Long-term intermittent compression increases arteriographic collaterals in a rabbit model of femoral artery occlusion.

OBJECTIVES: To assess the effects of intermittent limb compression on arterial collateral formation in a rabbit-model. DESIGN: Animal study. MATERIAL AND METHODS: New Zealand rabbits (n=11), aged 2-years, weight of at least 4.0 kg, underwent bilateral superficial femoral artery ligation. In ten of these, the experimental leg underwent 60 minutes of daily intermittent compression for a ten week period with 3 sec/90 mmHg pressure inflation and a cycle of 3 times per minute. The contra-lateral limbs were not treated. At the end of the ten-week period, high-resolution angiograms were obtained by barium infusion into the aorta. The angiograms were analyzed in a blinded manner and the number of collateral arteries larger than 100 microns, was counted. Following perfusion-fixation, histological specimens of transverse sections of the compressed semi-membranous muscle were examined. RESULTS: The compressed limbs demonstrated a significantly (8.1+/-.87 vs 6.0+/-.97; p<0.005) greater number of collateral vessels, ranging in size from 100-700 microns, as compared to the control sides. The mean size of collaterals in the compressed limbs was not significantly different (0.33+/-0.17 vs 0.31+/-0.16). Microscopic examination of the collaterals confirmed remodeling by a typical neo-intima consisting of 6-7 cell-layers. CONCLUSIONS: Intermittent limb compression increases the number of angiographical collateral arteries.

Limb salvage using high-pressure intermittent compression arterial assist device in cases unsuitable for surgical revascularization.

HYPOTHESIS: Intermittent compression therapy for patients with inoperable chronic critical ischemia with rest pain or tissue loss may have beneficial clinical and hemodynamic effects. STUDY DESIGN: Case series of 14 consecutive ischemic legs that underwent application of a 3-month treatment protocol during a 2(1/2)-year study. SETTING: Veterans Administration Hospital. PATIENTS: Thirteen patients with 14 critically ischemic legs (rest pain, n = 14; tissue loss, n = 13) who were not candidates for surgical reconstruction were treated with rapid high-pressure intermittent compression. The patients had a mean age of 76.2 years, 8 were diabetic, and they represented 10% of referrals for chronic critical ischemia. They were not amenable to revascularization owing to lack of outflow arteries (n = 7), lack of autogenous vein (n = 5), or poor general medical condition (n = 3). INTERVENTION: All patients were instructed to use the arterial assist device for 4 hours a day at home for a 3-month period. MAIN OUTCOME MEASURES: Limb salvage and calibrated pulse volume amplitude. RESULTS: After 3 months, 9 legs had a significant increase in pulse-volume amplitude (P< .05). These legs were salvaged, whereas the 4 amputated legs demonstrated no hemodynamic improvement. We noted a direct correlation between patient compliance and clinical outcome. Patients in whom limb salvage was achieved used their compression device for longer periods of time (mean time, 2.38 hours a day) compared with those who underwent amputation (mean time, 1.14 hours a day) (P< .05). These mean hours of use were derived from an hour counter built into the compression units. CONCLUSIONS: Intermittent high-pressure compression may allow limb salvage in patients with limb-threatening ischemia who are not candidates for revascularization. Further studies are warranted to assess intermittent compression as an alternative to amputation in an increasingly older patient population.

Rapid intermittent compression increases skin circulation in chronically ischemic legs with infra-popliteal arterial obstruction.

BACKGROUND: Intermittent pneumatic compression (IPC) has been shown, by duplex, to increase popliteal artery flow in normal legs and in legs with superficial femoral artery occlusion. The objective of this study was to see if IPC improves distal circulation in legs with severe infra-popliteal disease. PATIENTS AND METHODS: Sixteen chronically ischemic legs with arteriographically demonstrated crural or pedal disease were studied during compression with an ArtAssist compression-device. This device delivers rapid compression of the foot and calf. Cutaneous laser-Doppler flux was measured continuously at the dorsal aspect of the distal forefoot. The findings were compared to those in thirteen normal controls of similar age. RESULTS: In ischemic legs, the spontaneous changes in skin-flux are minimal: mean resting flux in sitting position was 0.87 +/- 0.46 AU (Arbitrary Units). Upon activation of the compression device the maximum flux increased to 4.55 +/- 1.35 AU. The difference was statistically significant (p < 0.001). This response was similar to that in normal controls. CONCLUSION: Arterial flow augmentation upon compression is associated with increased skin-flux. This response remains present in severe disease of the crural outflow-arteries. Further investigation to define the role of intermittent compression for management of chronic arterial disease is warranted.

