pulmonary system:
# Capillary dilatation all over respiratory tract leading to engorgement of nose, pharynx, larynx. trachea , bronchi and these make breathing difficult.
# Diaphragm is elevated 4cm by the uterus but without restriction to its movement.
# Ribcage displaced upwards and widens.
# Subcostal angle widens.
# Thoracic circumference increases by 6 cm.
# Abdominal muscles have less tone and less active make the respiratory movement thoracic.
** Due to relaxation of the muscles of conducting airways by the effect of hormones the dead space volume increases.
** Tidal volume: (amount of air inspired or expired during each respiration at rest ) increases gradually by(30% :50% ) with pregnancy.
** Total lung capacity: ( total amount of air in the lung at the end of maximum inspiration ) decreases by 5% due to elevation of diaphragm.
** The following are decreased by 20%
Functional residual capacity: ( amount of air remaining in the lung at the end of expiration ).
Residual volume: ( volume of air remaining in the lung at the end of maximal expiration ).
Expiration reserve: (maximum amount of air that can be expired from the resting end of respiration).
Inhalation volumes are increased and residual volumes are decreased ,so alveolar ventilation increases by 65% during pregnancy.
** Inspiration capacity: (maximum volume of air can be inspired at rest) increases by 5% :10%.
** Slight increase in respiratory rate,increase in minute ventilation,increase in tidal volume.
** Progressive increase in oxygen consumption 20% due to increase in metabolic needs of the mother and baby.
** When hyperventilation occurs ,decrease in alveolar carbon dioxide ,and decrease carbon dioxide in maternal blood occur this maneuvers under control of brain neurones protect the baby from high levels of carbon dioxide coming as products of increased metabolism.
** Oxygen saturation decreases with each uterine contraction and then return to precontraction level,so woman should take deep breath during contractions.
