Respiratory system

Question 1

Why do physiological respiratory changes occur in pregnancy

Answer 1

Increased need for O2 for the increased maternal metabolic rate and fetus/placenta
O2 consumption increases by 16-20% so increased demand for gaseous exchange

Question 2

How does upper respiratory tract change?

Answer 2

Increased blood flow to nasopharynx causes oedema
Increased secretion of mucus due to increased oestrogen
So causes nasal stuffiness and nose bleeds

Question 3

How does the lower respiratory tract change?

Answer 3

Placenta releases progesterone which relaxes smooth muscle of the bronchioles to reduce airway resistance, facilitating greater airway flow

Question 4

What changes occur in the thorax

Answer 4

Diaphragm moves up by 4cm
Muscles and cartilage of thorax relax increasing the transverse diameter
Subcostal angle increases (68 to 103) for more space for lungs

Question 5

Closed-glottis

Answer 5

Valsava method during labour, closed glottis
Breath-holding during pushing
Goal is for diaphragm to move down wards so it compresses the fundus to help with the descent of the fetus

Question 6

Open glottis

Answer 6

Breathing during pushing
The abdominal muscles contract compressing the uterus on both sides and allow the descending fetus to progress

Question 7

Changes in chemoreceptors in pregnancy

Answer 7

Progesterone released by placenta increases the sensitivity of central chemoreceptors to pCO2 stimulating hyperventilation
Results in having lower levels of arterial CO2 than non-pregnant women

Question 8

Changes in respiratory relating to CO2

Answer 8

Increased progesterone results in mild respiratory alkalosis (mum has low pCO2) which enables the gas gradients for exchange across the placenta, so fetus CO2 can diffuse across placenta into maternal bloodstream

Question 9

Changes in ventilation parameters

Answer 9

Respiratory rate increases as women are deepening their breaths
Tidal volume increases by 40%
Pulmonary ventilation increases by 40% due to progesterone
Residual volume decreases
Total lung capacity unchanged
Vital capacity increases by 100-200ml

Question 10

Change in postnatal period

Answer 10

Following birth, progesterone levels fall with the expulsion of the placenta
Intra abdominal pressure reduces following birth
pCO2 levels rise within 48hrs of giving birth
Ventilation parameters return to normal within 1-3weeks

Question 11

what produces surfactant

Answer 11

surfactant is produced by Type II penumocytes in the lung

Question 12

what is the role of surfactant

Answer 12

reduce the friction
decreases surface tension within the alveoli which makes it easier for the alveoli to expand and contract
reduce work of breathing
has detergent properties