Rick's b.log - entry 2021/06/26

I got vaccinated

I'm actually quite pleased with myself to just "talk" to the camera without the awkward hesitation that introverts get in real life conversations, and uh also um without uh you know like uh hundreds of uh unnecessary like filler words.
I didn't say everything that I wanted to (I omitted to mention that my hatred of needles is quite likely from having one shoved into my spine as a newborn), but, yeah, seven minutes of talking. That's almost a personal record. ☺
The cut for the electronic sphygmomanometer (or "blood pressure monitor" if the long word freaks you out - it's said sfig-moe-mah-nom-itah if case you're interested, or -iterr if you're American) was not because of an error, it's because I decided to add that in afterwards.

Sphygmomanometer

Typically you will see a nurse or doctor wrap an inflatable cuff around the upper arm and put the sound capturing end of a stethascope inside. The usual portable sort of pressure monitor uses a round dial, not unlike a barometer, and like a barometer it measures the pressure of the air in the cuff, and also like a barometer it requires periodic calibration.
The idea is to listen to the brachial artery. It's a major blood vessel in the upper arm. The arm is squeezed with the cuff to cut off the blood supply through this artery. Air is slowly released from the cuff, and at a certain point there will be a sort of whoosing sound as blood begins to squirt through the compressed artery. This is your systolic blood pressure (maximum during a heartbeat). Air is continually released from the cuff until the sounds can no longer be heard. This is your diastolic pressure (the minimum sustained pressure between two heartbeats). The measurements are given in millimeters of mercury over the ambient air pressure.
A normal resting blood pressure is quoted at 120 over 80, which is usually written as "120/80" and may be suffixed "mmHg" which just means millimeters of mercury.
Above 140/90 and we're getting into degrees of hypertension. The higher the blood pressure, the higher the risk of cardiovascular problems.
Interestingly, the blood pressure follows rhythms and is typically highest the early morning and the evening (uh... when I did both of mine!) and lowest at night. It also changes depending on a wide variety of factors - tiredness, stress, emotion, food, alcohol/drugs, gender, age, amount of recent physical exercise, etc etc. For that reason, a single unexpected measurement shouldn't necessarily be cause for concern. You're late, you one-shot your coffee on the way out, that bloody white van man, why is the carpark so full? Grrr! Rage! Anger!
On the other hand, repeated such readings indicate either you need to lay off the coffee and chill the hell out, or there's a medical problem that needs seen to.

Electronic sphygmomanometers work using a different method. Rather than listening (which is always subject to error due to ambient noise), they use a peizoelectric transducer connected to the pressurised chamber, that is to say, a device that gives small electric currents when flexed just like the ceramic needles of many of the cheaper record players. These devices are a lot less reliable than medical grade sphygmomanometers (and can easily be 5-15mm out). Sadly, with the widespread banning of mercury, even bringing your domestic sphygmomanometer to a doctor and comparing its readings against those performed by your doctor is not an absolute - if he or she is using an aneroid sphygmomanometer, when was the last time it was calibrated?
As you can see, something as simple as measuring blood pressure is not as easy as you would think. However there is value in keeping an eye on your own pressure, even if the readings of your device are slightly off, as one would expect them to be reasonably consistently incorrect.

My device uses an unknown JL SoC (looks like it says AC152QD40522 - wouldn't surprise me if it wasn't a Cortex-Msomething core in there) connected to a serial flash memory device with 16KiB capacity (for storing previous readings), a can crystal (I wonder what frequency, it wasn't marked), and it provides Bluetooth interfacing using an ARM powered generic Bluetooth module.

The circuit board.

The mechanics.

The device incorporates various safety features. It aborted pumping after about ten seconds when not attached to anything. It did likewise when I put it on my leg. So clearly, as it is pumping, it is also trying to detect a pulse or something. I wasn't able to fool it by tapping the cuff to mimic my heatbeat. Looking at the app, it looks like it pumps up to about 160mmHg.

Interestingly, it works when the cuff is wrapped around my wrist. It seems the main thing that affects the readings is how tightly the cuff is secured.

My blood pressure.

Why injections are in the arm muscle

Not having the precious red juice come out is definitely a benefit, but that's not why vaccines are injected into muscle.

The actual reason is partly because you want a controlled release into the body (rather than just having it distributed everywhere) and also because the active part of the vaccine is broken down very rapidly so it's important to get it where it can be effective as soon as possible.

But why the arm muscle? Muscles are important because they contain a lot of immune cells (dendritic cells). These cells recognise the viral element (called an antigen) and they begin to stimulate an immune system response, which is essentially your body reacting to a controlled dose of either an inert or related but inactive version of the virus in order that should the real thing present itself into your body, the immune system can kick seven shades out of it...before it does that to you.
That is pretty much it as far as the AstraZeneca, J&J, and usual flu vaccines go.

The mRNA vaccines take an additional step. Instead of containing an antigen, they contain a modified form of the virus RNA. That is to say, a blueprint of how the virus is constructed. More specifically, it is an instruction on how the Covid-19 spike protein is constructed. The spike protein is how the virus is able to attach itself to a host cell in your body, and enter it to begin doing its damage.
Interestingly, while the RNA strands may vary slightly in the different strains of Covid (such as the newer Delta variant), the spike proteins are the same. So if your immune system recognises the spike protein, then it will be able to deal with the virus no matter what variant it actually is.

The immune cells in the muscle pick up the antigen or mRNA and present it to the lymph nodes for processing. The lymph nodes begin the process of creating effective antibodies. And the reason for the muscle comes through again as not only is it an easy pathway to the lymph nodes, but it helps to keep everything localised. You will feel sore (and maybe have swelling) at the injection site, but side-effects aside you shouldn't have anything like, say, your leg swelling up. This could be a possibility if the antigens were injected directly into blood and were thusly spread all around the body (not to mention being a lot less useful as many of them may never make it to the lymph nodes).
But why the muscle in the upper arm? Well, basically there are a number of lymph nodes just under the armpit, so injecting into the upper arm means the antigen (or mRNA) doesn't have far to go. The less distance, the better condition it will be in, and the more effective the body's immune response.

