Background: The protease-antiprotease hypothesis proposes that inflammatory cells and oxidative stress in chronic obstructive pulmonary disease (COPD) produce increased levels of proteolytic enzymes (neutrophil elastase. matrix metalloproteinases [MMP]) which contribute to destruction of parenchyma resulting in progressive decline in forced expiratory volume in one second. Doxycycline... https://www.roneverhart.com/Clear-Zig-Zag-Pet-Gate/