How does morphine, which is a respiratory depressant, help people with dyspnoea to breathe more easily?
Dyspnoea can be described as shortness of breath or difficulty breathing. It can be a distressing and common symptom of lung or cardiac disease and in the end stages of a terminal disease. It also occurs as a result of strenuous exercise. The exact mechanism by which opioids palliate dyspnoea is not clear. Certainly opioids could work by reducing the perception of dyspnoea in a similar way that they reduce the perception of pain. Because the primary mechanism of opioid induced respiratory depression is a blunting of the respiratory centre in the brains response to carbon dioxide retention it is postulated that opioids at low dose may blunt this response in a patient with dyspnoea without producing adverse effects. However, it has been shown that the effect of opioids in relieving dyspnoea is independent of its effects on the respiratory centre. Opioids also cause vasodilation and may counteract the reflex vasoconstriction caused by increased blood carbon dioxide levels so that the perc
