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. Author manuscript; available in PMC: 2015 Sep 22.
Published in final edited form as: Eur Respir J. 2014 Jun 12;44(2):495–512. doi: 10.1183/09031936.00048514

Figure 4.

Figure 4

Steady-state ventilatory response to treadmill walking in young and elderly healthy subjects. PaCO2 is determined by the relationship of alveolar ventilation (V̇A) to CO2 production (V̇CO2) so that: PaCO2 = V̇CO2/V̇E − V̇d × k where V̇E is total minute ventilation, V̇d is dead space minute ventilation and k is a constant [26]. Note in the elderly that their dead space ventilation (Vd/VT) is greater than in younger subjects at rest and exercise. The older subjects adjust their total V̇E/V̇CO2 higher than in the young during mild to moderate exercise intensities resulting in similar V̇A/V̇CO2 and isocapnic hyperpnea. Data from Johnson et al. [71].