Changes in the respiratory system in pregnancy;

Anatomical changes:The lower ribs flare out,the subcoastal angles increases from 68 to 103 degree,transverse diameter of chest increases by 2 cm and the diaphragm rises about 4cm in pregnancy. Functional changes:Increase in ventilation in pregnancy is achieved by an increase in tidal volume by 40%.Minute ventilatory volume also increases.There is no change in vital capacity.The functional residual capacity and residual volume are decreased due to elevated diaphragm. TEXT BOOK OF OBSTETRICS,Sheila Balakrishnan,2nd edition,page no.80