Augmented ventilatory activities after airway anaesthesia in humans

The effect of airway anaesthesia by nebulization of 4% lidocaine was studied in 14 healthy human subjects. After airway anaesthesia, a small but significant increase in forced vital capacity and a decrease in expiratory peak flow rate were observed in the pulmonary function test. Blood gas analysis revealed the appreciable depression in arterial oxygen tension. This change was accompanied by the increased alveolar/arterial oxygen tension difference (p less than 0.01) and increased oxygen uptake (p less than 0.01). Resting respiratory rate increased. Although minute ventilation was not changed, mouth occlusion pressure (P0.2) was significantly elevated. Hypercapnic ventilatory responses were augmented, both in terms of VE/PETCO2 and P0.2/PETCO2 slopes. The load compensation ratio, expressed as P0.2 loaded/P0.2 unloaded at rest, was reduced. These results suggested that preferential blockade of vagally mediated pulmonary stretch receptors by airway anaesthesia rather than the irritant receptors may have resulted in augmentation in ventilatory activities.