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Aging is associated with a significant decline in aerobic capacity assessed by maximal exercise oxygen consumption (V̇ o 2max). The relative contributions of the specific V̇ o 2 components driving this decline, namely cardiac output (CO) and arteriovenous oxygen difference (A − V)O2, remain unclear. We examined this issue by analyzing data from 99 community-dwelling participants (baseline age: 21–96 yr old; average follow-up: 12.6 yr old) from the Baltimore Longitudinal Study of Aging, free of clinical cardiovascular disease. V̇ o 2peak, a surrogate of V̇ o 2max, was used to assess aerobic capacity during upright cycle ergometry. Peak exercise left ventricular volumes, heart rate, and CO were estimated using repeated gated cardiac blood pool scans. The Fick equation was used to calculate (A − V)O2diff,peak from COpeak and V̇ o 2peak. In unadjusted models, V̇ o 2peak, (A − V)O2diff,peak, and COpeak declined longitudinally over time at steady rates with advancing age. In multiple linear regression models adjusting for baseline values and peak workload, however, steeper declines in V̇ o 2peak and (A − V)O2diff,peak were observed with advanced entry age but not in COpeak. The association between the declines in V̇ o 2peak and (A − V)O2diff,peak was stronger among those ≥50 yr old compared with their younger counterparts, but the difference between the two age groups did not reach statistical significance. These findings suggest that age-associated impairment of peripheral oxygen utilization during maximal exercise poses a stronger limitation on peak V̇ o 2 than that of CO. Future studies examining interventions targeting the structure and function of peripheral muscles and their vasculature to mitigate age-associated declines in (A − V)O2diff are warranted. NEW & NOTEWORTHY: The age-associated decline in aerobic exercise performance over an average of 13 yr in community-dwelling healthy individuals is more closely associated with decreased peripheral oxygen utilization rather than decreased cardiac output. This association was more evident in older than younger individuals. These findings suggest that future studies with larger samples examine whether these associations vary across the age range and whether the decline in cardiac output plays a greater role earlier in life. In addition, studies focused on determinants of peripheral oxygen uptake by exercising muscle may guide the selection of preventive strategies designed to maintain physical fitness with advancing age. [ABSTRACT FROM AUTHOR]

A single early prostate-specific antigen (PSA) level has been correlated with a higher likelihood of prostate cancer diagnosis and death in younger men. PSA testing in older men has been considered of limited utility. We evaluated prostate cancer death in relation to age and PSA level immediately prior to prostate cancer diagnosis. Using the Veterans Affairs database, we identified 230,081 men aged 50-89 years diagnosed with prostate cancer and at least one prior PSA test between 1999 and 2009. Prostate cancer-specific death over time was calculated for patients stratified by age group (e.g., 50-59 years, through 80-89 years) and PSA range at diagnosis (10 ranges) using Kaplan-Meier methods. Risk of 10-year prostate cancer mortality across age and PSA was compared using log-rank tests with a Bonferroni adjustment for multiple testing. 10.5% of men diagnosed with prostate cancer died of cancer during the 10-year study period (mean follow-up = 3.7 years). Higher PSA values prior to diagnosis predict a higher risk of death in all age groups (p

In the early 1990s, the National Science Foundation funded many research projects for improving statistical education. Many of these stressed the need for classroom activities that illustrate important issues of designing experiments, generating quality data, fitting models, and performing statistical tests. Our paper describes such an activity on logistic regression that is useful in second applied statistics courses. The activity involves students attempting to toss a ball into a trash can from various distances. The outcome is whether or not students are successful in tossing the ball into the trash can. This activity and the adjoining homework assignments illustrate the binary nature of a response variable, fitting and interpreting simple and multiple logistic regression models, and the use of odds and odds ratios. (Contains 2 tables and 5 figures.)

