Which term means the total volume of air in the lungs after maximum inhalation?
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In this article we will look at the volumes and capacities within the lungs, how they are measured and how they are affected by pathology. Show
It is useful to divide the total space within the lungs into volumes and capacities. This allows for an assessment of the mechanical condition of the lungs, its musculature, airway resistance and the effectiveness of gas exchange at the alveolar membrane. These can be determined by simple, cheap and non-invasive tests. DefinitionsVolumeDescriptionAverageNotesTidal volumeVolume that enters and leaves with each breath, from a normal quiet inspiration to a normal quiet expiration0.5LChanges with pattern of breathing e.g. shallow breaths vs deep breaths Increased in pregnancy Inspiratory reserve volumeExtra volume that can be inspired above tidal volume, from normal quiet inspiration to maximum inspiration2.5LRelies on muscle strength, lung compliance (elastic recoil) and a normal starting point (end of tidal volume)Expiratory reserve volumeExtra volume that can be expired below tidal volume, from normal quiet expiration to maximum expiration1.5LRelies on muscle strength and low airway resistance Reduced in pregnancy, obesity, severe obstruction or proximal (of trachea/bronchi obstruction) Residual volume/reserve volumeVolume remaining after maximum expiration1.5LCannot be measured by spirometry
Often changes in disease Requires adequate compliance, muscle strength and low airway resistance Inspiratory capacityVolume breathed in from quiet expiration to maximum inspirationTidal volume + inspiratory reserve volume3LFunctional residual capacityVolume remaining after quiet expirationExpiratory reserve volume + residual volume3LAffected by height, gender, posture, changes in lung compliance. Height has the greatest influence.Total lung capacityVolume of air in lungs after maximum inspirationSum of all volumes6LRestriction < 80% predicted Hyperinflation > 120% predicted Measured with helium dilution Anatomical (serial) dead space is the volume of air that never reaches alveoli and so never participates in respiration. It includes volume in upper and lower respiratory tract up to and including the terminal bronchioles Alveolar (distributive) dead space is the volume of air that reaches alveoli but never participates in respiration. This can reflect alveoli that are ventilated but not perfused, for example secondary to a pulmonary embolus. By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons Fig 1 – Diagram showing various lung volumes. Measuring Volumes and CapacitiesSimple SpirometrySimple spirometry can measure tidal volume, inspiratory reserve volume and expiratory reserve volume. However, it cannot measure residual volume. Measured values are standardised for height, age and sex. Of these, height is the factor with the greatest influence upon capacities. Process British Lung Foundation Fig 2 – Simple spirometry Helium dilutionHelium dilution is used to measure total lung capacity. However, it is only accurate if the lungs are not obstructed. If there is a point of obstruction, helium may not reach all areas of the lung during a ventilation, producing an underestimate as only ventilated lung volumes are measured. Process After quiet expiration, the subject breathes in a gas with a known concentration of helium (an inert gas). They hold their breath for 10 seconds, allowing helium to mix with air in the lungs, diluting the concentration of helium. The concentration of helium is then measured after expiration. The volume of air which is ventilated is then calculated according to the degree of dilution of the helium. Nitrogen washoutA method for calculating serial/anatomical dead space in the conducting airways up to and including the terminal bronchioles (usually 150mL). Process The subject takes a breath of pure oxygen and then exhales through a valve which measures nitrogen levels. At first, pure oxygen is exhaled, representing the dead space volume as the air exhaled never reached the alveoli and underwent gaseous exchange. Then, a mixture of dead space air and alveolar air is expired, meaning the detected concentration of nitrogen increases as nitrogen rich air from the dead space reaches the valve. After a few breaths, the lungs are washed out of pure oxygen, meaning that purely alveolar air is expired, with the nitrogen levels reflecting that of alveolar air. The levels of nitrogen measured over time can be used to calculate the anatomical dead space volume of the lungs. Visualising lung volumesVitalographA vitalograph creates plots of volume against time, using data collected from spirometry tests. Two important spirometry volumes that can be measured from a Vitalograph are:
The proportion of air that can be exhaled in the first second compared to the total volume of air that can be exhaled is important in assessing for possible airway obstruction. This proportion is known as the FEV1/FVC ratio. This ratio is important in clinically for diagnosis of respiratory conditions. By National Heart Lung and Blood Insitute (NIH) (National Heart Lung and Blood Insitute (NIH)) [Public domain], via Wikimedia Commons Fig 3 – Image showing the process of spirometry using a spirometer. Flow volume loopThis plots flow over volume (showing expiratory flow and inspiratory flow as positive and negative values respectively). Important factors to consider when assessing flow-volume curves are as follows:
By Evgenios Metaxas MD MSc, Pulmonologist Ευγένιος Μεταξάς MD MSc, Πνευμονολόγος [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons Fig 4 – A flow-volume loop Nitrogen washout graphThis plots the percentage concentration of nitrogen in exhaled air (%N) against the total volume of air expired. The anatomical dead space is determined by the volume of exhaled air at which the volume below the washout curve (A1) is equal to the volume above the washout curve (A2). Boston University School of Medicine Figure 5 – A nitrogen washout curve Clinical relevance – Obstructive and Restrictive DeficitsProcessFEV1FVCFEV1/FVCObstructive<80% of predictedReduced, but not to same degree as FEV1<0.7Restrictive<80% of predicted<80% of predicted>=0.7In obstructive disease, the FEV1 is reduced due to increased resistance during expiration. Air trapping can also occur where more air is inspired than is expired. This can cause the residual volume to increase. In asthma, the obstruction is reversible which can aid in diagnosis. This means that FEV1/FVC will recover on re-test after the application of a bronchodilator such as salbutamol. The so-called ‘spooning‘ of a flow-volume curve in obstructive disease arises when the affected small airways begin to collapse. As air exits the thorax in expiration, the pressure within the small airways reduces and thus the small airways are no longer propped open. This increases resistance to expiration and therefore reduces flow. Examples of obstructive diseases are asthma, COPD (chronic bronchitis, emphysema), tracheal stenosis and large airway tumours. By User:Evgenios Metaxas MD MSc, Pulmonologist Ευγένιος Μεταξάς MD MSc, Πνευμονολόγος [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons Fig 6 – Spirometry of a patient with asthma, an obstructive disorder. In restrictive disease, the FVC is reduced due to poor lung expansion. This can be neurological, due to weak inspiratory muscles or due to an anatomical deformity. This causes the inspiratory reserve volume to be reduced as the lungs can’t inflate as much during maximum inspiration. Residual volume can also be reduced as expiration is more effective than inspiration. Examples of restrictive diseases are interstitial pulmonary fibrosis, muscle weakness, kyphoscoliosis, obesity, tense ascites. What is the term for the volume of air remaining in the lungs after a maximal exhalation that prevents the alveoli from collapsing?Residual volume (RV) is the volume of air remaining in the lungs after maximum forceful expiration. In other words, it is the volume of air that cannot be expelled from the lungs, thus causing the alveoli to remain open at all times.
What is the term for the volume of gas in the lungs at maximal inspiration?The total lung capacity (TLC) is the maximal volume of gas in the lungs after a maximal inhalation; thus it is the sum of the RV, ERV, VT, and IRV. TLC is approximately 6 L for a healthy 70-kg adult. The vital capacity (VC) is the maximal volume of gas exhaled during a forced exhalation after a forced inhalation.
What term describes the volume of gas remaining in the lungs after a maximum expiration?The residual volume (RV) is the amount of gas remaining in the lungs after maximum exhalation. The amount of gas that can be inhaled after inhaling during tidal breathing is called the inspiratory reserve volume (IRV).
What is the term for the lung volume that is the total amount of air that can be forcefully exhaled in 1 second?An important measurement taken during spirometry is the forced expiratory volume (FEV), which measures how much air can be forced out of the lung over a specific period, usually one second (FEV1). In addition, the forced vital capacity (FVC), which is the total amount of air that can be forcibly exhaled, is measured.
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