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Biomedical subjects

J M Porter

Publications and source records attributed to J M Porter.

At least 55 records · Page 3Linked to original sources
PubMed1999

Propionyl-L-carnitine dilates human subcutaneous arteries through an endothelium-dependent mechanism.

PURPOSE: The vasoactive effects of propionyl-L-carnitine (PLC) on human arteries, including endothelial and smooth muscle cell influences, were studied. METHODS: Small (less than 200 microm) subcutaneous fat arteries (n = 19), obtained from human patients undergoing vascular surgery, were dissected and mounted in an arteriograph system that allowed measurement of lumen diameter and control of transmural pressure. To investigate the role of the endothelium, arteries were compared intact, intact and in the presence of either 0.3 mmol/L nitro-L-arginine (an inhibitor of nitric oxide synthesis) or 10 micromol/L indomethacin (an inhibitor of prostaglandin synthesis), or denuded of endothelium. After a 1-hour equilibration at a pressure of 50 mm Hg, arteries were precontracted 50% with an intermediate concentration of norepinephrine, and clinically relevant concentrations of PLC (0.1 to 100 micromol/L) were cumulatively added to the bath while the lumen diameter was continually measured. RESULTS: Intact arteries dose-dependently dilated to PLC, with the half maximal dilation occurring at 2.9 +/- 1.2 micromol/L, increasing diameter 91% +/- 5% at 100 micromol/L. In contrast, PLC had significantly less effect on deendothelialized arteries, increasing diameter only 24% +/- 11% at 100 micromol/L (P <.01 vs. intact). This indicates the endothelial dependency of this compound. Blockade of nitric oxide did not inhibit this vasodilation, with the half-maximal response occurring at 8.6 +/- 7 micromol/L, increasing diameter 85% +/- 8% at 100 micromol/L ( P >.05 vs. intact). However, this vasodilation was significantly diminished in the presence of indomethacin, which dilated arteries only 53% +/- 18% at 100 micromol/L (P <.01 vs. intact; P >.05 vs. denuded). CONCLUSION: PLC is an endothelium-dependent vasodilator, the mechanism of which is partially mediated by prostaglandin synthesis, not nitric oxide. The beneficial effects of this compound may, in part, be related to vasodilation and enhanced blood flow.

Aged↗
PubMed1999

Prospective blinded study of the relationship between plasma homocysteine and progression of symptomatic peripheral arterial disease.

PURPOSE: An elevated plasma homocysteine level is an established risk factor for atherosclerotic coronary heart disease (CHD), cerebrovascular disease (CVD), and lower extremity occlusive disease (LED). An elevated plasma homocysteine level can be reduced by therapy with folate and vitamins B6 and B12. An accurate evaluation of the role of vitamin therapy requires knowledge of the influence of plasma homocysteine levels on the progression of CHD, CVD, and LED. METHODS: The Homocysteine and Progression of Atherosclerosis Study is a blinded prospective study of the influence of homocysteine and of other atherosclerotic risk factors on the progression of disease in patients with symptomatic CVD, LED, or both. This study is set in a university hospital vascular surgery clinic and the General Clinical Research Center. Consecutive patients with stable symptomatic CVD or LED underwent baseline clinical, laboratory, and vascular laboratory testing for homocysteine and other risk factors and were examined every 6 months. The primary endpoints were ankle brachial pressure index, duplex scan-determined carotid stenosis, and death. The secondary endpoints were the clinical progressions of CHD, LED, and CVD. The hypothesis that was tested was whether the progression of symptomatic CVD or LED was more frequent or more rapid in patients with elevated plasma homocysteine levels. plasma homocysteine levels. RESULTS: After a mean follow-up period of 37 months (range, 1 to 78 months) for deaths from all causes (>14 micromol/L; elevated, 18.6%; normal, 9.4%; P = .022), deaths from cardiovascular disease (elevated, 12.5%; normal, 6.3%; P = .05) and the clinical progression of CHD (highest 20% of homocysteine levels, 80%; lowest 20% of homocysteine levels, 39%; P = .007) were significantly more frequent or more rapid by life-table analysis when the homocysteine levels were elevated. Multivariate Cox proportional hazards regression model showed a significant independent and increasing relationship between the plasma homocysteine levels and the time to death (relative risk for highest one third of homocysteine values, 1.6; 95% confidence interval [CI], 1.04 to 2.56; P = 029; and relative risk for highest one fifth of homocysteine values, 3.13; 95% CI, 1.69 to 6.64; P = .0001). After an adjustment for age, smoking, hypertension, diabetes, cholesterol, and the vascular laboratory progression of CVD or LED, each 1.0 micromol/L increase in the plasma homocysteine levels resulted in a 3.6% increase (95% CI, 0.0% to 6.6%; P = .06) in the risk of death (all causes) at 3 years and a 5.6% increase (95% CI, 2.2% to 8.5%; P = .003) in the risk of death from cardiovascular disease. CONCLUSION: We conclude that elevated plasma homocysteine levels are associated significantly with death, with death from cardiovascular disease, and with the progression of CHD in patients with symptomatic CVD or LED. These results strongly mandate clinical trials of homocysteine-lowering vitamin therapy in such patients.

