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Biomedical subjects

A W Stanson

Publications and source records attributed to A W Stanson.

At least 55 records · Page 3Linked to original sources
PubMed1993

Pulmonary embolism: diagnosis with electron-beam CT.

Contrast material-enhanced electron-beam computed tomography (CT) (100-msec scan time) was performed to image the pulmonary vasculature in 86 patients, each suspected of having a pulmonary embolism (PE). Thromboembolic material was demonstrated in 39 patients; no emboli were demonstrated in 47. In 25 patients, angiographic or pathologic proof was available. There were 19 proved positive CT scans, four proved negative scans, one false-negative scan, and one false-positive scan. In the 21 patients with CT and angiographic correlation, evidence of thromboembolic disease was seen in 88 vascular zones. Fifty-three zones were positive for PE at both CT and angiography. Eighteen zones were positive for PE at angiography alone, and 17 zones were positive at CT alone. Electron-beam CT is a potentially effective noninvasive means of diagnosing PE.

Adult↗
PubMed1993

Fast-computed tomographic evaluation of the effect of route of breathing on upper airway size and function in normal men.

Nasal obstruction is associated with increased sleep disordered breathing (SDB), even in normal subjects. This increase in SDB may result from narrowing of the orohypopharyngeal (OHP) or retroglossal segment of the upper airway (UA) due to retropositioning of the jaw and tongue base as the mouth is opened and route of breathing changed from nasal to oral. It is postulated that significant narrowing of the OHP occurs with oral breathing even in the awake state. To ascertain the effect of route of breathing on the UA, fast-CT was used to study the UA response to the route of breathing in 30 normal, awake men, with each subject breathing via the nasal and oral routes under the following conditions: end-inspiration during tidal breathing (VTei) and functional residual capacity (FRC). In the velopharyngeal (VP) or retropalatal segment of the UA, minimum (Amin) and mean (Amean) cross-sectional areas (CSA) decreased 49 +/- 11 percent and 16 +/- 6 percent, respectively, with oral compared with nasal breathing at FRC. In the OHP, Amin at FRC increased by 26 +/- 15 percent with oral compared with nasal breathing with no significant change in Amean. Similar changes in CSA of both the VP and OHP were observed at VTei. Genioglossal electromyographic (EMGgg) activity increased from 12 +/- 1 microV breathing nasally to 27 +/- 4 microV breathing orally at FRC. Although the CSA of the VP segment decreased with conversion from nasal to oral breathing, Amin of the OHP segment was unexpectedly observed to increase with oral breathing. The doubling of EMGgg activity with oral breathing suggests that active contraction of the genioglossus may function to increase the patency of the OHP segment during oral breathing in supine, awake, normal subjects.

Adult↗
PubMed1992

Beam-shaping device for long-film angiography.

Uniform radiologic exposure from the pelvis to the ankles is often difficult to achieve when long films (51-inch) are used for femoral angiography. A unique device developed to shape the x-ray beam accomplishes this task by using a movable shutter to obscure a portion of the x-ray beam. A microprocessor-controlled stepper motor modulates the amount of beam cutoff by regulating the movement of the shutter from the foot end of the film. The goal is to match exposure factors to the patient's body shape. This beam-shaping device has been evaluated and tested in examinations of 500 patients over the past year. A substantial improvement in image quality over that achieved with earlier systems of graduated screens and multiple wedge filters was seen in all cases. The system is esy to use, flexible, and especially valuable in imaging obese patients or those who have legs disproportionately smaller than their pelvis or abdomen.

Abdomen↗
PubMed1992

Coronary artery calcification detected with ultrafast CT as an indication of coronary artery disease.

To assess the relationship of coronary artery calcification to angiographically detectable disease, the authors evaluated 100 patients less than 60 years of age who underwent clinically indicated coronary angiography and ultrafast computed tomography (CT). The ultrafast CT technique consisted of 3-mm-thick contiguous sections and a 100-msec acquisition time. All patients with clinically significant disease at angiography (defined as at least one stenosis with a diameter narrowing of at least 50%) had some coronary artery calcification present at ultrafast CT (100% sensitivity in this population). The absence of calcification at ultrafast CT had a 100% negative predictive value for clinically significant coronary artery disease. Specificity and positive predictive value were 47% and 62%, respectively. Sensitivity and specificity of ultrafast CT in the detection of patients with angiographically detectable disease were 94% and 72%, respectively. Ultrafast CT of the heart is an anatomically based, noninvasive test with high sensitivity for the detection of coronary artery calcification. Ultrafast CT may be beneficial in the screening of selected populations for the presence of atherosclerotic coronary disease.

