🫁 Dead Space Calculator
Calculate physiological dead space volume using the Bohr equation. Dead space is the volume of inhaled air that does not participate in gas exchange.
📊 Results
What Is Dead Space?
Dead space refers to the volume of inhaled air that does not participate in gas exchange. The term describes all lung tissue and airways except alveoli with active gas exchange. It includes parts of the respiratory system beyond the alveoli — like the nose, mouth, and trachea — as well as alveoli that are damaged and no longer function properly. Devices connected to the airways, such as diving equipment or breathing aids, also contribute to dead space.
This calculator determines the functional (physiological) dead space using the Bohr equation.
Types of Dead Space
Anatomical Dead Space
Anatomical dead space includes all air-conducting parts of the respiratory tract: the nasal cavity, oral cavity, pharynx, trachea, bronchi, and bronchioles. Air moves through these areas, but no gas exchange occurs.
Alveolar Dead Space
Alveolar dead space includes alveolar space that is not perfused and therefore cannot participate in gas exchange. If no blood flows through the alveoli, CO₂ cannot be released from the blood, nor can O₂ be absorbed. These alveoli were once functional but lost their function due to lung damage — for example, from smoking.
Functional (Physiological) Dead Space
Functional dead space is the sum of anatomical and alveolar dead space. In a healthy individual with no lung damage, there is no alveolar dead space, so anatomical dead space and functional dead space are the same.
Ventilation vs. Respiration
Ventilation is the movement of air in and out of the lungs. Respiration is the biochemical process where gas exchange occurs in the alveoli.
Dead space is the part of the respiratory system where only ventilation occurs — air moves through, but no gas exchange takes place. The remaining lung tissue is where respiration (gas exchange) happens.
The Bohr Equation — Dead Space Formula
Physiological dead space is calculated using the Bohr equation, named after Christian Bohr (father of physicist Niels Bohr):
Where:
- Alveolar CO₂ — the partial pressure of CO₂ in the alveoli
- Expiratory CO₂ — the partial pressure of CO₂ in exhaled air
- Tidal Volume — the volume of air breathed in per breath
Example Calculation
Given:
- Alveolar CO₂ = 40 mmHg
- Expiratory CO₂ = 30 mmHg
- Tidal Volume = 500 mL
25% of the tidal volume does not participate in gas exchange — quite normal for a healthy individual.
How to Interpret Your Results
Normal physiological dead space values for healthy adults:
| Parameter | Normal Range |
|---|---|
| Dead Space Volume | 150 – 200 mL |
| Dead Space Ratio (Vd/Vt) | 0.20 – 0.35 |
| Rule of Thumb | ~2 mL/kg body weight |
If your result falls outside this range, it could be due to:
- Smoking or air pollution
- Inflammatory conditions
- Old age or pregnancy
- Hyperventilation
- Pulmonary fibrosis or embolism
- Shock
- Other lung diseases
Note: An increased dead space is not always a reason for concern, but you should discuss your results with a doctor.
Frequently Asked Questions
What is the normal value of dead space?
The normal value ranges between 150 and 200 mL for healthy adults. A more precise estimate is approximately 2 mL per kilogram of body weight.
What is dead space ventilation?
Dead space ventilation means air flows through the dead space, but no gas exchange occurs. Ventilation refers to air movement, while respiration refers to the gas exchange happening in the alveolar capillaries.
How do I calculate dead space?
To calculate dead space: (1) Subtract the expiratory CO₂ from your alveolar CO₂. (2) Divide the result by the alveolar CO₂. (3) Multiply by your tidal volume.