MRCP2-4466

MRCP2-4466

A 28-year-old man presents to his GP with shortness of breath. This has been occurring for the past 6 months and is sometimes accompanied by wheezing, particularly later on during the day. He does not have any past medical history and occasionally takes over-the-counter antihistamines for hay-fever. His only recent travel history is a holiday to Spain, where he found he was less short of breath and he was less wheezy. His only family history of note is his mother who died of a heart attack aged 65. He works as a car mechanic and smokes 5 roll-up cigarettes per day and drinks on average 5-6 units of alcohol per week.

What investigation would be most helpful in determining the diagnosis of this 28-year-old man?