Using the lower limit of normal for the FEV1/FVC ratio reduces the misclassification of airway obstruction.

AIM: The prevalence of airway obstruction varies widely with the definition used. OBJECTIVES: To study differences in the prevalence of airway obstruction when applying four international guidelines to three population samples using four regression equations. METHODS: We collected predicted values for forced expiratory volume in 1 s/forced vital capacity (FEV(1)/FVC) and its lower limit of normal (LLN) from the literature. FEV(1)/FVC from 40 646 adults (including 13 136 asymptomatic never smokers) aged 17-90+years were available from American, English and Dutch population based surveys. The prevalence of airway obstruction was determined by the LLN for FEV(1)/FVC, and by using the Global Initiative for Chronic Obstructive Lung Disease (GOLD), American Thoracic Society/European Respiratory Society (ATS/ERS) or British Thoracic Society (BTS) guidelines, initially in the healthy subgroup and then in the entire population. RESULTS: The LLN for FEV(1)/FVC varied between prediction equations (57 available for men and 55 for women), and demonstrated marked negative age dependency. Median age at which the LLN fell below 0.70 in healthy subjects was 42 and 48 years in men and women, respectively. When applying the reference equations (Health Survey for England 1995-1996, National Health and Nutrition Examination Survey (NHANES) III, European Community for Coal and Steel (ECCS)/ERS and a Dutch population study) to the selected population samples, the prevalence of airway obstruction in healthy never smokers aged over 60 years varied for each guideline: 17-45% of men and 7-26% of women for GOLD; 0-18% of men and 0-16% of women for ATS/ERS; and 0-9% of men and 0-11% of women for BTS. GOLD guidelines caused false positive rates of up to 60% when applied to entire populations. CONCLUSIONS: Airway obstruction should be defined by FEV(1)/FVC and FEV(1) being below the LLN using appropriate reference equations.

FEV(6) is an acceptable surrogate for FVC in the spirometric diagnosis of airway obstruction and restriction.

We analyzed the FEV(1)/FEV(6) and FEV(1)/FVC results of 502 consecutive patients in the spirometric diagnosis of airway obstruction. We also examined the agreement between FEV(6) and FVC in the spirometric diagnosis of restriction. Technically acceptable test results were obtained from 337 subjects (67%). The sensitivity of FEV(1)/FEV(6) for diagnosing airway obstruction as defined by FEV(1)/ FVC was 95.0%; the specificity was 97.4%. When interpretations differed, the measured values were all close to the lower limits of the reference ranges. When analysis included +/- 100-ml variability in FEV(1) and FEV(6), the sensitivity increased to 99.5% and the specificity to 100%. The reproducibility of FEV(6) was superior to that of FVC. These results suggest that FEV(6) is an accurate, reliable alternative to FVC for diagnosing airway obstruction and that FEV(6) is reasonably comparable to FVC for the spirometric diagnosis of restriction. FEV(6) is more reproducible and less physically demanding for patients.

Prolonged exercise increases peripheral plasma ACTH, CRH, and AVP in male athletes.

We wished to determine whether the increased ACTH during prolonged exercise was associated with changes in peripheral corticotropin-releasing hormone (CRH) and/or arginine vasopressin (AVP). Six male triathletes were studied during exercise: 1 h at 70% maximal oxygen consumption, followed by progressively increasing work rates until exhaustion. Data obtained during the exercise session were compared with a nonexercise control session. Venous blood was sampled over a 2-h period for cortisol, ACTH, CRH, AVP, renin, glucose, and plasma osmolality. There were significant increases by ANOVA on log-transformed data in plasma cortisol (P = 0.002), ACTH (P < 0.001), CRH (P < 0.001), and AVP (P < 0.03) during exercise compared with the control day. A variable increase in AVP was observed after the period of high-intensity exercise. Plasma osmolality rose with exercise (P < 0.001) and was related to plasma AVP during submaximal exercise (P < 0.03) but not with the inclusion of data that followed the high-intensity exercise. This indicated an additional stimulus to the secretion of AVP. The mechanism by which ACTH secretion occurs during exercise involves both CRH and AVP. We hypothesize that high-intensity exercise favors AVP release and that prolonged duration favors CRH release.

The effect of glycerol and desmopressin on exercise performance and hydration in triathletes.

BACKGROUND: Hydration is an important determinant of athletic performance, and glycerol-containing solutions have been demonstrated to produce a state of hyperhydration. Secretions of arginine vasopressin (AVP) and/or other renal mechanisms may account for reduced urine output following glycerol ingestion. This study examined the effect of glycerol and the AVP analog desmopressin (DDAVP) on hydration and exercise performance in triathletes ingesting routine volumes of prerace fluids. METHODS: Eight male triathletes ages 19 to 43 participated. After determination of their VO(2peak), each athlete completed a strenuous exercise protocol three times involving 60 min of exercise at 70% VO(2peak) followed immediately by an incremental increase in workload every 2 min until exhaustion. RESULTS: Pretreatment with 1 gxkg(-1) glycerol or 20 microgram of DDAVP intranasally failed to produce hyperhydration or any enhancement of athletic performance. There was a significant difference in reduction in body mass between DDAVP and control (P < 0.05) but no change in sweat volume. No physiologically relevant differences in plasma sodium, renin, or hemoglobin were seen with either active agent. Plasma osmolality did have a different time course in response to exercise following glycerol (P < 0.03) owing to a smaller incremental increase. Urine osmolality was also raised at baseline following glycerol (P < 0.05). Responses to exercise of plasma AVP, cortisol, and indices of carbohydrate metabolism were similar, although AVP was elevated following DDAVP administration (P < 0.01) owing to assay cross-reactivity. CONCLUSION: Although maintaining adequate hydration remains important for the endurance athlete, the routine use of either glycerol of DDAVP before athletic training or competition in a thermoneutral environment does not seem to confer any advantage over conventional fluid replacement.