Maternal Physio - Pulmo

Question 1

Respiratory structure changes

Answer 1

• Transverse diameter increases ≈ 2 cm → subcostal angle widens
• Diaphragm rises about 4 cm
• Thoracic circumference ↑ about 6 cm
• Memory aid:*
• TDC - 2, 4, 6

Question 2

Diaphragmatic excursion is ____ {lesser/greater) in pregnancy

Answer 2

Greater

Question 3

If the thoracic circumference increases by 6 cms, will the residual volume also increase?

Answer 3

No; that change is not enough to prevent reduction in the RV created by the elevated diaphragm

Question 4

Respiratory parameter that is unchanged

Answer 4

• Respiratory rate
• Lung compliance
• Vital capacity
• Inspiratory reserve volume
• Summary:*
• C Rate IRV VC

Question 5

Respiratory parameter that is increased

Answer 5

• Tidal volume
• Minute ventilatory volume
• Minute oxygen uptake
• Inspiratory capacity
• Summary:*
• IC TV Minute by Minute increasingly

Question 6

Respiratory parameter that is decreased

Answer 6

• Functional residual capacity
• Expiratory reserve volume
• Residual volume
• Total lung capacity
• Memory aid:*
• Functional T REx Decreased

Question 7

Normal acid-base status in pregnancy and mechanism

Answer 7

Compensated respiratory alkalosis due to more CO2 being blown off (increased tidal volume)

Question 8

Cause of physiologic dyspnea

Answer 8

• Results from increased tidal volume that lowers the blood PCO₂, which paradoxically causes dyspnea
• Progesterone appears to act centrally:
  
  • lowers the threshold and increases the sensitivity of the chemoreflex response → ↑ respiratory effort

Question 9

Blood pH change and effect to dissociation curve

Answer 9

Increased only minimally

↓

Shift to the left of the oxygen dissociation curve

↓

↑ affinity of hemoglobin to maternal blood

↓

Compensation: increase in 2, 3-diphosphoglycerate in maternal erythrocytes to shift the curve back to the right

Question 10

Physiologic advantage of maternal hyperventilation

Answer 10

Hyperventilation

↓

Decreased CO₂

↓

Aids CO2 transfer from fetus to mother and facilitates O₂ release to fetus