IntroductionThe purpose of this study was to evaluate if ultrasound derived measures of diaphragm thickening, rather than diaphragm motion, can be used to predict extubation success or failure. Methods Sixty-three mechanically ventilated patients were prospectively recruited. Diaphragm thickness (tdi) was measured in the zone of apposition of the diaphragm to the rib cage using a 7-10 MHz ultrasound transducer. The percent change in tdi between end-expiration and end-inspiration (Δtdi%) was calculated during either spontaneous breathing (SB) or pressure support (PS) weaning trials. A successful extubation was defined as SB for >48 h following endotracheal tube removal. Results Of the 63 subjects studied, 27 patients were weaned with SB and 36 were weaned with PS. The combined sensitivity and specificity of Δtdi%≥30% for extubation success was 88% and 71%, respectively. The positive predictive value and negative predictive value were 91% and 63%, respectively. The area under the receiver operating characteristic curve was 0.79 for Δtdi%. Conclusions Ultrasound measures of diaphragm thickening in the zone of apposition may be useful to predict extubation success or failure during SB or PS trials.

Ultrasound has been used to evaluate diaphragm thickness in the zone of apposition of the diaphragm to the rib cage. The purpose of this study was to determine if ultrasonography could distinguish between a paralyzed and normally functioning diaphragm. We predicted that a paralyzed diaphragm would be atrophic and not shorten, therefore it would be thin and not thicken during inspiration. Thirty subjects (five with bilateral diaphragm paralysis, seven with unilateral diaphragm paralysis, three with inspiratory weakness but normally functioning diaphragms, and 15 healthy control subjects) had diaphragm ultrasound performed with a 7.5 to 10.0 MHz transducer placed over the lower rib cage in the mid-axillary line. The thickness of the diaphragm (tdi) was measured to the nearest 0.1 mm at FRC (t(di)FRC) and TLC (t(di)TLC). Diaphragm thickening during inspiration (delta t(di)) was calculated as (t(di)TLC - t(di)FRC)/t(di)FRC. In patients with unilateral paralysis, t(di) and delta t(di) for the paralyzed hemidiaphragm were significantly less than those values for the normally functioning hemidiaphragm (1.7 +/- 0.2 mm versus 2.7 +/- 0.5 mm [mean + SD] p < 0.01 for t(di), and -8.5 +/- 13% versus 65 +/- 26% [p < 0.001] for delta t(di)). The t(di) and delta t(di) for patients with bilateral diaphragm paralysis were significantly less than those values for the healthy volunteers (1.8 +/- 0.2 versus 2.8 +/- 0.4 and -1 +/- 15% versus 37 +/- 9% for t(di) and delta t(di), respectively) (p < 0.001). We conclude that ultrasound measurements of t(di) and delta t(di) can be used to determine if a diaphragm is paralyzed and confirm our predictions that a chronically paralyzed diaphragm is atrophic and does not thicken during inspiration.

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.-Ultrasound has been used to measure diaphragm thickness (T di ) in the area where the diaphragm abuts the rib cage (zone of apposition). However, the degree of diaphragm thickening during inspiration reported as obtained by one-dimensional M-mode ultrasound was greater than that predicted by using other radiographic techniques. Because two-dimensional (2-D) ultrasound provides greater anatomic definition of the diaphragm and neighboring structures, we used this technique to reevaluate the relationship between lung volume and T di . We first established the accuracy and reproducibility of 2-D ultrasound by measuring T di with a 7.5-MHz transducer in 26 cadavers. We found that T di measured by ultrasound correlated significantly with that measured by ruler (R 2 5 0.89), with the slope of this relationship approximating a line of identity (y 5 0.89x 1 0.04 mm). The relationship between lung volume and T di was then studied in nine subjects by obtaining diaphragm images at the five target lung volumes [25% increments from residual volume (RV) to total lung capacity (TLC)]. Plots of T di vs. lung volume demonstrated that the diaphragm thickened as lung volume increased, with a more rapid rate of thickening at the higher lung volumes [T di 5 1.74 vital capacity (VC) 2 1 0.26 VC 1 2.7 mm] (R 2 5 0.99; P , 0.001) where lung volume is expressed as a fraction of VC. The mean increase in T di between RV and TLC for the group was 54% (range 42-78%). We conclude that 2-D ultrasound can accurately measure T di and that the average thickening of the diaphragm when a subject is inhaling from RV to TLC using this technique is in the range of what would be predicted from a 35% shortening of the diaphragm. ultrasonography; diaphragm length; diaphragm thickness; diaphragm mechanics THE RELATIONSHIP BETWEEN diaphragm length (L di ) and lung volume has been well described in animals. Using sonomicrometers, previous investigators have found that the canine diaphragm shortens by 20-42% as lung volume increases from residual volume (RV) to total lung capacity (TLC) (5,6,8,11,14). Changes in L di have not been directly measured in humans. Instead, diaphragm shortening has been indirectly assessed by using radiographic techniques. Between RV and TLC, diaphragm shortening is estimated to be in the range of 25-35% (4, 9, 10, 17). It is likely that the diaphragm maintains a constant volume and increases its circumference minimally as it shortens; thus the diaphragm must thicken as it shortens. Measurements of diaphragm thickening, then, may provide an alternate means of assessing the relationship between L di and lung volume.Measurements of diaphragm thickness (T di ) have been made with the use of ultrasound to visualize the diaphragm in the area where it abuts the rib cage [zone of apposition (ZOA)] (12, 16). Wait et al. (16) used M-mode ultrasound to demonstrate inspiratory thickening of the diaphragm in the area of the ZOA; however, the degree of thickening and, therefore, the degree of shortening that they measured was greater than th...

