Behaviour of canine pulmonary vagal afferent receptors during sustained acute pulmonary venous pressure elevation.

1. The effects of an acute sustained increase in pulmonary venous pressure induced by partial obstruction of the mitral valve on the activity of the four types of pulmonary receptors, namely, slowly adapting, rapidly adapting, pulmonary C-fibre and bronchial C-fibre receptors, were studied in the dog. 2. Fifteen slowly adapting receptors, eleven rapidly adapting receptors and nine bronchial C-fibre receptors showed significant sustained increases in activity when stimulated by the elevated left atrial pressure by 9.4 +/- 0.2 mmHg for 15 min. Nine pulmonary C-fibre receptors did not show a significant increase (six of these nine receptors increased their activity in response to the stimulus). 3. When the left atrial pressure was increased in graded steps of 5 mmHg for 5 min each up to 15 mmHg, a significant graded response was found in all of seven slowly adapting receptors, five rapidly adapting receptors and five bronchial C-fibre receptors. The five pulmonary C-fibre receptors examined also showed increases, but the changes were not statistically significant. 4. In response to stimulation by the elevated left atrial pressure, increases in activity occurred within 1 min of application of the stimulus in all the receptors and returned to control levels within 1 min of removal of this stimulus. 5. It is concluded that in the dog, pulmonary vagal receptors are influenced by small increases in pulmonary venous pressure induced by partial obstruction of the mitral valve. The changes appeared to be greatest in the case of rapidly adapting receptors. The physiological significance of these responses remains to be investigated.