Biomedical subjects

J J Snyder

Publications and source records attributed to J J Snyder.

17 recordsLinked to original sources

PubMed2006

Mortality studies comparing peritoneal dialysis and hemodialysis: what do they tell us?

Several recent large-scale epidemiological studies comparing mortality among end-stage renal disease (ESRD) patients receiving hemodialysis (HD) versus peritoneal dialysis (PD) show conflicting results. In this paper, we undertake a critical review of these studies. Our goal is to determine if there are any consistent trends in outcomes between HD and PD within select subgroups of patients once methodological differences have been accounted for. A total of six large-scale registry studies and three prospective cohort studies conducted in the United States (US), Canada, Denmark, and the Netherlands were reviewed. Summary findings from these studies are presented for comparative purposes. Additional summary analyses based on previously reported data on 398 940 incident US Medicare patients are included for the purpose of comparing results from this population of patients to those of the other select studies when similar methods of analysis are applied. Results are summarized in terms of the relative risk of death for PD versus HD (RR[PD:HD]). Differences in results between the nine studies can be attributed to the degree of case-mix adjustment carried out and to the use of different subgroups when comparing mortality between HD and PD. When these differences are accounted for, we found a remarkable degree of synergism in results between the registry studies and, to a lesser degree, the prospective cohort studies. PD was generally found to be associated with equal or better survival among non-diabetic patients and younger diabetic patients in all four countries. However, among older diabetic patients, results varied by country. The Canadian and Danish registries showed no difference in survival between PD and HD among older diabetics while in the US, HD was associated with better survival for diabetics aged 45 and older. All studies show a time-dependent trend in the RR of death with PD generally associated with equivalent or better survival during the first year or two of dialysis. However, results on longer-term survival varied according to study and to different subgroups within studies. Subgroup analyses in the prospective cohort studies were limited by small numbers of patients resulting in highly varied and somewhat controversial results when compared to the larger registry-based studies. Based on our review of recent publications and additional analyses of US Medicare data, we conclude that overall patient survival is similar for PD and HD but that important differences do exist within select subgroups of patients, particularly those subgroups defined by age and the presence or absence of diabetes.

Humans↗

PubMed2001

Attentional momentum does not underlie the inhibition of return effect.

J. Pratt, T. M. Spalek, and F. Bradshaw (1999) recently proposed that attentional momentum is the mechanism underlying the inhibition of return (IOR) effect. They suggested that momentum associated with an attentional movement away from a peripherally cued location and toward an uncued opposite location is essential and fundamental to the finding of an IOR effect. Although it is clear from the present study and from a reanalysis of data from Pratt et al. that response time can be facilitated at an uncued opposite location, this putative effect of attentional momentum is neither robust nor reliable. First, it occurs for only a minority of participants. Second, it occurs in only a subset of the cued display positions. And finally, it is uncorrelated with the occurrence of IOR. Together the data indicate that the attentional momentum hypothesis is an overgeneralization and that it does not underlie the robust and reliable IOR effect.

Attention↗

PubMed2001

Inhibition of return at multiple locations in visual search: when you see it and when you don't.

Using a novel sequential task, Danziger, Kingstone, and Snyder (1998) provided conclusive evidence that inhibition of return (IOR) can co-occur at multiple non-contiguous locations. They argued that their findings depended crucially on the allocation of attention to cued locations. Specifically, they hypothesized that because subjects could not predict whether an onset event was a target or a non-target, all onset events had to be attended. As a result, non-targets were tagged with inhibition. The present study tested this hypothesis by manipulating whether target onset was predictable or not. In support of Danziger et al., three experiments revealed that multiple IOR was only observed when attention had to be directed to the cued locations. Interestingly, when attention did not need to be allocated to the cued locations, and multiple IOR was abolished, an IOR effect was still observed at the most recently cued location. Two possible accounts for this single IOR effect were presented for future investigation. One account attributes the effect to motor-based inhibition as hypothesized by Klein and Taylor (1994). The alternative account attributes the effect to weak attentional capture by a peripheral cue. Together the data support the view that multiple IOR is an attentional phenomenon and, as hypothesized by Tipper, Weaver, and Watson (1996), its presence or absence is largely under the control of the observer.

Cues↗

PubMed2000

Inhibition of return and visual search: how many separate loci are inhibited?

