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      Oxygenation Threshold Derived from Near-Infrared Spectroscopy: Reliability and Its Relationship with the First Ventilatory Threshold

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          Abstract

          Background

          Near-infrared spectroscopy (NIRS) measurements of oxygenation reflect O 2 delivery and utilization in exercising muscle and may improve detection of a critical exercise threshold.

          Purpose

          First, to detect an oxygenation breakpoint (Δ[O 2HbMb-HHbMb]-BP) and compare this breakpoint to ventilatory thresholds during a maximal incremental test across sexes and training status. Second, to assess reproducibility of NIRS signals and exercise thresholds and investigate confounding effects of adipose tissue thickness on NIRS measurements.

          Methods

          Forty subjects (10 trained male cyclists, 10 trained female cyclists, 11 endurance trained males and 9 recreationally trained males) performed maximal incremental cycling exercise to determine Δ[O 2HbMb-HHbMb]-BP and ventilatory thresholds (VT1 and VT2). Muscle haemoglobin and myoglobin O 2 oxygenation ([HHbMb], [O 2HbMb], SmO 2) was determined in m. vastus lateralis. Δ[O 2HbMb-HHbMb]-BP was determined by double linear regression. Trained cyclists performed the maximal incremental test twice to assess reproducibility. Adipose tissue thickness (ATT) was determined by skinfold measurements.

          Results

          Δ[O 2HbMb-HHbMb]-BP was not different from VT1, but only moderately related (r = 0.58–0.63, p<0.001). VT1 was different across sexes and training status, whereas Δ[O 2HbMb-HHbMb]-BP differed only across sexes. Reproducibility was high for SmO 2 (ICC = 0.69–0.97), Δ[O 2HbMb-HHbMb]-BP (ICC = 0.80–0.88) and ventilatory thresholds (ICC = 0.96–0.99). SmO 2 at peak exercise and at occlusion were strongly related to adipose tissue thickness (r 2 = 0.81, p<0.001; r 2 = 0.79, p<0.001). Moreover, ATT was related to asymmetric changes in Δ[HHbMb] and Δ[O 2HbMb] during incremental exercise (r = -0.64, p<0.001) and during occlusion (r = -0.50, p<0.05).

          Conclusion

          Although the oxygenation threshold is reproducible and potentially a suitable exercise threshold, VT1 discriminates better across sexes and training status during maximal stepwise incremental exercise. Continuous-wave NIRS measurements are reproducible, but strongly affected by adipose tissue thickness.

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          Most cited references28

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          Effects of aging, sex, and physical training on cardiovascular responses to exercise.

          John Holloszy, Tara G. Martin, Kenneth Schechtman … (1992)
          The relative contributions of decreases in maximal heart rate, stroke volume, and oxygen extraction and of changes in body weight and composition to the age-related decline in maximal oxygen uptake (VO2max) are unclear and may be influenced by sex and level of physical activity. To investigate mechanisms by which aging, sex, and physical activity influence VO2max, we quantified VO2, cardiac output, and heart rate during submaximal and maximal treadmill exercise and assessed weight and fat-free mass in healthy younger and older sedentary and endurance exercise-trained men and women. For results expressed in milliliters per kilogram per minute, a three-to-four-decade greater age was associated with a 40-41% lower VO2max in sedentary subjects and a 25-32% lower VO2max in trained individuals (p less than 0.001). A smaller stroke volume accounted for nearly 50% of these age-related differences, and the remainder was explained by a lower maximal heart rate and reduced oxygen extraction (all p less than 0.001). Age-related effects on maximal heart rate and oxygen extraction were attenuated in trained subjects (p less than 0.05). After normalization of VO2max and maximal cardiac output to fat-free mass, age- and training-related differences were reduced by 24-47% but remained significant (p less than 0.05). For trained but not sedentary subjects, maximal cardiac output and stroke volume normalized to fat-free mass were greater in men than in women (p less than 0.05). A lower stroke volume, heart rate, and arteriovenous oxygen difference at maximal exercise all contribute to the age-related decline in VO2max. Effects of age and training on VO2max, maximal cardiac output, and stroke volume cannot be fully explained by differences in body composition. In sedentary subjects, however, the sex difference in maximal cardiac output and stroke volume can be accounted for by the greater percentage of body fat in women than in men.
          Article 0 comments Cited 130 times – based on 0 reviews     Review now
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            Myoglobin O2 desaturation during exercise. Evidence of limited O2 transport.

