Effect of respiratory muscle function on exercise capacity of school-aged children born preterm

Background: Epidemiological evidence supports a link between preterm birth and reduced exercise capacity later in life. Recent studies also show that prematurity affects respiratory muscle (RM) function at the long term, albeit the effects on exercise capacity remain unknown. Aim: To investigate the role of RM function in the complex relationship between preterm birth and exercise capacity in childhood. Methods: 34 children (age 6.4 ± 0.2 years) born between 29 and 40 weeks of gestational age (GA), underwent spirometry, measurement of lung volumes, measurement of RM function, and cardiopulmonary exercise testing (standardized cycle-ergometer protocol). RM function was assessed by means of the tension-time index (TTmus), while exercise capacity by means of maximum oxygen consumption (VO2max) and maximum achieved work (Wmax). Results: Preterm-born children (N=16) had higher TTmus (0.11±0.02 vs. 0.09±0.02; P=0.014) compared to those born at term (N=18); they also achieved lower Wmax (116±8 vs. 124±7 Watts; P=0.005) and slightly lower VO2max (32.8±4.9 vs. 36.6±8.8 mlO2/kg/min; P=0.124). There were no differences in spirometric indices between the two groups. GA was significantly correlated with TTmus (r –0.551; P=0.001), and Wmax (r 0.539; P=0.001), but not with VO2max. TTmus, in turn, was significantly correlated with VO2max, especially in preterm-born children (r –0.519; P=0.039). The above relationship remained strong after adjustment for somatometric and spirometric characteristics (multivariable regression). Conclusions: Preterm birth influences RM function at the long term and, through this effect, may be a significant determinant of exercise capacity later in life.