Wednesday, November 4, 2015

Measuring REM Indirectly

REM (or Rapid Eye Movement) sleep is not only when you dream but repair as well. If you don't get your REM sleep, overall health can suffer. I'm concerned about this because I use a CPAP machine. Does it prevent me, for example, for getting enough REM. I've puzzled over this from the time I started using my CPAP machine.

The "direct" measurement of REM is by detecting the electrical patterns in the brain during rapid eye movements. This done in sleep studies and requires hooking up a lot of equipment and being monitored overnight. I vividly remember doing this because of the discomfort I experienced being hooked up in that way. Here is what Medline says about polysomnography. A bit of a hassle.

But suppose you didn't have to do anything? Except wearing your watch to bed. Then waking up the next morning to view a graph of your previous night's sleep states, including REM. The new Basis Peak does this indirectly, using heart rate, skin temperature, and algorithms that they have built into their watch.

REM sleep is the light blue at the top, running about 25% total sleep time. Light sleep is below it, followed by Deep sleep in the darker green. This is a typical night and typical proportions. I am getting enough REM, but I'm making it a point to get at least 8 hours a night, which means going to bed a little earlier than I normally do.

The identification of REM sleep is tricky. Some CPAPers believe they can tease REM sleep out of the CPAP data. I'm inclined to believe they can, but I can't do it myself at this point, but I do have the Basis data, which is based on algorithms which correlate with polysomnography data just as closely as Polar's OwnIndex is correlated with actual VO2 Max studies, or as closely as Benno Fricke's preference data predictions correlated with actual SAT results. Seems like magic, but isn't.

VO2Max: Indirect Measurement

Imagine that you are on a treadmill working hard, being pushed to the limit in fact. Not only that, but you have a face-mask and air-tube hookup so that all of the gases going through your lungs are being measured. When you are about ready to conk out, you hear the welcome, "Okay, you can stop." This is how to determine one's VO2 Max directly.

It is both costly and invasive. At least, I wouldn't do it if I didn't have to. But it is the gold standard for determining fitness. The higher the score, the more fit you are. A top athlete may have a VO2 Max in the 70's or even 80's Lance Armstrong sported one of 85. Miguel Indurain may have had one as high as 95. A very fit 70 year old male would have one in the 40's, as would an average-age male of average fitness.

Okay, now suppose you could get the same result by lying on a bed for five minutes relaxing. The same result! (Okay, maybe a couple of percent one way or the other. At my age, I'm not competing on my bike) Wouldn't it be a no brainer?

Well, it is possible. In fact there are several such indirect measurements. But I was intrigued by Polar's "OwnIndex" which is their term for their indirect measurement of VO2 Max. Polar uses the same units so 45 VO2 Max units are the same as 45 OwnIndex points. For a discussion of the units see Wiki's article here.

Here is Polar's description of how to perform the test and (below) a table for interpreting the results. Here are the reliability results offered by Polar. In particular,

"Validity of a test means that the test measures what it is supposed to measure and not something else. The Polar Fitness Test was originally developed on 305 healthy Finnish men and women in a study, where VO2max prediction was developed using artificial neural network analysis. The correlation coefficient between the laboratory measured VO2max and the neural network prediction value was 0.97 and the mean error in the VO2max prediction was 6.5 % which is good compared to any other predictive tests of VO2max."

I'm partial to Polar's OwnIndex because it takes into account HRV (Heart Rate Variability) as one of the predicting factors. But there are a variety of indirect VO2 Max predictors, as it turns out.

One of them (use this link) has a predictor which uses only your resting heart rate! I've tried it and it is not too bad. Polar shows my OwnIndex as of today as 41. The first test on this site returns 36 for me. 1/3 of my current heart rate of 66 is 22. Enter that and 36 is returned. But other factors such as age, weight, HRV or previous level of aerobic activity are obviously not taken into account, so I would go with Polar's. (Aside from the fact that is is higher and therefore better.)

Others from that site use more exercise-intensive tests. The second has you walk a mile, then key in your age, weight, time and pulse rate. At some point I will try this one and compare it to Polar's.

There is a 3-minute step test, but you need to find 16.5 in steps. I'd bet that you could do this on a StairMaster

BTW the site has expanded VO2 Max Fitness tables as well. (Polar doesn't include 70 year olds on the tables I've seen.). Click here to view the expanded tables.

With a score of 41, I'm right on the cusp between "Excellent" and "Superior" for males between 70-79. Or, looking at it another way, with a score of 41, I have a comparable VO2 Max to men 50-59 in "Good" condition (38-42). Or 20 years younger.

Anyway, I'd like to think so. Unless and until getting on a treadmill to do a direct VO2 Max test,  don't hold your breath!

Three Indirect Measures of Important Things

In this and the next postings I'm going to identify three important things that can be known about oneself which can be measured indirectly. If measured directly, there can be considerable hassle, as in the case of measuring one's O2 Max, a key fitness indicator, or in the case of REM sleep, where EEG leads need to be placed on your scalp.

