Abstract
Healthy subjects under rhythmic breathing have heart interbeat intervals with a respiratory band in the frequency domain that can be an index of vagal activity. Diabetes Mellitus Type II (DM) affects the autonomic nervous system of patients, thus it can be expected changes on the vagal activity. Here, the influence of DM on the breathing modulation of the heart rate is evaluated by analyzing in the frequency domain heart interbeat interval (IBI) records obtained from 30 recently diagnosed, 15 long standing DM patients, and 30 control subjects during standardized clinical tests of controlled breathing at 0.1 Hz, supine rest and standing upright. Fourier spectral analysis of IBI records quantifies heart rate variability in different regions: low-frequencies (LF, 0.04–0.15 Hz), high-frequencies (HF, 0.15–0.4 Hz), and a controlled breathing peak (RP, centered around 0.1 Hz). Two new parameters are introduced: the frequency radius rf (square root of the sum of LF and HF squared) and β (power of RP divided by the sum of LF and HF). As diabetes evolves, the controlled breathing peak loses power and shifts to smaller frequencies, indicating that heart rate modulation is slower in diabetic patients than in controls. In contrast to the traditional parameters LF, HF and LF/HF, which do not show significant differences between the three populations in neither of the clinical tests, the new parameters rf and β, distinguish between control and diabetic subjects in the case of controlled breathing. Sympathetic activity that is driven by the baroreceptor reflex associated with the 0.1 Hz breathing modulations is affected in DM patients. Diabetes produces not only a rigid heartbeat with less autonomic induced variability (rf diminishes), but also alters the coupling between breathing and heart rate (reduced β), due to a progressive decline of vagal and sympathetic activity.
Highlights
The autonomic nervous system modulates the cardiac cycle through central and peripheral oscillators that manifest as short and long-term oscillations in the heart rate
We investigate how cardiac dynamics is affected by Diabetes Mellitus type II (DM) using a frequency-domain analysis of interbeat interval (IBI) records taken during the standard cardiovascular reflex tests established by the American Diabetes Association (ADA) [4, 31]: heart rate measurement during supine rest, standing upright, and controlled breathing at 0.1 Hz
From the displacement of the respiratory peak (RP) peak in the diabetic patients, we deduce that the sympathetic activity that is driven by the baroreceptor may be affected in DM patients
Summary
The autonomic nervous system modulates the cardiac cycle through central (e.g. vasomotor and respiratory centers) and peripheral (e.g. arterial pressure and respiratory movements) oscillators that manifest as short and long-term oscillations in the heart rate. Parasympathetic modulation decreases the heart rate and cardiac contractility, whereas activity of the sympathetic branch opposes these effects and regulates peripheral vasoconstriction [1]. Loss of this balance, which is common in Diabetes Mellitus type II (DM) patients, is associated with a high risk of cardiovascular disease due to autonomic neuropathy [2,3,4,5,6]. A common measure of HRV is the power spectral density (PSD) of the signal, which reflects how the variance of the IBI time series is distributed as a function of frequency (f), revealing the cyclic components responsible for variability in the recording period [10]. One has to be cautious with this interpretation of the LF/HF ratio [15] because it is confused in patients with acute myocardial ischemia, exercise [16] or heart failure [17,18]
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