Operator's Manual

Rad-97 Chapter 1: Technology Overview
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Patient Sensor Acquisition
System
Respiratory airflow to sound Sound to
electrical signal
Electrical signal to
digital signal
Signal
Processing
Envelope
Detection
RRa Estimation
Digital signal to respiratory
measurement
Patient
The generation of respiratory sounds is primarily related to turbulent respiratory airflow in
upper airways. Sound pressure waves within the airway gas and airway wall motion contribute
to the vibrations that reach the body surface and are recorded as respiratory sounds.
Although the spectral shape of respiratory sounds varies widely from person to person, it is
often reproducible within the same person, likely reflecting the strong influence of individual
airway anatomy [2-6].
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.