Age effect on phase relations between respiratory oscillations of the RR interval and systolic pressure

Spectral analysis may allow the evaluation of (baroreflex) gain and phase b etween the RR interval and systolic pressure oscillations synchronous with respiration but, unlike baroreflex gain, the determinants of phase are not completely understood. We evaluated the correlates of spectral phase in 92 healthy subjects (44 men) aged 10-80 years. To do so, the cardiorespiratory signals during paced breathing at 16 breaths/min were continuously recorde d and analyzed. In addition, respiratory sinus arrhythmia and baroreflex ga in (two indices of cardiac vagal activity) and phase were calculated by usi ng an autoregressive spectral technique. Al univariate analysis, the phase correlated with age (r = 0.48, P <0.001), the RR interval (r = 0.32, P < 0. 01), respiratory sinus arrhythmia (r = -0.3, P < 0.01), baroreflex gain (r = -0.29, P < 0.01), and body mass index (r = 0.25, P < 0.05). At multivaria te analysis, age was the most important physiological correlate of phase, a ccounting for 23% of interindividual phase variation. Cardiac vagal activit y measures (which were higher in women than men) and the RR interval were a lso significant independent correlates of phase. We conclude that in additi on to the RR interval and cardiac vagal activity, age has a significant imp act on the phase relationship between respiratory related oscillations of t he RR interval and systolic blood pressure. This spectral measure may conta in additional information concerning the mechanisms that influence cardiova scular rhythms.