Some might wonder about a direct measurement of intelligence. There is probably no "magic bullet" to do this. That's why we have intelligence tests and even aptitude tests which purport to give some indication of brain power. But what if there were a way to predict performance on an aptitude test, say the verbal part of the Scholastic Aptitude Test (SAT) not by answering questions about difficult paragraphs, but on the basis of what you prefer; in effect, on the basis of a preference test. It would seem no cognitive test is being given (nor is it), yet this preference test can predict results on aptitude tests.

That's what triggered an interest, many years ago when I was a college freshman at the University of Michigan. I had just answered a series of preference questions (Agree or disagree: "I like cooked carrots rather than raw carrots," or "My stools are black and tarry.") These questions went on seemingly forever (actually, there were only 396 or them), but on the basis of these preferences, it was possible to predict my verbal SAT score almost exactly. I suspect that they could do the same with the math part as well. And maybe they did, but I to remember the verbal part. I was quite intrigued by this.

I had just taken what was affectionately known as Benno G. Fricke"s "Raw Carrots" test, which seems magical, indeed, because it could predict skills and aptitudes which would seem to have nothing to do with the chosen preferences. (I notice that Dr. Fricke was defending his 396 question test as late at 1975 in this Michigan Daily article.)

Just how this feat was accomplished I leave to colleagues far more versed in statistics than I am. But the basic idea is simple enough: you run correlations between student responses to the preference questions and what the same student got on his SAT test. (Michigan had all of this data, and the willingness to crunch it before computers went big league.)

Patterns would emerge. Perhaps on a subset of the preference questions. It might have worked this way: a set of responses to the 396 questions would emerge that correlated with top performance on the skill or aptitude test; another set with a less stellar performance, and so on. Within the grouping (all college freshmen), stable correspondences could be found. The test would not work, for example, on a random set of the US populations - I would think.)

So within this population, the predictions about aptitude, based simple on preference, would work and would seem magical.

The utility of the preference test does not matter. Some might say, you have the aptitude test results. What do you need the "predictor" tests for?  Good question. What if someone didn't have a SAT score. No problem. Fill it in with a really good estimate. Or perhaps, just perhaps, it would be interesting to see whether the preference test could predict skills in artistic perception or spatial perception, say in Gardener's 16 "intelligences. But this is for another time. For the present, note the ability to predict SAT scores indirectly.)

Okay. Enough about raw carrots. Now to the first of two measures that are important in assessing health: the indirect O2Max measure and the indirect REM measure.

Tuesday, November 3, 2015

Five Years Watching: Status Report

I began this Blog early in 2010, so a five-year "Snapshot" is in order.

My lipid profile remains good, with borderline "low" HDL readings. Exercise is good, with a recent 44 on Polar's OwnIndex, which correlates very well with the O2Max test, the gold standard in aerobic fitness.

This result puts me in the top category for those in the 60-65 age-range. At 74 I would think this is a good reading, but they haven't included us oldsters in their table.

I have also added the Basis Peak to my collection of health gadgets. More about this later, but it can track REM sleep. Preliminary results are excellent with on-target REM results.

Weight, however, remains an issue. It is steady at about 204 without clothes. In recent years, I've gotten it down to 189, but it creeps back up.

But the "presenting" issue of the past several months has been ferritin. My GP flagged this earlier this year. He was afraid it might indicated hemochromotosis. However, the two genetic tests were negative. At least I didn't have to be "bled" as in the Middle Ages.

But the ferritin is clearly tied into the constellation of factors that caused me to embark on this health project and this blog five years ago. I needed to become more pro-active.

I've now visited a highly-recommended endocrinologist, who has researched my past lab results, interviewed me thoroughly, and has recommended a battery of tests to complete, including another round of VAP tests. I'll also have another heart scan which we can compare to the earlier one done at Orange County, so we can see whether the level of obstruction has been stable. It is even possible that it has been rolled back slightly.  My risk level was "High" in 2010 with a score of 58. See this post.

I am reminded of the issue of whether the risk level remains high even with treatment that reduces cholesterol, etc. The Orange County results implied a 20% chance of heart incident, presumably if untreated. Does it remain at 20% if treated? What are the differences in percentage between treated and untreated cases. I assume my risk remains "High" even if treated. But my GP seemed to disagree. Well, I assume he would, otherwise, what's the point of treatment? I puzzled over this earlier.

So I will head to the labs next week to see what's up. At the five year point, this is a good thing to do. It is ten years since my serious look at my lipids at the time of my prostate procedure. I'll be able to revisit my VAP results, including the "small LDL trait"  that puzzled me first time around. I'll also be able to follow up by doing another calcium heart scan and checking progression. And deal with my diet. Good to be doing this.

Looks like some attention will be paid to my liver too.

I have appointments with my GP and cardiologist upcoming as well.
Stay tuned.