Zhu: Pulmonary Ventilation Flashcards
How is elasticity defined?
The ability to resume initial form. (Think of a balloon going back to it’s initial form after you blow air in it - very elastic)
What type of fibers aid in lung elasticity?
Collagen (help lung go back to its original form)
How is compliance defined?
stretchiness and distensibility
What is the relationship of elasticity and compliance?
They are inversely related. High elasticity means it’s strong enough to go back to it’s original form so it can’t be very stretchy = low compliance. bad balloon - blow it up and it doesn’t go back to its original form: low elasticity and high compliance
Why is there a pressure-volume difference in inspiration and expiration (WITHOUT surfactant)?
Hysteresis: difference between surface tension
How does elasticity of the lung change in emphysema?
elastic fibers are lost. “Destruction of the normal architecture of the lung” elasticity is decreased, so compliance is increased
How does elasticity of the lung change in pulmonary fibrosis?
Elasticity is increased. Lungs are stiff. “Marked thickening of the alveolar walls (extensive collagen deposition)” Compliance is decreased, therefore it’s hard to stretch/inhale.
The tendency of water molecules to bond together (versus water with air) _____________ surface area and ____________ surface tension.
decreases; increases
What causes the increased surface tension on alveoli?
a gas-water interface
What protects against collapse of alveoli with increased surface tension
Surfactant
Surface tension on alveoli _______________ compliance. Surfactant _______________ surface tension.
decreases; decreases. (think of a tension weight on top of the alveoli): surface tension decreases compliance and makes it harder to expand. Surfactant reduces the surface tension so alveoli can expand.
Your patient has a hard time on inhalation. You suspect her problem to be due to a loss of what type of cell?
alveolar Type II epithelial cells (they make surfactant)
Your patient has a hard time on inhalation. You suspect to find a decrease in?
-Ca2+ -DPPC (phospholipid dipalmitoyl phosphatidycholine) (*major component of surfactant) surfactant apoproteins
Your patient is pregnant at 25 weeks and is asking what complications she may have if she goes into labor this week or next. What do you tell her?
Baby will be a risk of IRDS: infant respiratory distress syndrome preemies have a hard time breathing due to lack of enough surfactant. It begins production around 24-28 weeks of gestation and gets to be sufficient around 35 weeks gestation.
Pressure and surface tension equation
P=(2*Surface tension)/Radius of alveolus surface tension is decreased by surfactant. a larger radius will have a decreased surfactant to alveolar surface area ratio and thus higher surface tension INCREASED PRESSURE IS THE DRIVING FORCE FOR MOVEMENT
***Three main functions of surfactant?
- increased COMPLIANCE (by huge reduction in ST) 2. Promote alveoli STABILITY 3. Keeps alveoli DRY
***Lack of surfactant leads to?
- reduced COMPLIANCE 2. alveolar ATELACTASIS (collapse) 3. Pulmonary EDEMA (lungs wet)
What is airflow frictional resistance due to?
20% tissue or viscous resistance (lung parenchyma, chest wall, abdominal structures) 80% airway resistance
What are the muscles of expiration and are they active or passive?
PASSIVE. (diaphragm relaxes) -INternal intercostals -abdominal muscles (during exercise)
What are the muscles of inspiration and are the active or passive?
ACTIVE. (diaphragm pushes down and out/lung vol is increased) -diaphragm -EXternal intercostals (during exercise) -also during exercise: SCM, anterior serratus, scalene muscles, alas nasi (nose)
Given Boyle’s Law, how are pressure and volume related?
Inversely proportional P1V1 = P2V2
Normal atmospheric pressure?
760 mmHg. In medicine = reference point is 0. So if P=+5; it’s 765.
What is the normal intrapleural pressure?
-5 cm H2O
On inspiration, the pleural pressure ___________.
decreases. Goes from -5 to -8.
On expiration, the pleural pressure _________.
increases. (back up to -5 from -8)
What is the intrapleural pressure maintained by?
lymph constantly taking water away; water being produced elsewhere….
**What happens in a pneumothorax?
Air enters the intrapleural space. This is the area that maintains the -5 pressure, keeping the lungs in place and preventing collapse. INTRAPLEURAL PRESSURE WILL INCREASE from -5 to 0. Air pressure outside the lungs is greater, so air will rush into the lesser pressure area to balance it out. This will in turn cause the lungs to collapse as it no longer has the in-tact intrapleural space to maintain the negative pressure necessary to hold them in place. Causes: trauma, rupture, surgery
What happens to alveolar (intrapulmonary) pressure on inspiration and expiration?
Inspiration: alveolar pressure decreases and volume increases Expiration: opposite (Net movement is from higher pressure to lower pressure)
**What is transpulmonary pressure?
Pressure difference between alveolar (intrapulmonary) pressure and intrapleural pleural pressure. (alveolar pressure MINUS intrapleural pressure) Should be always positive - tells you lung is well-inflated.
What are the 4 pulmonary volumes and 4 pulmonary capacities?
**remember on the exam: volume has no overlay. capacitiy = 2 or more volumes.
Volumes (TIRE):
Tidal Volume (TV) (500)
Inspiratory reserve volume (IRV) (exercise)
Expiratory reserve volume (ERV)
Residual Volume (RV)
Capacities:
Inspiratory capacity: TV+IRV
Functional Residual Capacity: ERV+RV
Vital Capacity: TV+IRV+ERV
Total lung capacity: TC+IRV+ERV+RV
**Minute respiratory volume
How much air you breathe in a minute:
TV*respiratory rate = 500*12 = 6000 ml/min
Which volumes and capacities can a spirometer measure?
Volumes: TV, IRV, ERV (NOT residual)
Capacities: Vital capacity, inspiratory capacity (NOT functional or total)
How can you measure your patient’s functional residulal capacity, total lung capacity, and residual volume?
Method of Helium Diultion:
FRC= [(Ci/Cf)-1]*ViSpir
RV=FRC-ERV
TLC=FRC+IC
What is the forced vital capacity in normal lungs (amount out in the first second of expiration)?
Emphysema?
Fibrosis?
Normal: 80%
Emphysema (obstructive; low elasticity): 42%
FIbrosis: (high elasticity, low compliance. can’t get air in well but can get it out very well): 90%
What happens to airway resistance during expiration?
it increases. volume and radius go down; therefore Resistance increases.
Dead Space and Alveolar Ventilation
ideal: physiologic = anatomic, so all air participates in gas exchange.
Alveolar ventilation (Va): the total volume of new air that reaches respiratory unit per minute.
Va = RR * (TV-Physiological dead space)
= 12*(500-150) = 4200 ml
