Stretch Reflexes from the Dog's Lung to the Systemic Circulation

Abstract

Evidence is presented that reflex systemic vasodilatation occurs after stretching dog's lungs by either mechanical traction or positive pressure ventilation under conditions of separate pulmonary and systemic perfusion. This reflex is mediated by the vagus.

Reflex Cardiovascular Depression Produced by Stimulation of Pulmonary Stretch Receptors in the Dog

“…5, and it shows that the effects on the cardiovascular system produced by inflation of the lungs were markedly lessened by interruption of the vagus nerves. DISCUSSION Partly in confirmation of previous findings (6,7) the results of the present investigation clearly indicate that pulmonary stretch receptors do affect cardiovascular function, and that their activation results in reflex inhibition of sympathetic tone with consequent decreases in myocardial performance, heart rate, and peripheral vascular resistance. That these observed depressor responses are indeed reflex in nature rather than the result of mechanical effects produced by inflation of the lungs is indicated by the fact that they were observed in animals on right heart bypass, which means that they were not merely the result of induced changes in venous return, since blood flow into the pulmonary artery was kept constant.…”

“…This conclusion is consonant with the observations of Salisbury et al (6) and Daly et al (7) who studied the effects of the pulmonary stretch reflex on the total systemic vascular bed. The marked diminution in the depressor effects after vagotomy further supports the contention that they are the result of a reflex rather than the consequence of mechanical changes produced in the circulation as a result of inflation of the lungs.…”

“…Exactly opposite conclusions were reached by Bronk, Ferguson, Margaria, and Solandt (3), Downing and Siegel (4), and Okada and Fox (5), all of whom found that, when respiratory groupings were present, inspiration was generally associated with a decrease in sympathetic nervous activity. This latter view has been supported by Salisbury, Galletti, Lewin, and Rieben (6) and by Daly, Hazzledine, and Ungar (7), who noted that systemic arterial pressure fell when the lungs were expanded. The interpretation of the data that has been accumulated by these investigators has been complicated by the fact that in some of the studies the experimental animals breathed spontaneously (1,5), in some they were artificially ventilated (3)(4)(5)(6)(7), and in some studies gas exchange was produced by diffusion respiration (2).…”

“…This latter view has been supported by Salisbury, Galletti, Lewin, and Rieben (6) and by Daly, Hazzledine, and Ungar (7), who noted that systemic arterial pressure fell when the lungs were expanded. The interpretation of the data that has been accumulated by these investigators has been complicated by the fact that in some of the studies the experimental animals breathed spontaneously (1,5), in some they were artificially ventilated (3)(4)(5)(6)(7), and in some studies gas exchange was produced by diffusion respiration (2). To try to resolve the question of whether or not pul-monary stretch receptors exert control over the cardiovascular system, experiments were designed that would allow separate assessment of the possible reflex effects of positive pressure inflation of the lungs on cardiac function and on the resistance of an isolated vascular bed, together with a reinvestigation of the effects produced by inflation of the lungs on the total peripheral vascular resistance.…”

The reflex effects of alterations in lung volume on systemic vascular resistance in the dog

“…They concluded on the basis of plethysmographic studies that this response was due to vasodilatation. Salisbury, Galletti, Lewin & Rieben (1959), using a preparation in which the systemic circulation was perfused at constant blood flow, found that inflation of the lungs caused a reduction in systemic arterial perfusion pressure. They did not find any correlation between the size of the response and the inflation pressure and reported no values for the inflation volumes used in their experiments.…”