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PubMed1988

Utility of impedance plethysmography in the diagnosis of recurrent deep-vein thrombosis.

Serial impedance plethysmography has been shown to be a safe and effective alternative to venography in the management of patients with clinically suspected acute venous thrombosis. The rate of normalization of an initial abnormal impedance plethysmogram and, consequently, the usefulness of impedance plethysmography in the management of patients with recurrent symptoms is, however, unknown. In a prospective cohort follow-up study, 161 consecutive patients with proved venous thrombosis and abnormal impedance plethysmograms were studied for one year. After 3, 6, 9, and 12 months, the impedance plethysmograms had normalized in 67%, 85%, 92%, and 95% of the patients, respectively. Thirty-five patients (22%) returned with clinically suspected recurrent thrombosis, of whom 31 had normal impedance plethysmograms prior to their return. In 18 of these patients, repeated tests were normal; these patients did not undergo anticoagulant therapy, and follow-up disclosed no subsequent adverse consequences. In the other 13 patients, the test again became abnormal; 11 patients were shown by venograms to have recurrent deep-vein thrombosis. Consequently, 29 (83%) of the 35 patients in whom the suspicion of recurrent thrombosis arose could have been managed with impedance plethysmography alone without the necessity for venography or anticoagulant therapy. It is concluded that normalization of impedance plethysmography tests occurs in almost all patients within nine months, and that serial impedance plethysmography is useful for patient management in nearly 90% of patients presenting with recurrent symptoms.

Acute Disease↗
PubMed1990

[Blood flow measurement with impedance plethysmography--experimental and clinical application in orthopaedic surgery].

Impedance plethysmography has been used clinically to measure the cardiac output. We have improved the apparatus of impedance plethysmography and applied it in the orthopaedic field. It is now possible to measure the blood flow in human fingers and in the extremities of rabbits. Experimentally, we measured the blood flow through the rabbit extremities with the measured values reflecting the ischemic condition. Clinically, we measured the blood flow through the fingers with arteriosclerosis obliterans with the measured values consistent with the angiographic findings. The measurement of blood flow in vascular injuries and attachment of fingers reflected the ischemic condition. By using the impedance plethysmography, we cannot obtain an absolute value because the measured value is affected by the type of electrode and the position of the electrode. We can nevertheless seek a relative value by comparing with the values at normal site. We can also identify any differences before and at the after change in blood flow. When the advantages and disadvantages of this method are better understood, this method will be of wide clinical use.

Animals↗
PubMedDate not supplied

A new interpretive method for impedance plethysmography.

Clinical experience revealed that Wheeler's interpretative method for impedance plethysmography studies resulted in a large number of false negative and borderline interpretations, so a new interpretative method was created using additional impedance plethysmography parameters. This study was performed to compare this new method with Wheeler's method in 21 patients with suspected deep venous thrombosis. The accuracy of each method was determined by comparing the impedance plethysmography interpretations with venography. The patients were divided into groups according to venogram results of no thrombosis, and tibial (calf) venous thrombosis. Nine of the 21 patients had no thrombosis on venogram. Wheeler's method and the new method both resulted in 56% true-negative interpretations. Twelve of the 21 patients had proximal deep venous thrombosis and/or tibial venous thrombosis on venogram. Wheeler's method resulted in 8% true-positive interpretations and 17% false-negative interpretations. Of the patients in the study, 62% had borderline interpretations. The new method resulted in 75% true-positive interpretations and no false-negatives. The new method decreased the borderline interpretations to 33%. By calculating a basal impedance difference between the patient's two legs, the new method did provide guidelines that could identify patients with borderline interpretations who would require additional testing. The new impedance plethysmography interpretative method did lower the number of borderline and false-negative interpretations, and it provided guidelines to identify patients with borderline interpretations who need further testing.

Algorithms↗
PubMed1983

[Quantitative aortic flow and cardiac output volume determinations in rabbits using tetrapolar impedance plethysmography].

