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The Importance of Environmental Charges in Influencing Heart Rate Variability: Increased Heart Rate Variability on Weekends in Healthy Active Subjects

Attila Frigy1, MD, Pawel Zagozdzon2, MD, Marek Malik2, MD, PhD

1 3rd Medical Clinic, University of Medicine and Pharmacy Targu-Mures
Romania

2Department of Cardiological Sciences, St. George’s Hospital Medical School
London, United Kingdom

Abstract
Introduction
Material and Methods
Results
Discussion and Conclusions
References

Abstract
Background: Heart rate variability (HRV) analysis is widely recognised as a powerful tool for characterising cardiac autonomic activity. However, the effect on HRV of the environmental charges encountered during a regular weekly activity has not been properly investigated. As HRV is likely to be influenced by charges in the external environment, a weekly pattern may have implications for clinical use of HRV.
Methods: In order to evidence weekly behaviour of HRV we performed 24-hours Holter recordings in 10 healthy subjects (5 female, 5 male, mean age 33,4 years) with regular weekdays working activity. The analysis was performed using a MARS 8000 system (Marquette Medical Systems). For each subject time domain (SDNN, SDANN, SDNNindex, rMSSD, pNN50) and spectral HRV parameters (total, VLF, LF and HF power, LF/HF ratio) were obtained from Tuesdays and Saturdays. The differences in the parameters were assessed using paired t-test.
Results: Compared to weekday recordings HRV was increased on Saturdays, the level of significance being reached by the MNN (771± 70.63 ms vs. 806± 66.03 ms, p=0.04), pNN50 (13.79± 7.05% vs. 16.06± 8.16%, p=0.048) and the LF/HF ratio (3.706± 1.6 vs. 3.16± 1.8, p=0.034).
Conclusions: (1) The finding of the lower heart rate and the increased parasympathetic parameters on Saturdays support the importance of weekly environmental charges (e.g. psychosocial and physical) in influencing HRV. (2) When HRV, and particularly changes in HRV, is analysed in outpatients, this weekly behaviour has to be considered.

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Background: Heart rate variability (HRV) analysis is widely recognised as a powerful tool for characterising and reflecting cardiac autonomic activity. Cardiac autonomic input results from the interplay of reflex and central nervous system (CNS) mechanisms. The latter affords the accommodation of cardiovascular system to external - environmental charges, consisting mainly of psychosocial stress. [ 1, 2, 3]

The effect on HRV of the environmental charges encountered during a regular weekly activity still has not been properly investigated. As HRV is likely to be influenced by charges in the external environment, a weekly pattern may have implications for clinical use of HRV.

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Material and Methods:  In order to evidence weekly behaviour of HRV we performed 24-hours Holter recordings in 10 healthy subjects (5 female, 5 male, mean age 33,4 years) with regular weekdays working activity (physicians and research nurses from our department). The analysis was performed using a MARS 8000 system (Marquette Medical Systems). For each subject time domain (MNN, SDNN, SDANN, SDNNindex, rMSSD, pNN50) and spectral HRV parameters (total, VLF, LF and HF power, LF/HF ratio) were obtained from Tuesdays and Saturdays. The differences in the parameters were assessed using paired t-test.

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Results: Compared to weekday recordings, all the parameters revealed an increased HRV on Saturdays, the level of significance being reached by the MNN (771± 70.63 ms vs. 806± 66.03 ms, p=0.04), pNN50 (13.79± 7.05% vs. 16.06± 8.16%, p=0.048) and the LF/HF ratio (3.706± 1.6 vs. 3.16± 1.8, p=0.034)- fig.1.

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Fig. 1. Variation of individual values of LF/HF

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Discussion and Conclusions:  It is a well known fact that in normal, healthy subjects HRV is related to age, gender, smoking, physical fitness and weight. Besides these "internal" factors, HRV also reflects the autonomic alarm state of the cardiovascular system induced by environmental charges of different nature. [ 4, 5, 6, 7]

The finding of the lower heart rate and the increased parasympathetic parameters on Saturdays support the importance of weekly environmental charges (mainly psychosocial) in influencing HRV. The relative sympathetic overactivity encountered during the working day could serves as an explanation for our results. This fact provides us practical considerations. When HRV, and particularly changes in HRV, is analysed in outpatients, this weekly behaviour has to be considered.

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References:

1. Makik M. Heart rate variability. Curr Opinion Cardiol, 1998; 13:36-44
2. Malik M, Camm AJ. Components of heart rate variability - what they really mean and what we really measure. Am J Cardiol, 1993; 72:821-822
3. ***Heart rate variability: origins, methods, and interpretating caveats - Committee report. Pscychophysiology, 1997; 34:623-648
4. Tsuji H, Venditti FJ, Manders ES, Evans JC, Larson MG, Feldman CL, Levy D. Determinats of heart rate variability. J Am Coll Cardiol, 1996;28: 1539-1546
5. Mc Craty R, Atkinson M, Tiller WA, Rein G, Watkins AD. The effect of emotions on short-term power spectrum analysis of heart rate variability. Am J Cardiol, 1995;76:1089-1093
6. Liao D, Barnes RW, Chambless LE, Simpson RJ, Sorlie P, Heiss G for the ARIC investigators. Age, race and sex differences in autonomic cardiac function measured by spectral analysis of heart rate variability - the ARIC study. Am J Cardiol, 1995; 76: 906-912
7. Umetani K, Singer DH, McCraty R, Atkinson M. Twenty-four hour time domain heart rate variability and heart rate: relations to age and gender over nine decades. J Am Coll Cardiol, 1998; 31: 593-601.

 

Questions, contributions and commentaries to the Authors: send an e-mail message (up to 15 lines, without attachments) to ARRITMIAS@listserv.rediris.es , written either in English, Spanish, or Portuguese.

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Update
Nov/03/1999