Browsing by Author "Nestorovic, Zorica (8230127600)"

The origin of heart rate variability (HRV) is largely in parasympathetic activity. The direct influence of sympathetic activity and other control mechanisms, especially at an increased HR, is not well understood. The objectives of the study were to investigate the influence of increasing HR on the properties of heartbeat interval (RR) series in young healthy subjects. ECG was recorded in 9 trained and 11 untrained young men during supine rest, standing, incremental running exercise and relaxation. During exercise, a breath-to-breath gas exchange was monitored. The RR time series analysis included the spectral analysis, detrended fluctuations analysis method and sample entropy (SampEn) calculation. During exercise, spectral powers were reduced dramatically in both groups. The dependence of short-term scaling exponent (α1) on the RR included a characteristic maximum, while SampEn for the same value of the RR had a minimum. The value of HR corresponding to the maximum of α1 and minimum of SampEn (IHR) corresponded to the intrinsic HR obtained by an autonomic blockade. In trained subjects, the curves α1 versus RR and SampEn versus RR were moved toward larger RR, compared with control. For HR values higher than IHR, α1 decreased and SampEn increased. These results reveal that the complexity of the heart rhythm above intrinsic HR decreases with an increase in HR. We suggest that at the highest HR intrinsic heart control is reflected in the heart rhythm. We point out the possibility of developing a new non-invasive method for the determination of intrinsic HR from the curve α1 versus RR. © 2008 Institute of Physics and Engineering in Medicine.

The origin of heart rate variability (HRV) is largely in parasympathetic activity. The direct influence of sympathetic activity and other control mechanisms, especially at an increased HR, is not well understood. The objectives of the study were to investigate the influence of increasing HR on the properties of heartbeat interval (RR) series in young healthy subjects. ECG was recorded in 9 trained and 11 untrained young men during supine rest, standing, incremental running exercise and relaxation. During exercise, a breath-to-breath gas exchange was monitored. The RR time series analysis included the spectral analysis, detrended fluctuations analysis method and sample entropy (SampEn) calculation. During exercise, spectral powers were reduced dramatically in both groups. The dependence of short-term scaling exponent (α1) on the RR included a characteristic maximum, while SampEn for the same value of the RR had a minimum. The value of HR corresponding to the maximum of α1 and minimum of SampEn (IHR) corresponded to the intrinsic HR obtained by an autonomic blockade. In trained subjects, the curves α1 versus RR and SampEn versus RR were moved toward larger RR, compared with control. For HR values higher than IHR, α1 decreased and SampEn increased. These results reveal that the complexity of the heart rhythm above intrinsic HR decreases with an increase in HR. We suggest that at the highest HR intrinsic heart control is reflected in the heart rhythm. We point out the possibility of developing a new non-invasive method for the determination of intrinsic HR from the curve α1 versus RR. © 2008 Institute of Physics and Engineering in Medicine.

Previous results on heart rate variability (HRV) analysis in anorexia nervosa (AN) include some apparently conflicting data. In order to find out the reason for different results and to improve understanding of autonomic control in AN we compare HRV in acute and chronic AN. Spectral powers, fractal scaling exponent and sample entropy were computed from 24 h RR series derived from Holter ECG recordings in 17 anorexic patients, nine chronic and eight healthy women. We found that all linear and non-linear HRV measures change in different direction in acute and chronic AN. Acute AN is characterized by decreased HR and increased HRV. In chronic AN, HR is increased, HRV reduced and the difference between awake and sleeping values is high. HRV measures are associated with body mass index only in chronic AN. As HRV measures are significantly different between acute and chronic AN, we propose that HRV analysis might provide additional data in clinical practice. © 2006 Blackwell Publishing Ltd.

Previous results on heart rate variability (HRV) analysis in anorexia nervosa (AN) include some apparently conflicting data. In order to find out the reason for different results and to improve understanding of autonomic control in AN we compare HRV in acute and chronic AN. Spectral powers, fractal scaling exponent and sample entropy were computed from 24 h RR series derived from Holter ECG recordings in 17 anorexic patients, nine chronic and eight healthy women. We found that all linear and non-linear HRV measures change in different direction in acute and chronic AN. Acute AN is characterized by decreased HR and increased HRV. In chronic AN, HR is increased, HRV reduced and the difference between awake and sleeping values is high. HRV measures are associated with body mass index only in chronic AN. As HRV measures are significantly different between acute and chronic AN, we propose that HRV analysis might provide additional data in clinical practice. © 2006 Blackwell Publishing Ltd.