E2: Respiratory: Neonatal Physiology

Question 1

What are the (3) things that MUST change to facilitate the trasition to breathing air?

Answer 1

1. Pulmonary Vascular Resistance (PVR) must fall
2. Pulmonary Perfusion must rise rapidly
3. Fetal Vascular shunts must begin to close to separate the systemic and pulmonary circulations

Question 2

What are the 6 mechanisms facilitating the transition to breathing air?

Answer 2

1. Large release of Fetal Adrenaline during labor stims pulmonary epithelial cells to stop secreting & start absorbing
2. Compression of fetal thorax & abdomen as they passed through the birth canal leading to lung liquid expulsion.
   
   1. Up to 1/3 of lung liquid is expelled
3. Transpulmonary pressure gradient during inspiration promotes movement of fluid into the interstitial tissue
4. As fluid is replaced by air, compression of the Pulmonary vasculature is reduced considerably, and in turn, resistance to BF is lowered
5. With each successive breath, lower pulmonary opening pressure is required
6. Surfactant lowers alveolar surface tension and helps maintain lung inflation by preventing alveolar collapse.

Question 3

When does Lung fluid transfer initially begin?

By what mechanism does it work?

Answer 3

Pre-labor stage;

Cortisol/ Thyroid H -> Epinephrine -> ENaC (highly selective)

Na+ & H2O move out

Question 4

Shifts in Direction of what (2) molecules accounts for the shift from Secretory to Absorptive?

Answer 4

1. Cl- Movement;
   
   1. Fetal/Secretory: Into Alveolus
   2. Neonatal/Absorptive: Out of Alveolus
2. Na+ & H2O;
   
   1. Fetal/Secretory: Into alveolus
   2. Neonatal/Absorptive: Out of Alveolus

Question 5

How does chest squeeze during labor affect Lung Fluid?

Answer 5

Chest Squeeze can cause the expulsion of 1/3 of lung fluid during labor

Question 6

Briefly detail the relative sizes of the Starling Forces @ birth

Answer 6

Question 7

What are the differences between the (3) Lung phases?

Answer 7

Question 8

What is closing volume and Closing Capacity?

Answer 8

Closing Volume: Vol. of lung inflated when small airways in the dependent parts of the lung begin to collapse during expiration

• CV < FRC in normal health
• Accounts for RV of lung at end of Expiration

Closing Capacity (CC): Vol. of lung at which it’s smallest airways (respiratory bronchioles) collapse

• CC > RV

Question 9

What occurs with children experiencing Respiratory Distress?

Why does it occur?

Answer 9

Children Grunt when in respiratory Distress in attempt to reduce the expired volume of air in order to minimize alveolar collapse

*It is harder to re-inflate collapsed Alveoli in children

Question 10

Describe the physiological differences between Neonate & adult?

Answer 10

Minute Ventilation: Neonate (100-150) > Adult (60-70)

VA/FRC Ratio: Neonatal (5:1) > Adult (2:1)

O2 Consumption: Neonatal 2x adult

Question 11

What are the trends in Hb-O2 curve changes?

Answer 11

O2 Content decreases with;

Increased birth weight

Increased Postnatal Age

Question 12

Describe changes observed with Respiratory Distress Syndrome

Answer 12

• Atelectasis
• Hypoventilation -> Hypoxemia/ Hypercarbia -> Resp. Metabolic acidosis -> Pulmonary Vasoconstriction

Question 13

What is Tachypnea?

Answer 13

Elevated respiratory rate

Question 14

Detail Bronchopulmonary Dysplasia

Answer 14

Question 15

Detail Meconium Aspiration Syndrome

Answer 15