Diaphragm thickening during inspiration

Abstract

.-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...

Ultrasonographic Assessment of Diaphragm Function in Critically Ill Subjects

“…The authors showed that diaphragm thickness measured by ultrasound was significantly correlated with that directly measured by a ruler. 92 Since then, several studies have been performed to establish reference values of diaphragm thickness in supine healthy subjects, showing for the right hemidiaphragm mean values of 0.32 cm 93 or 0.33 cm, 94 independent of sex, age, or body constitution. More recently, Baldwin et al 95 described a mean diaphragm thickness value of 1.73 mm (range 1.11-2.98) when measured at end expiration in healthy volunteers.…”

“…Other authors reported how left hemidiaphragm measurements could not be consistently obtained, whereas right hemidiaphragm thickness measurements are highly reproducible, particularly after marking the location of the probe. 87 Some authors evaluated the variation of thickness at different lung volumes from RV to TLC in normal subjects, [90][91][92][93] suggesting the use of this maximal contractile capacity of the diaphragm. Another study measured diaphragm thickness in subjects with diaphragm paralysis to monitor recovery of the muscle over time.…”

Disfunción diafragmática: una realidad en el paciente ventilado mecánicamente

“…Sus limitaciones residen en la variabilidad inter e intraobservador y en la posibilidad de aplicar el estudio dinámico (excursión diafragmática) solo en pacientes sin VM 67,68,69,70 . Por otra parte, son varios los estudios que han demostrado buena precisión y reproducibilidad de los ultrasonidos en la valoración de la función diafragmática, tanto en voluntarios sanos como en pacientes críticos 52,69 .…”

“…En esta área, el diafragma se observa como tres capas de distintas densidades dispuestas paralelamente (pleura, diafragma y peritoneo) 51,70 . El grosor diafragmático se mide mediante la realización de un modo M o con la imagen 2D durante una espiración no forzada (Figura 2).…”

A novel systematic ABC approach to Diaphragmatic Evaluation (ABCDE)

“…Other studies have shown that diaphragmatic function can be evaluated effectively simply by observing diaphragmatic thickening using US during the respiratory process. 3 Unfortunately, many anesthesiologists may not be familiar with this method of locating the diaphragm and so do not perform this helpful clinical evaluation.…”