Using a novel sequential visual search paradigm Danziger, Kingstone, and Snyder (1998) demonstrated that inhibition of return (IOR) can reside at three spatial locations. In the present study, we extended the work of Danziger et al. by investigating whether there is a limit to the number of locations that can be inhibited in a sequential visual search task. Our study revealed that IOR can be measured at a minimum of five locations. The magnitude of the IOR effect was largest at the most recently searched location and declined from there in an approximately linear fashion. Two models that can account for our data are presented.

Adult↗

PubMed1998

Brain tumors in the elderly: recent trends in a Minnesota cohort study.

OBJECTIVE: To compare the clinical presentation, time elapsed to diagnosis, and survival of elderly patients (> or = 65 years) with that in younger patients with malignant primary brain tumors. DESIGN: Retrospective cohort study. SETTING: Four hospitals in Minneapolis, Minn. PATIENTS: Seven hundred fourteen patients diagnosed as having and treated for primary malignant brain tumors between 1980 and 1995; 230 (32%) were 65 years or older. MAIN OUTCOME MEASURES: The type and duration of the chief presenting symptom, the time elapsed to diagnosis, the treatment modalities used, and patient survival were analyzed. RESULTS: Time elapsed from onset of symptom to diagnosis was not longer for elderly patients than younger ones, with the exception of patients aged 18 to 24 years, who had a significantly longer delay in diagnosis (P = .004). Elderly patients were significantly less likely to present with headache or seizure (P<.001), and more likely to present with confusion, aphasia, or memory loss (for each, P<.001). With the single exception of confusion, the duration of all other presenting symptoms was not significantly longer for patients 65 years and older compared with younger patients. Survival is significantly reduced in older patients, and appears to worsen significantly in patients 45 years and older (P<.001). A significantly higher proportion of patients 65 years and older with glioblastoma multiforme received no treatment (P = .004) if diagnosed after 1990. CONCLUSIONS: Elderly patients (> or = 65 years) with malignant brain tumors are diagnosed as promptly as younger patients, although they have a markedly different constellation of symptoms. Since diagnosis of brain tumors continues to improve in the elderly, it may be more difficult to ascribe the steady increase in incidence to artifactual factors.

Adolescent↗

PubMed1998

Inhibition of return to successively stimulated locations in a sequential visual search paradigm.

The inhibition of return (IOR) effect refers to a slowing in response time for a target that appears at a previously attended location. Many investigators have speculated that IOR's inherent ecological validity may be to ensure an efficient search of a complex environment by creating a bias against returning to locations that have already been investigated. Unfortunately, this intriguing idea has lacked compelling empirical support. The current study addressed this issue. It was shown that in a novel visual search task, the IOR could dwell at a minimum of 3 spatially noncontiguous locations. These data suggest that IOR may serve as an important mechanism for facilitating visual search in complex environments, by inhibiting attention from returning to previously inspected locations.

Adult↗

PubMed1995

Methamphetamine and amphetamine derived from the metabolism of selegiline.

Routine methamphetamine testing identified a urine specimen with inconsistent screening and confirmation results. The methamphetamine RIA screening test (Diagnostic Products Corporation) indicated a borderline positive specimen, while the achiral confirmatory GC/MS result showed 4690 ng/mL of methamphetamine and 1895 ng/mL of amphetamine. Analysis of the specimen after derivatization with S(-)-N-trifluoroacetylprolyl chloride showed only the presence of 1-amphetamine and 1-methamphetamine. It was later learned that the individual providing the specimen had been taking Selegiline. Selegiline, (-) propynylmethamphetamine, is a monoamine oxidase inhibitor used for the treatment of Parkinson's disease. It is sold under the trade name Eldepryl. Its major metabolites are 1-methamphetamine, 1-amphetamine and N-desmethylselegiline. Urine specimens from other Selegiline users were obtained and analyzed. A characteristic metabolic pattern was noted, exemplified by a ratio of 1-methamphetamine to 1-amphetamine of about 2.8. This is in contrast to what is observed in the urine of individuals who ingest pure 1-methamphetamine, such as with Vicks Inhaler, where the 1-methamphetamine to 1-amphetamine ratio in the urine is usually greater than 8. Caution is advised when interpreting methamphetamine results without using a chiral identification technique.

