The Effects of Aging on Microcirculatory Oxygen Delivery (QO 2 ) in Contracting Rat Spinotrapezius Muscle

Advancing age alters both the structural and functional determinants of convective muscle oxygen (O 2 ) 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 O 2 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 (F RBC ) and the lineal density of flowing capillaries (LD) were measured at rest and during contractions. QO 2m was calculated as F RBC x LD. Results: At rest, F RBC 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 QO 2m (Y: 723 ± 153, O: 773 ± 86 cells/s/mm). However, during contractions QO 2m 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 O 2 flux is severely impaired in muscles of older animals.