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Biomedical subjects

R B Patterson

Publications and source records attributed to R B Patterson.

At least 19 recordsLinked to original sources
PubMed2001

Exact sampling from nonattractive distributions using summary states.

Propp and Wilson's method of coupling from the past allows one to efficiently generate exact samples from attractive statistical distributions (e.g., the ferromagnetic Ising model). This method may be generalized to nonattractive distributions by the use of summary states, as first described by Huber. Using this method, we present exact samples from a frustrated antiferromagnetic triangular Ising model and the antiferromagnetic q=3 Potts model. We discuss the advantages and limitations of the method of summary states for practical sampling, paying particular attention to the slowing down of the algorithm at low temperature. In particular, we show that such slowing down can occur in the absence of a physical phase transition.

Journal Article↗
PubMed2001

Comparison of two progressive treadmill tests in patients with peripheral arterial disease.

In a vascular rehabilitation program, 28% of our frail elderly patients are unable to be tested with traditional progressive exercise protocols at program entry due to the high (2.0 miles/h or 3.2 km/h) initial treadmill speeds. The purpose of this investigation was to compare a new progressive treadmill protocol which has a reduced initial speed (1.0 mile/h or 1.6 km/h) to an established protocol performed at 2.0 miles/h (3.2 km/h) to determine the comparability and reproducibility of the new protocol. Eleven patients with arterial claudication performed three symptom-limited exercise tests in random order. Two tests used the new protocol while the remaining trial used the established protocol. Claudication pain was measured using a 5-point scale. Oxygen consumption, heart rate, minute ventilation, respiratory exchange ratio and blood pressure at peak exercise were similar among the three trials. There were strong intraclass correlations for peak oxygen consumption (r = 0.97), onset of claudication (r = 0.96) and maximum walking time (r = 0.98) between the two trials using the new protocol. There was also a significant correlation between the new protocol and the established protocol for peak oxygen consumption (r = 0.90) and maximum walking time (r = 0.89). The new progressive treadmill protocol represents a valid, reliable protocol for patients with arterial claudication. This protocol may be useful for testing patients with a low functional capacity so that clinically appropriate exercise prescriptions can be established and the efficacy of treatments can be determined.

Aged↗
PubMed2001

Oculopharyngeal muscular dystrophy complicating airway management.

Oculopharyngeal muscular dystrophy (OPMD) is an uncommon autosomal dominant disorder characterized by late onset and slow progression. Complications of OPMD include ptosis and progressive dysphagia leading to eventual malnutrition and aspiration. We report a rare case of OPMD complicating mechanical ventilator management following emergent surgery. OPMD and the resulting dysphagia contributed to multiple intubations, tracheostomy, aspiration pneumonia, and a prolonged hospital course. Awareness of the possibility of OPMD in intubated patients with a history of dysphagia is crucial for avoidance of complications.

Aged↗
PubMed1999

Components of an optimal exercise program for the treatment of patients with claudication.

Research in vascular exercise has demonstrated remarkable improvement in symptoms of claudication without more expensive and invasive interventions. During the past 5 years, 86 patients have graduated from The Brown University Supervised Vascular Exercise Program. Patients demonstrate a threefold improvement in maximum walking distance after 12 weeks of training. Information available on 22 patients at 1-year and 2-year follow-ups show walking distance is improved or maintained with continued training. Components of the program are presented in 3 phases. Phase 1 addresses the comprehensive nursing assessment, cardiac screening, and progressive treadmill testing. Phase II includes specific method of exercise prescription and educational needs of peripheral vascular disease patients. Phase III discusses the importance of maintenance and motivating patients to continue.

Aged↗
PubMed1997

Midaortic pseudoaneurysm complicating extensive endovascular stenting of aortic disease.

We report a case of successful surgical management of a potentially life-threatening complication of aortoiliac stent placement. A 59-year-old man who had Leriche syndrome underwent bilateral iliac artery and infrarenal aortic stent placement at another institution. His history was significant for retroperitoneal lymph node dissection at 19 years of age for testicular cancer. One week after stent placement, the patient was readmitted with abdominal pain, poor oral intake, and diffuse intermittent tenderness. Evaluation with computed tomographic scanning and endoscopy was unremarkable, and the patient was discharged. He was admitted to our institution 1 week later with persistent abdominal pain. A computed tomographic scan of the abdomen revealed a large pseudoaneurysm of the abdominal aorta. The patient underwent urgent exploration, and exclusion of his infrarenal aorta was achieved with aortobifemoral bypass grafting. After the operation, the patient's course was complicated by a large paraduodenal hematoma, which resulted in a gastric outlet obstruction, which was managed without operation. This case illustrates a potential life-threatening complication of extensive stent placement for aortoiliac occlusive disease. Injury to the abdominal aorta must be considered in a symptomatic patient after the placement of stents in the aortoiliac region, beyond the immediate periprocedural period.

