Jonah Patel
Total lung capacity (TLC) is defined as the volume of gas in the lungs at the end of a maximal inhalation. It is achieved when the maximal force generated by the inspiratory muscles is balanced by the opposing forces of lung expansion. The average total lung capacity of an adult human male is about 6 litres of air, but this can vary depending on age, sex, height, weight, ethnicity, and certain respiratory diseases. TLC can be calculated by measuring lung capacities such as inspiratory capacity (IC), functional residual capacity (FRC), and vital capacity (VC). Various techniques can be used to measure TLC, including spirometry, CT scans, nitrogen washout tests, helium dilution tests, and total-body plethysmography.
| Characteristics | Values |
|---|---|
| Definition | Total lung capacity (TLC) is the volume of gas in the lungs at the end of a maximal inspiration. |
| Calculation | TLC is calculated by measuring inspiratory capacity (IC), functional residual capacity (FRC), and vital capacity (VC). |
| Average Volume | The average total lung capacity of an adult human male is about 6 litres of air. |
| Variation | Lung capacity varies depending on age, body size, ethnicity, gender, and certain respiratory diseases. |
| Measurement Techniques | TLC can be measured using spirometry, body plethysmography, nitrogen washout, helium dilution, and CT scans. |
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What You'll Learn
Inspiratory capacity
IC is the amount of air that can be inspired from the end-expiratory level (inspiratory reserve volume (IRV) + TV). IRV is the air inspired with maximum inspiratory effort in excess of the tidal volume, and TV is the amount of air that moves in and out of the lungs during inspiration and expiration with quiet breathing.
IC can be directly measured by spirometry, along with tidal volume, vital capacity, inspiratory reserve volume, and expiratory reserve volume. However, total lung volume, FRC, and residual volume cannot be measured by spirometry, and alternative techniques must be used, such as the nitrogen washout test, helium dilution test, or total-body plethysmography.
The IC/TLC ratio is an important predictor of mortality in patients with chronic obstructive pulmonary disease (COPD). Patients with COPD and an IC/TLC ratio of less than 25% are at an increased risk for careful treatment monitoring, frequent hospital admissions, and all-cause and respiratory mortality. Additionally, a low or decreasing exercise inspiratory capacity can predispose individuals to dyspnoea-generating inspiratory constraints, such as "restrained breathing".
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Functional residual capacity
FRC is the sum of expiratory reserve volume (ERV) and residual volume (RV). Residual volume is the amount of air that remains in the lungs after expelling as much air as possible. It cannot be exhaled or measured by spirometry. FRC can be measured by body plethysmography, nitrogen washout, or helium dilution techniques. The nitrogen washout method involves giving a patient 100% oxygen to remove nitrogen gas from the lungs. The helium dilution method measures the equilibration of helium into the lungs.
FRC is affected by conditions that impact lung compliance, such as emphysema, interstitial lung diseases, decreased chest movements, and decreased thoracic volume. Obese and pregnant patients tend to have lower FRC in the supine position due to added tissue weight opposing the outward recoil of the chest wall. FRC also varies with age, height, and sex. It tends to increase with age due to changes in the static recoil of the lungs.
FRC is an important parameter in understanding pulmonary function and respiratory physiology. It is a key component in calculating total lung capacity (TLC), which is the volume of gas in the lungs at the end of a maximal inspiration. TLC can be calculated by measuring lung volumes at different phases of the respiratory cycle and by measuring the remaining volume of air in the lungs after maximum exhalation.
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Vital capacity
The vital capacity can be measured using a spirometer, either a wet or regular type. It can be measured as inspiratory vital capacity (IVC), slow vital capacity (SVC), or forced vital capacity (FVC). The FVC is similar to VC, but it is measured as the patient exhales with maximum speed and effort.
Additionally, vital capacity reflects the ability to breathe deeply and cough effectively. It indicates the strength of inspiratory and expiratory muscles. For a cough to be effective, the vital capacity should be at least three times greater than the tidal volume.
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Lung volumes and lung capacities
The average total lung capacity of an adult human male is about 6 litres of air. However, this can vary depending on several factors, including age, sex, height, weight, ethnicity, and body composition. For instance, the residual volume and the functional residual capacity increase with age, resulting in a decrease in vital capacity. Vital capacity also increases with height, while increasing BMI correlates with lower vital capacity.
