We used standard criteria to score each patients sleep record by 30-s epochs. An obstructive apnea was defined as an absence of tidal volume excursion for 10 s or longer, associated with paradoxical rib cage and abdominal movements. An obstructive hypopnea was defined as a diminution of tidal volume of 50 percent from baseline for 10 s. We measured apnea index (number of apneas per hour), duration of each apnea, mean overall oxygen saturation, mean oxygen saturation during apneas, lowest oxygen saturation and longest apnea period for each patient. A P.K. Morgan spirometer was used to make ventilatory measurements on each subject.

A board-certified pulmonologist used standard criteria to classify the ventilatory measurements as normal, obstructive, restrictive or mixed. Finally, a two-dimensional echocardiogram was performed on each patient in the standard views (parasternal long axis and short axis, apical, four-chamber and subcostal) with the use of a Hewlett-Packard Sonos 1000. Right ventricular wall measurements were obtained directly from the two-dimensional image in the parasternal view and verified by comparison with the subcostal view when adequate images were available.