Fig. 1.
Analysis of respiratory patterns focused on AT and MV. Measurements were made in conscious, spontaneously breathing restrained rats placed in nose-only volume-displacement plethysmographs (pressure = const.). Animals were exposed in three subsequent steps to air (15-min, pre-exposure baseline data), phosgene (30-min, hatched bar), and air again (30-min, recovery). Data averaged during time-periods of 45-sec and represent means + SDs from eight simultaneously exposed rats/group. The insert given in the lower panel shows two analog tracings that represent flow-derived (top) and integrated volume-derived (bottom) changes, respectively. X-axis: 200 ms/tick. The breath structure is characterized by three phases: IT, ET and AT. These phases are used to distinguish between upper airway respiratory tract irritants (bradypnea period between IT and ET; not observed) and lower respiratory tract irritants (apnea period between end of ET and start of new breath). Such pauses do not occur in air only exposed rats. The integrated volume over flow of one breath was the tidal volume (VT). The product of number of breaths (respiratory rate) × VT was taken as the respiratory minute volume. The stepped curves represent the accumulated Cxt over the duration of exposure to phosgene