Effect of dibenz(b,f)-1,4-oxazepine aerosol on the breathing pattern and respiratory variables by continuous recording and analysis in unanaesthetised mice

Abstract

A riot control agent has to be a sensory irritant of a reversible type without pulmonary irritation as the later can cause lung injury. The aim of the present study is to continuously record and analyse breathing pattern and respiratory variables of dibenz (b,f)-1,4-oxazepine (CR) in unanaesthetised mice during and after exposure. The lowest concentration of 0.65 mg/m³ did not produce any effect on the breathing pattern. As high as 500 fold increase (315.9 mg/m³) in the concentration was used and no mortality was observed. CR produced a concentration dependent sensory irritation, without pulmonary irritation or airflow obstruction, showing that it may not cause any lung injury. The sensory irritation was initiated within 5 min of exposure due to the activation of TRPA1 receptors of the upper respiratory tract. Immediate recovery of normal breath without sensory irritation was observed in all the concentrations except the highest concentration of 315.9 mg/m³. Corresponding to the sensory irritation there was concentration dependent respiratory depression. The 50 percent respiratory depression (RD₅₀) in this experiment was 152 mg/m³ and the estimated threshold limit value for occupational exposure was 4.56 mg/m³. The present study shows that CR causes sensory irritation only which is completely recoverable.

Keywords: Dibenz(b.f)-1,4-oxazepine; Inhalation; Mice; RD50; Respiratory rate; Riot control agent; Sensory irritation; TRPA1 receptor.

Graphical abstract

Fig. 1

Time response analysis for breath classification and respiratory variables for a group of four mice, before, during and after inhalation exposure to CR aerosols at 0.65 mg.m³. The arrow indicates the duration of exposure. N normal, S sensory irritation, A airway obstruction, P pulmonary irritation, and SA, SP, PA and SPA are combinations of breath classification. VT tidal volume, TI time of inspiration, TE time of expiration, VD mid expiratory flow, TB time of brake, TP time of pause and f respiratory frequency.

Fig. 2

Percent change in normal breath, sensory irritation, pulmonary irritation and airflow obstruction, during and after inhalation exposure to CR aerosols at different concentrations. The arrow indicates the duration of exposure. The values are mean ± SE of 8 mice. Statistical significance was tested compared to 0.65 mg.m³ concentration at 10, 30, 60 and 90 min. *Indicates statistically significant at respective time periods.

Fig. 3

Percent change in respiratory frequency and tidal volume, during and after inhalation exposure to CR aerosols at different concentrations. The arrow indicates the duration of exposure. The values are mean ± SE of 8 mice. Statistical significance was tested compared to 0.65 mg.m3 concentration at 10, 30, 60 and 90 min. *Indicates statistically significant at respective time periods.

Fig. 4

Percent change in time of brake (TB) between inspiration and expiration, time of pause (TP) between two respirations and mid expiratory airflow, during and after inhalation exposure to CR aerosols at different concentrations. The arrow indicates the duration of exposure. The values are mean ± SE of 8 mice. Statistical significance was tested compared to 0.65 mg.m³ concentration at 10, 30, 60 and 90 min. *Indicates statistically significant at respective time periods.

Fig. 5

Percent respiratory depression at various concentrations of CR aerosol exposure for three time periods – upto 10 min, 10–30 min and 30–60 min. Eight mice for each exposure concentration for the estimation of percent respiratory depression (RD₅₀).