Ventilation/carbon dioxide output relationships during exercise in health

Figures

• 

  FIGURE 1. Schematic representation of a) ventilation (V′E), b) ventilatory equivalent for CO2 (V′E/V′CO2) and c) physiological dead space fraction of the breath (VD/VT) as a function of CO2 output (V′CO2) during rapid-incremental (or ramp) exercise for work rates where arterial CO2 tension (PaCO2) is assumed to be stable. m: V′E–V′CO2 slope; c: V′E intercept. Modified with permission from a, b) [15] and c) [16].

• 

  FIGURE 2. Alveolar end-tidal PCO2 and PO2 (PACO2, PAO2), ventilation (V′E), CO2 output (V′CO2), O2 uptake (V′O2), arterial [HCO3−] and arterial pH as a function of work rate for a rapid-incremental cycle-ergometer exercise test. The lactate threshold occurs when arterial [HCO3−] starts to buffer the metabolic acidosis, evidenced in the accelerating V′CO2 response (left vertical dashed line). As V′E continues to respond in proportion to V′CO2, it therefore increases out of proportion to V′O2, and PAO2 therefore begins to rise. PACO2 remains stable until respiratory compensation for the metabolic acidosis develops (right vertical dashed line; isocapnic buffering). Beyond this point, V′E increases at a greater rate than V′CO2, and PACO2 therefore starts to decreases (respiratory compensation). Reproduced with permission from [3].

• 

  FIGURE 3. Schematic representation of a) the effects of a hypothetical intervention that increased the V′E–V′CO2 slope (m) with no change in the V′E intercept (c) on ventilation (V′E) and b) ventilatory equivalent for CO2 (V′E/V′CO2) as a function of CO2 output (V′CO2) during rapid-incremental (or ramp) exercise for work rates where arterial CO2 tension (PaCO2) is assumed to be stable. Solid profiles: pre-intervention; dashed profiles, post-intervention.

• 

  FIGURE 4. Schematic representation of a) the effects of a hypothetical intervention that increased the V′E-intercept (c) with no change in the V′E–V′CO2 slope (m) on ventilation (V′E) and b) ventilatory equivalent for CO2 (V′E/V′CO2) as a function of CO2 output (V′CO2) during rapid-incremental or ramp exercise for work rates where arterial CO2 tension (PaCO2) is assumed to be stable. Solid profiles: pre-intervention; dashed profiles, post-ntervention.

• 

  FIGURE 5. The V′E–V′CO2 relationship for ramp exercise in which arterial CO2 tension (PaCO2) has been demonstrated to increase progressively up to the lactate threshold [25, 56, 57] (dashed line), compared with that obtaining with PaCO2 constrained not to increase (solid line). Note the decreased slope in the former condition. Data taken from [56].

• 

  FIGURE 6. The corresponding V′E/V′CO2 relationships related to figure 5. Note the depressed V′E/V′CO2 profile consequent to the progressive PaCO2 increase (circles, dashed curve), compared with that obtaining with arterial CO2 tension (PaCO2) constrained not to increase (squares, solid curve). As a result, V′E/V′CO2min was decreased in the former condition.