Thursday, January 28, 2010

Who pays the piper for arterial stiffness?

General anaesthesia for horses is a remarkably high risk procedure. So high risk that most clued up anaesthetists will routine place an arterial catheter for direct measurement of arterial blood pressure, usually using an oscilloscope type display of the wave form, even for "short" procedures. Back in my training days I had the pleasure of many such events and, in those where there was not too much to worry us, my extremely well informed supervisor and I would discuss the applied physiology of keeping 500kg of unspeakably valuable equine alive, asleep and immobile. I remember just one brief comment about the double nature of the systolic pulse peak. Polly's comment was that it was something to do with a pressure wave reflection from the hind limbs (we usually had the catheter in the facial artery, up at the front end, as far away from the surgeons as we could get. If you've never been there...

Anyway. The heart contracts, there is a rise of pressure in the peripheral arteries to the systolic peak followed by a decay down to the diastolic plateau before the next beat. Except it's not smooth. A few milliseconds after the systolic peak, part way down the fall to diastole, there is a second peak. Who ordered that?

It turns out that this second peak really is due to a reflected pressure wave. The systolic pressure wave travels directly from the heart to the facial or the radial artery, wherever you have managed to get an arterial line in. The same pressure wave travels off down the aorta until it hits the resistance of the hind legs. Some of the pressure wave carries on, some is reflected back. The reflected portion goes back up the aorta in the wrong direction before spreading out through the arteries at the front end of the patient, those few milliseconds later.

If all horses where exactly the same size the time between the systolic pulse and the second peak would always be the same if the speed of travel of the pressure wave was always the same.

It's not. The speed of the wave is influenced by the stiffness of the aorta. The stiffer the aorta, the faster the wave travels and the shorter the time to that second peak. Also, the stiffer the aorta in a human the more likely that person is to die of cardiovascular disease. The two things are associated.

So, in a human, if you correct for height, the time difference between first and second peaks gives you an index of aortic stiffness. This usually worsens with age so you can then give a crude cardiovascular "age" to a person.

There are several methods for getting aortic pulse wave velocity and, luckily, most of them don't involve you having a catheter placed in an artery!

The easiest and most expensive way is to buy one of these machines, which is a commercialisation of the system described here. This is from the paper and the caption is self explanatory:

By an absolute quirk of fate I was put in touch with someone who owned one of these commercial machines. I was invited to play with it and came out with a cardiovascular age of 32 years. I think I was 51 or 52 at the time, already several years in to LC/high saturated fat eating. The girl who owned the machine was in to "healthy" eating plus arginine supplementation for her own CV issues. The CardioCheck gave her a CV age of about 70 years and she was having frequent palpitations. I was polite enough not to ask her chronological age but it was a sight younger than mine!

I lent her Life Without Bread. The palpitations stopped immediately on LC but it took six months to get her CV age down to her chronological age. I guess it's well below that now.

I don't have the equivalent of $3,999 in pounds sterling for a CardioCheck machine. But I do have access to a doppler ultrasound used for the determination of blood pressure in cats and dogs.

You can HEAR the double peak in the doppler arterial flow. You can also sit your computer next to the loud speaker of the doppler, record the sound output, smooth it electronically and actually measure the time between the peak systolic flow and the smaller second peak. Factor in your height and you have an aortic stiffness index.

I'm consistently equivalent to the low 30's in CV age. I've played with other people of my age who also eat LC and they too have a "young" CV system. Normal diet people come out all over the place, some scarily high.

So what?

Well, it's time to look at Bradley and Hunter's latest sugary offering.


EDIT added in response to comments

OK, the formula is simply height in metres divided by time between peaks in seconds. I can't find the graph anywhere on my hard drive so this jpeg is the closest I can come to putting values in to ball park areas.

One 50+ female LC friend has a time between peaks of 320ms and a height of about 1.65m giving an SI of 5.12. That puts her CV age somewhere in her 20s...

I can't convert the Audacity file to anything visual to show you. The estimations are pretty crude but if you check various pulses you get a reasonable idea of a typical waveform.

Relax before you try, be sitting, no crossed legs!



Anya said...

Peter, I own an 'angelsound' device (minidoppler for listening to your unborn baby's hearbeat). We used it for our third baby 2 years ago.
I tried it on my heart and I can distinctly 'hear' the second peak.
Would you mind going into a bit more detail on the methods/calculations you used for this ?

