A gravimetric plethysmograph and its evaluation in clinical use

Non-invasive measurement of limb and digit blood flow

There are many clinical applications for non-invasive measurements of limb and digit blood flow, but often plethysmographs are inconvenient to use. Most experimental work has been carried out on patients with vascular disease. The variation of blood flow with various environmental and physiological factors has been investigated. Little information is available on the effects of injury or surgical trauma on blood flow in limbs. Plethysmographic methods measure arterial flow or pulse volume by several techniques including volumetric displacement, electrical impedance, gravimetry and the mercury in rubber strain gauge. Calorimetric, Doppler and isotope clearance techniques have also been applied to the measurement of blood flow in digits. None of these methods fulfils all the criteria for the requirements of an ideal device and some are too complicated, uncomfortable or cumbersome for widespread use. The results from different techniques are compared and the reasons for variability are discussed. Possible mechanisms for the effects of trauma on limb blood flow are suggested. Experimental comparisons of different plethysmographs are described and the requirements for future development of these devices are defined.

The evaluation of blood flow measurement using gravimetric plethysmograph

The gravimetric plethysmograph is a simple, robust and inexpensive device which measures blood flow in the limb in terms of the increase in weight which follows temporary venous occlusion. Validation of the instrument using an artificial circuit shows that it is accurate and gives reproducible results.

The mean resting blood flow in the legs of 18 healthy volunteers was 3·95 ml 100 ml−1 tissue min−1 and this measurement was not reproducible. A 3-min period of arterial occlusion resulted in an immediate hyperaemic response of a mean 43·5 ml 100 ml−1 min−1, and this result was much more reproducible (r = 0·18).

The mean resting blood flow of 45 patients with occlusive arterial disease of the legs was 2·1 ml 100 ml−1 min−1, and this flow rate was variable (r = 0·71). Their immediate hyperaemic response of 5·18 ml 100 ml−1 min−1 was much less than that in normal volunteers, but was quite reproducible (r = 0·93). Following arterial reconstruction, their mean immediate hyperaemic response rose to 10·35 ml 100 ml−1 min−1, which was a significant increase compared to their preoperative values (P < 0·0005, Student's t test) and was associated with concomitant improvement in symptoms, treadmill performance and ankle/brachial systolic pressure indices. Measurement of the immediate hyperaemic response to temporary arterial occlusion with the gravimetric plethysmograph may assist in the evaluation of patients with occlusive arterial disease of the legs, and in their medical and surgical management.

Gravimetric plethysmography for measurement of blood flow in the leg

The gravimetric plethysmograph measures blood flow in the limb in terms of the increase in weight which follows temporary venous occlusion. Following validation of the device, blood flow in the leg was evaluated in normal subjects and in patients with intermittent claudication. Measurement of the immediate hyperaemic response to a three-minute period of arterial occlusion proved to be very reproducible in patients with occlusive arterial disease of the legs.