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. This volume is considered to be 30% of normal tidal volume (500 mL) therefore, the value of anatomic dead space is 150 mL. Anatomical dead space is represented by the volume of air that fills the conducting zone of respiration made up by the nose, trachea, and bronchi. The two types of dead space are anatomical dead space and physiologic dead space.
These findings show the potential for V(D)alv/V(T)alv to quantify the embolic burden of PE.Dead space represents the volume of ventilated air that does not participate in gas exchange. The V(D)alv/V(T)alv correlates with the lung perfusion defect and the pulmonary artery pressures in subjects with PE. Regression of V(D)alv/V(T)alv vs pulmonary artery pressures yielded r2 = 0.59. Regression of V(D)alv/V(T)alv vs perfusion defect yielded r2 = 0.41. Regression analysis was performed to show correlation between V(D)alv/V(T)alv and defect on V/Q scan or systolic pulmonary arterial pressure (SPAP).įor subjects with PE, the mean perfusion defect on lung scan was 38 +/- 22% the mean V(D)alv = 208 +/- 115 mL, V(T)alv = 452 +/- 251 mL, and V(D)alv/V(T)alv = 43 +/- 18%. Percentage perfusion defect was determined from V/Q scans by a radiologist blinded to other data. Airway dead space (V(D)aw) was subtracted to yield the alveolar dead space the percentage of alveolar volume occupied by alveolar dead space per breath = V(D)alv/V(T)alv x 100%.
The V(D)alv/V(T)alv was determined from volumetric capnography and arterial blood gas analysis, which permits measurement of the physiologic dead space, V(D)phys (mL) =. Pulmonary embolism was excluded by PAG in 20 subjects. Pulmonary embolism was diagnosed in 33 by high-probability ventilation/perfusion (V/Q) scan (n = 19) or by pulmonary arteriography (PAG, n = 14). To determine whether the alveolar dead space volume (V(D)alv), expressed as a percentage of the alveolar tidal volume (V(D)alv/V(T)alv), can predict the degree of vascular occlusion caused by pulmonary embolism (PE).įifty-three subjects with suspected PE were prospectively studied.
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