The development of valvular incompetence after deep vein thrombosis: a follow-up study with duplex scanning.

PURPOSE: Duplex ultrasonography with distal cuff deflation was used to establish the physiologic reflux duration in different segments of the deep venous system in healthy individuals, and to document the occurrence of deep vein valve incompetence in patients after deep vein thrombosis (DVT). METHODS: Two hundred fifty-two vein segments in 42 legs of 21 healthy individuals and 160 deep vein segments in 27 patients with phlebographically documented DVT were examined with duplex scanning. RESULTS: The duration of reflux in healthy subjects was significantly shorter in distal deep vein segments. Ninety-five percent of the values were less than 0.88, 0.8, 0.8, 0.28, 0.2, and 0.12 seconds, respectively, for the common femoral, superficial femoral, deep femoral, popliteal, and posterior tibial vein (at midcalf and ankle level). The 95 percentile for reflux duration in the superficial venous system was 0.5 seconds for all vein segments, regardless of the location. No significant correlation was found between the reflux peak flow velocity and reflux duration (R = 0.6). The reflux peak flow velocity is therefore not useful as a parameter of the degree of reflux. The patient group was examined with an interval of 18 to 51 months (mean 34 months) after DVT. Forty-five percent of the initially affected segments showed valve incompetence at follow-up (n = 54); only three of 40 segments initially free from thrombus showed pathologic reflux at follow-up (p < 0.01). Reflux durations in most of the incompetent vein segments were two or more times the normal value of reflux duration. The highest prevalence of valve incompetence was found in the superficial femoral and popliteal vein segment (p < 0.01). None of the patients showed valve incompetence at all levels of the deep venous system. A significant (p = 0.04) relation was found between the extent of the initial thrombosis and the number of refluxing vein segments at follow-up, but no correlation was found between the extent of initial thrombosis and the late clinical symptoms (p = 0.16); clinical symptoms could not be related to the number of incompetent vein segments. CONCLUSIONS: Duplex scanning allows a good discrimination between physiologic and abnormal reflux duration and is an important tool in the evaluation of the postthrombotic limb. Early assessment after DVT may have prognostic value in individual patients.

Augmentation of blood flow in limbs with occlusive arterial disease by intermittent calf compression.

PURPOSE: This study was designed to investigate the effect of intermittent calf compression on popliteal arterial blood flow and to see how flow is influenced by position of the subject and by arterial blood pressure at the ankle. METHODS: Volume flow in the popliteal artery of subjects in the sitting and prone positions was measured with duplex ultrasonography before inflation and immediately after deflation of a pneumatic cuff placed around the calf. Eleven legs of control subjects and 41 legs of patients with symptoms (32% patients with diabetes) with decreased ankle pressure were studied. Cuffs were inflated for 2 seconds at pressures ranging from 20 to 120 mm Hg. RESULTS: An increase in arterial blood flow of two to eight times (mean 4.4 +/- 2.0) was found on deflation of the cuff in seated control subjects. Little change in flow was observed when the subjects were in the prone position. In seated patients with arterial obstruction, the mean increase in arterial flow was 3.2 +/- 1.6 times the resting flow. Little correlation was found between the maximum increase in flow and the ankle/brachial index. CONCLUSIONS: An increased arteriovenous pressure gradient accounts for some but not all of the flow increase, much of which must be attributable to transient vasodilatation. Because the increase in flow does not depend on an increased inflow pressure and was not adversely affected by a low resting ankle-brachial pressure index or a low toe-pressure, intermittent external limb compression may deserve investigation as a possible adjunct to the nonoperative treatment of patients with severe arterial insufficiency.

