Okay, something is really wrong here. 65-70-80-85 might be your RESTING heart-rate, but certainly not an HR while exercising. My hunch is that you have the setting not on actual HR, but instead HR% It's taking your info and figuring at what % of your max-HR you are working. As example, if you are 40 you take 220-40 (your age) and that's your maximum HR. Ideally you don't want to exceed 80% your max-HR. My HR-watch shows actualy HR and then if you push the button it then shows HR%....bet you're seeing your HR%, which would also explain the jumps of 5% increments!
Get a good HR-monitor. Mine is made by Polar and it also counts calories, which is fun. A good monitor is solid, shows you what's up and it's a valuable training tool so you can guage how hard you're working: it's just like a car's tachometer. Get one, use it. When I'm on my bike, I can usually guess within +/- 2bpm my HR.
Okay...first-off, the human heart probably can't do 245...that number is inconceivable; it was an error! I've had that too. Before you put-on your chest-strap, be sure to thoroughly moisten the contact pads so that you get proper conductivity. You also want to hold the watch close to the chest-strap so they get a solid sync. Polar is darn good stuff, no reason it shouldn't work bang-on accurate. If you are near a microwave or other transmitting devices, it can screw with the numbers too.
When you peddle, your rpm is referred to as cadence. A good cadence is between 60-80 and it's not uncommon to do some sprints as high as 110 or even higher. An rpm of "17" makes no sense, perhaps that was a resistance level or something?
There's nothing wrong with 30 minutes....it's about 10 minutes past the amount of time it takes to bust through the sugars in your blood and start some fat-burning. I'd certainly shoot for 45 minutes or even an hour. You don't have to work like you're in a race. In fact, the slower you go, the greater % of your utilized fuel is actually fat, BUT you'll still burn more overall fat at higher intensities AND greater intensities also spurs metabolism and keeps things revved-up after your done with the exercise. Mix it up, but when you start to fade, just slow it down and keep on going. Use music, a small tv or whatever you need to get you through the routine. When you're done, you should be lathered in perspiration and dripping. Drink water while you exercise too.
Given your family history, DEFINITELY stay close with your doctor. Have your cholesterol checked regularly. As it turns-out, when you die you lose EVERYTHING....so treat your life as the most important thing you have. Cardio is an amazing tool at drastically reducing both cholesterol and the potential of having heart-disease. My triglycerides were crazy-high and my cholesterol bad...with exercise and proper diet, everything fell into place and I don't need meds now!
I won't get too detailed with a proper diet, but for the most part it involves whole carbs, lean protein, vegetables, healthy oils (EFA's, fish oil, etc) no fried foods, low salt, low refined sugar...and all the stuff you can read about with most solid diets. Keeping your weight down, exercising, weight-training, proper sleep, a good vitamin supplement.....there ya go!
