Sci is about to embark on what she suspects will be two or three months with very little sleep, due to various personal and professional matters, and of course, blogging matters. And while she was discussing this with some friends, one of them brought up something very interesting:
She said “does anyone else feel COLD when they don’t get sleep?”
And it occurred to me that she was very right. When I haven’t been sleeping enough, I get COLD. I wake up freezing and end up bundling up in various thick, fuzzy sweatshirts and grasping on to mugs of hot coffee (though the coffee, of course, has a dual purpose). And so we started wondering, is this normal or anecdotal?
Being an awesome scientist herself, my friend hit the Pubmed, and a few moments later, she handed me this:
*pauses for a moment to put on fuzzy slippers*
Vaara et al. “The effect of 60-h sleep deprivation on cardiovascular regulation and body temperature”. European Journal of Applied Physiology, 2009.
For this study, the authors were interested to study the effects of sleep deprivation for problems like sustained military operations, and some sports events. Sci also thinks that the following study would have great application among college and graduate students, as she remembers (back when writing a very very important paper) staying up to the point where coffee literally made her sick (don’t try this at home).
Sleep deprivation is obviously not a very good thing, though most people in the US are hypothesized to live under a good degree of it most of the time (especially those of Sci’s acquaintance who are new parents). It has negative effects on cognition, as well as important effects on things like inflammation and the endocrine system ,and Sci has also heard of negative effects on the immune system. What the authors of this study were concerned with, however, was with heart problems (cardiovascular regulation) and with body temperature. The cardiovascular regulation part is important, for those who are both young and old, constant changes due to sleep deprivation could increase the risk of cardiovascular disease, something which most of us obviously do not need.
So for this study, the authors recruited male and female active cadets (they have 17 males and 3 females, I wish they would do this study in an all female population as well, I don’t think they got a big enough sampling) with strictly regimented normal activity and sleep times. They sleep deprived all of them for 60 hours (that’s 2.5 days) of what I’m sure was a rollicking good time. Sci would not want to do this study unless she was getting some hefty compensation. During the time they were sleep deprived, physical activity was restricted to a minimum, but they were still in the military, and so performed tactical stuff, while also being allowed to do things like read, play cards, or watch TV. And they were constantly watched to make sure they wouldn’t fall asleep (one hopes the experimenters were willing to go to great lengths to make sure the people didn’t fall asleep. Doing silly dances, maybe singing karaoke with them til the wee hours…).
During the sleep deprivation time, the scientists took measures of heart rate, blood pressure, and body temperature, as well as heart rate variability tests to look at differences in high frequency and low frequency power, which are supposed to reflect the influence of tone from the vagus, part of the sympathetic nervous system associated with drops in blood pressure and heart rate.
And they got some very pretty graphs.
Above you can see the measures of heart rate (the dashed line is sitting, the solid line is standing) during the three days of the study. You can see that heart rate in all the participants decreased significantly during sleep deprivation (Sci has anecdotally noticed the opposite effect, but suspects it’s due to the vast amounts of caffeine she has imbibed during her sleep deprivation sessions). But the question is whether or not this is due to changes in vagal tone (increased sympathetic involvement which can lower heart rate) or some other factor. So they then show this:
This is high frequency power taken during an active orthostatic test. In an orthostatic test (which you could actually try at home if you really wanted, though I don’t recommend doing it on 60 hours of sleep deprivation), you lay down for 15 min (without falling asleep), and record the pulse. Then stand up, and 15 SECONDS later record the pulse again. It’s usually used to determine if an athlete is overtraining, apparently a large difference between the two is supposed to be indicative, but Sci’s no expert on this topic. It appears here they are using it as a measure of vagal stimulation
And as you can see above that the high frequency power increased drastically over the three days of sleep deprivation, indicating an increase in vagal stimulation which could account for the DECREASE in heart rate seen above. Interestingly, though:
You can see here that blood pressure over the study didn’t change. As vagal stimulation causes decreases in heart rate AND blood pressure, Sci found this a little surprising, but it’s very possible that there are other factors at work keeping the blood pressure up (stress, for example), and other studies have also shown no changes in blood pressure in response to sleep deprivation.
But now we get to the figure that Sci was most interested in:
Here we have measures of body temperature taken over three days, and you can see that body temperature does indeed DROP during sleep deprivation (though circadian rhythms were apparently maintained). The authors hypothesize that this could be due to a stress response, ,and possible reductions in activity of the hypothalamus, a regulatory center of the brain which has strong impacts on both body temperature and heart rate, and which could be responsible for some of the effects.
So it’s true, you do indeed get a little colder (though you can relax, it’s only by half a degree C) as you get sleep deprived. A good reason to get some sleep! Not for Sci, though. Gotta get some work done. No wonder work gives me the chills!
Vaara, J., Kyröläinen, H., Koivu, M., Tulppo, M., & Finni, T. (2008). The effect of 60-h sleep deprivation on cardiovascular regulation and body temperature European Journal of Applied Physiology, 105 (3), 439-444 DOI: 10.1007/s00421-008-0921-5