Well I have a sample of 5 rides with that 15 intervals and I have concluded that my cadence did not influence my HR. I tried three different cadences during 3 workouts in different orders. 82-85, 90-92 and 95-98. HR variability was not significant in any of the workouts. Tho I must say somehow with a higher cadence it did tent to rise faster but leveled out at about the same. This did influence the results in the way you should expect. That being that the average HR did go up a bit. But after taking out ramp up part the HR in all intervals was the same with a standard deviation of only 1. No significant correlation between cadence and HR was found for me in this test data. The power difference was like 97% of the HR variance in SPSS.
And yes I really did throw in the data in SPSS to find what really caused this.
I almost never use the licence for school so I thought might as well try.