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Biomedical subjects

D C Levin

Publications and source records attributed to D C Levin.

210 records · Page 12Linked to original sources
PubMedDate not supplied

Hemodynamic changes distal to selective arterial injections.

It has been assumed previously that the act of selectively injecting fluid through a catheter into an artery does not significantly alter hemodynamics in that vessel, provided open communication is maintained between the distal portion of the artery and the aortic lumen. In this study, blood flow was measured with an electromagnetic flow probe in distal branches of the left coronary or superior mesenteric arteries of 9 dogs while heparinized arterial blood was injected selectively into the parent vessels at varying rates up to 7 ml/sec. This resulted, in all experiments, in an abrupt and substantial rise in blood flow which was maintained for the duration of the injection. This phenomeon is due primarily to an increase in intraarterial pressure distal to the catheter tip, caused by the injection.

Angiography↗
PubMedDate not supplied

Vascular resistance changes distal to progressive arterial stenosis: a critical re-evaluation of the concept of vasodilator reserve.

Previous studies have shown that with progressive arterial stenosis, resting blood flow does not start to diminish until 85-95% luminal area stenosis is reached. However, during hyperemic states, peak flow starts to diminish at only 40-60% stenosis. An autoregulatory mechanism has been postulated, whereby peripheral arterioles undergo compensatory vasodilatation, thereby maintaining resting flow. During hyperemia, some vasodilator reserve is presumably already used up, resulting in flow dropoff at an earlier stage. We measured flow and pressure and calculated peripheral vascular resistance (Rp) distal to progressive iliac artery stenoses in five dogs. Contrast injections proximal to the stenoses allowed precise angiographic quantitation of the lesions and provided reproducible hyperemic stimuli. Flow-stenosis relationships proved similar to those discussed above, but Rp distal to the lesions failed to show progressive decrease as stenosis increased. Thus, compensatory peripheral vasodilatation does not occur during most phases of progressive arterial stenosis. The contours of resting and hyperemic flow-stenosis curves are not related to the concept of vasodilator reserve but instead are readily explained by basic hydrodynamic principles.

Animals↗
PubMedDate not supplied

Pulmonary artery hypertension in chronic obstructive pulmonary disease: determination by chest radiography.

Pulmonary artery hypertension is a frequent complication of severe chronic obstructive pulmonary disease (COPD). A study was undertaken to determine whether analysis of the chest radiograph can reveal the presence of pulmonary artery hypertension in COPD. Sixty-one men with COPD (forced expiratory volume in 1 second 0.97 +/- 0.35 liters, mean +/- SD) underwent right heart catheterization, and in 46 the mean pulmonary artery pressure was elevated (greater than 20 mmHg). Plain chest radiographs of the 61 patients and 42 normal control subjects were evaluated. The right descending pulmonary artery (RDPA) was enlarged (greater than 16 mm) in 43 of 46 patients (93%) with an elevated mean pulmonary artery pressure, and the left descending pulmonary artery (LDPA) diameter also was enlarged (greater than 18 mm) in 43 of 46. Combined increased RDPA and increased LDPA diameter measurements permitted correct diagnosis in 45 of 46 patients (98%) with pulmonary artery hypertension, including all 26 a mild elevation of mean pulmonary artery pressure (21-30 mmHg). There was a significant correlation between pulmonary artery pressure and both RDPA and LDPA measurements. Analysis of RDPA and LDPA diameters on the plain chest radiograph is a sensitive and accurate method of detecting the presence and severity of pulmonary artery hypertension in COPD.

Aged↗
PubMedDate not supplied

Reactive hyperemia as an indicator of peripheral vasodilation associated with arterial stenoses.

Reactive hyperemia occurs when an artery is temporarily occluded and the occlusion is then released. During a period of vascular occlusion, peripheral vascular dilatation develops distally, and is reversed only gradually after release of the occlusion. Reactive hyperemia was measured in the hind limbs of five mongrel dogs at different degrees of arterial stenosis to determine at what degree of stenosis compensatory vasodilatation of the peripheral vascular bed occurs. In the hind limbs of the dogs, which had been anesthetized, reactive hyperemia as an expression of peripheral vasodilatation did not occur until the critical stenosis (the stenosis at which resting flow started to drop) was reached. It began to occur only beyond the critical stenosis, and then increased as the vessel became totally occluded. This study contradicted the vasodilator reserve theory, which states that during progressive arterial stenosis the peripheral vascular bed dilates to maintain flow until the peripheral vascular bed is maximally dilated, when the critical stenosis is reached.

Animals↗
PubMedDate not supplied

Anatomic variations of the coronary arteries supplying the anterolateral aspect of the left ventricle: possible explanation for the "Unexplained" anterior aneurysm.

Coronary arteriograms of 418 adult patients were studied to ascertain the frequency of variations in blood supply of the anterolateral free wall of the left ventricle; 92.6% had from one to three ramus medianus or diagonal branches supplying this area. Complete absence of any ramus medianus or diagonal branches was exceedingly rare (only 0.5% in this series), and when this occurs the angiographer should suspect complete occlusion of one or more such branches immediately at their origins. Failure to detect ostial occlusion of a ramus medianus or diagonal branch may be a cause of significant misinterpretation of coronary arteriograms.

