Interference of cardiovascular sounds with phonopneumography in children.

We have used fast Fourier transform and power spectra analysis to determine possible interference of cardiovascular sounds with the analysis of breath sounds in children. Ten normal children, 8 to 13 yr of age, were studied with sound transducer over midprecordium, right upper lobe, and right lower lobe along with simultaneously recorded ECG and air flow. Detection of R-waves facilitated sampling of sound segments at defined flow rates, with inclusion or exclusion of heart sounds. Measurements during breath-holding and without heart sounds served as baseline values. Heart sounds were only slightly attenuated over the right upper lobe. There was a considerable overlap in the power spectra of heart and breath sounds, mainly in frequencies below 100 Hz. Analysis of low-frequency components of normal breath sounds requires sampling during parts of the cardiac cycle that are free of cardiovascular sounds.