Increasing insight into the complex human response to external states can be captured by measuring event-related cardiac sympathetic activity. However existing assays are either confounded by influence from other branches of the autonomic system, or require preprocessing steps that eliminate moment-to-moment capture of fluctuation. We accordingly tested a novel device (TREV) that measures cardiac impedance directly from the radial and ulnar arteries of the human forearm, while healthy human participants performed a small number of trials of a task known to elicit sympathetic drive, a maximum-strength grip task. TREV recorded robust estimates of contractility at each heartbeat, that allowed fully automated beatwise estimations. TREV further reliably described credible group-level departures from baseline aligned with each individual grip in the task. We conclude that the device can be a useful addition to a broadening field exploring event-related sympathetic perturbations.

The electrocardiogram (ECG) and impedance cardiography (ICG) are typically combined to estimate electromechanical features such as the pre-ejection period (PEP) and left ventricular ejection time (LVET); indicators of changes in the cardiac specific drive of the autonomic nervous system (ANS). Current methods of ICG are time intensive in subject preparation and the measurements are vulnerable to non-reproducible subject-specific electrode configuration. Furthermore, analysis of impedance waveforms can be time consuming and labeling of key time points can suffer from experimenter bias. Here we present a wearable heart monitor that includes ECG, but replaces the commonly used 8 ICG electrodes with a single accelerometer (ACC) placed at the suprasternal notch. The ACC indirectly measures movement of the arterial pulse wave as blood is ejected into the aorta and great vessels. The resulting ACC waveform is processed into two smooth and readily identified waves, corresponding to the timing of the opening and closing of the aortic valve. We tested the ACC’s utility and reliability for tracking cardiac ANS tone by comparing PEP and LVET measurements obtained simultaneously with conventional ICG and the ACC. Participants were recorded in the sitting and supine position with ECG, ICG, and ACC. While seated, they engaged in a classic physical stress task known to modulate ANS activity. There were obvious and significant associations between ICG and ACC estimates of PEP and LVET derivatives with respect to time. These findings support ACC as a complementary method for tracking ANS that is robust, time efficient, and readily accessible to researchers.

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We describe methods and software resources for a bioimpedance measurement technique, “trans-radial electrical bioimpedance velocimetry” that allows for the non-invasive monitoring of relative cardiac contractility and stroke volume, proxies of sympathetic cardiac tone. In addition to describing the general recording methodology, which requires impedance measurements of the forearm, we provide open source Jupyter based software (operable on most computers) for deriving cardiac contractility from the impedance measurements. We demonstrate the ability of this bioimpedance measurement for tracking event related contractility in a maximal grip force production task. Critically, the results demonstrate both a reactive increase in cardiosympathetic drive with force production as well as a learned increase in drive prior to grip onset, consistent with allostatic autonomic regulation. The method and software should be of broad utility for investigations of event related cardio-sympathetic regulation in psychophysical studies.