MINIMAL INTERVAL LENGTH FOR SAFE DETERMIN ATION OF SHORT-TERM HEART-RATE-VARIABILITY

After heart rate variability (HRV) had been established in the clinic, the question about the minimum interval length for analyzing electroc ardiograms emerged. Respiration rate, heart rate and heart rate variab ility were analyzed in 25 sport divers during 6 min intervals at contr ol, immersion, submersion and while SCUBA diving. Thereafter, the inte rval length was systematically shortened to 1 min. Results: Respiratio n rate was significantly reduced during submersion and diving. Heart r ate, in turn, remained essentially unchanged during the four experimen tal steps. The HRV measures in the time domain (standard deviation, co efficient of variation, RMSSD and pNN50) exhibited significant changes during immersion, submersion and diving compared to control condition s. The spectral density in the low frequency range was increased compa red to control, the increase being significant during diving. Immersio n, submersion and diving, thus, present strong stimuli for the autonom ic nervous system. The length of the HRV measures of the time domain c ould be shortened to 3 min without significant loss of information, ex cept for pNN50. Reduction of the respiration rate during diving consid erably shifted the respiratory arrhythmia from the high to the low fre quency range. Such shifts deserve special attention interpreting HRV m easures from the frequency domain. The interval length for the measure s in the frequency domain could only be shortened to 5 min. Conclusion : Measures from the time domain, in particular standard deviation and coefficient of variation? seem to be superior to measures from the fre quency domain in analyzing short-term HRV.