Blood flow and oxygenation in peritendinous tissue and calf muscle during dynamic exercise in humans

Abstract

1. Circulation around tendons may act as a shunt for muscle during exercise. The perfusion and oxygenation of Achilles' peritendinous tissue was measured in parallel with that of calf muscle during exercise to determine (1) whether blood flow is restricted in peritendinous tissue during exercise, and (2) whether blood flow is coupled to oxidative metabolism. 2. Seven individuals performed dynamic plantar flexion from 1 to 9 W. Radial artery and popliteal venous blood were sampled for O2, peritendinous blood flow was determined by 133Xe-washout, calf blood flow by plethysmography, cardiac output by dye dilution, arterial pressure by an arterial catheter-transducer, and muscle and peritendinous O2 saturation by spatially resolved spectroscopy (SRS). 3. Calf blood flow rose 20-fold with exercise, reaching 44 +/- 7 ml (100 g)-1 min-1 (mean +/- s.e.m. ) at 9 W, while Achilles' peritendinous flow increased (7-fold) to 14 +/- 4 ml (100 g)-1 min-1, which was 18 % of the maximal flow established during reactive hyperaemia. SRS-O2 saturation fell both in muscle (from 66 +/- 2 % at rest to 57 +/- 3 %, P < 0.05) and in peritendinous regions (58 +/- 4 to 52 +/- 4 %, P < 0.05) during exercise along with a rise in leg vascular conductance and microvascular haemoglobin volume, despite elevated systemic vascular resistance. 4. The parallel rise in calf muscle and peritendinous blood flow and fall in O2 saturation during exercise indicate that blood flow is coupled to oxidative metabolism in both tissue regions. Increased leg vascular conductance accompanied by elevated microvascular haemoglobin volume reflect vasodilatation in both muscle and peritendinous regions. However, peak exercise peritendinous blood flow reaches only approximately 20 % of its maximal blood flow capacity.

Figure 1

Schematic diagram of the experimental setup for plantar flexion exercise

Figure 6. Schematic diagram of Achilles' peritendinous region

Anatomical schematic diagram of the Achilles' peritendinous region displaying the vascular network and tendon structures, and the location of the near-infrared spectroscopy probes (NIRS) and ¹³³Xe depot.

Figure 2. Blood flow and oxygen uptake during exercise

Blood flow (BF), arterio-venous oxygen difference (a-vO₂ diff), and oxygen uptake (V_O2) in the lower leg, and peritendinous blood flow, at rest and during graded plantar flexion exercise. Values are means and s.e.m. Note that peritendinous blood flow increases along with calf blood flow during exercise.

Figure 3. Systemic and regional haemodynamics during exercise

Cardiac output (CO, ▪) and non-leg blood flow (NLBF,), TPR (▪) and non-leg vascular resistance (NLVR,), MAP, and LVC at rest and during plantar flexion exercise. Asterisks for NLVR indicate difference from the resting level (P < 0.05).

Figure 4. Near-infrared spectroscopy parameters during exercise

Spectroscopically determined oxygenation of calf muscle and Achilles' peritendinous tissue at rest and during exercise. Upper left panel, SRS-O₂ saturation; upper right panel, Hb; lower left panel, HbO₂; lower right panel, THb. ▪, muscle;and, Achilles' peritendinous region. Values are means and s.e.m. Asterisks indicate difference from the resting level (P < 0.05).

Figure 5. Near-infrared response during ischaemia and reperfusion

Near-infrared spectroscopy optical responses at rest, during resting ischaemia, and during reperfusion (n = 3). The top panel shows the O₂ saturation in calf muscle (continuous lines) and peritendinous tissue (dashed lines) determined by SRS. The bottom panel shows the corresponding THb volume.