INFLUENCE OF AGE ON THE SYMPATHETIC NEURAL ADJUSTMENTS TO ALTERATIONSIN SYSTEMIC OXYGEN LEVELS IN HUMANS (VOL 42, PG R690, 1997)

We tested the hypothesis that aging influences the regulation of sympa thetic nervous system activity (SNA) and arterial blood pressure durin g alterations in systemic O-2 levels in humans. To accomplish this, we performed direct (intraneural) measurements of SNA to skeletal muscle (MSNA) in 10 young and 7 older healthy normotensive men during room a ir breathing (normoxic control), moderate isocapnic hypoxemia [15 min of 10% fractional inspired O-2 (FIO2)], and hyperoxemia (10 min of 50% FIO2) In response to hypoxemia, arterial O-2 saturation (Sa(O2)) decl ined similarly in the young and older men. MSNA (burst frequency and t otal minute activity) increased significantly (P less-than 0.05) in bo th groups. The magnitudes of the absolute increases in MSNA and the De lta MSNA/Delta Sa(O2) were not significantly different in the young an d older men; however, because of the higher normoxic baseline levels, the percentage increases in burst frequency were smaller (P = 0.02) an d those for total minute activity tended to be smaller (P = 0.11) in t he older men. Arterial blood pressure increased modestly (P less-than 0.05) and similarly in both groups, although the older men demonstrate d a smaller increase in heart rate. In response to hyperoxemia, Sa(O2) increased and MSNA decreased (both P less-than 0.05) similarly in the young and older men. Arterial blood pressure did not change significa ntly from normoxic control levels in either group; however, a small (P less-than 0.05) reduction in heart rate was observed in both groups. In conclusion, aging does not obviously influence the regulation of ab solute levels of MSNA or arterial blood pressure during alterations in systemic O-2 levels in healthy men, although older men demonstrate a smaller percentage increase in MSNA from their elevated baseline level s, as well as an attenuated tachycardia in response to acute hypoxemia . As such, the present results are consistent with our previous findin gs on aging and sympathocirculatory control during other types of acut e stress in humans.