Chapter 14.
Answers A, B, and E are true statements, whereas C and D are false.
1. Standard affinity is the binding force between two molecules, when half of the binding sites are occupied (eg, at 50% saturation). In the case of oxyhaemoglobin the P50 is used. Here, standard affinity is 1/P50.
2. The dry CO-fraction (FACO). The following volume describes all the binding sites for CO and oxygen in the haemoglobin of this person: (148×1.34) =198.3 ml STPD per l. Thus, CO and oxygen occupy all binding sites. The following equation is always true for CO-haemoglobin (HbCO) and Oxy-haemoglobin (HbO2):
[HbCO]/PaCO = Standard affinity*[HbO2]/PaO2. Both sides of the equation can be multiplied with 1.34. Then the equation reads:
CaCO/PaCO = Standard affinity* CaO2/PaO2.
Using the data given:
28.3/PaCO = 260×170/100. PaCO = (28.3×100)/(260×170) = 0.064 mmHg. Since we have equilibrium between arterialized blood and alveolar air it follows that PaCO = PACO = 0.064 mmHg. FACO = PACO/(PB - 47) = 0.064/(760 - 47) = 0.00009 or 0.09 permille.
3. The CaO2 is 170 and the arteriovenous oxygen content difference is 50, so the oxygen concentration of the mixed venous blood is 120 ml STPD per l.
4. CaO2 = 7.78*148*1.34/9.18 = 170 ml STPD per l. The difference (170 – 50) 120 ml STPD per l is in the mixed venous blood of the anaemia patient.
5. The anaemic person has a reduced working capacity, but since his oxygen dissociation curve is switched strongly to the right, his mixed venous PO2 is much higher than that of the CO-poisoned with a mixed dissociation curve located to the left. This CO-poisoned person is disabled, whereas the anaemic person can function although tired.
1. The low lung volumes of the patient is characteristic for restrictive lung disorders. Both VC, IRV and ERV are small. FEV1 is normal relative to the FVC, but small in absolute terms. The specific (FRC) lung compliance is 1/6 of normal, which means that the lung Parenchyma is stiff.
2. The restrictive disorder is in the lung parenchyma, and not in the chest wall. A diffuse Pulmonary sarcoidosis has created a solid diffusion barrier for CO.
3. On a PO2 - PCO2 diagram (Fig.14-7) her arterial point (a = 8 kPa or 60 mmHg) is far from the ideal point i - that is a large alveolar (ideal) - arterial oxygen tension difference. The patient is hyperventilating lung regions with a minimum gas exchange (eg an increased alveolar dead space), and a large fraction of her cardiac output is passing unventilated lung regions, thus creating a functional veno-arterial shunt. Both factors in V°A /Q°- mismatch are demonstrated.
1. PAO2 = PIO2 - PACO2
PAO2 = 0.2093* (760 - 47) - 26 = (149 - 26) = 123 mmHg.
2. A mean alveolar gas composition is given by the ideal co-ordinates (100, 40) mmHg.
3. The ideal (PiO2) is 100 and the real PAO2 is 50, so the difference is (100 - 50) = 50 mmHg.
The lungs contain areas functioning as venoarterial shunts.
The total shunt is of considerable size.
4. The ideal PCO2 is 40 mmHg. The PaCO2 is 26 mmHg.
The difference depicts an alveolar dead space in other lung regions.
1. The tension difference (100 - 60) = 40 mmHg shows a significant veno-arterial shunt.
2. Chronically bronchitis with emphysema (COLD) with a severe functional shunt is the cause.
3. The alveolar value (A) deviate considerably from the ideal value (i in Fig. 14-7), so an abnormally high alveolar VD is demonstrated.
1. The disease is smoker’s lungs or chronic bronchitis & emphysema. This is an obstructive lung disease.
2. The condition now is acute respiratory failure with hypoxaemia and hypercapnia. The hypercapnia or acute respiratory acidosis is only moderately compensated by the kidneys.
3. The big lump of green sputum each morning arise from bronchial cavities (bronchiectasis) being emptied.
