Cross-spectral analysis of cardiovascular variables in supine diabetic patients.
ABSTRACT Cardiovascular autonomic neuropathy in diabetes is associated with a high risk of mortality, which makes its early identification clinically important. An easy method for identification of subjects with autonomic dysfunction would be of clinical benefit. We evaluated the autonomic function in 28 diabetic patients and 21 control subjects recording 12 min time series of heart period (RR) and systolic arterial pressure (SAP, Finapres) during supine rest and 60 degrees head-up tilt. The power of the high (respiratory) and low (LF approximately 0.1 Hz) frequency oscillations was quantified by spectral analysis. The central frequency of the LF oscillations (LF_freq), phase shift, and the transfer function gain between RR interval and SAP fluctuations were provided by cross-spectral analysis, and measured at the point of maximal coherence. In the supine position 15 patients (LF-) displayed atypical LF variability with the LF_freq being shifted towards lower frequencies (about 0.06 Hz). They also showed larger phase angle, lower values or even absence of coherence and smaller transfer function gain between RR and SAP fluctuations. 13 patients (LF+) and the controls showed the LF_freq around 0.1 Hz, higher coherence and transfer function gain values. The orthostatic maneuver induced the expected changes in the spectral parameters (increase in the LF components of both RR and SAP and decrease in the HF variability of RR) into the LF+ patients and all the control subjects and abnormal response in the other 15 LF-patients. These findings indicate that diabetic subjects with uncharacteristic response to the orthostatic test present abnormal LF variability already in the supine position. Crossspectral parameters while supine may be used for the identification of these subjects.
- Clinical Autonomic Research 11/2002; 12(5):349-52. · 1.48 Impact Factor
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ABSTRACT: 1. Parameters derived from frequency-domain analysis of heart period and blood pressure variability are gaining increasing importance in clinical practice. However, the underlying physiological mechanisms in human subjects are not fully understood. Here we address the question as to whether the low frequency variability (approximately 0.1 Hz) of the heart period may depend on a baroreflex-mediated response to blood pressure oscillations, induced by the alpha-sympathetic drive on the peripheral resistance. 2. Heart period (ECG), finger arterial pressure (Finapres) and respiratory airflow were recorded in eight healthy volunteers in the supine position with metronome respiration at 0.25 Hz. We inhibited the vascular response to the sympathetic vasomotor activity with a peripheral alpha-blocker (urapidil) and maintained mean blood pressure at control levels with angiotensin II. 3. We performed spectral and cross-spectral analysis of heart period (RR) and systolic pressure to quantify the power of low- and high-frequency oscillations, phase shift, coherence and transfer function gain. 4. In control conditions, spectral analysis yielded typical results. In the low-frequency range, cross-spectral analysis showed high coherence (> 0.5) and a negative phase shift (-65.1 +/- 18 deg) between RR and systolic pressure, which indicates a 1-2 s lag in heart period changes in relation to pressure. In the high-frequency region, the phase shift was close to zero, indicating simultaneous fluctuations of RR and systolic pressure. During urapidil + angiotensin II infusion the low-frequency oscillations of both blood pressure and heart period were abolished in five cases. In the remaining three cases they were substantially reduced and lost their typical cross-spectral characteristics. 5. We conclude that in supine rest conditions, the oscillation of RR at low frequency is almost entirely accounted for by a baroreflex mechanism, since it is not produced in the absence of a 0.1 Hz pressure oscillation. 6. The results provide physiological support for the use of non-invasive estimates of the closed-loop baroreflex gain from cross-spectral analysis of blood pressure and heart period variability in the 0.1 Hz range.The Journal of Physiology 03/2001; 531(Pt 1):235-44. · 4.38 Impact Factor
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ABSTRACT: Spectral analysis was utilized in order to determine the influence of low (0.7 microgram/kg)-dose atropine sulfate injections on the isolated spectral power components of heart rate fluctuations in contrast to moderate (0.02 mg/dose)-dose atropine and unmedicated states in human subjects during orthostatic load. Low-dose atropine decreased mean heart rate and increased respiration-related spectral power compared with controls in both the supine and standing posture. In supine subjects total power (0.01-0.5 Hz) was unchanged compared with controls due to a decreasing trend of low-frequency (0.01-0.05 Hz) and mid-frequency (0.05-0.15 Hz) heart rate spectral power. Standing upright, there was a distinct increase in total power with significantly higher values than in the controls resulting from an enormous activation of mid-frequency heart rate fluctuations. The peak frequency of the mid-frequency component was increased with a strong tendency compared with controls. Moderate-dose atropine increased mean heart rate and decreased total power, mid-frequency and respiration-related heart rate spectral power and peak frequency compared with controls in both positions. Our results suggest that low-dose atropine affects the interaction between sympathetic and parasympathetic limbs in the autonomic control of cardiac function in a complex manner producing a differentiated pattern of heart rate fluctuations dependent on the body posture. We suggest that low-dose atropine augments and moderate-dose atropine attenuates the vagal cardiac efferent activity in each position.Journal of the Autonomic Nervous System 05/1989; 26(3):223-30.