The Cushing responses in the systemic and pulmonary circulation: the role of adrenal glands, bronchial circulation and pulmonary innervation.

Systemic hypertension and increased total peripheral vascular resistance are the most consistent observations in the Cushing responses to an increase in intracranial pressure (ICP). In the present study, we evaluated the participation of adrenal glands, bronchial circulation and pulmonary innervation in the systemic and pulmonary hemodynamics following an intracranial hypertension (ICH). In a total of 18 anesthetized, vagotomized and open-chest dogs, total heart bypass was performed to perfuse the systemic and pulmonary circulation with constant flow. The venous outflows were diverted into reservoirs. The preparation allowed us to observe the simultaneous changes in the systemic vascular resistance (SVR) and capacity (SVC) as well as the pulmonary vascular resistance (PVR) and capacity (PVC). ICH was produced by inflation of an epidural balloon to elevate the ICP to a level of 165-175 mmHg for 1.5 min. Our data showed that ICH induced drastic increases in SVR and PVR accompanying decreases in SVC and PVC. Vascular occlusion of the adrenal glands (n = 6) did not affect the hemodynamic changes. Arrest of bronchial circulation (n = 6) or pulmonary denervation (n = 6) also did not affect the changes in systemic circulation (SVR and SVC), but greatly diminished the pulmonary hemodynamic changes (PVR and PVC). The results suggest that the adrenal glands are not involved in the systemic and pulmonary hemodynamic responses to this degree of ICH. The changes in the pulmonary vascular resistance and capacity require the integrity of bronchial blood supply and sympathetic innervation.