Abstract

Introduction

In COPD and critical illnesses, diaphragm ultrasound is a marker of disease severity and clinical outcomes. We report on quantitative values of diaphragmatic ultrasound variables and its predictors in the CF population, which are currently lacking.

Methods

CF patients were prospectively recruited. Diaphragm ultrasound was performed and compared to lung function tests, handgrip strength, fat-free mass (FFM), transthyretin, vitamin A, E and D levels, C-reactive protein (CRP), dyspnea levels and rate of acute exacerbation (AE). Diaphragm activity was reported as thickening fraction during maximal inspiration (TFmax, maximal contractile action) and TF%max (ratio of TF during tidal breathing and TFmax, representing contractile requirement of tidal breathing).

Results

110 patients were included [61 males, median (interquartile range) age 31 (27-38) years and FEV1 66 (46-82)% predicted]. Median TFmax was 86 (55-126)% and its lower 5th percentile was 30%. TF%max was not correlated to age, FFM or vitamin levels, but significantly correlated to transthyretin (rho=-0.27, p=0.005), CRP (rho=0.47, <0.001), FEV1 and handgrip strength (both p<0.05). TF%max was significantly higher in patients with >2 AE/year (44±25 vs 29±17, p=0.001), in those with mMRC score >2 (69±15 vs 31±18%, p<0.001) and was a better marker of dyspnea level than FEV1 (AUROC 0.87 vs 0.77, p=0.03).

Conclusion

In CF patients, the lower limit of normal for TFmax is 30%. TF%max is related to peripheral strength, markers of systemic inflammation, nutritional status and FEV1, and outperforms FEV1 as a marker of dyspnea levels.This lays the basis for studies evaluating diaphragmatic activity as a marker of prognosis and efficacity of interventions in CF.