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PRE-EJECTION PERIOD DETECTION AND REACTIVITY DURING NON-INVASIVE CARDIOVASCULAR AUTONOMIC CHALLENGES.

Abstract

Pre-ejection period (PEP) refers to the systolic interval between the mitral valve closure (Mc) and the aortic valve opening (Ao). In psychophysiology, PEP is employed as a marker of cardiac sympathetic activity because the timing of valve opening is driven by myocardial noradrenergic-driven pressure changes. This behavior have been observed during pharmacological and psychological tasks but not addressed on physical autonomic perturbations. PURPOSE: The aim of this research is to evaluate the reactivity of the PEP assessed via seismocardiography (SCG) during distinct autonomic challenges that induce both parasympathetic and sympathetic alterations of the cardiovascular system. METHODS: Twenty healthy adults underwent cold face (CF), cold-pressor (CPT), and lower-body negative pressure (LBNP) tests while being monitored on a 3-lead electrocardiogram (ECG) and a commercially available accelerometer placed at the mid sternum for SCG tracing. PEP was determined by the fiducial points between the onset of the Q-wave representing the Mc and the second upslope from the SCG representing Ao during systole. RESULTS: There were no observed changes of the PEP during either CF (Rest: 97.62 ± 11.9, Ice: 96.97 ± 17.0 ms, Recovery: 97.58 ± 17.2 ms, η2: 0.04, 95%CI: -0.22 – 0.31) nor CPT (WarmH2O: 92.67 ± 14.5 ms, ColdH2O: 95.37 ± 17.3 ms, Recovery: 96.09 ± 17.5 ms, η2: -0.17, 95%CI: -0.11 – 0.44). There was a significant elevation of PEP during the vacuum phase of LBNP (Rest: 97.66 ± 14.0 ms, Vacuum: 110.94 ± 14.8 ms, Recovery: 97.14 ± 14.6 ms, η2: 0.64, 95%CI: 0.6 – 1.10) despite the increase in heart rate (Rest: 61.9 ± 10.8 bpm, Vacuum: 86.5 ± 11.7 bpm, Recovery: 60.5 ± 9.9 bpm, p<0.001) in response to the drop in blood pressure (Rest: 122 ± 14.3 mmHg, Vacuum: 112.85 ± 15.5 mmHg, Recovery: 124.5 ± 12.7 mmHg, p<0.001) during LBNP. CONCLUSION: Contrary to our hypotheses, the PEP response did not widen during CF or compress during CPT. Further, the orthostatic challenge prolonged the PEP, opposite of what we would expect for a cardiac sympathetic inducing event. This suggests that PEP duration is also influenced by pre-load status rather than just sympathetic drive during non-invasive autonomic perturbations.

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