Assessing baroreflex gain from spontaneous variability in conscious dogs: role of causality and respiration
American Journal of Physiology. Heart and Circulatory Physiology
Assessing baroreflex gain from spontaneous variability in conscious dogs: role of causality and respiration. Am J Physiol Heart Circ Physiol 279: H2558-H2567, 2000.-A double exogenous autoregressive (XXAR) causal parametric model was used to estimate the baroreflex gain (␣ XXAR ) from spontaneous R-R interval and systolic arterial pressure (SAP) variabilities in conscious dogs. This model takes into account 1) effects of current and past SAP variations on the R-R interval (i.e.,
... e., baroreflex-mediated influences), 2) specific perturbations affecting R-R interval independently of baroreflex circuit (e.g., rhythmic neural inputs modulating R-R interval independently of SAP at frequencies slower than respiration), and 3) influences of respirationrelated sources acting independently of baroreflex pathway (e.g., rhythmic neural inputs modulating R-R interval independently of SAP at respiratory rate, including the effect of stimulation of low-pressure receptors). Under control conditions, ␣ XXAR ϭ 14.7 Ϯ 7.2 ms/mmHg. It decreases after nitroglycerine infusion and coronary artery occlusion, even though the decrease is significant only after nitroglycerine, and it is completely abolished by total arterial baroreceptor denervation. Moreover, ␣ XXAR is comparable to or significantly smaller than (depending on the experimental condition) the baroreflex gains derived from sequence, power spectrum [at low frequency (LF) and high frequency (HF)], and cross-spectrum (at LF and HF) analyses and from less complex causal parametric models, thus demonstrating that simpler estimates may be biased by the contemporaneous presence of regulatory mechanisms other than baroreflex mechanisms. cardiovascular variability; linear parametric modeling; identification techniques EVALUATION OF THE BAROREFLEX GAIN is considered an important tool in clinical practice (16). The baroreflex Address for reprint requests and other correspondence: A.