Not too up on HRV but bradycardia is a common thing in P.D.
My average pulse rate is somewhere around between 42 and 50 beats per minute and I'm no athlete!
Been told it's all part of a day in the shoes of a parky ....well not exactly but I like that line Vicki!
It's related to our autonomic nervous system not functioning as it should
Cheers,
Lee