E-22 Free Communication/Poster - Blood Flow: JUNE 3, 2011 7:30 AM - 12:30 PM: ROOM: Hall B
PURPOSE: We sought to explore the effect of α1-adrenoreceptor blockade (Prazosin) on dynamic cerebral autoregulation (dCA) during rest, mild and moderate intensity dynamic exercise in humans.
METHODS: Ten healthy human subjects (seven men and three women; age, 27 ± 1 years, height, 176 ± 4 cm, weight, 76± 4 kg; mean ± SE) volunteered to participate in the present investigation. Their baseline data was collecting during 15 min of rest in a seated position on the bicycle ergometer. Following rest, subjects pedalled at the rate of 60 rpm at mild workload (10W) for 10 min [Ex80, heart rate (HR) 88±4 bpm]. After 10 min of mild intensity exercise, the workload was increased to raise and mainatain steady-state HR at 130 bpm (Ex130). Subjects exercised at this moderate intensity for 10 min. After the 10 min of rest from the exercise, the subjects ingested α1-adrenoreceptor blocker, Prazosin (.05mg/kg body weight) and recovered at seated rest for 2 hours to achieve the maximum pharmacologic action of the drug. The 'rest-Ex80-Ex130' protocol was then repeated. Five minutes of steady-state data were collected for spectral and transfer function analysis.
RESULTS: A decrease in low frequency (LF) (0.07-0.2 Hz) transfer function gain was observed at Ex130 in the control condition (mean ± SEM, 0.88 ± 0.08 to 0.72 ± 0.05, P < 0.05) indicating an increase in dCA. In contrast, α1-adrenoreceptor blockade caused a significant increase in LF gain from control at rest (0.88 ± 0.08 to 1.09 ± 0.11, P<0.004), identifying impairment in CA. Furthermore, Prazosin ingestion resulted in a significant increase in LF gain at Ex80 and for the Ex130 condition from control (Ex80 control 0.79 ± 0.06 to Prazosin 0.98 ± 0.09, and Ex130 control 0.72 ± 0.05 to prazosin 1.01 ± 0.11, P<0.05). The coherence between MAP and MCA V for all the exercise and drug conditions remained above 0.5 and was accompanied by a decrease in phase shift in the Prazosin condition.
CONCLUSION: These findings indicate that α-1 adrenergic receptor blockade results in the impairment of dynamic cerebral autoregulation.
Partially funded by the Cardiovascular Research Institute of UNTHSC and Texas chapter-ACSM