Exercise Strain-Gauge Venous Plethysmography: Evaluation of a "New" Device for Assessing Lower Limb Venous Incompetence
Thom W. Rooke, M.D. J.L. Heser, B.S. and P.J. Osmundson, M.D.
ROCHESTER, MINNESOTA
Abstract be used to detect and assess venous incompetence in the lower extremities. The authors recently evaluated a new device designed for this purpose that uses strain gauges to determine changes in lower extremity circumference occurring with (and immediately after) exercise. The device plots a curve of volume against time for each limb and automatically calculates key values such as the volume of blood expelled from the lower limb veins during exercise and the time required for the veins to refill following exercise. The apparatus was incorporated into their noninvasive vascular laboratory and used (along with other standard tests) to study patients referred for suspected venous
Plethysmography
can
incompetence. They observed the following: (1) A shortened postexercise refilling time accurately identified limbs with venous incompetence. (2) The clinical severity of venous incompetence was inversely related to the refilling time. (3) Exerciseinduced changes in lower extremity volume correlated well with simultaneously determined changes in venous pressure. (4) Valvular incompetence could be localized to the deep or superficial veins based upon the improvement in refilling times seen following placement of elastic tourniquets around the lower limb. (5) The type of exercise performed (knee bends while the patient was standing versus ankle reflexes while sitting) had little effect on results. The authors conclude that exercise venous plethysmography is a useful noninvasive tool for assessing lower limb venous incompetence. From the Department of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, Rochester, Minnesota Presented at the 32nd Annual Meeting, International College of Angiology, Toronto, Canada, June, 1990.
219
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
220
FIG. 1. Attachment of strain gauges to lower limbs.
Introduction
incompetence is a common condition in patients referred laboratory. Unfortunately, the usual noninvasive methods used to identify and assess venous incompetence (such as clinical evaluation of venous emptying and refilling, continuous wave or color flow Doppler analysis of retrograde venous flow during the Valsalva maneuver, photoplethysmography, etc) are not always reliable. Problems may occur when one is attempting to: (1) document the presence of venous incompetence, (2) quantify the severity of venous incompetence, or (3) localize venous incompetence to the superficial or deep venous system. Improved vascular laboratory techniques for the evaluation of venous incompetence are clearly needed. We therefore evaluated the ability of a newly developed computerized strain-gauge plethysmographic device to diagnose, quantify, and localize lower limb venous valvular incompetence. Lower limb
venous
valvular
to the noninvasive vascular
Materials and Methods
Study subjects consisted of patients referred to the Mayo Clinic’s noninvasive vascular laboratory for evaluation of known or suspected venous incompetence. The principles of strain-gauge plethysmography have been previously described. 1,2 Briefly, mercury-in-
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
221
Silastic strain gauges were placed around the lower limbs just proximal to the ankle and the patient was instructed to stand quietly (Fig. 1). The plethysmographic device automatically determined when a stable baseline (ie, lower limb volume) had been reached; at that point the patient was instructed to begin exercise by performing deep knee bends. The number of knee bends and the rate at which they were performed were preselected, and the device automatically signaled the subject with a beeping sound each time a knee bend was to be performed. We elected to use an exercise protocol involving fifteen deep knee bends performed at a rate of one every two seconds. The exercise produced venous emptying and a subsequent drop in lower limb volume, which was recorded by the plethys-
mograph. Following exercise, the patient stood quietly while the veins refilled with blood and lower limb volume recovered. The time required (in seconds) for 50% (so) and 90% (T9o) refilling was automatically calculated, as was the volume required to refill the lower limb (refill volume or RV) (Fig. 2A). A &dquo;venous index&dquo; (RV x TSO) was also calculated by the
FIG. 2. Calculations of T5o, Tgo, and refill volume (or pressure change) when recovery required 60 seconds or less (A), or more than 60 seconds (B). These values were calculated automatically by the plethysmographic device or manually in the case of direct pressure measurements. The device provided a fourcolor printout of the volume recovery curve along with values for T 50, Too, and venous index.
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
222
device. In order to reduce testing time, the device was programmed to stop recording changes in volume after sixty seconds; calculations of Tso, T9o, RV, and the venous index were subsequently made by the device based upon the recovery in volume that had occurred up to that point (Fig. 2B). This programming modification was made with the assumption that recovery times greater than sixty seconds would reflect normal venous valvular competence. In some studies a 21-gauge needle was inserted into a dorsal foot vein and connected by fluid-filled tubing to a hydraulic strain gauge; this allowed changes in venous pressure to be measured along with the volume changes. The maximum exercise-induced venous pressure changes and postexercise pressure recovery times were calculated by using the same methods as for the volume calculations (Fig. 2).
