BACKGROUND: Spatially resolved near-infrared spectroscopy-determined frontal lobe tissue oxygenation (ScO2) is reduced with administration of phenylephrine, while cerebral blood flow may remain unaffected. We hypothesized that extracranial vasoconstriction explains the effect of phenylephrine on ScO2.
METHODS: We measured ScO2 and internal and external carotid as well as vertebral artery blood flow in 7 volunteers (25 [SD 4] years) by duplex ultrasonography during IV infusion of phenylephrine, together with middle cerebral artery mean blood velocity, forehead skin blood flow, and mean arterial blood pressure.
RESULTS: During phenylephrine infusion, mean arterial blood pressure increased, while ScO2 decreased by −19% ± 3% (mean ± SE; P = 0.0005). External carotid artery (−27.5% ± 3.0%) and skin blood flow (−25.4% ± 7.8%) decreased in response to phenylephrine administration, and there was a relationship between ScO2 and forehead skin blood flow (Pearson r = 0.55, P = 0.042, 95% confidence interval [CI], = 0.025–0.84; Spearman r = 0.81, P < 0.001, 95% CI, 0.49–0.94) and external carotid artery conductance (Pearson r = 0.62, P = 0.019, 95% CI, 0.13 to 0.86; Spearman r = 0.64, P = 0.012, 95% CI, 0.17–0.88).
CONCLUSIONS: These findings suggest that a phenylephrine-induced decrease in ScO2, as determined by INVOS-4100 near-infrared spectroscopy, reflects vasoconstriction in the extracranial vasculature rather than a decrease in cerebral oxygenation.
From the *Department of Biomedical Engineering, Toyo University, Kawagoe-Shi, Saitama; †Research Institute of Physical Fitness, Japan Women’s College of Physical Education, Tokyo; ‡Department of Environmental Physiology for Exercise, Osaka City University Graduate School of Medicine; §Faculty of Health Sciences, Morinomiya University of Medical Sciences, Osaka, Japan; ‖Department of Anesthesia, The Copenhagen Muscle Research Center, University of Copenhagen, Copenhagen, Denmark; and ¶Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
Accepted for publication January 8, 2014.
Funding: The Copenhagen Muscle Research Center. This study was supported partly by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Science, Sports and Culture (#21700704 to KS).
The authors declare no conflicts of interest.
Reprints will not be available from the authors.
Address correspondence to Shigehiko Ogoh, PhD, Department of Biomedical Engineering, Toyo University, 2100 Kujirai, Kawagoe-shi, Saitama 350–8585, Japan. Address e-mail to firstname.lastname@example.org.