Noninvasive flowmetry in vascular surgery: use of a noninvasive electromagnetic flowmeter

Using an in vitro model, the measurements made using a noninvasive electromagnetic flowmeter have been validated using standard square wave electromagnetic flowmetry. Clinically, the noninvasive electromagnetic flowmeter provides information as to the functional significance of vascular occlusive disease that is not available through other techniques, gives an accurate, quantitative measurement of the peak pulsatile blood flow through a limb, thus providing an index of tissue perfusion and therefore, the degree of involvement of the disease in the peripheral vascular system.     

Ultrasonic flow wave pattern as a prognostic indicator in peripheral arterial reconstruction

A prognostic flowmetric study on 80 reconstructed arteries of the lower extremity was carried out to assess the flow wave patterns detected using a bidirectional doppler flowmeter. In 21 of 80 arteries, changes in the flow wave pattern were noted. For 10 of 21 affected arteries, an immediate arteriography revealed localized stenotic lesions at the distal anastomosis in a short segment of the implanted autogenous vein graft or at the proximal host artery. Immediate repairs for the lesions were successfully performed by a minor surgery in 8 of 10 cases and the flow wave pattern reverted to normal. Two were not successful, as the occlusion was complete before attempting the repair. The remaining 11 are now under conservative management as these patients refused further surgery. The ultrasonically driven flow wave pattern proved to be a useful indicator to assess the patency of the reconstructed peripheral artery to detect possible stenosis and thereby to take proper corrective measures and hence prevent a late occlusion. Presented at the Postcongress Meeting on Noninvasive Flowmetry in Angiology of the 21st Congress of the Japanese College of Angiology fukuoka, Japan, October 30–November 1, 1980.     

Direct intraoperative measurements of aortic and pulmonary blood flows in patients with severe pulmonary artery hypertension

BACKGROUND: Evaluate the significance of direct intraoperative measurements of aortic and pulmonary blood flows by electromagnetic flowmeter as an absolute decision basis for operability in patients with ventricular septal defect/complete atrioventricular septal defect and severe pulmonary artery hypertension. METHODS: EXPERIMENTAL DESIGN: Prospective study. SETTING: Institutional practice. Patients: Eight patients with marginal operability based on preoperative Doppler echocardiography and cardiac catheterization (pulmonary-to-systemic flow ratio=1.1-2.3, pulmonary-to-systemic resistance ratio=0.34-0.91, and pulmonary vascular resistance=4.6-18.2 units x m2) underwent direct intraoperative measurements of aortic and pulmonary blood flows by electromagnetic flowmeter. Operation would be performed according to the results of direct intraoperative measurements in every patient. RESULTS: Aortic flow by direct intraoperative measurements ranged from 0.9 to 3.2 L/min/m2, and pulmonary blood flow from 4.1 to 8.4 L/min/m2. Pulmonary-to-aortic flow ratio was calculated at 2.1-6.6. Pulmonary vascular resistance ranged from 2.6 to 7.7 units x m2. We assessed that all patients still had operability, and performed corrective operations. Postoperative courses corresponded with the data from the direct intraoperative measurements. CONCLUSIONS: When some clinical findings, particularly Doppler echocardiographic findings, of these patients are slightly in favor of reversibility of pulmonary vascular disease despite discrepant data of preoperative cardiac catheterization under a tight control of carbon dioxide tension, we recommend that direct intraoperative measurement of aortic and pulmonary blood flows is especially useful in decision making for the operability of patients with severe pulmonary artery hypertension.     

Quantitative assessment of low blood flow using an electromagnetic flowmeter

This study evaluated the behavior and reliability of an electromagnetic flowmeter for the quantitative assessment of low mean blood flow. Cuff-type probes with lumen diameters of 0.75, 1.0, 1.5, and 2.0 mm were used on excised canine vessels of external diameter less than 4.0 mm for in vitro calibrations. Flows ranged from 0 to 30 ml/min. Standard calibration plots were linear through zero with a mean error of ± 4.2%. Linear plots were significantly shifted by vascular constrictions of 50% and greater. Mechanical occlusion of the vessel for zero baseline determination was found to be important. To date, this report is the most extensive and accurate quantitative study of low blood flow with small transducers. We feel that the equipment can function as a valuable surgical tool.     

