Biomedical subjects
Publications and source records attributed to R W Barnes.
An optical method is described for studying the spatial and temporal characteristics of broad-band ultrasonic pulses propagating in transparent media. The simplicity of the approach suggests its consideration as a method for calibration and comparison of the transmitted pulse characteristics of medical ultrasound systems.
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Indirect periorbital screening techniques may detect obstruction of the extracranial internal carotid artery, but they do not distinguish operable stenosis from inoperable occlusion. In an attempt to overcome this limitation, direct interrogation of carotid artery flow velocity by Doppler ultrasound was added to periorbital screening of 97 arteries in 53 patients. Analysis of results suggests that this assessment can improve diagnostic accuracy and distinguish stenosis from occlusion of the internal carotid arteries in stroke-prone patients.
We compared the ankle pressure response during reactive hyperemia to the response to treadmill exercise in 28 limbs of 14 normal individuals and 26 legs of 15 patients with arterial occlusive disease. The mean percent maximum drop in ankle blood pressure during reactive hyperemia in normal limbs, 17% +/- 11% (+/- 1 SD) was significantly less than that of legs with arterial disease, 54% +/- 15% (P less than .001). Abnormal values were recorded in all but three diseased limbs. There was good correlation between the ankle pressure responses to reactive hyperemia and treadmill exercise (r = 0.71, P less than .001). This study suggests that measurement of ankle pressure during reactive hyperemia may be a useful substitute for treadmill testing to determine the functional capacity of the circulation during stress in patients with arterial occlusive disease. Reactive hyperemia testing requires less time and equipment and may be performed in patients who might be at risk or unable to carry out treadmill exercise.
Most studies demonstrating an increased risk of venous thromboembolism in women on oral contraceptives are based on clinical manifestations of the disease. Because of the fallibility of the clinical diagnosis of suspected leg vein thrombosis, Doppler ultrasonic evaluation (with a 93% accuracy compared to venography) was performed for clinical manifestations in deep vein thrombosis in 54 women taking birth control pills and 75 women of similar age who were not on contraceptives. The clinical diagnosis was confirmed by Doppler in only 16.7% of the women taking contraceptives and 30.7% of women not taking contraceptives (P = 0.052). This study suggests that the clinical diagnosis of leg vein thrombosis is frequently erroneous, particularly in women taking oral contraceptives. Future investigations reporting venous thromboembolism associated with oral contraceptives should be based on diagnoses validated by accurate objective techniques.
The first derivative thoracic impedance cardiogram, phonocardiogram, and electrocardiogram were recorded in three groups of 22 subjects each. In Group 1 (control), simultaneous impedance cardiogram, phonocardiogram, and aortic valve echocardiograms showed that the X point of the impedance cardiogram occurred synchronously with the aortic second heart sound and with echocardiographic aortic valve closure. In group 2 (clinical diagnosis of aortic regurgitation) the scalar magnitude of the impedance cardiogram O wave and the ratios of the impedance cardiogram wave form X/dz/dtmax and O/dz/dtmax were different from control. In addition, the early diastolic (X) and systolic portions (S) of the impedance cardiogram wave form of group 3 patients were planimetered and expressed as the ratio X/S, called the impedance cardiographic aortic regurgitant fraction (aortic RFI). The aortic RFI was increased by handgrip, a manoeuvre which acutely increases the magnitude of aortic regurgitation. The difference between Fick cardiac output and left ventricular angiographic output was used to calculate aortic valvular regurgitant fraction, which related closely to the impedance cardiogram. These data suggest that it is useful in the noninvasive assessment of aortic regurgitation.
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Doppler ultrasound is the most simple, inexpensive, accurate and versatile of the available noninvasive screening techniques to assess peripheral vascular diseases. The four fundamental components of peripheral arterial evaluation with this technique are assessment of blood velocity signal, measurement of resting ankle pressure, determination of segmental leg blood pressures, and measurement of ankle pressure response to exercise or reactive hyperemia. Plethysmography permits graphic recording of pulse-wave morphology, determination of digit blood pressure, and pulsatile responses to compression maneuvers. These techniques are useful in objectively quantifying peripheral arterial occlusive disease, predicting the results of operative therapy, monitoring the success of arterial reconstruction during surgery, and following the physiologic status of the patient after surgery.
Noninvasive diagnostic techniques permit objective assessment of the presence, location, and hemodynamic alterations associated with congenital or acquired arteriovenous fistulas. Doppler ultrasound may be used to assess abnormal velocity signals and directional blood flow in afferent and efferent limbs of the fistula, as well as abnormal pressure gradients in the involved extremity. Plethysmography permits graphic qualitative assessment of pulse wave form alterations before and after compression of the fistula. In addition, venous occlusion plethysmography permits quantitation of limb or digit blood flow before and after fistula. In addition, venous occlusion plethysmography permits quantitation of limb or digit blood flow before and after fistula compression. Illustrative cases of congenital and acquired arteriovenous fistulas demonstrate the utility of these noninvasive techniques in the objective assessment of patients.
