Cardiac autonomic functions derived from short-term heart rate variability recordings associated with heart rate recovery after treadmill exercise test in young individuals.

Analysis of short-term heart rate variability (HRV) may provide useful information about autonomic nervous control of heart rate recovery. We studied 495 individuals (273 men), age range 19-85 years, submitted to treadmill exercise tests and short-term HRV evaluations over time (standard deviation of the normal-to-normal interval [SDNN], the square root of the mean squared differences of successive normal-to-normal intervals [RMSSD], the number of interval differences of successive normal-to-normal intervals greater than 50 ms [NN50 count], the proportion derived by dividing NN50 count by the total number of normal-to-normal intervals [pNN50]) and frequency (low-frequency power [LF], high-frequency power [HF], total power) domains. Among 495 patients, 106 patients (68 men) were elderly (age ≥ 65 years). Male gender and hypertension were significantly higher in elderly patients. The young patients had higher HRR after exercise. HRR at 4 min (54 ± 13 vs 60 ± 12 beats/min; P = 0.003) was the most significant predictor for positive exercise test result. In the young group, both time domain measures (SDNN: correlation coefficient 0.34, P < 0.001; RMSSD: correlation coefficient 0.37, P < 0.001) and frequency domain measures (LF: correlation coefficient 0.21, P < 0.001; HF: correlation coefficient 0.13, P = 0.01; total power: correlation coefficient 0.22, P < 0.001) were significantly associated with HRR at 4 min. HRR at 4 min was significantly associated with short-term HRV of time and frequency domains in young individuals, but not elderly ones, receiving treadmill exercise test.