Open AccessStudying cerebral hemodynamics and metabolism using simultaneous near‐infrared spectroscopy and transcranial Doppler ultrasound: a hyperventilation and caffeine study
Author(s) -
Yang Runze,
Brugniaux Julien,
Dhaliwal Harinder,
Beaudin Andrew E.,
Eliasziw Misha,
Poulin Marc J.,
Dunn Jeff F.
Publication year - 2015
Publication title -
physiological reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.918
H-Index - 39
ISSN - 2051-817X
DOI - 10.14814/phy2.12378
Subject(s) - hypocapnia , transcranial doppler , hyperventilation , cerebral blood flow , anesthesia , caffeine , middle cerebral artery , hemodynamics , placebo , medicine , deoxygenated hemoglobin , oxygenation , cardiology , ischemia , hypercapnia , pathology , hemoglobin , acidosis , alternative medicine
Caffeine is one of the most widely consumed psycho‐stimulants in the world, yet little is known about its effects on brain oxygenation and metabolism. Using a double‐blind, placebo‐controlled, randomized cross‐over study design, we combined transcranial Doppler ultrasound ( TCD ) and near‐infrared spectroscopy ( NIRS ) to study caffeine's effect on middle cerebral artery peak blood flow velocity (V p ), brain tissue oxygenation (S t O 2 ), total hemoglobin ( tH b), and cerebral oxygen metabolism ( CMRO 2 ) in five subjects. Hyperventilation‐induced hypocapnia served as a control to verify the sensitivity of our measurements. During hypocapnia (~16 mmHg below resting values), V p decreased by 40.0 ± 2.4% (95% CI , P < 0.001), while S t O 2 and tH b decreased by 2.9 ± 0.3% and 2.6 ± 0.4%, respectively ( P = 0.003 and P = 0.002, respectively). CMRO 2 , calculated using the Fick equation, was reduced by 29.3 ± 9% compared to the isocapnic‐euoxia baseline ( P < 0.001). In the pharmacological experiments, there was a significant decrease in V p , S t O 2 , and tH b after ingestion of 200 mg of caffeine compared with placebo. There was no significant difference in CMRO 2 between caffeine and placebo. Both showed a CMRO 2 decline compared to baseline showing the importance of a placebo control. In conclusion, this study showed that profound hypocapnia impairs cerebral oxidative metabolism. We provide new insight into the effects of caffeine on cerebral hemodynamics. Moreover, this study showed that multimodal NIRS / TCD is an excellent tool for studying brain hemodynamic responses to pharmacological interventions and physiological challenges.