 Respiratory muscles the muscles used to breathe need more blood and oxygen when their workload increases. It is difficult to measure respiratory muscle blood flow RMBF without invasive techniques. We will evaluate a new, much less invasive technique to measure RMBF in 2 groups: Healthy Volunteers and Critically Ill patients on breathing machines. The purpose of this study is to determine the accuracy of this new monitoring technique called Near Infrared Spectroscopy Utilizing Indocyanine Green Dye when compared with traditional measurements. The information gained from this study will help us to provide better care to patients with severe lung problems. 