Abdominal Pain↗
PubMed1997

Value of a supervised exercise program for the therapy of arterial claudication.

PURPOSE: This study was performed to test the effectiveness of a formal supervised exercise program against a home-based exercise program for both walking ability and quality of life endpoints. METHODS: Patients with arterial claudication were randomized to either a 12-week supervised exercise program (SUPEX) with weekly lectures relating to peripheral vascular disease or to a home exercise group (HOMEX) who attended an identical lecture program and received weekly exercise instruction. The study population included 29 men and 26 women, with a mean age of 69.1 +/- 8.1 years. Forty-seven patients completed the 12-week program, 46 were available for testing at completion, and 38 for 6-month testing. Claudication pain time (CPT) and maximum walking time (MWT) on a progressive treadmill exercise test were assessed at baseline, program completion, and 6 months. The Medical Outcomes Study Short Form-36 (SF-36) was administered at these intervals to assess effects on quality of life. RESULTS: Each group improved (p < 0.001) in both CPT and MWT at the completion of the 12-week program, which was sustained at the 6-month follow-up. Increase in HOMEX CPT from baseline (3.6 +/- 2.73 minutes) to 6-month follow-up (6.6 +/- 3.17 minutes) was less than for the SUPEX group (3.8 +/- 2.74 to 11.2 +/- 4.02 minutes, respectively); similar results were obtained for MWT. At both completion and 6 months, there was a significant intergroup difference for CPT and MWT (p < 0.004) favoring SUPEX. For both groups, measures of health perception based on the SF-36 demonstrated improvement (p < 0.002) in Physical Function Subscale, Bodily Pain Subscale, and Physical Composite Score. There were no between-group differences on the subsets of the SF-36 at the three assessment intervals. CONCLUSIONS: Supervised exercise programs provide superior increased walking ability in the noninterventional therapy of arterial claudication, and both supervised and home based exercise therapy result in improved SF-36 functional measures. The lack of intergroup differences in these measures may be a result of the high degree of interaction with healthcare providers in the HOMEX group. Although a supervised program results in optimal walking benefits, a highly structured home-based program provides similar functional improvement and may be a satisfactory alternative for patients with lesser walking requirements.

Aged↗
PubMed1997

Critical pathways and cost-effective practice.

With increasing pressure by third-party payers and federal reimbursement systems to reduce health care expenditures, cost-effective means to care for the resource intensive vascular surgical population must be explored. The challenge of meeting these cost-saving priorities while maintaining or improving quality of care can result in conflicting demands on surgeons, particularly in academic practices. The adaptation of an industrial management tool-the critical pathway method-to health care delivery is an attempt to reduce length of stay and improve efficiency. Utilization of vascular nurse practitioners, concentration of vascular patients into a dedicated unit, reduction in angiography through more aggressive use of the vascular laboratory, and optimal use of rehabilitation units and skilled nursing facilities are important adjuncts to reduce length of stay without sacrificing quality of care. This report describes the critical pathway method as implemented in a university teaching hospital, and the integration of other modalities in the care of vascular patients that has reduced length of stay by as much as 40% for some vascular surgical procedures.

Cardiology Service, Hospital↗
PubMed1993

Prevalence of unsuspected abdominal aortic aneurysms in male veterans.

