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…
..above which expiratory forces are passive and inspiratory forces must be active.
..below which inspiratory forces are passive and expiratory forces must be active.
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.