Hrv premium software v 3

Heart rate variability (HRV) was used as an indirect measurement of autonomic balance of the heart (Del Rio et al., 2016 (link); Andrade et al., 2017 (link)). The first derivative of the BP (Dp/dt) signal was used to calculate the HR. Autoregressive algorithm, after Hann windowing with 50% overlap, was used to obtain power spectral density of HRV. Cut-off frequencies were defined as low frequency (LF_HRV): 0.04–0.6 Hz and high frequency (HF_HRV) 0.6–2.4 Hz (Andrade et al., 2017 (link)). Additionally, we used LF/HF_HRV ratio as an indicator of autonomic balance of the heart. LF_HRV and HF_HRV were expressed as normalized units (n.u.). Analysis was performed within a 10 min window. This analysis was performed in LabChart 7.3.8 HRV module software (ADInstruments, Bella Vista, NSW, Australia). In addition, to estimate the autonomic contribution on BR function, spectral non-stationary analysis was used (2-s resolution). The HF_HRV component (0.6–2.4 Hz) was used as an indicator of parasympathetic modulation. This analysis was performed with Kubios HRV Premium Software V 3.1 (Kubios, Finlandia).

The HRV was assessed as an indirect measure of autonomic balance of the heart (Camm, 1996 (link)). From the 3-lead ECG recording, time series were obtained from R-R interval and a time-varying spectrogram was used to obtain the power spectral density (PSD) of HRV (2 s resolution, Tarvainen et al., 2014 (link)). Cut-off frequencies were defined as very low frequency [Very low frequency (VLF_HRV; 0.00–0.04 Hz), low frequency (LF_HRV; 0.04–0.10 Hz), and high frequency (HF_HRV; 0.10–0.40 Hz) (Yuda et al., 2018 (link))]. Additionally, we used the LF/HF_HRV ratio as an indicator of global autonomic balance of the heart. The LF_HRV and HF_HRV were expressed as normalized units (n.u.), calculated as follow: LF n.u. = LF power/(total power – VLF); and HF n.u. = HF power/(total power – VLF) (Camm, 1996 (link)); thereafter the area under curve (AUC) of the total responses was calculated, as previously described (Andrade et al., 2020 ). The baseline values and the maximum apnea event were analyzed using Kubios HRV Premium Software v3.1 (Kubios, Kuopio, Finland).