Crossover designs for clinical trials

I discuss three-period crossover designs for an efficient comparison of two test treatments with special application to clinical trials which often have many practical limitations. In this paper I specify a subset of three-period crossover designs so that the investigators are not left with the problematic two-period two-sequence design, should the trials be terminated after the second period. I show that there is a dramatic reduction in variability for estimating the direct and residual treatment effects in three-period designs compared to two-period designs. I also show that the universally optimal design with ABB and BAA sequences is unsuitable when a complex form of residual effects is suspected, such as the second-order residual effects or treatment by period interactions. The design with ABB, BAA, AAB, and BBA sequences is relatively robust to these uncertain model assumptions. I also discuss missing data problems and conclude that, even with a large proportion of missing values, the three-period design is far more efficient than the two-period design.     

Correlative MR-anatomic study of the median nerve

OBJECTIVE: The purpose of our study was to evaluate the effectiveness of MR imaging for showing the intrinsic anatomy of a peripheral nerve. Cadaver wrist specimens that included the median nerve were imaged with MR imaging at 3 T, then sectioned, stained, and inspected grossly and microscopically. The size, shape, and signal intensity of the sheath and axonal structures in the median nerve were identified in MR images by comparison with anatomic sections. CONCLUSION: This study suggests that MR imaging with sufficiently high-resolution techniques shows the internal structure of peripheral nerves. These results suggest that MR imaging may be a means to distinguish neuritis, tumor, degeneration, or fatty proliferation in a peripheral nerve and to evaluate the nerve before microsurgical anastomosis.     

Preference of invasive cytotrophoblast for maternal vessels in early implantation in the macaque

The interaction of cytotrophoblast with maternal endometrium, especially endometrial blood vessels, was examined in macaque gestational stages between 2 and 8 days after the onset of implantation. Serial sectioning of these early implantation sites allowed immunostaining of consecutive sections with a number of different antibodies, facilitating cell identification. In the earliest implantation site, immunostaining showed that antibody to cytokeratin stained cytotrophoblast, syncytial trophoblast, epithelial plaque and endometrial gland cells. However, only those cytotrophoblast cells near the maternal-fetal border and within vessels showed surface staining for neural cell adhesion molecules and only syncytial trophoblast showed SP1 reactivity. Even at this early stage cytotrophoblast filled the lumen of superficial arterioles, whereas dilated venules contained only a few cytotrophoblast cells. In later stages endovascular cytotrophoblast not only plugged many spiral arterioles but also migrated into the walls of these arterioles, and progressed into deeper coils. Displacement of endothelial cells and disruption of vessel walls were illustrated with antibody to factor VIII, TGF alpha, and desmin. Clusters of cytotrophoblast cells at the fetal-maternal interface tended to bypass clusters of epithelial plaque cells and larger clusters of maternal fibroblasts, but readily entered all vascular spaces. Consequently the vascular system constituted a major pathway of invasion, although the arterioles were the only component substantially invaded beyond the trophoblastic-shell/endometrial border.     

Glucokinase gene variants in the common form of NIDDM

To determine whether a structural defect in glucokinase could be a primary cause of glucose intolerance in the common form of NIDDM, the prevalence of mutations in the gene in 60 American black NIDDM patients was investigated. First, by Southern blot analysis of DNA from a subset of randomly selected subjects (n = 20), no gross deletions, insertions, or rearrangements of the gene were detected. Next, the 5'-untranslated and coding regions of the gene were amplified directly from genomic DNA by the polymerase chain reaction. PCR products were screened for mutations by using single-strand conformational polymorphism analysis. A total of nine variants were identified, with two in the 5'-UT regions of islet exon 1, two in the 5'-UT region of liver exon 1, and five in the coding regions. For islet exon 1, 5 of 60 NIDDM patients had both variants in the 5'-UT region; and for liver exon 1, two variants each occurred in 1 of 60 NIDDM patients. The coding region variants included a missense mutation in islet exon 1, substitution of Ala11 (GCC) with Thr11 (ACC), found in 2 patients. The biological consequences of this mutation and the mutations in the 5'-UT portion of the gene have yet to be determined. The rest of the variants were third base pair changes of codons, i.e., silent. A common polymorphism, which was in linkage equilibrium with microsatellite repeats GCK1 and GCK2, was found in intron 9, and a variant in intron 2 in both alleles of 1 patient.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cadmium uptake by Caco-2 cells. Effect of some milk components