In 25 normal rabbits the transthoracic impedance changes were continually registered at rest and during pharmacological exercise by use of various types of electrodes. These changes were quantified by the formula of Kubicek for estimation of cardiac output. The obtained values were compared with the values of cardiac output and the flow in the aorta descendens measured by electromagnetic flowmetry in the aorta descendens. Linear regression analyses for several intervals of ejection and various types of electrodes showed a high and significant correlation between the values estimated by both methods (r greater than or equal to 0.96, p less than or equal to 0.001). The analyses of confidence intervals of the parameters of linear regression showed that the functional relations can be described by uniform parameters of regression. On this basis were estimated coefficients of correction which allow quantitative evaluation of the cardiac output and the flow in the aorta descendens in rabbits by use of tetrapolar impedance plethysmography. For cardiac output: (Formula: see text) for the flow in the aorta descendens: (Formula: see text) Tetrapolar impedance plethysmography is a noninvasive method, which allows quantitative and dynamic evaluation both of the cardiac output and the flow in the aorta descendens in rabbits.

Animals↗
PubMed1998

A simple clinical model for the diagnosis of deep-vein thrombosis combined with impedance plethysmography: potential for an improvement in the diagnostic process.

OBJECTIVES: We recently demonstrated the utility of a clinical model combined with ultrasonography to assist the diagnostic approach in patients with suspected deep-vein thrombosis (DVT). In this study we also sought to demonstrate that the model is useful with impedance plethysmography, a less accurate and less utilized diagnostic test. The original clinical model is slightly cumbersome to use; thus at the completion of the study we attempted to develop a simpler scoring system with a goal of maintaining accuracy. DESIGN: An open, nonrandomized, multicentre trial. SETTING: Three centres, two in Canada, and one in Italy. SUBJECTS: Ambulatory patients with suspected deep-vein thrombosis. INTERVENTIONS: All patients were assessed clinically to determine the probability for deep-vein thrombosis prior to performing impedance plethysmography and venography. We compared the accuracy of impedance plethysmography between the three pretest probability categories of high, moderate and low. All of the above were performed and interpreted by independent observers. When the study was completed, we revised the clinical model by first performing a simple regression analysis then a multiple logistic regression analysis; a scoring system was devised using the latter. RESULTS: Impedance plethysmography is significantly more sensitive and less specific for all DVT in patients with high pretest probability for deep-vein thrombosis (P = 0.001). The post- test probability (positive predictive value) for deep-vein thrombosis with an abnormal impedance plethysmography result was significantly different (P = 0.0001) between the three pretest probability categories. Multiple regression analysis has provided a new model with only nine variables and a simple scoring system. The retrospective application of the revised clinical model, which is simpler to use, suggests it will provide similar results as the original clinical model when combined with impedance plethysmography. The combination of impedance plethysmography and the clinical model suggests patients are likely to have false positive results if they have a low or moderate pretest probability for deep-vein thrombosis and false negative results if the pretest probability is high. The combination of a low pretest probability and a normal impedance plethysmography result may exclude the need for serial testing, and represented more than 50% of our patient population. CONCLUSIONS: The use of the clinical model in conjunction with impedance plethysmography would decrease the number of false positive and negative diagnoses and could markedly decrease the need for serial impedance plethysmography. Combining the clinical model with impedance plethysmography could overcome the fact that impedance plethysmography is clearly less accurate than venous ultrasound imaging. The use of the revised clinical model may increase acceptability and utility, but prospective testing is required before widespread use.

Diagnosis, Differential↗
PubMed1990

Impedance plethysmography of thoracic region: impedance cardiography.

Impedance plethysmograms were recorded from thoracic region in 254 normal subjects, 183 patients with coronary artery disease, 391 patients with valvular heart disease and 107 patients with congenital septal disorder. The data in 18 normal subjects and 55 patients showed that basal impedance decreases markedly during exercise in patients with ischaemic heart disease. Estimation of cardiac index by this technique in a group of 99 normal subjects has been observed to be more consistent than that of the stroke volume. Estimation of systolic time index from impedance plethysmograms in 34 normal subjects has been shown to be as reliable as that from electrocardiogram, phonocardiogram and carotid pulse tracing. Changes in the shape of plethysmographic waveform produced by valvular and congenital heart diseases are briefly described and the role of this technique in screening cardiac patients has been highlighted.

