I teach the first year medical students about breathlessness. I also teach the FY docs, ST docs, nurses, physios, and anyone who’ll listen, about breathlessness.

I’m a stickler for minutiae, so I spend at least one slide, usually a couple, teaching, then reminding, that breathlessness is a symptom, not a sign. One cannot tell if someone *feels* breathless, just by looking at them. I can be certain that someone is using their accessory muscles of respiration, or they are tachypnoeic, or they have respiratory distress, but only the person can tell me if they’re breathless.

But we often say that people look breathless, don’t we? I’m being ludicrously pedantic, obviously. But I do it to demonstrate that breathlessness is completely subjective. I went for a run tonight – it’s pretty cold out, and my training plan asked for 6 x 1km intervals at under 4 min/km pace, with 2 mins recovery between the intervals. During each of these intervals I was tachypnoeic, using pretty much every accessory muscle I coul recruit, I increased my tidal volume by about 10-fold, and by the end, I had fairly noisy breathing. But I wouldn’t say I was particularly *breathless* until the last interval. Ok, the second last.

But my expectation is that to train hard I will have to breathe hard, so the physiological responses to exercise – increased RR, increased Vt, increased work of breathing – are no surprise to me, so I don’t perceive them as abnormal. In fact, I think it’s very normal to feel like that when I exercise.

I see a lot of breathless patients. It’s not particularly my area of interest, or specialist expertise, but general medicine clinic has its share of breathless patients. I don’t mean to generalise here (I have the data to back me up), but it’s rare to see a “breathless query cause” patient with a BMI of under 30. A bit of physics reminds us that work is force times distance, and the force required to move anything is proportional to its mass – any engine can move a certain load before it becomes overwhelmed. So the most likely diagnosis is always one of obesity, and lack of fitness.

At the ERS a couple of years ago I went to a presentation on the phenomenon of “Fat but fit”. There are certainly patients who are obese, sometimes orbidly so, but are very well conditioned, and have a sufficiently large ‘engine’ to carry the load. But I don’t see that very often, if ever.

But morbidly obese patients can have lung pathology too. A number of years ago a colleague saw a patient who was morbidly obese, normal CXR, normal-ish lung function, breathless on minimal exertion, and clearly unfit. He told her she was overweight and should lose weight, and discharged her.

She returned a year later, no lighter, but more breathless. Her CXR showed her lungs to be strikingly smaller than the previous year. She was referred for a biopsy, but the surgeon felt she was too high risk. She became house bound, then bed bound, then hospital bound. We eventually discovered that she had Shrinking Lung Syndrome, a very rare entity indeed.

But for every zebra there are ninety-nine horses. So is it reasonable to stop at the simple tests (CXR, spirometry) and discharge stating that the cause if obesity? 99 times out of 100 we’ll probably be right. Or should be pursue a diagnosis in every one? HRCT, V/Q, CPET…

An A&E adage is: You’re only dead once you’re warm and dead.

Should we adopt: You’re only breathless once you’re thin and breathless?

Probably not. Because we’re always looking for the zebra.

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