Role of carotid sinus baroreflex in attenuating systemic arterial pressure variability studied in anesthetized dogs.

Attenuation of systemic arterial pressure (SAP) variability by the carotid sinus baroreflex (CSBR) was quantified in nine anesthetized, vagotomized dogs. SAP amplitude spectrum was compared between open-loop [SAPo(f)] and closed-loop [SAPc(f)] operation of the CSBR. At 0.002 Hz, SAPc amplitude was 3.5 +/- 2.2 (SD) mmHg, and SAPo was 9.6 +/- 3.5 mmHg (P < 0.01). At 0.02 Hz, SAP(c) amplitude was 2.8 +/- 1.2 mmHg, and SAPo was 4.3 +/- 1.2 mmHg (P < 0.05). At higher frequencies, SAPo(f) was indistinguishable from SAPc(f). With the opened CSBR, intracarotid sinus pressure (CSP) was pseudorandomly varied, and the resulting SAP responses were recorded to determine the transfer function from CSP to SAP [HCSP.SAP(f)]. From SAPo(f) and the determined HCSP.SAP(f), we estimated SAP(f) if the CSBR was closed [SAPc,est(f)] and compared it with SAPc(f). These two spectra were similar in each dog over a frequency range of 0.002-0.15 Hz, the differences between SAPo(f) and SAPc(f) being reconcilable with HCSP.SAP(f). Although the anesthetized state and vagotomy may have distorted the transfer characteristics of the CSBR from those in conscious (with the intact vagi) states, the results of the present study indicate that the CSBR attenuated SAP variability mainly in a low-frequency range below 0.02 Hz and that this attenuation was attributable to the transfer properties of the CSBR.