Year: 2008
Type: article
Abstract: Advancing age is accompanied by reductions in VO2 max and impaired muscle function. Despite disturbances in the central regulation of cardiac output, it is likely that peripheral mechanisms constitute an important role in reducing blood-muscle oxygen (O2) flux during exercise. Specifically, muscle capillary red blood cell (RBC) hemodynamics constitute a principal determinant of O2 extraction during exercise. Despite maintenance of microcirculatory O2 delivery at rest, it is not currently known if aging alters the RBC hemodynamics during muscular contractions. PURPOSE: To test the hypothesis that, compared to their younger counterparts, old rats exhibit significant alterations of muscle capillary hemodynamics during electrically-stimulated contractions. METHODS: Surgical exposure and exteriorization of the left spinotrapezius muscle was performed on 8 old (O: 26-30 month-old) and 5 young (Y: 6-8 month-old) Fischer 344 x Brown Norway rats. The ventral aspect of the muscle was visualized via intravital microscopy (x1180 magnification). Wire electrodes elicited 1-Hz (6-8 volts) contractions for 3 minutes. Data was recorded future analysis. Using frame-byframe playback techniques, capillary RBC flux (FRBC), velocity (VRBC), and hematocrit (HCAP) were measured at rest and during the steady-state of contractions. Comparisons between Y and O were made by Student's t-test (P ≤ 0.05). RESULTS: At rest, FRBC (Y: 22.6 ± 3.2, O: 34.1 ± 3.2 cells/s) and VRBC (Y: 272.8 ± 28.2, O: 408.2 ± 55.9 μ/s) were elevated (P < 0.05) in O compared to Y rats, while there was no difference in HCAP (Y: 0.225 ± 0.014, O: 0.206 ± 0.029 cells/μ) between groups. From rest to the contracting steady-state, ΔFRBC (Y: 28.8 ±7.7, O: −1.6 ± 1.9 cells/s), ΔVRBC (Y: 252.5 ± 68, O: −11.5 ± 16.8 μ/s) and ΔHCAP (Y: 0.024 ± 0.022, O: −0.028 ± 0.013 cells/μ) were all lower (P< 0.05) in O compared to Y rats. CONCLUSION: These results support the surprising conclusion that it is possible to actively contract this aged skeletal muscle without increasing in FRBC, VRBC, and HCAP within the microcirculation. This suggests the presence of age-related changes in both the mechanical (muscle pump) and vasoregulatory determinants of capillary RBC hemodynamics. Supported by: AHA Heartland Affiliate Grants-in-Aid to DCP and TIM
Institution: Kansas State University
Language: English
Subfield: Complementary and alternative medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2032720239