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CHANGES IN HEART RATE VARIABILITY PARAMETERS DURING EXERCISE DO NOT RELIABLY PREDICT CHANGES IN CARDIAC AUTONOMIC TONE DURING EXERCISE

Abstract

R.Stevens1, M.G. Pham2, A.V. Le2 and J.A. Moffitt1.1Stephens College, Columbia, Missouri; 2Arkansas College of Osteopathic Medicine, Fort Smith, Arkansas

PURPOSE: The use of heart rate variability (HRV) analysis to reflect cardiac autonomic tone in humans at rest is well established. However, the use of HRV to derive cardiac autonomic tone during exercise is controversial, due to the conflicting results. HRV has been used as an indicator of cardiac tone during exercise, while other investigators have determined that HRV analysis during exercise is more indicative of the changes in ventilation and peripheral hemodynamics. In the present study we sought to determine if changes in HRV parameters during exercise in two body positions reliably predicted changes in cardiac autonomic tone during exercise. METHODS: Following IRB approval, two groups of subjects completed supine (S;n=10) or upright(U; n=13) cycling exercise. For each subject, HRV was recorded continuously at 1,000 Hz for 20 minutes of rest prior to exercise, 15 minutes during exercise at 40-65% of age predicted maximum heart rate and 10 minutes of recovery post-exercise using a Lead II electrocardiogram. Unpaired t-tests were used to compare the delta values derived from the difference between spectral HRV parameters at rest and exercise in each group. RESULTS: The change in heart rate was not different between the groups (S: 29 +2.3 vs. U: 21+3.3bpm) nor was the change in SDNN (S: -41 +9.8 vs. U: -23+5.0ms). Changes in frequency domain indices were significantly(pCONCLUSION: Because HRV parameters did not predictably change as established in terms of changes in cardiac autonomic tone during exercise, it is hypothesized that HRV analysis during exercise likely reflects changes in ventilation and peripheral hemodynamics. The greatest limitation in this study was that different groups of subjects were used for supine versus upright exercise. Future studies are intended to verify these findings by having the same group of subjects undergo exercise in both body positions and attempt to clarify the mechanisms behind the primary findings.

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