Adult↗
PubMed1992

Fast-computed tomography evaluation of age-related changes in upper airway structure and function in normal men.

The reasons for the increase prevalence of snoring and sleep-disordered breathing in elderly adults are not clear. We hypothesized that age-related reductions in upper airway (UA) size, increased UA collapsibility, and/or inadequate compensatory action of the UA dilator muscles were contributory factors. Fast-computed tomography (CT) was used to examine UA size at FRC and atmospheric pressure, as well as its collapsibility and distensibility in response to negative and positive UA pressures actively generated by the subjects at FRC. The electromyographic activity of the genlogiossal muscle group (EMGgg) was recorded to assess UA dilator muscle response. Thirty adult men with normal overnight polysomnography (mean AHI = 4 +/- 1/h) were studied, and three subgroups of 10 subjects each, young (20-39), middle-age (40-59), and old (60-79), were compared. Unexpectedly, minimal UA cross-sectional area (Amin) at FRC and atmospheric pressure was larger in the old group than in the young group (73 +/- 9 versus 49 +/- 7 mm2, p = 0.04). In response to negative UA pressures of -10 and -50 cm H2O, there were no significant age group differences in Amin, indicating that no age-related increase in UA collapsibility was present. Although no significant difference in tonic EMGgg activity at FRC and atmospheric pressure was detected between groups, the old group demonstrated greater EMGgg activity than did the younger age groups in response to negative UA pressure loading (p less than 0.05). This finding indicated increased compensatory UA dilator muscle activity in response to negative pressures in the older subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Fast-CT evaluation of the effect of lung volume on upper airway size and function in normal men.

The present study was performed to evaluate the regional changes in pharyngeal cross-sectional area (CSA) that occur with changes in lung volume in normal men. Fast-CT and genioglossal electromyogram (EMGgg) were used to study upper airway (UA) size and dilator muscle activity at TLC, lung volume at end-tidal inspiration (VTei), FRC, and residual volume (RV) in 30 men with a mean age of 46 +/- 3 yr and no significant sleep-disordered breathing, mean AHI = 4 +/- 1 per hour. Compared with values at FRC, minimum CSA (Amin) increased 154 +/- 31% at TLC (p = 0.0001), 19 +/- 10% at VTei (p = 0.03), and there was a trend toward a decrease of 31 +/- 12% at RV (p = 0.07). Similar but smaller changes were observed in mean CSA (Amean), with an increase of 69 +/- 14% at TLC (p = 0.0001), 8 +/- 5% at VTei (p = 0.01), and a decrease of 17 +/- 7% at RV (p = 0.01). Both the velopharyngeal (VP) and orohypopharyngeal (OHP) segments of the UA increased in size with increasing lung volume. Both Amin and Amean of the OHP segment at TLC were larger (55 +/- 19 and 38 +/- 14%, respectively) than the respective measurements in the VP segment. EMGgg activity doubled from 12 +/- 1 microV at FRC to 25 +/- 1 microV at TLC (p = 0.006). There was no change in EMGgg with tidal ventilation or with exhalation to RV. Changes in CSA directly paralleled changes in lung volume in this group of normal awake nonobese men.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

The effects of transcutaneous electrical stimulation during wakefulness and sleep in patients with obstructive sleep apnea.

Upper airway (UA) collapse in obstructive sleep apnea (OSA) is considered in part to result from the decrease in UA dilator muscle tone that occurs during sleep. We hypothesized that augmentation of UA muscle function by transcutaneous electrical stimulation (TES) might function to enlarge UA size during wakefulness and/or prevent UA collapse during sleep in patients with OSA. Eight male patients with OSA were studied both awake and asleep, with TES administered to the submental region in two patients and to both the submental and subhyoid regions in six patients. Fast-CT scans obtained at FRC and end-inspiration (VTei) demonstrated increased UA size with tidal breathing, p less than or equal to 0.05. The active generation of -10 cm H2O pressure at FRC substantially decreased UA size, p less than or equal to 0.001. However, no changes in UA size were detected at either FRC or VTei with TES applied at 50 and 100% of the maximal tolerated intensity. The collapsibility of the UA in response to the generation of -10 cm H2O pressure was also unchanged by TES. In contrast to the lack of effect of TES on UA size, voluntary protrusion of the tongue increased cross-sectional area (CSA) of the orohypopharyngeal (OHP) segment of the UA, p less than 0.05, and to a lesser extent the CSA of the distal velopharyngeal segment, p = 0.06. When applied during sleep, TES failed to prevent or improve either sleep-disordered breathing or sleep architecture.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1992

Reconstruction of large veins for nonmalignant venous occlusive disease.

