ABSTRACT

The aim of this treatise is to summarize the current understanding of the mechanisms for blood flow control to skeletal muscle under resting conditions, how perfusion is elevated (exercise hyperemia) to meet the increased demand for oxygen and other substrates during exercise, mechanisms underlying the beneficial effects of regular physical activity on cardiovascular health, the regulation of transcapillary fluid filtration and protein flux across the microvascular exchange vessels, and the role of changes in the skeletal muscle circulation in pathologic states. Skeletal muscle is unique among organs in that its blood flow can change over a remarkably large range. Compared to blood flow at rest, muscle blood flow can increase by more than 20-fold on average during intense exercise, while perfusion of certain individual white muscles or portions of those muscles can increase by as much as 80-fold. This is compared to maximal increases of 4- to 6-fold in the coronary circulation during exercise. These increases in muscle perfusion are required to meet the enormous demands for oxygen and nutrients by the active muscles. Because of its large mass and the fact that skeletal muscles receive 25% of the cardiac output at rest, sympathetically mediated vasoconstriction in vessels supplying this tissue allows central hemodynamic variables (e.g., blood pressure) to be spared during stresses such as hypovolemic shock. Sympathetic vasoconstriction in skeletal muscle in such pathologic conditions also effectively shunts blood flow away from muscles to tissues that are more sensitive to reductions in their blood supply that might otherwise occur. Again, because of its large mass and percentage of cardiac output directed to skeletal muscle, alterations in blood vessel structure and function with chronic disease (e.g., hypertension) contribute significantly to the pathology of such disorders. Alterations in skeletal muscle vascular resistance and/or in the exchange properties of this vascular bed also modify transcapillary fluid filtration and solute movement across the microvascular barrier to influence muscle function and contribute to disease pathology. Finally, it is clear that exercise training induces an adaptive transformation to a protected phenotype in the vasculature supplying skeletal muscle and other tissues to promote overall cardiovascular health.

Contents

• 1. Introduction
• 2. Anatomy of Skeletal Muscle and Its Vascular Supply
  • 2.1 SKELETAL MUSCLE ANATOMY
  • 2.2 VASCULAR ANATOMY IN SKELETAL MUSCLE
  • 2.3 LYMPHATICS IN SKELETAL MUSCLE
• 3. Regulation of Vascular Tone in Skeletal Muscle
  • 3.1 BASAL HEMODYNAMICS
  • 3.2 BASAL VASCULAR TONE
  • 3.3 CONTROL OF VASCULAR SMOOTH MUSCLE (VSM) CONTRACTION
  • 3.4 OPENING POTASSIUM CHANNELS INDUCES VASODILATION IN SKELETAL MUSCLE
  • 3.5 TRANSIENT RECEPTOR POTENTIAL (TRP) CHANNELS ARE CATION GATES THAT MODULATE VASOMOTOR TONE
  • 3.6 ENDOTHELIUM-DEPENDENT MECHANISMS IN THE CONTROL OF VSM CONTRACTION
  • 3.7 INTRINSIC (LOCAL) MECHANISMS REGULATING VASCULAR RESISTANCE
  • 3.8 DIFFERENTIAL CONTROL OF VASOREGULATION ALONG THE ARTERIAL TREE
  • 3.9 LOCAL CONTROL PHENOMENON IN SKELETAL MUSCLE
  • 3.10 PERICYTES AND VASOMOTOR CONTROL IN SKELETAL MUSCLE?
  • 3.11 MECHANICAL EFFECTS OF CONTRACTION—THE MUSCLE PUMP
  • 3.12 EXTRINSIC (REMOTE) CONTROL OF SKELETAL MUSCLE BLOOD FLOW
• 4. Exercise Hyperemia and Regulation of Tissue Oxygenation During Muscular Activity
  • 4.1 CARDIOVASCULAR ADJUSTMENTS TO EXERCISE
  • 4.2 MATCHING OXYGEN AND SUBSTRATE DELIVERY TO MEET THE DEMAND FOR OXYGEN AND NUTRIENTS BY ACTIVE MUSCLES
  • 4.3 SKELETAL MUSCLE FLOW IS PULSATILE DURING RHYTHMIC EXERCISE
  • 4.4 SKELETAL MUSCLE BLOOD FLOW VARIES BY MUSCLE FIBER TYPE COMPOSITION AT REST AND EXERCISE
  • 4.5 POSTEXERCISE HYPOTENSION AFTER PROLONGED EXERCISE
  • 4.6 LOCAL CONTROL MECHANISMS AND THE REGULATION OF SKELETAL MUSCLE BLOOD FLOW DURING EXERCISE
  • 4.7 CENTRAL CONTROL PROCESSES INFLUENCE EXERCISE HYPEREMIA
  • 4.8 CHRONIC EXERCISE TRAINING INDUCES ADAPTIVE CHANGES IN THE SKELETAL MUSCLE CIRCULATION
  • 4.9 REGULATION OF TISSUE OXYGENATION DURING MUSCULAR ACTIVITY
• 5. Microvascular Fluid and Solute Exchange in Skeletal Muscle
  • 5.1 GENERAL PRINCIPLES AND FUNCTIONS OF TRANSCAPILLARY FLUID FILTRATION
  • 5.2 ULTRASTRUCTURAL PATHWAYS
  • 5.3 EFFECT OF SOLUTE CHARGE, SIZE, CONFORMATION AND MICROVASCULAR SURFACE AREA FOR EXCHANGE
  • 5.4 FLUID EXCHANGE ACROSS THE MICROCIRCULATION
  • 5.5 TRANSCAPILLARY FLUID AND SOLUTE EXCHANGE IN SKELETAL MUSCLE DURING EXERCISE
  • 5.6 EDEMA SAFETY FACTORS LIMIT FLUID ACCUMULATION IN SKELETAL MUSCLES DURING EXERCISE
  • 5.7 TRANSENDOTHELIAL FILTRATION MODIFIES ARTERIOLAR, CAPILLARY, AND VENULAR FUNCTION
  • 5.8 FLUID FLOW IN INTERSTITIUM MODIFIES THE FUNCTION OF TISSUE CELLS
• 6. Skeletal Muscle Circulation in Disease States and Aging: Protective Effects of Exercise
  • 6.1 ISCHEMIA/REPERFUSION (I/R) INJURY
  • 6.2 HYPERTENSION, HYPERCHOLESTEROLEMIA, OBESITY, AND DIABETES
  • 6.3 PORTAL VENOUS HYPERTENSION INDUCES SKELETAL MUSCLE HYPEREMIA
  • 6.4 REGULAR PHYSICAL ACTIVITY INDUCES A PROTECTIVE PHENOTYPE IN VASCULAR TISSUES
  • 6.5 SKELETAL MUSCLE BLOOD IN AGING AND THE PROTECTIVE EFFECTS OF EXERCISE
• References
• Author Biography