of Pulmonary Function in Schoolchildren and Adolescents


Measured variables

Physiopathological diagnosis

Spirometry and flow/volume loop

Forced flows and volumes:

Expiratory: PEF, FVC, FEV0.5, FEV0.75, FEV1, FEV6, FEV1/FVC, FEF25, FEF50, FEF75, FEF25–50

Inspiratory: FIF50, FEF50/FIF50

Obstructive ventilatory alteration (with or without decreased FVC)

Restrictive ventilatory alteration

Bronchodilator response

Fixed central airway obstruction

Variable intra- or extrathoracic central airway obstruction

Measurement of static lung volumes:


 Nitrogen washout

 Helium dilution

Volumes and capacities not measurable with spirometry: FRC, RV, TLC

Restrictive lung disease

Air trapping


Bronchial challenge test

Direct: methacholine, histamine

Indirect: exercise, mannitol, adenosine



Increased airway resistance

Presence and degree of bronchial hyperreactivity

Airway resistance




Specific resistance and airway conductance

Airway resistance

Fres, Rrs5, Rrs20, Xrs5, Zrs, reactance area

Increase in airway resistance

Increase or decrease in compliance (IOS)

Bronchodilator response

Bronchial hyperreactivity

Diffusing capacity of the lung for carbon monoxide


Alteration of the diffusing capacity of the alveolar–capillary membrane

Measurement of static pressures



Sniff nasal test

Cough PEF

Strength of inspiratory muscles

Strength of expiratory muscles

Ability to mobilize secretions

Maximal voluntary ventilation

Maximum amount of air inhaled and exhaled within 1 minute

Thoracopulmonary capacity

Resistance to fatigue, airway resistance, respiratory drive

6-Minute walk test

Distance traveled

Functional capacity to exercise

Cardiac capacity, respiratory capacity, muscular function capacity

CO carbon monoxide, DLCO diffusing capacity of the lung for carbon monoxide, FEF25, FEF50, FEF75 forced expiratory flow at 25%, 50%, or 75% of FVC, FEF25–75 forced expiratory flow at 25–75% of FVC, FEV0.5, FEV0.75, FEV1, FEV6 forced expiratory volume in 0.5, 0.75, 1, or 6 seconds, FIF50 forced inspiratory flow at 50% of forced inspiratory capacity (FVC), FRC functional residual capacity, Fres resonance frequency, FVC forced vital capacity, IOS impulse oscillometry, MEP maximum expiratory pressure, MIP maximum inspiratory pressure, PC20 methacholine or histamine concentration that causes a 20% drop in FEV1, PEF peak expiratory flow, Rint interrupter resistance, Rrs5 resistance at 5 Hz, Rrs20 resistance at 20 Hz, RV residual volume, TLC total lung capacity, Xrs5 reactance at 5 Hz, Zrs respiratory impedance

Spirometry and the Flow/Volume Curve

Spirometry measures lung volume and flow on the basis of forced expiration following maximum inspiration to reach the total lung capacity (TLC). Table 9.2 lists lung volumes, flows, and capacities.

Table 9.2

Definitions of lung volumes, flows, and capacities

Tidal volume (TV) : volume of inspired and expired air during normal breathing

Inspiratory reserve volume (IRV) : volume of air that enters the lungs when a deep inspiration is performed, above TV

Expiratory reserve volume (ERV) : volume of air exhaled during a deep expiration after a normal expiration

Residual volume (RV) : volume of air remaining in the lungs after a maximum expiration

Vital capacity (VC): sum of the maximum expired volume after a maximal inspiration

SVC: slow vital capacity

FVC: forced vital capacity

Inspiratory capacity (IC) : maximum amount of air that can be inspired after normal expiration

Functional residual capacity (FRC) : volume of air that remains in the lungs after normal expiration

Total lung capacity (TLC) : maximum volume of air that the lungs can contain

RV/TLC ratio: percentage of RV in relation to TLC

Forced expiratory volume in a given time (FEVt) : volume of air expired during the FVC maneuver from TLC in a given time (e.g., 0.5, 0.75, 1, or 6 seconds)

FEV1/FVC ratio: percentage of exhaled volume in 1 second in relation to FVC

Forced expiratory flow at 2575% of FVC (FEF2575) : slope of the spirometric volume/time curve between 25% and 75% of FVC