Abdominal aortic aneurysms (AAA) are potentially lethal arterial lesions that are best managed by elective surgical repair. However, asymptomatic AAAs may go undetected on routine physical examination or patients with such lesions may not consult a physician. To determine the prevalence of asymptomatic AAAs in a high-risk population, we retrospectively reviewed all abdominal CT scans on veterans > 50 years of age that had been ordered for indications other than aneurysmal disease during a recent 10-month period. Of the 111 patients studied, 15 (13.5%) had suprarenal and/or infrarenal AAAs (one patient had both). Patients with AAAs were significantly older (p = 0.0001) and were heavier tobacco users (p = 0.003). For patients > 60 years of age with peripheral vascular occlusive disease and a history of tobacco use, there was a 29.2% prevalence for AAA compared with 0% in those without any of these risk factors (p = 0.04). There was a very definite trend suggesting that patients with peripheral vascular disease (p = 0.06) were more likely to have an AAA. Because of the high prevalence of AAAs found in this population we then conducted a prospective study over a 24-month period during which patients > 60 years of age with known peripheral vascular disease and a history of smoking who presented to the vascular laboratory for evaluation of problems not related to AAA were asked to undergo an abdominal CT scan. Fifty-six volunteers agreed to participate in the study. Seven patients had AAAs and one patient had an isolated iliac aneurysm, for a 14.3% overall prevalence of aneurysms.2+ d

Aged↗
PubMed1992

The ischemic window: a method for the objective quantitation of the training effect in exercise therapy for intermittent claudication.

Twenty-two patients with intermittent claudication were prospectively enrolled in a 12-week program of supervised, graded treadmill exercise therapy. Severity and distribution of arterial occlusive disease were ascertained by noninvasive determination of segmental lower extremity blood pressures and waveforms. No attempt was made to modify risk factors for atherosclerotic occlusive disease. The exercise-induced reduction of the ankle pressure and its recovery were recorded over time, and the area under this curve, the "ischemic window," represents the severity of the ischemic deficit. Absolute systolic ankle pressure, ankle-brachial index, maximum walking time, claudication pain time, and the ischemic window were measured before and after exercise training in all subjects. Maximum walking time and claudication pain time increased 659% and 846%, respectively, among the 19 patients completing the 12-week program (p = 0.001; p = 0.0002). These patients underwent a mean reduction of 58.7% in the ischemic window after a standardized workload (p less than 0.05), and this correlated with the degree of symptomatic improvement. Absolute ankle pressure and ankle-brachial index were unchanged after exercise training. This study confirms the utility of supervised exercise therapy in the treatment of intermittent claudication. The ischemic window is a useful method for quantifying the ischemic deficit produced by exercise and provides a reproducible means of documenting functional improvement in patients undergoing exercise training.

Aged↗
PubMed1991

Prevalence of hemodynamically significant stenosis of the carotid artery in an asymptomatic veteran population.

The results of previous studies have suggested that significant stenosis of the carotid artery occurs in less than 6 per cent of asymptomatic patients. However, some populations studied were not representative of those seen by most vascular surgeons. Accordingly, we examined two cohorts of patients at the Veterans Administration Medical Center using Duplex scanning. There were 153 volunteers in group 1, all more than 50 years of age, who were being treated at our outpatient department for nonvascular problems. There were 116 patients of similar age in group 2 but who were known to have significant arterial occlusive disease of the lower extremity. The majority of patients were men with a mean age of 64.4 years. Risk factors in the total population included hypertension, diabetes mellitus, coronary arterial disease, peripheral vascular disease and smoking. Over-all, significant (greater than 50 per cent diameter) stenosis of the carotid artery was discovered in 25 of 269 patients. The prevalence for those in group 1 was 6.5 per cent versus 12.9 per cent for those in group 2 (p = 0.058). The prevalence in patients with cardiac disease was 15.2 per cent compared with 6.8 per cent in those without cardiac disease (p = 0.032). Smoking was associated with a 10.6 per cent rate of significant disease compared with a 2.3 per cent rate in nonsmokers (p = 0.065). Hypertension and diabetes were not significant risk factors. Significant stenosis of the carotid artery was found in seven of 40 patients in whom coronary arterial disease, peripheral vascular disease and smoking were all present.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Preferential use of EPTFE for above-knee femoropopliteal bypass grafts.

We have used polytetrafluoroethylene preferentially for bypasses to the above-knee popliteal artery since 1979. Since this approach has recently been challenged, we reviewed our experience with 138 grafts in 128 patients. The majority (74%) of patients were male with a mean age of 63.2 years. Risk factors included: smoking (85%), hypertension (55%), diabetes mellitus (45%), and coronary artery disease (41%). The indications for operation were disabling claudication (18%), rest pain (42%), gangrene/tissue loss (33%), and miscellaneous (7%). Perioperative (30 day) mortality was 3% and morbidity (excluding amputation or graft failure) was 5%. Patients were followed for up to eight years with a mean follow-up of 22.1 months. Grafts which remained patent, but did not prevent major amputation, were classified as "failed". Primary patency was 75% at one year and 54% at five years. Limb salvage was 88% at one year and 70% at five years. Risk factors, indication for operation and arteriographic runoff had no statistically significant impact on short- or long-term patency. However, bypass grafts to isolated popliteal segments had a significantly (p = 0.025) increased perioperative failure rate compared to all other grafts. Our data support the continued use of polytetrafluoroethylene for above-knee femoropopliteal bypass except perhaps in patients who require grafting to an isolated popliteal segment where higher early failure rates were seen.

