Additive pressor effects of caffeine and stress in male medical students at risk for hypertension.

The effects of caffeine on blood pressure (BP) and cortisol secretion were examined during elevated work stress in medical students at high versus low risk for hypertension. Among 31 male medical students who were regular consumers of caffeine, 20 were considered at low risk for hypertension (negative parental history and all screening BP < 125/78 mm Hg) and 11 at high risk based on epidemiologic criteria (positive parental history and average screening BPs between 125/78 and 139/89 mm Hg). Cortisol levels and ambulatory BP were measured with and without caffeine during two lectures (low work stress) and two exams (high work stress) in a randomized, double-blind, crossover trial. Caffeine consumption and exam stress increased cortisol secretion in both groups (P < .05). BP increased with caffeine or exam stress in both groups, low versus high risk, respectively (Caffeine: + 5/4 vs + 3/3 mm Hg; Stress: + 4/1 vs + 7/3 mm Hg; P < .05). The combination of stress and caffeine caused additive increases in BP (Low Risk + 9/5 mm Hg, High Risk + 10/6 mm Hg) such that 46% of high-risk participants had average systolic BP > or = 140 mm Hg. This combined effect of stress and caffeine on BP suggests that it may be beneficial for individuals at high risk for hypertension to refrain from the use of caffeinated beverages, particularly at times when work demands and attendant stressors are high. For the same reasons, recent intake of caffeine should be controlled in patients undergoing BP measurement for the diagnosis of hypertension.

Acute blood pressure elevations with caffeine in men with borderline systemic hypertension.

Whether the vasoconstrictive actions of caffeine are enhanced in hypertensive persons has not been demonstrated. Thus, caffeine (3.3 mg/kg) versus placebo was tested in 48 healthy men (aged 20 to 35 years) selected after screening on 2 separate occasions. Borderline hypertensive men (n = 24) were selected with screening systolic blood pressure (BP) of 140 to 160 mm Hg and/or diastolic BP 90 to 99 mm Hg. Low-risk controls (n = 24) reported no parental history of hypertension and had screening BP < 130/85 mm Hg. Participants were then tested on 2 occasions after 12-hour abstinence from caffeine in each of 2 protocols; this required a total of 4 laboratory visits. Caffeine-induced changes in diastolic BP were 2 to 3 times larger in borderline subjects than in controls (+8.4 vs +3.8 mm Hg, p < 0.0001), and were attributable to larger changes in impedance-derived measures of systemic vascular resistance (+135 vs +45 dynes.s.cm-5, p < 0.004). These findings were consistent and reached significance in both protocols. The percentage of borderline subjects in whom diastolic BP changes exceeded the median control response was 96%. Consequently, whereas all participants exhibited normotensive levels during the resting predrug baseline, 33% of borderline subjects achieved hypertensive BP levels after caffeine ingestion. Thus, in borderline hypertensive men, exaggerated responses to caffeine were: selective for diastolic BP, consistent with greater vasoconstriction, replicated in 2 protocols, and representative of nearly all borderline hypertensives. We suspect that the potential for caffeine to stabilize high resistance states in susceptible persons suggests that its use may facilitate their disease progression, as well as hinder accurate diagnosis and treatment.

Caffeine and behavioral stress effects on blood pressure in borderline hypertensive Caucasian men.

Caffeine in dietary amounts raises blood pressure (BP), and its use increases during work stress; however, caffeine combined with behavioral stress has not been tested in borderline hypertensive (BH) men. Accordingly, this study tested a psychomotor stressor plus caffeine (3.3 mg/kg, equivalent to 2-3 cups of coffee) using a double-blind, crossover design in 24 BH men (140/90 mmHg < or = BP < or = 160/95 mmHg) and 24 controls (BP < or = 135/85 mmHg). BH men had modestly larger BP increases to the task and showed a greater combined effect of caffeine plus the task (+15/+11 mmHg) than controls (+10/+6 mmHg). BH men maintained response to the stressor in the face of an exaggerated BP response to caffeine, suggesting that use of caffeine during behavioral stress may elevate BP in BH individuals to a clinically meaningful degree.

