Studies of Pulmonary Function in Asthmatic Children

Pulmonary functions were studied in 188 asymptomatic children with bronchial asthma and 272 healthy children. Ventilatory function was measured by the spirogram and maximum expiratory flow volume (MEFV) curve. Although the forced vital capacity (FVC) and peak expiratory flow rate (PEFR) were of the same values in normal and asthmatic subjects, the maximal mid-expiratory flow rate (MMF), the maximal flow rate at 50% (V50) and that at 25% (V25) of vital capacity were definitely lower in asthmatic children than those in healthy children, particularly in children with severe asthma. Arterial blood gas tensions and pH were measured in 180 asthmatic children with various clinical symptoms and 102 asthmatic children with disturbance of consciousness. Hypocapnia was detected even in the asymptomatic state, and carbon dioxide tensions (Pco2) were markedly high values only on very severe attacks. There was a linear fall in arterial oxygen tension (Po2) and oxygen saturation (So2) with increasing severity of attack. A complication of metabolic acidosis was frequent in the subjects who suffered from severe attacks. Children with severe asthma had small airways obstruction even in the asymptomatic state. This pulmonary disturbance appears to induce mild sustained hypocapnia and respiratory alkalosis as acceleration of ventilatory drive. Therefore, the development of hypercapnia, even if it is mild, may be considered to represent somewhat severe impairement of the pulmonary function in children with bronchial asthma.