In a cystometrogram, LaPlace's law has application at:

Since bladder is hollow viscous, Laplace law is applicable at any volume in the bladder But to be precise, the real applicability of Laplace's law is in phase-Ib Cystometrogram, is pressure volume relationship in urinary bladder. Phase Ia = bladder is filled up to 100ml Phase Ib = bladder is filled up to 100-400ml = Laplace's law is applicable. From 100-400ml | in vol, tension of the bladder wall increases so does the radius, So the pressure remain the same. Beyond that point is Phase II, radius cannot increase fuher but bladder wall tension goes on increasing beyond 400ml thus, pressure increases.