where k is a constant. Equation (1) can also be expressed as tl'ao,
where VE is ventilation, VD is the physiological dead-space, and VT is tidal volume.
In normal individuals PaCO2 is maintained within a narrow range during most daily activities involving a variety of metabolic demands. Even more astonishing is the fact that most patients affected by respiratory diseases also exhibit a normal PaCO2. In some patients, however, the control system of breathing can be so disrupted that they lose the ability to maintain an adequate VA for a given VCO2 with a resultant increase of PaCO2 above the normal limits (> 45 mmHg). This condition is defined by the synonyms hypoventilation, hypercapnia, or ventilatory failure.
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