Are any of your writers aware of any proven links between heart rate variability as a marker of ANS balance (or imbalance) and specific pathologies? I am aware of its link with a decreased threshold for ventricular fibrillation, diabetic neuropathy and an increased risk of acute cardiac failure after an MI, but I cannot seem to find more.
After a search of the literature, I can find two references to ANS (autonomic nervous system) and HRV (heart rate variability), although neither has to do with ANS stability or imbalance. This is the research from the American College of Sports Medicine:
1. Relationship between Daily Physical Activity and ANS Activity in Patients with CHF
Purpose: Heart rate variability (HRV) indices are powerful independent prognostic factors of cardiovascular events and all cause mortality in patients with chronic heart failure (CHF). This study evaluates the influence of lifestyle on HRV in CHF patients.
Methods: Thirty-nine CHF patients (33 men, ischemic/dilated cardiomyopathy (18/21), 52.4 +/- 11.2 yr, NYHA I to III, LVEF 33.4 +/- 5.1%) filled out a physical activity questionnaire providing an individual complete qualitative and quantitative picture of their physical activity and daily energy expenditure (PAEE/DEE) corrected for age, weight, severity of the condition and autonomy. Frequency and time domain indices of HRV were calculated from ECG Holter recordings on a typical weekday. Nighttime indices were calculated in order to avoid the confounding factor of physical activity that might alter 24-h frequency analysis of HRV.
Results: DEE was significantly different between classes I and II and classes I and III (P = 0.01 both) patients. Time spent in activities above 3 METs decreased significantly with the severity of the condition. Global and parasympathetic indices of 24-h HRV analysis were correlated to DEE and PAEE (Ptot24h = 78.80*PAEE (J [middle dot] min-1 [middle dot] kg-1) -1061.80, R = 0.72, P < 0.0001). Multiple regression analysis revealed that PAEE was the sole independent factor on established HRV prognostic indices (P < 0.05) and especially within PAEE dimensions, only activities above 3 METs were correlated with established prognostic HRV indices (P < 0.05).
Conclusion: These results indicate that rather than total DEE, moderate to intensive physical activity may counteract the decline in HRV with chronic heart disease. This may be linked to longer time spent in higher intensity activities and not to total activity time.
2. Individual Interdependence between Nocturnal ANS Activity and Performance in Swimmers
Purpose: Variations in autonomic nervous system activity (ANS) and variations in performances have been shown to be correlated at the group level in swimmers. The aim of the study was to investigate the strength of that relationship at the individual level.
Methods: Seven regional-level swimmers (four male, age 16.6 +/- 05 yr, 6.4 +/- 0.9 yr of practice) were included in the study. They performed maximal aerobic performance on a 400-m freestyle race before and after a three week intensive training period and following a two week tapering period. ANS activity was assessed through heart rate variability (HRV) indices measured the night before each race and twice a week, along the protocol.
Results: All HRV indices were altered, with global and parasympathetic indices decreasing from W1 to W3 in the whole group, while they increased until W5 in five swimmers and continuously decreased in two. Best performances were respectively realized when global and parasympathetic indices of HRV were highest. Importantly, the relationship between the changes in performances and the changes in HRV indices was strong ([DELTA]Perf = -1.232 to 1.625[middle dot][DELTA]HFwavelet, R2 = 0.5); the greater the rebound in ANS activity after W3, the greater the performance improvement and reciprocally.
Conclusion: Performance is correlated with nocturnal ANS activity at an individual level. The decrease in ANS activity during intensive training is correlated with the loss in performance and the rebound in ANS activity during tapering tracks with the gain in performance. Interestingly, the speed of the rebound during the tapering period was quite different between swimmers. ANS activity measurement may be useful to design and control individual training periods and to optimize the duration of tapering.
Heart rate variability is a relatively new marker so there are few studies to date. The question is valuable, especially with the ability for trainers and fitness professionals to use heart rate tools to measure HRV. To date, the most valuable use of HRV is that of “performance status” or as a way of measuring training adaptability and response.
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