Volume tests for chronic venous insufficiency: an appraisal.

Chronic venous disease is increasingly treated surgically with a variety of experimental procedures. Noninvasive volume tests are commonly used before surgery to select patients and after surgery to assess results. Rapid volume changes are considered to indicate regurgitation. Rigorous statistical validation of tests and the confounding nature of unmeasured arterial inflow are seldom considered. Volume changes were measured in 29 control limbs and 35 limbs with venous disease, with mercury-in-silicone rubber strain gauges, for both exercise and elevation. Normalization for arterial flow permitted calculation of the regurgitation rate. Normal (95% confidence) limits for measured and calculated parameters were determined. Specificity was shown by the percent of normal parameter values for control limbs and sensitivity by the percent of abnormal values for extremities with venous disease. Arterial flow significantly altered volume curves. Normalization increased specificity and sensitivity significantly. Calf exercise tests, even normalized, were too insensitive to be reliable. Elevation tests were significantly more sensitive for determining regurgitation. However, exercise tests were useful and supplied important information about the calf muscle pump. We conclude that, as currently used, many limb volume test procedures are unsuitable but could be improved significantly by normalization to reduce the confounding effect of regional arterial flow and use of an elevation test to measure regurgitation.

Foot blood flow measurements improve venous plethysmographic studies.

The time for foot volume restoration after exercise is widely used as a measure of venous regurgitation. Since this is also a function of arterial inflow rate, we have tested the hypothesis that uncorrected for arterial inflow, these tests may be misleading. Change in venous foot volume after elevation and on exercise was measured in 44 subjects. Arterial inflow was also determined. In a few patients arterial flow was varied by cooling or by exercise. The times of half-volume restoration were measured. Calculated were: the rate of total blood flow into the foot; the rate of venous regurgitation; and "venous sufficiency indices" for elevation and for exercise with and without correction for arterial inflow rate. These indices combine volume and time data in a single numeric value. Volume change on elevation was uninfluenced by the rate of arterial inflow. Volume change on exercise and the halftime of volume restoration varied significantly with the rate of arterial inflow as did the "venous sufficiency indices." These variances were significantly reduced by correcting for arterial inflow rate. We conclude that for foot volume studies to measure regurgitation and for data obtained at different times to be comparable, corrections must be made for the rate of arterial inflow to the foot.

Noninvasive evaluation of chronic venous insufficiency. Use of foot mercury strain-gauge plethysmography.

Twenty-seven patients (40 extremities) with chronic venous insufficiency and 30 controls (60 extremities) were studied using noninvasive measurements of foot volume (foot mercury strain-gauge plethysmography [FMSGP]). Tests were performed with exercise (sitting) and with elevation (Trendelenburg), with and without tourniquets, to evaluate muscle pump efficiency and valvular competence. Empiric venous sufficiency indexes were calculated for exercise and for Trendelenburg's test. Test results were compared with invasive ambulatory venous pressure (AVP) data (13) and with ascending and retrograde venography (25). Distinctive plethysmographic patterns revealed the insufficiency was saphenous (four), calf perforators (14), saphenous plus perforators (seven), and deep venous (15), including occlusion (four). Correlation with AVP and venography was good but FMSGP was more discriminating, providing precise anatomical information, better reproducibility, and distinguishing poor muscle pump function from regurgitation. Patients accept FMSGP well. Repeated postoperative data are readily obtained for evaluation of surgical procedures.

Urinary osmolal changes in renal dysfunction following open-heart operations.

Forty consecutive patients who underwent open-heart procedures using a hyperosmolar perfusion prime were studied to determine the significance of free-water clearance and urinary osmolality early after bypass in predicting the likelihood of postoperative renal dysfunction, defined as a blood urea nitrogen (BUN) level over 50 mg/100 ml. Urinary osmolality increased in all patients during the first 18 hours after bypass, but the increase was substantially less for those who subsequently developed renal dysfunction. Free-water clearance, which was significantly less negative in the patients with renal dysfunction by 2 hours after bypass and remained so throughout the 18 hours of this study, served as an early postoperative indicator of impaired renal function in the patients who eventually developed BUN elevation. Moreover, it was more sensitive as an index of renal dysfunction than was osmolality alone. Early recognition of renal impairment is important, as it may prevent dangerous fluid overloading and allow for corrective measures to be undertaken before frank renal failure develops.

Functional changes in platelets during extracorporeal circulation.

An in vitro trauma test was conducted to determine the effects of extracorporeal circulation on platelet count and function. Fresh human blood was circulated in two identical in vitro circuits for six hours at a rate of 500 ml per minute (500 recirculations). One circuit included a G.E.--Peirce membrane lung and the other was a control. Platelet aggregation induced by adenosine diphosphate (ADP), epinephrine, or collagen was studied before and after six hours of perfusion. No important drop in platelet count occurred in the control circuit (Control-C) following bypass, but there was a 20% drop for the lung circuit (Lung-C). Platelet aggregation was reduced by about 30% for the control circuit and 65% for the lung circuit. The large decrease in platelet function accompanied by only a moderate decrease in platelet count is discussed in terms of loss of the youngest and most active platelets, platelet inhibition due to ADP released by red blood cell lysis, and platelet trauma.

Extracorporeal membrane oxygenation for massive pulmonary thromboembolism.

