How does patient monitor measure RESP?

author: Myra | Engineer of International Sales | UTECH

2024-02-29

Respiratory monitoring methods

There are three methods for measuring respiration: impedance method, respiratory airflow method, and airway pressure method.

Respiration (RESP) measurement

1. Place white and red electrodes diagonally to obtain the best respiratory wave;
2. Respiratory rate is expressed in terms of the number of times the lungs inhale and exhale per minute;
3. When using ECG cables to extract respiratory waves, attention should be paid to the position of the electrodes on the chest;
4. Respiration signals will be interfered by ECG signals.

Respiration measurement principle

1.Impedance method

Most respiratory measurements in monitors use the impedance method. This method is based on the impedance changes caused by the rise and fall of the chest during the human body's breathing process to obtain the respiratory signal. This impedance change is 0.1-3Ω. The amplitude of the respiratory signal is only μV level. It uses a high-frequency carrier signal of 10-100kHz through the two electrodes of the ECG and is loaded into the chest of the human body in the form of a constant current source. The signal of the respiratory impedance change is picked up on the electrodes.

2. Breathing airflow method

A thermal sensor is used to sense exhaled hot airflow. Method: Place a respiratory airflow guide tube in the patient's nasal cavity. When the nasal airflow passes through the position of the thermal element, the thermistor is subject to heat exchange by the flowing airflow, and the temperature and resistance value change. When the nostril airflow periodically passes through the thermal When the thermistor is used, the thermistor value also changes periodically. According to this principle, by connecting the thermistor to an arm of the Wheatstone bridge, a periodically changing voltage signal can be obtained.

3. Airway pressure method

The piezoelectric sensor is placed in or connected to the airway, and the airway pressure "presses" the sensor to produce pressure changes, electrical signals, data processing, and respiratory rate display.

RESP measurement precautions

1. Respiratory monitoring is not suitable for patients with a large range of motion, because this may lead to false alarms;

2. The liver area and ventricle should be avoided on the connection line of the respiratory electrode, so as to avoid artifacts caused by heart coverage or pulsatile blood flow, which is especially important for newborns.

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