1. Near‐infrared spectroscopy estimation of combined skeletal muscle oxidative capacity and O2 diffusion capacity in humans
- Author
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Pilotto, Andrea M, Adami, Alessandra, Mazzolari, Raffaele, Brocca, Lorenza, Crea, Emanuela, Zuccarelli, Lucrezia, Pellegrino, Maria A, Bottinelli, Roberto, Grassi, Bruno, Rossiter, Harry B, and Porcelli, Simone
- Subjects
Health Sciences ,Sports Science and Exercise ,Clinical Research ,Humans ,Muscle ,Skeletal ,Oxidative Stress ,Oxygen ,Oxygen Consumption ,Spectroscopy ,Near-Infrared ,biopsy ,capillary density ,mitochondria ,recovery kinetics ,skeletal muscle ,Biological Sciences ,Medical and Health Sciences ,Physiology ,Biological sciences ,Biomedical and clinical sciences ,Health sciences - Abstract
The final steps of the O2 cascade during exercise depend on the product of the microvascular-to-intramyocyte PO2${P}_{{{\rm{O}}}_{\rm{2}}}$ difference and muscle O2 diffusing capacity ( DmO2$D{{\rm{m}}}_{{{\rm{O}}}_2}$ ). Non-invasive methods to determine DmO2$D{{\rm{m}}}_{{{\rm{O}}}_2}$ in humans are currently unavailable. Muscle oxygen uptake (m V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ) recovery rate constant (k), measured by near-infrared spectroscopy (NIRS) using intermittent arterial occlusions, is associated with muscle oxidative capacity in vivo. We reasoned that k would be limited by DmO2$D{{\rm{m}}}_{{{\rm{O}}}_2}$ when muscle oxygenation is low (kLOW ), and hypothesized that: (i) k in well oxygenated muscle (kHIGH ) is associated with maximal O2 flux in fibre bundles; and (ii) ∆k (kHIGH - kLOW ) is associated with capillary density (CD). Vastus lateralis k was measured in 12 participants using NIRS after moderate exercise. The timing and duration of arterial occlusions were manipulated to maintain tissue saturation index within a 10% range either below (LOW) or above (HIGH) half-maximal desaturation, assessed during sustained arterial occlusion. Maximal O2 flux in phosphorylating state was 37.7 ± 10.6 pmol s-1 mg-1 (∼5.8 ml min-1 100 g-1 ). CD ranged 348 to 586 mm-2 . kHIGH was greater than kLOW (3.15 ± 0.45 vs. 1.56 ± 0.79 min-1 , P < 0.001). Maximal O2 flux was correlated with kHIGH (r = 0.80, P = 0.002) but not kLOW (r = -0.10, P = 0.755). Δk ranged -0.26 to -2.55 min-1 , and correlated with CD (r = -0.68, P = 0.015). m V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ k reflects muscle oxidative capacity only in well oxygenated muscle. ∆k, the difference in k between well and poorly oxygenated muscle, was associated with CD, a mediator of DmO2$D{{\rm{m}}}_{{{\rm{O}}}_2}$ . Assessment of muscle k and ∆k using NIRS provides a non-invasive window on muscle oxidative and O2 diffusing capacity. KEY POINTS: We determined post-exercise recovery kinetics of quadriceps muscle oxygen uptake (m V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ) measured by near-infrared spectroscopy (NIRS) in humans under conditions of both non-limiting (HIGH) and limiting (LOW) O2 availability, for comparison with biopsy variables. The m V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ recovery rate constant in HIGH O2 availability was hypothesized to reflect muscle oxidative capacity (kHIGH ) and the difference in k between HIGH and LOW O2 availability (∆k) was hypothesized to reflect muscle O2 diffusing capacity. kHIGH was correlated with phosphorylating oxidative capacity of permeabilized muscle fibre bundles (r = 0.80). ∆k was negatively correlated with capillary density (r = -0.68) of biopsy samples. NIRS provides non-invasive means of assessing both muscle oxidative and oxygen diffusing capacity in vivo.
- Published
- 2022