41.1 - Static lung volumes and capacities and their functional importance. Anatomical and physiological dead space. Estimation of external respiration.

sections

pulmonary volumes

pulmonary capacities

anatomical and physiological dead space

external respiration and estimation

pulmonary volumes

1. tidal volume: the volume of air that goes in and out of the lungs with each normal breath (0.5L)

2. inspiratory reserve volume: the max volume of air that can be inhaled after normal tidal volume inhalation (3L)

3. expiratory reserve volume: the max volume of air that can be exhaled after normal tidal volume inhalation (0.7-1L)

4. residual volume: volume of air remaining in the lungs after max exhalation (~1.2L)

5. Minute volume: the amount of air breathed during a minute while the person is at rest, 1216 breaths/minute, ~ 6-8 L/minute

6. Inspiratory capacity

7. TVC- theoretical vital capacity- calculed from body heigh using a coefficient

8. Vital capacity- volume change that occurs between max inhalation and max exhalation-

pulmonary capacities

• pulmonary capacities are a combination of two or more lung volumes together and are used in describing events in the pulmonary cycle.

• The important capacities are:

  1. Inspiratory capacity = tidal volume + inspiratory reserve volume(3.5L) begins max vol of air that can e inhaled forecefully after normal tidal inhalation IC=TV +IRV

  2. Functional residual capacity = expiratory reserve volume + residual volume (~2300ml) volume of air in the lungs after normal tidal exhalation

  3. Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume the max.~4600ml VC=TV+IRV+ERV volume change that occurs between max inhalation and max exhalation

  4. Total lung capacity = vital capacity + residual volume : the max. volume to which the lungs can be expanded (~5800ml)

anatomical and physiological dead space

• Source of the air that’s inspired does not reach the sides of gas exchange instead this air fills up spaces – respiratory passages which do not participate in gas exchange.

• Theses passages include- the nose, pharynx and trachea.

  1. Anatomical dead space: it is the portion of airways which conducts gas to the alveoli but no gas exchange is possible in these spaces.

  2. Alveolar/pulmonary dead space: it is the sum of alveoli which have little or no blood flowing through their pulmonary capillaries and thus cannot take part in gas exchange. It is very low in normal healthy persons but can increase in lung diseases.

• The total dead space (physiological dead space) =sum of the anatomical dead space plus the alveolar dead space.

external respiration and estimation

• External respiration refers to gas exchange across the respiratory membrane in the lungs between alveoli and venous blood (deoxygenated blood).

• As venous blood flows through the pulmonary capillaries

• oxygen diffuses into the blood and carbon dioxide diffuses into the alveolar gas.

• Each gas diffuses down its own partial pressure gradient - that is, from a high to low partial pressure.