FIG. 3. Values for T,o, T,~, refill volume, and venous index in normal limbs (n 40) and limbs with deep venous insufficiency documented by continuous-wave Doppler (n 40). In all cases the mean values for limbs with deep venous incompetence are significantly different from normal. =
=
Paired t tests, unpaired t tests, and linear regressions were performed as required by use of a standard computerized statistical package. Values of p < 0.05 were considered significant, and only significant differences are discussed. Results
Five separate studies were performed to evaluate the mography in the assessment of venous incompetence.
utility of exercise venous plethys-
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
223
Study 1-Correlation Between Plethysmographic and Continuous-Wave Doppler Findings Limbs with (n 40) and without (n 40) deep venous incompetence were studied by =
=
venous plethysmography, continuous-wave Doppler, and impedence Valvular incompetence was defined as the presence of significant, susplethysmography. tained venous flow reversal (as documented by continuous-wave Doppler) occurring at or distal to the superficial femoral vein in response to either the Valsalva maneuver or manual compression of the limb performed proximally to the site of Doppler examination. Limbs were excluded from analysis if significant varicose veins were present on clinical examination or if deep venous obstruction (as documented by a positive impedence plethysmogram) was noted; these exclusions were made to help eliminate confusion caused by patients with normal deep veins but incompetent superficial veins or by those with deep venous obstruction. The difference in T9o, Tso, RV, and venous index between limbs with and without deep venous insufficiency are shown in Figure 3. The T9o provided a perfect separation between normal and abnormal limbs, with all abnormal limbs having a T9o < twenty-five seconds and all normal limbs having a value > twenty-five seconds. Because a T9o cutoff value of twenty-five seconds appeared to be the best parameter for separating normal from abnormal limbs, it was used for all other analyses. means
of exercise
Study 2-Exercise-Induced Changes in Lower Limb Venous Pressure and Volume Exercise-induced changes in lower limb venous pressure (measured directly) and volume (measured with strain gauge plethysmography) were simultaneously determined in limbs with varying degrees of venous insufficiency (81 trials involving 28 limbs). Good correlations (Figs. 4A, B) were observed between the exercise-induced changes in pressure and volume (r = 0.83) and the postexercise T9o recovery times for pressure and volume 0.92). (r =
Study 3-Correlation Between Volume Recovery Time ~90) and the Clinical Severity of Venous Incompetence Eighty-six consecutive limbs with documented deep venous insufficiency were evaluated with exercise venous plethysmography, and the T9o volume recovery times were determined. These limbs were divided into four clinical categories based upon symptoms: asymptomatic, swelling only, venous stasis skin changes (ie, hemosideran pigmentation deposition, indurated cellulitis, other trophic changes, etc), and venous ulcerations. Although considerable overlap between groups existed, there was a definite trend toward lower T90s in limbs with more severe symptoms (Fig. 5).
Study 4-Localization (Superficial vs Deep) Venous Incompetence Sixty-three consecutive limbs with varicose veins were evaluated; 30 had no evidence of significant deep venous insufficiency by continuous-wave Doppler (ie, primary varicose veins) while in 33 there was Doppler evidence of significant deep venous insufficiency (ie, secondary varicose veins). The postexercise volume recovery times (T 90S) were similar in both groups (12.1 vs. 9.0 seconds, NS). After baseline measurements were made, elastic tourniquets were applied above and below the knee as needed to occlude flow through
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
224
FIG. 4. Correlation between (A) exercise-induced changes in venous pressure and ankle volume and (B) between the postexercise recovery times for venous pressure and ankle volume.
superficial veins; where perforator veins could be identified they were also manually compressed to prevent superficial venous reflux. Following tourniquet placement and/or manual compression of the perforating veins, the limbs with primary varicose veins had a marked improvement in T9o, while those with secondary varicose veins did not (Fig.
the
6A, B).
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
225
Fm. 5.
Relationship
between the clinical severity of
venous
insufficiency and T9o.
Study 5-Comparison between Different Types of Exercise®Deep Knee Bends
vs.
