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(Circulation. 2003;108:292.)
© 2003 American Heart Association, Inc.

Clinical Investigation and Reports

Variability of Phase Shift Between Blood Pressure and Heart Rate Fluctuations

A Marker of Short-Term Circulation Control

Josef Halámek, PhD; Tomá Kára, MD; Pavel Jurák, PhD; Miroslav Souek, MD, PhD; Darrel P. Francis, MD, MRCP; L. Ceri Davies, MD, MRCP; Win K. Shen, MD, PhD; Andrew J.S. Coats, DM, FRCP; Miroslav Novák, MD, PhD; Zuzana Nováková, MD, PhD; Roman Panovsk, MD; Jií Toman, MD, PhD; Josef umbera, MD, PhD; Virend K. Somers, MD, PhD

From the Institute of Scientific Instruments (J.H., P.J.), Academy of Sciences; St Anne’s University Hospital (T.K., M.S., M.N., R.P., J.T., J.S.); and the Faculty of Medicine (Z.N.), Masaryk University, Brno, Czech Republic; Mayo Clinic (T.K., W.K.S., V.K.S.), Rochester, Minn; Chelsea & Westminster Hospital (D.P.F.), London; Colchester General Hospital (L.C.D.), Colchester; and the National Heart & Lung Institute (A.J.S.C.), London, UK.

Reprint requests to Josef Halámek, PhD, Institute of Scientific Instruments, AS CR, Královopolská 147, 612 64 Brno, Czech Republic. E-mail josef{at}isibrno.cz

Background— We postulated that the variability of the phase shift between blood pressure and heart rate fluctuation near the frequency of 0.10 Hz might be useful in assessing autonomic circulatory control.

Methods and Results— We tested this hypothesis in 4 groups of subjects: 28 young, healthy individuals; 13 elderly healthy individuals; 25 patients with coronary heart disease; and 19 patients with a planned or implanted cardioverter-defibrillator (ICD recipients). Data from 5 minutes of free breathing and at 2 different, controlled breathing frequencies (0.10 and 0.33 Hz) were used. Clear differences (P<0.001) in variability of phase were evident between the ICD recipients and all other groups. Furthermore, at a breathing frequency of 0.10 Hz, differences in baroreflex sensitivity (P<0.01) also became evident, even though these differences were not apparent at the 0.33-Hz breathing frequency.

Conclusions— The frequency of 0.10 Hz represents a useful and potentially important one for controlled breathing, at which differences in blood pressure–RR interactions become evident. These interactions, whether computed as a variability of phase to define stability of the blood pressure–heart rate interaction or defined as the baroreflex sensitivity to define the gain in heart rate response to blood pressure changes, are significantly different in patients at risk for sudden arrhythmic death. In young versus older healthy individuals, only baroreflex gain is different, with the variability of phase being similar in both groups. These measurements of short-term circulatory control might help in risk stratification for sudden cardiac death.

Key Words: baroreceptors • respiration • death, sudden

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