Biomedical subjects
Publications and source records attributed to I Faris.
This paper reports the use of a vein cuff to facilitate the anastomosis of a prosthetic graft to a small artery. This technique makes it easier to perform a good anastomosis and may improve the chances of long-term patency.
This review examines the pathology, clinical effects and physiological disturbances produced by vascular disease and autonomic neuropathy in the lower limb in diabetic subjects. Atherosclerosis is a major factor in causing foot lesions in diabetics. The distribution of the disease frequently makes vascular reconstructive surgery difficult or impossible but an aggressive approach to reconstruction is justified because the results of major amputations are bad. Arterial calcification probably has no significant effect on the blood supply to the foot. There is some evidence that disease of arteries in the foot may be associated with the development of ulcers or gangrene. Disease of the arterioles and capillaries is frequent, but there is little evidence that this microangiopathy causes lesions. Autonomic neuropathy affecting the limb is also common, and although there are several mechanisms by which this might predispose to ulcers or gangrene, there is little evidence of such a direct relationship. In a patient presenting with ulceration or gangrene of the foot it is often impossible to determine the relative roles of vascular disease, affecting large or small vessels, and neuropathy, either somatic or autonomic, in the development of the lesion. Further progress depends on the development of more direct methods for assessing microvascular and autonomic nervous function.
Autoregulation of blood flow was studied in skeletal muscle and subcutaneous tissue in seven Type 1 (insulin-dependent) diabetic patients (median age: 36 years) with nephropathy and retinopathy and in eight normal subjects of the same age. Blood flow was measured by the local 133Xe washout technique. Reduction in arterial perfusion pressure was produced by elevating the limb 20 and 40 cm above heart level. Blood flow remained within 10% of control values when the limb was elevated in normal subjects. In five of the seven diabetic subjects blood flow fell significantly in both tissues when the limb was elevated 40 cm indicating impaired autoregulation. The results suggest that intrinsic vascular (arteriolar) mechanisms (myogenic and/or metabolic) underlying the normal autoregulatory response are defective in some diabetic patients with microangiopathy.
Two-plane angiography and direct segmental pressure measurements in the femoral and popliteal arteries and indirectly on the arm and ankle were performed in 101 limbs seeking to establish a relationship between angiographic assessment of the patency of the popliteal artery and the trifurcation vessels and the popliteal ankle pressure difference. When the tiberoperoneal trunk or the trifurcation vessels were occluded or more than 50% of the lumen was stenosed, the pressure difference exceeded 10 mmHg in 30/40 limbs (75%). When three, two, or only one of the tibial vessels were patent, the pressure difference exceeded 10 mmHg in 2/58 limbs (3%). One month following above knee femoropopliteal bypass (48 limbs), patients with a popliteal-ankle difference less than 10 mmHg obtained a significantly higher ankle pressure index (PI 0.86, range 0.56-1.20) (p less than 0.01) than those with a pressure difference exceeding 10 mmHg (PI 0.66, range 0.40-0.91). The clinical state 6 months following femoropopliteal bypass did not demonstrate that patients with a low popliteal-ankle difference fared better than patients with a higher pressure difference; however, the PI appeared significantly lower in the latter group compared to the former. The graft material was correlated to the popliteal-ankle pressure difference. It appeared that prosthetic grafts failed within 6 months when the difference exceeded 10 mmHg in 10/12 limbs (83%), but autologous vein grafts only failed in 2/10 limbs (20%). Finally, it was possible to predict the postoperative ankle pressure index significantly from data derived from the pressure measurements.
The study was performed in order to determine whether a local sympathetic venoarteriolar "reflex" is present in the dog hindleg. Femoral artery blood flow was measured by an electromagnetic flowmeter probe, and blood flow in the thigh muscle and subcutaneous tissue distally in the paw was measured by the local 133Xe washout technique. Twenty experiments were carried out in seven dogs unilaterally sympathectomized 2-4 weeks previously. Resting vascular tone did not differ in the sympathectomized and nonsympathectomized legs. In the control leg, venous pressure elevation caused a decrease in femoral blood flow of 49% corresponding to an increase in vascular resistance of 58%. In muscle and subcutaneous tissue vascular resistance increased by 81% and 35%, respectively. In the denervated leg, venous stasis caused no change in total vascular resistance. In muscle the vascular resistance increased by only 24%. In subcutaneous tissue, vascular resistance decreased by 12%. The effect of acute lumbar sympathectomy was studied in another group of seven dogs. Operation caused an immediate decrease in vascular resistance of 40%. The increase in vascular resistance during venous stasis in the total leg, as well as in muscle and subcutaneous tissue, was not affected. However, acute lumbar sympathectomy combined with injection of phenoxybenzamine into the femoral artery almost abolished the vasoconstriction induced by venous stasis. In muscle, the increase in vascular resistance was still present, but considerably attenuated. In subcutaneous tissue, the normal response was completely blocked. Finally, local suction induced vasoconstriction in an adjoining area not subjected to changes in vascular transmural pressure, an effect that could be blocked by local neural blockade at the site of suction. The results strongly suggest that a local sympathetic veno-arteriolar (axon) "reflex" is present in muscle and subcutaneous tissue in the dog hindleg.
