Respiratory Flashcards
Most prevalent component of surfactant
DPPC (dipalmitoyl phosphatidylcholine)
Also most physiologically active component
- Most abundant surfactant protein
- Most physiologically important surfactant protein
- A
- B
A is _A_bundant but B is _B_etter for you
Laplace’s law and it’s implication/role re: surfactant
P=2T/r (distending pressure, surface tension, radius)
- Normally smaller a sphere is, higher pressure’s needed to distend or maintain volume*
- Surfactant decreases surface tension so helps mitigate that effect (AKA lowers P)*
FRC is roughly equivalent to ___ in embryology
Fetal lung fluid (20-30ml/kg)
Two channels most responsible for maintaining fetal lung fluid (FLF)
- ENaC
- Na-K-ATPase
* Prenatally transport of Cl into lung space makes FLF; during labor active transport of Na OUT helps get rid of FLF*
Compliance equation
Compliance= change in volume/change in pressure
Compliance is the “slope” on a pressure/volume curve
Greatest in the middle when volume is around FRC
Resistance equation (the “simple” one)
Resistance= change in pressure/change in flow
In neonates primary resistance is airway, and that’s nasal
Time constant equation
tc= Resistance x Compliance
- Time constant in neonates is very short*
- Takes 3-5 time constants to allow adequate inspiration/expiration*
- Things that change tc: RDS (decr), CLD (incr), atelectasis or overdistention (AKA when not at FRC)*
Time constant in healthy newborn vs. RDS
Healthy newborn tc: 0.1-0.15 sec
RDS (preemie) tc: 0.05 sec
Thus giving an iT of 0.4-0.45 sec vs. 0.2-0.25 sec (due to big decrease in compliance [nominal incr in resistance])
Role of Na-K-ATPase and ENaC during and after labor
Na-K-ATPase actively pushes Na out of cells (into interstitium)
ENaC passively pulls Na into cells from lung lumen, Cl and H20 follow
Net effect: fluid out of lumen into interstitium
ENaC is rate-limiting step
Relationship between time constant and i-time
i-time is 3-5x the time constant, AKA amount of time for 95-99% of volume to be exchanged
Main driver of the shortened time constant in RDS
Compliance worsening (AKA lower)
Resistance actually is higher but the decrease in compliance is greater than increase in resistance
Factors that increase ENaC activity (4)
- Glucocorticoids (incr ENaC synthesis and slow degradation)
- Catecholamines
- Oxygen tension
- Presence of alveolar-air interface
What is a normal A-a (alveolar-arterial) oxygen gradient in a newborn?
25-30 mmHg
PAO2 equation (alveolar partial pressure of oxygen)
PAO2 = [FiO2 x (PB - PH2O)] - (PaCO2/R)
PB (sea level)=760, PH2O=47, R=0.8 or 1 depending on patient
Can reason this out: alveolar O2 pressure is what fraction of atmospheric pressure O2 was (and water took some of that), minus CO2 you have in your lungs
Who should be referred to a cystic fibrosis (CF) center and what are the criteria to undergo sweat chloride testing?
Any with abnormal newborn screen (AKA elevated IRT, even if secondary screen for genetic mutations is negative, since does not include every mutation)
Should be >2 weeks old and >2 kg
At what amount of hemoglobin desaturation is cyanosis evident
3g/dL
Means the more Hb, faster cyanosis appears (AKA with a higher Hb, cyanosis apparent at a higher SpO2 since SpO2’s a fraction)
What stage of embryology do TEFs occur
Embryonic (the earliest!), 4 weeks
Makes sense since it is due to inappropriate tube formations/separations
Regarding V/Q, what is shunting?
Shunting is where flow (Q) is occurring and ventilation is now
Shunting always refers to blood flowing
What does a rightward shift in the oxygen dissociation curve mean physiologically?
Release O2 more easily (decreased affinity)
Think of tissue circumstances where you’d need more O2 (are sick) so you’d want it offloaded
What types of things result in a leftward shift in the oxygen dissociation curve
Things that indicate tissues are doing better so it’s OK to release less O2 there (normal pH, low PCO2)
2,3-DPG does what to the oxygen dissociation curve
Shifts it rightward (facilitates O2 dissociation, decreases Hb affinity for O2)
Fetal hemoglobin shifts the oxygen-dissociation curve ____
Leftward
Binds it more tightly, so it has a predilection for fetal>maternal Hb
What is the ability of the (term) body to compensate for primary respiratory acidosis (in terms of bicarbonate)
Acutely: Increase HCO3 1mEq for every 10 of PaCO2
Chronically: Increase HCO3 4mEq for every 10 of PaCO2
- HCO3 >35 almost always means there’s a primary metabolic component*
- http://www.ucdenver.edu/academics/colleges/medicalschool/departments/medicine/intmed/imrp/CURRICULUM/Documents/Evaluation%20of%20Acid%20Base%20Disorders.pdf*
A rare cause of pulmonary hypertension seen in about 5-25% of infants with BPD (ie chronic lung disease of prematurity)
Pulmonary vein stenosis
Is a venous pulmonary hypertension/congestion, highly variable frequency in BPD in literature
