V d V t = P A C O 2 − P e C O 2 P A C O 2 Ī common step is to then presume that the partial pressure of carbon dioxide in the end-tidal exhaled air is in equilibrium with that gas' tension in the blood that leaves the alveolar capillaries of the lung. In a healthy adult, alveolar dead space can be considered negligible. The respiratory zone is comprised of respiratory bronchioles, alveolar duct, alveolar sac, and alveoli. The original formulation by Bohr, required measurement of the alveolar partial pressure P A. Physiologic or total dead space is equal to anatomic plus alveolar dead space which is the volume of air in the respiratory zone that does not take part in gas exchange. The Bohr equation is used to quantify the ratio of physiological dead space to the total tidal volume, and gives an indication of the extent of wasted ventilation. Physiological dead space is approximately 1/3 of tidal volume (30) During exercise, both increase, but tidal volume increases more, reducing the dead space/tidal volume ratio. It differs from anatomical dead space as measured by Fowler's method as it includes alveolar dead space. Effectively, 1/3 of a TV of inhaled air is rebreathed due to dead space. Anatomic, and therefore physiological, dead space normally is estimated at 2 mL/kg of body weight and comprises 1/3 of the TV in a healthy adult patient it is even higher in pediatric patients. This is given as a ratio of dead space to tidal volume. Alveolar dead space is typically negligible in a healthy adult. The Bohr equation, named after Danish physician Christian Bohr (1855–1911), describes the amount of physiological dead space in a person's lungs. Not to be confused with the Bohr model or the Bohr effect.
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