Ultra short term heart-rate variability analysis at maximum stress. Differences between physical and emotional stress

Heart rate variability analysis (HRVa) is used to quantify autonomous nervous system (ANS) responses to psychological stress (PS), but Standard Short term (SST) (5-minutes) intervals) might be too long to assess transient ANS response to acute PS acutely occurring during police tactical task (PTT) when ANS response due to physical effort (PhE) and to PS may overlap. This study was aimed to evaluate if Ultra-short term (UST) HRVa can provide information useful to differentiate ANS response induced by PhE and by PS. Methods: 12-lead ECG continuously recorded in 130 healthy volunteers. 80 police officers during PTT training; 50 during maximum exercise testing with a bicycle ergometer. SSTHRVa was performed according to ESC. USTHRVa was performed from 30 sec and 60 sec recording intervals. Results: SSTHRVa didn’t evidence short-lasting fluctuations of LF/HF ratio correlated with acute tactical stress. USTHRVa showed LF predominance at the beginning of exercise and at medium workload. LF decreased at the maximum workload, almost disappeared at the zenith of HR and reappeared in the early recovery. The % decrease of LF was higher in PhE in respect of PS, whereas the % increase of HF was higher in PS. The % decrease of LF/HF ratio was similar in PS and PhE. Interval selection did not affected USTHRVa in PhE, but was critical evaluating acute tactical stress. Quantitative estimate of FD parameters evidenced significant differences between PS ad PhE. Discussion: SSTHRVa is inadequate to detect short-lasting ANS response due to acute stress. USTHRVa identifies fluctuations of FD components, at the onset/offset of sudden PS, similar to those found during maximum PhE activity. Quantitative estimate of HRV parameters was significantly affected by interval duration in PS (being 60 s too long to detect short-lasting changes due to acute stress response) and evidenced significant differences between PS ad PhE, which suggest that different mechanisms might contribute to HR adaptation during PS.