An obsession with CO2

Jones, Norman L.
August 2008
Applied Physiology, Nutrition & Metabolism;Aug2008, Vol. 33 Issue 4, p641
Academic Journal
The concept that underlies this paper is that carbon dioxide (CO2) removal is at least as important as the delivery of oxygen for maximum performance during exercise. Increases in CO2 pressure and reductions in the pH of muscle influence muscle contractile properties and muscle metabolism (via effects on rate-limiting enzymes), and contribute to limiting symptoms. The approach of Barcroft exemplified the importance of integrative physiology, in describing the adaptive responses of the circulatory and respiratory systems to the demands of CO2 production during exercise. The extent to which failure in the response of one system may be countered by adaptation in another is also explained by this approach. A key factor in these linked systems is the transport of CO2 in the circulation. CO2 is mainly (90%) transported as bicarbonate ions - as such, transport of CO2 is critically related to acid-base homeostasis. Understanding in this field has been facilitated by the approach of Peter Stewart. Rooted in classical physico-chemical relationships, the approach identifies the independent variables contributing to homeostasis - the strong ion difference ([SID]), ionization of weak acids (buffers, Atot) and CO2 pressure (PCO2). The independent variables may be reliably measured or estimated in muscle, plasma, and whole blood. Equilibrium conditions are calculated to derive the dependent variables - the most important being the concentrations of bicarbonate and hydrogen ions. During heavy exercise, muscle [H+] can exceed 300 nEq·L-1 (pH 6.5), mainly due to a greatly elevated PCO2 and fall in [SID] as a result of increased lactate (La-) production. As blood flows through active muscle, [La-] increase in plasma is reduced by uptake of La- and Cl- by red blood cells, with a resultant increase in plasma [HCO3-]. Inactive muscle contributes to homeostasis through transfer of La- and Cl- into the muscle from both plasma and red blood cells; this results in a large increase in [HCO3-]. In the lungs, oxygenation of hemoglobin increases red blood cell [A-] aiding rapid conversion of HCO3- into CO2 in red cells (containing carbonic anhydrase), with diffusion of CO2 into alveoli, but full equilibration of the CO2 system in plasma may not occur during the short pulmonary capillary circulation time in heavy exercise. The ionization state of imidazole groups on protein histidine may provide integration between acid-base homeostasis, membrane anion transfer proteins, and activation of rate-limiting enzymes. L’élimination du gaz carbonique (CO2) est aussi importante que l’apport de l’oxygène quand il est question de performance physique; cet énoncé constitue la thèse de cet article. L’augmentation de la pression partielle du gaz carbonique et la diminution de l’acidité du tissu musculaire ont un effet sur les propriétés contractiles, sur l’activité des enzymes limitantes dans le métabolisme du muscle et sur la diminution des symptômes associés à l’arrêt de l’effort. L’approche théorique de Barcroft est un bel exemple de physiologie intégrée quand ce dernier décrit les ajustements respiratoires et circulatoires en réponse à la production de gaz carbonique durant un exercice physique. Dans cette approche, on démontre comment l’échec d’un système est compensé par l’ajustement de l’autre. Le facteur clé réunissant ces deux systèmes est le transport du gaz carbonique dans les vaisseaux sanguins. Le gaz carbonique, principalement (90 %) transporté sous forme d’ions de bicarbonate est de ce fait intimement relié à l’équilibre acidobasique. C’est grâce à l’approche théorique de Peter Stewart qu’on a pu comprendre davantage ce domaine. Inscrite dans la relation physicochimique classique, cette approche identifie des variables indépendantes contribuant à l’homéostasie la différence de concentration des ions ([SID]), la dissociation des acides faibles (tampons, concentration totale des acides faibles ou Atot) et la pression partielle du gaz carbonique (PCO2). Il est possible d’obtenir une estimation fiable de la mesure des variables indépendantes dans le muscle, le plasma et le sang ; on évalue les conditions d’équilibre pour déterminer les variables dépendantes, les plus importantes étant les concentrations de bicarbonate et d’ions d


Related Articles

  • Influence of expiratory flow-limitation during exercise on systemic oxygen delivery in humans. Aliverti, A.; Dellacà, R. L.; Lotti, P.; Bertini, S.; Duranti, R.; Scano, G.; Heyman, J.; Lo Mauro, A.; Pedotti, A.; Macklem, P. T. // European Journal of Applied Physiology;Oct2005, Vol. 95 Issue 2/3, p229 

    To determine the effects of exercise with expiratory flow-limitation (EFL) on systemic O2 delivery, seven normal subjects performed incremental exercise with and without EFL at ~0.8 l s−1 (imposed by a Starling resistor in the expiratory line) to determine maximal power output under...

