Vibration response imaging: a novel noninvasive tool for evaluating the initial therapeutic effect of noninvasive positive pressure ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease

Abstract

Background: The popular methods for evaluating the initial therapeutic effect (ITE) of noninvasive positive pressure ventilation (NPPV) can only roughly reflect the therapeutic outcome of a patient's ventilation because they are subjective, invasive and time-delayed. In contrast, vibration response imaging (VRI) can monitor the function of a patient's ventilation over the NPPV therapy in a non-invasive manner. This study aimed to investigate the value of VRI in evaluating the ITE of NPPV for patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

Methods: Thirty-six AECOPD patients received VRI at three time points: before NPPV treatment (T1), at 15 min of NPPV treatment (T2), and at 15 min after the end of NPPV treatment (T4). Blood gas analysis was also performed at T1 and at 2 hours of NPPV treatment (T3). Thirty-nine healthy volunteers also received VRI at T1 and T2. VRI examination at the time point T2 in either the patients or volunteers did not require any interruption of the on-going NPPV. The clinical indices at each time point were compared between the two groups. Moreover, correlations between the PaCO2 changes (T3 vs T1) and abnormal VRI scores (AVRIS) changes (T2 vs T1) were analyzed.

Results: No significant AVRIS differences were found between T1 and T2 in the healthy controls (8.51 ± 3.36 vs. 8.53 ± 3.57, P > 0.05). The AVRIS, dynamic score, MEF score and EVP score showed a significant decrease in AECOPD patients at T2 compared with T1 (P < 0.05), but a significant increase at T4 compared with T2 (P < 0.05). We also found a positive correlation (R2 = 0.6399) between the PaCO2 changes (T3 vs T1) and AVRIS changes (T2 vs T1).

Conclusions: VRI is a promising noninvasive tool for evaluating the initial therapeutic effects of NPPV in AECOPD patients and predicting the success of NPPV in the early stage.

Figure 1

Typical VRI Image of an AECOPD before, during and stop NPPV treatment. The typical VRI image changes with NPPV treatment. Panel A (T1), B (T2) and C(T4) represent the MEF (upper row), EVP (middle row) and QLD (lower row) characteristics at the T1,T2 and T4 stages, respectively. The VRI indices during treatment (such as MEF, EVP and QLD) improved dramatically compared with those before treatment; however, after stop NPPV treatment, these indices partly recovered. Abbreviations: T1 = Before NPPV treatment, T2 = at 15 min of NPPV treatment, T4 = at 15 min after the end of NPPV treatment, MEF = maximal energy frame Image, EVP = Expiratory vibration energy peak, QLD = Quantitative lung data.

Figure 2

Individual changes of VRI image score during and at the end of NPPV treatment. 1 Similarity: The similarity of vibrational energy curve (VEC) among respiratory cycles. 2 Inspiratory steep: Steep peak in VEC caused by sudden increased energy during inspiratory phase. 3 Plateau: Platform in VED, representing little change in vibrational energy. 4 Sag: Concave segment in VED. 5 Low and flat expiration (LFE): low and flat segment in VED during expiration phase. 6 Unsmooth edge of MEF image. 7 Midline bending of MEF image. 8 MEF image defect: abnormal decreased or absent gray-scale intensity in MEF image. 9 Pneumatocele: abnormal increased gray-scale intensity in MEF image. 10 Image jumping: rapid and discontinuous shift of the energy center in dynamic VRI. 11 Occurrence and development disorder: abnormal evolution of the dynamic VRI. In normal subjects, the dynamic VRI appears from upper medial to lower lateral, and disappears from lower lateral to upper medial. 12 Asynchronization: the evolution of bilateral lungs is asynchronous in dynamic VRI. 13 Lag: the dynamic changes of VRI in one lung falls behind another one). 14 Inverse dominance: the dominant side of VRI intensity inverted when breathing cycle changes from inspiratory phase to expiratory phase. 15 Pneumatocele at inspiratory phase: abnormal increased gray-scale intensity in MEF image at inspiratory phase. 16 Pneumatocele at expiratory phase: abnormal increased gray-scale intensity in MEF image at expiratory phase. 17 EVP synchronization: temporal synchronization of EVP between bilateral lungs. 18 EVP difference: amplitude difference of EVP between bilateral lungs.

Figure 3

Correlation between clinical improvement and VRI image score in AECOPD group. The change of AVRIS (T2 vs T1) is positively correlated with the changes of PaCO₂ (T3 vs T1).