I'm eating Low Carb for 2,5years of which Higher (fresh/wild/animal/quality)fat 1,5 years now and my Cholesterol values have gone up to the point my doctor keeps insisting on statins. I need ammunition for myself and for him then he needs to back-off about statins.

Ed said...

Peter, please help us parse the abstract. They say,

The change in overall systemic arterial stiffness was, however, significantly different between diets (P = 0.04); this reflected a significant decrease in augmentation index following the low-fat diet, compared with a nonsignificant increase within the low-carbohydrate group. CONCLUSIONS: [...] The difference in augmentation index may imply a negative effect of low-carbohydrate diets on vascular risk.

What is the augmentation index? When they say "a negative effect on vascular risk", is that meaning the vascular risk goes down or up? I can't tell if there is a double-negative in that statement or not.

Ed said...

Peter, since you've already done it, could you post a summary of the math? I see that we could use Audacity to look at the sound wave on our computers, and the Angelsound doppler device is around $35 on Amazon.This could be an interesting DIY experiment.

Nigel Kinbrum said...

As an ex-RF Engineer, this article brought back happy(!) memories of using Time Domain Reflectometry equipment to measure where reflections due to mis-matches were occurring in a coaxial cable/RF connector/antenna etc system. It's nice to see the same technique being applied in medicine.

Nigel Kinbrum said...

Have you seen Hunter SJ's latest "sugary offering"?

Session 4: CVD, diabetes and cancer Diet, insulin resistance and diabetes: the right (pro)portions?

"However, based on the results of diabetes prevention trials focusing on lifestyle measures, evidence favours low-fat diets as the preferred approach for weight loss and diabetes prevention."

Laughing too hard is bad for my blood pressure.

zach said...

At this rate you should live to be what-150? That's what Dr. Rosedale says. I hope he's right but personally believe that's a load of bull.

Peter said...

Audacity works fine, the SI is a simple division and there is a graph in the paper of age vs SI I'll edit in to the post as soon as I can...


Robert McLeod said...

The distensibility of arteries is really key to their function. If arteries were a rigid pipe, you would expect the flow rate to go up as a function of radius^2. However with a distensible artery it goes up with radius^4.

So atheroscelerosis is a double whammy. Not only does it reduce the radius, it also tends to result in calcification which makes it more like a rigid pipe.

To be an elite endurance athlete on a carbohydrate-heavy diet, I would think your immune system must be relatively insensitive to wheat and sugars.

Unknown said...

Hmmm... we bought a doppler heart monitor off eBay during the last pregnancy. It does have a 1/8" port for audio capture...

So I guess that all we really need is the timing chart to explain the measurement.

Unknown said...

And to answer a question above: the augmentation index appears to be a calculated factor based on the very same reflection wave being discussed here.

(I guess we shouldn't be too surprised that the linked article is directly on-topic).

eltesoMm said...

Dear Good Dr. Peter, A book recommendation for you. “The Other Brain” by R. Douglas Fields, PhD. It’s about the 85% of the cells in our brains that aren’t neurons, but glial cells. Our brains are fatty. The glia and axons (axons are in the body also, all 100,000 miles of them if stretched out and laid end to end) are fatty fat fat fat fat fat fatty fat-hyperlipidinous. I just got the book. Can’t put it down, except to comment here.

Mavis said...

Hello, Peter. Frequent reader, first time commenter, I think.

Does blood pressure have any relationship to aortic stiffness and so on? Mine is remarkably low. I'm not on a low-carb diet - more of a Weston A. Price-inspired one. Anyhow, my blood pressure, always lowish, has gotten very low since embarking on this. But it's not pathological, my doctor says. What do you think?

Anonymous said...

Completely off topic, but I thought I might share this with you for your thoughts on it:


blogblog said...
This comment has been removed by the author.
blogblog said...

Robert said:
"To be an elite endurance athlete on a carbohydrate-heavy diet, I would think your immune system must be relatively insensitive to wheat and sugars."

Athletes are automatically considered to be insulin dependent diabetics at age 35 by the doping authorities (insulin is slightly anabolic).

Sir Steve Redgrave suffered from diabetes and chronic IBS during his rowing career.

mtflight said...

This is cool stuff. Now you have me curious as to measuring mine.

Ken said...

Informative and encouraging post.

A correction, it's only centenerian women who tend to be of a slight physique.

