Cardiovascular fitness is often measured in the laboratory by conducting
exercise stress tests on a treadmill or cycle ergometer. During the process, the
amounts of oxygen utilized and carbon dioxide expired are measured at
predetermined sub-maximal exercise capacities to determine the subjects VO2
max values. In NHANES, trained technicians performed cardiovascular fitness tests.
Measures of heart rate, respiratory rate and blood pressure were used as surrogate
measures for VO2 max. These measurements were taken in series consisting of
about a two minute warm up exercise, then a three minute exercise test performed
twice, and finally a two minute rest period. The goal was to elicit 75% of a
predetermined age-specific heart rate by the end of the stress test. The heart rate
was continuously measured at each stage and the blood pressure was measured at
the end of each stage of the exercise. VO2 max was estimated by substituting these
measures into an accepted derived equation (see Appendix).
Cd was measured in the laboratory by taking urine samples of participants and
then passing them through the process of Inductively Coupled Plasma Mass
Spectrometry (ICP-MS). Because molybdenum tends to interfere with Cd
measurements leading to inaccurate results, Cd values were corrected using
Dynamic Reaction Cell (DRC) Technology to eliminate effects of molybdenum
oxide in samples. Urine samples were analyzed by NHANES-appointed certified
laboratory technicians. More details are available elsewhere (CDC, 2007)