Dysrhythmias in Laypersons during Centrifuge-Simulated Suborbital Spaceflight

Introduction: There are limited data on cardiac dysrhythmias in laypersons during hypergravity exposure. We report layperson electrocardiograph (ECG) findings and tolerance of dysrhythmias during centrifuge-simulated suborbital spaceflight. Methods: Volunteers participated in varied-length centrifuge training programs of 2-7 centrifuge runs over 0.5-2d, culminating in two simulated suborbital spaceflights of combined +Gz and +Gx (peak +4.0Gz, +6.0Gx, duration 5s). Monitors recorded pre- and post-run mean arterial blood pressure (MAP), 6s-average heart rate (HR) collected at pre-specified points during exposures, documented dysrhythmias observed on continuous 3-lead ECG, self-reported symptoms, and objective signs of intolerance on real-time video monitoring. Results: 148 subjects (43 women) participated in the study. Documented dysrhythmias included sinus pause (n=5), couplet premature ventricular contractions (n=4), bigeminy (n=3), accelerated idioventricular rhythm (n=1), and relative bradycardia (RB, defined as a transient HR drop of >20bpm; n=63). None were associated with subjective symptoms or objective signs of acceleration intolerance. Episodes of RB occurred only during +Gx exposures. Subjects had a higher post-run vs pre-run MAP after all exposures but demonstrated no difference in pre- and post-run HR. RB was more common in men, younger individuals, and subjects experiencing more centrifuge runs.
Discussion: Dysrhythmias in laypersons undergoing simulated suborbital spaceflight were well tolerated, though RB was frequently noted during short-duration +Gx exposure. No subjects demonstrated associated symptoms or objective hemodynamic sequelae from these events. Even so, heightened caution remains warranted when monitoring dysrhythmias in laypersons with significant cardiopulmonary disease or taking medications that modulate cardiac conduction.