Complex sentence: In respiratory physiology, the diffusing capacity has a long history of great utility, representing conductance of gas across the alveolar-capillary membrane and also takes into account factors affecting the behaviour of a given gas with hemoglobin.
Split into simpler sentences: In respiratory physiology, the diffusing capacity has a long history of great utility, representing conductance of gas across alveoli. I.e the test measures "diffusion" across the alveolar-capillary membrane and also takes into account factors affecting the behaviour of a given gas with hemoglobin.