Ventilation Flashcards
Anatomic Dead Space
Space in conducting system up to terminal bronchioles, which doesn’t facilitate gas exchange. About 150 mL/lb
Why Pressure in Venous Blood (706) < Arterial Blood (755)
pO2 decreases from 95 to 40 cause we remove it, and we add less CO2 (and CO2 can be transported as other compounds)
Tidal Volume (TV)
Volume fluctuation during normal resting breathing, about 500 mL
Functional Residual Capacity (FRC)
Volume of gas in lungs at end of resting expiration, = ERV + RV
Expiratory Reserve Volume (ERV)
Maximum expiration from resting expiratory level to maximum expiratory level (about 1 L)
Inspiratory Reserve Volume (IRV)
Maximum inspiration from top of tidal volume to maximum inspiratory level (about 3L)
Inspiratory Capacity
Volume b/w resting expiratory level and maximum inspiratory level ( = TV + IRV)
Vital Capacity
Maximum inspiratory volume to maximum expiratory level (= IRV + TV + ERV)
Residual Volume
Fixed amount of gas that can’t be expired, about 1.2 L
How to Estimate RV
Use helium bc insoluble in blood, put in known conc in known volume of spirometer and let person breath to equilibrate. Then you can just calculate w/:
C(HeSp) x Vsp = C(He Equil) x ( Vsp + RV)
Dynamic Lung Volumes (explanation and normal/2 pathological conditions)
Measure Forced Expired Volume in 1 sec (FEV1) and Forced Vital Capacity (FVC)
In normal pt, FEV1/FVC ~ 0.8
In asthmatic, obstructive block so FEV1/FVC < 0.8
In fibrotic (restrictive) pt, FEV1/FVC >= 0.8 (bc FVC isn’t much itself)
Peak Expiratory Flow and Effort Dependence
On expiration, increasing part of curve is effort dependent but decreasing is independent because P collapses airways. This doesn’t happen in inspiration because airways stay open
PEF and Diseases
Decreased in both obstructive disease and restrictive disease, but lung volume is much larger than normal in obstructive (bc of compensation measures, huge RV though) and smaller in restrictive
Minute Volume
Amount of expired gas/minute = Respiratory rate x TV
Alveolar Ventilation
(tidal volume - dead space) x respiratory rate
2 Primary Muscles of Inspiration
Diaphragm (main) and external intercostals bc lift ribcage up, increase front-back diameter
2 Accessory Muscles of Inspiration
Sternocleidomastoids and scalenes
2 Muscles in Expiration
Internal intercostals (bc lower ribcage) and abdominal muscles
Transpulmonary Pressure =
Alveolar pressure (about 1 atm) - intrapleural pressure
Hysteresis
Difference in pressure required for certain amount of inflation and deflation: it is a property of surfactant that it is more difficult to stretch than to maintain stretch
Atelectasis
Collapse of alveoli
Compliance of Lung
Change in V/Change in P, about 0.2 L/cm H2O
Laplace Surface Tension Eq
Pressure = 4xTension/Radius (or 2xTension/Radius if only one surface is involved
Problem w/ no Surfactant
Smaller alveoli would have higher pressure, so air would leave them and continually inflate larger alveoli
3 Functions of Surfactant
- Reduces surface tension, increasing compliance and decreasing force needed to inflate lungs
- Stabilizes alveoli bc as SA decreases (smaller alveoli), surfactant conc is higher so surface tension decreases and low pressure causes air to travel from larger alveoli to smaller
- Keeps alveoli dry bc reduced surface tension decreases effect of drawing water out of capillaries
Alveolar Interdependence
Neighboring alveoli keep each other open
Lung and Chest Wall Natural Tensions
Each require about 5 cm H2O (in opposite directions) just to keep at Resting Expiratory Level, so P is about 0 there. However together lung-chest wall system has shallower slope than either lung or chest wall alone bc in series
Compliance in Series
1/C = 1/C1 + 1/C2 (like lung and chest wall, so takes more effort to move the two together)
Compliance in Parallel
C = C1 + C2 + … (like two lungs and alveoli, so if you remove 1 or part of 1 harder to breathe bc decreased compliance)
Pneumothorax
With hole in chest wall, chest wall is able to expand and lung able to collapse like they want. All pressures equalize to 0
Resistance to flow =
K/Radius^4
Rate of Flow =
Pressure difference/resistance
Lung Volume and Resistance
Greater lung volume = less resistance, because elastic tissue actually pulls in every direction on airways keeping them open
Check Valve Mechanism
Transairway pressure is negative bc pressure outside airway is larger than P inside airway, so airway can collapse