Coping with CLIA, Part 10. CLIA '88 penalties and how to avoid them.

If CLIA '67 penalties were lethal, CLIA '88 punishments are merely life-threatening. With careful preparation, however, you can avoid suffering.

Foundations for validation of quantitative analytical methods in the clinical laboratory.

This article explores federal requirements for validation of analytical methods and available resources. We focus on the contributions of the National Committee for Clinical Laboratory Standards to the problems of method validation. Illustrations are selected from the Committee's EP5-T Evaluation of Precision, EP10-T Preliminary Evaluation of Clinical Chemistry Methods, EP11 Uniformity of Claims, and the National Reference System for the Clinical Laboratory. We also include a list of applicable national and international organizations. Calcium assay by atomic absorption spectrometry using an imprecise diluter illustrates the application of the evaluation protocols as a method validation tool.

Linearity and calibration. A clinical laboratory perspective.

This article discusses the relationship of calibration and linearity using the example of glutaraldehyde assayed by high-performance liquid chromatography. Assuming adequate precision and a lack of interference, the relationship of calibration to a method's linear range becomes all important to achieving quality analytical results. Linearity is an objective description of the relationship between a quantitative method's final answer and true analyte concentration. Calibration brings this relationship into correspondence with calibrator concentration. The reportable range is that range within which a specified method produces results within defined allowable error without resorting to dilution of the specimen. The reportable range assumes a linear relationship between true analyte concentration and analytical results.

Coping with CLIA, Part I. How to obtain a CLIA certificate without getting stuck in the details.

Welcome to the sticky world of HCFA's form 109. Prepare it with clinically strict accuracy. Believe it or not, the future of your laboratory depends on how well you fill out this form.

Effects of caffeine on pressor regulation during rest and exercise in men at risk for hypertension.

Caffeine-induced blood pressure elevations are well documented in habitual consumers, occurring through both vasoconstrictive and cardiostimulatory actions. Whether caffeine hinders pressor regulation during exercise has been uncertain, particularly in those at risk for hypertension. Thus effects of caffeine versus placebo were studied during supine bicycle exercise in healthy men (ages 20 to 35). Hypertension risk was defined during screening: high risk (HRISK) = 135 to 154/85 to 94 mm Hg plus parental hypertension (n = 20); low risk (LRISK) = less than or equal to 132/84 mm Hg and no parental hypertension (n = 14). Exaggerated pressor responses (greater than or equal to 230/100 mm Hg) seen during exercise after placebo identified a subgroup of seven HRISKs indistinguishable at rest from the remaining HRISK men. This subgroup showed a larger resting diastolic response to caffeine (p less than 0.05) than LRISKs and other HRISKs. Compared with placebo, caffeine increased the number of LRISK (0% to 36%) and HRISK (35% to 50%) men reaching abnormal exercise blood pressures, and blunted normal increments in cardiac index at higher workloads among HRISK men (p = 0.05). Thus restriction of caffeine before exercise might benefit persons with either risk for hypertension or unusual sensitivity to caffeine.

Hypertension risk and caffeine's effect on cardiovascular activity during mental stress in young men.

Examined the cardiovascular effects of caffeine plus behavioral stress in men low versus high in risk of essential hypertension. Caffeine (3.3 mg/kg, equivalent to 2 to 3 cups of coffee) or placebo was given on alternate days to 19 low-risk men (negative for parental hypertension and low-normal resting blood pressure, BP) and 20 high-risk men (positive history, high-normal BP). Forty minutes later, each worked for 15 min on a demanding psychomotor task during which BP, cardiac output, and vascular resistance were determined. During rest, caffeine raised vascular resistance in both groups. During the task, it supra-additively increased the systolic BP response by enhancing the rise in cardiac output, producing equivalent BP rises in both groups. Due to the higher resting pressures of the high-risk men, caffeine plus the task resulted in 50% of these having transient BP of 140/90 mg Hg or greater. Caffeine in combination with mental stress may produce undesirable BP in those at risk for hypertension.