Gas‐exchange impairment: its correlation to lung mechanics in acute airway obstruction (studies on a rabbit asthma model)

A rabbit model was developed for the studies of ventilation/perfusion relationships (VA/Q) and thorax mechanics during bronchial provocation tests. Baseline data from 14 anaesthetized rabbits show a VA/Q distribution that is broader (less efficient VA/Q match) than that of lung-healthy humans, dogs and horses. Airway provocation was created by inhalation of ammonia, prostaglandin (PGE1) and methacholine bromide. Methacholine bromide was the only substance that triggered measurable VA/Q changes. Measurements 5 min after methacholine provocation showed markedly increased thorax resistance, widened VA/Q distribution and in some rabbits an increased shunt. Fifteen minutes after provocation that was still a broad VA/Q distribution and in several rabbits a further increase of shunt. Both thorax resistance and perfusion of regions with low VA/Q were reduced. Our results suggest a correlation between thorax resistance and perfusion of regions with low VA/Q. However, the slower normalization in VA/Q disturbance and the remaining or increased shunt suggests that factors other than airway resistance contribute to the gas-exchange impairment. These factors might be alveolar oedema, or mucus and oedema in the smallest airways.