Definitions
This term is the volume of gas per minute that reaches the alveoli and participates in gas exchange.
What is alveolar ventilation?
Explanation: Alveolar ventilation (V̇A) represents the rate of fresh gas delivery to the alveolar space where gas exchange actually occurs. It equals minute ventilation minus dead space ventilation, calculated as: V̇A = (VT - VD) × respiratory rate.
This is the alveolar dead space in a patient that has a physiological dead space of 250 mL and an anatomical dead space of 150 mL.
What is 100 mL?
Alveolar dead space is calculated as physiological dead space minus anatomical dead space. 250 mL - 150 mL = 100 mL.
In healthy lungs, alveolar ventilation is highest in this region.
What are the lung bases?
Explanation: Gravity creates a vertical gradient in pleural pressure, making basal alveoli smaller at rest but capable of greater expansion during inspiration. This results in preferential ventilation to the bases in upright individuals, though perfusion is even more preferentially distributed to these regions.
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What is Tennis?
This term represents the volume of the conducting airways from the nose/mouth to the terminal bronchioles.
What is anatomical dead space?
Explanation:
Anatomical dead space is a fixed structural component determined by airway geometry and correlates with body size, particularly height. In healthy adults, anatomical dead space is approximately 150 mL or roughly 2 mL/kg body weight.
If tidal volume is 500 mL and anatomical dead space is 150 mL, this is the alveolar ventilation per breath.
What is 350 mL?
Alveolar ventilation per breath equals tidal volume minus dead space: 500 mL - 150 mL = 350 mL. This represents the volume of fresh gas reaching the alveoli with each breath.
In healthy upright individuals, this lung region has the highest V̇A/Q̇ ratio due to gravitational effects on blood flow.
What are the lung apices?
Explanation: Gravity causes blood flow to decrease more steeply than ventilation from base to apex. While both ventilation and perfusion are lower at the apex, perfusion decreases more dramatically due to hydrostatic pressure effects on the pulmonary vasculature. This creates regions with relatively more ventilation than perfusion (higher V̇A/Q̇ ratios).
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This term represents the sum of anatomical and alveolar dead space.
What is physiological dead space?
Explanation: Physiological dead space encompasses all ventilation that does not participate in gas exchange, including both the conducting airways (anatomical) and unperfused or poorly perfused alveoli (alveolar). It represents "wasted ventilation."
With a respiratory rate of 12 breaths/min, tidal volume of 500 mL, and dead space of 150 mL, this is the minute alveolar ventilation.
What is 4.2 L/min? (or 4200 mL/min)
Explanation: Minute alveolar ventilation = (VT - VD) × RR: (500 - 150) mL × 12 breaths/min = 4200 mL/min or 4.2 L/min. This is the primary determinant of alveolar and arterial PCO₂.
This condition, characterized by ventilated but unperfused alveoli, classically increases alveolar dead space.
What is pulmonary embolism?
Explanation: Pulmonary embolism creates regions with high V̇A/Q̇ ratios or complete absence of perfusion, resulting in increased alveolar dead space.
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What is Butterfly?
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In healthy lungs, alveolar ventilation is highest in this region.
What are the lung bases?
Explanation: Gravity creates a vertical gradient in pleural pressure, making basal alveoli smaller at rest but capable of greater expansion during inspiration. This results in preferential ventilation to the bases in upright individuals, though perfusion is even more preferentially distributed to these regions.
If anatomical dead space is 150 mL and physiological dead space is 250 mL in a patient with a tidal volume of 500 mL, what is the alveolar dead space as a fraction of tidal volume?
What is 0.2 or 20%?
Explanation: Alveolar dead space equals physiological minus anatomical dead space. VDalv = 250 - 150 = 100 mL. As a fraction of VT: 100/500 = 0.2 or 20%. This represents ventilated but poorly perfused alveolar units.
In Acute Respiratory Distress Syndrome, an elevated dead space fraction at disease onset is associated with an increase in this clinical outcome.
What is mortality?
Elevated physiological dead space in early ARDS is a validated prognostic marker. The mechanism primarily involves higher VD/VT, and correlates with worse outcomes.
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This equation, named after a Danish physiologist, calculates physiological dead space using arterial PCO₂ as a substitute for alveolar PCO₂.
What is the Bohr-Enghoff equation?
Explanation: The Bohr-Enghoff modification substitutes PaCO₂ for alveolar PCO₂ in the original Bohr equation: VD/VT = (PaCO₂ - PeCO₂)/PaCO₂. This simplification allows bedside calculation but overestimates true dead space in the presence of shunt, as venous admixture elevates PaCO₂ above true alveolar levels.
This is the VD/VT of a ventilated patient has a tidal volume of 600 mL, PaCO₂ of 50 mmHg, and mixed expired PCO₂ of 30 mmHg.
What is 0.4 or 40%? [(50-30)/50]
Explanation: The Bohr-Enghoff equation calculates physiological dead space fraction: VD/VT = (PaCO₂ - PeCO₂)/PaCO₂ = (50-30)/50 = 0.4. An elevated VD/VT indicates increased wasted ventilation and has prognostic significance in ARDS
This technique measures actual alveolar PCO₂ from the CO₂ expirogram, allowing calculation of true Bohr dead space.
What is volumetric capnography (VCap)?
Explanation: Volumetric capnography measures actual alveolar PCO₂ from the CO₂ expirogram, allowing calculation of true Bohr dead space rather than the Enghoff approximation. This technique provides more accurate dead space assessment, particularly in patients with significant V̇A/Q̇ mismatch
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What is This is Spinal Tap?
(Rest in Peace Rob Reiner)