Aged↗
PubMed1999

Duplex scanning alone is not sufficient imaging before secondary procedures after lower extremity reversed vein bypass graft.

PURPOSE: Duplex surveillance of lower extremity reversed vein bypass grafts (LERVG) is a means of identifying patients at risk for occlusion. The perceived accuracy of duplex scan as a means of identifying stenoses has led many surgeons to perform graft revision on the basis of duplex scan alone. This may result in missing additional lesions that are threatening patency. To assess the role of duplex scan as the sole imaging method before revision of LERVGs, we reviewed consecutive patients undergoing revisions who underwent preoperative arteriography after identification of duplex scan abnormalities. METHODS: Duplex scan results, operative reports, and preoperative arteriograms for patients undergoing LERVG revision from January 1990 to December 1997 were reviewed. A standard duplex scan surveillance protocol was followed, and attempts were made to survey the entire graft, including inflow and outflow. Duplex scan results were compared with the results of preoperative arteriograms and the operation performed to determine if all significant lesions were identified by means of duplex scan alone. RESULTS: Two hundred five LERVG revisions were performed. The 5-year assisted primary patency rate was 91%. In 119 cases (58%), arteriography did not contribute significantly to duplex scan findings. Arteriography significantly contributed to operative planning in 86 cases (42%). In 38 cases (19%), only a low-flow state was identified by means of duplex scan, and a correctable stenosis was identified by means of arteriography. In 48 cases (23%), additional significant lesions corrected at operation were identified by means of arteriography. These included 26 inflow, 16 graft, and 8 outflow lesions. Arteriography was most useful as a means of determining the revision procedure performed when there were inflow lesions (P <.05) or when the proximal anastomosis was to the profunda or superficial femoral arteries (P <.05). All frequently performed bypass graft configurations had some discrepancy between arteriographic and duplex scan findings. CONCLUSION: Available data do not permit prediction of which LERVG are immune from missed lesions in a duplex scan surveillance protocol. This suggests to us that arteriography is mandatory before LERVG revisions.

Aged↗
PubMed1999

The effects of ropivacaine hydrochloride on coagulation and fibrinolysis. An assessment using thromboelastography.

Amide local anaesthetics impair coagulation by inhibition of platelet function and enhanced fibrinolysis. The potential therefore exists that the presence of amide local anaesthetics in the epidural space could contribute to the therapeutic failure of an epidural autologous blood patch. Ropivacaine is an aminoamide local anaesthetic increasingly used for epidural analgesia and anaesthesia, particularly in obstetric practice. This study was undertaken to investigate whether concentrations of ropivacaine in blood, which could occur clinically in the epidural space, alter coagulation or fibrinolysis. Thromboelastography was used to assess clotting and fibrinolysis of blood to which ropivacaine had been added. Although modest alterations in maximum amplitude, coagulation time and alpha angle were observed, the effect of ropivacaine on clotting and fibrinolysis was not clinically significant. We conclude that it is unlikely that the presence of ropivacaine in the epidural space would reduce the efficacy of an early or prophylactic epidural blood patch.

