BACKGROUNDS: While hypercapnia activates central chemoreflex and induces sympatho-excitation, its interaction with the baroreflex regulation of sympathetic nerve activity (SNA) has not been quantified. This study aimed to examine the impact of the central chemoreflex on the baroreflex function using an open-loop analysis. METHODS/RESULTS: In 7 anesthetized SD rats, we controlled intra-sinus pressure (CSP, baroreceptor sensed pressure) and recorded SNA and aortic pressure (AP). Hypercapnia was induced by inhalation of 3% CO2 gas. Hypercapnia markedly increased SNA (δSNA=53.4±7.1%, p<0.01) irrespective of CSP, indicating the resetting of the neural arc (CSP-SNA relation). In contrast, the peripheral arc (SNA-AP relation) did not change. The transfer function of the neural arc approximated a high-pass filter, while that of the peripheral arc approximated a low-pass filter. Hypercapnia did not affect either neural or peripheral arc transfer function. CONCLUSION: Chemoreflex activation reset the baroreflex neural arc upward without compromising its dynamic and static function.
