Tissue Doppler Imaging of the Diaphragm in Healthy Subjects and Critically Ill Patients

Abstract

Rationale: Tissue Doppler imaging (TDI) is an echocardiographic method that measures the velocity of moving tissue. Objectives: We applied this technique to the diaphragm to assess the velocity of diaphragmatic muscle motion during contraction and relaxation. Methods: In 20 healthy volunteers, diaphragmatic TDI was performed to assess the pattern of diaphragmatic motion velocity, measure its normal values, and determine the intra- and interobserver variability of measurements. In 116 consecutive ICU patients, diaphragmatic excursion, thickening, and TDI parameters of peak contraction velocity, peak relaxation velocity, velocity–time integral, and TDI-derived maximal relaxation rate were assessed during weaning. In a subgroup of 18 patients, transdiaphragmatic pressure (Pdi)-derived parameters (peak Pdi, pressure–time product, and diaphragmatic maximal relaxation rate) were recorded simultaneously with TDI. Measurements and Main Results: In terms of reproducibility, the intercorrelation coefficients were >0.89 for all TDI parameters ( P < 0.001). Healthy volunteers and weaning success patients exhibited lower values for all TDI parameters compared with weaning failure patients, except for velocity–time integral, as follows: peak contraction velocity, 1.35 ± 0.34 versus 1.50 ± 0.59 versus 2.66 ± 2.14 cm/s ( P < 0.001); peak relaxation velocity, 1.19 ± 0.39 versus 1.53 ± 0.73 versus 3.36 ± 2.40 cm/s ( P < 0.001); and TDI-maximal relaxation rate, 3.64 ± 2.02 versus 10.25 ± 5.88 versus 29.47 ± 23.95 cm/s 2 ( P < 0.001), respectively. Peak contraction velocity was strongly correlated with peak transdiaphragmatic pressure and pressure–time product, whereas Pdi-maximal relaxation rate was significantly correlated with TDI-maximal relaxation rate. Conclusions: Diaphragmatic tissue Doppler allows real-time assessment of the diaphragmatic tissue motion velocity. Diaphragmatic TDI-derived parameters differentiate patients who fail a weaning trial from those who succeed and correlate well with Pdi-derived parameters.

Tissue Doppler Imaging of the Diaphragm: A New Kid on the Block?

“…Despite an overlap in values for inspiratory velocity, patients who failed weaning trials had significantly higher peak dome velocities and higher dome maximal relaxation rates than patients who weaned from the ventilator. In the small group of patients in whom transdiaphragmatic pressure (Pdi) was measured, the peak Pdi, the diaphragmatic pressure-time index, and the maximal relaxation rates of Pdi were also higher in the patients who failed weaning (16).…”

“…In this issue of the Journal, Soilemezi and colleagues (pp. 1005-1012) applied cardiac TDI methods to study the diaphragm (16). They identified a ROI of the posterior third of the diaphragm dome and measured how quickly this ROI moved toward (inspiration) and away from (expiration) the ultrasound transducer.…”

“…The study by Soilemezi and colleagues reemphasizes the relationship between velocity of muscle contraction and muscle endurance (16). Diaphragm performance can be interpreted in the construct of its Pdi-inspiratory flow (VI) relationship, analogous to the force-velocity relationship of a contracting muscle (1).…”

“…Soilemezi and colleagues have provided an important first step for implementing TDI to assess diaphragm function (16). However, more questions need to be addressed before TDI can be established as a valuable tool for the intensivist.…”

“…There is a similar trade-off between Pdi and VI for a given level of V̇ o 2 ( 17 ). Because high contraction velocities can lead to fatigue, it is not surprising that Soilemezi and colleagues found that subjects who failed weaning had higher velocities of dome motion ( 16 ).…”