Pulse Plethysmograph (PPG)

As the human or mammal heart beats, a fresh 'shot' of blood is pumped into body tissue. The elastic properties of the tissue result in that blood then flowing out of that tissue, a little more slowly. This sharp ascent followed by the slower elastic decay is referred to as the Pulse Plethysmograph signal, or PPG. The PPG signal reflects the cyclical enlargement then shrinking of that tissue as a result of the beating of the heart.

There are a number of ways to sense the PPG. The increase then decrease in the size of the tissue can be detected by the model 1010. This piezo-electric PPG transducer is about the simplest way possible to see what the heart is doing. In addition, the tissue will also exhibit subtle changes in the reflectivity and transmission of light as blood is pumped in (increasing the light that is transmitted) and then flows out (decreasing the light that is transmitted). The model 1020 takes this approach, using infra-red light so as to minimize sensitivity to ambient light. And our THRIM system supplies the PPG signal, sensed as the change in impedance as blood is pumped in (dropping the impedance), then flows out (which increases the impedance).

The PPG phenomenon, and the signals that can be sensed from it, do have shortcomings. The main concern is subject motion, which can easily cause motion of the blood within the tissue being sensed, causing artifacts and in some cases overwhelming the PPG signal. Also, both breathing and ambient temperature can have a sometimes substantial effect on the size of the PPG and associated signals, especially whan you are looking at 'extremity' (hands, for example) locations.

Still, the PPG can be useful. At the very least, the PPG signal can supply the subject's heart rate. Both the 1010 and 1020 supply this sensing solution in a very unintrusive manner. And if you place the PPG transducer at a peripheral location (fingers), and have access to the ECG as well, you can calculate the Pulse Transit Time, the time from the R wave to the ascent of the PPG pulse.

For both the 1010 and 1020, we can also supply a 2121 9V battery powered portable amplifier configured to provide a high-level signal from the 1010 or 1020, for connection to your existing data collection system. The 1010 or 1020 are also easily interfaced to our SC2000 Simple Scope. We can also add a connector to the 1010 or 1020 to provide direct plug-in for many available signal conditioners.

The 3991 and 3992 Biolog platforms are excellent choices for ambulatory recording of the PPG signal. These recorders allows other signals to be recorded along with the PPG should this be desired.

The PPG can be included as a measure in our Multi-Subject Data Collection System installations.

If you still have questions, or if you don't see what you need, drop us a line, and we will see how we can help you!