The ratio of the muscular cross-sectional area of the diaphragm (CSA(di)) to the axially projected area of the thorax (A(thor)) theoretically determines the strength of the inspiratory pump. We studied these dimensions in 37 healthy subjects by ultrasonography and anthropometry. In 21 subjects who did not train with weights, thickness of the diaphragm (t(di)), circumference of the rib cage (c(di)), and CSA(di) increased with height and with body weight. The increase of thoracic cavity dimensions with weight was similar to that described across a wide range of mammals and was consistent with the scaling principle of elastic similarity. CSA(di)/A(thor) showed considerable variability and was not systematically dependent on height or weight. The 15 adults who trained with weight-lifting had thicker diaphragms for comparable height and greater CSA(di)/A(thor) than the adults who did not train. We conclude that (1) the structural dimensions of the diaphragm and thorax show substantial variability, some of which is systematic with stature; (2) the variations of structure predict substantial variation of inspiratory strength which is not systematic with stature; (3) the muscular cross-section of the diaphragm is increased by general or specific training.

Pulmonary complications due to respiratory muscle dysfunction are commonly a source of morbidity and mortality in patients with neuromuscular diseases. This review discusses the adverse effects of respiratory muscle weakness on pulmonary mechanics and examines the role that inspiratory muscle training may play in reversing pulmonary dysfunction in these individuals. In asymptomatic persons, it is well established that the inspiratory muscles can be trained to increase both force and endurance. In patients with neuromuscular diseases, the effects of training protocols on force and endurance are more controversial. This article reviews seven studies that have evaluated respiratory muscle training in a total of 75 patients with varied neuromuscular disorders. Training regimens included breathing through inspiratory resistive loads and isocapnic hyperpnea. Despite methodologic differences among studies, investigators have generally shown that the inspiratory muscles are similar to other skeletal muscle groups in that they can be trained for both force and endurance in these patients. The training-related improvements in inspiratory muscle performance are more pronounced in patients who are less severely affected by their disease. In those patients who have disease to the extent that they are already retaining carbon dioxide, there is little change in force or endurance with training. In these individuals, the inspiratory muscles may already be working at a level sufficiently severe to provide a training stimulus with each breath. No adverse effects of inspiratory muscle training were reported. Inspiratory muscle training can improve force and endurance in patients with neuromuscular weakness.(ABSTRACT TRUNCATED AT 250 WORDS)

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Patients with chronic obstructive pulmonary disease have abnormal breathing and ventilatory muscle recruitment patterns at rest and during exercise, and these alterations may contribute to the limited exercise capacity seen in this disease. Lung volume reduction surgery (LVRS), a recently described treatment for emphysema, is reported to improve exercise performance. We studied the breathing and ventilatory muscle recruitment (VMR) patterns in eight patients with severe chronic obstructive lung disease (median FEV1 = 0.79 L, range 0.46 to 1.13 L) by measuring esophageal and gastric pressure measurements as well as tidal volumes (VT), respiratory rates (f), inspiratory (TI) and expiratory (TE) times, and watts at rest and during maximal exercise, before and 3 mo after lung volume reduction surgery. Maximal exercise capacity increased a median of 49% (median increase 17 watts, range 6 to 44 watts, p < 0.05) and maximal minute ventilation (VEmax) increased by a median of 22% (median increase 6.5 L/min, range 3 to 25 L/min, p < 0.05). At isowatt exercise after surgery, VT increased 0.31 L (range 0.07 to 0.69 L) and f decreased four breaths/min (range +0.5 to -15 breaths/min). Dyspnea scores as measured by a visual analog scale (VAS) decreased significantly at rest and at peak exercise after surgery. End-expiratory esophageal (Pes) and gastric (Pga) pressures at rest and at isowatt exercise decreased. A rightward shift in the slope of the Pes versus Pga plot was also observed suggesting increased use of the diaphragm after surgery. Our data indicate that LVRS improves the mechanics of breathing both at rest and during exercise.