Spirometry

SPIROMETRY and static lung volumes

SPIROMETRIC TRACK: thanks to the spirometer it is possible to measure the volume changes of the respiratory system. After having made the patient perform a rough inhalation that is not abrupt, expel all the air 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 a strenuous exercise the respiratory rate can go from 12 acts that are normally recorded in resting conditions 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 large subjects. A value of 8.1 liters was measured in an Olympic gold medal cross-country skier.

As the age passes, the residual volume tends to increase, while the inspiratory and expiratory reserve volumes are reduced.

Higher than normal lung capacity does not increase performance. It has been shown that even during a maximal exercise there is a functional reserve by the respiratory system equal to 15-35%. Therefore, in a healthy subject there is no limitation of respiratory performance even though this may not be completely true in the two extreme cases, ie for the sedentary and for the very high level middle distance runner

SPIROMETRY, the forced expiration curve and the measurement of dynamic values

Subsequently the subject is invited to perform a maximal inspiration (up to CPT), followed by a rapid, decisive and complete exhalation (up to VR). The patient's collaboration during spirometry is therefore essential. Technical requirements for good spirometry:

Obtain at least three acceptable spirograms (VEMS and FVC must not differ more than 200 ml or 5%)

Complete inspiration before the test

Satisfactory start of exhalation (maximum effort, no hesitation)

Absence of cough during the first second

Adequate duration of the test (expiration lasting no less than 6 seconds or 15 seconds in case of bronchial obstruction)

Perfect tightness and patency of the mouthpiece (the patient must be invited to tighten the spirometer mouthpiece firmly between the lips in order to avoid leaks).

CONTRAINDICATIONS TO SPIROMETRY

• previous cerebrovascular episodes
• lung infections
• recent submission to thoracic, abdominal or ocular surgeries

  myocardial infarction in the last 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: at each instant the instantaneous flow (ordinate) and the exhaled volume (abscissa) are reported.

Flow-volume curve derived from the recording in succession of a vital capacity forced in inspiration and expiration

NOTES: Caucasian subjects have the highest values ​​of FEV1 and vital capacity, the Polynesians are among the lowest. The black race is characterized by values ​​10-15% lower than the Caucasian one, since at the same age, height and sex they have a shorter torso and longer legs. On the other hand, there is little difference between the various ethnic groups as regards PEF

Analyzing the parameters obtained with spirometry, it is possible to evaluate pulmonary function and diagnose the presence of any pathologies. In particular, the forced expiration curve can tell us if pulmonary insufficiency is obstructive or restrictive.

Restrictive pulmonary insufficiency: the airways have a normal size but the lungs have a reduced capacity for expansion, or there is a reduction in the pulmonary ventilatory surface (obesity, myopathies, pleurisy, polio, pulmonary edema, etc.). The vital capacity and the various volumes decrease proportionally.

Obstructive-type pulmonary insufficiency: inside the airways there is an obstacle to the outflow of inhaled air or the calibers of these streets become narrower becoming lower 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 VEMS / CVF ratio is normal or increased, it is probably a restrictive restriction. To confirm the diagnosis it is necessary to evaluate static lung volumes by slow spirometry and plethysmography: if the total lung capacity (CPT) is less than 80% it is actually restrictive pulmonary insufficiency.

The VEMS / CVF ratio in normal adult patients fluctuates between 70% and 80%; a value below 70% indicates an obstructive deficit and high probability of COPD. This report gives us INDICATIVE information that must always be confirmed by comparing the recorded value of FEV1 with the normal values:

If VEMS / FCV <70% and VEMS ≥ 100%, it may be a physiological variable, especially in healthy subjects and athletes (to perform plethysmography, diffusion, EGA)

If VEMS / FCV <70% and VEMS ≤100% ≥ 70% slight obstruction

If VEMS / FCV <70% and VEMS ≤70% ≥ 60% moderate obstruction

If VEMS / FCV <70% and VEMS ≤60% ≥ 50% moderately severe obstruction

If VEMS / FCV <70% and VEMS ≤50% ≥ 34% severe obstruction

If VEMS / FCV <70% and VEMS <34% very severe obstruction

The reversibility character of bronchial obstruction is evaluated based on the results of a second spirometry performed after administration of a bronchodilator. The patient is given a drug (salbutamol) that dilates the bronchial tubes and repeats the spirometry after 20 minutes:

• If the FEV1 increases at least 12% in percentage 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 terms and if this increase is greater than 200mL in absolute value, but remains however less than 80% of the aforementioned, we speak of partially reversible obstructive ventilatory deficit (typical of partially reversible COPD )
• If the FEV1 increases less than 12% in percentage 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 a particularly useful tool in monitoring the evolution of COPD (at least one annual check-up is recommended) and in assessing those at risk (heavy smokers, workers exposed to chemical or gaseous pollutants, etc.). An early diagnosis of COPD greatly helps the treatment of the disease, blocking it in the bud.