Amphetamine↗

PubMed1994

Amphetamine as an artifact of methamphetamine during periodate degradation of interfering ephedrine, pseudoephedrine, and phenylpropanolamine: an improved procedure for accurate quantitation of amphetamines in urine.

During periodate degradation of interfering ephedrine, pseudoephedrine, and phenylpropanolamine in the extraction of methamphetamine from urine, it was observed that a small amount of methamphetamine was demethylated to amphetamine. although all three interfering phenylpropanolamines could be degraded by periodate at pH 5.2 and above, this periodate-mediated transformation of methamphetamine to amphetamine was observed only at pH 9.1 and above. Therefore, to avoid this transformation, a pH of 6.2 was used for the oxidative degradation of phenylpropanolamines. The excess periodate was then reduced with thiosulfate or ascorbic acid prior to the extraction of methamphetamine using a basic pH.

Amphetamine↗

PubMed1993

Simultaneous analysis of codeine, morphine, and heroin after B-glucuronidase hydrolysis.

Analysis of the opiates, morphine and codeine, often proceeds by way of acid hydrolysis for release of the parent morphine from its glucuronide formed during metabolism. Following use, heroin is rapidly deacetylated to 6-monoacetylmorphine (6-MAM), which can be detected in the urine for a short time following injection of heroin. Only a small amount of 6-MAM may be further metabolized to morphine glucuronide. Thus, in general, the urine specimen has not been hydrolyzed prior to analysis for heroin, using a separate procedure from morphine and codeine. Simultaneous analysis of morphine, codeine, 6-MAM and heroin would be complicated by loss of identity between morphine and heroin when heroin converts to morphine following acid hydrolysis for removal of the glucuronide moiety from morphine glucuronide. Another significant problem in simultaneous analysis is the relative disparity in concentration between morphine/codeine and 6-MAM/heroin (which might be present in the urine specimen). In the proposed method of analysis, free morphine resulting from B-glucuronidase rather than acid hydrolysis of morphine glucuronide is derivatized with propionic anhydride to form dipropionylmorphine. Heroin that does not react with B-glucuronidase remains unhydrolyzed as the diacetylmorphine derivative. Some of the more exacting steps for the acid procedure are eliminated altogether making overall costs for the enzyme procedure comparable to those of the acid hydrolysis method. The enzyme reaction mixture is purified through a solid phase column system. The optimal conditions for concentration of enzyme, temperature of hydrolysis and pH are individually characterized for B-glucuronidase hydrolysis and the ions which identify the propionyl derivatives are characterized for the simultaneous analysis of morphine, codeine, 6-MAM and heroin.

Codeine↗

PubMed1977

Biological markers in breast carcinoma. III. Clinical correlations with carcinoembryonic antigen.

Plasma CEA levels were evaluated by radioimmunoassay in patients with breast carcinoma in relation to clinical-pathologic staging, clinical tumor burden, prognosis and organ sites of involvement. Elevated levels were observed in 83/117 (70.9%) patients with metastatic disease, 2/14 preoperative patients and in 3/39 one-six month postoperative patients. Preoperative levels were elevated in two patients; the levels fell to normal after operation. Changes of elevated CEA levels followed the clinical response to therapy in 22/22 metastatic disease patient-trials. The levels decreased with a response in 15 trials and rose with progressive disease or relapse in seven trials. The incidence of CEA elevations and quantitative CEA levels both rose with increasing clinical tumor burden from the postoperative state through the preoperative state to two or more organ sites of metastatic involvement. No relationship was demonstrable among limited samples between preoperative or postoperative CEA levels and prognosis; however, in metastatic disease, pretherapy CEA levels greater than 5 ng/ml were associated with low response rates and early therapeutic failure to chemotherapy. The highest frequency of elevated CEA levels was observed in patients with osseous involvement (79%) and the lowest frequency with skin (52%) and breast (50%) metastases. Liver and osseous disease were also associated with higher mean CEA levels than were other sites of metastatic involvement. CEA levels appear to be elevated in the majority of patients with metastatic disease and be of prognostic importance in metastatic disease. The level in patients with metastatic disease appears to reflect the therapy-associated tumor burden of the host, especially in patients with elevated levels.

Breast Neoplasms↗

PubMed1977