Nasal contribution to exhaled nitric oxide at rest and during breathholding in humans

Am J Respir Crit Care Med. 1996 Feb;153(2):829-36. doi: 10.1164/ajrccm.153.2.8564139.


We characterized the nasal contribution to exhaled nitric oxide (NO) at rest and during breathholding in humans. Exhaled NO was greater during nose breathing (141 +/- 17 nl/min/M2, mean +/- SEM) compared with mouth breathing (68 +/- 6 nl/min/M2, n = 8, p < 0.001). After voluntary closure of the soft palate (VCSP) to eliminate nasal NO, exhaled NO from the mouth decreased further (30 +/- 4 nl/min/M2, p < 0.001). Release of NO into nasal passages during VCSP (217 +/- 19 nl/min/M2) was greater than exhaled NO during nasal breathing (141 +/- 17 nl/min/m2, p < 0.001), suggesting that nasal NO is taken up by the respiratory tract. During mouth breathing or nose breathing, NO concentrations sampled with a bronchoscope were higher in the nasopharynx than at the epiglottis or in the trachea in five subjects. Increased peak exhaled NO after a breathhold (33 +/- 7 ppb) was reduced (10 +/- 4 ppb, p < 0.001) after balloon occlusion of the nasopharynx. NO concentration during breathholding increased to a greater extent in the nasopharynx than in the pharynx or trachea. We conclude that the majority of exhaled NO at rest and during a breathhold originates in the nasopharynx.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Carbon Dioxide / analysis
  • Humans
  • Male
  • Middle Aged
  • Mouth Breathing
  • Nasal Mucosa / metabolism*
  • Nasopharynx
  • Nitric Oxide / analysis
  • Nitric Oxide / metabolism*
  • Pharynx
  • Respiration*
  • Trachea


  • Carbon Dioxide
  • Nitric Oxide