Ecg amplifier

Vagal tone was assessed using noninvasive Electrocardiogram (ECG) recordings, obtained with a Biopac ECG amplifier (Goleta, CA) according to accepted guidelines (Fox & Leavitt, 1995 ). Participants were instructed to sit quietly without moving for 5 minutes. We used a modified Lead II configuration, placing electrodes on the right clavicle, left lower torso, and right leg (ground). ECG data, sampled at 1.0 kHz, were collected using Biopac MP150 hardware and Acknowledge software. Trained raters, blinded to violence exposure of participants, visually inspected automatic R-peak detection of the ECG data using Mindware Heart Rate Variability (HRV) Software (Mindware Technologies, Gahannah, OH). Visual inspection focused on detecting ectopic beats and confirming accurate detection of R-peaks in the ECG waveform. From IBI time series, we calculated RSA in 1-minute bins. To calculate RSA, the HRV module detrended the data using a first order polynomial to remove the mean and any linear trends, cosine tapered the data, submitted it to Fast Fourier Transformation, and took the natural log integral of high frequency power in the appropriate respiratory frequency band based on participant age (0.24–0.40 Hz for 8–12 years of age, and 0.18–0.40 Hz for 13–16 years of age), (Shader et al., 2018 (link)).

Electrocardiogram (ECG) recordings were obtained with a Biopac ECG amplifier (Goleta, CA) using a modified Lead II configuration. Cardiac impedance recordings were obtained with a Bio-Impedance Technology model HIC-2500 impedance cardiograph (Chapel Hill, NC). A Colin Prodigy II oscillometric blood pressure machine (Colin Medical Instruments, San Antonio, TX) measured blood pressure recordings (see McLaughlin et al., 2014 (link)). CO for each minute was calculated as heart rate*stroke volume (SV; the amount of blood ejected from the heart on each cardiac cycle). We calculated TPR using the standard formula: (Mean Arterial Pressure/CO)*80 (Sherwood et al., 1990 (link)). Data were scored by two independent raters. SV differences greater than 5% were adjudicated by the second author. CO and TPR reactivity were calculated from the first minute of the baseline, speech preparation, speech, and math periods. Various physiological data points could not be scored due to faulty sensors or signal loss or noise (<8% of data), resulting in varying degrees of freedom for CO and TPR reactivity for the different TSST periods.

Continuous cardiac measures were recorded noninvasively according to accepted guidelines (Sherwood et al., 1990 (link)). Electrocardiogram (ECG) recordings were obtained with a Biopac ECG amplifier (Goleta, CA) using a modified Lead II configuration (right clavicle, left lower torso, and right leg ground). Biopac MP150 hardware and Acknowledge software were used to acquire the ECG data (sampled at 1.0 kHz). ECG data were scored by trained professionals blind to group status. Signals were visually inspected and scored using Mindware Heart Rate Variability (HRV) Software (Mindware Technologies, Gahannah, OH).
RSA was calculated from interbeat interval time series using spectral analysis conducted in Mindware HRV Software. RSA was calculated for the frequency band 0.12–0.40Hz.