Diaphragm Fatigue and the Strategy of Breathing in COPD A. Grassino, M.D., F. Bellemare, M.D., D. Laporta, M.D.  CHEST  Volume 85, Issue 6, Pages 51S-54S (June 1984) DOI: 10.1378/chest.85.6_Supplement.51S Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 1 The tension-time index is the time integral of the transdiaphragmatic pressure swing. Pressure is expressed as a fraction of maximal transdiaphragmatic pressure and inspiratory time as a fraction of cycle duration. CHEST 1984 85, 51S-54SDOI: (10.1378/chest.85.6_Supplement.51S) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 2 Fatigue threshold represents a TTdi that can be sustained for 1 hr or longer, and has a value of .15-.18 in the normal human diaphragm. TTdi threshold can be achieved with a large variety of Pdi and TI/TT Patterns in the “fatigue zone” will result in fatigue in less than 1 hr. Patterns in nonfatigue zone can be sustained indefinitely. The circle represents TTdi during resting breathing in normal subjects. CHEST 1984 85, 51S-54SDOI: (10.1378/chest.85.6_Supplement.51S) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 4 Axes as in Figure 2. Open circles indicate resting breathing pattern in 5 COPD patients. The imposed pattern was held at the highest TTdi. The arrow indicates the return to their resting pattern as soon as the imposed pattern was discontinued. CHEST 1984 85, 51S-54SDOI: (10.1378/chest.85.6_Supplement.51S) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 5 Upper, Schematic mean tidal volume and time in 5 COPD at control and imposed pattern. Lower, H/L: High-frequency, low-frequency power components of the EMG of the diaphragm. Pdi is mean transdiaphragmatic pressure; Peo is mean esophageal pressure; C is control. Breath number started at the beginning of the imposed pattern run. CHEST 1984 85, 51S-54SDOI: (10.1378/chest.85.6_Supplement.51S) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 6 Upper; Schematic breathing cycle in 6 COPD patients before (control) and at end of exercise (left) and before (control) and at the end of imposed pattern (right). Lower, bars represent the values obtained in imposed pattern (I) and during exercise (Ex). Values are mean ± SD. VE – ventilation. Ppl is peak pleural pressure and TI/TT as defined in Figure 1 . CHEST 1984 85, 51S-54SDOI: (10.1378/chest.85.6_Supplement.51S) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 3 A run during submaximal exercise in a COPD patient. Left, axes as shown in Figure 2. Isopleths represent TTdi of .05, .10, and .15. The closed circles represent breath number during the course of an exercise run from beginning (0) to breath 120 (end). Right, VT: tidal volume, and f, frequency. The breaths indicated are the same as in the left panel. CHEST 1984 85, 51S-54SDOI: (10.1378/chest.85.6_Supplement.51S) Copyright © 1984 The American College of Chest Physicians Terms and Conditions