125 Clinical Science (2000) 99, 125–132 (Printed in Great Britain) Very-low-frequency oscillations in heart rate and blood pressure in periodic breathing: role of the cardiovascular limb of the hypoxic chemoreflex Darrel P. FRANCIS *†, L. Ceri DAVIES*†, Keith WILLSON†, Piotr PONIKOWSKI*, Andrew J. S. COATS*† and Massimo PIEPOLI*‡ *National Heart & Lung Institute, Imperial College of Science, Technology and Medicine, London, U.K., †Royal Brompton Hospital, London, U.K., and ‡Piacenza Hospital, Piacenza, Italy A B S T R A C T In chronic heart failure, very-low-frequency (VLF) oscillations (0.01–0.04 Hz) in heart rate and blood pressure may be related to periodic breathing, although the mechanism has not been fully characterized. Groups of ten patients with chronic heart failure and ten healthy controls performed voluntary periodic breathing with computer guidance, while ventilation, oxygen saturation, non-invasive blood pressure and RR interval were measured. In air, voluntary periodic breathing induced periodic desaturation and prominent VLF oscillations when compared with free breathing in both patients [RR interval spectral power from 179 to 358 ms 2 (P  0.05) ; systolic blood pressure (SBP) spectral power from 3.44 to 6.25 mmHg 2 (P  0.05)] and controls [RR spectral power from 1040 to 2307 ms 2 (P  0.05) ; SBP spectral power from 3.40 to 9.38 mmHg 2 (P  0.05)]. The peak in RR interval occurred 16–26 s before that in SBP, an anti- baroreflex pattern. When the patients followed an identical breathing pattern in hyperoxic conditions to prevent desaturation, the VLF RR interval spectral power was 50 % lower (179.051.7 ms 2 ; P  0.01) and the VLF SBP spectral power was 44 % lower (3.510.77 mmHg 2 ; P  0.01) ; similar effects were seen in controls (VLF RR power 20 % lower, at 1847899 ms 2 , P  0.05; VLF SBP power 61 % lower, at 3.680.92 mmHg 2 , P  0.01). Low- and high-frequency spectral powers were not significantly affected. Thus periodic breathing causes oxygen-sensitive (and by implication chemoreflex-related) anti-baroreflex VLF oscillations in RR interval and blood pressure in both patients with chronic heart failure and normal controls. INTRODUCTION Patients with chronic heart failure may show discrete very-low-frequency (VLF) oscillations in heart rate and blood pressure with a period of approx. 1 min (frequency 0.010–0.040 Hz). This phenomenon may be linked to the presence of a fluctuating tidal volume of respiration Key words : heart failure, periodic breathing, reflex. Abbreviations : DBP, diastolic blood pressure ; HF, high-frequency ; LF, low-frequency ; PO  , partial pressure of oxygen ; PCO  , partial pressure of carbon dioxide ; SBP, systolic blood pressure ; VLF, very-low-frequency. Correspondence : Dr D. P. Francis, Heart Failure Unit, Royal Brompton Hospital, National Heart & Lung Institute, Sydney St, London SW3 6NP, U.K. (e-mail d.francischeerful.com). (periodic breathing) [1–3] and episodic oxygen desatu- ration. Periodic breathing is associated with increased mortality in chronic heart failure [4,5]. Fluctuating ventilation may itself directly entrain heart rate and blood pressure into these slow rhythms. Alternatively, the oscillations in arterial partial pressure of oxygen (PO  ) and carbon dioxide (PCO  ) which inevitably accompany  2000 The Biochemical Society and the Medical Research Society