Adult↗
PubMedDate not supplied

Variations in the blood supply of the left ventricular apex.

Contraction or perfusion abnormalities of the left ventricular apex are generally assumed to result from left anterior descending (LAD) artery disease since this vessel is the usual source of blood supply to this area of myocardium. Such an assumption may be erroneous since the left ventricular apex may be supplied by the LAD alone, both the LAD and posterior descending (PD) branch of the right coronary artery, or the PD alone. Blood supply of the left ventricular apex was prospectively studied angiographically in 431 adult patients. In 77.7%, the apex was totally supplied by the LAD. In 12.1%, the apex received dual blood supply from both the LAD and PD. In 10.2%, the LAD terminated well before the apex, which was totally supplied by the PD. With the latter two anatomic variations, the LAD tended to be shorter and smaller in caliber than usual, while the PD was longer and larger than usual. A short, narrow LAD therefore does not necessarily indicate coronary disease if the left ventricular apex is partially or completely supplied by the PD. Dysfunction or perfusion abnormalities of the apex do not necessarily indicate LAD disease.

Coronary Angiography↗
PubMedDate not supplied

Reactive hyperemia vs. pharmacologic hyperemia in the canine iliac circulation. A comparison.

Different methods of selective vasodilation have been described. One method is reactive hyperemia, which occurs when an arterial occlusion is released, and another method involves injection of vasodilator drugs. Since both arteriography and pressure measurements are often performed during hyperemia, it is important to know whether these two methods differ in the degree or duration of hyperemia achieved. We measured reactive hyperemia in the hind limb of five anesthetized mongrel dogs after arterial occlusion times between 20 seconds' and 20 minutes' duration and after selective intra-arterial injection of 5, 10, and 20 cc of Renografin-76. Only 5 cc of Renografin-76 created greater and longer lasting hyperemia than the maximum reactive hyperemia achieved after 10 minutes of arterial occlusion. For this reason, contrast material-induced hyperemia appears to be preferable to reactive hyperemia as an aid to peripheral arteriography and as an aid to the evaluation of aortoiliac stenoses.

Angiography↗
PubMedDate not supplied

In vivo imaging and evaluation of platelet accumulation vs. time at arterial injury site.

The feasibility of quantitatively imaging platelet deposition over time following angioplasty of the abdominal aorta in a rabbit model, with and without antiplatelet treatment, was investigated. Ten male 3-4 kg rabbits were balloon de-endothelialized and placed on 2% cholesterol diet for eight weeks. Group A was untreated. In Group B, donors and recipients were treated with aspirin (5 mgm/kg) prior to and after angioplasty. Platelets were labelled with indium-111. Labelled platelets were injected just prior to PTA and images of 100,000 counts were obtained immediately and at 30 minutes, 1 hour, and 24 hours. In Group A, increased activity of angioplasty site vs. nonangioplastied aorta was seen immediately. This focal increase became more marked in hypercholesterolemic animals over the 24-hour period. In Group B, both hypercholesterolemic and normocholesterolemic, no focal uptake could be documented on sequential scans. This method and model are promising for in vivo evaluation of platelet-vessel wall interactions, in the setting of angioplasty and antiplatelet therapy.

Angioplasty, Balloon↗
PubMedDate not supplied

Filter wheel equalization in DSA: simulation results.

Digital subtraction angiography (DSA) is a valuable and frequently used diagnostic technique which allows the evaluation of vascular anatomy and pathology. In order to improve the utility and diagnostic performance of DSA, a filter wheel system is presented which can provide mechanically simple, rapidly adaptable, and clinically practical radiographic equalization to DSA images. The filter wheel equalization system consists of a series of computer-driven filter wheels, mounted between the x-ray tube and collimator. Each wheel has an annular area of attenuator material which intersects the x-ray beam and carries a rotationally varying compensation pattern on it. Rotation of the filter wheel modulates the attenuator pattern in the x-ray field under computer control, in a manner designed to increase the x-ray exposure to underexposed areas in the image. A system with eight wheels has 10(19) possible equalization patterns. The compensation patterns are removed in the subtracted DSA images. Computer simulation techniques were used to evaluate various design scenarios for the filter wheel system, using a data base of 191 clinical DSA mask images. For a practical implementation of the filter wheel system, an improvement in the signal to noise ratio of 23%, averaged over the image, was found.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Prospectively gated cardiac CT. Preliminary results in normal and postinfarction animal models.

Cardiac motion introduces significant artifacts into standard CT images obtained through the heart. A newly developed prospectively gated CT system produced 87 gated scan sets in ten normal and infarcted dogs. Each cycle can provide up to 24 37-70 msec composite images of one transverse slice, equally spaced in time through the cardiac cycle. Eight to 12 2-second scans, obtained during a constant infusion of contrast, were required to collect the data for each gated set. The left and right ventricular myocardium was clearly seen, regions of myocardial infarction were identified, and atrial and ventricular filling and emptying were visualized. In areas of infarction, wall thickness was unchanged from diastole to systole. In addition to improved resolution, a gated CT series evaluation of wall motion abnormalities may provide a better means of locating myocardial infarction than the ungated CT image.

Animals↗