Selective effects of colds and influenza on human performance efficiency: a critical appraisal.

This paper provides an appraisal of the results published from the MRC Common Cold Unit on human performance efficiency during minor upper respiratory tract infection, i.e., colds and influenza. Despite strict controls employed in the methods of data collection, the robustness of the results and some of the conclusions drawn are questioned. In particular, the claim that colds and influenza lead to selective (and different) effects is criticised as being based on incomplete data. The lack of replication, the small sample sizes, possible response biases and use of controls are considered. Overall, it is argued that there are insufficient data to provide conclusive evidence for selective effects and that over-generalisation from such studies can be misleading.

The effects of caffeine, impulsivity and time of day on performance, mood and cardiovascular function.

Two experiments were carried out to examine the effects of caffeine on performance, mood and cardiovascular function. The results showed that the effects of caffeine depended on the dose, time of administration, the function being examined and the impulsivity of the subject. Changes in blood pressure were only observed when a high dose (3 mg/kg) was used. The effects of this dose on performance depended on the impulsivity of the subject, with high impulsives performing worse in the de-caffeinated condition but getting a greater benefit from the caffeine. The high dose of caffeine also removed the post-lunch dip in sustained attention. The second experiment, which used a lower dose of caffeine (~60 mg), failed to demonstrate any caffeine x impulsivity or caffeine x time of day effects on performance. However, caffeine improved performance on a logical reasoning task and caffeine x time of day x impulsivity effects were found in analyses of visual search tasks. The mood data also support the view that the effects of caffeine depend on a combination of factors similar to those outlined for performance.

Critical appraisal of two methods for determining aluminum in blood samples.

We report two methods for determining aluminum concentrations in blood. Method 1, proposed for routine monitoring of patients with chronic renal failure, includes a collection procedure that can be adopted by any renal dialysis unit, with a minimum of sample contamination. Plasma samples are diluted fourfold with HNO3/Triton X-100 matrix modifier. Method 2 is proposed for determining aluminum concentrations in patients with normal renal function, e.g., in drug studies and environmental monitoring. Samples are diluted with an equal volume of Mg(NO3)2 matrix modifier and atomized from a L'vov platform. By either method, analytical recovery of aluminum added to serum ranged between 92% and 105% throughout the linear calibration range. The reference interval (mean +/- SD) for aluminum in 22 healthy subjects by method 2 was 0.044 +/- 0.030 mumol/L.

Effects of caffeine given before and after lunch on sustained attention.

Previous research has shown that caffeine increases alertness and improves sustained attention. In contrast to this, consumption of lunch leads to a decline in the ability to maintain attention. The main aim of the present study was to determine whether caffeine removes or reduces the postlunch drop in performance, an issue which is of considerable practical importance and theoretical interest. The results showed that caffeine improved performance on the Bakan vigilance task and removed the post-lunch dip observed in the decaffeinated condition. Similar effects were observed in one of the conditions of a mental rotation task. The lunch X caffeine interaction observed in the Bakan task did not change over the course of the task. In contrast to the performance data, lunch X caffeine interactions were not observed in analyses of cardiovascular function or subjective mood.

Micro-quantity tissue digestion for metal measurements by use of a microwave acid-digestion bomb.

We describe a simple and convenient method for processing small amounts of tissue samples for trace-metal measurements by atomic absorption spectrometry, by use of a modified Parr microwave digestion bomb. Digestion proceeds rapidly (less than or equal to 90 s) in a sealed Teflon-lined vessel that eliminates contamination or loss from volatilization. Small quantities of tissue (5-100 mg dry weight) are digested in high-purity nitric acid, yielding concentrations of analyte that can be measured directly without further sample manipulation. We analyzed National Institute of Standards and Technology bovine liver Standard Reference Material to verify the accuracy of the technique. We assessed the applicability of the technique to analysis for aluminum in bone by comparison with a dry ashing procedure.

Lithium determined in serum with an ion-selective electrode.

We evaluated the performance of the lithium ion-selective electrode (ISE) in the Du Pont Na/K/Li analyzer. Lithium concentrations in 106 serum samples from patients being treated with lithium were measured in duplicate with the ISE and by flame photometry. The slope of the regression line for the two methods was 1.004 with a standard error of the estimate of 0.049 mmol/L (x = flame photometry, y = ISE). Lithium measurements by the ISE method in serum or aqueous standards were linear to greater than 2.0 mmol/L. Within-run CVs for low (0.31 mmol/L) and high (1.15 mmol/L) lithium controls were 5.9% and 1.7%, respectively (n = 20). Day-to-day CVs for the same controls were 9.8% and 3.3%, respectively (n = 20). There was no significant interference when the concentrations of sodium, potassium, calcium, or magnesium were varied, nor did intervening urinary lithium analyses affect the measurement of serum lithium. Results for lithium measurement in four serum-based survey materials compared well with results by isotope dilution/mass spectrometry.

Evaluation of a bromocresol purple method for the determination of albumin adapted to the DuPont aca discrete clinical analyzer.

We evaluated a new method for the determination of albumin on the DuPont aca discrete clinical analyzer that utilized an albumin selective dye, bromocresol purple (BCP). This dye minimizes globulin interference that occurs with bromocresol green (BCG) methods that have long (greater than 30 s) incubation times. Good correlation was observed between the new BCP method and two methods which do not show significant globulin interference: an immunological method and a rapid BCG method. Comparisons with alternate BCG methods (SMA 12/60, SMAC, and the aca) were generally not as good. The albumin results by the BCP method on specimens with elevated globulins were similar to results from the immunological and rapid BCG methods. The reference interval was 34-50 g/L. The between-day coefficient of variation ranged from 0.9 to 3.5% at three evaluation sites on 2 levels of 8 different control materials. The method was linear between 6-70 g/L. No interference was observed from hemoglobin at levels less than or equal to 5.00 g/L or from bilirubin at levels less than 342 mumol/L. Also, no interference was observed from nine common drugs that are known to bind to albumin. These studies show that accuracy, reproducibility and linearity of the BCP albumin method on the aca are acceptable for clinical use.

Optimization and evaluation of cardiac enzymes and isoenzymes measured on a random access analyzer.

Four serum enzymes and isoenzymes used in the diagnosis of acute myocardial infarction (AMI), lactate dehydrogenase LD and LD-1, creatine kinase (CK), and CK-MB have been adapted to the Technicon RA-1000 automated clinical chemistry analyzer. Analytical parameters have been adjusted to provide clinically acceptable precision for all four assays. Correlations with centrifugal analyzer procedures gave correlation coefficients ranging from 0.998 to 0.999. A limited clinical study of the CK-MB assay indicated that a discriminant value of 13 U per L could separate AMI from non-AMI patients.

Adaptation of EMIT drug assays to a random-access automated clinical analyzer.

Enzyme multiplied immunoassay technique (EMIT) assays for theophylline, carbamazepine, phenytoin, phenobarbital, valproic acid, acetaminophen, gentamicin and tobramycin, have been adapted to the Technicon RA-1000 random access analyzer. Working reagents are stable for a period of at least one week, and calibration need only be performed when preparing fresh reagents. Between-day precision ranged from 2.2 to 5.5 percent and correlations with similar EMIT assays performed on a centrifugal analyzer were satisfactory. Excellent results were obtained on proficiency testing samples when analyzed for theophylline, phenobarbital, phenytoin and acetaminophen. The procedures have been adapted to emergency testing of these four drugs.