Background: Aging associated changes in sympatho-vagal activities have been widely studied. However, little is known about the association between cardiorespiratory fitness level and cardiac autonomic nervous activities in conjunction with baroreflex sensitivity in healthy older men.
Methods: We performed an incremental submaximal exercise test in 24 healthy, older men aged 60-70 years. They were divided into physically fit (PF, oxygen uptake at anaerobic threshold [ATO(2)] = 25.2 +/- 0.85 ml.kg(-1).min(-1)) and physically unfit (PU, ATO(2) = 19.6 +/- 0.42 ml.kg(-1).min(-1)) groups, based upon the results of an incremental exercise stress test. The cardiac autonomic nervous system (ANS) activities were assessed by means of power spectral analysis of heart rate variability. Baroreflex sensitivity (BRS) testing was performed using simultaneous beat-by-beat blood pressure and heart rate measurement during a transition from supine horizontal position to 60 degrees head-up-tilting (HUT).
Results: At rest conditions, the high-frequency component ( p =.03) and total power ( p =.04) of heart rate variability spectrum were significantly higher in the PF group. The BRS assessed during passive HUT was also significantly higher (7.5 +/- 0.5 vs 3.0 +/- 0.4 ms.mm Hg(-1), p =.001) in the PF compared with the PU group. In addition, a significant correlation coefficient (r =.73, p =.001) was found between ATO(2) and BRS among the subjects.
Conclusions: The maintenance of high cardiorespiratory function, i.e., higher ATO(2) through a life-long active lifestyle including endurance exercise, may play an important role in reserving cardiac ANS and BRS in older men.