Color-flow duplex scanning of carotid arteries: new velocity criteria based on receiver operator characteristic analysis for threshold stenoses used in the symptomatic and asymptomatic carotid trials.

PURPOSE: Duplex scanning has become the standard for noninvasive evaluation of carotid arteries. However, current ultrasound criteria for internal carotid artery (ICA) stenosis (16% to 49%, 50% to 79%, 80% to 99%) may not be applicable to the categories (30% to 49%, 50% to 69%, 70% to 99%) used in ongoing symptomatic and asymptomatic carotid endarterectomy trials. This study was undertaken to determine new velocity criteria consistent with these categories. METHODS: From January 1, 1989 through October 30, 1992, 5871 color-flow duplex scans were obtained in our laboratories. After inadequate arteriograms and patients with a contralateral ICA occlusion were excluded, 770 peak systolic velocity (PSV) and 229 end-diastolic velocity (EDV) measurements were available for comparison with arteriography. ICA PSV and EDV were subjected to receiver operator characteristic curve analysis to determine optimum criteria for identifying stenoses of 30%, 50%, and 70%. RESULTS: For 70% to 99% carotid artery stenosis, PSV greater than 130 plus EDV greater than 100 provided the best sensitivity (81%), specificity (98%), positive predictive value (89%), negative predictive value (96%), and overall accuracy (95%). For 50% to 69% stenosis, a PSV greater than 130 and EDV of 100 or less cm/sec proved to be the best combination: sensitivity (92%), specificity (97%), positive predictive value (93%), negative predictive value (99%), and accuracy (97%). Stenoses in the 30% to 49% range were less accurately identified. CONCLUSION: These redefined criteria may prove useful for analyzing duplex ultrasound velocity data in reference to the classification of ICA stenosis used in recent clinical trials of the safety and efficacy of carotid endarterectomy.

Does air plethysmography correlate with duplex scanning in patients with chronic venous insufficiency?

PURPOSE: Duplex ultrasonography with distal cuff deflation was used to determine the presence and size of incompetent veins and compare the results with those of air plethysmography in patients with chronic venous insufficiency. METHODS: Thirty-two legs underwent a detailed study with both modalities. Sixteen legs had venous ulceration, six had stasis dermatitis, and ten had symptomatic varicose veins without skin changes. RESULTS: Although the venous filling index (VFI) in limbs with ulcers (5.4 +/- 3.8 ml/sec) and dermatitis (7.7 +/- 4.6 ml/sec) was significantly higher (p < 0.05) than it was in limbs with varicose veins (2.6 +/- 1.7 ml/sec), there was a large amount of overlap. Only 13% of ulcerated legs had VFI greater than 10 ml/sec. Sixty-three percent of legs with ulcers, 33% of legs with dermatitis, and 90% of legs with varicose veins had VFIs less than 5 ml/sec. Mean ejection fractions (EFs) in the three groups were similar, ranging from 45% to 52%. Combining VFI and EF did not lessen the overlap between groups. Forty-one percent of limbs with ulcers or dermatitis had air plethysmography parameters in the normal or intermediate area (VFI < 5 ml/sec; EF > 40%), which in previous studies corresponded to an incidence of ulceration of only 2%. VFI had a significant but weak correlation (r = 0.39) with the diameter of incompetent veins at the knee and a somewhat stronger relationship (r = 0.55) with the diameter of lower leg veins. Total venous volume correlated moderately well with calf vein diameter (r = 0.75). The clinical status of the leg did not correlate with the diameters of incompetent veins at the knee or calf levels. All limbs with an obstructed outflow had EFs less than 60% and ulcers or dermatitis. CONCLUSIONS: We conclude that plethysmographic measurements of functional venous parameters (VFI,EF) do not discriminate well between limbs with uncomplicated varicose veins and limbs with ulcers or stasis dermatitis and that VFI correlates poorly with the presence of incompetent veins and their diameters. Both duplex scanning and plethysmography seem to be necessary for a complete evaluation of limbs with chronic venous insufficiency.

