Ultrasound assessment of diaphragm thickness and related determinants in healthy female adolescents: a retrospective study

The diaphragm plays a crucial role in respiration and is influenced by changes in body composition. However, data on the relationship between diaphragm thickness, respiratory muscle strength, and body composition in healthy adolescents are limited. This study aimed to investigate the clinical indicators of diaphragm thickness and their relationships with respiratory muscle performance and body composition in a healthy female adolescent population. This study included 87 healthy female adolescents (mean age 17.5 ± 2.5 years) within the 15–24 age range, aligning with the broad definition of adolescence. Pulmonary function and respiratory muscle strength (MIP, MEP) were measured using a spirometer. Diaphragm thickness was evaluated using a single ultrasound device with a linear transducer, and measurements were taken three times during breath-holding at both inspiration and expiration. Body composition was assessed using a bioelectrical impedance analyzer. Diaphragm thickness during inspiration showed positive correlation with fat-free mass (FFM) ( r = 0.383, p = 0.006), height ( r = 0.292, p = 0.029), and weight ( r = 0.323, p = 0.015). Diaphragm thickness during expiration was positively correlated with FFM ( r = 0.359, p = 0.010), weight ( r = 0.297, p = 0.026), and FVC ( r = 0.271, p = 0.045). No significant associations were found between diaphragm thickness and MIP, MEP, or other spirometric measures. Regression analyses demonstrated FFM was the strongest predictor of diaphragm thickness ( p < 0.05). Diaphragm thickness in healthy female adolescents is significantly associated with FFM and anthropometric measures. These findings may indicate that diaphragm thickness could provide structural information about general muscle status during growth.