User's Manual

Radius-7 Chapter 1- Technology Overview
www.masimo.com 26 Masimo
Acoustic Sensor
The sensor captures respiratory sounds (and other biological sounds) much like a microphone
does. When subjected to a mechanical strain, (e.g., surface vibrations generated during
breathing), the sensor becomes electrically polarized.
The degree of polarization is proportional to the applied strain. The output of the sensor is an
electric signal that includes a sound signal that is modulated by inspiratory and expiratory
phases of the respiratory cycle.
Acquisition System
The acquisition system converts the electric signal provided by the sensor into a digital
signal. This format allows the signal to be processed by a computing device.
Signal Processing
The digital signal produced by the acquisition system is converted into a measurement that
corresponds to the respiratory parameter of interest. As shown in the previous figure, this can
be performed by, for example, determining the digital signal envelope or outline which in turn
may be utilized to determine the respiratory rate. In this way, a real-time, continuous breath
rate parameter can be obtained and displayed on a monitor which, in many cases, may be
real-time and continuous.
The respiratory cycle envelope signal processing principle is similar to methods that sample
airway gasses and subsequently determine a respiratory rate.
Citations
[1] A.R.A. Sovijärvi, F. Dalmasso, J. Vanderschool, L.P. Malmberg, G. Righini, S.A.T. Stoneman.
Definition of terms for applications of respiratory sounds. Eur Respir Rev 2000; 10:77,
597-610.
[2] Z. Moussavi. Fundamentals of respiratory sounds analysis. Synthesis lectures on
biomedical engineering #8. Morgan & Claypool Publishers, 2006.
[3] Olsen, et al. Mechanisms of lung sound generation. Semin Respir Med 1985; 6: 171-179.
[4] Pastercamp H, Kraman SS, Wodicka GR. Respiratory sounds – Advances beyond the
stethoscope. Am J Respir Crit Care Med 1977; 156: 974-987.
[5] Gavriely N, Cugell DW. Airflow effects on amplitude and spectral content of normal breath
sounds. J Appl Physiol 1996; 80: 5-13.
[6] Gavrieli N, Palti Y, Alroy G. Spectral characteristics of normal breath sounds. J Appl
Physiol 1981; 50: 307-314.