  • Loss of CO from the intravascular bed and its impact on the optimised CO-rebreathing method. Prommer, Nicole; Schmidt, Walter // European Journal of Applied Physiology;Jul2007, Vol. 100 Issue 4, p383 

    Total haemoglobin mass can be easily measured by applying the optimised CO-rebreathing method (oCOR-method). Prerequisite for its accurate determination is a homogenous CO distribution in the blood and the exact knowledge of the CO volume circulating in the vascular space. The aim of the study...

  • Impact of Low Filter Resistances on Subjective and Physiological Responses to Filtering Facepiece Respirators. Roberge, Raymond J.; Kim, Jung-Hyun; Powell, Jeffrey B.; Shaffer, Ronald E.; Ylitalo, Caroline M.; Sebastian, John M. // PLoS ONE;Dec2013, Vol. 8 Issue 12, p1 

    Ten subjects underwent treadmill exercise at 5.6 km/h over one hour while wearing each of three identical appearing, cup-shaped, prototype filtering facepiece respirators that differed only in their filter resistances (3 mm, 6 mm, and 9 mm H2O pressure drop). There were no statistically...


    Background. Research aim was to establish the influence of a prior anaerobic load on the kinetics of ventilation (VE) and carbon dioxide output (VCO2) during on- and off-transition phases of intermittent increasing cycling exercise. Methods. The seven healthy, physically active females...

  • Neuroprotective Effects of Individual or Combined Exposure to Hypoxia and Hypercapnia in the Experiment. Tregub, P.; Kulikov, V.; Bespalov, A.; Vvedensky, A.; Osipov, I. // Bulletin of Experimental Biology & Medicine;Jul2013, Vol. 155 Issue 3, p327 

    We studied the effects of hypoxic, hypercapnic, and hypercapnic-hypoxic exposures on brain tolerance to ischemia. All respiratory training modes had a neuroprotective effect, but the most pronounced effect was observed after exposure to hypercapnic hypoxia. Experimental stroke in rats...

  • BREATHING LESSONS. Gazzola, Alex // Foods Matter (UK);May2008, p8 

    The article focuses on the association of breathing with gastro-intestinal, food intolerance and food allergy symptoms. According to Jen Tiller of Reality Quest, once a person reaches a certain level of carbon dioxide loss, the defence mechanisms kick in to prevent further loss. Air swallowing...

  • Ventilatory responses to hypercapnia in divers and non-divers: effects of posture and immersion. Delapille, P.; Verin, E.; Tourny-Chollet, C.; Pasquis, P. // European Journal of Applied Physiology;Nov2001, Vol. 86 Issue 1, p97 

    The aim of this study was to determine the effects on respiratory drive of two factors, one mechanical (lung volume) and one chemical (sensitivity to hypercapnia), that are involved in determining the breath-hold duration (BHD). Functional residual capacity was measured by helium dilution with...

  • hypercapnia. Peters, Michael // BMA A-Z Family Medical Encyclopedia;2004, p394 

    An encyclopedia entry for "hypercapnia" is presented. It refers to an excess of carbon dioxide in the blood that is caused by failure of internal mechanisms, such as breathing rate, that normally control the levels of blood carbon dioxide. The condition also leads to respiratory acidosis.

  • Relationship Between Ventilation and Predicted Arterial CO2 Pressure During Recovery From an Impulse-Like Exercise Without Metabolic Acidosis. R. AFROUNDEH; T. ARIMITSU; R. YAMANAKA; C. S. LIAN; K. SHIRAKAWA; T. YUNOK; T. YANO // Physiological Research;2013, Vol. 62 Issue 4, p387 

    We investigated ventilation (VE) control factors during recovery from light impulse-like exercise (100 watts) with a duration of 20 s. Blood ions and gases were measured at rest and during recovery. VE, end tidal CO2 pressure (PETCO2) and respiratory exchange ratio (RER) were measured...


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics