Growth and other factors affecting peak expiratory flow rate.

By means of a simple questionnaire and measurements of height, weight, and peak expiratory flow rates 3061 children from city and rural populations were studied. Children with asthma or other respiratory diseases had lower peak expiratory flow rates, and younger children living in rural areas had higher rates. In 2828 healthy children the peak expiratory flow rate increased with age, height, and weight. There was an increase in the slope of this line for both age and height--at 12 years and 145 cm in girls, and at 14 years and 155 cm in boys. This continued for two to three years and 15 cm, respectively, before it declined. Previous surveys have obscured this change associated with height by reporting small numbers and using linear regression analysis. This type of analysis can underestimate the mean peak expiratory flow rate of small children by half to one standard deviation. A centile graph against age is recommended to describe normal values and their differences.