Deep inspirations prior to oscillometry for detecting lung alterations in a mouse model of asthma: Yea or nay?

Deep inspirations are avoided prior to oscillometry in humans because they transiently improve respiratory mechanics and thereby mask abnormalities in patients with lung diseases. In mice, oscillometry is measured under anesthesia and deep inspirations are contrastingly recommended since they optimize mechanical ventilation and reduce intersubject variability by recruiting closed airways. However, while modeling asthma, a lung disorder burdened by airway closure, deep inspirations may be counterproductive and mitigate differences between mice with and without experimental asthma. Herein, the effect of deep inspirations on respiratory mechanics was quantified in mice with and without experimental asthma. Male BALB/c and C57BL/6 mice were exposed once-daily to either saline or house-dust mite for 10 consecutive days. The day after the last exposure, respiratory mechanics were measured by oscillometry before and after two deep inspirations. In addition to decrease intersubject variability, deep inspirations improved respiratory mechanics in both mouse strains to a magnitude related to the initial level of impairment. Whether deep inspirations mask the detection of alterations caused by experimental asthma depended on the mouse strain. In fact, this question became irrelevant in BALB/c mice when it was discovered that all oscillometric readouts are unchanged by experimental asthma in this mouse strain. In C57BL/6 mice though, the worsening of respiratory mechanics caused by experimental asthma was largely abolished by deep inspirations. Deep inspirations are thus recommended in BALB/c mice since they reduce intersubject variability. However, their utility in C57BL/6 mice is debatable, since the reduced variability may be outweighed by a decreased effect size.