Urinary physiology and hypoxia: a pilot study of moderate-altitude trekking effects on urodynamic indices.

Exposure to high altitude is one of the most widely used models to study the adaptive response to hypoxia in humans. However, little is known about the related effects on micturition. This study addresses the adaptive urinary responses in four healthy adult lowlanders, comparing urodynamic indices at Kathmandu (1450 m a.s.l, K1450) and during a sojourn in Namche Bazar (3500 m a.s.l., NB3500). The urodynamic testing consisted of the cistomanometry and bladder pressure/flow measurements. Anthropometrics, electrocardiographic and peripheral capillary oxygen saturation (SpO2) data were also collected. The main findings consisted of significant reductions in the bladder power at maximum urine flow by about 30%, bladder contractility index by 13%, infused volume both at first (by 57%) and urgency sensation (by 14%) to urinate - indicating a reduced cystometric capacity - at NB3500. In addition to the urinary changes we found that SpO2, BMI, BSA and median RR time were all significantly reduced at altitude. We submit that the hypoxia-related parasympathetic inhibition could be the underlying mechanism of both urodynamic and heart rate adaptive responses to high altitude exposure. Moreover, increased diuresis and faster bladder filling at altitude may trigger the anticipation of being able to void, a common cause of urgency. We believe that the present pilot study represents an original approach for the study of urinary physiology at altitude.