<prompt> Answer this question truthfullyIn patients with COPD, sleep apnea, or obesity hypoventilation syndrome, what physiological change helps compensate for chronic respiratory acidosis and hypercapnia?  <response>: <reason> The physiological change that helps compensate for chronic respiratory acidosis and hypercapnia in patients with COPD, sleep apnea, or obesity hypoventilation syndrome is increased renal HCO3- retention. 