Total Lung Count (TLC) (Lung Function Test)
Abbreviation
TLC
Normal value
Male 5.09±0.87L Female 4.00±0.83L
Clinical significance
TLC is the total amount of gas contained in the lungs after deep inspiration, i.e. equal to lung volume plus residual air volume. Increase: emphysema, senile lung; decrease: various conditions leading to restrictive ventilation disorders significantly decrease the total lung volume. Note: Normal total lung volume does not necessarily mean normal lung function, as increases and decreases in lung volume and residual air volume can compensate for each other.
Tidal volume (VT) (Pulmonary function test)
Abbreviation
VT
Normal value
Approximately 0.5L
Clinical significance
VT is the amount of gas entering and leaving the lungs in one calm breath.
Replacement Inspiratory Volume (IRV) (Lung function test)
Abbreviation
IRV
Normal value
Male 2.16L Female 1.50L
Clinical significance
IRV is the volume of air inhaled at the end of a calm inspiration followed by a forceful inspiration.
Expiratory Volume (ERV) (Pulmonary Function Test)
Abbreviation
ERV
Normal value
Male 0.91L Female 0.56L
Clinical significance
ERV is the volume of air exhaled at the end of a calm expiration followed by a forceful exhalation.
Deep inspiratory volume (IC) (Lung function test)
Abbreviation
IC
Normal value
Male 2.6L Female 1.9L
Clinical significance
IC is the volume of air inhaled by best effort inspiration at the end of calm expiration, i.e. tidal volume plus compensatory inspiratory volume. IC is the main component of spirometry.
Residual air volume (RV) (Pulmonary function test)
Abbreviation
RV
Normal value
Male 1.38±0.63L Female 1.30±0.47L
Clinical significance
RV is the volume of air remaining in the lungs after deep listening to the air. Increase: emphysema, premature closure of small airways, etc. Significant increase in RV and FRC suggests chronic obstructive ventilation disorders, such as emphysema and pulmonary heart disease.
Functional residual air volume (FRC) (Lung function test)
Abbreviation
FRC
Normal value
Male 2.27±0.81L Female 1.86±0.55L
Clinical significance
Decreased: pulmonary fibrosis, post-pneumonectomy, etc.
Spirometry (VC) (Lung function test)
Abbreviation
VC
Normal value
Male 3.47L Female 2.44L
Clinical significance
VC is the volume of air exhaled with best effort at the end of deep inspiration. Reduction: various parenchymal lung lesions, emphysema, pleural lesions, thoracic deformities, respiratory muscle weakness or paralysis, etc. Note: VC is affected by age, sex, length, body surface area, etc. Therefore, the percentage of expected value should be used as an indicator to judge. It is 100±20% for normal population and <80% for decrease. Expected value % - actual measured value / expected value × 100%. Counting formula of expected value: Male: [27.63-(0.112×age)] × height (CM); Female: [21078-(0.10×age)] × height (CM)
Residual air volume/total lung volume ratio (pulmonary function test)
Normal value
Male 0.307; Female 0.29
Clinical significance
RV is the volume of air remaining in the lungs after deep listening to the air. Increase: emphysema, small airways in over closure, etc. Significant increase in RV and FRC suggests chronic obstructive ventilation disorders, such as emphysema, pulmonary heart disease, etc. RV/TLC ratio is age-related and increases with age, up to 0.50 in the elderly.
Resting ventilation per minute (VE) (Lung function test)
Abbreviation
VE
Normal value
Male 6.66±0.20L Female 4.22±0.16L
Clinical significance
VE is the ventilation volume to maintain normal gas exchange in the resting state and is equal to tidal volume × respiratory rate per minute. In general, >10 L can confirm hyperventilation, while <3 L is considered hyperventilation. VE is affected by dead space volume, so normal VE does not necessarily indicate normal ventilation.
Ineffective air volume/tidal volume ratio (pulmonary function test)
Normal value
0.3 to 0.4
Clinical significance
Increase in the ratio: indicates a decrease in effective ventilation.
Maximum Ventilation Volume (MVV) (Pulmonary Function Test)
Abbreviation
MVV
Normal value
Male 104±2.71L Female 82.5±2.17L
Clinical significance
MVV is the volume of air breathed at maximum speed and amplitude for 1 min (or 15s of air volume × 4). An expected value of 0.60 is considered abnormal and is seen in lesions of the thorax, airway and lung tissue. Expected value calculation formula: Male: [85.5 – (0.522 × age)] × body surface area (m2) Female: [71.2 – (0.47 × age)] × body surface area (m2)
Ventilatory storage ratio (pulmonary function test)
Normal value
>0.93
Clinical significance
Ventilation storage ratio is a good indicator of ventilation storage function. A value of 0.86 indicates inadequate ventilation reserve. It is often used in the assessment of pulmonary function before thoracic surgery and in the workforce assessment of patients with occupational diseases. Ventilation reserve ratio = (maximal ventilation – resting ventilation)/maximal ventilation
Forceful lung volume (time lung volume) (FVC) (Lung function test)
Abbreviation
FVC
Normal value
1 second 0.83 2 seconds 0.96 3 seconds 0.99
Clinical significance
FVC is the volume of air exhaled forcefully at the end of deep inspiration at the fastest rate. In the presence of airway obstruction, FVC < VC. In obstructive ventilation, FVC decreases and expiration time increases, while in restrictive ventilation, expiration time is advanced. The ratio of FEV1.0 to the expected value of VC can reflect the type and degree of ventilation disorders.
Expiratory volume in one second with force (pulmonary function test)
Normal value
Male 3.18±0.12L Female 2.31±0.05L
Clinical significance
FVB is the volume of air exhaled forcefully at the end of a deep exhalation at the fastest rate. In the presence of airway obstruction, FVC < VC. In obstructive ventilation, FVC decreases and expiration time is prolonged, and in restrictive ventilation, expiration time is advanced. The ratio of FEV1.0 to the expected value of VC can reflect the type and degree of ventilation disorders.
Expiratory volume per second/exertional spirometry ratio (pulmonary function test)
Normal value
>0.80
Clinical significance
FVB is the volume of air exhaled forcefully at the end of deep inspiration and at the fastest rate. In the presence of airway obstruction, FVC < VC, in obstructive ventilation, FVC decreases and expiration time increases, in restrictive ventilation, expiration time is advanced. The ratio of FEV1.0 to the expected value of VC can reflect the type and degree of ventilation disorders.
Maximum mid-expiratory flow rate (pulmonary function test)
Normal values
Male 3.37L/s Female 2.89L/s
Clinical significance
MMFR mainly reflects the ventilation status of small airways (tube diameter <2mm).
Gas distribution (pulmonary function test)
Normal values
Primary expiratory (nitrogen dilution) method ＜0.015 Repeated breath (nitrogen purge) method ＜0.025
Clinical significance
Gas distribution measurement is mainly used to understand the distribution of ventilation. Since abnormal gas distribution can occur in the absence of obstructive or restrictive ventilation, it is a sensitive measure of ventilation function.
Carbon monoxide diffusion (pulmonary function test)
Normal value
3.3 to 4.6 ml・kPa-1/s
Clinical significance
Decrease: Extensive damage to lung tissue, pulmonary edema, pulmonary fibrosis, etc.