Spirometry is the most common test for evaluating lung function. It is a particularly effective and widespread diagnostic tool as it is standardized, painless, easily reproducible and objective.
Spirometry is frequently used in the diagnosis and evaluation of lung function in people with restrictive or obstructive airway diseases.
During the examination, a particular instrument called a spirometer is used, capable of evaluating the different lung volumes.
SPYROMETRY and static lung volumes
SPIROMETRIC TRACE: thanks to the spirometer it is possible to measure the volume variations of the respiratory system. After making the patient perform a maximal, not abrupt inhalation, all the air is exhaled with a slow maneuver.
or
Forced vital capacity (CVF or FVC)
NOTE:
During a physical exercise the tidal volume increases considerably, drawing on both the inspiratory reserve volume and the expiratory reserve volume.
During strenuous exercise, the respiratory rate can go from 12 acts that are normally recorded in conditions of rest to 35-45 cycles / min.
Lung volumes vary according to age, sex and especially in relation to height and body size. High values of vital capacity are not uncommon in subjects of large size. A value of 8.1 liters was measured in a cross-country skier Olympic gold medal.
With the passing of age the residual volume tends to increase, while the inspiratory and expiratory reserve volumes are reduced.
A higher than normal lung capacity does not increase the performance level. In fact, it has been shown that even during maximal exercise there is a functional reserve on the part of the respiratory system equal to 15-35%. In a healthy subject, therefore, there is no limitation of the performance of respiratory origin even if this may not be entirely true. in the two extreme cases, that is for the sedentary and for the top-level middle-distance runner
SPIROMETRY, the forced expiration curve and the measurement of dynamic values
Subsequently, the subject is invited to perform a "maximal inhalation (up to CPT), followed by a rapid, decisive and complete exhalation (up to VR). The patient's cooperation during spirometry is therefore essential. Technical requirements for good spirometry:
Obtain at least three acceptable spirograms (FEV1 and FVC should not differ by more than 200ml or 5%)
Full inspiration before the test
Satisfactory start of exhalation (maximum effort, no hesitation)
Absence of cough during the first second
Adequate test duration (exhalation lasting no less than 6 seconds or 15 seconds in case of bronchial obstruction)
Perfect seal and patency of the mouthpiece (the patient should be asked to tightly squeeze the mouthpiece of the spirometer between the lips in order to avoid leaks).
CONTRAINDICATIONS TO SPIROMETRY
- previous cerebrovascular episodes
- lung infections
- recent undergoing thoracic, abdominal or ocular surgery
myocardial infarction within the past six months, or unstable angina pectoris - aneurysms
severe arterial hypertension - presence of symptoms that could interfere with spirometry (nausea, vomiting)
It is possible to represent the forced expiration maneuver with a flow-volume curve: the instantaneous flow (ordinates) and the exhaled volume (abscissas) are reported at each instant.
Flow-volume curve derived from the sequential registration of a vital capacity forced in inspiration and exhalation
By analyzing the parameters obtained with spirometry it is possible to evaluate lung function and diagnose the presence of any pathologies. In particular, the forced expiration curve can tell us whether the pulmonary insufficiency is obstructive or restrictive.
Restrictive pulmonary insufficiency: the airways have a normal caliber but the lungs have a reduced capacity for expansion, or there is a reduction in the pulmonary ventilatory surface (obesity, myopathy, pleurisy, poliomyelitis, pulmonary edema, etc.). The vital capacity and the various volumes decrease proportionally.
Pulmonary insufficiency of obstructive type: inside the airways there is an obstacle to the outflow of the inspired air or the calibres of these airways become smaller than normal. All this may be due to the presence of secretions or to the thickening and destruction of the elastic component (interstitial pulmonary fibrosis, COPD, asthma, acute bronchitis, chronic bronchitis).
If the FEV1 / FVC ratio is normal or increased, this is likely a restrictive limitation. To confirm the diagnosis it is necessary to evaluate the static lung volumes by means of a slow spirometry and plethysmography: if the total lung capacity (CPT) is less than 80% it is actually a restrictive type of lung insufficiency.
Functional Indices
Restrictive ventilatory inability
Obstructive ventilatory inability
CVF
Decreased
Normal or decreased
FEV1 (FEV1)
Decreased in proportion to the FVC
Decreased more than the FVC
FEV1 (FEV1) / CVF
Normal
Decreased
The FEV1 / CVF ratio in normal adult patients ranges from 70% to 80%; a value below 70% indicates an obstructive deficit and a high probability of COPD. This ratio gives us INDICATIVE information that must always be confirmed by comparing the recorded value of FEV1 with the normal values:
If FEV1 / FCV <70% and FEV1 ≥ 100%, it may be a physiological variable, especially in healthy subjects and athletes (to learn more, perform plethysmography, diffusion, EGA)
If FEV1 / FCV <70% and FEV1 ≤100% ≥ 70% mild obstruction
If FEV1 / FCV <70% and FEV1 ≤70% ≥ 60% moderate obstruction
If FEV1 / FCV <70% and FEV1 60% ≥ 50% moderately severe obstruction
If FEV1 / FCV <70% and FEV150% ≥ 34% severe obstruction
If FEV1 / FCV <70% and FEV1 <34% very severe obstruction
COPD classification
RISK FEATURES 0 Normal spirometry THE SLIGHT
FEV1 / FCV <70%; FEV1 ≥ 80% of predicted with or without chronic symptoms (cough, sputum)
II MODERATE FEV1 / FCV <70%; 50% ≤ FEV1 <80% of predicted with or without chronic symptoms (cough, sputum, dyspnoea) III SERIOUS
FEV1 / FCV <70%; 30% ≤ FEV1 <50% of predicted with or without chronic symptoms (cough,
sputum, dyspnoea)VERY IV
SERIOUSFEV1 / FCV <70%; FEV1 <30% of theoretical or FEV1 <50% of theoretical in the presence of
respiratory failure or clinical signs of right heart failure
The reversibility character of bronchial obstruction is assessed on the basis of the results of a second spirometry performed after administration of a bronchodilator. The patient is given a drug (salbutamol) which dilates the bronchi and the spirometry is repeated after 20 minutes:
- If the FEV1 increases by at least 12% in percentage value and if this increase is greater than 200mL in absolute value, the bronchial obstruction is completely reversible (bronchial asthma)
- If the FEV1 increases by at least 12% in percentage value and if this increase is greater than 200mL in absolute value, but still remains less than 80% of the predicted one, we speak of a partially reversible obstructive ventilatory deficit (typical of partially reversible COPD )
- If the FEV1 increases by less than 12% in percentage value or if this increase is less than 200mL in absolute value, we speak of non-reversible ventilatory deficit (typical of non-reversible COPD)
Spirometry is also a particularly useful tool in monitoring the evolution of COPD (at least one annual check-up is recommended) and in assessing subjects at risk (heavy smokers, workers exposed to chemical or gaseous pollutants, etc.). An early diagnosis of COPD greatly helps the treatment of the disease, stopping it in the bud.
