Chemoreflex and metaboreflex responses to static hypoxic exercise in aging humans.
OBJECTIVE
We tested the hypothesis that aging decreases the contribution of metaboreceptors to sympathetic responses during exercise in hypoxia.


METHODS
We recorded sympathetic nerve traffic to muscle circulation (MSNA), heart rate (HR), blood pressure (BP), minute ventilation (VE), and blood lactate (BL) in 12 older (55 +/- 10 yr) and 12 younger (22 +/- 2 yr) normal subjects during three randomized interventions: isocapnic hypoxia (chemoreflex activation), isometric handgrip exercise (HG) in normoxia (metaboreflex activation), and HG during isocapnic hypoxia (concomitant metaboreflex and chemoreflex activation). All interventions were followed by a forearm circulatory arrest period to allow metaboreflex activation in the absence of exercise and chemoreflex activation.


RESULTS
Older subjects had higher resting MSNA (38 +/- 12 vs 23 +/- 9 bursts per minute; P < 0.01) and BP (P < 0.001). Heart rate, minute ventilation, and blood lactate did not differ (all P > 0.5). MSNA responses to HG in normoxia (P < 0.05) and in hypoxia (P < 0.05) were smaller in the older subjects, but were similar during hypoxia alone. The increase in HR was smaller in the older subjects for all interventions (all P < 0.05). In contrast, the increase in systolic and diastolic BP, VE, and BL were similar in both groups (P > 0.05). During the local circulatory arrest, MSNA and BP remained elevated in both groups after HG in normoxia (P < 0.01) and in hypoxia (P < 0.01), but MSNA changes were smaller in the older subjects (P < 0.05).


CONCLUSIONS
Aging reduces sympathetic reactivity to isometric handgrip, but does not prevent the metaboreceptors to remain the main determinant of sympathetic activation during exercise in hypoxia.
Department of Physiology, Erasme Hospital, Brussels, Belgium.
Anne
A
Houssiere
Boutaina
B
Najem
Atul
A
Pathak
Olivier
O
Xhaët
Robert
R
Naeije
Philippe
P
Van De Borne
D000328:Adult; D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D001794:Blood Pressure / Q000502:physiology; D002628:Chemoreceptor Cells / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D018737:Hand Strength / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007773:Lactates / Q000097:blood; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000098:blood supply; D013564:Sympathetic Nervous System / Q000502:physiology*
D007773:Lactates