Abstract
It has long been recognised that the distribution of inhaled particulate within the human lung is non-uniform, and changes with time post-exposure. However, lack of information as to the magnitude of such non-uniformities has resulted in the calibration of lung monitoring equipment being based on the assumption of a uniform lung distribution. This assumption is believed to be a source of considerable error in the calibration process. This work is aimed at providing information on the actual spatial distribution of inhaled material in the human lung, to allow corrective measures to be applied to the calibration process. An experimental procedure is developed to map the spatial distribution of inhaled particulate of two different aerodynamic diameters within the lungs of human volunteers. The procedure included measurements at rest and during exercise, to study the effect of breathing pattern on particle distribution. Details, and the results of a pilot study are presented. This study maps the low resolution spatial distribution of 1 mum particles in the lungs of eight volunteers for a period of approximately eight weeks past inhalation. Reference to measurements made over calibration phantoms is made in order to interpret the results of the distribution mapping. A study of the suitability of the phantoms to simulate the anatomy of the subjects is undertaken, which raises doubts concerning the phantoms' lung size and shape. Mathematical models of the lungs of both the phantom and one of the subjects are developed as an analytical tool and measurement results are compared with count distributions predicted by these models. Results analysed in this manner suggest a much more uniform distribution than that previously experienced for larger particles. Information obtained from the pilot study on the distribution of inhaled particles within the lungs is used to identify a detector configuration that would provide an efficient lung coverage. This configuration is used in the development of a new in-vivo monitoring facility at AWE. An Appendix deals with aspects of phantom lung production and verification of the attenuation properties of the phantom lung material. The best subject position for routine use in the new AWE in-vivo monitoring facility is also considered in an appendix.