The lungs have various functions, such as respiratory function, endocrine function, and metabolic function, but the clinical reference to pulmonary function measurement generally refers to the measurement of pulmonary ventilation and air exchange function. For patients with LAM disease, it generally includes three main aspects of pulmonary ventilation function, diffusion function, and bronchodilatation test (also called reversibility test).
Pulmonary function test is a painless, non-invasive, accurate and reliable test that reflects the functional status of the lungs. Pulmonary function tests are performed using the subject’s respiratory signal as the signal source, and are therefore inevitably influenced by the subject, especially in the case of force spirometry, where the subject’s cooperation is the most critical aspect of a successful test. Pulmonary function values usually need to be repeated more than three times to obtain accurate and reliable results.
All measured values (Act column) are compared to the individual normal expected value (also known as Pred column), which is calculated based on the individual’s age, gender, height, weight, etc. A range of 80-120% of the normal expected value (Act/Pred%) is considered normal. Pulmonary function can be used to evaluate the degree and type of damage to pulmonary function in LAM disease, to understand the changes in the disease and the effectiveness of treatment, but it cannot be used to diagnose LAM disease. regular pulmonary function tests can evaluate whether the disease is progressing. patients with LAM disease can have normal pulmonary function tests initially.
Later, due to hyperinflation of the lungs and increase in total lung volume, obstructive or mixed ventilation dysfunction gradually appears, as well as a decrease in diffusion function.
2.Lung ventilation function
It is possible to measure how much gas is inhaled or exhaled, and at what rate it is exhaled. The most important parameters are FEV1, FVC and FEV1/FVC, which represent the amount of gas that can be exhaled with maximum effort in one second. The normal value is 70~85%, and an FEV1/FVC value of less than 70% can determine airway obstruction.
FEV1 is a major indicator of airway obstruction, and is usually reduced in patients with LAM disease, so its severity can be evaluated by FEV1, and regular review can determine the prognosis and assess the effectiveness of treatment.
How much gas enters and exits the lungs during breathing and how much gas remains in the lungs? To answer this question, a lung volume test is performed in a body tracer. The most important of these are: residual air volume (RV) – the amount of gas that remains in the lungs after forceful exhalation; and total lung volume (TLC) – the volume of the lungs that can be reached after maximum effort and deep inspiration. is significantly increased. Usually, RV/TLC (%) ≤ 35, 36-45 is considered mild emphysema, 46-55 is moderate emphysema, and ≥ 56 is severe emphysema.
However, some patients may be affected by pneumothorax performed pleural adhesions, etc., and her pulmonary function may be restricted ventilation dysfunction, as shown by normal FEV1/FVC, but FEV1, FVC and TLC can be reduced.
Table 1 Grading judgment of the degree of pulmonary function impairment
Severity
FEV1 % expected value
Mild: ≥70
Moderate: 60-69
Moderately severe: 50-59
Severe: 35-49
Very severe: <35
2.Diffusion function test
Diffusion function test is the most common test to determine the exchange capacity of oxygen from alveoli into blood and carbon dioxide from blood into lungs, reflecting the lung gas exchange capacity. It is usually measured by inhalation of a small amount of carbon monoxide, and usually requires breath-holding during the test. Diffusion of carbon monoxide (DLCO) is a more sensitive indicator of early LAM disease lung involvement. The literature shows that the degree of DLCO impairment reflects the severity of the disease and helps predict the prognosis of patients with LAM disease.
Table 2 Grading of abnormalities in diffusion function
Grade
% of expected value
Normal: 80-120
Mildly decreased: 60-79
Moderate decline: 40-59
Severe decline: 20-39
Very severe decrease: <20
3.Bronchodilator test
Bronchodilatation test is performed to determine the reversibility of airway obstruction by measuring the change in FEV1 before and after the patient inhales bronchodilator. Some patients with LAM disease may have obstructive ventilation dysfunction effective to bronchodilator or combined with chronic obstructive pulmonary disease. Therefore, we usually request this test.
The test starts with a general pulmonary ventilation function measurement. Once a routine pulmonary function test indicates an FEV1/FVC of less than 70%, obstructive ventilation dysfunction is present. Generally, we will inhale salbutamol aerosol for 15-30 minutes and then test FEV1. If FEV1 increases by 12% compared with the basal value and the improvement value is greater than 200 ml, we can judge that the bronchodilator test is positive, which means the bronchodilator has a diastolic effect on the obstructed airway and suggests that the clinician can try bronchodilator to help relieve the respiratory distress.