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Impact of aging on muscle blood flow in chronic heart failure

Clarenburg Research Laboratory, Departments of Kinesiology, Anatomy and Physiology, Kansas State University, Manhattan, Kansas

Submitted 18 August 2004 ; accepted in final form 26 March 2005

Chronic heart failure (CHF) is manifested principally in the elderly population. Therefore, to understand the causes of exercise intolerance in CHF patients, it is imperative to resolve the effects of aging on muscle blood flow (BF) in CHF. To address this issue, we determined the muscle BF response to submaximal treadmill exercise (20 m/min, 5% grade) in young (Y_CHF: 6–8 mo, 412 ± 11 g, n = 11) and old (O_CHF: 27–29 mo, 494 ± 10 g, n = 8) Fischer 344 x Brown Norway rats with similar degrees of myocardial infarction-induced left ventricular (LV) dysfunction [resting LV end-diastolic pressure: Y_CHF = 24 ± 2, O_CHF = 22 ± 2 mmHg; derivative of LV pressure over time: Y_CHF = 5,168 ± 285; O_CHF = 5,050 ± 165 mmHg/s; lung weight normalized to body weight: Y_CHF = 9.14 ± 0.72; O_CHF = 8.21 ± 0.29 mg/g (all P > 0.05)]. The exercising heart rate response was blunted in O_CHF compared with Y_CHF rats (Y_CHF = 454 ± 8, O_CHF = 395 ± 9 beats/min; P < 0.05). BF (radiolabeled microspheres) to the total hindlimb musculature and to each of the 28 individual muscles examined was similar between Y_CHF and O_CHF rats under resting conditions. During exercise, BF to five of the hindlimb muscles that normally possess a majority of slow-twitch oxidative and fast-twitch oxidative glycolytic muscle fibers increased significantly less (–25 to –42%) for O_CHF compared with Y_CHF rats. In contrast, BF to 14 of the hindlimb muscles that normally possess a majority of fast-twitch glycolytic muscle fibers was increased (+22 to +337%) for O_CHF vs. Y_CHF rats, which contributed to a greater mass-specific total hindlimb BF response in O_CHF rats (Y_CHF = 78 ± 5, O_CHF = 100 ± 11 ml·min^–1·100 g^–1; P < 0.05) and coincided with greater reductions in BF to the kidneys and splanchnic organs during exercise in O_CHF vs. Y_CHF. In conclusion, there appears to be a profound age-related redistribution of BF from the highly oxidative to the highly glycolytic muscles of the hindlimb during exercise in O_CHF compared with Y_CHF rats. This phenomenon is qualitatively similar to that reported previously for healthy young and old rats.

myocardial infarction; exercise; fiber type; left ventricular dysfunction; exercise hyperemia