The sensitivity of magnetic resonance imaging to biochemical and biophysical changes in the extracellular matrix of articular cartilage give it the potential to noninvasively detect the earliest changes of cartilage damage. The transverse relaxation time (T2) of cartilage has been shown to be a sensitive parameter for evaluation of early degeneration in articular cartilage, particularly changes in water and collagen content and tissue anisotropy. Although initial application has been in microimaging of small cartilage explants, in vivo techniques have been developed for cartilage T2 mapping of human joints. In addition to potential application in development of new pharmaceuticals and surgical techniques for preserving cartilage, in vivo cartilage T2 mapping can improve understanding of arthritis, cartilage aging, and response of cartilage to exercise.

Aging is associated with an asymptomatic increase in T2 of the transitional zone of articular cartilage. Preliminary results indicate this diffuse increase in T2 in senescent cartilage is different in appearance than the focally increased T2 observed in damaged articular cartilage.

There is a reproducible pattern of increasing T2 that is proportional to the known spatial variation in cartilage water and is inversely proportional to the distribution of proteoglycans. The authors postulate that these regional T2 differences are secondary to the restricted mobility of cartilage water within an anisotropic solid matrix.

Skeletal muscle metaboreceptor responses are impaired in heart failure. Because MSNA responses during static exercise are similar in the two groups, mechanisms aside from metaboreceptor stimulation must be important in increasing sympathetic nervous system activity.