Cardio-respiratory coupling depends on the pons.

Cardio-respiratory coupling is reciprocal; it is expressed as respiratory-modulated sympathetic nerve activity and pulse-modulated respiratory motor activity. In the brainstem, the neuraxis controlling cardio-respiratory functions forms a ventrolateral cell column which extends to the dorsolateral (dl) pons. Our general working hypothesis is that these control systems converge at points with the common purpose of gas exchange and that neural activity along this axis coordinates both arterial pulse pressure and breathing. Here, we review the data showing that pontine nuclei modulate heart rate, blood pressure and breathing, and present new results demonstrating a vagal influence on pontine activity modulated with both arterial pulse pressure and phrenic nerve activity in the decerebrate cat. Generally with the vagi intact, dl pontine activity was weakly modulated by both arterial pulse pressure and respiratory pattern. After bilateral vagotomy, the strength and consistency of respiratory modulation increased significantly, although the strength and consistency of arterial pulse pressure modulation did not change significantly for the group; a decrease in some (62%) was offset by an increase in others (36%) neurons. Thus, the vagus shapes the envelope of the cycle-triggered averages of neural activity for both the respiratory and cardiac cycles. These data provide insight into the neural substrate for the prominent vagal effect on the cardio-respiratory coupling pattern, in particular respiratory sinus arrhythmia. While these results support convergence of inputs to neural populations controlling breathing and cardiovascular functions, the physiologic role of balancing ventilation, vascular resistance, heart rate and blood flow for the benefit of tissue oxygenation, remains hypothetical.