Publications

Ultrahigh molecular weight polyethylene (UHMWPE) is a bearing surface material for total joint implants. It is radiation cross-linked for high wear resistance and is melted or treated with vitamin E for oxidative stability. We investigated high pressure crystallization (HPC) of irradiated UHMWPE as an alternative method to improve the mechanical strength while stabilizing the residual free radicals from radiation cross-linking. HPC of uncross-linked UHMWPE has resulted in the formation of extended chain crystals and increased crystallinity, leading to improved strength. We hypothesized that increased cross-link density would hinder crystallization during HPC due to decreased chain mobility. Therefore, we investigated the crystalline structure and tensile mechanical properties of high pressure crystallized 25-, 65- and 100-kGy irradiated UHMWPE. We also determined free radical content and wear. The strength of 25- and 65-kGy irradiated UHMWPEs was improved by HPC with increased crystallinity and crystal size. 100-kGy irradiated UHMWPE did not show improved strength, supporting our hypothesis that decreased chain mobility would hinder crystal formation and strength improvement. None of the HPC irradiated UHMWPEs contained detectable free radicals and their wear properties were maintained, suggesting oxidative and mechanical stability in the long term. Therefore, HPC can be used effectively for imparting oxidative stability while strength improvement can be achieved for irradiated UHMWPE with low to moderate cross-link density.

GOALS

We sought to identify factors associated with gastroenterology clinic attendance in an urban safety net healthcare system.

BACKGROUND

Missed clinic appointments reduce the efficiency and availability of healthcare, but subspecialty clinic attendance among patients with established healthcare access has not been studied.

STUDY

We performed an observational study using secondary data from administrative sources to study patients referred to, and scheduled for an appointment in, the adult gastroenterology clinic serving the safety net healthcare system of San Francisco, CA. Our dependent variable was whether subjects attended or missed a scheduled appointment. Analysis included multivariable logistic regression and classification tree analysis. A total of 1833 patients were referred and scheduled for an appointment between May 2005 and August 2006. Prisoners were excluded. All patients had a primary care provider.

RESULTS

Six hundred eighty-three patients (37.3%) missed their appointment; 1150 patients (62.7%) attended. Language was highly associated with attendance in the logistic regression; non-English speakers were less likely than English speakers to miss an appointment [adjusted odds ratio 0.42 (0.28, 0.63) for Spanish, 0.56 (0.38, 0.82) for Asian language, P<0.001]. Other factors were also associated with attendance, but classification tree analysis identified language to be the most highly associated variable.

CONCLUSIONS

In an urban safety net healthcare population, among patients with established healthcare access and a scheduled gastroenterology clinic appointment, not speaking English was most strongly associated with higher attendance rates. Patient-related factors associated with not speaking English likely influence subspecialty clinic attendance rates, and these factors may differ from those affecting general healthcare access.

BACKGROUND

Social smoking is increasingly prevalent and poses a challenge to traditional cessation practices. Tobacco companies conducted extensive research on social smokers long before health authorities did and marketed products to promote this smoking behavior.

PURPOSE

Research is described and mechanisms identified that are used to promote social smoking to help improve cessation strategies in this growing group.

EVIDENCE ACQUISITION

Searches from 2006 to 2008 of previously secret tobacco industry documents using keywords social smoker, light smoker, casual smoker, youth smoker, and occasional smoker, followed by snowball searching. Data analysis was conducted in 2008.

EVIDENCE SYNTHESIS

Tobacco industry research identified characteristics of social smokers that include: (1) denial of personal nicotine addiction; (2) self-categorization as a nonsmoker; (3) propensity for decreased tobacco use in response to smoke-free laws; (4) variations in age, education, ethnicity, and socioeconomic backgrounds; and (5) a perceived immunity to personal health effects of tobacco but fear of consequences to others. Tobacco companies developed marketing strategies aimed at social smokers, including "non-habit forming" cigarettes.

CONCLUSIONS

Previously considered a transient behavior, social smoking is also a stable consumption pattern. Focused clinical questions to detect social smoking are needed and may include, "Have you smoked any cigarettes or used any tobacco products in the past month?" as opposed to "Are you a smoker?" Clinicians should recognize that social smokers might be motivated to quit after education on the dangers of secondhand smoke rather than on personal health risks or with pharmacotherapy.

BACKGROUND

Claims in the medical literature suggest that neck fullness and witnessed neck pulsations are useful in the diagnosis of typical AV nodal reentrant tachycardia (AVNRT).

HYPOTHESIS

Neck fullness and witnessed neck pulsations have a high positive predictive value in the diagnosis of typical AVNRT.

METHODS

We performed a cross-sectional study of consecutive patients with palpitations presenting to a single electrophysiology (EP) laboratory over a 1 year period. Each patient underwent a standard questionnaire regarding neck fullness and/or witnessed neck pulsations during their palpitations. The reference standard for diagnosis was determined by electrocardiogram and invasive EP studies.

RESULTS

Comparing typical AVNRT to atrial fibrillation (AF) or atrial flutter (AFL) patients, the proportions with neck fullness and witnessed neck pulsations did not significantly differ: in the best case scenario (using the upper end of the 95% confidence interval (CI), none of the positive or negative predictive values exceeded 79%. After restricting the population to those with supraventricular tachycardia (SVT) other than AF or AFL, neck fullness again exhibited poor test characteristics; however, witnessed neck pulsations exhibited a specificity of 97% (95% CI: 90%-100%) and a positive predictive value of 83% (95% CI: 52%-98%). After adjustment for potential confounders, SVT patients with witnessed neck pulsations had a seven-fold greater odds of having typical AVNRT, p = 0.029.

CONCLUSIONS

Although neither neck fullness nor witnessed neck pulsations are useful in distinguishing typical AVNRT from AF or AFL, witnessed neck pulsations are specific for the presence of typical AVNRT among those with SVT.

OBJECTIVES

Antimalarial combination therapy is used in persons with HIV infection in the absence of data on drug interactions. The objective of this study was to investigate the pharmacokinetics (PK) of antimalarial combination artemether/lumefantrine (AL) when administered with the protease inhibitor combination lopinavir/ritonavir (LPV/r) in HIV-uninfected healthy volunteers to determine if important drug interactions exist between these agents.

DESIGN

Open-label study in healthy HIV-seronegative adults.

METHODS

Participants received standard 6-dose treatment courses of AL 80/480 mg twice daily on days 1-4 and 28-31. LPV/r 400/100 mg twice daily was administered on days 16-41 after a 2-week washout period. Plasma concentrations of AL, dihydroartemisinin (DHA, artemether metabolite), lopinavir, and ritonavir were measured.

RESULTS

PK of lumefantrine was influenced by LPV/r resulting in 2- to 3-fold increases in area under the curve (AUC) (AUC0-264: 413 versus 931 h.microg.mL; AUC0-inf: 456 versus 1073 h.microg.mL). For artemether, trends toward Cmax and AUC decreases (Cmax 14.3 versus 11.2 ng/mL and 42.7-62.0 versus 25.9-40.5 h.ng.mL for AUC) were noted during coadministration. For DHA, decreases in Cmax (58.8 versus 37.3 ng/mL) and AUC (190-198 versus 104-109 h.ng.mL) were observed during coadministration without changes in DHA:artemether AUC ratios. AL did not affect LPV/r PK.

CONCLUSIONS

Coadministration of artmether/lumefantrine and LPV/r can be carried out for patients coinfected with malaria and HIV. Formal safety analysis of concomitant therapy should be addressed by future studies among individuals living in malaria-endemic regions.