Does Optiflow Nasal High Flow therapy provide positive pressure/PEEP?

Yes.
 
 There is a degree of pressure generated by Optiflow NHF therapy, but it’s very different from the pressure generated by CPAP:

1. It’s dynamic, not set, and not constant. The level of pressure changes throughout the breath cycle and is affected by several factors, e.g., size of cannula prongs, breathing rate, whether the patient is breathing with their mouth opened or closed, i.e., the pressure level can fluctuate significantly.
2. However, research suggests that when all things are treated as equal, NHF generates approximately one cmH₂O of pressure for every 10 liters of flow in adults. That means roughly a pressure level of 6 cmH₂O at the flow rate of 60 L/min.

Ritchie et al. 2011; Parke et al. (Aug) 2011; Groves and Tobin. 2007.