Digital Blood Flow I. Correlative Study of the Electrical Impedance and the Venous Occlusive Plethysmographs * *From the Cardiopulmonary Laboratory, Department of Internal Medicine, University of Texas Southwestern Medical School. This work was supported by a grant from the American Heart Association

The effect of therapeutic modalities on blood flow in the human calf

Presented at the Sports Physical Therapy Section Team Concept Meeting, December 1990, Orlando, FL. Local blood flow to the calf of human subjects during the application of therapeutic modalities was estimated using impedance plethysmography. The modalities compared included ice massage, ice pack, ultrasound, hot pack, ice massage and ultrasound, and hot pack and ultrasound. It was found that neither ice pack nor ice massage significantly decreased blood flow compared to the control. The hot pack caused a significant increase in blood flow during application. Ultrasound was found to significantly increase blood flow up to 45 minutes following application. The use of hot packs prior to the ultrasound treatment did not significantly enhance the effect of ultrasound. It was concluded that neither ice massage nor ice pack treatments would decrease blood flow. Ultrasound may be beneficial in increasing blood flow during rehabilitation. Treatment with a modality prior to ultrasound will not enhance the effect on blood flow. J Orthop Sports Phys Ther 1991;13(1):23-27.

Measurement of digital blood flow using the laser Doppler, impedance and strain-gauge methods

Digital volume changes and blood flow have been measured with impedance and strain-gauge plethysmography as well as with laser Doppler flowmetry. A good agreement was found between the impedance and strain-gauge flow measurements with a correlation coefficient of 0.905. The laser Doppler method recorded minor changes in finger skin blood flow following changes in posture from 30 cm below heart level to 60 cm above heart level. This result can be explained as a consequence of the limited penetration depth of laser light into the skin or as a sign of autoregulation of skin blood flow. In these experiments the total blood flow to the finger underwent major changes.

Measurement of pulsatile limb and finger blood flow by electrical impedance plethysmography: criteria for the diagnosis of abnormal flow

The range of pulsatile arm and finger blood flow, measured by electrical impedance plethysmography, has been investigated in a hospital ward. The range of absolute blood flows, in ml min-1, was found to be too wide to be used as a standard for identifying single blood flow readings as being abnormal. A blood flow ratio was calculated by dividing the blood flow in the right forearm or middle finger by the blood flow in the left forearm or middle finger. This ratio was found to have a clearly defined range. A blood flow in a unilaterally injured or otherwise abnormal arm or finger was considered to be significantly altered if the blood flow ratio fell outside the previously defined normal range. The diagnosis of significantly altered arm and finger blood flow from abnormalities in the blood flow ratio was tested in a series of experiments, in which artificial changes in upper limb flow were created by high elevation of the right hand. The ratio was measured in 11 patients with unilateral upper limb injuries and in 3 patients who required an urgent assessment of the upper limb circulation. Abnormalities in the ratio were identified in 12 out of 18 subjects after high elevation of the hand and in 8 out of the 14 patients.

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.