            Jason R. Richardson, Elizabeth A. Noyszewski, K Kendrick … (1995)
            The assumption that cellular oxygen pressure (PO2) is close to zero in maximally exercising muscle is essential for the hypothesis that O2 transport between blood and mitochondria has a finite conductance that determines maximum O2 consumption. The unique combination of isolated human quadriceps exercise, direct measures of arterial, femoral venous PO2, and 1H nuclear magnetic resonance spectroscopy to detect myoglobin desaturation enabled this assumption to be tested in six trained men while breathing room air (normoxic, N) and 12% O2 (hypoxic, H). Within 20 s of exercise onset partial myoglobin desaturation was evident even at 50% of maximum O2 consumption, was significantly greater in H than N, and was then constant at an average of 51 +/- 3% (N) and 60 +/- 3% (H) throughout the incremental exercise protocol to maximum work rate. Assuming a myoglobin PO2 where 50% of myoglobin binding sites are bound with O2 of 3.2 mmHg, myoglobin-associated PO2 averaged 3.1 +/- .3 (N) and 2.1 +/- .2 mmHg (H). At maximal exercise, measurements of arterial PO2 (115 +/- 4 [N] and 46 +/- 1 mmHg [H]) and femoral venous PO2 (22 +/- 1.6 [N] and 17 +/- 1.3 mmHg [H]) resulted in calculated mean capillary PO2 values of 38 +/- 2 (N) and 30 +/- 2 mmHg(H). Thus, for the first time, large differences in PO2 between blood and intracellular tissue have been demonstrated in intact normal human muscle and are found over a wide range of exercise intensities. These data are consistent with an O2 diffusion limitation across the 1-5-microns path-length from red cell to the sarcolemma that plays a role in determining maximal muscle O2 uptake in normal humans.
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              Validation of near-infrared spectroscopy in humans.

              Hongling Li, Jonathan J. Wilson, D Mancini … (1994)
              Near-infrared (NIR) spectroscopy is a noninvasive technique that uses the differential absorption properties of hemoglobin to evaluate skeletal muscle oxygenation. Oxygenated and deoxygenated hemoglobin absorb light equally at 800 nm, whereas at 760 nm absorption is primarily from deoxygenated hemoglobin. Therefore, monitoring these two wavelengths provides an index of deoxygenation. To investigate whether venous oxygen saturation and absorption between 760 and 800 nm (760-800 nm absorption) are correlated, both were measured during forearm exercise. Significant correlations were observed in all subjects (r = 0.92 +/- 0.07; P < 0.05). The contribution of skin flow to the changes in 760-800 nm absorption was investigated by simultaneous measurement of skin flow by laser flow Doppler and NIR recordings during hot water immersion. Changes in skin flow but not 760-800 nm absorption were noted. Intra-arterial infusions of nitroprusside and norepinephrine were performed to study the effect of alteration of muscle perfusion on 760-800 nm absorption. Limb flow was measured with venous plethysmography. Percent oxygenation increased with nitroprusside and decreased with norepinephrine. Finally, the contribution of myoglobin to the 760-800 nm absorption was assessed by using 1H-magnetic resonance spectroscopy. At peak exercise, percent NIR deoxygenation during exercise was 80 +/- 7%, but only one subject exhibited a small deoxygenated myoglobin signal. In conclusion, 760-800 nm absorption is 1) closely correlated with venous oxygen saturation, 2) minimally affected by skin blood flow, 3) altered by changes in limb perfusion, and 4) primarily derived from deoxygenated hemoglobin and not myoglobin.
              Article 0 comments Cited 93 times – based on 0 reviews     Review now
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                Author and article information

                Contributors
                Gordon Fisher: Role: Editor
                Journal
                Journal ID (nlm-ta): PLoS One
                Journal ID (iso-abbrev): PLoS ONE
                Journal ID (publisher-id): plos
                Journal ID (pmc): plosone
                Title: PLoS ONE
                Publisher: Public Library of Science (San Francisco, CA USA )
                ISSN (Electronic): 1932-6203
                Publication date (Electronic): 15 September 2016
                Publication date Collection: 2016
                Volume: 11
                Issue: 9
                Electronic Location Identifier: e0162914
                Affiliations
                [1 ]Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands
                [2 ]Department of Physiology, VU Medical Center, Amsterdam, the Netherlands
                [3 ]Faculty of Sports and Nutrition, Amsterdam University of Applied Sciences, Amsterdam, the Netherlands
                University of Alabama at Birmingham, UNITED STATES
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                • Conceptualization: SvdZ RTJ MJH KL DAN AdH JJdK WvdL CJdR.