Videodensitometric quantitation of mean blood flow

Standard angiography demonstrates the anatomy of arterial occlusive disease but does not define its physiological significance. However, measurement of flow in a compromised vessel at rest and following peripheral dilatation provides important physiological information. Using digital subtraction angiography, femoral arterial flows determined by the cross-correlation transit time technique were compared to measurements by electromagnetic flowmeter. Thirty-five femoral arterial flow measurements were obtained in nine dogs instrumented with an electromagnetic flow probe and balloon occluder. Renografin 76 (7 cc) was power-injected at 14 cc/sec into the distal abdominal aorta. Angiographic flow measurements correlated well with electromagnetic flowmeter measurements (r = 0.94, standard deviation of the difference (SDD) = 15 ml/min). Intravenous studies provided somewhat poorer correlation due to difficulties in defining dimensions (r = 0.72, SDD = 36). Paired contrast injections (2 injections in succession) in 11 studies increased flow from an average of 80 to 250 ml/min (a 210 +/- 100% increase), providing an estimate of a vessel's capacity to provide increased flow during peripheral dilatation. Thus, reliable angiographic flow determinations may be obtained by arterial and intravenous contrast injections, adding physiological information to anatomical definition.     

Operative correction of total left anomalous pulmonary venous return.

The evaluation, surgical repair, and follow-up are described in an asymptomatic 27-year-old man with unilateral total anomalous pulmonary venous return from the left lung through an innominate vein and a patent foramen ovale. The anomalous vein was divided and anastomosed directly to the left atrium using a vascular technique that produced an orifice larger than the vein diameter. Radionuclide scanning accurately identified the anomaly before operation and allows periodic noninvasive reevaluation after operation. Correction is recommended in all patients with unilateral anomalous pulmonary venous return because disease in the one normal lung could be fatal.     

Schwindende Fachgrenzen zwischen Gefäßchirurgie und interventioneller Radiologie aus Sicht des Gefäßchirurgen

Demographic development leads to an exponential increase of cardiovascular illness. Additionally, technical development of conservative and invasive treatment modalities adds to an increase of specified therapy. Both items lead to increased specialization and a new orientation of vascular specialties. This concept implies that specific contents are referred and contained to the partner specialties. Angiology, vascular surgery and radiology are primary partners in this concept, however, in the following article the focus lies on vascular surgery and radiology.     

Usefulness of sequential bypass technique in arterial reconstruction

Although sequential bypass grafting has been recommended for surgical treatment of lower limb ischemia in patients with complex multisegmental arterial occlusion, hemodynamic evaluation of the sequential bypass procedure remains to be resolved. The present study was undertaken to evaluate the sequential bypass operation to assess its usefulness from the standpoint of hemodynamics. A model was made simulating a sequential bypass in the mongrel dogs, and blood flow through the sequential bypass graft much more increased than through the standard one, measured by an electromagnetic flowmeter. By flow visualization in a glass tube model, type of flow separation and stagnation region in case of a side-to-side anastomosis was similar to those in case of an end-to-side one. The stagnation area at the anastomotic site was widened when the vascular resistance increased in the ramified vessel which corresponded to the host distal artery. It was considered reasonable to blockade the retrograde blood flow through the anastomotic site by ligating the host artery proximal to the anastomotic point when the retrograde blood perfusion was unnecessary. Clinical results of 21 cases with the sequential bypass grafting were presented and the usefulness of the technique was discussed from a hemodynamic viewpoint.     

The effect of blood viscosity on blood flow in the experimental saphenous flap model

A study has been made of the effect of lowering blood viscosity with ancrod (Arvin) on blood flow in an experimental island skin flap. Blood flow was measured directly using an electromagnetic flowmeter. It was observed that blood flow into the flap increased significantly (p less than 0.02) as a result of lowering blood viscosity.     

