Biomedical subjects

Ingeborg van der Tweel

Publications and source records attributed to Ingeborg van der Tweel.

23 records · Page 2Linked to original sources

PubMed2003

Early stopping in clinical trials and epidemiologic studies for "futility": conditional power versus sequential analysis.

Early stopping of a clinical trial is well accepted when there is enough evidence for a significant effect. However, during the course of a trial, there can be reasons to consider early termination for "futility." In epidemiologic studies, costly or destructive laboratory tests or slow case accrual can make it desirable to stop a study early for reasons of efficiency. Estimation of the conditional power (CP) is proposed as a decision tool to stop a study early or to continue it. We consider the disadvantages of this method. We propose (group) sequential continuation of the trial or study as a less arbitrary strategy. We re-analyzed two data sets from the literature to illustrate the advantages of a sequential approach. We conclude that (group) sequential analyses have several advantages over CP. More studies should consider a sequential design and analysis to enable early stopping when enough evidence has accumulated to conclude a lack of the expected effect. Such a strategy can save valuable resources for more promising hypotheses.

Antibodies, Viral↗

PubMed2002

Cataract after total body irradiation and bone marrow transplantation: degree of visual impairment.

PURPOSE: To assess the degree of visual impairment as a result of cataract formation after total body irradiation (TBI) for bone marrow transplantation. METHODS AND MATERIALS: The data from 93 patients who received TBI in 1 or 2 fractions as a part of their conditioning regimen for bone marrow transplantation were analyzed with respect to the degree of visual impairment as a result of cataract formation. The probability to develop severe visual impairment (SVI) was determined for all patients, and the degree of visual impairment was assessed for 56 patients with stabilized cataract, using three categories: no, mild, or severe. RESULTS: For all 93 patients, the probability of developing a cataract causing SVI was 0.44. For allogeneic patients, it was 0.33 without and 0.71 with steroid treatment (p <0.001). All SVI-free probability curves reached a plateau distinct from the cataract-free curves. Apparently, cataracts developing late in the follow-up period rarely cause SVI. Of the patients with stabilized cataract, 32% had no visual impairment, 16% had mild, and 52% severe impairment. No or mild visual impairment was present in 61% of all patients with stable cataract and no steroid treatment compared with only 13% of the patients treated with steroids (p = 0.035). CONCLUSION: SVI occurs in only some of the patients (52%) with stable cataract after TBI for bone marrow transplantation in 1 or 2 fractions. Steroid treatment markedly increases the probability of developing visual problems as result of a cataract after TBI.

Acute Disease↗

PubMed2002

Risk indicators for pressure ulcers during surgery.

Patients undergoing surgery are prone to develop pressure ulcers during surgery. The aim of this study was to identify pressure ulcer risk indicators in patients undergoing surgery which lasted more than four hours. A prospective follow-up study was conducted in 208 patients. Data on presence or absence of pressure ulcers and risk indicators were collected preoperatively, during surgery, and postoperatively. The results show that of the many indicators recorded, the only predictor of pressure ulcers was length of surgery. Because it is not possible to influence the length of the surgery, prevention should primarily be aimed at decreasing pressure and shearing forces during surgery.

Adolescent↗

PubMed2002

Volume changes in gray matter in patients with schizophrenia.

OBJECTIVE: Schizophrenia is generally characterized by a progressive decline in functioning. Although structural brain abnormalities, particularly decrements in gray matter volume, are considered important to the pathology of schizophrenia, it is not resolved whether the brain abnormalities become more prominent over time. METHOD: Magnetic resonance brain images from 159 patients with schizophrenia and 158 healthy comparison subjects between 16 and 70 years of age were compared. Using linear regression analysis, the authors analyzed the relationship between the volumes of the total brain, gray and white matter, cerebellum, and lateral and third ventricles with patient age. RESULTS: Total brain (-2.2%), cerebral gray matter (-3.3%), prefrontal gray matter (-4.4%), and prefrontal white matter (-3.5%) volumes were smaller, and lateral (27%) and third (30%) ventricle and peripheral CSF (11%) volumes were larger in schizophrenia patients. A significant group-by-age interaction for gray matter volume was found, as shown by a steeper regression slope between age and gray matter volume in patients (-3.43 ml/year) than in healthy comparison subjects (-2.74 ml/year). CONCLUSIONS: The smaller brains of the patients with schizophrenia can be explained by decreases in gray matter volume. Moreover, the finding that the smaller gray matter volume was more pronounced in older patients with schizophrenia may suggest progressive loss of cerebral gray matter in schizophrenia patients.

Adolescent↗

PubMed2002

The sulfonylurea glyburide induces impairment of glucagon and growth hormone responses during mild insulin-induced hypoglycemia.

OBJECTIVE: The sulfonylurea (SU) glyburide may cause severe and prolonged episodes of hypoglycemia. We aimed at investigating the impact of glyburide on glucose counterregulatory hormones during stepwise hypoglycemic clamp studies. RESEARCH DESIGN AND METHODS: We performed stepwise hypoglycemic clamp studies in 16 healthy volunteers (7 women and 9 men aged 44 +/- 10 years). We investigated counterregulatory hormonal and symptom responses at arterialized venous plasma glucose levels (PG) of 3.8, 3.2, and 2.6 mmol/l, comparing 10 mg glyburide orally and placebo in a double-blind, randomized crossover fashion. RESULTS: The increase in plasma glucagon with time from PG = 3.8 onward was smaller for glyburide than for placebo (P = 0.014). Plasma glucagon area under the curve (AUC)(60-180) was lower after glyburide than after placebo (1,774 +/- 715 vs. 2,161 +/- 856 pmol. l(-1). min, P = 0.014). From PG = 3.8 onward, plasma growth hormone (GH) levels with placebo were nearly two times (1.9 [95% CI 1.2-2.9]) as high as with glyburide (P = 0.011). AUC(60-180) for GH was lower after glyburide than after placebo (geometric mean [range] 665 [356-1,275] and 1,058 [392-1,818] mU. l(-1). min, respectively; P = 0.04). No significant differences were observed for plasma cortisol, epinephrine and norepinephrine, or incremental symptom scores. CONCLUSIONS: The SU glyburide induces multiple defects in glucose counterregulatory hormonal responses, notably decreases in both glucagon and GH release.

Adult↗