I do wonder what your 2D:4D is though, if it's pretty low the health of your circulatory system may not be entirely down to diet.

Ken said...
This comment has been removed by the author.
Peter said...

Hi Ken,

My D2:D4 is 0.92 which is, I think, quite favourably below the mean of 0.98 for males.

The subject is interesting as my wife attended a seminar on Wednesday about androgen failure in the development of all sorts of things from hypospadia to low sperm count. Low sperm count was the researcher's main topic. This correlates directly with degree of westernisation in a given country and the effect occurs in the first few weeks of foetal life. In Denmark one in 8 children is born to couples where medical assistance is needed due to low male sperm count. The chap is convinced it is not oestrogens doing it, but doesn't know what is.

For me, born in 1956, I'm lucky to have gotten through early foetal life before andorgenic failure (whatever exactly that means) had become commonplace.

You do have to wonder how much of me being me is a fluke, down to what my mother ate in week 5 of gestation... I've never really felt I personally could take much credit for my academic achievement. If it all comes down to androgens in early foetal life that would fit in well with this viewpoint!


Peter said...

Hi Ed,

I think the next post answers these questions...


Peter said...

Anya, I assume you are female? I didn't realise there was even any correlation between cholesterol and heart disease in women? Why statinate women???


Peter said...

Hi EltesoMm,

Johnny Roughan's PhD suggested consciousness is controlled by potassium fluxes from glial cells. He gave me the papers years ago but they're quite abstruse and I lost the paper copies... The abstracts don't tell you much! Interesting ideas!


Anonymous said...

@Anya: In the movie Fathead ( Sally Fallon (President of the Weston A. Price Foundation) stated that the higher a woman's cholesterol (I think Mary Dan Eades said the same thing, Drs. Eades wrote Protein Power), the longer that woman will live. I don't know the source, but I think statins targeted at women is 100% detrimental.

Peter said...


When I finish with this paper I want to go back to arteriosclerosis, calcification, stable and unstable plaque. But it's slow! And not at all intuitive...

I'm not so sure re athletes. I suspect they suffer for success. Kurt's comments on marathon runners jibe well with blogblog's comments on an elite rower.


Peter said...

Nigel, yes, physics is a very basic science!


Peter said...

Hi Helen,

Probably a normal blood pressure for a non acculturated human is around 120/70 from Paal Røiri's work on the Greenland Eskimo. Similar numbers come from the fish eating Bantu. Range for systolic seems to be +/-20mmHg, less for diastolic.....


Peter said...

Hi Jeromie,

I read Stephan very carefully. I'm waiting to see.... I still avoid fibre but it's hard to get it seriously low if you eat real foods and want some variety. So I'm hedging my bets a bit anyway, by accident!


Mavis said...

Hi Peter,

My blood pressure has been 90/50 and 78/47 at most recent readings, the first with two kids with me, crying.

I guess I was wondering if systolic blood pressure could be a stand-in for the kind of estimate of arterial stiffness you describe here - with less technology involved. And hoping that my low systolic indicates arteries = pretty flex.

It used to be between 100-110 (systolic) in my previous semi-veg incarnation.

ItsTheWooo said...

Totally interesting. Thanks peter.

Peter said...


That's about the values my wife comes out with. I would suspect it is hard to get a BP this low wit a rigid aorta...


Mavis said...

Must be all the butter I'm eating.

Renaud said...

Hi Peter,

I just tried to compute a rough stiffness index, using FreezeFramer (HRV measurement tool) to display my pulse from an earlobe sensor.
Here is what i did, with a screenshot and formula used. Lenghth are in arbitrary unit from my drawing software.

I did multiple measurement, and got SI between 7.5 and 9.

Do you thing this is a corect way of doing it ?

Age estimation is a bit above my real age (42) but i was a smoker until yesterday ;-)
I hope that will help me to track improvement as month goes...

I was eating mainly arround 50-60g carbs for a few months, but recently dit a test with (much) higher carbs for two weeks.

Marc Rouleau said...

Any thoughts on the arterial stiffness measure produced by the Bio Clip Cuff?

Peter said...

Hi Renaud, sorry I missed this, seems a bit late to comment!

Marc, at $125 it seems reasonable. How good it is really depends on the quality of the hardware and software. In principle it should be useful. The previous tool I played with was 30 times the cost... But that was poss 10 years ago and the cost have come way down.