Evaluation of the uncertainty of molecular mass measurement by electrospray ionization mass spectrometry.

Electrospray ionization (ES) is a novel method used in mass spectrometry (MS) for producing gas-phase ions from substances in solutions. Common practices for molecular mass estimation from ES spectra summarize the spectrum as a single peak giving no estimate of uncertainty or treat each peak as an independent molecular mass measurement. ES-MS data analysis showed that each peak in an ES spectrum does not always provide an independent measure of molecular mass. Underestimation of measurement uncertainty is a possible result. An elementary time series method, the Yule-Walker equations, was applied to molecular mass estimation from ES data.

The logistic analysis of epidemiologic prospective studies: investigation by simulation.

We performed a Monte Carlo computer simulation of the Walker-Duncan logistic regression technique in a typical epidemiologic prospective setting and analysed the results with respect to the accuracy and reliability of the regression estimates and the associated statistical significance tests (Z-tests). The results strongly suggest that the estimates were neither accurate nor reliable. The magnitude of the difference between the average estimated regression coefficient and its true population value did not necessarily decrease as the sample size increased. The average estimated standard deviation of the estimate of the regression coefficient either overestimated or underestimated the actual standard deviation, the former occurring most, but not all, of the time. The significance tests (a two-tailed Z-test with a significance level of 0.05) had actual type I errors ranging from 0.00 to 0.24 for different samples. This approach is therefore inadequate as an epidemiologic tool for analysis of a Framingham-type prospective study. Further simulation studies are indicated.

Symposium on intensive care: 3. Upper gastrointestinal bleeding in the intensive care unit.

Bleeding from hemorrhagic erosions in the stomach or duodenum of seriously ill patients is associated with a high mortality. While the pathogenesis of such lesions is by no means certain, it is known that they are universal after shock, sepsis or severe burns. Fiberoptic endoscopy has become the most valuable means of diagnosis. This should be preceded by gastric irrigaiton, which usually sufficies to control bleeding caused by acetylsalicylic acid or alcohol, or both. Neutralization of gastric acidity is essential. The histamine HI-receptor antagonist, cimetidine, was used in 27 patients with erosive gastritis, and bleeding ceased in 24. There is a prospect that sugh agents will obviate the necessity of total gastrectomy in the occasional resistant cases in favour of conservative surgery.