The effect of some milk components on the cellular uptake of cadmium has been studied using a human intestinal cell line (Caco-2). Cadmium uptake by Caco-2 cells increased with the concentration of this metal in the culture medium, in a saturable way. These cells were exposed to different concentrations of cadmium and the synthesis of metallothionein was studied by a cadmium-saturation method. The levels of metallothionein increased with the cadmium concentration in the medium up to 20 microM of metal. Supplementation of the culture medium with 10% bovine milk caused a 25% decrease in the uptake of cadmium with respect to that internalized by the cells maintained in the culture medium alone. However, the uptake of cadmium from the medium supplemented with 10% human milk was similar to that with serum-free medium. beta-Lactoglobulin interacted with cadmium when studied by equilibrium dialysis, showing a stoichiometric binding constant of 5 x 10(4) l/mol. Interaction of lactoferrin with cadmium, however, was negligible. When Caco-2 cells were incubated in culture medium containing lactoferrin, cadmium uptake decreased with respect to that observed incubating the cells in a medium containing beta-lactoglobulin or in the free-protein medium. The inhibitory effect of lactoferrin on the uptake of cadmium might be due to a reduction of the cell surface charge, through its binding to the membrane.     

p53 expression in neurofibroma and malignant peripheral nerve sheath tumor. An immunohistochemical study of sporadic and NF1-associated tumors

OBJECTIVES--(1) to evaluate regional cerebral blood flow (rCBF) with single photon emission computed tomography and 99mTc-hexamethylpropyleneamine oxime in patients with the idiopathic adult hydrocephalus syndrome (IAHS); (2) to examine regional cerebral blood flow (rCBF), gait, and psychometric functions before and after CSF removal (CSF tap test); (3) to assess abnormalities in subcortical white matter by MRI. METHODS--Thirty one patients fulfilling the criteria for IAHS (according to history and clinical and neuroradiological examination) were studied. Quantified gait measurements, psychometric testing, and rCBF before and after removal of CSF were obtained. Pressure of CSF and CSF outflow conductance were investigated with a constant pressure infusion method. Brain MRI was used to quantify the severity of white matter lesions and periventricular hyperintensities. In IAHS a widespread rCBF hypoperfusion pattern was depicted, with a caudal frontal and temporal grey matter and subcortical white matter reduction of rCBF as the dominant feature. Removal of CSF was not accompanied by a concomitant increase in rCBF. Significant white matter lesions were detected only in a minority of patients by MRI. An altered CSF hydrodynamic state with a higher CSF pressure and lower conductance was confirmed. IAHS is characterised by an abnormal CSF hydrodynamic state, associated with a widespread rCBF reduction with preference for subcortical white matter and frontal-temporal cortical regions. Furthermore in most patients MRI did not show white matter changes suggestive of a coexistent subcortical arteriosclerotic encephalopathy. At least in the idiopathic group of patients with AHS, measurements of rCBF before and after temporary relief of the CSF hydrodynamic disturbance will not provide additional information that would be helpful in the preoperative evaluation but is suggestive of a preserved autoregulation of rCBF.     

Long-term evaluation of the ventricular defibrillation energy requirement

INTRODUCTION: Defibrillation energy requirements in patients with nonthoracotomy defibrillators may increase within several months after implantation. However, the stability of the defibrillation energy requirement beyond 1 year has not been reported. The purpose of this study was to characterize the defibrillation energy requirement during 2 years of clinical follow-up. METHODS AND RESULTS: Thirty-one consecutive patients with a biphasic nonthoracotomy defibrillation system underwent defibrillation energy requirement testing using a step-down technique (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, and 1 J) during defibrillator implantation, and then 24 hours, 2 months, 1 year, and 2 years after implantation. The mean defibrillation energy requirement during these evaluations was 10.9+/-5.5 J, 12.3+/-7.3 J, 11.7+/-5.6 J, 10.2+/-4.0 J, and 11.7+/-7.4 J, respectively (P = 0.4). The defibrillation energy requirement was noted to have increased by 10 J or more after 2 years of follow-up in five patients. In one of these patients, the defibrillation energy requirement was no longer associated with an adequate safety margin, necessitating revision of the defibrillation system. There were no identifiable clinical characteristics that distinguished patients who did and did not develop a 10-J or more increase in the defibrillation energy requirement. CONCLUSION: The mean defibrillation energy requirement does not change significantly after 2 years of biphasic nonthoracotomy defibrillator system implantation. However, approximately 15% of patients develop a 10-J or greater elevation in the defibrillation energy requirement, and 3% may require a defibrillation system revision. Therefore, a yearly evaluation of the defibrillation energy requirement may be appropriate.