Mechanisms of activity-related breathlessness in healthy human pregnancy.

We examined the contribution of alterations in central ventilatory control, static and dynamic respiratory mechanics and their interaction to exertional breathlessness in healthy human pregnancy. Detailed ventilatory, respiratory mechanical/muscular and perceptual responses to incremental cycle exercise were compared in the third trimester (TM(3)) and again approximately 5 months post-partum (PP) in women with (B, n = 12) and without (NB, n = 15) clinically significant activity-related breathlessness (measured by the baseline dyspnea index). In contrast to NB, breathlessness intensity ratings were significantly higher at any given work rate during exercise in TM(3) versus PP within B. This difference could not be explained by differences in central ventilatory control or respiratory mechanical/muscular factors. When compared with NB, the B group had an exaggerated ventilatory response to exercise in PP and TM(3), and appeared to lack central desensitization to the perceptual effects of maternal hyperventilation that was manifest within the NB group. In conclusion, gestational breathlessness could not be explained by alterations in central ventilatory control or respiratory mechanical/muscular factors, but reflected the normal awareness of increased ventilation.