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

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.