Adult↗
PubMed1999

The sitting position in neurosurgery: a critical appraisal.

The potential for serious complications after venous air embolism and successful malpractice liability claims are the principle reasons for the dramatic decline in the use of the sitting position in neurosurgical practice. Although there have been several studies substantiating the relative safety compared with the prone or park bench positions, its use will continue to decline as neurosurgeons abandon its application and trainees in neurosurgery are not exposed to its relative merits. How can individual surgeons continue to use this position? Will individual, difficult surgical access cases be denied the obvious technical advantages of the sitting position? Limited use of the sitting position should remain in the neurosurgeon's armamentarium. However, several caveats must be emphasized. Assessment of the relative risk-benefit, based on the individual patient's physical status and surgical implications for the particular intracranial pathology, is of paramount importance. The patient should be informed of the specific risks of venous air embolism, quadriparesis and peripheral nerve palsies. Appropriate charting of patient information provided and special consent issues are essential. An anaesthetic input into the decision to use the sitting position is a sine qua non. The presence of a patient foramen ovale is an absolute contraindication. Preoperative contrast echocardiography should be used as a screening technique to detect the population at risk of paradoxical air embolism caused by the presence of a patent foramen ovale. The technique involves i.v. injection of saline agitated with air and a Valsalva manoeuvre is applied and released. Use of this position necessitates supplementary monitoring to promptly detect and treat venous air embolism. Doppler ultrasonography is the most sensitive of the generally available monitors to detect intracardiac air. The use of a central venous catheter is recommended, with the tip positioned close to the superior vena cava junction with the right atrium, to aspirate intravascular gas. Measures to minimize hypotension associated with the sitting position include a slow, staged positioning over 5-10 min and use of the 'G suit' inflated with compressed air applied to the lower extremities and pelvis. Use of the sitting or upright position for patients undergoing posterior fossa and cervical spine surgery presents unique challenges for the anaesthetist. With appropriate patient selection and preparation, and using prudent intraoperative monitoring and anaesthetic techniques, selected patients should still benefit from the optimum access to mid-line lesions, improved cerebral venous decompression, lower intracranial pressure and enhanced gravity drainage of blood and CSF associated with the sitting position.

Anesthesia↗
PubMed1999

The surgical intensive care unit as a cost-efficient substitute for an operating room at a Level I trauma center.

Critically ill patients in the surgical intensive care unit (SICU) continue to require operative procedures. Traditionally, this has meant the transport of these critically ill patients out of the safe, monitored confines of the SICU to the operating room (OR). This can be hazardous to the patient, as well as expensive. Performing the procedures in the OR can avoid both the dangers of transport and the expense of the OR. Herein is a descriptive study of 80 procedures performed on 36 patients in the SICU. We believe that these data show that the SICU can be a cost-effective alternative to the OR in a trauma center in critically ill patients. Significant cost savings may be realized without increasing the iatrogenic or infectious complications.

Cost-Benefit Analysis↗
PubMed1999

Antioxidant therapy in the prevention of organ dysfunction syndrome and infectious complications after trauma: early results of a prospective randomized study.

Reactive oxygen species have been implicated in the etiology of multiorgan dysfunction syndrome and infectious complications in trauma patients by either direct cellular toxicity and/or the activation of intracellular signaling pathways. Studies have shown that the antioxidant defenses of the body are decreased in trauma patients; these include glutathione, for which N-acetylcysteine is a precursor, and selenium, which is a cofactor for glutathione. Eighteen trauma patients were prospectively randomized to a control or antioxidant group where they received N-acetylcysteine, selenium, and vitamins C and E for 7 days. As compared with the controls, the antioxidant group showed fewer infectious complications (8 versus 18) and fewer organs dysfunctioning (0 versus 9). There were no deaths in either group. We conclude that these preliminary data may support a role for the use of this antioxidant mixture to decrease the incidence of multiorgan dysfunction syndrome and infectious complications in the severely injured patient. This remains to be confirmed in larger trials.

