As to the spike/errant reading: The graph is a Distance graph. If I had placed it on the Time oriented axis, it would have shown that it was 5 minutes before my bpm was below 190. So, I suspect this is an accurate reading.
Indysteel: Yes, it was Boltinghouse Road. An article last week in the local paper featured one guy who did it 14 times in one hour last week. Eek
Deanna: No traffic lights...a very rural area.
Interestingly as to my level of exhaustion approaching the hill, I road down the hill before turning around and riding up. The downhill was exhausting and made every muscle ache. The road was rough, so I had to ride the brakes all the way down. I was braking hard the entire way and couldn't slow to less than 15 mph. Now that I know where it is, I'll come at it from the opposite direction next time and see if that helps.