Pathophysiological background of the disease
The oxygen sensors in the kidney control the hematocrit, produce
erythropoietin in the cortex, and are able to translate tissue oxygen
pressure into a measure of plasma volume [94]. However, in severe
hypoxia below pO2 40 mmHg, glomerular filtration rate
declines, leading to sodium retention and water retention [95, 96].
Hence, renal function in chronic respiratory failure, like OSA or COPD,
is often impaired and these patients show fluid and sodium retention
[97]. This excess retention has also been described at high
altitude, especially in altitude maladapted individuals [98]. The
effect of hypoxia on patients with impaired renal function can be
studied in hypoxia models and this would have implications for
determining their risks of long air travel or dwelling at high altitude.