Formalin saline solution

PPE-induced changes in air space were measured in both a satellite group of rats and on the ex vivo lungs used for hp ⁸³Kr MRI. Lungs from both groups were similarly prepared by inflating to forced vital capacity (25 cm H₂O) with 5% formalin–saline solution (Sigma-Aldrich Ltd, Gillingham, UK). The trachea was then tied off and the lungs and heart removed en bloc and placed in formalin. After at least 24 h in formalin, an experienced histologist processed the lungs. Sections were cut from the wax embedded samples using a microtome and stained with H&E.
Experimental emphysema was assessed by measuring average air space area using a method describe by Belloni et al. [50 (link)] and used previously [40 ]. Briefly, computer-assisted image analysis was performed using an Olympus BX40 microscope and Zeiss image-processing software (Imaging Associates, Bicester, UK). Using colour thresholding techniques, the total alveolar air space area and the number of air spaces was measured from five random fields per sample. From these figures the mean air space area was calculated. Any fields containing airways or vasculature were excluded. The person assessing the slides was blinded to the treatment. Details of control and PPE-treated lungs are shown in table 1 with average measurements of mean alveolar area (MAA) in the satellite group and in those lungs processed post ex vivo hp ⁸³Kr MRI.