Sustained High Hear Rate

My training runs are often in the 170's, and I have a hard time keeping the HR lower than that without losing form.  When I race, I generally average 180 on the nose - it's kinda creepy, actually.  I've seen a max of 196. 

The one thing I've noticed (and I'm sure this isn't rocket science, but I finally put two and two together)... is that the more I train at those high heart rates, the more susceptible I am to injury.  I'm working on getting rid of a calf injury that happened as a result of training too long at too hard an intensity.  Once I heal up, I'll try to return to running at a lower intensity.  Not sure if this is an issue for you...

General injuries have not been an issue for me.  Had some shin splints last year but I believe that to be a combination of too many miles on the shoes and maybe ramping up mileage too fast.  Been conscious of both those factors this year and all is well so far.

Out of curiousity I wore my HRM around the house last night.  Sitting upright and doing paper work it was in the 50's and 60's and laying in bed reading got as low as 46.  I know I know, we're all different and it doesn't mean much, but I wanted to confirm that my resting hr was in the range of a typical fit 31 year old, and I'm guessing it is.

Company here.  I regularly hit and sustain HR in the 180s even on my slow run workouts (10 plus minute miles).  My resting HR is also in the low 40s. 

This bothered me so much that I finally went to the doctor who basically told me not to worry about it unless my chest hurt or the beat became irregular.