Finger Plethsymograph to measure blood resistivity
Our goal is to design a finger plethysmograph to measure blood resistivity. In order to accomplish this, we will need to design and build a data acquisition device to acquire the signal from the finger. The device should mechanically immobilize the test subjects’ finger such that motion artifacts are kept to a minimum. This device should be able to detect the electrical potential (voltage) change across the finger so that the change in resistance may be determined. It should be able to detect the velocity-dependent change in blood resistivity due to arterial blood pulsations. In addition, we will need to build an electrical circuit to perform signal processing and analysis. This circuit should be capable of rectifying the alternating current (AC) signal from the finger data acquisition device and modulate it into a direct current (DC) signal to be analyzed. The circuit should be capable of discerning or visually displaying the voltage changes caused by correlated changes in blood resistivity. As an added feature, this circuit may contain an automatic reset function capable of adjusting one of the differential amplifier inputs to that of the output from the data acquisition (finger holder) device.
This will allow the device to easily accommodate fingers having different electrical resistances and will prevent having to manually adjust voltages using a potentiometer to match independences with each new test subject or finger position.