Thirty-six legs in thirty-three diabetic patients with ischemia at rest and multiple level arterial disease were studied preoperatively. Direct intraarterial femoral and popliteal artery blood pressures were measured together with indirect arm and foot blood pressures. Based on the systolic segmental pressure gradients it was predicted preoperatively whether it was necessary to make a one- or two-level reconstruction. The ankle pressure measured one month postoperatively correlated well with predicted values. Of the seventeen occlusions within the observation time hemodynamic factors played an important role in eleven cases. In the femoro-crural segment one occluded in which an iliac stenosis with a pressure gradient of 28% had been disregarded. In the femoro-popliteal above knee segment four occlusions occurred in cases where the postoperative ankle pressures were less than 80% of the preoperatively predicted value, suggesting stenosis at the anastomosis. A popliteal to ankle gradient of 39% was measured preoperatively in the fifth case which occluded 2 months postoperatively. In the aortofemoral segment five occlusions occurred all having femoral to ankle pressure gradients exceeding 40% of femoral artery pressure. Retrospectively, seven of the failures might have been prevented by two-level reconstructions and four failures by a secondary arterioplasty.
This study was undertaken to determine whether the distensibility of a passive vascular bed is reduced in Type 1 (insulin-dependent) diabetic patients with microangiopathy. The change in blood flow induced by 45 degrees head-up tilting was studied in two systems: (a) following maximal ischaemic exercise and (b) in a vascular bed locally paralysed by the injection of papaverine. Five normal subjects, six patients with long-standing Type 1 diabetes and six non-diabetic patients with severe atherosclerosis affecting the legs were studied. Blood flow was measured in the anterior tibial muscle by the isotope washout technique. The median increase in blood flow produced by tilting was greater in normal subjects than in diabetic subjects in both the locally-relaxed bed (58% and 14% respectively) and after maximal ischaemic exercise (45% and 4% respectively). In the atherosclerotic subjects, the increase in blood flow in the locally relaxed bed was 77%. The results are consistent with the hypothesis that the reduced distensibility seen in the diabetic subjects was related to the presence of microvascular disease and that the behaviour of a vascular bed relaxed by the local injection of papaverine might be an appropriate model to study this condition.
This paper describes a method for studying the clearance of 133Xenon from the subcutaneous tissue of the calf and foot over 24-h periods. The average blood flow over this period can be estimated from the clearance constant obtained. Two series of measurement of the radioactivity are made, the first 2 h after the injection of 1-2 mCi 133Xenon in saline and the second 18-24 h later. The distance between the detector and the depot is reproduced using a cylinder 20 cm long. The median washout rate of the isotope (k) in 25 patients was 2.57 X 10(-3) min-1 for the calf and 2.39 X 10(-9) min-1 for the foot. The median difference between repeated measurements in the same patient ws 0.24 X 10(-3) min-1 in the calf and 0.43 X 10(-3) min-1 in the foot. This method, which can be used to estimate the average blood flow over 24 h while the patient undertakes his normal activities, should be useful in assessing the effect of therapy on the blood flow to the limb.
Knowledge of the tissue to blood partition coefficient (lambda) is essential for calculation of the perfusion coefficient in a single tissue based on measurements of the washout of locally injected isotopes. No measurements of lambda for Xenon in subcutaneous tissue in the leg have been done in patients with occlusive arterial disease. In 12 patients with occlusive arterial disease in the legs lambda for Xenon was determined in subcutaneous tissue in the calf region and foot as the ratio between the washout rate constant of 131I-Antipyrine and 133Xe. A mixture of the two indicators was injected subcutaneously laterally on the calf and in the first interosseous space on the foot. The time until the curves followed a monoexponential course varied between 15 and 45 min in the calf and 5 and 45 min in the foot. The calculated lambda for Xe showed a great variance between individuals in calf as well as foot. Mean value was 3.7 ml X g-1 (range: 1 X 7-10 X 7) in the calf and 2 X 7 ml X g-1 (range: 1 X 2-4 X 9) in the foot. It is concluded that lambda measurements are necessary for determination of subcutaneous blood flow from 133Xe washout curves in these patients. Determination of lambda is especially important when comparisons are made between individuals.
