Effect of Rapid Shallow Breathing on the Distribution of ¹⁸O-Labeled Ozone Reaction Product in the Respiratory Tract of the Rat

Abstract

We examined the effect of breathing pattern on ozone reaction product content within the respiratory tract. Thirty-four anesthetized, male Wistar rats were exposed to oxygen-18 (¹⁸O)-labeled ozone at 1.0 ppm for 2 h using a dual-chamber, negative-pressure ventilation system. Frequency was set at 80 (n = 9), 120 (n = 7), 160 (n = 8), or 200 (n = 10) breaths per minute (bpm), while tidal volume (V_t) was set to provide a constant minute ventilation of 72.8 ml/min/100 g body weight. Airways sampled were from the midlevel trachea and the mainstem bronchi and parenchyma of the cranial and caudal right lobes. ¹⁸O content in each airway sample was quantified and normalized to surface area. Across frequencies, there was significantly greater (p <. 05) ¹⁸O content in the trachea and bronchi (conducting airway epithelium) compared to the parenchyma sampling sites. Tracheal ¹⁸O content decreased between 80 and 160 bpm, but then underwent an increase at 200 bpm. In comparison, ¹⁸O content gradually increased between 80 and 200 bpm at the right cranial and caudal bronchi sites. Right cranial parenchymal ¹⁸O content decreased at 200 bpm compared to 80, 120, and 160 bpm. Right caudal parenchymal ¹⁸O content was relatively constant over all breathing frequencies. We concluded that the development of rapid shallow breathing from 80 to 160 bpm results in a reduced deposition of O₃ in the trachea, while only mildly affecting to ozone deposition in parenchyma supplied by short and long airway paths.

Supported in part by the National Institute for Environmental Health Sciences, RO1 ES006791. The authors thank Chad Stewart for his invaluable technical assistance with the experimental protocol, Bobby Crissman at the U.S. EPA for his assistance in analyzing the tissue for ¹⁸O content, William F. Walby for editing and graphic art assistance, and Jennifer M. Bratt for her graphic art assistance.

The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S.

Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.