My lungs hate me

So I hit the track today for the first real speed work I've done in ages. Just a nice simple 6 x 440 which I rounded down to 6 x 400 since I was on a minuscule 200m track. Went through a decent warm-up and stretch, then hit the sprints, and man did they hurt! The sprints were supposed to be at 5k pace, but I don't know what my 5k pace is just yet. I can tell you that I'd like my 5k pace to be about 5:30 miles (~1:22 400s), so that's what I aimed for. With about even rest on each sprint I went:

1:13.1 / 180hr
1:20.2 / 185hr
1:27.3 / 182hr
1:27.9 / ???hr
1:27.6 / 196hr - ?
1:28.5 / 184hr

So an average of 1:24.1, or just off my goal. Man did they hurt! I'm still getting over a major chest cold, but I haven't felt my lungs burn like that in ages. And although I found a good pace for the last four, I don't think I could do that for 5k, at least not yet. Sprints aren't my thing: there is very little muscle on my body to begin with, and I think the vast majority it is made up of slow-twitch fibers. Clearly I need more speed work in general, even if it isn't needed for the marathon goals.

On another note, you'll notice that I had some heart rate monitor problems in the middle there. Polar's plastic straps just don't fit my svelte frame well, so if anyone wants to buy me to buy be their WearLink Coded Transmitter and Belt Set (XS - S), I'd be very appreciative!