Aged↗
PubMed1990

Protection against postischemic spinal cord injury using a new 21-aminosteroid.

Ischemic spinal cord injury following repair of the thoracoabdominal aorta is an unpredictable and devastating complication. Recently, a new class of agents has been developed, the 21-aminosteroids, which have been demonstrated to reduce ischemic neurologic injury in several animal models. We performed this study to determine if the 21-aminosteroid U-74006F exerted a protective effect in a rabbit model of spinal cord ischemia. Nineteen New Zealand rabbits were anesthetized and then subjected to 25 min of temporary infrarenal aortic occlusion. Nine rabbits were given 3.0 mg/kg U-74006F iv 10 min prior to clamping the aorta, followed by 0.75 mg/kg every hour for 6 hr beginning 1 hr after the clamp was removed. Ten rabbits received equivalent doses of an aqueous buffered vehicle. The rabbits were neurologically graded upon awakening and then daily using the following scale: grade 0 = complete paralysis, grade 1 = partial deficit, grade 2 = normal. In the U-74006F-treated group, five animals were normal, one had a partial deficit, and three were paraplegic. In the vehicle group, only one animal was normal and nine were paraplegic. The difference between the mean neurologic grading scores of the two groups was statistically significant (P = 0.013). It is believed that U-74006F acts at the cell membrane level during reperfusion by inhibiting lipid peroxidation and lipid hydrolysis. Our data suggest that this agent may significantly reduce the incidence of postischemic spinal cord injury following temporary aortic occlusion.

Animals↗
PubMed1990

Is the continued use of ocular pneumoplethysmography necessary for the diagnosis of cerebrovascular disease?

The combination of duplex scanning and ocular pneumoplethysmography (OPG) has been used by many vascular laboratories for noninvasive evaluation of the carotid arteries. This study was undertaken to determine if OPG significantly improved the accuracy of duplex scanning alone. Three hundred eighty-five carotid arteries were studied in 190 patients with angiograms, duplex scans, or OPG. A total of 329 carotid arteries were examined with all three modalities. Three different criteria were used to interpret the OPG results, one each intended to deliver a high sensitivity, specificity, and overall accuracy. Depending on the criteria used, sensitivity of OPG alone for detecting hemodynamically significant (greater than 50%) stenosis ranged from 53% to 83%, with a specificity of 59% to 94%. Duplex scanning alone had a sensitivity of 87% and a specificity of 90% for similar lesions. If patients with only intracranial arterial stenosis were excluded, the sensitivity of the duplex scan rose to 91%. The addition of OPG to the duplex scan slightly increased sensitivity (range 91% to 95%; difference not significant) but significantly decreased specificity (range 56% to 84%; p less than 0.005). For detecting stenoses greater than 80%, the duplex scan alone had a sensitivity of 90% and a specificity of 88%. The addition of OPG to duplex scanning slightly increased sensitivity for these high-grade lesions but significantly decreased specificity (p less than 0.001) and overall accuracy. These results were unaffected by the presence or absence of intracranial disease. Because the addition of OPG to duplex scanning reduces specificity and accuracy without any significant increase in sensitivity, we no longer use it as part of our routine noninvasive cerebrovascular examination.

Carotid Arteries↗
PubMed1990

Repositioning of partially dislodged Greenfield filters from the right atrium by use of a tip deflection wire.

Dislodgement of a Greenfield filter in the right atrium is one of the most serious complications of this procedure. Retrieval of such a misplaced filter may require surgical intervention by means of cardiopulmonary bypass surgery, which is very hazardous in these often severely ill patients. We describe two cases in which the filter became partially dislodged from its carrier in the right atrium. We were able to successfully reposition the filter by using a tip deflection wire, thereby obviating the need for an open cardiac procedure.

