STRAIN-GAUGE PLETHYSMOGRAPHY AND DOPPLER ULTRASOUND IN THE MEASUREMENT OF LIMB BLOOD-FLOW

The maintenance of adequate oxygen delivery (DO2) and tissue uptake (V O2) has become central dogma in the management of the critically ill. However, these parameters are derived using gas tensions measured in m ixed venous blood and may not reflect changes in regional blood flow. Therefore, it has become necessary to provide estimates of blood flow to specific organs and to evaluate the most adequate techniques availa ble. In order to define the best means of assessing blood flow to the lower limb noninvasively in normal subjects, measurements of superfici al femoral arterial blood flow using Doppler ultrasound (DU) and strai n gauge plethysmography (SGP) were compared in 10 normal volunteers at rest and during exercise. To evaluate the effect of strain gauge posi tioning, results of measurements made under four different combination s of cuff/strain gauge placement were compared in 15 other volunteers. The correlation of the limb blood how obtained using the two methods at rest and exercise was 0.57 and 0.62 and the limits of agreement (($ ) over bar d +/- 2SD) were 0.40 +/- 2.49 and - 0.86 +/- 5.22 ml 100 ml (-1) tissue min(-1) at rest and on exercise, respectively. Results obt ained using SCP were more reproducible (Coef. repeat. 0.45 vs. 0.94 ml 100 ml(-1) tissue min(-1), for SGP and DU, respectively). The various combinations of cuff/strain gauge positioning showed a tendency to ov er-read when the latter was placed on the thigh, but were not signific antly different (P > 0.05). Measurements of limb blood flow obtained u sing DU and SGP correlate poorly over a wide range of blood flow and d o not agree, the results from the latter being more reproducible. Alth ough the same position of cuff and strain gauge should be maintained t hroughout an experiment, varying the positions studied yields comparab le results.