Question

Wynona, a 62 year-old female, comes to the clinic complaining of fatigue and persistent shortness of breath, which becomes worse during exercise. She has a history of respiratory infections and has a chronic cough that is worse in the morning. She worked for 20 years in an automobile manufacturing plant and was laid off 5 years ago. Wynona has smoked cigarettes since he was a teenager and currently estimates smoking one pack of cigarettes a day.

8. [1 point] What would you expect Wynona’s Arterial Blood Gas (ABG) test results to reveal (i.e. serum pH, PCO₂, PO₂ and serum HCO₃^-)?

9. In the case of an exacerbation of her condition would providing Wynona with pure oxygen be recommended? Explain how such a pure oxygen treatment would affect her ABG values.

10. Certain long-acting Beta-adrenergic agonists used to treat COPD trigger bronchodilation by i) inhibiting myosin kinase and ii) blocking membrane Ca²⁺ channels in bronchiolar smooth muscle cells. Explain how each of these actions will promote relaxation in smooth muscle cells.

Answer 1

Answer :

# ABG (Arterial blood gas analysis) is likely to show chronic type 2 respiratory failure with respiratory acidosis and compensatory metabolic alkalosis characterized by increased PCO2 (PCO2 > 45 mm Hg) and low PO2 ( < 55 mm Hg) . ABG is likely to show acidosis ( pH < 7.35) and raised bicarbonate level (> 24 mmoL/L).

# No, pure oxygen should not be administered generally in these cases. Administering pure oxygen will abolish the hypoxic respiratory drive. Additionally carbon dioxide binding capacity decreases as haemoglobin oxygen saturation increases (Haldane effect). These mechanisms may worsen hypercapnia (increase partial pressure of carbon dioxide) and may cause CO2 narcosis.

# Beta agonist on binding with beta - 2 receptors (G-protein coupled receptors) activate adenyl cyclase enzyme which increases concentration of cAMP (second messanger), this cAMP will decrease calcium release and will activate protein kinase A. Activated protein kinase A inhibits myosin kinase. All these mechanisms lead to relaxation of bronchial muscle cells and cause bronchodilation and thus relieve the symptoms.

Discussion and explanation :

Chronic obstructive pulmonary disease is a condition characterised by persistent airflow limitation that is usually progressive.

Chronic bronchitis and emphysema are two ends of COPD. In a patient both components can coexist in variable combinations.

Main risk factors implicated in development of COPD are chronic smoking and air pollution.

These patients experience frequent exacerbation of symptoms characterized by increased shortness of breath and sputum production.