Physiologic respiratory changes during pregnancy:
By term, oxygen consumption and minute ventilation increase by about 50%. As the uterus enlarges, the diaphragm is pushed cephalad. This elevation is compensated by an increase in the anteroposterior diameter of the chest. Thoracic breathing is favored over abdominal breathing. Diaphragmatic motion is NOT restricted.
Total lung capacity, vital capacity, and closing capacity are largely unchanged.
Tidal volume increases by about 40%, and respiratory rate increases by about 10%.
Functional reserve capacity is decreased by about 20%. This is due to decreased expiratory reserve volume as a result of the increased tidal volumes.
Tidal flow-volume loops are unaffected, except for the increased volume.
References
- LoMauro A, Aliverti A. Respiratory physiology of pregnancy. Breathe (Sheff). 2015 Dec;11(4):297-301. PubMed Link
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