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Phenylephrine Alteration of Cerebral Blood Flow During Orthostasis; Effect on N-Back Performance in Chronic Fatigue Syndrome

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By Marvin S. Medow et al.
 
ABSTRACT
 
Chronic Fatigue Syndrome (CFS), with orthostatic intolerance is characterized by neurocognitive deficits, impaired working memory, concentration, and information processing.
 
In CFS, upright tilting (HUT) caused decreased cerebral blood flow velocity (CBFv) related to hyperpnea/hypocapnia and impaired cerebral autoregulation; increasing orthostatic stress resulted in decreased neurocognition.
 
We loaded the baroreflex with phenylephrine to prevent hyperpnea, and performed N-Back, neurocognition testing in 11 controls and 15 CFS patients. HUT caused a significant increase in HR (109.4±3.9 vs. 77.2±1.6 bpm, p<0.05) and respiratory rate (20.9±vs. 14.2±1.2 bpm, p<0.05) and decrease in ETCO2 (42.8±vs. 33.9±1.1 Torr, p<0.05) in CFS vs. control. HUT caused CBFv to decrease 8.7% in controls, but fell 22.5% in CFS. In CFS, phenylephrine prevented the HUT-induced hyperpnea/hypocapnia and the significant drop in CBFv with HUT (-8.1% vs. -22.5% untreated).
 
There was no difference in control subject N-Back normalized response time (nRT) comparing supine to HUT (106.1±6.9 vs. 97.6±7.1 msec at n=4), and no difference comparing control to CFS while supine (97.1±7.1 vs 96.5±3.9 msec at n=4).
 
However, HUT of CFS subjects caused a significant increase in nRT (148.0±9.3 vs. 96.4±6.0 msec at n=4) compared to supine. Phenylephrine significantly reduced the HUT-induced increase in nRT in CFS to levels similar to supine (114.6±7.1 vs 114.6±9.3 at n=4).
 
CONCLUSIONS: Compared to control, CFS subjects are both more sensitive to orthostatic challenge and to baroreflex/chemoreflex-mediated interventions. Increasing BP with phenylephrine can alter CBFv. In CFS subjects, mitigation of the HUT-induced CBFv decrease with phenylephrine has a beneficial effect on N-Back outcome.
 
Source: Marvin S. Medow, Shilpa Sood, Zachary R. Messer, Seli Dzogbeta, Courtney Terilli, Julian M. Stewart. Phenylephrine Alteration of Cerebral Blood Flow During Orthostasis; Effect on N-Back Performance in Chronic Fatigue Syndrome. Journal of Applied Physiology. Published 2 October 2014 Vol. no. ,DOI: 10.1152/japplphysiol.00527.2014

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