User's Manual

1-8
Rad-87 Pulse CO-Oximeter Operator’s Manual
1
Rainbow Acoustic Monitoring
Rainbow Acoustic Monitoring is a real time, continuous, non-invasive method for measuring
respiration rate based on respiratory sounds. Respiratory sounds include sounds related to
respiration such as breath sounds (during inspiration and expiration), adventitious sounds, cough
sounds, snoring sounds, sneezing sounds, and sounds from the respiratory muscles [1]. These
respiratory sounds often have different characteristics depending on the location of recording [2]
and they originate in the large airways where air velocity and air turbulence induce vibration in the
airway wall. These vibrations are transmitted, for example, through the lung tissue, thoracic wall
and trachea to the surface where they may be heard with the aid of a stethoscope, a microphone
or more sophisticated devices.
Rainbow Acoustic Monitoring Architecture
The following figure illustrates how a respiratory sound produced by a patient can be turned into
a numerical measurement that corresponds to a respiratory parameter.
Patient Sensor
Acquisiton
System
Signal
Processing
Respiratory
Airflow to
Sound
Sound to
Electrical
Signal
Electrical
Signal to
Digital Signal
Digital Signal
to Respiratory
Measurement
Envelope
Detection
RRa
Estimation
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 and transmits 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. This is known as the ‘Piezoelectric effect’ in this manual. 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 electrical signal provided by the sensor into a digital signal.
This format allows the signal to be processed by a computing device.
Overview