Spectral analysis of airflow sounds in patent versus occluded tracheostomy tubes: a pilot study in tracheostomized adult patients

Evaluation of the different sleep-disordered breathing patterns of the compressed tracheal sound

OBJECTIVE

Suitability of the compressed tracheal sound signal for screening different sleep-disordered breathing patterns was evaluated. The previous results suggest that the plain pattern in the compressed sound signal represents mostly normal, unobstructed breathing, the thick pattern consists of periodic apneas/hypopneas and during the thin pattern, flow limitation in the nasal cannula signal is abundant.

METHODS

Twenty-seven patients underwent a polysomnography with a tracheal sound and oesophageal pressure monitoring. The tracheal sound data was compressed and scored visually into three different breathing patterns. The percentage of oesophageal pressure values under -8cm H2O, the minimum pressure value and the average duration of the breathing cycles were extracted from 10-min episodes of those plain, thick and thin patterns. In addition, the spectral contents of the tracheal sound during the different breathing patterns were evaluated.

RESULTS

The percentage of time when the oesophageal pressure negativity increased was highest during the thin pattern and lowest during the plain pattern. In addition, the thin pattern presented most high frequency components in the 1001-2000Hz frequency band of the tracheal sound.

CONCLUSIONS

The results confirmed our previous findings that both the thick and thin patterns seem to consist of obstructed breathing, whereas during the plain pattern the breathing is normal, unobstructed.

SIGNIFICANCE

Most screening methods for sleep-disordered breathing reveal only periodic apneas/hypopneas, but with the compressed sound signal the sustained partial obstruction can be estimated as well.

Acoustic analysis of upper airway obstruction in the excised human larynx

Upper airway obstruction is an emergency that requires quick and decisive intervention. Stridor is the sound created by airflow through a partially obstructed airway, and has been described to vary with the site and degree of obstruction. This study sought to determine the sound characteristics of stridor in the excised human larynx. Five fresh cadaver human larynges were harvested and subjected to obstructions at supraglottic, glottic, and subglottic subsites. Subglottic pressure, airflow, and audio signal were recorded. Data were analyzed on the basis of laryngeal obstruction subsite and the degree of laryngeal resistance. Visual inspection demonstrated certain trends in peak spectral energy depending on the site and, more significantly, the amount of obstruction. Statistical analysis of spectral waveforms showed better correlation with the amount of obstruction than with the site of obstruction. In summary, the frequency distribution of stridor produced in an excised human larynx was influenced by the amount of laryngeal resistance, but not by the site of airway obstruction.

Auscultation revisited: the waveform and spectral characteristics of breath sounds during general anesthesia

Although auscultation is commonly used as a continuous monitoring tool during anesthesia, the breath sounds of anesthetized patients have never been systematically studied. In this investigation we used digital audio technology to record and analyze the breath sounds of 14 healthy adult patients receiving general anesthesia with positive pressure ventilation. Sounds recorded from inside the esophagus were compared to those recorded from the surface of the chest, and corresponding airflow was measured with a pneumotachograph. The sound samples associated with inspiratory and expiratory phases were analyzed in the time domain (RMS amplitude) and frequency domain (peak frequency, spectral edge, and power ratios). There was a positive linear correlation (R2 > 0.9) between inspiratory flow and sound amplitude in the precordial and esophageal samples of all patients. The RMS amplitude of the inspiratory and expiratory sounds was approximately 13 times greater when recorded from inside the esophagus than from the surface of the chest in all patients at all flows (p < 0.001). The peak frequency (Hz) was significantly higher in the esophageal recordings than the precordial samples (298 +/- 9 vs 181 +/- 10, P < 0.0001), as was the 97% spectral edge (Hz) (740 +/- 7 vs 348 +/- 16, P < 0.0001). In the adult population esophageal stethoscopes yield higher frequencies and greater amplitude than precordial stethoscopes. Quantification of lung sounds may provide for improved monitoring and diagnostic capability during anesthesia and surgery.

Tracheal sound spectra depend on body height

Tracheal sounds originate from turbulent flow in upper and central airways. Turbulent flow characteristics are influenced by conduit dimensions. Because tracheal dimensions are a function of body height, we hypothesized that there should be a correlation between sound spectra and body length. We recorded tracheal sounds at standardized airflows in 21 healthy children 9.1 +/- 0.6 yr of age (mean +/- SE) and in 24 healthy adults 30.2 +/- 0.8 yr of age. A contact sensor was attached at the suprasternal notch of the sitting subject, and airflow was measured at the mouth with a calibrated pneumotachograph. Tracheal sounds were low-pass-filtered at 2.4 kHz and digitized at 10 kHz. A 2048 point FFT was applied at a successive 100-ms intervals, using a Hanning data window. Resulting spectra were normalized to a reference power of 0.1 (mV)2/5 Hz. We applied a gating algorithm to extract sounds at inspiratory flows of 1 L/s (+/- 10% tolerance), and we computed average power spectra from the collected samples. We calculated the average spectral power (Pavg), the quartile frequencies below which 25% (Q1), 50% (Q2), and 75% (Q3) of the power in the range of 50 to 2,000 Hz was contained, the spectral edge frequency (SE95) below which 95% of the power was found, and the frequency where spectral power rolled off sharply (Fcut).(ABSTRACT TRUNCATED AT 250 WORDS)

Tracheal sounds in upper airway obstruction

A boy with subglottic narrowing secondary to laryngotracheitis presented with noisy breathing. Acoustic measurements of tracheal sounds at standardized air flows correlated well with the clinical course and with spirometric assessments. This indicates the potential value of respiratory sound characterization in patients with upper airway obstruction.