A new ventilator for monitoring lung mechanics in small animals

Researchers investigating the genetic component of various disease states r ely increasingly on murine models. We have developed a ventilator to simpli fy respiratory research in small animals down to murine size. The new venti lator provides constant-flow inflation and tidal volume delivery independen t of respiratory parameter changes. The inclusion of end-inspiratory and en d-expiratory pauses simplifies the measurement of airway resistance and com pliance and allows the detection of dynamic hyperinflation (auto-positive e nd-expiratory pressure). After bench testing, we performed intravenous meth acholine challenge on two strains of mice (A/J and C57bl/bj) known to diffe r in their responses by using the new ventilator. Dynamic hyperinflation an d a decrease in compliance developed during methacholine challenge whenever respiratory rates of 60-120 breaths/min were employed. In contrast, if dyn amic hyperinflation was prevented by lengthening expiratory time, (respirat ory rate = 20 breaths/min), static compliance remained constant. More impor tantly, the coefficient of variation of the results decreased when lung vol ume shifts were prevented. In conclusion, airway challenge studies have gre ater precision when dynamic hyperinflation is prevented.