••• Chapter 3^ Physiology of Normal Pregnancy^35
❍ What are the normal pregnancy-induced changes known in pulmonary function tests?
Tidal volume, inspiratory capacity, minute ventilatory volume, and minute oxygen uptake increase by as much
as 40% as pregnancy advances. Respiratory rate changes little but may be slightly increased. In general, all of
the residual measures are reduced-including functional residual capacity, residual volume, and expiratory reserve
volume. The maximum breathing capacity, forced expiratory volume (FEV1), and peak expiratory flow rate
remain unchanged.
❍ Why are the residual capacities of the lungs decreased in pregnancy?
The resting level of the diaphragm is 4 cm higher in pregnancy.
❍ How much do oxygen requirements increase in pregnancy?
30 to 40 mL/min.
❍ What anatomic changes occur in the pregnant lungs to facilitate maximal oxygenation?
- Diaphragm excursion increases from 4.5 cm (prepregnancy) to 6 cm at term.
- The subcostal angle increases from 68 degrees to 100 degrees.
- The diameter of the thoracic cage increases by 2 cm.
- The pulmonary diffusing capacity or rate at which gases diffuse from the alveoli to the blood is increased.
❍ Does pCO 2 increase or decrease during pregnancy?
There is normally a dramatic decrease in the pCO 2 from a nonpregnancy range of 35 to 40 mmHg to 28 to
30 mmHg in pregnancy. This occurs from the increased respiratory drive induced by progesterone on the
respiratory center. Medroxyprogesterone has been shown to stimulate the respiratory drive in obese nonpregnant
patients who hypoventilate.
❍ Describe the trend of gastric acid production in pregnancy.
It is reduced into the second trimester (36 mg/45 min) from prepregnancy values (60 mg/45 min) but begins
to increase in late pregnancy (100 mg/45 min). Keep in mind that mucous production increases with a
protective effect
❍ Does peptic ulcer disease (PUD) improve or worsen during pregnancy?
Because there is a decrease in HCl production, PUD is rarely found in pregnancy. Disease that is already present
usually improves during the pregnant state.
❍ What is thought to be the cause of the decreased transit time throughout all parts of the alimentary system
in pregnancy?
Increased progesterone levels cause smooth muscle relaxation. Decreased levels of motilin cause loss of smooth
muscle-stimulating effects. This is evidenced by decreased esophageal, gastric, and intestinal motility and decreased
lower esophageal sphincter tone.
❍ What is epulis of pregnancy?
A focal, highly vascular swelling of the gums that regresses spontaneously after delivery.