Strain Gauge Plethysmograph SGP

This device measures circumference of a selected limb segment. Circumference is related to segment cross-sectional area, and cross-sectional area multiplied by length is volume. In using SGP the following assumptions are made. First, blood volume is the only significant variable with time, and second, arterial blood volume change is small compared to venous blood volume changes.

The device is constructed using a small hollow elastic tube, mercury, and an electrical circuit capable of measuring voltage across the tubing length. The hollow flexible tube is filled with mercury, which conducts electricity well.

The tube containing the mercury is carefully placed around the limb segment of interest and connected to the electric circuit. The subject is asked to perform a series of maneuvers, and outputs from the device are recorded. The maneuvers and outputs are similar for all plethysmographs described in this chapter and are given later. As the limb segment circumference is changed secondary to venous blood volume, the length of elastic tube changes. The voltage is measured and displayed by the circuit. By measuring circumference as a function of time, venous blood volume as a function of time may be measured.7,8

This technique has a number of drawbacks. First, the instrumentation is difficult to construct. Second, the assumption that circumference measured over a very small slice of the limb segment represents volume change in the segment is often not true. Third, as in the case of IPG, the signal-to-noise-ratio is low. Along with IPG, this method is rarely used in contemporary clinical settings.

How To Deal With Rosacea and Eczema

How To Deal With Rosacea and Eczema

Rosacea and Eczema are two skin conditions that are fairly commonly found throughout the world. Each of them is characterized by different features, and can be both discomfiting as well as result in undesirable appearance features. In a nutshell, theyre problems that many would want to deal with.

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