Abnormal temporal dynamics of blood pressure and RR interval regulation in patients with chronic heart failure: relationship to baroreflex sensitivity

Abstract

It is not known whether the temporal relationship between blood pressure (BP) and RR interval is modulated by the same mechanisms in normal controls and patients with chronic heart failure (CHF). We investigated this under conditions of controlled slow breathing. Fifty patients with CHF and 17 age-matched normals underwent recordings of BP and RR interval during 0.1 Hz controlled breathing. Fourier analysis was used to determine the phase relationships between the oscillations in respiration, BP and RR interval. There was no significant difference between patients and normals in the distribution of phase angle between respiration and BP ( P=0.06) or between respiration and RR interval ( P=0.21). There was, however, a significant difference in the phase relationship between BP and RR interval ( P=0.03): in normals, BP led RR interval by a mean phase angle of 48.4° (S.D. 16.8°). In patients with CHF, the distribution of phase difference was much wider [34.4° (S.D. 62.8°)]. The source of this wide distribution was patients with attenuated baroreflex sensitivity (BRS), with those with preserved BRS showing a relationship between BP and RR interval similar to the normal group. During controlled respiration, normal subjects exhibit a stereotyped relationship between oscillations in BP and RR interval, which is mediated by the baroreflex. This relationship is maintained in those patients with CHF who have a preserved BRS. In contrast, patients with an attenuated BRS show a wide distribution in the relationship between BP and RR interval ranging from completely in phase, to anti-phase. This may have important implications for the measurement and interpretation of BRS in patient groups where BRS is weak.