the anatomic dead space) changes little with bronchoconstriction or when breathing hard during exercise.īirds have a disproportionately large anatomic dead space (they have a longer and wider trachea than mammals the same size), reducing the airway resistance. Despite the flexibility of the trachea and smaller conducting airways, their overall volume (i.e. In Fowler's original study, the anatomic dead space was 156 ± 28 mL (n=45 males) or 26% of their tidal volume. The normal value for dead space volume (in mL) is approximately the lean mass of the body (in pounds), and averages about a third of the resting tidal volume (450-500 mL). Thus, a snorkel increases the person's dead space by adding even more "airway" that doesn't participate in gas exchange. Even though one end of the snorkel is open to the air, when the wearer breathes in, they inhale a significant quantity of air that remained in the snorkel from the previous exhalation. In adults, it is usually in the range of 150 mL.ĭead space can be increased (and better envisioned) by breathing through a long tube, such as a snorkel. In humans, about a third of every resting breath has no change in O 2 and CO 2 levels. Inspired air is humidified, improving the quality of airway mucus.Particulate matter is trapped on the mucus that lines the conducting airways, allowing its removal by mucociliary transport.Inspired air is brought to body temperature, increasing the affinity of hemoglobin for oxygen, improving O 2 uptake.Carbon dioxide is retained, making a bicarbonate-buffered blood and interstitium possible.Contentsīenefits do accrue to a seemingly wasteful design for ventilation that includes dead space. Mammals breathe in and out of their lungs, wasting that part of the inspiration which remains in the conducting airways where no gas exchange can occur. In other words, not all the air in each breath is available for the exchange of oxygen and carbon dioxide. In physiology, dead space is the volume of air which is inhaled that does not take part in the gas exchange, either because it (1) remains in the conducting airways, or (2) reaches alveoli that are not perfused or poorly perfused.
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