The temporal dynamics of blood flow in the human lung have been largely unexplored due to the lack of appropriate tools. Using the MRI method of arterial spin labeling (ASL) with subject-gated breathing, we produced a dynamic series of flow-weighted images with a spatial resolution of ~1 cm3 and a temporal resolution of ~10 s. The mean flow pattern determined from a set of reference images was removed to produce a time series of blood flow fluctuations. The fluctuation dispersion (FD), defined as the spatial standard deviation of each flow fluctuation map, was used to quantify the changes in distribution of flow in 6 healthy subjects in response to 100 breaths of hypoxia (FIO2 = 0.125) or hyperoxia (FIO2 = 1.0). Two reference frames were used in calculation, one determined from the initial set of images (FDglobal), and one determined from the mean of each corresponding baseline or challenge period (FDlocal). FDlocal thus represented changes in temporal variability as a result of intervention, whereas FDglobal encompasses both FDlocal and any generalized redistribution of flow associated with redistribution between two steady-state patterns. Hypoxia challenge resulted in a significant increase (96%, P<0.001) in FDglobal from the normoxic control period, as well as in FDlocal (46%, P=.0048), but there was no corresponding increase in spatial relative dispersion [spatial standard deviation of the images divided by the mean] (8%, NS). There was a smaller increase in FDglobal in response to hyperoxia (47%, P=.0015) suggestive of a response of the pulmonary circulation to a change from normoxia to hyperoxia. The results clearly demonstrate a temporal change in the distribution of pulmonary blood flow in response to hypoxia, which is not observed when considering only the relative dispersion of the spatial distribution.
- Pulmonary blood flow
- time course
- hypoxic pulmonary vasoconstriction
- Copyright © 2012, Journal of Applied Physiology