Presentation and natural history of internal carotid artery occlusion.

PURPOSE: This retrospective study was undertaken to investigate the effect of presenting neurologic symptoms, vascular risk factors, and degree of contralateral internal carotid artery stenosis on subsequent stroke and death rates of patients with internal carotid artery occlusion (ICO). METHODS: One hundred sixty-seven patients with ICO were evaluated over a 5-year period. Mean follow-up was 39 months. Initial symptoms included transient ischemic attack in 29 patients (17%), stroke in 71 patients (43%), nonhemispheric symptoms in 22 patients (13%), and no symptoms in 45 patients (27%). Ninety percent of the presenting strokes occurred ipsilateral to the ICO. RESULTS: During follow-up 54 (32%) patients died, 10 (19%) of stroke and 22 (41%) of heart disease. The 5-year cumulative survival rate was 63%. Subsequent neurologic events occurred in 26% of the patients. Thirty patients (18%) had a stroke during follow-up, of which 20 (67%) occurred ipsilateral to the ICO. The 5-year stroke-free rate was 76%. Patients who had a stroke had a less favorable 4-year stroke-free rate (67%) than those who had transient ischemic attack (92%) or those who originally had no symptoms (89%), p = 0.03 and p = 0.04, respectively. In addition, there was a trend towards a worse 5-year contralateral stroke-free rate in patients with contralateral stenosis of 50% to 99% (77%) compared with patients with less than 50% contralateral stenosis (94%), p = 0.08. Twenty patients underwent carotid endarterectomy on the nonoccluded side. There were no perioperative strokes or deaths. Carotid endarterectomy seemed to reduce the long-term stroke morbidity rate (p = 0.10) on the operated side in patients with 80% to 99% contralateral stenosis but did not perceptibly improve stroke-free rates on the occluded side or in patients with 50% to 79% stenosis. CONCLUSION: Patients with ICO have a variable prognosis. There is a significant incidence of subsequent stroke, which seems to be related to the presenting neurologic event and the degree of stenosis in the contralateral internal carotid artery.

Routine surveillance after carotid endarterectomy: does it affect clinical management?

PURPOSE: Although routine noninvasive surveillance is recommended after carotid endarterectomy (CEA), there are little data to show that identification and eradication of recurrent carotid artery stenosis are necessary to avoid the risk of subsequent neurologic complications. METHODS: We reviewed our experience over a 16-year period in 380 consecutive patients undergoing 409 CEAs who underwent serial postoperative ultrasonic scanning at 6 weeks, 6 months, and 1 year after CEA and then yearly thereafter. RESULTS: Recurrent stenoses (> or = 50% diameter reduction) were detected in 44 arteries (10.8%) during follow-up from 1 to 177 months (mean 42.0 months). Most (70.5%) occurred within 2 years of CEA. Cumulative recurrence rates were 5.8%, 9.9%, 13.9%, and 23.4% at 1, 3, 5, and 10 years, respectively. Recurrent stenoses were more frequent in female (p = 0.02) and younger patients (p = 0.01) and less frequent in those having a vein patch repair (p = 0.02). Most recurrences (84%) were in the 50% to 79% stenosis range. In four patients 80% to 99% stenoses developed and in three patients total occlusions developed, for a severe recurrence rate of 2.1%. Only 10 (22.7%) of the recurrent stenoses were initially symptomatic, and only one (2.9%) of the asymptomatic restenoses later became symptomatic. One patient with recurrent stenosis suffered a stroke (0.3%). Cumulative 5-year ipsilateral stroke-free rates in patients with recurrent stenosis (94.4%) were practically identical (p = 0.76) to those in patients without recurrent stenosis (94.2%). Life-table ipsilateral stroke-free survival rates at 5 years were 94.2% in patients with recurrent stenosis and 78.4% in patients without recurrent stenosis (p = 0.16). Four (9%) recurrent stenoses and 12 lesions (27%) in the contralateral artery progressed. Only seven patients (1.7%) underwent repeat operation for ipsilateral disease, four for symptoms and three for recurrent stenosis. CONCLUSIONS: Recurrent carotid artery stenosis occurs early after CEA, is typically benign, and remains stable over a prolonged follow-up period. Our results question the importance of routine noninvasive surveillance after CEA and suggest that a more conservative approach would be equally beneficial in terms of clinical relevance and cost-effectiveness.

