Dead Spaces Anatomic Dead Space volume of conducting airways that does not participate in gas exchange Physiologic Dead Space (VD) volume of airway and lungs that does not participate in gas exchange anatomic dead space of conducting airways functional dead space in alveoli "ventilated alveoli that do not participate in gas exchange" e.g., ventilation/perfusion (V/Q) mismatch apex of lung is largest contributor of functional dead space in normal lungs, physiologic dead space ≈ anatomic dead space VD= physiologic dead space (mL) TV = tidal volume (mL) PaCO2 = PCO2 of arterial blood (mm Hg) PECO2 = PCO2 of mixed expired air (mm Hg) Ventilation Rates Minute Ventilation minute ventilation = TV x RR TV = tidal volume (mL) RR = respiratory rate (breaths/min) Alveolar Ventilation minute ventilation corrected for physiologic dead space VA = (TV - VD) x RR