Response of Choroid and Forehead Blood Flow to Systemic Phenylephrine Infusion

The present study used laser Doppler flowmetry (LDF) to non-invasively evaluate changes in blood flow and microvascular oscillations in both the choroid and forehead in response to phenylephrine infusion. Six healthy volunteers were recruited for forehead and choroidal LDF monitoring during phenylephrine infusion. Data were analyzed with the Wilcoxon Signed Ranks Test. Choroid and forehead flux increased in 5 out of 6 subjects in response to phenylephrine by an overall mean of 22.8% (range -87.2 to +109.4) and 21.7% (range -10.3 to 48.0), respectively. Choroid and forehead flux did not differ significantly from baseline or from each other (p=0.5). Spectral domain analysis of forehead flux showed that the power of the dominant parasympathetic oscillations increased in all 6 subjects, (p=0.03) for increase from baseline. Analysis of the choroid demonstrated that 5 out of 6 subjects showed increased oscillatory power in the parasympathetic range following phenylephrine administration (p=.048). In light of the preservation of forehead and choroid blood flow, the observed increase in oscillations within the parasympathetic frequency range may constitute a manifestation of a generalized autoregulatory mechanism in the microvasculature that permits the maintenance of regional perfusion despite systemic vasocontriction