Ventilation And Compliance Flashcards
Define the Anatomical dead space volume
- is 150mL
- volume of gas occupied by the conducting airways
- this gas is not available for exchange
Define TV
- Tidal Volume
- the volume of air breathed in and out of the lungs at each breath
Define ERV
- expiratory reserve volume
- the maximum volume of air which can be expelled from the lungs at the end of a normal expiration
Define IRV
- inspiratory reserve volume
- the maximum volume of air which can be drawn into the lungs at the end of normal inspiration
Define RV
- residual volume
- the volume of gas in the lungs at the end of maximal expiration
Define VC
- vital capacity
- tidal volume + inspiratory reserve volume + expiratory reserve volume
Define TLC
- total lung capacity
- vital capacity + the residual volume
Define IC
- inspiratory capacity
- tidal volume + inspiratory reserve volume
Define FRC
- functional residual capacity
- expiratory reserve volume + residual volume
Describe the significance of FEV1:FVC
Fraction of forced vital capacity expired in 1 second (forced exploratory volume in 1 second divided by forced vital capacity)
Define pulmonary ventilation
The total air movement into/out of lungs.
Define alveolar ventilation
The volume of fresh air getting to alveoli and therefore available for gas exchange.
State how to calculate pulmonary ventilation
Multiply the tidal volume by respiration rate
State how to calculate alveolar ventilation
Multiply the air to alveoli by respiration rate
State the units used to measure pulmonary and alveolar ventilation
L/min
Define partial pressure
The pressure of a gas in a mixture of gases, that is equivalent to the percentage of that particular gas in the entire mixture, multiplied by the pressure of the whole gaseous mixture
State the units used to measure partial pressure
mmHg or kPa
What effect does increasing [gas]mixture have on partial pressure and why?
Partial pressure increases as all gas molecules exert same pressure
Describe resting alveolar Po2 and Pco2 under normal conditions
Remains constant
State the normal alveolar and arterial gas pressure for oxygen
13.3kPa (100mmHg)
State the normal alveolar and arterial gas pressure for carbon dioxide
5.3kPa (40mmHg)
Define hyper ventilation and describe what happens to Po2 and Pco2 during hyper-ventilation
- increased alveolar ventilation
- Po2 rises to ~120mmHg
- Pco2 falls to ~20mmHg
Define Hypo-ventilation and describe what happens to Po2 and Pco2 during Hypo-ventilation
- decreased alveolar ventilation
- Po2 falls to ~30mmHg
- Pco2 rises to ~100mmHg
Describe features of healthy lungs
- very elastic
- stretched slightly open even at the end of a relaxed expiration (tendency to recoil)
Describe the 2 cell types that make up the alveolar walls
- Thin walled ‘Type I’ => permit gas exchange
- Specialised ‘Type II’ => secrete surfactant fluid
What is surfactant?
Detergent like fluid produced by Type II alveolar cells
Where does surface tension occur?
Where ever there is an air-water interface (air and water meet)
Refers to the attraction between water molecules
State the functions of surfactant
- reduces surface tension on alveolar surface membrane => reduces tendency for alveoli to collapse
- increases lung compliance
- reduces lung’s tendency to recoil
- makes work of breathing easier
Where is surfactant most effective?
In small alveoli (as opposed to large alveoli) because surfactant molecules come closer together => more concentrated
Describe the development of surfactant production during gestation
- Starts ~25 weeks gestation
- Complete ~36 weeks
- stimulated by thyroid hormones and cortisol which increase towards end of pregnancy
Describe why premature babies can suffer Infant Respiratory Distress Syndrome
Their lungs are developmentally deficient in surfactant, causing air-spaces to collapse and become difficult to expand.
Symptoms include fast breathing, chest wall retractions, blue discolouration of the skin during breathing efforts.
Define compliance
- Change in volume relative to change in pressure
- Represents the stretchability of the lungs
- Changes in disease states/age
Define high compliance
large increase in lung volume for small decrease in IP pressure
Define low compliance
small increase in lung volume for large decrease in IP pressure