The influence of carotid siphon stenosis on short- and long-term outcome after carotid endarterectomy.

PURPOSE: This study was designed to determine whether the presence of ipsilateral carotid siphon stenosis influenced the risk of early and late stroke and death after carotid endarterectomy (CEA). METHODS: The outcomes of patients with moderate (20% to 49%), severe (> 50%), and no siphon stenosis were compared over a 16-year period from April 1976 to February 1992. Complete angiographic data were available in 393 carotid arteries. RESULTS: Siphon stenosis was found ipsilateral to the CEA in 84 (21.4%) of the arteries. Most lesions were in the 20% to 49% diameter-reducing range (77.4%), with the remainder in the greater than 50% range (22.6%). There were no occlusions. The perioperative mortality rate was nearly identical for the groups with and without siphon stenosis, 0.0% versus 0.6%, respectively (p = 0.99). Perioperative stroke morbidity rates (no stenosis, 2.3%; moderate stenosis, 3.1%; > 50% stenosis, 5.3%) were acceptable and were not statistically different (p > 0.38). Late ipsilateral stroke-free rates were similar in the groups with and without siphon stenosis. The 5- and 7-year stroke-free incidences were 88.5% and 83.4% versus 94.9% and 94.9%, respectively (p > 0.20) for the two groups. Long-term ipsilateral stroke-free rates were not significantly different in the subgroups with moderate (20% to 49%) and hemodynamically significant (> 50%) siphon stenosis. The 3- and 5-year ipsilateral stroke-free rates were 96.7% and 87.9% versus 94.6% and 94.6%, respectively (p = 0.69). Late death was more common in the group with siphon stenosis than it was in the group without siphon stenosis, 23.8% versus 12.5% (p = 0.02). Heart disease was responsible for most late deaths, 47% in both groups. Late stroke-related deaths were infrequent: 1.3% in patients with and 0.0% in patients without siphon stenosis. CONCLUSIONS: Although carotid siphon stenosis seemed to be associated with a higher risk of late death, it did not alter the short- and long-term stroke morbidity rates after carotid endarterectomy significantly. We conclude that the presence of carotid siphon stenosis should not influence the decision to perform carotid endarterectomy in patients with the appropriate indications.

Does correction of stenoses identified with color duplex scanning improve infrainguinal graft patency?

PURPOSE: This study was undertaken (1) to determine whether correction of infrainguinal bypass stenoses detected with color duplex scanning (CDS) improved graft survival and (2) to define the natural history of grafts that did not undergo revision. METHODS: Over a 39-month period 462 color-flow duplex scans were obtained on 170 limbs with autogenous vein grafts. Grafts were scanned within 3 months of operation, at 6 and 12 months, and then yearly. Doubling of the velocity at any point in the graft-arterial system compared with the velocity immediately above or below (velocity ratio > or = 2.0) was the criterion adopted for identification of a hemodynamically significant (> or = 50%) diameter reduction. RESULTS: One hundred ten stenoses were detected in 62 (36%) of the limbs, of which 9 (8%) were in native vessels, 30 (27%) were at the anastomoses, and 71 (65%) were in the graft itself. Seventy-seven percent of the stenoses were detected in the first year. Twenty-four (39%) of the grafts with positive scans were revised. During follow-up, occlusions occurred in 10 (9%) of the 108 grafts with negative scans (NEG), in 2 (8%) of the 24 revised grafts with positive scans (PR), and in 10 (26%) of the 38 non-revised grafts with positive scans (PNR). Cumulative patency rates of NEG grafts were 90% at 1 year and 83% at 2 through 4 years. Similar patency rates were found in the PR vein grafts: 96% at 1 year and 88% at 2 through 4 years. In contrast, patency rates in PNR grafts with 50% or greater stenoses were only 66% at 1 year and 57% at 2 through 4 years. Log-rank tests showed a significant difference between the cumulative patency rates of NEG and PNR grafts (p < 0.002) and between PR and PNR grafts (p = 0.02). Flow velocities less than 45 cm/sec and ankle/brachial indexes did not discriminate well between grafts with or without 50% or greater stenoses or identify those grafts that subsequently occluded. CONCLUSIONS: The results of this study suggest that CDS detects graft-threatening lesions, that a velocity ratio of 2.0 or greater is the most highly predictive parameter, and that revision of grafts with stenoses identified with CDS prolongs patency.

