Some Basics Wet Spirometer — device which measures pulmonary subdivisions. Lung Volumes — discrete values; no one value overlaps with another. Lung Capacities — include two or more lung volumes. Inspiratory capacity (IC) and Vital Capacity (VC) can be directly measured by a spirometer;
Functional Residual Capacity (FRC) and Total Lung Capacity (TLC) must be computed. Volumes Tidal volume— the volume of air inhaled and exhaled during any single expiratory cycle. Changes with exertion. Resting tidal volume is approx. 500 — 750 ml for an adult male. Inspiratory Reserve Volume (IRV) — amount of air that can be inspired with maximal effort after normal tidal breathing. Can vary from 1500 — 2500 cc. Expiratory
Reserve Volume (ERV)— volume of air that can be forced out of lugs with maximal effort after normal tidal breathing. Usually around 1500 — 2000 cc in a young adult. Residual Volume (RV)— quantity of air that remains in the lungs and airways even after maximum exhalation. We cannot speak on this air; it remains even after death (!). Ranges from about 1000 — 1500 cc. Capacities Inspiratory Capacity (IC) —
maximum volume of air that can be inhaled at the end point of rest tidal breathing. IC = IRV + TV. Vital Capacity (VC) — the quantity of air that can be exhaled after as deep an inhalation as possible. VC = IRV + TV + ERV. In adult males ranges from 3500 — 5000 cc. Functional Residual Capacity (FRC) — the quantity of air in the lungs and airways at the resting expiratory level. FRC = ERV + RV. Approx. 2300 cc in young
males. Total Capacity — (TC or “TLC” “Total Lung Capacity”). Quantity of air the lungs are capable of holding at the height of a maximum inhalation. TC = IRV + ERV + RV. Passive/Active Forces in Respiration Speech and song require fairly constant subglottal pressure. Active Muscular Forces — result from active contraction of the rib cage, diaphragm, and abdomen. Passive Muscular Forces — generated by the elastic properties of tissues (incl. lungs, muscles, rib cage tendons). Also known as “recoil” forces. Recoil forces are summarized in the relaxation-pressure curve. Chest wall and lungs have different recoils — At high volume, both recoil. At lower volume (about 500 — 55% of Vital Capacity) the chest wall is neutral, but the lungs tend to collapse. At FRC — chest wall “wants to” expand, while lungs tend to collapse — these forces balance out. Thus, the lung-chest unit is balance. An important cutoff on the relaxation pressure curve is 38% of VC. This is an equilibrium point… Speech typically involves a checking action during exhalation. That is, the inspiratory muscles are used to control the rate of lung deflation. Obstructive Lung Diseases — emphysema, asthma, chronic bronchitis, cystic fibrosis. Restrictive Lung Diseases — restrict lung inflation, thus — obesity, myesthenia gravis. Definitions
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 Deficits
In 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 volume of air that can be exhaled after tidal expiration?Expiratory reserve volume (ERV) is the amount of air that can be forcibly exhaled beyond a tidal exhalation (about 1200 ml for men & 700 ml for women).
What is the maximum amount of air you can exhale called?Vital Capacity(VC)
It is the total amount of air exhaled after maximal inhalation. The value is about 4800mL and it varies according to age and body size. It is calculated by summing tidal volume, inspiratory reserve volume, and expiratory reserve volume. VC = TV+IRV+ERV.
Is the maximum amount of air that can be inhaled past a normal tidal expiration is the sum of the volume and reserve volume?Answer and Explanation: The maximum amount of air that can be inhaled after a normal tidal expiration is referred to as inspiratory capacity. It is the sum of tidal volume and inspiratory reserve volume. If the expiratory reserve volume is also added to the inspiratory capacity, one can compute the vital capacity.
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