A prospective study was carried out comparing two techniques of segmental arterial pressure measurements of the leg to detect, localize and quantify regional arterial occlusive disease. The measurement of pressures of the proximal and distal parts of the thigh with the narrow cuff technique permitted correct anatomic localization of aortoiliac, femoropopliteal or combined disease in 78 per cent of diseased extremities, including all limbs with isolated aortoiliac or femoropopliteal disease. A single wide cuff arterial pressure measurement of the thigh correctly localized arterial obstructions in only 19 per cent of diseased extremities. Although a wide cuff is associated with less artifactual elevation in measured arterial pressure at the thigh, this advantage is outweighed by the limitation of diagnostic accuracy in localizing segmental arterial occlusive disease. We recommend that segmental arterial pressure measurements of the limb be made at four levels on the lower extremity, including arterial pressures of the proximal and distal parts of the thigh to achieve maximal diagnostic accuracy.
The effect of hypovolemia on femoral artery vascular resistance and directional arterial flow velocity was determined in six mongrel dogs. Progressive withdrawal of blood was associated with an increase in femoral arterial resistance and reverse flow velocity and a decrease in forward flow velocity. The percentage increase in the ratio of peak reverse to peak forward flow velocity (Vr/Vf) varied in a positive linear fashion with the percent increase in femoral artery vascular resistance, (r = 0.69, P less than 0.001). The femoral arterial peripheral vascular resistance and peak Vr/Vf increased significantly before arterial pressure declined. These alterations in peak Vr/Vf occur early in the course of hypovolemia and are a sensitive index of extremity hemodynamics associated with hemorrhagic induced hypovolemia.
The Doppler ultrasonic velocity detector is a simple, inexpensive and versatile device for intraoperative monitoring of the integrity and hemodynamics result of vascular reconstructive surgical procedures. With this instrument, an ankle-arm systolic pressure index may be obtained before and after aortoiliac and femoral reconstructive surgical procedures. If the ankle pressure index does not increase following aortofemoral bypass and a thromboembolic vascular accident has been ruled out, it is unlikely that the patient will be significantly helped by that procedure alone. The use of a sterile Doppler probe permits qualitative assessment of arterial velocity signals following femoropopliteal bypass, carotid endarterectomy and mesenteric or renal vascular procedures. The Doppler detector may also be used to assess periorbital flow dynamics following carotid endarterectomy. Selective intraoperative arteriography can be based upon the presence of residual flow abnormalities detected by Doppler ultrasound.
Obesity has been considered as a high risk factor in the development of thromboembolism. To test the validity of this hypothesis, the records of 564 morbidly obese patients who underwent gastric bypass for control of their obesity were reviewed. Four patients, 0.7 per cent, had proved fatal pulmonary emboli and three demonstrated detectable, but not fatal, embolization. Fifty-seven patients were studied prospectively with Doppler examinations of the lower extremities, and only one patient had a transient abnormality of venous thrombosis of the calf, which proved to be associated with a nonfatal pulmonary embolus. The morbidly obese patients are not at high risk from thromboembolism, and the prophylactic use of low dose heparin, which may increase known wound morbidity, is discouraged. Doppler ultrasound of the lower extremities, however, has proved usefulness to differentiate deep venous thrombosis of the lower extremity from other causes of pain in the leg of the morbidly obese.
A prospective randomized trial evaluated graded-compression antiembolism stockings for prevention of leg vein thrombosis as assessed by Doppler ultrasound, in patients undergoing total hip replacement. The study was terminated after the evaluation of 18 patients revealed a significantly greater incidence of deep vein thrombosis, documented by phlebography, in patients without stockings (5 of 10) compared to those with stockings (none of 8, p less than 0.03). Three of the patients with thrombosis developed pulmonary emboli. Although the sample size of this study is small, the implication that graded-compression stockings reduce the incidence of leg vein thrombosis is strong and is supported by the results of other recent trials. These findings are at variance with earlier studies which failed to document efficacy of elastic stockings, which involved products which did not provide graded limb compression.
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The efficacy of concomitant lumbar sympathectomy in improving results of aortoiliac reconstruction was assessed by a prospective, randomized study of 51 patients undergoing operation for occlusive or aneurysmal disease. Sympathectomy was performed on 50 limbs, while 52 extremities served as controls. Sympathectomy resulted in a significant reduction in foot vascular resistance determined by plethysmography. However, the procedure had no effect on leg circulation, assessed by ankle/arm pressure indices determined by Doppler ultrasound. In the sympathectomy group, there were three early postoperative amputations for ischemia, despite patent grafts. In the control group, there was one late graft occlusion, caused by progressive atherosclerotic disease. Although sympathectomy may improve pedal circulation, the procedure does not appear to improve the results of aortoiliac reconstruction.
To evaluate the effect of wound dressing upon wound healing, fifty-one patients undergoing below-knee amputation using a long posterior myocutaneous flap technic were randomly allocated into a soft or plaster dressing group. Neither wound dressing technic proved superior, as wounds healed in 85.2 per cent of the plaster dressing group and 83.3 per cent of the soft dressing group.