I just bought my brother a Riva 510. Has anyone else had trouble with choking on the vape with this PV? He's explains it like this: "What's happening is a lot like when you first start smoking. When I inhale my lungs just freeze up and then send me into a coughing fit. I've read tons of forums and tried every technique I can think of. Straight draw, draw into mouth before inhale, bit inhale, little inhale. I dunno what's going on." He is coming off of smoking cigarillos and I thought halo's freedom juice would be a good change over drop. I've been using an eGo T and have had zero problems with coughing or choking. Any input?