Forced expiratory flow at 25%, 50%, or 75% of FVC (FEF25, FEF50, FEF75): forced expiratory flow when 25%, 50%, or 75% of FVC has been exhaled

Forced inspiratory flow at 50% of forced vital capacity (FVC) (FIF50): forced inspiratory flow measured at the 50% point of the inspiratory part of the flow/volume curve

Peak expiratory flow (PEF) : maximum flow velocity observed during the forced expiratory maneuver

Spirometry is indicated to diagnose alterations in lung function in patients with respiratory symptoms and signs (pathologies that can directly or indirectly affect lung function) or with exposure to risk factors such as smoking, environmental contamination, radiotherapy, chemotherapy, or other drugs with known pulmonary toxicity. Spirometry is also indicated to assess anesthetic and surgical risks and the prognosis of patients with respiratory pathologies, to assess the response to different treatments (bronchodilators, inhaled corticosteroids, kinesiotherapy), and to control the advance of progressive pathologies such as neuromuscular diseases and cystic fibrosis.

The equipment used for spirometry should be calibrated daily.

The maneuver is performed with a maximum and rapid inspiration to reach the total pulmonary capacity, followed by a maximum expiratory effort 3–6 seconds in duration and/or a plateau of at least 1 second.

The test yields two graphic registers—the volume/time curve and the flow/volume curve—which should be analyzed to assess the acceptability of the examination. The volume/time curve (Fig. 9.1a) relates the volume of exhaled air to the time taken to exhale. It has an initial rapid increase and then reaches a plateau. The flow/volume curve (Fig. 9.1b) distinguishes between the inspiratory and expiratory phases. The inspiratory phase goes from the residual volume (RV) to TLC, constituting the lower part of the graph and forming a semicircle in which it is possible to measure the maximum inspiratory flow at 50% of forced vital capacity (FVC): (FIF50). The expiratory phase has a triangular profile, with a rapid ascent from the total pulmonary capacity to the peak expiratory flow (PEF), and a slow descent with a constant slope until RV is reached. In the first part of the expiratory phase, in which pulmonary volume is high, the flow depends on effort, but after expiration of the first third of the vital capacity (VC), at the level of low pulmonary volumes, the flows are independent of effort. The shape of the flow/volume curve indicates the presence of fixed or variable obstruction of the central airway (Fig. 9.2). At least three curves that comply with international criteria for acceptability should be obtained, and at least two of these should be repeatable—that is, with variability of less than 5% in the forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1). A numerical report should be produced for FVC, FEV1, FEV1/FVC, and forced expiratory flow at 25–75% of FVC (FEF25–75).


Fig. 9.1

Spirometric curves. a Volume/time curve showing the forced expiratory volume in 1 second (FEV1) and in 6 seconds (FEV6). b Flow/volume loop showing the forced expiratory flow (FEF) at 25% (FEF25), 50% (FEF50), and 75% (FEF75) of the forced vital capacity (FVC), and the forced inspiratory flow (FIF) at 50% of the inspiratory loop. FEFmax maximum instantaneous flow achieved during a FVC maneuver


Fig. 9.2

Alterations in the flow/volume loop: forms of the loop that display pathophysiological changes in the airway and lungs. Airway: Extrathoracic airway Obstruction; Intrathoracic airway Obstruction; Fixed airway obstruction

The spirometry test is repeated 15 minutes after administration of 400 μg of salbutamol in an aerosol form to assess the response to the bronchodilator. Any increase of 12% in FEV1 and/or 30% in FEF25–75 is considered a significant response (provided that the postbronchodilatory FVC does not vary more than 10% from the basal value).

The reference values that are used should be registered in the report. Those most widely used at present are Knudson, NHANES III (National Health and Nutrition Examination Survey III), and Gutierrez. The Global Lung Function Initiative (GLI) has recently developed reference equations that address an age range from 3 to 90 years, with differences according to the ethnicity of the population. A spirometry reading is considered normal when the values are above P5 or within ±1.64 standard deviations (Z score) of the reference values.

Obstructive and restrictive alterations in ventilation, with or without a decrease in FVC, can be distinguished (Table 9.3).
Nov 7, 2020 | Posted by in Uncategorized | Comments Off on of Pulmonary Function in Schoolchildren and Adolescents
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