Pulmonary Volumes and Capacities—Spirometry A simple method for studying pulmonary ventilation is to record the volume movement of air into and out of the lungs, a process called spirometry. spirogram is a fig.. derived from spirometry indicating changes in lung volume under different conditions of breathing. For ease in describing the events of pulmonary ventilation, the air in the lungs has been subdivided in this diagram into four volumes and four capacities, which are the average for a young adult man.

1. The tidal volume is the volume of air inspired or expired with each normal breath; it amounts to about 500 milliliters in the adult male. 2. The inspiratory reserve volume is the extra volume of air that can be inspired over and above the normal tidal volume when the person inspires with full force; it is usually equal to about 3000 milliliters. 3. The expiratory reserve volume is the maximum extra volume of air that can be expired by forceful expiration after the end of a normal tidal expiration; this normally amounts to about 1100 milliliters. 4. The residual volume is the volume of air remaining in the lungs after the most forceful expiration; this volume averages about 1200 milliliters. Pulmonary Volumes

Pulmonary Capacities In describing events in the pulmonary cycle, it is sometimes desirable to consider two or more of the volumes together. Such combinations are called pulmonary capacities. 1. The inspiratory capacity(IC = TV + IRV) equals the tidal volume plus the inspiratory reserve volume. This is the amount of air (about 3500 milliliters) a person can breathe in, beginning at the normal expiratory level and distending the lungs to the maximum amount. 2. The functional residual capacity (FRC = ERV + RV) equals the expiratory reserve volume plus the residual volume. This is the amount of air that remains in the lungs at the end of normal expiration (about 2300 milliliters). 3. The vital capacity(VC = IRV + TV + ERV) equals Inspiratory reserve volume plus the tidal volume plus the Expiratory reserve volume. VC or forced vital capacity (VC or FVC), represents the maximum volume that is available to us for inspiration

4. The total lung capacity(sum of all lung volumes) is the maximum volume to which the lungs can be expanded with the greatest possible effort (about 5800 milliliters), it is equal to the vital capacity plus the residual volume. All pulmonary volumes and capacities are about 20 to 25 per cent less in women than in men, and they are greater in large and athletic people than in small and asthenic people.

Typical Range for Volumes and Capacities 3.4 – 4.5 Vital Capacity VC 2.6 – 3.4 Functional Residual Capacity FRC 2.3 – 3.0 Inspiratory Capacity IC 4.9 – 6.4 Total Lung Capacity TLC 1.5 – 1.9 Residual Volume RV 1.1 – 1.5 Expiratory Reserve Volume ERV 0.4 – 0.5 Tidal Volume TV 1.9 – 2.5 Inspiratory Reserve Volume IRV Vol. Range (L)Volume/Cap.Abbr.

Spirometry Vol/Time Volume (L) Time (s) FEV 1 In normal circumstances FEV 1 should be ~80% of total volume expired FEV 1 /FVC ratio 4.5/5.5*100=~80% Slope of the initial line gives the flow rate FEF Vital Capacity From fully inspired state patient expels all air in their lungs as forcefully as possible FEV 2 FEV 3 25% 75% 6

Spirometry in Disease States Volume (L) Time (s) Restrictive Lung Disease e.g. lung fibrosis Total Volume reduced FEV 1 reduced But FEV 1 /FVC ratio =normal FEV 1/ FVC = 4.5/5.5*100 = ~80% FEV 1/ FVC = 2.5/3*100 = ~80% 7

Spirometry in Disease States Volume (L) Time (s) Obstructive Lung Disease ( COPD, chronic bronchitis, emphysema, asthma) Total Volume may be normal but FEV 1 is reduced And FEV 1 /FVC ratio <0.8 FEV 1 /FVC = 4.5/5.5*100 = ~80% FEV 1 /FVC = 2.5/5.5*100 = ~45% 8

Minute Ventilation Definition – volume of air moved out of the lungs per unit time V T tidal volume – typically ~500 ml f breathing frequency Therefore minute ventilation – (0.5 liters)x(12 min -1 ) = 6 liters min -1 9

Anatomic DEAD SPACE - Space in the respiratory passages filled with air where gas exchange does not take place. i.e. mouth, pharynx, larynx, trachea, bronchi, bronchioles – all conducting airways. Typically 150 ml. These areas are ventilated, i.e. air moves into them, but since they do not contribute to gas exchange it is known as wasted ventilation. Alveolar DEAD SPACE – Some gas exchange surfaces are not as efficient as they should be. Some alveoli are poorly ventilated or ventilated but with no or poor perfusion. The volume of air ventilated into regions that should be gas exchanging but is NOT is the alveolar dead space Physiologic Dead Space = Anatomic + alveolar In a normal healthy individual the physiological dead space should be only slightly larger than the anatomic dead space. Alteration in ventilation/perfusion changes this pattern (see later)

Alveolar Ventilation Minute ventilation(VE) gives volume flow per minute through lung But – not all that ventilation contributes to gas exchange (ventilation to the dead space is called wasted ventilation-Vd) Ventilation contributing to gas exchange is the alveolar ventilation – which is the minute ventilation minus the dead space ventilation VA = VE – Vd 11