C-25 Free Communication/Poster - Cardiovascular: Acute Exrcise: MAY 29, 2008 7:30 AM - 12:30 PM: ROOM: Hall B
Reduced cerebral blood flow and arterial pressure may underlie reports of acute symptoms associated with post-exercise orthostatic instability. Inspiratory resistance (IR) increases arterial pressure and cerebral blood velocity (CBV) in supine humans, and increases CBV oscillations while reducing symptoms of orthostatic instability induced by a squat-stand test.
PURPOSE: To test the hypothesis that inspiratory resistance limits reductions of CBV and arterial pressure, and increases oscillations of CBV during standing after cycle exercise.
METHODS: On two separate occasions, we recorded the ECG, beat-by-beat finger arterial pressure, and CBV (transcranial Doppler ultrasound) in 10 healthy subjects (4 male, 6 female; age 24 ± 1 yr; height 174 ± 4 cm; weight 72 ± 3 kg) . Following a standing baseline, subjects cycled at 75% of their estimated maximum heart rate for 5 min. After exercise they stood for an additional 5 min while breathing with no IR (0 mmHg), or with -7 mmHg IR (randomized). Data were analyzed in both time and frequency (Fourier transform) domains.
RESULTS: Compared with baseline, exercise increased mean arterial pressure (MAP) by 22%, and mean cerebral blood velocity (CBVmean) by 10% (both p<0.001). Both MAP and CBVmean fell upon standing but were not different from baseline. Breathing with IR did not alter MAP or CBVmean reductions during standing (p>0.05), but increased respiratory frequency (0.15 to 0.4 Hz) oscillations of CBVmean from 2.6 ± 0.5 to 10.1 ± 2.2 cm/s2 (p=0.003). None of the subjects studied reported symptoms of orthostatic instability under both control and IR conditions.
CONCLUSION: Although arterial pressure and CBV fall acutely after cycle exercise, the absence of an IR effect on MAP was associated with no hypotension during postexercise standing. We confirm that IR increases CBV oscillations. This increase in CBV oscillations may provide a protective effect to individuals who are susceptible to symptoms associated with post-exercise orthostatic instability.