Heart rate variability: Standardisation of methodology

Abstract

Introduction: The use of heart rate variability (HRV) as a non-invasive indicator of cardiac function and autonomic nervous system (ANS) function in athletes and patients has increased exponentially. However, the availability of clinical acknowledged standards are spares and non-standardization in data collection methods produce inconsistent study results. The aim of this study was to determine the influence of (a) different tachogram lengths (3, 5, 7 and 10 min) and (b) to determine whether comparable HRV are obtained when calculated from various 3 min segments of a 10 min tachogram. Methodology: Healthy active volunteers (n = 150, age = 20.2 yrs, mass = 61.11 kg; height = 165.88 cm) participated. RR intervals were sampled for 10 min in the supine position and 10 min during an orthostatic stressor. HRV were quantified with time domain, frequency domain and the Poincaré analysis. The SAS procedure MIXED was used to determine the effect of the different time intervals on each of the HRV measurements. Results and conclusions: Results obtained in the supine position showed that the mean values of HRV indicators influenced by parasympathetic efferent activity (pNN50, RMSSD, SD1, and HFms2) did not differ (p > 0.05) when measured over different tachogram lengths. However, these indicators did show a tachogram length dependency during an orthostatic stressor. HRV indicators influenced by the sympathetic as well as the parasympathetic branches, (STDHR, STDRR, SD2 and LFms) showed significant (p < 0.05) tachogram length dependency in supine and standing positions. In the supine position the variability indicated by SD2, HFms and HFnu (p < 0.05) were influenced by the specific segment of the tachogram used. HRV values (RMSSD, pNN50, SD1, LFms2, SD2, HFms2 and LF/HF) determined during the initial period (0–3 min) of the orthostatic stressor were significant different from mean values determined during the second dataset (3–6 min standing) and third data set (6–9 min standing). These results indicate that, due to the activation and de-activation of normal homeostatic mechanisms for the maintenance of blood pressure, the starting time of the tachogram during a posture change is critical. This effect renders comparisons unreliable if recording times and periods are not standardised. This study proposes standardized tachogram lengths and starting times that could facilitate comparability between studies, thereby strengthening the use of HRV as a non-invasive probe of cardiac function and ANS.