Introduction
The Piezo-Electric Respiration (PZT) sensor is a popular entry-level respiration sensor applied in a variety of different applications in which respiration monitoring is required.
This post presents two recommended sensor positioning options, (a) thoracic and (b) abdominal (as presented in the following illustration below), both based on commonly used respiration monitoring methods. In addition, the impact of the positioning on the acquired raw signal is highlighted.
The signals presented in this post have been acquired using two PZT sensors simultaneously, with one measuring respiration around the thorax (position a) and one around the abdomen (position b). Note that the sensing strips of the respiration bands have been centered at the front of the thorax and abdomen.
Position A – Thoracic Respiration Monitoring
The thoracic-based method measures respiration by monitoring the changes in the volume of the thorax caused by the respiration mechanics (increase or decrease of the lungs’ volume). An example signal of such an acquisition is presented in the following plot where a maximum peak-to-peak volume of 0.6V can be measured.
Position B – Abdominal Respiration Monitoring
The abdominal-based method measures respiration by monitoring the changes in volume of the abdomen caused during the respiration cycles. An example signal of such an acquisition is presented in the following plot where a maximum peak-to-peak volume of 1.2V can be measured.
Comparison – Thoracic vs. Abdominal
It can be noted that the respiration signal acquired at the abdomen results in greater peak-to-peak amplitudes as compared to the thoracic results, with the first being twice as high in this experiment (thoracic: 0.6V vs. abdominal: 1.2V). A comparison is presented in the following plot figure.
Although both results provide reliable data as the respiration cycles are visible in both, the difference in peak-to-peak amplitudes can be of importance in applications where artifacts can be induced, such an in high motion activities.
In such cases, one can benefit from the advantages of greater peak-to-peak amplitudes as those are easier to extract from artifact induced data (for example, due to greater possibility of standing out from motion artifact distorted baselines) as compared to the thoracic respiration signal with smaller peak-to-peak artifacts.