This study was undertaken to determine whether extracorporeal membrane oxygenation (ECMO) could modify the effects of massive lethal thromboembolism and prevent death. Twenty anesthetized dogs were prepared for venoarterial perfusion with a demand pump and membrane lung and were perfused slowly for 1 1/2 hours to lessen homologous blood shock; 1 ml per kilogram of 24-hour-old tantalum-impregnated thrombus was injected intravenously. The dogs had profound systemic hypotension with an elevated mean pulmonary artery pressure (62.9 +/-4.5 mm Hg) immediately after embolization. Control animals generally died within 15 minutes. Four of the 10 ECMO-supported animals lived for six days, at which time they were restudied and killed. Not only can ECMO maintain an animal that would otherwise die quickly of massive pulmonary thromboembolism, but such support, even though temporary, can greatly improve the chances of survival.

Clinical trials of a new polytetrafluoroethylene-silicone graft.

A self-sealing polytetrafluoroethelene (PTFE)-silicone graft designed to be used early after implantation was placed in 30 end-stage renal disease patients. Thirty-five conventional PTFE grafts were used in the control group. All patients were followed for 1 year. In the PTFE-silicone graft group, median time for first use was 1 day after implantation. Conventional PTFE grafts were first used 2 to 4 weeks after implantation. Early punctures of the PTFE-silicone grafts (first 10 sessions), although more difficult to perform than late punctures, were not more difficult than punctures of conventional PTFE grafts. Late punctures in PTFE-silicone grafts were easier than conventional PTFE graft punctures. Bleeding after needle removal was significantly decreased after early and late punctures of PTFE-silicone grafts compared with conventional PTFE grafts (p less than 0.001). The PTFE-silicone graft can be used immediately after implantation, sparing patients additional access procedures for short-term dialysis. This results in less morbidity, decreased bleeding complications, shorter hospital stay, and a significant reduction in expenses.

Arterial flow in venous volume studies.

The rate of venous refilling after exercise is commonly used in noninvasive exercise tests to assess chronic venous regurgitation. Volume refilling is the sum of venous regurgitation and arterial blood flow. Our hypothesis is that volume data do not accurately measure regurgitation unless blood flow is known. Foot volume data after exercise and elevation were obtained, using the mercury-in-silastic strain gauge, for 68 control and 131 extremities with venous disease. Measured values for the time of half-volume refilling were compared to values corrected for arterial flow. The arterial flow accounted for virtually half the volume change, but showed wide and unpredictable variations. Corrected times of half-volume refilling had significantly narrower variations and regurgitation was better estimated (p less than 0.001). For regurgitation to be comparable between patients or over time in venous volume tests, arterial flow must be determined.

Therapeutic implications of phlebographic obstruction in chronic venous stasis.

The purpose of this work was to evaluate the functional characteristics of the venous system of patients with chronic obstruction of their deep veins proved by phlebography. Sixty-eight extremities in 34 normal volunteers and 21 extremities in 17 patients with chronic venous stasis and phlebographically demonstrated obstruction of their deep veins (popliteal-superficial femoral in 33.3%, common femoral in 23.8%, iliac in 33.3% and inferior vena cava in 9.5%) were evaluated using mercury in silastic strain gauges on the feet to measure venous volume changes on elevation and exercise. Regurgitant flow, corrected for arterial foot blood flow, was calculated. In the control group, the apparent regurgitation range was 0 to 2.3 ml %/min (mean +/- 2 SD). Sixty-two percent of extremities with obstructed deep veins had significant functional regurgitation. Regurgitation was detected by phlebography in only 14.3% of cases. From these results we conclude that obstruction of the deep venous system by phlebography may or may not signify functional obstruction and, in itself, therefore, does not indicate that bypass surgery is an appropriate method of treatment. Selection for surgical correction requires quantitative determination of insufficiency since higher grades of regurgitation probably contraindicate venous bypass.

A practical method of differential hypothermia to permit use of a low pump oxygenator flow.

By cooling the blood just before returning it to the body, marked reduction in the temperature of the heart, brain, liver, and kidney can be produced easily and with great economy in heat transfer, since the great bulk of the animal or patient, consisting of skin, muscle, and bone, is cooled much more slowly. This results in a marked oxygen saving, due to the direct antimetabolic effect of the cooling. Metabolic acidosis can be avoided and so far no irreversible effects of the cooling have been discoverable. Warming is so greatly facilitated by the heat stored in the nonvital areas that it is not necessary to warm the blood returning from the extracorporeal circuit. The use of safe, low, extracorporeal flows offers a number of possible advantages including great simplicity of cannulation and of the pump oxygenator design and operation.

Pathophysiologic evaluation of chronic venous stasis with ambulatory venous pressure studies.

Seven normal controls and 51 lower extremities with venous insufficiency in 45 patients were studied with ambulatory venous pressure. Measurements were done at rest and during 15 seconds of exercise without a tourniquet and with 1 or 2 tourniquets at different levels of the extremity. The decrease in pressure during exercise and the time to return to standing levels were used to calculate a venous sufficiency index. Six pathologic categories were identified in patients with chronic venous stasis. Incompetence of perforators was present in 17 cases. A combination of long saphenous vein and perforator incompetence was detected in 10 cases. Thirteen cases had a pattern of regurgitant deep vein incompetence. Two cases had incompetence of the saphenous system. A deep vein obstruction pattern was present in 3 other patients. Ascending and retrograde phlebography was done in 30 of these cases. There was an 83.3% correlation between the venous pressure and phlebographic tests. Contrast studies were found to be complementary and added extra-anatomical information. Based on these special studies, a rational approach to the treatment of venous insufficiency has evolved. The early results are encouraging.