To evaluate the effectiveness of venous grafting, we reviewed the management and clinical course of 28 patients (21 males and seven females) who underwent 29 reconstructions of large veins for benign disease. There were 12 patients with superior vena cava (SVC) syndrome, two with subclavian vein thrombosis, and 15 with occlusion of the inferior vena cava (IVC) or iliac veins. One of these patients underwent both IVC and SVC reconstructions. Reconstruction of the SVC was performed with spiral saphenous vein graft (SSVG) in nine patients and expanded polytetrafluoroethylene (ePTFE) in three. All seven straight SSVGs had documented patency at a median of 7 months (2 weeks to 5 years) after reconstruction. Six patients had complete relief of symptoms. Two patients with bifurcated SSVG had early occlusion of one graft limb. Two of the three ePTFE grafts needed early thrombectomy. One graft reoccluded at 6 months and two were patent at 2 and 5 years. The two subclavian vein reconstructions with axillary-jugular ePTFE grafts with an arteriovenous fistula had documented early patency. Both patients had rapid resolution of symptoms. The IVC or iliac vein was reconstructed with ePTFE graft in 11 patients, SSVG in three, and Dacron in one. A femorofemoral arteriovenous fistula was added in eight patients with ePTFE grafts. Seven of the 11 ePTFE grafts had documented patency at the last follow-up (median 9 months; range 2 weeks to 5 years). None of the three SSVGs had documented long-term patency. The one Dacron cavoatrial graft occluded at 3 years. A straight SSVG continues to be our first choice for SVC replacement. Short, large-diameter ePTFE grafts perform the best in the abdomen. Femorocaval or long iliocaval grafts need an arteriovenous fistula to maintain patency. Long-term patency after closure of the fistula is still unknown. Femorocaval grafts with poor venous inflow have limited chance of success. Failed or failing grafts may be salvaged by early thrombectomy. Venous reconstruction to treat selected patients with symptoms with large vein occlusion continues to be a viable option.

Adult↗
PubMed1991

Ischemic injury to the spinal cord or lumbosacral plexus after aorto-iliac reconstruction.

Between January 1, 1980, and June 30, 1989, 9 patients (6 males and 3 females) developed ischemic injury to the spinal cord or lumbosacral plexus following 3,320 operations on the abdominal aorta (0.3%). The incidence of this complication was 0.1% (2 of 1,901) after elective and 1.4% (3 of 210) after emergency abdominal aortic aneurysm repair, and 0.3% (4 of 1,209) after repair for occlusive disease. Three of the latter had prior clinical evidence of distal embolization. Eight grafts were bifurcated (aorto-iliac:four, aorto-femoral: three, aorto-ilio-femoral:one). One patient underwent extra-anatomic revascularization. Only two patients had supraceliac aortic cross-clamping and one patient underwent exclusion of both internal iliac arteries. Four patients had hypotension. Early mortality was 22% (two of nine). Severe perioperative complications, mostly due to associated visceral and somatic ischemia and sepsis, were present in seven of the nine patients. The extent and type of the neurologic injury correlated with long-term outcome. Patients with ischemic injury of the lumbosacral roots or plexus had better recovery. Attention to the pelvic circulation and the collateral blood supply is important. Use of gentle technique to prevent embolization, avoidance of hypotension and prolonged supraceliac cross-clamping, revascularization of at least one internal iliac artery, and the use of heparin may decrease but not eliminate paraplegia. Once this unexpected complication occurs, careful neurologic evaluation should be done to localize the lesion and aid prognosis.

Aged↗
PubMed1991

Microvascular pedal bypass for salvage of the severely ischemic limb.

