Effect of heart failure on muscle capillary geometry: implications for 02 exchange.

Abstract

There is strong evidence that chronic heart chronic heart failure (CHF) impairs skeletal muscle function independent of blood flow and bulk O2 delivery. This investigation sought to determine whether alterations in muscle capillary geometry and surface area that are thought to be primary determinants of the efficacy for blood-tissue 02 exchange might be altered in CHF and contribute to these changes. Plantaris (fast twitch) and soleus (slow twitch) muscles from control (C) and 6- to 7-wk post myocardial infarcted (CHF) rates were perfusion-fixed in situ. These muscles were analyzed using morphometric techniques that facilitated determination of muscle sarcomere length fiber cross-sectional area, capillary tortuosity and branching coefficient (c(K,0)), capillary length, volume, and surface area. Normalized to a sarcomere length of 2.1 microns, plantaris fiber cross-sectional area decreased by 21% (P < 0.05), and capillary-to-fiber ratio decreased from 2.05 +2- 0.07 in C to 1.79 +2- 0.04 (P < 0.05) in CHF, but these variables were unchanged in soleus. These was no change in c(K,0) or capillary diameter in either muscle, and thus capillary length and surface area per fiber volume remained unchanged. From the measured fiber atrophy and capillary involution in plantaris reductions of total muscle capillary length, volume, and surface area of 11%, 9% and 17%, respectively, are estimated. These changes, coupled with reduced blood flow may impair the effective matching of muscle fiber 02 delivery to 02 requirement during repeated muscle contractions (i.e. exercise). The scenario is expected to reduce intramyocyte 02 partial pressure and thereby contribute to the greater fatigability characteristic of the CHF condition.