I don't know what effect the BP meds would have, but totally agree that you should not rely on a chart to determine your functional threshold HR or power. Google those terms to find different ways to calculate your theoretical maximum HR and your threshold level. One of the best ways to calculate threshold HR is to ride a long uphill ride at full effort and see what your average heart rate is for that hour. You can also pay to have it calculated in a fitness lab setting. These numbers will give you the parameters within which to train. When I first trained I used a chart and it calculated my threshold HR way too low. I had pretty dismal results. Turns out I am a statistical outlier. I'm 56 and my HR threshold is about 171 and my max is just north of 196 (that's the highest I've seen on my computer). A "standard" chart would normally put my maximum at between 164-180 bpm. The other significant part of your story is the amount of weight you have now as compared to your better days in the past. You are almost 20 pounds heavier than you were at your peak form and those pounds totally mess with your strength to weight ratio (watts to kilos)--a ratio that matters the most when you are going uphill. Good luck with your recovery.