Dor-
sal Ankle Flexes Not all patients sent to the noninvasive vascular laboratory were able to perform deep knee bends, usually because of an orthopedic problem involving the hip or lower extremity. We therefore performed a limited trial to determine whether an alternate form of exercise could be used to assess venous incompetence. After the standard protocol involving deep knee bends was performed, patients (n 30 limbs) were seated in a chair with both feet flat on the floor. After a period of equilibration, the patients were instructed to dorsiflex their feet (15 flexes at two-second intervals) thus causing intermittent calf muscle compression. Postexercise recovery times for lower limb volume were recorded and compared with those obtained following deep knee bends (Fig. 7), and a good correlation (r = 0.85) was observed. =
Discussion The noninvasive vascular laboratory is frequently called upon to evaluate patients with lower limb venous incompetence. Unfortunately, all the standard methods currently employed by most laboratories for this purpose have distinct shortcomings. Continuous-wave Doppler’ can be used for the detection and diagnosis of deep venous incompetence in the major veins but is a poor method for quantifying the severity of the incompetence or for assessing incompetence in the superficial veins. Echo/Doppler duplex scanning&dquo;’ with or without color flow is a better technique than continuous-wave Doppler because it allows
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
226
FIG. 6. Effect of elastic
tourniquet application
on
limbs with
(A) primary and (B) secondary varicose veins.
the examiner to directly image the veins of interest prior to performing the Doppler study; direct imaging not only provides a more specific analysis of the affected deep vein(s) but also enables some of the larger superficial veins to be studied. It remains difficult, however, to determine the hemodynamic or functional significance of venous insufficiency by duplex scanning since the simple documentation of incompetence at any given level of the venous system does not necessarily imply that the incompetence is significant. For example, apparently severe incompetence in a given vein might be rendered hemodynamically and functionally insignificant by competent valves at proximal and/or distal sites. Alternatively, areas of venous valvular incompetence might appear relatively mild by Doppler or color flow assessment and yet be of considerable hemodynamic importance. The hemodynamic/functional significance of venous incompetence has traditionally been evaluated by the technique of direct lower extremity venous pressure measurement’ during and after exercise (such as walking, deep knee bends, etc). The drop in venous pressure occurring with exercise and the time required after exercise for venous pressure to return to baseline are the two measurements most frequently used to determine the hemodynamic/functional significance of venous incompetence. Unfortunately, this method is time consuming and relatively invasive. Noninvasive techniques such as foot volumetry’ and photoplethysmography’ have been used to detect and quantify venous insufficiency, although significant limitations exist with both of these. Strain-gauge plethysmographic devices have been used in the past to assess venous incompetence and have
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
227
FIG. 7. Postexercise recovery times (T9o) following deep knee bends and ankle dorsiflexions.
shown promise.9 More recently a new air plethysmographic device has been developed and evaluatedo,&dquo;; data obtained with its use suggest that exercise-induced changes in lower limb volume measured this way can be used to accurately quantify venous incompetence. This study evaluated a new plethysmographic device that uses mercury-in-Silastic strain gauges to measure exercise-induced changes in lower limb volume. It has two relative advantages over most other currently available plethysmographic devices: (1) both lower limbs can be studied simultaneously and (2) it is very easy to use and interpret, owing to a computerized system that (among other things) automatically measures, calculates, and prints out volume changes and recovery times. Its major theoretical disadvantage relative to devices such as the air plethysmograph is the fact that a strain gauge, which measures changes in the circumference of the lower limb at one site only, may be subject to sampling error that could lead to false conclusions. Fortunately, this did not prove to be a significant problem. We found that patients with deep venous incompetence (documented by continuous-wave Doppler) had consistently shorter volume recovery times than patients with normal veins. Because a T9o of twenty-five seconds provided the best separation between the two populations, we believe that this cutoff value should be used clinically. Alternatively, a Two cutoff of seven seconds also provided reasonably good separation. Other findings, such as the good correlation between exercise-induced plethysmographic and pressure changes, the inverse relationship between clinical disease severity and recovery time, the correction of superficial venous incompetence by use of elastic tourniquets, and the similarity of results obtained with use of different types of lower extremity exercise, all support the clinical validity and utility of this device as a means of assessing venous incompetence.
