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. 2021 Jan 12;11:610000. doi: 10.3389/fphys.2020.610000

FIGURE 3.

FIGURE 3

Cardiorespiratory, autonomic, and thermal regulation. (A) Mean and (B) lowest heart rate were quantified via electrocardiography at rest. (C) Respiratory rate was algorithmically determined via beat-by-beat R–R intervals at rest. (D) Autonomic time domain mean R–R intervals and (E) mean Root Mean Square of Successive Differences (RMSSD) were derived from electrocardiography R to R time intervals at rest. R–R intervals were not normally distributed and logarithmically transformed lnRR. (F) Autonomic frequency domain mean Total power, (G) very low frequency (VLF; <0.04 Hz), (H) low frequency (LF; 0.04–0.15 Hz), (I) normalized low frequency [nLF; nLF = (LF/(Total Power-VLF)], (J) high frequency (HF; 0.15–0.4 Hz), and (K) ratio of low frequency to high frequency (LF/HF) were all quantified from resting electrocardiography R to R time intervals at rest. (L) Poincaré perpendicular (SD1), (M) parallel (SD2) standard deviation, and (N) SD1/SD2 were determined via non-linear assessment of heart rate variability by quantitative two-dimensional vector analysis of a Poincaré plot at rest. (O) Short- (DFAα1) and (P) long-term detrended fluctuation analysis (DFAα2) used to analyze non-stationary systems at rest. (Q) Stress, (R) sympathetic nervous system (SNS), and (S) parasympathetic nervous system (PNS) were analyzed as composite metrics of each respective arm of autonomic regulation at rest. (T) Body temperature was gathered via skin thermistor during rest. (A,D–S) N = 7 (male, n = 5; female, n = 2). (B,C,T) N = 6 (male, n = 6) Data: Mean ± SD. RMSSD, Root Mean Square of Successive Differences; VLF, very low frequency; LF, low frequency; nLF, normalized low frequency; HF, high frequency; SD1, Poincaré Perpendicular Standard Deviation; SD2, Poincaré Parallel Standard Deviation; DFAα1, short-term detrended fluctuation analysis; DFAα2, long-term detrended fluctuation analysis; SNS, sympathetic nervous system; PNS, parasympathetic nervous system. *p < 0.05, **p < 0.01. Raw p-values are reported for non-significant changes where p ≤ 0.10.