Time Domain Indices of Heart Rate Variability in Well-Trained Middle-Aged Men: 1267: Board #30 May 30 11:00 AM - 12:30 PM

Analysis of the timing between ventricular contractions has provided quantitative evidence of the cardio-protective effects of excellent aerobic fitness. Increased fitness levels have demonstrated a shift in autonomic control of the heart rhythm in favor of enhanced vagal modulation. The variability in the intervals between heartbeats generally increases with aerobic training and decreases with age. The PURPOSE of this investigation was to determine which time domain measures of heart rate variability (HRV) are related to work capacity in a group of active middle-aged men.

METHODS: Eleven generally healthy, ft (Balke maximal treadmill stress time 21.0 ± 4.8 min) and actively training (25 ± 5.5 mi/wk) middle-age males (age 45.5 ± 5.7 yrs, BMI 26.3 ± 2.8 kg/m²) served as subjects for the investigation. Resting heart rate data were recorded from 12-lead EKG (Welsh Allyn, Inc., Skaneateles Falls, NY) for 5 min of supine (SUP) rest. CardioPerfect® software provided the data analysis. Time domain indices of HRV include the standard deviation between the normal beats (SDNN) and the root mean square of the difference between successive normal beats (RMSSD), as well as a triangular interpolation of the histogram of normal beats (TINN).

RESULTS: Mean SUP resting heart rate was 55 ± 8 bpm. Mean HRV (±SD) during SUP was 78.1 ± 28.2 ms for SDNN, 72.4 ± 36.7 ms for RMSSD, and 229.1 ± 96.3 f TINN. Aerobic fitness level as determined by Balke treadmill time was significantly (r=0.81, p<05) related to TINN and unrelated to SDNN and RMSSD (r=0.56 and r=0.33, respectively p>.05).

CONCLUSION: The triangular interpolation of the histogram of normal beats identified the relationship of aerobic conditioning and HRV in well conditioned middle-aged men.