Geert Kleinnibbelink

Post-Exercise Hypotension in Hypoxia 5 129 DISCUSSION The aim of this study was to investigate the impact of hypoxia on PEH, and whether the magnitudeof PEH relates to theBP-loweringeffect of 12-weekhypoxic endurance exercise- training. We present the following findings. First, the magnitude of PEH does not differ when exercise, matched at relative intensity, is performed under hypoxia or normoxia. Second, the magnitude of PEH during the first exercise bout was positively related to the magnitude of the BP-lowering effect of 12-weeks high-intensity running exercise training under hypoxia. Taken together, our results demonstrate that hypoxia does not alter the PEH response, whilst we reveal the close relationship between acute and chronic changes in BP in response to high-intensity running exercise in healthy individuals. Post-exercise hypotension in normoxia and hypoxia Our study showed that a 45-minute high intensity running exercise bout leads to a decrease in mean arterial blood pressure of ~3 mmHg after exercise in healthy individuals, supporting the presence of PEH. This observation confirms findings from several previous studies that demonstrated the presence of PEH after a variety of types, durations and intensities of endurance exercise. 11, 12, 15, 26 However, in contrast to our hypothesis, the magnitude of PEH was not altered by hypoxia (FiO 2 14.5%). Under physiological conditions, changes in CO and TPR lead to alterations in BP. 27 After exercise, PEH seems to be largely explained by a decrease in TPR, likely due to a combination of centrally (i.e. arterial baroreflex resetting with inhibition of sympathetic outflow) and locally mediated vasodilatormechanisms, which is not compensated by adequate elevations in CO. 3 Several previous studies have shown that hypoxia represents a powerful vasodilator signal for cerebral and peripheral arteries, subsequently leading to a decrease in TPR. 18-20 Despite the decrease in TPR under hypoxia, BP and PEH did not differ between normoxia and hypoxia, possibly because of a compensatory increase in HR and CO under hypoxia. The elevated HR and CO under hypoxia may be explained by a preserved and well-functioning baroreflex sensitivity in healthy young individuals under hypoxia 28 , or the hypoxia-induced chemoreceptors stimulation promoting greater sympathetic activation. 29, 30 Interestingly, HR recovery tend to be slower under hypoxia (Table 3), while total work done was lower under hypoxia. These differences in HR recovery and total work may also have contributed to the preserved PEH response under normoxia versus hypoxia. 13, 31, 32