Lectorial Respiratory Physiology

Question 1

You asked your client to consult her local GP. A week later your client shows you the results of her spirometry the GP has ordered. It shows an increased Residual Volume (RV) and a decreased Vital Capacity (VC).
Name TWO (2) major respiratory diseases that cause an increased RV and decreased VC.

Answer 1

Asthma and emphysema

• The sudden onset and the fact that breathing problems were exercise induced suggest asthma

Question 2

diseases briefly explain the underlying cause and mechanism for this obvious early airway closure.
ASTHMA

Answer 2

bronchoconstriction and mucus built- up in bronchioles leads to increased small airway resistance. Upon forced expiration the pressure in the small airways decreases quicker thus the equal pressure point of small airway pressure and intrapleural pressure is reached early, which results in early small airway closure, trapping more air within the alveoli hence the residual volume is increased and the vital capacity is decreased.

Question 3

diseases briefly explain the underlying cause and mechanism for this obvious early airway closure.
Emphysema

Answer 3

Emphysema is a loss of lung tissue that results in a lower recoil of the lungs. This leads to a smaller transmural pressure gradient and an increased intrapleural pressure. During forced expiration the equal pressure point of intrapleural pressure and small airway pressure is reached earlier leading to an increased residual volume and decreased forced vital capacity.

Question 4

Does breathing pure oxygen during exercise would increase his performance. What would you suggest to him? Why?

Answer 4

No benefit: Hb is fully saturated after it has passed the pulmonary circulation. Oxygen therapy would increase arterial PO2, but because Hb is already fully saturated, the O2 content would increase only by the small amount of extra dissolved O2 in plasma.

Question 5

After your discussion he completes a vigorous 4-hour weight training. About 20 minutes after his weight training you see him sitting down still breathing rather heavily. Briefly explain his increased ventilation after a 20-minute resting period.

Answer 5

Lactic acid built-up leads to metabolic acidosis. Heavy breathing suggests respiratory compensation of metabolic acidosis that reduces the CO2 induced [H+] thus relieving the acidosis.

Question 6

A person who has a decreased arterial partial pressure of CO2 but normal arterial oxygen content would most likely be

Answer 6

___hyperventilating____

Question 7

Briefly explain a cause or mechanism that would lead to a decreased Residual Volume (RV)

Answer 7

Pulmonary surfactant deficiency and pneumothorax. The former is often seen in premature babies leading to Infant Respiratory Distress Syndrome. Pulmonary Surfactant Deficiency increases the alveolar surface tension thus increases the overall recoil of the lung. This in turn leads to late small airway closure, hence decreased RV

Question 8

An increased arterial PO2, decreased arterial PCO2 but a decreased blood ph indicates what?

Answer 8

 Respiratory compensation of metabolic acidosis

Question 9

A decreased arterial PO2, increased arterial PCO2 but a increased arterial bicarbonate concentration and normal blood ph indicate what?

Answer 9

 Renal compensation of respiratory acidosis brought on by hypoventilation

Question 10

The CO-Hb dissociation curve.

Answer 10

Carbon monoxide combines with haemoglobin at the same point on the haemoglobin molecule as does oxygen. Furthermore, it binds with approximately 210 - 240 times as much tenacity as oxygen.

Question 11

How much would the oxygen carrying capacity be reduced if blood were exposed to air containing 0.1% carbon monoxide?

Answer 11

1 part CO to 1 part O2

so by 50%

Question 12

Adaptations of deep-diving mammals

Answer 12

Elimination of blood flow to most organs, except heart, brain and adrenal gland
 Reduction of body temperature by up to 3°C
 Bradycardia (2-6 beats/min)
 Exhalation before dive, reduces buoyancy
 Smaller lungs with special airways to store remaining gases after the lungs collapse below 40m that prevent the gases to enter the circulation

Question 13

Adaptation of high-fliers, eg the bar-headed goose, who can reach an altitude of 9000m

Answer 13

 A very low P50 of 10mmHg!
 Counter-current perfused flow-
through lungs
 Increased Myoglobin?