induced cardiovascular adjustments, which are thought to conserve blood flow and oxygen for delivery to the brain and heart. We aimed to characterise the cerebrovascular responses to TGS under isocapnic conditions, and those evoked by generalized sympathetic activation during thermoreceptor stimulation with ice water hand immersion (cold pressor test; CPT). In eight healthy men (23±6 years) continuous recordings of middle cerebral artery velocity (MCA Vmean; transcranial Doppler), HR (ECG), mean BP (Finometer) and the partial pressure of end‐tidal carbon dioxide (P ET CO 2 ) were obtained. Cerebral vascular conductance index (CVCi) was calculated as; MCA Vmean/MAP. Participants underwent 3 minutes of CPT, with ice water (4°C) right hand immersion, and 3 minutes of TGS evoked by ice packs placed on the forehead and cheeks. Trials were randomized and separated by a 20‐minute resting period. Supplemental CO 2 was added to the inspired air in order to maintain isocapnia throughout the TGS and CPT trials. During TGS a decline in heart rate was observed, while mean BP rose progressively (p<0.05). MCA Vmean did not change significantly with TGS (baseline; 56.9 ± 3.4 cm/s, minute 3; 56.2 ± 3.3 cm/s, p>0.05), while CVCi was reduced (baseline; 0.79 ± 0.50 cm/s, minute 3; 0.66 ± 0.47 cm/s, p<0.05). In contrast, CPT was associated with a transient increase in HR during the first minute, and a constant elevation in mean BP (p<0.05). MCA Vmean was significantly increased during CPT (baseline; 57.5 ± 2.9 cm/s, minute 3; 64.6 ± 3.6 cm/s; p<0.05) and CVCi decreased (baseline; 0.73 ± 0.41 cm/s, minute 2; 0.64 ± 0.38 cm/s, p<0.05). P ET CO 2 remained unchanged from baseline in both TGS and CPT trials. These preliminary findings suggest that cerebral perfusion is elevated during generalized sympathetic activation evoked by the CPT, whereas MCA Vmean remains unchanged during TGS under isocapnic conditions. Support or Funding Information JPF is funded by the British Heart Foundation.