Maternal Physio - Pulmo Flashcards
Respiratory structure changes
- Transverse diameter increases ≈ 2 cm → subcostal angle widens
- Diaphragm rises about 4 cm
- Thoracic circumference ↑ about 6 cm
- Memory aid:*
- TDC - 2, 4, 6
Diaphragmatic excursion is ____ {lesser/greater) in pregnancy
Greater
If the thoracic circumference increases by 6 cms, will the residual volume also increase?
No; that change is not enough to prevent reduction in the RV created by the elevated diaphragm
Respiratory parameter that is unchanged
- Respiratory rate
- Lung compliance
- Vital capacity
- Inspiratory reserve volume
- Summary:*
- C Rate IRV VC
Respiratory parameter that is increased
- Tidal volume
- Minute ventilatory volume
- Minute oxygen uptake
- Inspiratory capacity
- Summary:*
- IC TV Minute by Minute increasingly
Respiratory parameter that is decreased
- Functional residual capacity
- Expiratory reserve volume
- Residual volume
- Total lung capacity
- Memory aid:*
- Functional T REx Decreased
Normal acid-base status in pregnancy and mechanism
Compensated respiratory alkalosis due to more CO2 being blown off (increased tidal volume)
Cause of physiologic dyspnea
- 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
Blood pH change and effect to dissociation curve
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
Physiologic advantage of maternal hyperventilation
Hyperventilation
↓
Decreased CO2
↓
Aids CO2 transfer from fetus to mother and facilitates O2 release to fetus
