REVERSAL OF NITROUS OXIDE-INDUCED DEPRESSION OF HYPOXIC PULMONARY VASOCONSTRICTION BY LIGNOCAINE HYDROCHLORIDE DURING COLLAPSE AND VENTILATION HYPOXIA OF THE LEFT LOWER LOBE

The blood flow to the left lower lobe (L), and total (T) pulmonary blood flow, were measured in 10 open-chest dogs usingelectromagnetic flowmeters. Ventilation of the left lower lobewith 7% oxygen in nitrogen produced a greater reduction in L/T (41%) than lobar ventilation with 7% oxygen in nitrous oxide(33%). Lobar collapse reduced QL/QT by 65%, but there was nochange in L/T when 50% nitrous oxide was administered to theright lung. The i.v. infusion of lignocaine hydrochloride duringventilation of the lobe with 7% oxygen in nitrogen producedno change in L/T. However, lignocaine infusion during lobar ventilationwith 7% oxygen in nitrous oxide produced a further reductionin L/T to a value which was not significantly differentfrom that observed during ventilation with 7% oxygen in nitrogen.Lignocaine had no effect on L/T during lobar collapse whether theright lung was ventilated with 50% oxygen in nitrogen or 50%oxygen in nitrous oxide. It is concluded that lignocaine reversesthe depression of hypoxic pulmonary vasoconstriction producedby lobar ventilation with nitrous oxide.