What causes hypercapnia? Won't breathe, can't breathe or something in between?

@article{Cherniack2008WhatCH,
  title={What causes hypercapnia? Won't breathe, can't breathe or something in between?},
  author={Neil S. Cherniack},
  journal={Respiration; international review of thoracic diseases},
  year={2008},
  volume={75 3},
  pages={251-2}
}