Respiratory

Question 1

Most prevalent component of surfactant

Answer 1

DPPC (dipalmitoyl phosphatidylcholine)

Also most physiologically active component

Question 2

1. Most abundant surfactant protein
2. Most physiologically important surfactant protein

Answer 2

1. A
2. B

A is _A_bundant but B is _B_etter for you

Question 3

Laplace’s law and it’s implication/role re: surfactant

Answer 3

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)*

Question 4

FRC is roughly equivalent to ___ in embryology

Answer 4

Fetal lung fluid (20-30ml/kg)

Question 5

Two channels most responsible for maintaining fetal lung fluid (FLF)

Answer 5

1. ENaC
2. Na-K-ATPase
   * Prenatally transport of Cl into lung space makes FLF; during labor active transport of Na OUT helps get rid of FLF*

Question 6

Compliance equation

Answer 6

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

Question 7

Resistance equation (the “simple” one)

Answer 7

Resistance= change in pressure/change in flow

In neonates primary resistance is airway, and that’s nasal

Question 8

Time constant equation

Answer 8

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)*

Question 9

Time constant in healthy newborn vs. RDS

Answer 9

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])

Question 10

Role of Na-K-ATPase and ENaC during and after labor

Answer 10

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

Question 11

Relationship between time constant and i-time

Answer 11

i-time is 3-5x the time constant, AKA amount of time for 95-99% of volume to be exchanged

Question 12

Main driver of the shortened time constant in RDS

Answer 12

Compliance worsening (AKA lower)

Resistance actually is higher but the decrease in compliance is greater than increase in resistance

Question 13

Factors that increase ENaC activity (4)

Answer 13

1. Glucocorticoids (incr ENaC synthesis and slow degradation)
2. Catecholamines
3. Oxygen tension
4. Presence of alveolar-air interface

Question 14

What is a normal A-a (alveolar-arterial) oxygen gradient in a newborn?

Answer 14

25-30 mmHg

Question 15

PAO2 equation (alveolar partial pressure of oxygen)

Answer 15

PAO2 = [FiO2 x (P_B - P_H2O)] - (PaCO2/R)

P_B (sea level)=760, P_H2O=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

Question 16

Who should be referred to a cystic fibrosis (CF) center and what are the criteria to undergo sweat chloride testing?

Answer 16

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

Question 17

At what amount of hemoglobin desaturation is cyanosis evident

Answer 17

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)

Question 18

What stage of embryology do TEFs occur

Answer 18

Embryonic (the earliest!), 4 weeks

Makes sense since it is due to inappropriate tube formations/separations

Question 19

Regarding V/Q, what is shunting?

Answer 19

Shunting is where flow (Q) is occurring and ventilation is now

Shunting always refers to blood flowing

Question 20

What does a rightward shift in the oxygen dissociation curve mean physiologically?

Answer 20

Release O2 more easily (decreased affinity)

Think of tissue circumstances where you’d need more O2 (are sick) so you’d want it offloaded

Question 21

What types of things result in a leftward shift in the oxygen dissociation curve

Answer 21

Things that indicate tissues are doing better so it’s OK to release less O2 there (normal pH, low PCO2)

Question 22

2,3-DPG does what to the oxygen dissociation curve

Answer 22

Shifts it rightward (facilitates O2 dissociation, decreases Hb affinity for O2)

Question 23

Fetal hemoglobin shifts the oxygen-dissociation curve ____

Answer 23

Leftward

Binds it more tightly, so it has a predilection for fetal>maternal Hb

Question 24

What is the ability of the (term) body to compensate for primary respiratory acidosis (in terms of bicarbonate)

Answer 24

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*

Question 25

A rare cause of pulmonary hypertension seen in about 5-25% of infants with BPD (ie chronic lung disease of prematurity)

Answer 25

Pulmonary vein stenosis

Is a venous pulmonary hypertension/congestion, highly variable frequency in BPD in literature