hypoventilation

[hī′pə-vĕn′tl-āshən]
n.
  1. Reduced or deficient ventilation of the lungs, resulting in reduced aeration of blood in the lungs and an increased level of carbon dioxide in the blood.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.