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Flashcards in Ventilation Deck (14):
1

Describe the difference between minute ventilation and alveolar ventilation.

Minute ventilation: the volume of air that flows into or out of the lung in one minute (Tidal Volume (TV) x Breathing rate)
Alveolar ventilation: the volume of air that flows into or out of the alveolar space in one minute.

Because minute ventilation includes air flowing in the conducting paths, as well as alveoli, it will always be
larger than alveolar ventilation. Typical values for minute and alveolar ventilation under resting conditions, respectively, are 6 L and 4.2 L. Alveolar ventilation is usually designated V(sub)A

2

Describe factors that influence lung ventilation, including the role of gravity.

*Bronchodilators and constrictors: factors that influence airway resistance also alter ventilation. Bronchodilators increase alveolar ventilation, whereas bronchoconstrictors reduce ventilation
*Exercise: During moderate exercise, ventilation can increase ~10-fold in order to meet the demands of increased CO2 production
*Altitude: Ventilation increases to meet the increased demands of O2
*Obstructive diseases and restrictive diseases: can reduce ventilation by increasing airway resistance or altering lung compliance. For mild-to-moderate forms, overall ventilation does not go down, but there are reductions in ventilation regionally that are balanced by increases elsewhere
*Gravity: see other card

3

Describe the work of breathing and its influence on breathing rate and tidal volume.

Breathing involves a certain amount of “work” that is done by the respiratory muscles on the lungs. The work done in moving the lungs has two major components: (a) work done against the elastic recoil of the lungs and (b) work done against airway resistance. An increase in the work of breathing can occur because of an increase in elastic recoil (decreased compliance) of the respiratory system, because of an increase in airway resistance, or a combination of the two.

Tidal volume is the volume of air in each breath. Someone who has a decrease in respiratory compliance (e.g., with pulmonary fibrosis) would breath at a smaller tidal volume with an increase in respiratory rate, in order to reduce the
elastic work

4

Define anatomical, alveolar, and physiologic dead-space.

Of the 500 ml of air in each breath (the average tidal volume), about 150 ml (or 30%) remains in the conducting path. This air is termed anatomic dead-space.

Alveolar dead space: alveoli that are well-ventilated but nevertheless do not participate in gas exchange. Such alveoli do not eliminate CO2, just like the conducting airways. Such alveoli would be those that are in unperfused regions of the lung

Physiologic dead-space: The sum of the anatomic dead-space and the alveolar dead-space. Significant differences between anatomic and physiologic dead space are an indication of disease

5

Describe different lung volumes and how they are used to diagnose respiratory disorders.

Residual volume RV: the volume of air remaining in the lungs after a maximal expiration

Functional residual capacity: The volume of gas present in the lung and upper airways at the end of a normal
expiration

Tidal volume: the difference in lung volume between a normal inspiration and normal expiration. Tidal volume is, thus, also the volume of air that enters and exits the lungs in one normal breathing cycle

Minute ventilation or minute volume: The tidal volume (ml) × frequency of breathing (breaths/min)

Restrictive diseases show change in the vital capacity
Obstructive diseases effect dynamic measurements of expiration. Decrease in vital capacity

6

Describe the work of breathing and its influence on breathing rate and tidal volume.

Breathing involves a certain amount of “work” that is done by the respiratory muscles on the lungs. The work done in moving the lungs has two major components: (a) work done against the elastic recoil of the lungs and (b) work done against airway resistance. An increase in the work of breathing can occur because of an increase in elastic recoil (decreased compliance) of the respiratory system, because of an increase in airway resistance, or a combination of the two

Reduced respiratory compliance causes an increase in the
Elastic Work component, resulting in higher breathing frequency and lower tidal volume. In contrast, someone whose primary problem is an increase in airway
resistance would want to breath with larger tidal volumes in order to reduce the resistance work

7

Describe the work of breathing and its influence on breathing rate and tidal volume.

x

8

Describe different lung volumes

Residual volume: volume of air remaining in the lungs after a maximal expiration (~1.5 L)

Functional residual capacity: The volume of gas present in the lung and upper airways at the end of a normal
expiration (~2.5L)

Total lung capacity: The volume of air inside the lungs at the end of a maximal inspiration (~7.5L)

Tidal volume: the difference in lung volume between a normal inspiration and normal expiration. Tidal volume is, thus, also the volume of air that enters and exits
the lungs in one normal breathing cycle (~5L)

Vital capacity: Volume of air exhaled after a maximal inspiration followed by a maximal expiration (VC = TLC -RV)

9

Define anatomical, alveolar, and physiologic dead-space.

Anatomical: Of the 500 ml of air in each breath (the average tidal volume), about 150 ml (or 30%) remains in the conducting path
Alveolar: alveoli that are well-ventilated but nevertheless do not participate in gas exchange. Such alveoli do not
eliminate CO2, just like the conducting airways. Such alveoli would be those that are in unperfused regions of the lung
Physiologic: The sum of the anatomic dead-space and the alveolar dead-space

10

Describe different lung volumes and how they are used to diagnose respiratory disorders.

x

11

Describe affect of gravity in lung ventilation

Intrapleural pressure (pressure outside of the lung) is not uniform; it is smaller at the base than the apex of the lung.. Because the intrapleural pressure is larger (more negative) at the apex, the bronchioles and alveoli there will have larger volumes (the vacuum in the intrapleural space essentially pulls them open). Somewhat counter-intuitively, the larger volume means that they will be less well ventilated

12

How are different lung volumes used to diagnose respiratory disorders.

x

13

How are different lung volumes used to diagnose respiratory disorders.

Restrictive diseases: change in the vital capacity,
VC, since the difficulty in expanding the lung will prevent the patient from inflating his lung maximally upon a forced inspiration. However, these diseases do not affect resistance, so you may not see changes in rate of air-flow during dynamic measurements of expiration

Obstructive diseases: associated with
increases in airway resistance. Thus, there are pronounced effects on dynamic measurements of expiration (FEV1.0/FVC ratio decreases significantly).

14

Changes in lung volumes seen in emphysema

Unlike the other obstructive diseases, emphysema can be associated with unchanged or small increases (not decreases) in vital capacity. That’s because the increase in lung compliance allows emphysema patients to achieve higher maximal lung volumes (total lung capacity) upon forced inspiration.