                • Data curation: SvdZ IJB CA JMV AdU CJdR.

                • Formal analysis: SvdZ IJB CA JMV AdU CJdR.

                • Funding acquisition: RTJ MJH DAN AdH JJdK WvdL CJdR.

                • Investigation: SvdZ IJB CA JMV AdU CJdR.

                • Methodology: SvdZ IJB CA JMV AdU RTJ MJH KL DAN AdH JJdK WvdL CJdR.

                • Project administration: SvdZ RTJ AdH JJdK CJdR.

                • Resources: SvdZ IJB CA JMV AdU CJdR.

                • Software: SvdZ, MJH CJdR.

                • Supervision: RTJ AdH JJdK CJdR.

                • Validation: SvdZ IJB CA JMV AdU CJdR.

                • Visualization: SvdZ.

                • Writing – original draft: SvdZ CJdR.

                • Writing – review & editing: SvdZ RTJ IJB CA JMV AdU MJH KL DAN AdH JJdK WvdL CJdR.

                Author information
                http://orcid.org/0000-0002-8296-828X
                Article
                Publisher ID: PONE-D-16-04742
                DOI: 10.1371/journal.pone.0162914
                PMC ID: 5025121
                PubMed ID: 27631607
                SO-VID: 90b91ac7-5945-4ec7-87eb-c57248b0c515
                Copyright © © 2016 van der Zwaard et al
                License:

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                Date received : 2 February 2016
                Date accepted : 30 August 2016
                Page count
                Figures: 3, Tables: 3, Pages: 16
                Funding
                Funded by: Stichting voor de Technische Wetenschappen (NL)
                Award ID: 12891
                Award Recipient :
                This work was supported by Technologiestichting STW (NL). Award number: 12891. Recipient: JJdK. URL: http://stw.nl/nl/projecten. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Subject: Research Article
                Subject: Research and Analysis Methods
                Subject: Spectrum Analysis Techniques
                Subject: Infrared Spectroscopy
                Subject: near-Infrared Spectroscopy
                Subject: Biology and Life Sciences
                Subject: Anatomy
                Subject: Biological Tissue
                Subject: Adipose Tissue
                Subject: Medicine and Health Sciences
                Subject: Anatomy
                Subject: Biological Tissue
                Subject: Adipose Tissue
                Subject: Physical Sciences
                Subject: Chemistry
                Subject: Chemical Elements
                Subject: Oxygen
                Subject: Research and Analysis Methods
                Subject: Bioassays and Physiological Analysis
                Subject: Muscle Analysis
                Subject: Medicine and Health Sciences
                Subject: Public and Occupational Health
                Subject: Physical Activity
                Subject: Physical Fitness
                Subject: Exercise
                Subject: Medicine and Health Sciences
                Subject: Sports and Exercise Medicine
                Subject: Exercise
                Subject: Biology and Life Sciences
                Subject: Sports Science
                Subject: Sports and Exercise Medicine
                Subject: Exercise
                Subject: Physical Sciences
                Subject: Physics
                Subject: Electromagnetic Radiation
                Subject: Light
                Subject: Light Scattering
                Subject: Physical Sciences
                Subject: Physics
                Subject: Scattering
                Subject: Light Scattering
                Subject: Research and Analysis Methods
                Subject: Mathematical and Statistical Techniques
                Subject: Statistical Methods
                Subject: Regression Analysis
                Subject: Linear Regression Analysis
                Subject: Physical Sciences
                Subject: Mathematics
                Subject: Statistics (Mathematics)
                Subject: Statistical Methods
                Subject: Regression Analysis
                Subject: Linear Regression Analysis
                Subject: Research and Analysis Methods
                Subject: Research Assessment
                Subject: Reproducibility
                Custom metadata
                Data Availability All relevant data are within the paper and its Supporting Information files.

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