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
228
Conclusion Given the rising popularity of imaging modalities such as duplex scanning, it is fair to question whether purely functional tests such as venous plethysmography still have a role to play in the noninvasive assessment of venous disease. With regard to venous incompetence, the answer at this time appears to be yes. Exercise venous plethysmography provides an accurate, quick, and relatively inexpensive way to screen for and/or document venous incompetence. In addition, it yields quantitative information about the severity of venous insufficiency that cannot be readily obtained with other noninvasive methods. The selected use of exercise venous plethysmography should, therefore, be considered by any noninvasive vascular laboratory in which venous disease is routinely assessed.
Thom W. Rooke, M.D. Mayo Clinic 200 First St., S. W. Rochester, MN 55905
References 1. Sumner DS: Mercury strain-gauge plethysmography. In: Noninvasive Diagnostic Techniques in Vascular Disease, St. Louis: CV Mosby Company, 1985, pp
133-150. 2. Barnes RW, Collicott PE, Sumner DS, et al: Noninvasive quantitation of venous hemodynamics in the postphlebitic syndrome. Arch Surg 107:807-814, 1973. 3. Nicolaides A, Christopoulos D, Vasdekis S: Progress in the investigation of chronic venous insufficiency. Ann Vasc Surg 278-292, 1989. 4. Rooke TW, Martin RP: Lower extremity venous imaging for the echocardiologist. J Am Soc Echo 3:158-169, 1990. 5. Vasdekis SN, Clarke GH, Nicolaides AN: Quantification of venous reflux by means of duplex scanning. J Vasc Surg 10: 670-677. 1989. 6. Pollack AA, Taylor BE, Myers TT, et al: The effect of exercise and body position on the venous pressure at the ankle in patients having venous valvular defects. J Clin Invest 28:559-563, 1949.
7. Sumner DS: Foot volumetry. In: Noninvasive Diagnostic Techniques in Vascular Disease. St. Louis: CV Mosby Company, 1985, pp 828-833. 8. Rosfors A: Venous photoplethysmography: Relationship between transducer position and regional distribution of venous insufficiency. J Vasc Surg
11:436-440, 1990. 9. Sumner DS: Strain-gauge plethysmography. In: Noninvasive Diagnostic Techniques in Vascular Disease. St. Louis: CV Mosby Company, 1985, pp 742-754. 10. Christopoulos D, Nicolaides AN, Szendro G, et al: Air plethysmography and the effect of elastic compression on venous hemodynamics of the leg. J Vasc Surg 5:148-159, 1987. 11. Christopoulos D, Nicolaides AN, Cook A, et al: Pathogenesis of venous ulceration in relation to the calf muscle pump function. Surgery 106:829-835, 1989.
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
Thom W. Rooke, M.D. J.L. Heser, B.S. and P.J. Osmundson, M.D.
ROCHESTER, MINNESOTA
Abstract be used to detect and assess venous incompetence in the lower extremities. The authors recently evaluated a new device designed for this purpose that uses strain gauges to determine changes in lower extremity circumference occurring with (and immediately after) exercise. The device plots a curve of volume against time for each limb and automatically calculates key values such as the volume of blood expelled from the lower limb veins during exercise and the time required for the veins to refill following exercise. The apparatus was incorporated into their noninvasive vascular laboratory and used (along with other standard tests) to study patients referred for suspected venous
Plethysmography
can
incompetence. They observed the following: (1) A shortened postexercise refilling time accurately identified limbs with venous incompetence. (2) The clinical severity of venous incompetence was inversely related to the refilling time. (3) Exerciseinduced changes in lower extremity volume correlated well with simultaneously determined changes in venous pressure. (4) Valvular incompetence could be localized to the deep or superficial veins based upon the improvement in refilling times seen following placement of elastic tourniquets around the lower limb. (5) The type of exercise performed (knee bends while the patient was standing versus ankle reflexes while sitting) had little effect on results. The authors conclude that exercise venous plethysmography is a useful noninvasive tool for assessing lower limb venous incompetence. From the Department of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, Rochester, Minnesota Presented at the 32nd Annual Meeting, International College of Angiology, Toronto, Canada, June, 1990.
219
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
220
FIG. 1. Attachment of strain gauges to lower limbs.
