['We hypothesised that obstructive sleep apnoea (OSA) may cause pulmonary artery dilatation through excessively negative intrathoracic pressure generated during inspiratory efforts against the upper airway collapse during obstructive apnoeas. To test this hypothesis, we examined the association between OSA severity and pulmonary artery dilatation.', 'A total of 173 patients who were clinically suspected of having OSA underwent chest radiography and polysomnography. We measured the right descending pulmonary artery diametre (RDPAD) on the chest radiogram and defined an abnormal increase in the RDPAD as RDPAD\u2009>\u200916\u2009mm in males and RDPAD\u2009>\u200915\u2009mm in females.', 'An abnormal increase in the RDPAD was more prevalent in patients with severe OSA (46.3%) compared to those with no or mild OSA (14.5%) and those with moderate OSA (21.6%). A univariate logistic regression analysis showed that severe OSA was associated with an abnormal increase in the RDPAD (odds ratio 3.94, 95% confidence interval 1.98-7.87). After controlling for age, gender, body mass index, smoking history and partial pressure of arterial oxygen, severe OSA still remained significantly associated with an abnormal increase in the RDPAD (odds ratio 4.06, 95% confidence interval 1.82-9.07).'] Is severe obstructive sleep apnoea independently associated with pulmonary artery dilatation?