Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 106

1 3.1 ASee Fig. 3.1.

2 3.2 BThe normal FEV:VC and reduced FEV1 imply restriction. The reduced KCO suggests the cause is intrapulmonary.

3 3.3 DThe pH is low, so this is an acidosis. The PCO2 is high, so this is a respiratory acidosis. The bicarbonate is high, suggesting there has been time to attempt to compensate (chronic). However, the pH would be in the normal range had this been a chronic stable state, so there must be an acute component. Remember, too, that physiological compensatory mechanisms don’t overcompensate.

4 3.4 AIf you assume the patient is breathing room air (PIO2 = 21 kPa), then the alveolar–arterial gradient (see Chapter 1) will be negative (partial pressure of oxygen higher in the arterial blood than in the alveoli), suggesting the patient is a net contributor of oxygen to the environment. This seems unlikely. The inspired PO2 therefore must be greater than 21 kPa.The condition is clearly not stable; the pH is outside the normal range. As we aren’t given the PIO2, we can’t conclude the lungs are normal. The A–a gradient may be very high.

5 3.5 AThis is a primary respiratory alkalosis, so the answer must be either anxiety‐driven hyperventilation or pulmonary embolism. The alveolar arterial gradient is increased, implying a problem within the lungs (affecting V/Q matching), which anxiety cannot explain.

6 3.6 DAt 80% of the predicted value, the result is still well within the normal range and therefore can be found within the normal population (of course, this doesn’t mean you can conclude that there is no disease present).

7 3.7 BMuscular weakness can inhibit the ability to fill the lungs to their capacity, therefore when the FVC manoeuvre is performed there’s less than the normal amount of air to be expelled. Although a reduced FVC may be seen in lung fibrosis, it is seen in many other conditions and therefore cannot be taken to ‘suggest’ fibrosis in isolation.

8 3.8 CMuscle weakness is an example of an extrapulmonary restrictive defect. Therefore, FEV1 and FVC will be reduced (approximately in proportion) and the gas transfer per unit lung volume (KCO) will be elevated (see text).

9 3.9 BIn pulmonary haemorrhage, obesity and asthma, KCO is typically elevated (see text). Thyrotoxicosis is a high cardiac output condition with more than the average amount of blood in the pulmonary circulation. There is therefore increased capacity to absorb CO (KCO may therefore be high).

10 3.10 A,B,C,EKCO is increased in restrictive defects caused by extrapulmonary factors.