Bypass to the pedal arteries was performed with use of the operating microscope and standard microsurgical technique in 37 patients with severe, chronic ischemia of a lower extremity. Twenty-one patients (57%) had three or more cardiovascular risk factors, and 22 (59%) had diabetes. Preoperative arteriography identified a pedal artery suitable for bypass in all but one patient. The greater or lesser saphenous vein was used in all patients, most frequently as a nonreversed, translocated vein graft. An arm vein was used as part of a composite graft in only one patient. No early deaths occurred, and only one patient had a perioperative myocardial infarction. Although five grafts occluded within 30 days, four were successfully revised, and 36 patients had a patent graft at the time of dismissal from the hospital. At 1 year, the primary graft patency rate (patency without revision) was 60.8%, and the secondary patency rate was 68.8%. One early and six late amputations were performed; the cumulative 1-year limb salvage rate was 82.4%. Grafts with an intraoperative flow rate of 50 ml/min or more had a better patency rate than those with a lower flow rate. The presence of diabetes did not adversely affect long-term patency. Of the 34 patients who were alive at the time of this report, 27 (79%) had a functional foot that allowed ambulation, had no rest pain, and had no substantial loss of tissue. Pedal bypass should be considered for critical, chronic ischemia, even if the patient has an increased surgical risk and advanced distal atherosclerotic disease.

Adult↗
PubMed1991

Klippel-Trenaunay syndrome: the risks and benefits of vascular interventions.

Our experience with Klippel-Trenaunay syndrome (KTS), a rare congenital malformation, has increased considerably in recent years and now includes 144 patients (65 male and 79 female patients). Hemangioma was present in 137 patients (95.1%), varicosity in 110 (76.4%), and hypertrophy of the soft tissues or bones in 134 (93.1%). In most patients (71.5%) the disease involved one lower extremity. Diagnostic workup included roentgenogram to document limb length discrepancy, noninvasive arterial and venous evaluation, contrast venography, and nuclear magnetic resonance imaging. Most patients did well without treatment or with elastic compression only. Surgical treatment for the vascular malformation in KTS is rarely needed and it continues to be controversial. To evaluate the risks and benefits of vascular interventions, we examined in detail the clinical histories of nine patients who in the last decade underwent operation for a vascular malformation of the lower extremity. In seven patients we removed varicose veins or resected hemangioma of the lower extremity. Although none was cured, all five who underwent resection of varicose veins and one of the two patients who underwent resection of a hemangioma improved. Two additional patients, however, who underwent resection of varicose veins in another institution had worsening of the symptoms. In one patient we performed deep venous reconstruction for atresia of the superficial femoral vein, using the contralateral saphenous vein. Such operation in KTS has not been reported previously. The patient has a patent graft with a competent valve and clinical improvement 6 months after the operation. Although patients with severe chronic venous insufficiency, disturbing cosmetic appearance, or complications of hemangioma may benefit from surgical treatment, detailed preoperative imaging of the extremity and pelvis with magnetic resonance imaging and contrast venography is needed to decrease complications. Rarely, reconstruction for atresia or hypoplasia of the deep veins may be needed.

Adolescent↗
PubMed1990

Radiologic evaluation of penetrating aortic atherosclerotic ulcer.

Patients with penetrating atherosclerotic ulcers of the aorta present with back or chest pain that mimics classic aortic dissection. The pathologic findings, however, are distinctly different from those of aortic dissection in that an atherosclerotic lesion with ulceration penetrates into the internal elastic lamina, allowing hematoma formation within the media of the aortic wall. This may lead to false aneurysm or, rarely, transmural rupture of the aorta. Imaging findings of penetrating aortic atherosclerotic ulcers are also different from those of classic aortic dissection. We have found computed tomography to be especially useful in differentiating between these entities and present several illustrative cases.

Aged↗
PubMed1990

Intravascular US of the distal aorta and iliac vessels: initial feasibility studies.

Intravascular ultrasound (US) imaging is a new, evolving technique in which a high-frequency transducer is placed on the tip of a catheter. With this device it is possible to obtain high-resolution images of vessel structure in real time. This may provide valuable information about the degree of stenosis, as well as the type and extent of atherosclerotic plaque, in relation to the underlying tunica media and adventitia. The intravascular US catheter was used in seven patients undergoing transfemoral angiography because of arteriosclerosis obliterans. High-resolution images were obtained in all seven patients, and no complications were noted. Various US findings were demonstrated and correlated with the angiographic findings.

