Small airway involvement in HP partially revealed by UPG, IOS tests
Patients with chronic hypersensitivity pneumonitis (HP) have small airway abnormalities that may be observed partially using ultrasonic pneumography (UPG) and impulse oscillometry (IOS), according to a study. Furthermore, treatment with azathioprine and prednisone results in improvement in lung volumes but not gas exchange.
The study included 20 consecutive patients (median age 50 years; 80 percent female) with chronic HP. All patients completed UPG, IOS, spirometry, body plethysmography, single-breath carbon monoxide diffusing capacity (DLCO) and the 6-minute walk test (6MWT). Eosinophilic airway inflammation was evaluated by obtaining the fraction of exhaled nitric oxide (FENO). Assessments were performed at diagnosis and after 4 weeks of treatment.
At diagnosis, UPG phase 3 slope was abnormally high, consistent with maldistribution of ventilation. Moreover, IOS data showed all patients had low reactance at 5 Hz and elevated reactance area reflecting low compliance. Only eight patients (40 percent) had elevated R5 (resistance at 5 Hz [total]) and R5–20 (resistance at 5 Hz–resistance at 20 Hz [peripheral]) attributed to small airway resistance.
In comparison, FENO parameters were within normal limits.
After treatment, significant improvements were observed in forced vital capacity (FVC), 6MWT and the distribution of ventilation, but not in DLCO.
The present data suggest that phase 3 slope by UPG may be helpful in the medical care of HP patients due to improvement with treatment and negative correlation with forced vital capacity, researchers said.
HP is a complex clinical syndrome occurring as a result of an abnormal immune lung response to diverse inhaled antigens. In Mexico for example, the most frequent antigens linked to HP are bird-derived proteins, and most cases are attributed to chronic exposure to ornamental birds kept inside homes. HP can progress to pulmonary fibrosis, and small airway involvement is characterized pathologically by interstitial mononuclear infiltration with non-necrotizing, poorly formed granulomas and varying degrees of fibrosis. [Respir Med 2011;105:608–14; Chest 2012;142:208–17; Am J Respir Crit Care Med 2012;186:314–24]