Photoplethysmography reexamined: lack of correlation with duplex scanning.

In a prospective study a comparison was made between the results of photoplethysmography and ultrasonic duplex scanning in 151 consecutive legs with swelling, aching, and suspected venous insufficiency. Thirty-four percent of the legs had a history of previous deep venous thrombosis, 26% had undergone previous superficial vein surgery, and 11% had active or healed ulceration. Photoplethysmographic findings were normal in 86 (57%) of these legs and indicated deep venous disease in 33 (22%). With duplex scanning, incompetent vein segments were found in 140 legs (93%). The kappa coefficient of agreement between the result, classified as either normal, superficial disease only, or deep incompetence, was 0.12 +/- 0.06. In legs with superficial disease, the number of incompetent levels was no greater in legs with abnormal results of photoplethysmography than in legs with normal results of photoplethysmography. In general, an abnormal photoplethysmographic result is related to multilevel reflux and the presence of visible skin changes. Photoplethysmography had the same value, in these patients, to predict the presence of multilevel reflux as had inspection of the skin of the goiter area. These results do not warrant the continued use of photoplethysmography for surgical decision making in patients with suspected venous insufficiency.

Thrombus regression in deep venous thrombosis. Quantification of spontaneous thrombolysis with duplex scanning.

BACKGROUND: Thrombus regression in heparin-treated, acute deep venous thrombosis of the lower extremity is poorly documented in the literature; different rates of thrombus resolution and recanalization are reported. METHODS AND RESULTS: In a prospective follow-up study, duplex scanning was used to evaluate the thrombus regression in patients with documented acute femoropopliteal thrombosis. Eighty vein segments in 20 legs of 18 patients were subjected to repeat duplex scans at 1, 3, 6, 12, and 26 weeks after diagnosis; 49 segments showed thrombus at diagnosis. The popliteal vein showed the highest thrombus load at diagnosis, followed in descending order by the superficial femoral, profunda femoris, and common femoral vein segments (p less than 0.001). Thrombus regression was significant (p less than 0.001) in all segments and proceeded at an exponential rate that was equal in the different vein segments of the upper leg. Both thrombus resolution and recanalization appeared to be a function of the initial thrombus load and could not be related to individual vein segments. Recanalization was seen in 23 of 31 initially occluded segments and occurred within the first 6 weeks after diagnosis in 20 of 23 segments. Extension of thrombus despite anticoagulant therapy was observed in 15 vein segments and was not related to the initial thrombosis score (p = 0.1) or individual vein segments (p = 0.23). Thrombus extension in seven patients with prethrombotic conditions was not different (p = 0.9) from the other patients. CONCLUSIONS: Duplex scanning is an important noninvasive tool to quantify thrombus regression in acute deep venous thrombosis in detail without unnecessary discomfort to the patient.

Status of the valves in the superficial and deep venous system in chronic venous disease.

The relationship between the functional status of the venous valves in the superficial and deep veins and ulceration was evaluated in 42 patients. Twenty-five patients had ulcers, 12 of these patients had a history of previous deep venous thrombosis and 13 of these patients denied such an event. Seventeen patients had normal ankle skin, 10 of these patients had a documented history of deep vein thrombosis and seven of these patients had varicose veins only. An ultrasonic duplex scanner was used to document the presence of reflux in all segments of the superficial and deep system. In the entire group of 25 limbs with ulceration, valvular incompetence was noted in 22 limbs at levels involving segments that communicated with the ulcer-bearing area. Of the 17 limbs with normal ankle skin, in only two instances was a single segment of posterior tibial vein in midcalf found to be incompetent. For those patients with normal ankle skin and a history of varicose veins, the deep veins below the common femoral vein level were always competent.

