Am. J. Respir. Crit. Care Med., Vol 151, No. 5, May 1995, 1504-1511.
Effects of nitrous acid exposure on human mucous membranes
TR Rasmussen, M Brauer and S Kjaergaard
Institute of Environmental and Occupational Medicine, University of Aarhus, Denmark.
Nitrous acid (HONO) is formed both indirectly from the reaction of nitrogen
dioxide (NO2) with water on indoor surfaces, and directly during
combustion. This gaseous pollutant may be a previously unrecognized causal
factor in assessments of nitrogen oxide exposure effects. The present study
is the first attempt to evaluate exposure effects of HONO on the human
airways and the mucous membranes of the eyes and nose. Fifteen healthy
adult nonsmokers were exposed for 3.5 h in a double-blind, balanced
protocol to clean air, 77, and 395 ppb HONO. Each exposure was preceded by
a 1-h baseline measurement period, and exposures were separated by 1 wk.
There was a 10-min exercise period during exposure. Effects measurements
included assessment of bronchial reactivity, measurement of specific airway
conductance, spirometry, acoustic rhinometry, nasal lavage, tear-fluid
cytology, a CO2 eye-provocation test, evaluation of eye redness, and
subjective sensations. Effects of HONO exposure on the eyes were found as
exposure- related changes in tear-fluid cytology. In particular, the number
of squamous cells increased by 20, 67, and 80% following exposure to clean
air, 77, and 395 ppb HONO, respectively (p = 0.004). Possible indications
of exposure effects on sensitivity to CO2 eye provocation and on specific
airway conductance were also measured. For specific airway conductance
there was an approximate 10% decrease in conductance following exercise in
association with HONO exposure, compared with a 2% decrease with clean air
(p = 0.038).
