Table 2.

Mean (SD) Puff Parameters for Directed and Ad Libitum E-Cigarette-Use Bouts

Condition	Duration, s	Volume, mL	Flow rate, mL/s	IPI, s	Puff number
Mouthpiece
Directed	4.51a (1.55)	124.56a (89.13)	27.78 (19.48)	25.19a (1.55)	9.97 (0.12)
Ad libitum	5.29 (2.08)	148.52 (119.6)	27.47 (22.63)	102.77 (63.07)	62.55 (32.34)
No mouthpiece
Directed	N/A	N/A	N/A	N/A	10
Ad libitum	N/A	N/A	N/A	N/A	62.10 (39.99)

N/A indicates values that were not measured for that particular topography variable and condition.

^aSignificant difference between the directed and ad libitum bouts in the topography condition.