Effect of Inspiration/Expiration on Height Measurement

BACKGROUND: Growth parameters are a powerful screening tool in pediatric care. Accuracy assumes differing importance in different clinical settings. A small error is not clinically significant when height is obtained as a screening tool during annual well child visits. However, when assessing annual growth velocity using shorter interval visits, an error of equal magnitude might influence further management decisions. AIM AND HYPOTHESIS: To explore the effect of inspiration or expiration on height measurement. Our hypothesis was that height measurements obtained in inspiration would be greater than those obtained in expiration or without specific instructions as to status of respiration (unspecified). METHODS: Heights of 99 individuals 8 years and older were measured in inspiration, expiration and unspecified respiratory status by two pediatric endocrinologists. Patients were measured three times in each mode. The p values were adjusted by Tukey procedure for multiple comparisons among three modes. RESULTS: Height measurement performed in inspiration, expiration or without specific instruction as to breathing (unspecified) did affect height measurement. Mean difference +/- SEM (95% CI) between height obtained in inspiration and expiration was 0.22 +/- 0.03 cm (95% CI: 0.15, 0.29); between inspiration and unspecified 0.31 +/- 0.04 cm (95% CI: 0.22, 0.40); and between expiration and unspecified 0.092 +/- 0.03 cm (95% CI: 0.03, 0.16). CONCLUSIONS: Based on these results, we recommend multiple height measurements using uniform technique including inspiratory/expiratory status, especially when calculating 'annualized' height velocity over short intervals.