22.3
Capacité pulmonaire
L’air dans les poumons est mesuré en volumes et capacités. Les mesures du volume pulmonaire reflètent la quantité d'air absorbée, dégagée ou restante…
- La taille des poumons peut varierselon l'expérience et la taille du corps. La quantité d'air qui peut entrer ou sortir des poumonsest mesurée en 4 volumes,des fonctions uniques comme l'inhalation,et 4 capacités, des taux comparatifs de plusieurs volumes. La quantité d'air normalement inhalée et expiréeest appelée "volume courant",et l'air qui peut être encore inhalé ou expiréaprès une inhalation ou expiration normaleconstitue les volumes de réserve inspiratoireet expiratoire.
Le 4ème volume est la quantité d'airrestant dans les poumonsaprès expiration du volume de réserve. On l'appelle volume résiduel. C'est la petite quantité qui ne quitte pas les poumons,pour les garder gonflés.
Cette quantité, combinées aux autres volumes,forme la capacité pulmonaire totale,la quantité totale d'air que peuvent contenir les poumons,soit approximativement 6L. En un seul cycle respiratoire,la quantité maximale d'air qui peut entrer ou sortirforme la capacité vitale :c'est la somme des volumes courants et de réserve. Les capacités restantes sont la capacité inspiratoire,quantité pouvant être inhalée après une expiration normale,et la capacité fonctionnelle résiduelle,quantité d'air restante après l'expiration.
Au final, ces mesures sont utiliséespour diagnostiquer des maladies pulmonaires comme l'asthme,dans laquelle plus d'air reste dans les poumons,ce qui rend l'expiration plus longue,ou la fibrose pulmonaire,dans laquelle le volume est rapidement expulsé,entraînant un souffle court.
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Q1: What is the difference between lung volumes and lung capacities?
Lung volumes measure air during single respiratory functions like inhalation or exhalation, while lung capacities represent sums of two or more volume measures. There are four lung volumes: tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume. Four capacities combine these volumes to show total air movement potential during breathing cycles.
Q2: How much air does tidal volume represent in normal breathing?
Tidal volume is the amount of air normally inhaled and exhaled during a regular breath without forced effort. This is the baseline air movement during quiet, resting breathing. It represents the air exchanged during each normal respiratory cycle before any reserve volumes are engaged.
Q3: What is residual volume and why does it matter?
Residual volume is the small amount of air remaining in the lungs after forced exhalation, keeping the lungs inflated and preventing collapse. This air cannot be voluntarily expelled. Combined with other volumes, residual volume contributes to total lung capacity, approximately six liters in adult males and 4.2 liters in adult females.
Q4: What does vital capacity measure during breathing?
Vital capacity is the maximum volume of air that can be exhaled after maximal inhalation, representing the sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume. It measures the maximal amount of air that can be moved in or out during a single respiratory cycle, excluding residual volume.
Q5: How do inspiratory and expiratory reserve volumes differ?
Inspiratory reserve volume is the additional air that can be inhaled after normal inhalation, while expiratory reserve volume is the extra air that can be exhaled after normal exhalation. Together with tidal volume, these reserves determine how much extra breathing capacity exists beyond routine respiration and are essential for activities requiring increased oxygen intake.
Q6: How are lung capacity measurements used to diagnose respiratory diseases?
Lung capacity measurements help identify diseases by revealing abnormal air retention or rapid emptying patterns. In asthma, more air remains in the lungs, prolonging exhalation. In pulmonary fibrosis, lung volume empties rapidly, causing shortness of breath. These measurements provide objective data for diagnosing and monitoring respiratory conditions.
Q7: What is functional residual capacity and how is it calculated?
Functional residual capacity is the volume of air remaining in the lungs after normal exhalation, calculated as the sum of expiratory reserve volume and residual volume. This measurement shows how much air stays in the lungs during quiet breathing and is important for understanding gas exchange and transport during the respiratory cycle.