Journal of applied physiology
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Venous compliance is lower in older adults compared with younger adults. It is possible that alterations in venous smooth muscle tone and responsiveness may contribute to the age-related differences in venous compliance. To determine the effects of sympathetic activation [cold pressor test (cold pressor test); rhythmic ischemic handgrip (rhythmic ischemic handgrip)] and endothelium-independent decreases in smooth muscle tone [sublingual nitroglycerin (nitroglycerin)] on venous compliance in young and older adults, forearm and calf venous compliance was measured in 12 young (22 +/- 1 yr) and 12 old (65 +/- 1 yr) supine subjects using venous occlusion plethysmography. ⋯ Venous compliance was not effected by the cold pressor test test, rhythmic ischemic handgrip, or sublingual nitroglycerin in either group. Data suggest that forearm and calf venous compliance is lower in older adults compared with young. However, this difference probably cannot be explained by alterations in smooth muscle tone or responsiveness.
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Studies in experimental animals indicate that chronic increases in neural drive to limb muscles elicit a fast-to-slow transformation of fiber-type proportions and myofibrillar proteins. Since neural drive to the parasternal intercostal muscles (parasternals) is chronically increased in patients with severe chronic obstructive pulmonary diseases (COPDs), we carried out the present study to test the hypothesis that the parasternals of COPD patients exhibit an increase in the proportions of both slow fibers and slow myosin heavy chains (MHCs). Accordingly, we obtained full thickness parasternal muscle biopsies from the third interspace of seven COPD patients (mean +/- SE age: 59 +/- 4 yr) and seven age-matched controls (AMCs). ⋯ We conclude that the parasternal muscles of patients with severe COPD exhibit a fast-to-slow transformation in both fiber-type and MHC proportions. Previous workers have demonstrated that remodeling of the external intercostals, another rib cage inspiratory muscle, elicited by severe COPD is characterized by a slow-to-fast transformation in both fiber types and MHC isoform proportions. The physiological significance of this difference in remodeling between these two inspiratory rib cage muscles remains to be elucidated.