A pneumograph, also known as a pneumatograph or spirograph, is a device for recording

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

and force of chest movements during

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

. While

spirometry Spirometry (meaning ''the measuring of breath'') is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is h ...

measures

respiratory rate The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute. Measurement The respiratory rate in humans is mea ...

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

accelerometer An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...

piezoelectric sensor A piezoelectric sensor is a device that uses the piezoelectric effect to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. The prefix ''piezo-'' is Greek for 'press' or 'squeeze ...

s, or a

fiber Bragg grating A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in th ...

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 Ohm's law states that the electric current through a Electrical conductor, conductor between two Node (circuits), points is directly Proportionality (mathematics), proportional to the voltage across the two points. Introducing the constant of ...

Z = \frac

. 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.

References

External links

Detailed article on pneumography (1905)

Measuring volume and flow
{{Respiratory system procedures Respiratory system procedures Respiratory therapy Medical testing equipment Impedance pneumography Impedance pneumography