A pneumograph, also known as a pneumatograph or spirograph, is a device for recording velocity and force of chest movements during respiration, used in medical equipament to determine the respiration rate of a person.
There are various kinds of pneumographic devices, which have different principles of operation, the one that will be developed here is based on impedance measument. 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 (R = V/I). Current flows less easily through the chest as the lungs fill, so the resistance rises with increasing lung volume. (Taken from Wikipedia)
This is a unversity project and i decided to share it here. The aim is to create a cheap Pneumograph and send data to a PC to plot it in real time.
The basics structures of this project are shown bellow,
The first part of my work will be in the current source block. That block is important because it will inject the current in the patient to create the voltage that will be later measured by the rest of the circuit.
For the current source i have selected a topology called " Howland Current Pump". Its basically a OPAMP and a bunch of resistors/capacitors. I will be designing and testing this part of the circuit and as soon as i have some results, i will be posting them online.