Respiratory

LUNG VOLUMES AND CAPACITIES + PULMONARY FUNCTION TESTS

Learning Objectives

At the end of today's practical, student will be able to:

• Explain the principles of spirometry and how integration of the flow signal gives a volume. • Relate your recorded lung volumes and capacities, to those of a typical person of the same gender, height and age. • Perform pulmonary function tests, describe the common measurements made from them (PIF, PEF, FVC and FEV1) and relate these measurements to those of a typical person of the same gender, height and age. • Describe the effect of airway restrictions on PIF, PEF, FVC and FEV1.

Primary Lung Volumes

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VT: Tidal volume – air inhaled during quiet breathing. IRV: Inspiratory reserve volume – maximal volume inhaled from quiet breathing. ERV: Expiratory reserve volume - maximal volume exhaled from quiet breathing. RV: residual volume – volume remaining after maximal exhalation.

Lung Capacities = Sum of Primary Lung Volumes

TLC: Total lung volume- The volume of the lung after maximal inspiration. The sum of all four lung volumes, cannot be measured by spirometry because it includes residual volume: IRV+ TV + ERV + RV = IC + FRC VC: Vital capacity – volume exhaled from maximal inspiration to maximal expiration IRV + TV + ERV = IC + ERV FRC: Functional residual capacity – Volume of gas remaining in lung after normal expiration, cannot be measured by spirometry because it includes residual volume: ERV + RV IC: Inspiratory capacity- maximal volume inhaled from FRC IRV + TV

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Spirometry

• Measurement of air movement in and out of the lung during different respiratory maneuvers. • Values measured are:

– FVC: Forced Vital Capacity – FEV1: The forced expiratory volume in one second – MVV: Maximum Voluntary Ventilation

Importance

• Patients and physicians have inaccurate perceptions of severity of airflow obstruction and/or severity of lung disease by physical exam. • Provides objective evidence in identifying patterns of...