Introduction
incompetence is a common condition in patients referred laboratory. Unfortunately, the usual noninvasive methods used to identify and assess venous incompetence (such as clinical evaluation of venous emptying and refilling, continuous wave or color flow Doppler analysis of retrograde venous flow during the Valsalva maneuver, photoplethysmography, etc) are not always reliable. Problems may occur when one is attempting to: (1) document the presence of venous incompetence, (2) quantify the severity of venous incompetence, or (3) localize venous incompetence to the superficial or deep venous system. Improved vascular laboratory techniques for the evaluation of venous incompetence are clearly needed. We therefore evaluated the ability of a newly developed computerized strain-gauge plethysmographic device to diagnose, quantify, and localize lower limb venous valvular incompetence. Lower limb
venous
valvular
to the noninvasive vascular
Materials and Methods
Study subjects consisted of patients referred to the Mayo Clinic’s noninvasive vascular laboratory for evaluation of known or suspected venous incompetence. The principles of strain-gauge plethysmography have been previously described. 1,2 Briefly, mercury-in-
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
221
Silastic strain gauges were placed around the lower limbs just proximal to the ankle and the patient was instructed to stand quietly (Fig. 1). The plethysmographic device automatically determined when a stable baseline (ie, lower limb volume) had been reached; at that point the patient was instructed to begin exercise by performing deep knee bends. The number of knee bends and the rate at which they were performed were preselected, and the device automatically signaled the subject with a beeping sound each time a knee bend was to be performed. We elected to use an exercise protocol involving fifteen deep knee bends performed at a rate of one every two seconds. The exercise produced venous emptying and a subsequent drop in lower limb volume, which was recorded by the plethys-
mograph. Following exercise, the patient stood quietly while the veins refilled with blood and lower limb volume recovered. The time required (in seconds) for 50% (so) and 90% (T9o) refilling was automatically calculated, as was the volume required to refill the lower limb (refill volume or RV) (Fig. 2A). A &dquo;venous index&dquo; (RV x TSO) was also calculated by the
FIG. 2. Calculations of T5o, Tgo, and refill volume (or pressure change) when recovery required 60 seconds or less (A), or more than 60 seconds (B). These values were calculated automatically by the plethysmographic device or manually in the case of direct pressure measurements. The device provided a fourcolor printout of the volume recovery curve along with values for T 50, Too, and venous index.
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
222
device. In order to reduce testing time, the device was programmed to stop recording changes in volume after sixty seconds; calculations of Tso, T9o, RV, and the venous index were subsequently made by the device based upon the recovery in volume that had occurred up to that point (Fig. 2B). This programming modification was made with the assumption that recovery times greater than sixty seconds would reflect normal venous valvular competence. In some studies a 21-gauge needle was inserted into a dorsal foot vein and connected by fluid-filled tubing to a hydraulic strain gauge; this allowed changes in venous pressure to be measured along with the volume changes. The maximum exercise-induced venous pressure changes and postexercise pressure recovery times were calculated by using the same methods as for the volume calculations (Fig. 2).
FIG. 3. Values for T,o, T,~, refill volume, and venous index in normal limbs (n 40) and limbs with deep venous insufficiency documented by continuous-wave Doppler (n 40). In all cases the mean values for limbs with deep venous incompetence are significantly different from normal. =
=
Paired t tests, unpaired t tests, and linear regressions were performed as required by use of a standard computerized statistical package. Values of p < 0.05 were considered significant, and only significant differences are discussed. Results
Five separate studies were performed to evaluate the mography in the assessment of venous incompetence.
utility of exercise venous plethys-
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
223
Study 1-Correlation Between Plethysmographic and Continuous-Wave Doppler Findings Limbs with (n 40) and without (n 40) deep venous incompetence were studied by =
=
venous plethysmography, continuous-wave Doppler, and impedence Valvular incompetence was defined as the presence of significant, susplethysmography. tained venous flow reversal (as documented by continuous-wave Doppler) occurring at or distal to the superficial femoral vein in response to either the Valsalva maneuver or manual compression of the limb performed proximally to the site of Doppler examination. Limbs were excluded from analysis if significant varicose veins were present on clinical examination or if deep venous obstruction (as documented by a positive impedence plethysmogram) was noted; these exclusions were made to help eliminate confusion caused by patients with normal deep veins but incompetent superficial veins or by those with deep venous obstruction. The difference in T9o, Tso, RV, and venous index between limbs with and without deep venous insufficiency are shown in Figure 3. The T9o provided a perfect separation between normal and abnormal limbs, with all abnormal limbs having a T9o < twenty-five seconds and all normal limbs having a value > twenty-five seconds. Because a T9o cutoff value of twenty-five seconds appeared to be the best parameter for separating normal from abnormal limbs, it was used for all other analyses. means
of exercise
Study 2-Exercise-Induced Changes in Lower Limb Venous Pressure and Volume Exercise-induced changes in lower limb venous pressure (measured directly) and volume (measured with strain gauge plethysmography) were simultaneously determined in limbs with varying degrees of venous insufficiency (81 trials involving 28 limbs). Good correlations (Figs. 4A, B) were observed between the exercise-induced changes in pressure and volume (r = 0.83) and the postexercise T9o recovery times for pressure and volume 0.92). (r =
Study 3-Correlation Between Volume Recovery Time ~90) and the Clinical Severity of Venous Incompetence Eighty-six consecutive limbs with documented deep venous insufficiency were evaluated with exercise venous plethysmography, and the T9o volume recovery times were determined. These limbs were divided into four clinical categories based upon symptoms: asymptomatic, swelling only, venous stasis skin changes (ie, hemosideran pigmentation deposition, indurated cellulitis, other trophic changes, etc), and venous ulcerations. Although considerable overlap between groups existed, there was a definite trend toward lower T90s in limbs with more severe symptoms (Fig. 5).
