RESUMEN
PURPOSE: Respiratory mechanics and the role of sex hormones in pregnancy are not well elucidated. We examined longitudinal and positional changes in lung mechanics in pregnancy and investigated the role of sex hormones. METHODS: A longitudinal study enrolled 135 women with obesity in early pregnancy. Fifty-nine percent of women identified as White; median body mass index at enrollment was 34.4 kg/m2. Women with respiratory disease were excluded. We obtained measurements of airway resistance and respiratory system reactance in various positions using impedance oscillometry and sex hormones in early and late pregnancy. RESULTS: With pregnancy progression, there was a significant increase in resonant frequency (Fres) (p = 0.012), integrated area of low frequency reactance (AX) (p = 0.0012) and R5-R20Hz (p = 0.038) in the seated position, and a significant increase in R5Hz (p = 0.000), Fres (p = 0.001), AX (p < 0.001 = 0.000), and R5-R20Hz (p = 0.014) in the supine position. Compared to the seated position, the supine position was associated with a significant increase in R5Hz, R20Hz, X5Hz, Fres, and AX in early (p-values < 0.026) and late pregnancy (p-values ≤ 0.001). Changes in progesterone levels between early and late pregnancy predicted the change in R5, Fres, and AX (p-values ≤ 0.043). CONCLUSION: Resistive and elastic loads increase with pregnancy progression and a change in body position from seated to supine increases resistive and elastic loads in both early and late pregnancies. The increase in airway resistance is primarily related to an increase in peripheral rather than central airways resistance. There was an association between the change in progesterone levels and airway resistance.