The effect of pregnancy on respiratory function

Pregnancy is a paraphysiological condition that affects the respiratory system through biochemical and mechanical factors.Hormonal patterns cause ventilatory changes.The enlarging uterus alters chest wall configuration. We aimed to quantify these changes:optoelectronic plethysmography was used for ribcage(RC) geometry,ventilatory and thoraco-abdominal pattern,while ultrasound for diaphragmatic function(thickness and displacement). 11 primiparous women were analyzed during quiet breathing at each trimester of pregnancy. 11 nulliparous were the control group. Subcostal angle,antero-posterior and mediolateral RC diameters progressively increased,while RC height decreased with constant RC volume.Breathing frequency increased,while tidal volume did not change although the reduced RC contribution at the third trimester.No changes in terms of diaphragmatic thickness and displacement(Figure1). During pregnancy there is a reorganization of RC geometry, mainly due to a bucket-handle upward shift of the lower costal margin, in terms of shape but not of volume. In this way, the lung is not restricted while leaving space to accommodate the abdominal expansion. Although our results suggest no effects on the diaphragm, the enlarging uterus increases the abdominal load and stretches the diaphragm.The preserved thickness indicates that it increases in total size. We can speculate that pregnancy has a training effect on the diaphragm, being propaedeutic for the delivery phase.