Screening for asymptomatic cardiovascular disease with noninvasive imaging in patients at high-risk and low-risk according to the European Guidelines on Cardiovascular Disease Prevention: the SMART study

OBJECTIVE: To assess the prevalence of atherosclerotic risk factors and to investigate the added value of noninvasive imaging in detecting asymptomatic cardiovascular diseases in patients at low risk and high risk according to the European Guidelines on Cardiovascular Disease Prevention. METHODS: In the vascular screening program of the University Medical Center Utrecht, patients aged 18 to 79 years who had recently received a diagnosis of manifest vascular disease (coronary heart disease, cerebrovascular disease, abdominal aortic aneurysm, or peripheral arterial disease [PAD]) or had a risk factor (hypertension, hyperlipidemia, or diabetes mellitus) were assessed for atherosclerotic risk factors and (other) arterial diseases by noninvasive means. The European guidelines were applied to quantify the number of high-risk patients. RESULTS: Eighty-eight percent of 3950 patients were considered to be at high-risk. More than 80% had hyperlipidemia, approximately 50% had hypertension, 21% had diabetes mellitus, and 31% were current smokers. An asymptomatic reduced ankle-brachial index (< or = 0.90) was most frequently observed in patients with cerebrovascular disease (21%); an asymptomatic abdominal aortic aneurysm (> or = 3.0 cm) in patients with PAD (5%) or cerebrovascular disease (5%); and an asymptomatic carotid stenosis (> or = 50%) in patients with PAD (15%). On the basis of noninvasive measurements, 73 (13%) of 545 patients initially considered as low risk were reclassified as high risk. CONCLUSIONS: This study confirmed a high prevalence and clustering of modifiable atherosclerotic risk factors in high-risk patients. The yield of noninvasive vascular measurements was relatively low but identified a sizable number of high-risk patients. Standard screening for asymptomatic atherosclerotic disease identified a limited number of vascular abnormalities that necessitated immediate medical attention in patients already identified as high-risk patients.     

Contralateral testicular blood flow during unilateral testicular torsion

Changes in contralateral testicular blood flow during unilateral testicular torsion were evaluated using an electromagnetic flowmeter in 13 adult male New Zealand White rabbits. There was an immediate and then a progressive decrease during torsion and a gradual increase following detorsion. A decrease in testicular blood flow over a critical period of time may be associated with contralateral testicular damage following unilateral testicular torsion.     

The hot-film anemometer--a method for blood velocity determination. II. In vivo comparison with the electromagnetic blood flowmeter

Using a constant temperature hot-film anemometer and an electromagnetic blood flowmeter, volumetric flows and velocity profiles were registered in the pulmonary artery, ascending aorta, abdominal aorta and superior vena cava of mongrel dogs. The anemometer registered in 3 out of 4 dogs in the ascending aorta and in 4 out of 5 dogs in the pulmonary artery. The flow profile in these two vessels was flat with a slight deviation with the highest velocity nearer to the posterior wall. In the abdominal aorta the flow profile was sinusoid and in the superior vena cava irregular. In 22 simultaneous measurements anemometer mean results were 97 +/- 23% (+/- SD) of flowmeter results and peak results correspondingly 113 +/- 23%. None of these differences were significant. It is stressed that both qualitatively and quantitatively hot-film anemometer results are comparable to electromagnetic flowmeter results. However, certain differences have been demonstrated.     

Gründung des Österreichischen Verbandes für Gefäßmedizin

The Austrian Union of Vascular Medicine was founded in January 2010 as an umbrella organization for the following societies: Austrian Society of Vascular Surgery, Austrian Society of Internal Angiology, Austrian Society of Interventional Radiology, Austrian Society of Phlebology and Austrian Society of Vascular Biology. The aim of the Union is the coordination and cooperation of all issues in prophylaxis, diagnostics and therapy for vascular diseases. In addition it should serve as a platform for all health institutions concerning vascular medicine.     