Finally, muscle tissue can also act as a buffer, meaning that although some of the antigens in the muscle will become inactive, others will still remain viable so they can be transferred up to the lymph nodes over a span of time, rather than dumping the lot in one go. This provides the body with a longer lasting training session, which allows for a better eventual immune response.
Having your arm be sore and red for a few days, and maybe some minor lymph node swelling... these are good things. They are indications that your immune system is doing what it needs to do.

This whole process relies upon an important facet of the immune system - that it has memory. That it can learn (from controlled vaccinations) how to combat certain types of virus, and then recall that learning should the virus itself turn up in the body.

Why two doses of some vaccines? While the first dose does provide the body with a chance to deal with the virus, it is a fairly weak response. It is the process of getting the immune system going. By providing a time delay and then injecting the same thing again, the immune system no longer treats it as an unknown element. It now recognises this as something nasty and is able to deal with it, but at the same time boost its own behaviour in response (this is partly why side effects are more prominent with the second dose, your body has a much stronger reaction the second time around).

The waiting time between doses is partly due to politics, partly due to distribution, and partly due to necessity. Moderna, for example, recommend 28 days between doses. Pfizer-BioNTech recommend 21 days. My next vaccination will be 42 days after my first. This is likely to allow a much larger number of people to be given their first dose. The CDC have given guidance that it is permissible to give second doses up to six weeks later, and that's exactly what France appears to be doing here, although there is - as yet - no data on whether or not this delay has an impact on the effectiveness of the vaccination.

It is necessary to have at least two weeks to allow the immune system to work its magic. And, likewise, you shouldn't consider yourself to be in any way Covid-proof until at least two weeks after your second dose. That's not to say the first dose is useless, a Pfizer study suggests that the effectiveness of the vaccine after 15 days (and a single dose) ws 89-91%.
With Moderna, the effectiveness appears to be around 50% within the first 14 days, rising to around 92% afterwards.

After the second dose, both of the mRNA vaccines appear to be in the mid-90s after 14 days. Now, a mere hop from the low 90s to the mid 90s might make it seem as if the second dose isn't really necessary, and this has been discussed a lot. The current thinking is that omitting the second dose could affect immune responsiveness, which could lead to the creation of more variants if an unsuccesfully vaccinated person catches the virus, and the virus is able to pick up something from the immune response that might make it able to evade current vaccination.
This is, actually, a great problem with antibiotics and part of why doctors these days are very reluctant to deal out antibiotics. The amounts given in the past, and the amounts excreted from the body after use and ending up in water supplies and the like, has helped teach bacteria how to evade them. A well known example is MRSA (Methicillin-resitant Staphylococcus aureus) which is a type of staph-infection. It began being resistant to Methicillin, as its name implies, though it is now known to be resistant to cephalosporin and all forms of penicillin.
The same things can happen with viri. It's part of why there's a yearly flu injection. The vaccination you may have had for last year's flu might be useless for the one coming this year.
Indeed, it may be that we'll need a yearly Covid vaccination too? It's not know at this time if it will die out as more people become vaccinated, or if it's something we'll just have to accept and live with.

ESP32-CAM failure

I thought, at first, that the camera module had packed up. Maybe too much sunlight or something? Trying the camera module in the other ESP device showed that it was working just fine.
I noticed, as I was switching the camera modules, that the metal shielding was pretty hot to the touch. So something inside the ESP chip has failed which has partially broken the ability to retrieve images from the camera (all the diagnostics on the serial port indicate that it is working), until the thing heats up enough that it completely fails.

I'm reading seventy degrees!

Not sure what, how, or why... but that's six euros and nine centimes in the bin.
Oh well, that's less than a Big Mac meal.

Moral of the story - overworked chip stuffed into a metal enclosure - gotta think about cooling!

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Gavin Wraith, 26th June 2021, 18:47

Usual Latin pomposity: the plural of virus is not viri but virus (with a long u - wiroose). The word viri means men.

Rick, 26th June 2021, 20:22

But "virii" and "viruses" and... ;)

Steve Drain, 26th June 2021, 22:34

It is a risk to challenge Gavin, but the Latin word 'virus' is very rare and has never been seen in the plural. It might well be translated as 'stench', which is an uncountable noun in English. The adopted word 'virus' in English has come to mean a discrete particle and is countable, so its only reasonable plural is 'viruses'. ;-)

VinceH, 27th June 2021, 00:10

If my BP monitor had a voice or played music, I'd probably introduce it to a hammer. I use it every morning and evening, so I wouldn't want it to *contribute* to the problem! 8)

Gavin Wraith, 27th June 2021, 12:49

Yes, I'd go for viruses. As Steve says, it is a rare word in Latin, but unfortunately all too common in English.  Just done a Lateral Flow test but it was negative - an asymptomatic neighbour has just tested positive.

Rick, 27th June 2021, 13:09

"Viri" might be wrong for those who actually know a little bit of Latin, but I prefer it to "viruses" that just seems somehow unsettling.    As to which is correct, Wiki has a lot to say: https://en.wikipedia.org/wiki/Plural_form_of_words_ending_in_-us#Virus

Rick, 27th June 2021, 13:13

I had what felt like a raging cold last night. Headaches, gunked up sinus, and extremely tired.  I'm guessing this is a side effect of the vaccination.  Thankfully it seems better today, so my immune system is dealing with things...  Luckily I didn't have a fever with it all well.

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