C-35 Free Communication/Poster - Vascular Function MAY 29, 2008 7:30 AM - 12:30 PM ROOM: Hall B
The classic calculation of cerebral vascular resistance using steady-state values of arterial pressure and cerebral blood flow indicates that flow stops only when the perfusion pressure is zero. However, dynamic pressure-flow relationships observed within the cerebral circulation indicate that when the critical closing pressure (CCP; a functional index of the vascular tone) is reached flow stops.
PURPOSE: The aim of the present study was to calculate CCP at rest and during exercise to identify the changes that occur in cerebral vascular tone during exercise.
METHODS: Six subjects were seated upright at rest for fifteen minutes and then performed fifteen minutes of one legged knee extension exercise at 80% maximal workload (WLmax). The middle cerebral artery flow velocity (MCA V) and arterial blood pressure in the radial artery were continuously recorded. The CCPs were calculated by linear extrapolation from steady-state beat-to-beat waveforms of velocity and pressure.
RESULTS: The mean arterial pressure was significantly elevated from rest during 80% WLmax (91±4 to 110±5 mmHg; P=0.001); the mean MCA V was increased from 54.4±4.1 to 60.3±5.1 cm/s (P=0.033); and the cerebral vascular resistance index was increased from 1.72±0.14 to 1.88±0.15 mmHg s/cm (P=0.023). The correlation between the dynamic pressure and flow at rest was r=0.94±0.02 and during 80% WLmax was r=0.96±0.01. The CCP during 80% WLmax increased from rest (10.1±3.7 to 23.0±5.1 mmHg, P=0.015).
CONCLUSION: These findings suggest that the sympathoexcitation associated with high intensity exercise increases cerebral vascular tone. Supported in part by NIH grant #HL045547.