A pneumograph, also known as a pneumatograph or spirograph, is a device for recording velocity and force of chest movements during respiration. While spirometry measures respiratory rate and other markers of respiratory health via analysis of the airflow from the lungs during inhalation and exhalation, pneumography measures the respiratory rate via chest motion.
Principle of operation
There are various kinds of pneumographic devices, which have different principles of operation.
Mechanical
In one mechanism, a flexible rubber vessel is attached to the chest. The vessel is equipped with sensors such as
, piezoelectric sensors, or a fiber Bragg grating
to measure chest motion and obtain respiratory rate.
Electrical
Other mechanisms are impedance based. In these methods, a high-frequency (tens to hundreds of kHz), low-amplitude current is injected across the chest cavity. The voltage resulting from this current injection is measured and the resistance is derived from the application of Ohm's Law:
. Current flows less easily through the chest as the lungs fill, so the resistance rises with increasing lung volume.
[Grenvik et al., (1973). "Impedance Pneumography: Comparison between Chest Impedance Changes and Respiratory Volumes in II Healthy Volunteers", Chest, 62:439-443.]
External links