Cardiography, Impedance↗
PubMed1993

A comparison of real-time compression ultrasonography with impedance plethysmography for the diagnosis of deep-vein thrombosis in symptomatic outpatients.

BACKGROUND: Impedance plethysmography performed serially over a one-week period has been shown to be an effective diagnostic strategy for patients with clinically suspected acute deep-vein thrombosis. Compression ultrasonography has a high sensitivity and specificity for the detection of proximal-vein thrombosis. The clinical value of repeated ultrasonography in the management of symptomatic deep-vein thrombosis is unknown. METHODS: We conducted a randomized trial in 985 consecutive outpatients with clinically suspected deep-vein thrombosis to compare the diagnostic value of serial impedance plethysmography (494 patients) and serial compression ultrasonography (491 patients). We compared the positive predictive values of both tests for the diagnosis of venous thrombosis, using contrast venography as a reference. The frequencies of venous thromboembolism during a six-month follow-up period were also compared in patients with repeatedly normal results in order to evaluate the safety of withholding anticoagulant therapy from such patients. RESULTS: The positive predictive value of an abnormal ultrasonogram was 94 percent (95 percent confidence interval, 87 to 98 percent), whereas the predictive value of impedance plethysmography was 83 percent (95 percent confidence interval, 75 to 90 percent) (P = 0.02). In patients with repeatedly normal results, the incidence of venous thromboembolism during the six-month follow-up period was 1.5 percent (95 percent confidence interval, 0.5 to 3.3 percent) for serial compression ultrasonography, as compared with 2.5 percent (95 percent confidence interval, 1.2 to 4.6 percent) for serial impedance plethysmography. CONCLUSIONS: In making the diagnosis of deep-vein thrombosis in symptomatic outpatients, serial compression ultrasonography is preferable to impedance plethysmography, in view of its superior performance in detecting venous thrombosis.

Adolescent↗
PubMed1982

The detection of deep venous thrombosis by impedance plethysmography in hip surgery patients.

Cuff impedance plethysmography has been performed on 120 patients undergoing total hip replacement surgery, all of whom have had venography. The low incidence of thrombosis (17.5%) precluded any accurate data on sensitivity, but specificity was 85%, positive accuracy 48%, negative accuracy 92% and validity 82%. There was a high false positive rate in the first postoperative week (40% of 25 negative venograms). The technique is of value for the exclusion of thrombi in such patients after the eighth postoperative day. Venography will still be required for the positive identification of thrombi in any research protocol.

Aged↗
PubMed1981

Alterations of occlusive cuff impedance plethysmography results in the obstetric patient.

Impedance plethysmography (IPG) is an attractive diagnostic method for evaluating deep vein thrombosis in the pregnant patient because it is noninvasive and it avoids x-ray or radionuclide exposure. However, the accurate diagnosis of deep venous thrombosis by IPG in pregnant patients might be altered by the normal physiologic and anatomic changes that occur during pregnancy. We evaluated 50 healthy women by IPG throughout their pregnancies and during their nonpregnant state. We found that venous capacitance during pregnancy increases 50% over venous capacitance during the non pregnant state. Most of this change occurs during early pregnancy because of a decrease in venous tone caused by rising levels of progesterone and estradiol. During the third trimester of pregnancy venous outflow is diminished compared to outflow during early pregnancy. Venous obstruction by the gravid uterus and fetal head engaging in the pelvis are factors that contribute to this finding. The IPG results in four patients with ileofemoral thrombosis and in three with postpartum pulmonary emboli are also reported. IPG may be utilized as an accurate diagnostic technique in the pregnant woman if the physiologic and anatomic alterations of pregnancy, which are reflected as significant changes in venous capacitance and outflow on IPG testing, are considered.

Adolescent↗