Breath sound analysis and wheezing in cystic fibrosis

Abstract

Wheezes are musical sounds caused by obstructed airways and depend on airflow, a critical pressure and a geometrical airway distortion.

Objective: to characterize wheezing and the lung sound spectra in cystic fibrosis (CF).

Patient and Methods: 14 patients (8 boys), aged 14.2 ± 2 years, 6 children had DF508/DF508 mutation. Subjects peathed through a pneumotachograph at flows of 0.5 ± 0.05 l/s. Respiratory sounds were recorded using contact sensors on the supra-sternal notch and on the thoracic region corresponding to the right lower lobe. Sound signals were low-pass filtered, amplified and Fourier analisis was applied to sounds within the target flow range. From averaged spectra, power at low (100-200 Hz = P₁) and high frequencies (400-2 000Hz = P₂) were calculated. We measured the frequencies below in which 50% (F50) and 99% (SEF99) of the spectral power between 100-2 000 Hz were contained. After baseline recording, patients received inhaled salbutamol (200 mcg) and 15 minutes later the measurements were repeated. 

Results: Baseline spirometry was FVC 56 ± 15%, FEV₁44 ± 12%, FEF₂₅-₇₅: 40 ± 14% and SaO₂93.4 ± 2%. Only in 6/14 patients we obtained a sinusoidal waveform of a typical wheeze, the others had complex waveforms. There was a significant increase in P₁and decrease in P₂during inspiration after salbutamol (p < 0.001) with a significant correlation between FEV₁vs F50 and SEF99 (p < 0.01). 

Conclusion: Our results show that CF patients have both complex and classical wheezes and that the sound spectral analysis correlates with lung function. Lung sounds analysis is a useful method to study ponchial obstruction mechanisms in CF patients.