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MP - Lecture 25

Airways, Ventilation, and Properties of Gases

Medical Physiology – Lecture 25 Airways, Ventilation, and Properties of Gases
In a steady state: Nothing is building up or depleting (Consumption Rate = Input Rate)
At the beginning of exercise, O2 consumption is briefly: Higher than O2 intake
At the end of exercise, O2 intake is briefly: High than O2 consumption
O2 moves by: Diffusion down partial pressure gradients
Increase in partial pressure gradient differences causes hypoxia because: No molecular O2 pump to move against upward gradients
Path of O2 transport: Inspired > Alveolar > Arterial > Venous > Tissue (reverse for CO2)
Airway conducting zones are: Nose, larynx, trachea, bronchi, and bronchioles
Volume of conducting airways makes up the: Anatomic dead space, ~150 mL
How much gas exchange occurs between air and blood in conducting zones? No gas exchange
Functions of conducting airways Move air by bulk flow, warm and humidify inspired air, and remove particles
Removal of particles in conducting airways is by: Filtration Impaction, mucocilliary escalator
Cystic fibrosis patients have abnormal: CFTR Cl- channels causing inadequate fluid secretion
Geometry of airway represents balance between: Anatomic dead space (large airway) and airway resistance (small airway)
Total cross-sectional area in airway geometry is: Increasing from trachea to terminal bronchiole
Laying down causes FRC to: Decrease
Decrease in FRC when laying down is due to: Gravity no longer able to help relax and depress abdominal contents
Total Lung Capacity = TLC = IRV + TV + ERV + RV
Functional Residual Capacity = FRC = ERV + RV
Vital Capacity = VC = IRV + TV + ERV
Spirometry measures: Changes in volume
Volumes measured by spirometer are: IRV, TV, ERV, and VC
Spirometer cannot measure: RV or related values TLC and FRC
Measuring FRC is done by: Helium dilution method
Helium Dilution Method Helium concentration in lungs equals concentration in spirometer after many breaths because of low helium solubility
At the end of expiration, anatomic dead space contains: Unexpired alveolar air
At the end of inspiration, anatomic dead space contains: Humidified atmospheric air
Initial portion of inspired air (~150 mL) into alveoli is: Old unexpired air from anatomic dead space
Latter portion of inspired air (~350 mL) into the alveoli is: New humidified atmospheric air
Alveolar air expired or new air in alveoli = VT – VD
Minute Ventilation = VT x (Breaths/Min)
Alveolar Ventilation = (VT – VD) x (Breaths/Min)
Measure anatomic dead space by: (Fowler) Inspire 100% O2 and measure % N2 in expired air
Expiration in Fowler method contains: No N2 in first 150 mL, followed by ~70% N2 in alveolar air
Anatomic dead space in fowler curve is: Point of inflection
Sigmoid shape of Fowler curve due to: Mixing of gases
Partial Pressure = P = nRT/V
PO2 in Dry Air = (0.21) x (760 mmHg) = 160 mmHg
Pressure of water in humidified in alveolar air is: 47 mmHg
PO2 in Humidified Air = (0.21) x (760 – 47) mmHg = 150 mmHg
Rate of diffusion for dissolved gases at equilibrium is: No net diffusion
Driving for diffusion of gas is: Partial pressure gradient
At equilibrium there is more CO2 than O2 dissolved because: CO2 has 20x the solubility of O2
Concentration of dissolved gas is directly proportional to: Partial pressure
Slope of line in solubility curve depends on: Solubility coefficient, different for each gas
Created by: emyang



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