Question

For each item A–E related to control of ventilation, select the most appropriate option from the list below. 

1. Voluntary hyperventilation. 

2. Reflex hyperventilation. 

3. Hypoventilation. 

4. Ventilation controlled from the medulla 

5. Ventilation controlled from above 

5. oblongata. 5. the medulla oblongata. 

6. Ventilation associated with dyspnoea. 

A. An athlete’s ventilation may increase from a normal value of 6 litres per minute to over 100 litres per minute while running a race. 

B. A student breathes a mixture of 5 per cent carbon dioxide and finds that, without apparent effort, the breathing is much deeper than normal. 

C. Another student is asked to breathe rapidly and deeply for three minutes. Towards the end of the time there is a strong wish to reduce the breathing and there is a feeling of lightness and discomfort in the head. 

D. In normal people breathing continues steadily during sleep. 

E. In people with COPD the lungs are over-inflated and it may be harder to breathe in than breathe out.

Answer 1

A. Option 4 Ventilation controlled from above the medulla oblongata. The commonest situation for this huge minute volume is strenuous exercise in a normal person. This is not a reflex from a fall in arterial oxygen levels, which remain normal, but is controlled from higher levels where circulatory and respiratory activities are coordinated with muscular activity. This activity is sometimes identified with ‘the exercise centre’ though this is more a function of the brain than a localized area. 

B. Option 2 Reflex hyperventilation. The increased ventilation is reflexly produced via chemoreceptors in the region of the medulla oblongata. These respond to the huge rise in hydrogen ions produced centrally from the rise in carbon dioxide level. 

C. Option 1 Voluntary hyperventilation. The hyperventilation lowers the carbon dioxide level. This causes a respiratory alkalosis and constricts cerebral arterioles. There has been a suggestion that people who are most distressed by this activity are the most likely to suffer from severe symptoms at high altitudes where such changes are the result of reflex hyperventilation. 

D. Option 4 Ventilation controlled from the medulla oblongata. The spontaneous rhythmicity in the inspiratory and expiratory centres here generate the basic breathing pattern upon which other more complicated activities, including voluntary control as in respiratory function testing, are built. 

E. Option 6 Ventilation associated with dyspnoea. With severe over-inflation lung compliance falls; this increases the work of breathing in and may be less severe when breathing out (patients vary in this). The extra effort is interpreted as something wrong with the breathing (dyspnoea means bad breathing). In Option 1 the problem is not with the breathing but with the effects it produces. In Option 2 the increased breathing is not experienced as particularly unpleasant. In Option 5 the increased breathing of exercise is recognized as normal.