BRONCHOMOTOR AND PULMONARY ARTERIAL PRESSURE RESPONSES TO NERVE STIMULATION

Experiments on isolated perfused lungs and on the perfused whole animal preparation under "negative" pressure respiration are described. Attempts have been made to evaluate the bronchomotor mechanisms responsible for the changes of pulmonary arterial pressure (P.A.p.) which occur as a result of stimulation of the caudal end of the cervical vagosympathetic nerves (C.V.S.). When complete bronchoconstriction occurs, its rate of onset, which determines the intrapulmonary pressure change, and the final position in the respiratory cycle in which the lungs are immobilised, are the main factors in determining the degree and direction of P.A.p. change. When partial bronchoconstriction takes place the P.A.p. change is chiefly governed by the direction of change of the mean air volume of the lungs. Evidence is presented in support of the view that the C.V.S. nerves contain true pulmonary vasomotor fibres, but their functional activity cannot be unequivocally demonstrated by electrical stimulation if concomitant bronchomotor effects occur. Experiments are described showing that C.V.S. stimulation may produce broncho-constriction or -dilatation. The conditions governing the type of response have not been evaluated. We wish to express our thanks to the Government Grants Committee of the Royal Society for defraying the cost of the investigation by a grant to one of us (I. de B. D.).