 HYPOTHESIS 3: We speculate, based on previous authors, that the blood flow rates in respiratory muscles for a given WOB will be different in clinical populations that in healthy volunteers. We hypothesize that the slope of the linear regression analysis relating BFI to WOB both transpulmonary pressure gradients and EMG will be steeper in clinical populations, suggesting that one reason for respiratory failure and weaning difficulties in these populations may be inefficient respiratory muscle oxygen utilization. 