Acetylcysteine↗
PubMed1999

Does endovascular grafting represent a giant step forward?

Endovascular repair of abdominal aortic aneurysms was first reported in 1991 by Parodi et al. Since then, there has been widespread development of many stent-grafts for abdominal aortic aneurysm (AAA) repair. Available data support the proposition that stent-grafts are generally safe, although their long-term efficacy remains completely unknown. Importantly, endovascular AAA repair has neither fewer complications nor lower mortality rates than open repair; in fact, the opposite appears true. Along with most new techniques come new complications, and endovascular repair of AAA has brought forth the concept of both "endoleak" and device failure. Although it is uncommon, delayed AAA rupture after seemingly successful endovascular repair of AAA has been reported. In our opinion, these faults unique to endovascular repair mandate a cautious approach to the clinical application of stent-grafts. Until ongoing phase 2 and future phase 3 studies are completed with a minimum of 2 to 3 years' follow-up, we shall not know whether endovascular repair of AAA represents a giant step forward or merely an industry-driven overuse of proprietary technology.

Aortic Aneurysm, Abdominal↗
PubMed1999

Preferred route of tracheostomy--percutaneous versus open at the bedside: a randomized, prospective study in the surgical intensive care unit.

Percutaneous tracheostomy has been touted as the preferred route of tracheostomy. However, to date, no prospective randomized study comparing bedside percutaneous (BP) to bedside open (BO) tracheostomy has been performed. Surgical intensive care unit (sICU) patients were randomized to receive either a BP or a BO tracheostomy. Patients were monitored for complications. Procedure time was documented. A group of medical ICU patients had open tracheostomies in the operating room (OR) and served as contemporaneous controls. Over 11 months, there were 24 surgical ICU patients randomized to receive either BP tracheostomy or BO tracheostomy, 12 in each group. Forty-six medical ICU patients received standard open tracheostomy in the OR. The number of ventilator days before placing the tracheostomy was similar between the BP and BO groups, 9.8 and 12.4, respectively. The clinical indications for tracheostomy were similar between the two groups. The procedure time for the BP group was 14.5 minutes, whereas 25.2 minutes for the BO group. There were no postprocedure complications in the BP and BO groups. There was a trend toward more complications in the BP group, including the loss of the airway, leading to death. The procedure time and complications were similar between the BO and OR groups. These data do not support that BP tracheostomy is the preferred route of tracheostomy when compared with BO tracheostomy. These data support that experienced surgical intensivists can perform BO tracheostomies with lower risk and cost, when compared with BP tracheostomy.

Adult↗
PubMed1998

General surgery.

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Abdominal Injuries↗
PubMed1998

A critical reappraisal of indications for fasciotomy after extremity vascular trauma.

OBJECTIVE: To critically reevaluate the indications for fasciotomy in vascular trauma of the extremities. DESIGN: Case-control study. SETTING: Level I trauma center. MATERIALS AND METHODS: One hundred sixty-three vascular injuries to the extremeties were analyzed. Fasciotomy as an adjunct to vascular repair was performed in 45 limbs (28%), based either on the nature of injury or measured compartment pressure of greater than 35 mm Hg. MAIN OUTCOME MEASURES: Need for fasciotomy or limb amputation. RESULTS: Fasciotomy was performed for 29.5% of isolated arterial injuries, 15.2% of isolated venous injuries, and 31.6% of combined arterial and venous injuries, and was not related to venous repair or ligation. Seven delayed fasciotomies were performed either for vascular repair failure (5 patients) or compartment syndrome (2 patients). The highest incidence was for popliteal vessel injury (arterial 57%, combined 61%). Of the 33 lower-extremity fasciotomies, 58% were for popliteal vessel injury. In 51 combined injuries of the lower extremity, only 7 (19%) of 38 patients with injury above the knee required fasciotomy, as compared with 8 (62%) of 13 with injury to the popliteal vessels (P<.001), with or without venous repair. There were 3 amputations, all resulting from vascular repair failure. CONCLUSIONS: The presence of a combined vascular injury or the need for venous ligation does not necessitate routine fasciotomy. The need for fasciotomy may be maximal for injuries to popliteal vessels.

