In healthy subject hyperoxia enhances metaborefl ex sensitivity during static exercise. However the infl uence of chronic heart failure on metaborefl ex sensibility remains a matter of controversies. Moreover the effect of hyperoxia on this refl ex in CHF patients is unknown. This is of importance since these patients regularly receive chronic administration of nasal oxygen during hospital admission.
The effects of breathing 21 % (normoxia) and 100 % oxygen (hyperoxia) at rest and during isometric handgrip at 30 % of maximal voluntary contraction on MSNA, heart rate (HR), blood pressure (systolic, diastolic, mean and pulse pressure) and O2 saturation (SaO2) were determined in 14 patients with heart failure. The isometric handgrips were followed by 3min of postexercise circulation arrest (PE-CA) to allow metaborefl ex activation in the absence of other refl ex mechanisms.
In normoxia, hangrip and PE-CA induced an expected increase in MSNA and hemodynamic parameters (BP, HR; all p<0,05). Hyperoxia enhanced resting diastolic, mean blood pressure and SaO2 (all p<0,05), but without effects on MSNA responses. Hyperoxia did not modifi y expected response of sympathetic and hemodynamic parameters during exercice (all p<0,05) but response after PE-CA was blunted.
In patients with chronic heart failure, hyperoxia did not altered mecanorefl ex MSNA activation. In contrast, hyperoxia attenuates metaborefl ex activation. This effect could lead to a diminished activation of the sympathetic nervous tone in heart failure and have benefi cial effects.
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