March 21, 2013Open Access
Systemic and vastus lateralis muscle blood flow and O2 extraction during ramp incremental cycle exercise
Key Result
Ramp incremental cycling exercise resulted in a linear increase in systemic blood flow with oxygen uptake, whereas active muscle microvascular blood flow displayed a nonlinear, inverted sigmoidal response.
Study Design
Type
Cross-Sectional (n=20)
Multicenter
No
Structured PICO
P
Population
20 healthy, recreationally active young adults (10 men, 10 women) who performed maximal incremental cycling tests to evaluate systemic and microvascular blood flow.
E
Exposure
Two maximal incremental cycling tests on separate days
O
Outcome
Systemic cardiac output (Q), pulmonary O2 uptake (Vo2p), systemic arterio-venous O2 difference, and near-infrared spectroscopy-derived muscle deoxygenation (Δ[HHb])surrogate
Systemic blood flow and O2 delivery do not reflect the profile of blood flow changes at the level of the active muscle microvasculature during incremental exercise.
Limitations
- Use of the NIRS-derived Δ[HHb] signal as a measure of O2 extraction as a replacement for a-vO2diff in the Fick equation to derive an estimate of QVL.
- The number of subjects composing the overall response was progressively reduced as exercise intensity increased.
- Evaluating only the vastus lateralis muscle does not provide a complete picture of the skeletal muscle blood flow response to exercise.
Abstract
During ramp incremental cycling exercise increases in pulmonary O2 uptake (Vo2p) are matched by a linear increase in systemic cardiac output (Q). However, it has been suggested that blood flow in the active muscle microvasculature does not display similar linearity in blood flow relative to metabolic demand. This study simultaneously examined both systemic and regional (microvascular) blood flow and O2 extraction during incremental cycling exercise. Ten young men (Vo2 peak = 4.2 ± 0.5 l/min) and 10 young women (Vo2 peak = 3.2 ± 0.5 l/min) were recruited to perform two maximal incremental cycling tests on separate days. The acetylene open-circuit technique and mass spectrometry and volume turbine were used to measure Q (every minute) and breath-by-breath Vo2p, respectively; systemic arterio-venous O2 difference (a-vO2diff) was calculated as Vo2p/Q on a minute-by-minute basis. Changes in near-infrared spectroscopy-derived muscle deoxygenation (ΔHHb) were used (in combination with Vo2p data) to estimate the profiles of peripheral O2 extraction and blood flow of the active muscle microvasculature. The systemic Q-to-Vo2p relationship was linear (~5.8 l/min increase in Q for a 1 l/min increase in Vo2p) with a-vO2diff displaying a hyperbolic response as exercise intensity increased toward Vo2 peak. The peripheral blood flow response profile was described by an inverted sigmoid curve, indicating nonlinear responses relative to metabolic demand. The ΔHHb profile increased linearly with absolute Vo2p until high-intensity exercise, thereafter displaying a "near-plateau". Results indicate that systemic blood flow and thus O2 delivery does not reflect the profile of blood flow changes at the level of the microvasculature.