Functional status of the deep venous system after an episode of deep venous thrombosis.

An episode of deep venous thrombosis is often followed by the opening of collaterals, fibrinolysis, recanalization and valvular dysfunction. The effect of these processes on the peak flow velocity in the superficial femoral and popliteal veins after simulated contraction of the calf muscles was tested in a group of normal subjects and three groups of patients who had deep venous thrombosis. There were 12 patients followed less than two years with no skin changes. The second group consisted of 12 patients followed for 8-15 years without ulceration. The third group of 12 patients had active or healed ulcers. The peak flow velocity in the superficial femoral and popliteal veins was assessed by rapidly inflating cuffs about the calf and ankle to 100 mmHg. The velocities generated by cuff compression were lower in patients than in normal subjects. This was particularly true in the superficial femoral vein. This change in velocity may be secondary to incomplete recanalization with resulting stenosis or valvular incompetence in the calf.

The mechanism of venous valve closure. Its relationship to the velocity of reverse flow.

Venous valves will close when the reversal of the normal pressure gradient generates a sufficient reverse flow velocity. By testing 20 healthy subjects with ultrasonic duplex scanning and controlled limb compression. It was found that the velocity of reflux is related to the external compression pressure. Valve closure is an abrupt cessation of reverse flow. In this study, with subjects in a supine position, valve closure was achieved only after reverse velocities exceeded 30 cm/s. This velocity was not generated by manual compression of the limb. With a Valsalva maneuver, this velocity is achieved only in the common femoral vein in 90% of the tested individuals. The reflux velocities in response to a Valsalva maneuver are progressively lower in more distal veins--the profunda femoris, the superficial femoral vein, and the popliteal vein. With reverse velocities lower than 30 cm/s, the valves will not close and reflux can persist. Valsalva's maneuver only allows a diagnosis of valvular competence at the most proximal level in the venous tree.

Visualization of calf veins by color flow imaging.

Both indirect and direct noninvasive tests have been shown to be useful for the detection of deep venous thrombi involving the proximal veins (popliteal to inferior vena cava). However, thrombi that are confined to the calf veins will not affect venous outflow and cannot be detected by the plethysmographic methods. B-mode imaging, while excellent for the major deep veins, is also limited in the calf region because the veins are small, and imaging resolution is not always adequate to permit visualization of these smaller veins. With the availability of duplex scanning with "slow flow" color capability, these veins lend themselves to study. In 30 normal subjects, we were able to visualize all paired veins from the level of the ankle to the popliteal fossa. The clinical implications of this approach are discussed.

Quantitative segmental evaluation of venous valvular reflux with duplex ultrasound scanning.

The duration of deep venous valvular reflux was studied in 192 venous segments of the legs of 32 patients in good health. Three methods were used to elicit reflux in the supine and upright positions--Valsalva's maneuver, proximal limb compression, and release of distal limb compression. Standardized compressions were achieved with pneumatic cuffs. When this approach was used to study valve function, the time to complete closure of the valve and cessation of retrograde flow was found to be shorter than that for conventional methods of closure. The distal cuff deflation method is the only one that permits a quantitative and reproducible method to measure duration of venous reflux at all levels of the lower limb. Normal values obtained with this test are presented for the common femoral, deep femoral, and superficial femoral veins and for the popliteal and posterior tibial veins midway between knee and ankle level and the posterior tibial vein at the ankle. In the popliteal vein, median duration of reflux is 0.19 second; 95% of the values in the popliteal vein are less than 0.66 second. In distal areas, duration of reflux is short and uniform. The advantage of the cuff deflation test over the Valsalva method is that the cuff method is not hindered by the presence of ileofemoral valves. A better understanding of the relative importance of deep valve dysfunction at different levels and the expected benefit of valve repair may be obtained with this test.