We assessed the performance of three air-coupled and four contact sensors beneath standardized conditions of lung hale recording.

We assessed the performance of three air-coupled and four contact sensors beneath standardized conditions of lung hale recording. Recordings were obtained from three of the investigators at the best site forward the posterior lower chest as determined according to auscultation. Lung sounds were band-pass filtered between 100 and 2000 Hz and sampled simultaneously with calibrated airflow at a rate of 10 kHz Fourier techniques were used for power spectral analysis. Average spectra for inspiratory goods at flows of 2 [+ or -]05 L/ were referenc against background noise at nothing flow. Aircoupled and contact sensors had comparable maximum signal-to-noise ratios and gave similar values for principally spectral parameters. Unexpectedly, less sensitivity (lower signal-to-noise ratio) at high frequencies was observ in the air-coupled devices. Sensor performance penurys to be characterized in studies of lung unimpaireds We suggest that lung perfect spectra should be averaged at known airflows above several breaths and that all measurements should be reported relative to hales recorded at zero flow.

(Chest 1993; 104:1518-5)

[F.sub.omega] = highest oftenness at which the lung unimpaired signal reaches background noise level

A coustical signals from the respiratory arrangement traditionally are assessed by subjective auscultation. During fresh years, there has been an increasing number of publications forward computer-assisted acquisition and analysis of these signals. Digital signal processing techniques have been shown to provide details onward respiratory sounds that surpass the limits of human auditory perception.

Studies upon the frequency content and distribution of normal respiratory healthys indicate a potential value for clinical application. During bronchial provocation for example, inspiratory goods are said to show an increase in median common occurrence that correlates with the station of airflow obstruction even in the absence of wheeze, the couple over the lung[1] and at the trachea.[2] Another application for respiratory acoustical measurements is in upper and central airway obstruction where a choke correlation between sound spectra and airway patency has been described in physical models[3] and also observ clinically[4]

Advances in microprocessor technology have accelerated the introduction of respiratory healthy analysis systems into clinical laboratories. Unfortunately, investigators around the world use various way s that differ from the choice of entire sensors, through the sampling and processing of uninjured signals, to the measurement and presentation of springs The need for standardization in this area lately has been emphasized.[5]

Microphones and other unmutilated sensors are fundamental parts in any recording of respiratory acoustical signals. Advantages and disadvantages of air-coupled - versus contact-type sensors previously have been described if it be not that not formally compared in actual recording of respiratory sounds[6] We, therefore, decided to evaluate the relative performance of a representative selection of sensors in situ. Also, the efficiency of different techniques for processing of the recorded respiratory unhurts was assessed, and suggestions of informative regularitys for presentation of the acoustical data were present forth.

controls and Methods

We used seven sensors that are representative of those commonly used for respiration acoustic studies (Table 1) Three of us serv as make submissives for the recording of lung unmutilateds after giving informed consent. The research protocol was approved by the Purdue University Committee forward the use of human subdues All three participants were healthy male nonsmokers, ranging in age from 24 to 47 years, in height from 166 to 183 cm and in weight from 62 to 83 kg None of the controls had a respiratory tract infection during the month before the study

[TABULAR DATA OMITTED]

The recording of lung perfects took place at the educate of Electrical Engineering, Purdue University. The enthralls sat in a soundproof chamber and breathed end a calibrated pneumotachograph while they observ the run signal on an oscilloseope. The target arise range was set at 2 [+ or -] 05 L/ The point of maximum hale intensity over the posterior lower chest was identified through auscultation before the experiment and marked for successive placement of the different sensors.

The sensors were attached to the skin with double-sided adhesive tape rings. Contact sensors were affixed directly while air-coupled sensors were first placed in coupling chambers. The plastic chamber for the Sony microphones weighed 33 g and had internal dimensions of 8-mm height and 10-mm diameter. External height was 18 mm and diameter, 20 mm The chamber cavity was spiracleed to ambient pressure by a lateral bore cavity The coupler for the Radio Shack microphone was a closed-cell foam disk, 8 mm in height and 31 mm in diameter, with a central lair of 5.5 mm in diameter for placement of the microphone. The Hewlett-Packard sensor was taped to the chest surface with standard masking tape. The recording site was kept the same for each enthrall throughout the study.

...