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Effects of aging on capillary geometry and hemodynamics in rat spinotrapezius muscle

2003; American Physical Society; Volume: 285; Issue: 1 Linguagem: Inglês

10.1152/ajpheart.01086.2002

1522-1539

John A. Russell, Casey A. Kindig, Brad J. Behnke, David C. Poole, Timothy I. Musch,

Heart Rate Variability and Autonomic Control

The effects of aging on muscle microvascular structure and function may play a key role in performance deficits and impairment of O 2 exchange within skeletal muscle of senescent individuals. To determine the effects of aging on capillary geometry, red blood cell (RBC) hemodynamics, and hematocrit in a muscle of mixed fiber type, spinotrapezius muscles from Fischer 344 × Brown Norway hybrid rats aged 6–8 mo [young (Y); body mass 421 ± 10 g, n = 6] and 26–28 mo [old (O); 561 ± 12 g, n = 6] were observed by high-resolution transmission light microscopy under resting conditions. The percentage of RBC-perfused capillaries (Y: 78 ± 3%; O: 75 ± 2%) and degree of tortuosity and branching (Y: 13 ± 2%; O: 13 ± 2%, additional capillary length) were not different in O vs. Y muscles. Lineal density of RBC-perfused capillaries in O was significantly reduced (Y: 30.7 ± 1.8, O: 22.8 ± 3.1 capillaries/mm; P < 0.05). However, RBC-perfused capillaries from O rats ( n = 78) exhibited increased RBC velocity ( V RBC ) (Y: 219 ± 12, O: 310 ± 14 μm/s; P < 0.05) and RBC flux ( F RBC ) (Y: 27 ± 2, O: 41 ± 2 RBC/s; P < 0.05) vs. Y rats ( n = 66). Thus O 2 delivery per unit of muscle was not different between groups (Y: 894 ± 111, O: 887 ± 118 RBC · s -1 · mm muscle -1 ). Capillary hematocrit was not different in Y vs. O rats (Y: 26 ± 1%, O: 28 ± 1%: P > 0.05). These data indicate that in resting spinotrapezius muscle, aging decreases the lineal density of RBC-perfused capillaries while increasing mean V RBC and F RBC within those capillaries. Whereas muscle conductive O 2 delivery and capillary hematocrit were unchanged, elevated V RBC reduces capillary RBC transit time and may impair the diffusive transport of O 2 from blood to myocyte particularly under exercise conditions.