There's only a way to improve your static results...You've to hold your breath, but before it you must do some breathing exercises. First of all you've to do pranayama ventilation but you can search it on google...
To improve your results you can try so: if you can stay 2 minutes (for example) whitout breathing, you can improve your times followed this table:
(I made it by myself and it's subjective)
relax:4 min -- apnoea: 1.40
4 min -- 1.50
4 min -- 2.00
5 min -- 2.05
5 min -- 2.10
5 min -- 2.15
(it's just an example but you may structure you table in base of your times)
P.S.
Sorry for my bad english but how you can think i'm italian

!
P.P.S.
This is just a summary, but if you want more elucidations you can ask...