VENOUS TONE EVALUATION BY ELASTIC-MODULUS AND THERAPEUTIC IMPLICATIONS

The venous system plays an important role in the determination of card iac output and venous return. Venous tone is a property of the venous system which reflects the venous resistance and pressure. An increased Venous tone caused by venoconstriction leads to an increased net capi llary filtration by increasing the venous resistance and venous pressu re. Use of a phlebotonic agent to increase the Venous tone would prove useful in treating venodilation associated with worsening venous insu fficiency. Various methods have been used to investigate the venous to ne and these include: 1. isolated vein segment technique; 2. determina tion of the mean circulatory filling pressure; 3. constant cardiac out put-reservoir techniques; 4. venous occlusion plethysmography to asses s pressure-volume relationship. These methods have their inherent limi tations and their suitability for determining the effects of drugs on the venous tone is sometimes in doubt. Venous occlusion plethysmograph y using strain gauge plethysmography and measurement of venous pressur es with the aid of a needle inserted into a vein on the dorsum of the foot have been used to assess the function of the Vein wall by quantif ying the elastic modulus <<K>>. The elastic modulus is calculated from the change in pressure and the corresponding change in volume which a re measured from the linear high pressure part of the pressure volume curve. Results obtained using this method show a clear difference in e lasticity between normal limbs (K=17.24) and limbs with varicose veins (K=1.26) and deep venous incompetence (K=1.21). The limbs of normal i ndividuals that are at a high risk of developing varicose Veins have a n abnormal K(K=1.33). This method is however invasive and we have deve loped a non-invasive method of calculating the elastic modulus <<K>> u sing air plethysmography. This method has shown a good reproducibility in 3 healthy volunteers examined and this technique can be used to st udy the effect of a phlebotonic agent on the venous tone in patients a t high risk of developing venous insufficiency.