Study 4-Localization (Superficial vs Deep) Venous Incompetence Sixty-three consecutive limbs with varicose veins were evaluated; 30 had no evidence of significant deep venous insufficiency by continuous-wave Doppler (ie, primary varicose veins) while in 33 there was Doppler evidence of significant deep venous insufficiency (ie, secondary varicose veins). The postexercise volume recovery times (T 90S) were similar in both groups (12.1 vs. 9.0 seconds, NS). After baseline measurements were made, elastic tourniquets were applied above and below the knee as needed to occlude flow through
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
224
FIG. 4. Correlation between (A) exercise-induced changes in venous pressure and ankle volume and (B) between the postexercise recovery times for venous pressure and ankle volume.
superficial veins; where perforator veins could be identified they were also manually compressed to prevent superficial venous reflux. Following tourniquet placement and/or manual compression of the perforating veins, the limbs with primary varicose veins had a marked improvement in T9o, while those with secondary varicose veins did not (Fig.
the
6A, B).
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
225
Fm. 5.
Relationship
between the clinical severity of
venous
insufficiency and T9o.
Study 5-Comparison between Different Types of Exercise®Deep Knee Bends
vs.
Dor-
sal Ankle Flexes Not all patients sent to the noninvasive vascular laboratory were able to perform deep knee bends, usually because of an orthopedic problem involving the hip or lower extremity. We therefore performed a limited trial to determine whether an alternate form of exercise could be used to assess venous incompetence. After the standard protocol involving deep knee bends was performed, patients (n 30 limbs) were seated in a chair with both feet flat on the floor. After a period of equilibration, the patients were instructed to dorsiflex their feet (15 flexes at two-second intervals) thus causing intermittent calf muscle compression. Postexercise recovery times for lower limb volume were recorded and compared with those obtained following deep knee bends (Fig. 7), and a good correlation (r = 0.85) was observed. =
Discussion The noninvasive vascular laboratory is frequently called upon to evaluate patients with lower limb venous incompetence. Unfortunately, all the standard methods currently employed by most laboratories for this purpose have distinct shortcomings. Continuous-wave Doppler’ can be used for the detection and diagnosis of deep venous incompetence in the major veins but is a poor method for quantifying the severity of the incompetence or for assessing incompetence in the superficial veins. Echo/Doppler duplex scanning&dquo;’ with or without color flow is a better technique than continuous-wave Doppler because it allows
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
226
FIG. 6. Effect of elastic
tourniquet application
on
limbs with
(A) primary and (B) secondary varicose veins.
the examiner to directly image the veins of interest prior to performing the Doppler study; direct imaging not only provides a more specific analysis of the affected deep vein(s) but also enables some of the larger superficial veins to be studied. It remains difficult, however, to determine the hemodynamic or functional significance of venous insufficiency by duplex scanning since the simple documentation of incompetence at any given level of the venous system does not necessarily imply that the incompetence is significant. For example, apparently severe incompetence in a given vein might be rendered hemodynamically and functionally insignificant by competent valves at proximal and/or distal sites. Alternatively, areas of venous valvular incompetence might appear relatively mild by Doppler or color flow assessment and yet be of considerable hemodynamic importance. The hemodynamic/functional significance of venous incompetence has traditionally been evaluated by the technique of direct lower extremity venous pressure measurement’ during and after exercise (such as walking, deep knee bends, etc). The drop in venous pressure occurring with exercise and the time required after exercise for venous pressure to return to baseline are the two measurements most frequently used to determine the hemodynamic/functional significance of venous incompetence. Unfortunately, this method is time consuming and relatively invasive. Noninvasive techniques such as foot volumetry’ and photoplethysmography’ have been used to detect and quantify venous insufficiency, although significant limitations exist with both of these. Strain-gauge plethysmographic devices have been used in the past to assess venous incompetence and have
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
227
FIG. 7. Postexercise recovery times (T9o) following deep knee bends and ankle dorsiflexions.
