Multiple inert gases elimination tecnique(MIGET)and gas exchange in obstructive respiratory diseases

Among the traditional causes of arterial hypoxemia and hypercapnia, ventilation-perfusion ratio (VA/Q) inequality is the most important mechanism of gas exchange impairment in respiratory diseases. In the mild 1970s a new technique, named “multiple inert gases elimination technique” (MIGET), was developed able to study VA/Q distributions. The first study of present thesis, (“Adenosine 5’-monophosphate (AMP) challenge in mild asthma: cellular and gas exchange responses”), is focused on the comparative evaluation, in mild asthma, of the effects of two different challenge tests (AMP and methacholine [MCh]) on lung function, including VA/Q relationships, and induced sputum. Results showed similar spirometric and gas exchange responses (severe bronchonstriction, VA/Q and PaO2 worsening) after both tests but a neutrophils increase in the sputum only after AMP challenge, supporting the hypothesis that indirect agents of bronchoconstriction (AMP) offer a better estimate of airway inflammation than direct agents (Mch). The second study (“Effects of nebulized salbutamol on pulmonary gas exchange during COPD exacerbations and in stable conditions”) investigated the effects of salbutamol on ventilation-perfusion (VA/Q) inequalities in COPD patients during exacerbations (E) and in stable clinical condition (S). In both phases of the study we observed similar spirometric (increased FEV1 and IC) and hemodynamic (increased cardiac output and decreased mean arterial pressure) responses to salbutamol. By contrast, patients showed at phase S more marked and prolonged negative effects on gas exchange (hypoxemia and VA/Q mismatch) than during E, likely as effect of pulmonary vasodilatation. In conclusion, this effect was more evident in stable condition as pulmonary vasculature tone is more relaxed and liable to vasodilatation than during exacerbations (hypoxic pulmonary vasoconstriction).