Lung gas mixing efficiency in exercise.

The aim of this thesis was to examine the effects of exercise on gas mixing in the lung during exercise. There were four major stages. Firstly, the existing equipment used with resting subjects was applied to the exercising subject and was found to be inappropriate. Secondly, an in-line system of measuring flow and gas concentration was devised. Thirdly this system was validated with the aid of a physical model and resting subjects. Finally, nitrogen wash-out data were collected from 24 subjects at rest and during progressive exercise at three standard exercise intensities. The dynamic response characteristics of the bag-in-box spirometer at high breathing frequencies (50 min-1) were such that tidal volume was underestimated by almost 50%. The box was too small and its response too a linear for adequate correction factors to be applied. The in-line system, based on a linear relationship between flow and several argon, oxygen, carbon dioxide and nitrogen mixtures ( r = + 0.99, p<0.01 , Y = 0.2687 FAr + 0.995 ), measured tidal volumes reliably ( CV