Lungs dead space vs shunt3/1/2024 ![]() ![]() The physiologic dead space is the volume of inspired air that does not participate in gas exchange. Ventilation is the movement of air through the respiratory tract into (inspiration) and out of (expiration) the respiratory zone ( lungs ). Physiologic dead space is ventilation of poor perfused alveoli. Shunt is perfusion of poorly ventilated alveoli. ![]() The ratio of physiologic dead space to tidal volume is usually about 1/3. Summary The main function of the respiratory system is gas exchange (O 2 and CO 2 ). There are 2 types of mismatch: dead space and shunt. Alveolar dead space is the volume of gas within unperfused alveoli (and thus not participating in gas exchange either) it is usually negligible in the healthy, awake patient. exercise cardiac output vasodilation of apical. Ventilation/perfusion matching is essential for ideal gas exchange of O2 and CO2. Anatomic dead space is the volume of gas within the conducting zone (as opposed to the transitional and respiratory zones) and includes the trachea, bronchus, bronchioles, and terminal bronchioles it is approximately 2 mL/kg in the upright position. Q pulmonary blood flow (perfusion) 'Normal' V/Q depends on 'normal' respiratory rate, tidal volume, and cardiac output. Basically dead space causes the hypercarbia because your effective minute ventilation is reduced from baseline. ![]() Physiologic or total dead space is the sum of anatomic dead space and alveolar dead space. Dead space and shunt are just the extreme ends of the the V/Q equation. Dead space is the volume of a breath that does not participate in gas exchange. ![]()
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