Use of a piezoelectric film sensor for monitoring vascular grafts

Detection of failing arterial reconstructions requires intensive surveillance by frequent physical examination and noninvasive laboratory testing. However, many grafts fail during the intervals between these examinations. For this reason, we have developed an implantable miniaturized piezoelectric flow detection device whose function can be monitored externally by radiotransmission across the skin. Sensors were constructed from ultrathin polyvinylidene fluoride (PVF2) with piezoelectric activity and attached with silicone fixative to 6-mm polytetrafluoroethylene grafts. Ten of these grafts were placed in mongrel dogs as iliofemoral bypasses. Real time data were acquired from the sensors at a rate of 200 Hz, using a DATAQ A/D data acquisition board and CODAS data acquisition software, while simultaneous blood flow (using an electromagnetic flowmeter) and intraluminal pressure were processed by using separate channels of the same data acquisition board. The data were stored on computer storage media and analyzed by the ASYST software, which allows simultaneous signal curves to be compared using regression analysis. In the resting state, the mean blood flow was 123 +/- 16 mL and the mean intraluminal pressure was 124/78 mm Hg, and there was perfect correlation between the PVF2 sensor and the flowmeter and between the sensor and the intraluminal pressure (correlation coefficient, r greater than or equal to 0.99 and r greater than or equal to 0.93, respectively). A tourniquet was applied to the iliac artery proximal to the graft to reduce the flow to approximately half of the resting state (mean flow after tourniquet: 66 +/- 6 mL/minute). Signal tracings from the three sources showed a remarkable similarity with a very high correlation coefficient (r greater than or equal to 0.99 between sensor and flowmeter and r greater than or equal to 0.92 between sensor and the pressure signal). These preliminary results show that the sensors made from low-profile and low-mass PVF2 material have the potential of being implanted around grafts for long-term, continuous monitoring of graft function. Further studies involving long-term implantation to assess the effect of tissue ingrowth and loss of compliance are necessary before this device can be used clinically.     

Preoperative evaluation of cardiac risk using dobutamine-thallium imaging in vascular surgery

Coronary artery disease is frequently present in patients undergoing evaluation for reconstructive peripheral vascular surgery. Dobutamine-thallium imaging has been shown to be a reliable and sensitive noninvasive method for the detection of significant coronary artery disease. Eighty-seven candidates for vascular reconstruction underwent dobutamine-thallium imaging. Forty-eight patients had an abnormal dobutamine-thallium scan. Twenty-two patients had infarct only, while 26 had reversible ischemia demonstrated on dobutamine-thallium imaging. Fourteen of 26 patients with reversible ischemia underwent cardiac catheterization and 11 showed significant coronary artery disease. Seven patients underwent preoperative coronary artery bypass grafting or angioplasty. There were no postoperative myocardial events in this group. Three patients were denied surgery on the basis of unreconstructible coronary artery disease, and one patient refused further intervention. Ten patients with reversible myocardial ischemia on dobutamine-thallium imaging underwent vascular surgical reconstruction without coronary revascularization and suffered a 40% incidence of postoperative myocardial ischemic events. Five patients were denied surgery because of presumed significant coronary artery disease on the basis of the dobutamine-thallium imaging and clinical evaluation alone. Thirty-nine patients with normal dobutamine-thallium scans underwent vascular reconstructive surgery with a 5% incidence of postoperative myocardial ischemia. Dobutamine-thallium imaging is a sensitive and reliable screening method which identifies those patients with coronary artery disease who are at high risk for perioperative myocardial ischemia following peripheral vascular surgery. Presented at the Annual Meeting of the Peripheral Vascular Surgery Society, New York, New York, June 17, 1989.     

Quantitative Assessment of Peroneal Artery Pressure at the Ankle With Noninvasive Vascular Testing

Although the foot and ankle derives its arterial supply from a combination of the anterior tibial artery (ATA), posterior tibial artery (PTA), and peroneal artery (PA), the focus of clinical examination techniques and noninvasive vascular testing is primarily on the ATA and PTA and not on the PA. The objectives of the present investigation were to evaluate the feasibility of incorporating an assessment of the PA into a noninvasive vascular testing protocol and to collect normative data of pressure measurements of the PA at the ankle. We attempted to locate a Doppler signal of the PA posterior to the lateral malleolus in consecutive patients undergoing our institution's standard protocol for lower extremity noninvasive vascular testing using the ankle-brachial index and photoplethysmography. An audible signal of the PA with an available pressure measurement recording posterior to the lateral malleolus was found in a large majority (92.0%) of the studied legs with peripheral arterial disease. We also found pressure measurements in the PA generally equivalent to that of the ATA and PTA. The mean ± standard deviation systolic pressure of the PA was 130.33 ± 44.74 (range 54 to 255) mm Hg, with a corresponding ankle-brachial index of 0.92. The results of the present investigation provide unique information on a potentially underappreciated aspect of lower extremity vascular anatomy with the potential to affect rearfoot surgical decision making and planning.     

