EFFECT OF RESPIRATORY RATE ON THE RELATIONSHIPS BETWEEN RR INTERVAL AND SYSTOLIC BLOOD-PRESSURE FLUCTUATIONS - A FREQUENCY-DEPENDENT PHENOMENON

Objective: The aims of this stud!: were to determine the relationships between oscillations in systolic blood pressure and heart period at d ifferent breathing frequencies and to investigate the role of sympathe tic contribution to this relationship, Methods: Fourteen healthy volun teers underwent three randomized periods of controlled breathing at 6, 10 and 16 breaths/min. ECG (RR), respiratory signal (RESP) and systol ic blood pressure (SBP) were continuously recorded. The component of R R and SEP oscillations related to respiration (RRResp and SEPResp) was defined by means of uni- and bivariate spectral analysis. The squared coherence (K-2) and phase between RR and RESP, and RR and SEP (RR-SBP ) were also assessed. When the K-2 of RR-SBP in the respiratory band w as > 0.5, we considered the phase and calculated the closed-loop gain between the two signals. Seven subjects were also studied after chroni c metoprolol treatment. Results: Although the mean values of RR and SE P did not differ between the three periods of breathing, the higher th e respiratory rate, the smaller the RRResp and SBPResp. The phase was always negative (SBPResp changes preceded RRResp changes preceded RRRe sp changes), thus suggesting a baroreflex link. The higher the respira tory rate, the lower the gain and phase. Pharmacological beta-adrenoce ptor blockade increased the gain and shifted the phase, but the relati onships found at baseline between the respiratory rate and both the ga in and phase remained unchanged. Conclusions: The effect of breath rat e on the relationship between heart rate and systolic pressure variabi lities is a frequency-dependent phenomenon that is also independent of the sympathetic drive. (C) 1998 Elsevier Science B.V. All rights rese rved.