Marked pericardial inhomogeneity of specific ventilation at total lung capacity and beyond.

We measured regional ventilation at 1l above functional residual capacity (FRC+1L) and total lung capacity (TLC) in three normal subjects and four elite breath-hold divers, and above TLC after glossopharyngeal insufflation (TLC+GI) in the divers. Hyperpolarized (3)He MRI was used to map the local ventilation per unit volume over the entire lung. At TLC and above, there was markedly increased regional ventilation of the lungs in the pericardial region compared with the relatively uniform ventilation throughout the rest of the lung. The distribution of fractional ventilation regionally was relatively uniform at FRC+1L, with a small non-gravitational cephalocaudal gradient of specific ventilation in the supine posture. Our observations at high lung volumes are consistent with the effect of high pleural tension in the concave pericardial region, which promotes expansion of the subjacent lung, leading to a higher local effective compliance and a higher specific ventilation.