Least squares regression is the most common method of fitting a straight line to a set of bivariate data. Another less known method that is available on Texas Instruments graphing calculators is median-median regression. This method is proposed as a simple method that may be used with middle and high school students to motivate the idea of fitting a straight line to data. The median-median line may also be viewed as a method that is not greatly affected by outliers (robust to outliers). Our paper briefly reviews the median-median regression method, considers various examples to compare the median-median line to the least squares line, and investigates the properties of the median-median line versus the least squares line using a simulation study. (Contains 8 figures and 6 tables.)

Objective. To determine the predictors of incidence of metabolic syndrome (MetS) (Adult Treatment Panel III criteria) and to determine if longitudinal changes in specific MetS components differ by age or gender in participants who developed versus those who did not develop MetS. Methods. A total of 506 men and 461 women (baseline age 52.4 [+ or -] 17.5 years) from the Baltimore Longitudinal Study on Aging (BLSA) were followed longitudinally (ar least two study visits), and censored when they developed the MetS or reported use of antihypertensive or lipid-lowering medications. Results. After a follow-up period of 6 years, the incidence of the MetS was 25.5% in men and 14.8% in women. As many as 66% of men and 73% of women with one or two altered MetS components at baseline did not develop the MetS. Predictors of developing MetS were higher baseline abdominal obesity or triglycerides and lower high-density lipoprotein cholesterol (area under receiver-operated curve [AUC] = 0.84 in men. 0.88 in women). Addition of the rate of changes in MetS components over time slightly improved predictive accuracy (AUC = 0.94 in men, 0.92 in women). Men were more likely than women to have the MetS without obesity, whereas women were more likely than men to have the MetS without an altered glucose metabolism. Conclusions. The patterns of MetS components and the longitudinal changes that lead to the MetS are different in men and women. Interestingly, components with the highest prevalence prior to MetS development, such as elevated blood pressure, are not necessarily the stronger risk factors. Key Words: Metabolic syndrome--Incidence--Longitudinal studies--Abdominal obesity.

Background. This article examines how different parameterizations of age and time in modeling observational longitudinal data can affect results. Methods. When individuals of different ages at study entry are considered, it becomes necessary to distinguish between longitudinal and cross-sectional differences to overcome possible selection biases. Results. Various models were fitted using data from longitudinal studies with participants with different ages and different follow-up lengths. Decomposing age into two components--age at entry into the study (first age) and the longitudinal follow-up (time) compared with considering age alone--leads to different conclusions. Conclusions. In general, models using both first age and time terms performed better, and these terms are usually necessary to correctly analyze longitudinal data. Key Words: Mixed-effects models--Multilevel modeling--Observational study--Recruitment bias--Regression.

Factors that mediate increases in salt sensitivity of blood pressure with age remain to be clarified. The present study investigated 1) the effects of high-NaCl intake on two Na pump inhibitors, endogenous ouabain (EO) and marinobufagenin (MBG), in middle-aged and older normotensive Caucasian women; and 2) whether individual differences in EO and MBG are linked to variations in sodium excretion or salt sensitivity. A change from 6 days of a lower (0.7 mmol*[kg.sup.-1]*[day.sup.-1])- to 6 days of a higher (4 mmol*[kg.sup.-1]*[day.sup.-1])-NaCl diet elicited a sustained increase in MBG excretion that directly correlated with an increase in the fractional Na excretion and was inversely related to age and to an age-dependent increase in salt sensitivity. In contrast, EO excretion increased only transiently in response to NaCl loading and did not vary with age or correlate with fractional Na excretion or salt sensitivity. A positive correlation of both plasma and urine levels of EO and MBG during salt loading may indicate a casual link between two Na pump inhibitors in response to NaCl loading, as observed in animal models. A linear mixed-effects model demonstrated that age, dietary NaCl, renal MBG excretion, and body mass index were each independently associated with systolic blood pressure. Thus, a sustained increase in MBG in response to acutely elevated dietary NaCl is inversely linked to salt sensitivity in normotensive middle-aged and older women, and a relative failure of MBG elaboration by these older persons may be involved in the increased salt sensitivity with advancing age. marinobufagenin; ouabain; hypertension