Pulmonary edema in dogs fails to cause reflex responses

Pulmonary edema has been proposed as a stimulus for pulmonary C-fibers. Stimulation of pulmonary C-fibers causes depression of cardiovascular function and either tachypnea or apnea. Our objective was to determine whether pulmonary edema, induced by either increasing pulmonary vascular permeability with alloxan or hydrostatic challenges, would elicit depression of cardiovascular function or changes in frequency of inspiratory activity. Utilizing a preparation in which the left pulmonary vessels and left airway were isolated, we monitored systemic blood pressure (BP), heart rate (HR), and diaphragm contractions (DC) in 13 anesthetized dogs. Injection of alloxan into the left pulmonary artery (LPA) produced transient decreases in HR, BP, and frequency of DC within 20 s of injection with no subsequent cardiorespiratory changes up to 5 min. These alloxan injections also caused coagulation necrosis. Generation of hydrostatic pulmonary edema in the left lung caused no changes in HR, BP, or in the frequency and amplitude of DC. We conclude that alloxan does stimulate reflex cardiorespiratory depression consistent with C-fiber stimulation, but these reflex responses are probably caused by alloxan's caustic effect and not by the resultant edema. We also conclude that pulmonary edema induced by increased hydrostatic pressure does not evoke any reflex cardiovascular responses or changes in frequency of inspiratory activity.