In health and in a normoxic environment, V o 2 max is/is not limited primarily by cardiac output and locomotor muscle blood flow

POINT-COUNTERPOINT COMMENTSIn health and in a normoxic environment, V̇o2 max is/is not limited primarily by cardiac output and locomotor muscle blood flowPhilippe Connes, Ozlem Yalcin, Oguz Baskurt, Jean-Frédéric Brun, and Max HardemanPhilippe Connes, Ozlem Yalcin, Oguz Baskurt, Jean-Frédéric Brun, and Max HardemanPublished Online:01 Jun 2006https://doi.org/10.1152/japplphysiol.00279.2006MoreSectionsPDF (30 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations The following letter is in response to the Point:Counterpoint series “In health and in a normoxic environment, V̇o2max is/is not limited primarily by cardiac output and locomotor muscle blood flow” that appeared in the February issue (vol 100: 744–748, 2006, http://jap.physiology.org/content/vol100/issue2).To the Editor:Among the factors that potentially limit V̇o2 max, hemorheological factors are often neglected by exercise physiologists. However, V̇o2 max and blood viscosity factors are strongly correlated (2), but in a complicated way. At high hematocrit, there is increased oxygen binding capacity; however, the simultaneous increase in blood viscosity may limit the transport capacity. These counteracting effects result in an optimal hematocrit value for maximal oxygen availability to tissues (4). Because the viscosity of blood is shear rate dependent, the optimal hematocrit may differ under different circumstances, e.g., rest, exercise, but also in different parts of the circulation. Blood rheological properties are thus able to influence the cascade of oxygen from lungs to exercising muscles.Impairment in red blood cell (RBC) deformability can alter the diffusing capacity for oxygen from lungs to blood capillaries that may participate to the occurrence of exercise-induced hypoxemia, which may limit V̇o2 max (3). In the heart, any increase in blood viscosity raises peripheral vascular resistance, which may cause a decrease in maximal stroke volume and, therefore, a decrease in V̇o2 max. In muscular microcirculation, enhanced RBC aggregation causes depressed eNOS activity, resulting in deteriorated NO-mediated relaxation of arterioles (1). This effect of RBC aggregation is explained by the enhanced axial migration of blood cellular elements, reducing the frictional forces affecting on the endothelial cells and downregulating NO synthesis mechanisms.Although the debate concerning the factors limiting V̇o2 max is far from being closed (5), central mechanisms seem to play an important role, with hemorheology being among the key factors.REFERENCES1 Baskurt OK, Yalcin O, Ozdem S, Armstrong JK, and Meiselman HJ. Modulation of endothelial nitric oxide synthase expression by red blood cell aggregation. Am J Physiol Heart Circ Physiol 286: H222–H229, 2004.Link | ISI | Google Scholar2 Brun JF, Khaled S, Raynaud E, Bouix D, Micallef JP, and Orsetti A. The triphasic effects of exercise on blood rheology: which relevance to physiology and pathophysiology? Clin Hemorheol Microcirc 19: 89–104, 1998.PubMed | ISI | Google Scholar3 Connes P, Bouix D, Durand F, Kippelen P, Mercier J, Prefaut C, Brun JF, and Caillaud C. Is hemoglobin desaturation related to blood viscosity in athletes during exercise? Int J Sports Med 25: 569–574, 2004.Crossref | ISI | Google Scholar4 Hardeman MR. Exercise, red cells and blood doping; a conclusive role for LORCA? Biorheology 42: 92–93, 2005.Google Scholar5 Saltin B and Calbet JA; Wagner PD. Point:Counterpoint: In health and in a normoxic environment, V̇o2 max is/is not limited primarily by cardiac output and locomotor muscle blood flow. J Appl Physiol 100: 744–748, 2006.Link | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Cited ByConcerted phenotypic flexibility of avian erythrocyte size and number in response to dietary anthocyanin supplementation24 February 2023 | Frontiers in Zoology, Vol. 20, No. 1Elevation and blood traits in the mesquite lizard: Are patterns repeatable between mountains?Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, Vol. 276Comparison of hematological traits and oxygenation properties of hemoglobins from highland and lowland Asiatic toad (Bufo gargarizans)19 April 2021 | Journal of Comparative Physiology B, Vol. 191, No. 6Contrasting response of haematological variables between long-term training and short exercise bouts in zebra finches ( Taeniopygia guttata )18 February 2019 | Journal of Experimental Biology, Vol. 222, No. 4Lower haematocrit, haemoglobin and red blood cell number in zebra finches acclimated to cold compared to thermoneutral temperature6 April 2018 | Journal of Avian Biology, Vol. 49, No. 3A Mountain or a Plateau? 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