Lung volumes can be measured by spirometry, including tidal volume, inspiratory reserve volume, and expiratory reserve volume. However, residual volume, functional residual capacity, and total lung capacity cannot be measured by spirometry and require alternative techniques such as the nitrogen washout test, helium dilution test, or total-body plethysmography.
The four lung volumes are:
- Inspiratory reserve volume (IRV)
- Expiratory reserve volume (ERV)
- Tidal volume (TV)
- Residual volume (RV)
The four lung capacities are:
- Total lung capacity (TLC)
- Vital capacity (VC)
- Inspiratory capacity (IC)
- Functional residual capacity (FRC)
TLC is defined as the volume of gas in the lungs at the end of a maximal inspiration, achieved when the maximal force generated by the inspiratory muscles is balanced by the opposing forces of lung expansion. It can be calculated by measuring lung capacities like IC, FRC, and VC, or by directly measuring lung volumes at different respiratory cycle phases and the remaining volume of air in the lungs after maximum exhalation.
VC refers to the maximum volume of air that can be exhaled following maximum inhalation. It is calculated by summing tidal volume, inspiratory reserve volume, and expiratory reserve volume. FRC is the volume of gas remaining in the lungs at the end of a normal exhalation, calculated by adding residual and expiratory reserve volumes.
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Lung capacity and aging
Lung capacity refers to the volume of gas in the lungs at a given time during the respiratory cycle. It is calculated by measuring inspiratory capacity, functional residual capacity, and vital capacity. The average total lung capacity of an adult human male is about 6 litres of air. Lung capacity varies depending on factors such as depth of respiration, ethnicity, gender, age, and body composition.
Age-related changes in the lungs can affect lung capacity. The lungs typically achieve maximal lung function around age 20 in females and 25 in males. After this, a gradual decline in lung function occurs with age. The composition of the epithelial lining fluid (ELF) changes with age, increasing susceptibility to environmental toxins. The cumulative cohort effect estimates that each generation has a lower vital capacity by approximately 5 ml/year compared to the previous generation. However, due to improvements in techniques, equipment, and repeated measurements, studies have shown an average increase in forced expiratory volume (FEV1) in both men and women over time.
Functional residual capacity (FRC) and residual volume (RV) tend to increase with age, resulting in a lower vital capacity. FRC is influenced by the balance of the lungs' elastic properties and the chest wall's recoil. Conditions such as emphysema and asthma can increase FRC, while fibrosing alveolitis, pleurisy, obesity, and scarring of the thorax can decrease it. RV can be significantly high in obstructive lung diseases with incomplete emptying of the lungs, increasing the risk of barotrauma, pneumothorax, infection, and reduced venous return.
Aging can also cause structural changes in the lungs, such as a loss of shape and elasticity in the air sacs, making them baggy. These changes can trap air in the lungs, leading to breathing difficulties as oxygen and carbon dioxide exchange becomes impaired. Furthermore, the weakening of the automatic breathing functions and a decrease in the sensitivity of nerves triggering coughing can make it harder to clear particles like smoke or germs from the lungs.
The effects of aging on lung capacity are often compounded by heart and lung diseases, especially those caused by smoking. Maintaining physical activity is important as lying in bed or sitting for long periods can allow mucus to collect in the lungs, increasing the risk of lung infections.
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Frequently asked questions
Total lung capacity (TLC) is the volume of gas in the lungs at the end of a maximal inhalation. The average total lung capacity of an adult human male is about 6 litres of air.
TLC is calculated by measuring the lung capacities: inspiratory capacity (IC), functional residual capacity (FRC), and the vital capacity (VC). The volume of air that makes up the TLC can be calculated by directly measuring the lung volumes at different phases of the respiratory cycle.
Several factors affect TLC, including age, sex, height, weight, ethnicity, and respiratory diseases. For instance, the residual volume and the FRC increase with age, resulting in a decrease in TLC.
TLC can be measured using various techniques such as nitrogen washout test, helium dilution test, total-body plethysmography, and CT scans.
VC refers to the maximum volume of air that can be exhaled following maximum inhalation. It is about 80% of TLC, or 4.8 litres, as some air remains in the lungs after exhalation.