shown promise.9 More recently a new air plethysmographic device has been developed and evaluatedo,&dquo;; data obtained with its use suggest that exercise-induced changes in lower limb volume measured this way can be used to accurately quantify venous incompetence. This study evaluated a new plethysmographic device that uses mercury-in-Silastic strain gauges to measure exercise-induced changes in lower limb volume. It has two relative advantages over most other currently available plethysmographic devices: (1) both lower limbs can be studied simultaneously and (2) it is very easy to use and interpret, owing to a computerized system that (among other things) automatically measures, calculates, and prints out volume changes and recovery times. Its major theoretical disadvantage relative to devices such as the air plethysmograph is the fact that a strain gauge, which measures changes in the circumference of the lower limb at one site only, may be subject to sampling error that could lead to false conclusions. Fortunately, this did not prove to be a significant problem. We found that patients with deep venous incompetence (documented by continuous-wave Doppler) had consistently shorter volume recovery times than patients with normal veins. Because a T9o of twenty-five seconds provided the best separation between the two populations, we believe that this cutoff value should be used clinically. Alternatively, a Two cutoff of seven seconds also provided reasonably good separation. Other findings, such as the good correlation between exercise-induced plethysmographic and pressure changes, the inverse relationship between clinical disease severity and recovery time, the correction of superficial venous incompetence by use of elastic tourniquets, and the similarity of results obtained with use of different types of lower extremity exercise, all support the clinical validity and utility of this device as a means of assessing venous incompetence.
Downloaded from ang.sagepub.com at BRIGHAM YOUNG UNIV on May 19, 2015
228
Conclusion Given the rising popularity of imaging modalities such as duplex scanning, it is fair to question whether purely functional tests such as venous plethysmography still have a role to play in the noninvasive assessment of venous disease. With regard to venous incompetence, the answer at this time appears to be yes. Exercise venous plethysmography provides an accurate, quick, and relatively inexpensive way to screen for and/or document venous incompetence. In addition, it yields quantitative information about the severity of venous insufficiency that cannot be readily obtained with other noninvasive methods. The selected use of exercise venous plethysmography should, therefore, be considered by any noninvasive vascular laboratory in which venous disease is routinely assessed.
Thom W. Rooke, M.D. Mayo Clinic 200 First St., S. W. Rochester, MN 55905
References 1. Sumner DS: Mercury strain-gauge plethysmography. In: Noninvasive Diagnostic Techniques in Vascular Disease, St. Louis: CV Mosby Company, 1985, pp
133-150. 2. Barnes RW, Collicott PE, Sumner DS, et al: Noninvasive quantitation of venous hemodynamics in the postphlebitic syndrome. Arch Surg 107:807-814, 1973. 3. Nicolaides A, Christopoulos D, Vasdekis S: Progress in the investigation of chronic venous insufficiency. Ann Vasc Surg 278-292, 1989. 4. Rooke TW, Martin RP: Lower extremity venous imaging for the echocardiologist. J Am Soc Echo 3:158-169, 1990. 5. Vasdekis SN, Clarke GH, Nicolaides AN: Quantification of venous reflux by means of duplex scanning. J Vasc Surg 10: 670-677. 1989. 6. Pollack AA, Taylor BE, Myers TT, et al: The effect of exercise and body position on the venous pressure at the ankle in patients having venous valvular defects. J Clin Invest 28:559-563, 1949.
7. Sumner DS: Foot volumetry. In: Noninvasive Diagnostic Techniques in Vascular Disease. St. Louis: CV Mosby Company, 1985, pp 828-833. 8. Rosfors A: Venous photoplethysmography: Relationship between transducer position and regional distribution of venous insufficiency. J Vasc Surg
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