Adult↗
PubMed1989

A comparison between fibronectin and Matrigel pretreated ePTFE vascular grafts.

Two distinct series of experiments were performed to compare the behavior of ePTFE vascular grafts coated with basement membrane gel to that of identical grafts coated with fibronectin. Bilateral carotid interposition grafts (10 cm long) were interposed in 16 conditioned mongrel dogs. In the first series of experiments (n = 10), each graft was seeded with radiolabeled endothelial cells and initial endothelial cell adherence was determined. Following restoration of blood flow in the grafts, endothelial cell retention was measured for 24 hours. Seeding efficiency was 66.48% (+/- 13.2) for fibronectin-coated grafts and 56.58% (+/- 13.51) for gel-coated grafts. There was a slow, constant loss of activity during the first 90 minutes of imaging, and at 24 hours of observation the activity remaining on the fibronectin-coated graft was 13.2 +/- 3.98% of the initial graft activity. Although the basement membrane gel had a higher mean activity at 24 hours (18.9 +/- 7.22%), the difference was not statistically significant at any interval. In the second series of animals (n = 6), radiolabeled platelets were injected within 60 minutes following restoration of flow. Total platelet activity on the explanted grafts was 3.36 (+/- 1.35) x 10(5) counts per gram/0.2 minute for the fibronectin-coated grafts. The gel-coated grafts had 2.74 (+/- 1.33) x 10(5) counts per gram/0.2 minute, a difference that was not statistically significant. Thus, despite its theoretical appeal, basement membrane gel was no better than fibronectin in increasing endothelial cell adherence and retention, and the resulting flow surface of grafts treated with either compound appeared to attract platelets to an equal degree.

Animals↗
PubMed1989

Functional failure of patent femorodistal in situ grafts.

We have treated several patients who required major, proximal extremity amputations despite a patent infrainguinal in situ saphenous vein bypass graft. To determine those factors predisposing to such paradoxical limb loss, we studied a group of 45 patients who underwent 48 in situ, femorodistal bypass grafts for tissue necrosis and who maintained a patent graft throughout the perioperative period. Within this cohort, we compared two distinct subgroups: Group I, whose limbs (n = 8) ultimately required a major proximal amputation; Group II, whose limbs (n = 40) emerged with a viable foot and did not require a major amputation. There was no significant difference in the incidence of diabetes, renal failure, smoking, or postoperative ankle/brachial index between the two groups. The presence of gangrene (88% vs 45%), invasive sepsis (63% vs 23%), and combined gangrene and sepsis (63% vs 18%) was significantly (p less than 0.05) more prevalent in Group I versus Group II. Forty-three percent of patients with both gangrene and foot sepsis required a major proximal amputation despite a patent graft. Such patients are at high risk for limb loss even if they undergo successful revascularization.

Aged↗
PubMed1989

The potential unreliability of indium 111 oxine labeling in studies of endothelial cell kinetics.

The current widespread use of indium 111 oxine for labeling endothelial cells to study their interaction with various bioprosthetic flow surfaces presupposes a high retention of the radioisotope within the cell and a lack of significant adherence of any marker released from the cell to the surface under study. We measured the loss of indium 111 from freshly harvested, canine, venous endothelial cells, and their viability in cell culture, for varying intervals up to 24 hours. At prescribed intervals, aliquots of the radiolabeled endothelial cell suspension were centrifuged, and the supernatant was separated from the cell pellet. The relative radioactivity of each was measured in a gamma well counter and the spontaneous loss of marker from the endothelial cells was calculated. Spontaneous loss of indium 111 was 7.8% +/- 1.9% at 1 hour and 47.6% +/- 1.8% at 24 hours. Loss of activity was virtually constant between 14 and 24 hours. Endothelial cell viability was 80% at 24 hours. We next studied the in vitro affinity of indium 111 oxine and indium 111 transferrin for untreated expanded polytetrafluoroethylene vascular grafts and for similar grafts treated with two surfactants commonly used to increase the "wetability" of expanded polytetrafluoroethylene, a nonionic sufectant (Nonidet) and tridodecylmethylammonium chloride, and with two glycoproteins, fibronectin and basement membrane gel. A minimum of three graft segments were studied in each group. The affinity of graft material for indium 111, in both its oxine and transferrin complex, was significantly increased by treating the graft with a wetting agent, and it was further increased by the addition of a glycoprotein.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