Direct measurement of the femoral artery pressure before operation has been used to predict the postoperative change in ankle and toe pressure in 102 limbs (83 patients) that underwent aortoiliac surgery for the treatment of atherosclerotic occlusion or stenosis affecting both the aortoiliac and femoral artery segments. Rest pain or gangrene was present in 74 limbs. In 26 other limbs simultaneous aortoiliac and femoral artery reconstructions were performed. The changes in both toe and ankle pressures could be confidently predicted from the preoperative data. A predicted toe pressure of lower than 25 mm Hg was associated with a high probability that amputation would be required. The chances of an amputation were less than 3% if a toe pressure higher than 40 mm Hg was predicted. If the predicted ankle pressure index was lower than 0.56, there was a 90% chance that intermittent claudication would persist. Measurement of the femoral artery pressure allows prediction of the toe and ankle pressure response to surgery to be made with sufficient accuracy to permit a preoperative decision to be made between the need for a single-level or a two-level arterial reconstruction: no patients who had an aortoiliac reconstruction needed a subsequent downstream repair of the femoral segment.
This paper describes a method, using an interactive computer programme, for fitting a curve to data which is expected to assume a sigmoid form. The programme is specifically designed to generate best estimates of the limits and maximum slope of stimulus-response curves for the carotid sinus baroreceptor reflex, but is applicable to curve-fitting tasks in other fields such as immunology, pharmacology, biochemistry and neurophysiology.
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Vascular disease is the major factor in the development of many lesions in diabetics, although the independent role of neuropathy has been increasingly recognized. The major problem in assessment is to decide the severity of ischaemia and neuropathy present in a particular patient. Healing after local surgery can be expected in those lesions which are painless, and peripheral (that is, are situated on the toes or forefoot), especially if the ankle pulses are present. Operation must provide adequate drainage and wound care must be meticulous. The problem of prevention of recurrences remains unsolved, but recurrences can probably be delayed or prevented by a careful follow-up.
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In the period 1957-72, 426 patients were operated upon for calculous disease of the biliary tract. For various reasons pre-exploratory operative cholangiography was not performed in 26 patients, but in the remaining 400 patients this examination was the major determinant as to whether or not the common duct contained calculi, and hence required exploration. Analysis of this series of 400 patients shows that without operative cholangiography (a) ductal stones would have been overlooked in 16 of the 78 patients with stones in the common duct (4 per cent of the whole series; 20-5 per cent of those with stones in the common bile duct); (b) exploration of the common duct would have been required in a further 48 (15 per cent) of the 322 patients without stones in the common duct, giving a positive yield from operative cholangiography in 64 patients (16 per cent) in the whole series. Negative exploration of the common duct was performed in only 31 patients, that is 29 per cent of the patients whose duct was explored but only 7-8 per cent of the whole group. The criteria by which an operative cholangiogram should be assessed were re-evaluated in the light of the findings in these 400 patients. In general the criteria of normality previously described were affirmed, and the following points established: a. In the absence of a filling defect the diameter of the duct is the most important indication of the presence of a stone. b. There is a statistically significant increase in the diameter of the common duct with age, and though not great this could, if neglected, give rise to error in the interpretation of the cholangiogram in younger patients. c. Even within the overall normal range of duct diameter (less than 12 mm) the wider the duct, the greater is the chance of it harbouring a stone. d. Impaired flow of contrast material into the duodenum is significantly related to duct diameter. e. Impaired flow of contrast material into the duodenum and failure to delineate the terminal segment of the duct tend to occur together; they may occur in a duct free of stones and if they are the only abnormality the examination should be repeated after the inhalation of amyl nitrite. This study confirms that operative cholangiography is the most accurate method at present available of determining whether or not the common duct contains a stone (or stones), and hence requires exploration.
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A case of empyema of the gallbladder caused by Haemophilus parahaemolyticus is reported. This is believed to the the first report of such an infection. The literature relating to pathogenicity of this organism is reviewed.
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