Respiratory Muscle Strength in Healthy Children Aged 6 Years and Under: An Observational Study

Measurement of respiratory muscle strength is important in the assessment and management of neuromuscular diseases. Reference data are essential for interpretation of clinical findings, but are lacking in infants and young children. This study aimed to provide reference data for maximum inspiratory (PImax) and maximum expiratory (PEmax) pressures in children aged 6 years and under. Healthy, term-born children were eligible for inclusion. Age, height, weight and BMI were recorded, and height/weight/BMI-for-age percentiles calculated. PImax and PEmax were measured using a tight-fitting face mask attached to a pressure transducer during maximal inspiratory and expiratory efforts respectively, induced via crying in younger participants and volitionally in older children. The greatest pressure was reported from three values within 20% of one another. Repeat measurements were obtained within a week where possible. Sixty-nine children aged 0.08-6.85 years were recruited, from whom technically-acceptable PImax and PEmax data were obtained in 45 and 38 cases respectively. PImax was significantly and inversely related to age (Spearman's rho -0.339, p = 0.046); PEmax was not related to any anthropometric characteristics. Neither PImax or PEmax differed between male and female participants. Predicted PImax was 120 + (-3.89xage); mean (SD) PEmax was 80.3 (21.7) cmH2O. Repeatability coefficient was 17.2 cmH2O for PImax and 26.3 cmH2O for PEmax (based on eleven and nine children respectively). This study provides the first contiguous reference range from infancy through to school age. Reference data are provided for PImax and PEmax along with information on repeatability.