Adolescent↗
PubMed1998

Predictors of outcome of forefoot surgery for ulceration and gangrene.

BACKGROUND: Surprisingly little is known about the long-term outcome of forefoot surgery for limb salvage. METHODS: From January 1, 1992 through December 31, 1996, patients requiring toe amputation or forefoot surgery were prospectively entered into a computerized database and followed up for healing, need for repeat foot surgery, or major amputation (below or above knee). RESULTS: A total of 162 patients (mean age 65 years), 72% diabetic, 10% with end-stage renal disease (ESRD), and 73% without palpable pulses, were entered into the study. Mean follow-up was 25 months. Of patients without palpable pulses (n = 98), 83% underwent concomitant or subsequent limb revascularization. Eleven of 98 revascularization procedures (11%) were hemodynamically unsuccessful. Nonhealing of the initial forefoot procedure occurred in 14%, and late repeat foot surgery (following initial healing) was required in an additional 14%. Major amputation was eventually required in 30 (18.5%) patients. Multivariate analysis indicated that unsuccessful revascularization, but not diabetes or ESRD, predicted nonhealing and major amputation (P <0.0001). Patients presenting with palpable pulses and neuropathic ulcers were at risk for late, repeat foot surgery, but not major amputation (P = 0.0015). CONCLUSIONS: In patients requiring toe or partial forefoot amputation, success of revascularization is the primary predictor of initial healing and freedom from major amputation. Neuropathic ulceration predicts need for repeat foot surgery following healing.

Adult↗
PubMed1998

Surgical treatment of infected aortic aneurysm.

BACKGROUND: We report results of infected aortic aneurysms treated by a single group over 20 years. METHODS: Retrospective review. RESULTS: Seventeen patients were treated, 10 with infrarenal and 7 suprarenal infections. All had abdominal/back pain, 88% were febrile, 71% had leukocytosis, and 24% were hemodynamically unstable. The most common responsible organism was Staphylococcus aureus (29%) followed by Salmonella organisms (24%). All suprarenal infections were gram-positive organisms. Infrarenal infections were treated with preliminary axillofemoral bypass followed by aortic resection. Suprarenal infections were treated with either in situ prosthetic graft or patch repairs. Operative survival was 90% for infrarenal and 57% for suprarenal infections. Operative deaths occurred in the setting of overwhelming sepsis and/or severe preoperative hemodynamic instability. There was no limb loss, renal failure, or intestinal ischemia. Late deaths occurred in 4 patients at 1.3 to 6.3 years postoperatively and were unrelated to their aortic repairs. Nine patients remain alive with a median follow-up of 2 years. There have been no late aortic or graft infections. CONCLUSIONS: In the absence of hemodynamic instability and uncontrolled sepsis, infected aortic aneurysms can be successfully repaired with durable results.

Adult↗
PubMed1998

Seat pressure measurement technologies: considerations for their evaluation.

Interface pressure measurement has generated interest in the automotive industry as a technique which could be used in the prediction of driver discomfort for various car seat designs, and provide designers and manufacturers with rapid information early on in the design process. It is therefore essential that the data obtained are of the highest quality, relevant and have some quantitative meaning. Exploratory experimental work carried out with the commercially available Talley Pressure Monitor is outlined. This led to a better understanding of the strengths and weaknesses of this system and the re-design of the sensor matrix. Such evaluation, in the context of the actual experimental environment, is considered essential.

Automobile Driving↗