Traumatic arteriovenous fistula. Clinical evaluation and intraoperative monitoring with the doppler ultrasonic flowmeter

The Doppler ultrasonic flowmeter is a relatively inexpensive device with which the surgeon may audibly study the hemodynamics of the vasculature transcutaneously and atraumatically. It is of great value in the study of vascular anomalies and in the evaluation of peripheral arterial occlusive disease. It is of even greater value when used intraoperatively to ascertain vascular patency during arterial reconstruction and to determine the obliteration or repair of arteriovenous malformations whether they are congenital or traumatic in origin. The use of the Doppler flowmeter to follow up patients in the clinic is readily accepted by the patient, as the process is atraumatic and results in a saving of time and money to both the patient and the hospital.     

Venous reconstruction for iliofemoral venous occlusion facilitated by temporary arteriovenous shunt. Long-term results in nine patients

In nine patients with iliofemoral venous occlusion, venous reconstructions using a temporary arteriovenous shunt were performed by open thromboendvenectomy with autogenous vein patch angioplasty in four, expanded polytetrafluoroethylene (ePTFE) bypass grafts (including two with external ring-supported ePTFE) in four, and Palma's procedure in one patient. There was an adequate function in the reconstructed venous segments in two of four who underwent thromboendvenectomy and in all four with ePTFE bypass grafting for nine months to 13 years after surgery. In those with a temporary arteriovenous shunt, prepared to maintain patency of the reconstructed venous segments, blood flow through the shunt exceeded 100 mL/min, determined by an electromagnetic flowmeter. Postoperative shunt closure was readily facilitated, using a looping technique and a 2-0 nylon. The increased blood flow through the graft made feasible by the temporary arteriovenous shunt enhanced the patency of the reconstructed venous graft and hence there was an improvement in the affected limb.     

The Ejector Flowmeter and Its Clinical Application

The ejector flowmeter is designed for the quantitative removal of excess anaesthetic gases.
By passing compressed air or gas at 2.0-3.5 kg/cm² pressure through a narrow injector nozzle across the upper end of an ordinary flowmeter tube, a sufficient vacuum is created in the flowmeter to obtain an adjustable removal of gas through the flowmeter; for instance, an anaesthetic gas mixture. The driving gas conveys the anaesthetic gas mixture through a narrow antistatic rubber tube to the nearest ventilation channel or along the floor or ceiling into fresh air through an opening in an outer wall.
The ejector flowmeter may be mounted on any anaesthetic machine, being independent of national standard dimensions. It can be attached to all current anaesthetic circuits, including those with an anaesthesia ventilator. The float secures visual control of proper flowmeter function. The evacuation capacity is adjustable up to 15 1/min, and the full capacity is 20-25 1/min. The consumption of driving gas is about 6 1/min. This elimination of gas involves no explosion risk.     

Intraoperative evaluation of carotid endarterectomy with electromagnetic flowmetry and portable DSA

In order to perform carotid endarterectomy more safely, we have evaluated, intraoperatively, the result of an operation with electromagnetic flowmeter and portable digital subtraction angiography (DSA). During surgery, flow of the exposed internal and common carotid artery was measured with an electromagnetic flowmeter, before and after endarterectomy. After the closure of the arteriotomy, portable DSA was carried out by injecting contrast medium from the common carotid artery. Our simple portable DSA system consists of a surgical X-ray television set, image processor (Sigma X) and still video-recorder. This system almost gives us a real-time presentation of a subtracted view of angiography. There were twenty patients including one patient with major stroke, 14 with minor stroke, three with transient ischemic attack, and two asymptomatic patients. Increase of the flow through the internal carotid artery was documented with an electromagnetic flow-meter in 13 of 20 patients following endarterectomy. Flow reduction was seen in two patients, one of whom was found to have an intimal flap from residual plaque visualized in the portable DSA. The plaque was removed by reopening the artery. Among twenty patients, intraoperative portable DSA showed an intimal flap in three patients and a step in four patients. Although the incidence of abnormal findings was high, degree of abnormality was not severe enough to reopen the artery except in one case. The purposes of carotid endarterectomy is two-fold. It is used for the removal of the plaques which can be a source of emboli, and also for the augmentation of flow in the narrowed segment of the artery.(ABSTRACT TRUNCATED AT 250 WORDS)