The Effects of Aging on Microcirculatory Oxygen Delivery (QO2) in Contracting Rat Spinotrapezius Muscle

Abstract

Advancing age alters both the structural and functional determinants of convective muscle oxygen (O2) flux. However, capillary red blood cell (RBC) hemodynamics have not been investigated during contractions in muscles of older animals.Purpose:To test the hypothesis that, during muscle contractions, old rats exhibit capillary RBC hemodynamics that constrain convective muscle O2 flux.Methods:The spinotrapezius muscle was observed via intravital microscopy in 8 old (O: 26–30 months) and 5 young (Y: 6–8 months) Fischer 344 x Brown Norway rats. Electrodes elicited 1‐Hz (6–8 volts) contractions for 3 minutes. Capillary RBC flux (FRBC) and the lineal density of flowing capillaries (LD) were measured at rest and during contractions. QO2m was calculated as FRBC x LD.Results:At rest, FRBC was elevated (Y: 23 ± 3, O: 34 ± 3 cells/s, P < 0.05) and LD was reduced (Y: 30 ± 1, O: 24 ± 1 capillaries/mm, P < 0.05) in O compared to Y rats, resulting in a similar QO2m (Y: 723 ± 153, O: 773 ± 86 cells/s/mm). However, during contractions QO2m was reduced in O muscles (Y: 1615 ± 472, O: 781 ± 120 cells/s/mm, P < 0.05). In contrast to Y, during contractions O muscles exhibited stoppage of flow in some capillaries where continuous flow was observed at rest.Conclusion:These data indicate that capillary convective O2 flux is severely impaired in muscles of older animals.