Aged↗
PubMed1990

Takayasu's arteritis. Carotid duplex sonographic appearance, including color Doppler imaging.

Takayasu's arteritis (also known as pulseless disease, aortoarteritis, and aortic arch syndrome) is a chronic inflammatory arteriopathy that affects the aorta and its main branches as well as the pulmonary arteries. We report the carotid duplex sonographic findings of Takayasu's arteritis in three patients. Takayasu's arteritis can be suspected by noting a long segment of diffuse, homogeneous, circumferential vessel wall thickening in the proximal common carotid artery, resulting in narrowing of the lumen. The internal and external carotid arteries are normal.

Adult↗
PubMed1990

Roentgenographic findings in major vasculitic syndromes.

Angiography provides valuable diagnostic information in vasculitis. The diagnosis of vasculitis is made by identifying specific arterial abnormalities and their patterns of distribution. Based upon the specific disease in question, the scope of the angiographic procedure needs to be tailored to provide the answer. Other diagnostic modalities, such as Doppler ultrasound, computed tomography, and magnetic resonance imaging, have limited but important roles that have not been fully explored.

Angiography↗
PubMed1990

Fast-CT evaluation of the upper airway during wakefulness in patients with obstructive sleep apnea.

Fast-CT scanning was used to study the dynamic changes in the upper airway (UA) during quiet tidal ventilation (VT) in 25 patients with obstructive sleep apnea (OSA). Ten fast-CT scans were sequentially obtained over one respiratory cycle from the level of the hard palate to the hypopharynx with the patients awake in the supine position. The patients were 44 +/- 2 years old, weighed 104 +/- 5 kg, and had moderately severe OSA with an apnea plus hypopnea index (AHI) of 59 +/- 7 per hour. Maximum and minimum UA cross-sectional areas (Amax -Amin) were determined for each UA level and percent reductions in UA size or collapsibility index (CI) were computed as (Amax -Amin)*100/Amax. The lower velo-pharynx was the narrowest (Amin = 80 +/- 12 mm2) and most collapsible segment of the UA (Cl = 55 +/- 5%). Amin was less than 25, 50, or 75 mm2 in 64%, 76%, and 88% of the patients, respectively. Significant narrowing was confined to the proximal segment (levels 1 to 4) in the majority, with the remaining patients having narrowing in both the proximal and distal segments. None of the patients had major narrowing confined to the distal segment alone. Mean UA cross-sectional area (Amean) was generally largest at end-inspiration and smallest at end-expiration. In conclusion, fast-CT has documented substantial changes in UA cross-sectional area during quiet VT in awake supine patients with OSA. The velopharyngeal (retropalatal) segment was the narrowest and most collapsible region. Maximal narrowing was greatest at end-expiration, consistent with relaxation of UA dilator muscle activity.

Adult↗
PubMed1989

Effect of platelet inhibitors on platelet and fibrin deposition following transluminal angioplasty of the atherosclerotic rabbit aorta.

Experimental atherosclerosis was induced in a rabbit model by intimal damage of the infrarenal aorta followed by two months cholesterol feeding. The influence of four different antiplatelet drug regimens on acute platelet and fibrin deposition after transluminal angioplasty of the atherosclerotic abdominal aorta was then evaluated. The study group consisted of 32 New Zealand rabbits: 7 controls, 7 treated with prostacyclin (10 mg/kg/min i.v.), 5 treated with low-dose acetylsalicylic acid (2 mg/kg i.v.), 7 treated with acetyl-salicylic acid (5 mg/kg i.v.) and dipyridamole (2 mg/kg i.v.), and 6 treated with low molecular dextran (5 ml/kg). By 2 hours after angioplasty, there was a significant increase of the deposition of platelets (P less than 0.001) as well as fibrin (P less than 0.01) when comparing dilated to non-dilated segments in the control animals. There was no significant difference in the amount of platelets and fibrin deposition among the control and drug treated groups. Thus, in this animal model there appears to be no immediate benefit in using antiplatelet drugs during transluminal angioplasty. Although, this study did not address the potential long-term effects of antiplatelet drug therapy, future evaluation of the clinical benefits of these drugs in conjunction with transluminal angioplasty seems warranted.

Angioplasty, Balloon↗