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
Vital capacity is increased
Subcostal angle remains unchanged
Tidal volume remains unaltered
Residual volume Is decreased
Medical, surgical and gynaecological illness complicating pregnancy