Study group discussion: Single Breath Count test in Guillain Barre syndrome

I was reading about Guillain Barre syndrome and came across single breath count test.

Does any one know what is it / how to perform it?

GBS can cause respiratory paralysis. So you do the breath count test to know the level of respiratory compromise. The exact mechanism.. I am not sure..But you ask the patient to take a breath and count as many numbers he can starting from one.

Is it done to measure inspiration or expiration? They say that inspiration is affected in GBS but I think counting is expiration.. So I am confused.

I haven't read much into it..Can't answer that with confidence.

I tried Googling. No satisfactory answers. Maybe someone else in the group knows!

SBC is measured by asking patients to take a deep breath and count as far as possible in their normal speaking voice without taking another breath. It's measure your fvc (forced volume capacity).
Normal values are 40 to 44.

If the patient can count to 10 on one breath they likely have a forced vital capacity of about 1000 ml, if they can count to 25 then the vital capacity can be estimated at about 2000 ml.

Normal fvc values are 3000 ml to 4000 ml.

FVC is sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.

Meaning SBC value is not just for your inspiration or expiration. But the whole capacity of lung to perform either of the function.

Thank you so much!