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Abstract
BackgroundOne of the central physiological functions of the lungs is to transfer inhaled gases from the alveoli to pulmonary capillary blood. However, current measures of alveolar gas uptake provide only global information and thus lack the sensitivity and specificity needed to account for regional variations in gas exchange.Methods and Principal FindingsHere we exploit the solubility, high magnetic resonance (MR) signal intensity, and large chemical shift of hyperpolarized (HP) 129Xe to probe the regional uptake of alveolar gases by directly imaging HP 129Xe dissolved in the gas exchange tissues and pulmonary capillary blood of human subjects. The resulting single breath-hold, three-dimensional MR images are optimized using millisecond repetition times and high flip angle radio-frequency pulses, because the dissolved HP 129Xe magnetization is rapidly replenished by diffusive exchange with alveolar 129Xe. The dissolved HP 129Xe MR images display significant, directional heterogeneity, with increased signal intensity observed from the gravity-dependent portions of the lungs.ConclusionsThe features observed in dissolved-phase 129Xe MR images are consistent with gravity-dependent lung deformation, which produces increased ventilation, reduced alveolar size (i.e., higher surface-to-volume ratios), higher tissue densities, and increased perfusion in the dependent portions of the lungs. Thus, these results suggest that dissolved HP 129Xe imaging reports on pulmonary function at a fundamental level.
Highlights
Enabling the diffusive exchange of alveolar gases with pulmonary blood is the most fundamental physiological function of the lungs
The features observed in dissolved-phase 129Xe magnetic resonance (MR) images are consistent with gravity-dependent lung deformation, which produces increased ventilation, reduced alveolar size, higher tissue densities, and increased perfusion in the dependent portions of the lungs
Diffusing capacity is most commonly measured using carbon monoxide (DLCO), which is currently the primary means of directly assessing normal gas uptake and diagnosing pathological changes in gas exchange that occur in such disorders as interstitial lung disease and chronic obstructive pulmonary disease [2,3]
Summary
Enabling the diffusive exchange of alveolar gases with pulmonary blood is the most fundamental physiological function of the lungs. The uptake of alveolar gases, referred to as the diffusing capacity or conductance, consists of two serially ordered components [1]. Diffusing capacity is most commonly measured using carbon monoxide (DLCO), which is currently the primary means of directly assessing normal gas uptake and diagnosing pathological changes in gas exchange that occur in such disorders as interstitial lung disease and chronic obstructive pulmonary disease [2,3]. DLCO is only a global measure of gas uptake and, cannot provide information about normal spatial variations in gas exchange or, more importantly, heterogeneity caused by disease. One of the central physiological functions of the lungs is to transfer inhaled gases from the alveoli to pulmonary capillary blood. Current measures of alveolar gas uptake provide only global information and lack the sensitivity and specificity needed to account for regional variations in gas exchange
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