On a long stressed sigh

[Xinfu]

p.81 'Oh,' on a long stressed sigh. 'Oh, thank you. I do [...]'

What does on mean?

[Rusty]

The word 'oh' is accompanied by a long stressed sigh. I picture a sigh of relief and someone saying 'oh' at the same time.

[Xinfu]

Excellent answer. Thank you.