Chapter Text
“She was given extensive training in the covert arts, and then her physiology was altered, drastically slowing her heart, which turned her skin cold and blue and numbed her ability to experience human emotion.”
Blood pressure control in humans is a subject of intense study, and one which there is still much to be learned. In general words, it may be defined as the strength the blood pushes against the walls of its vessels. As rule of thumb, three things have great effect on blood pressure: the volume of blood in circulation, the peripheral vascular resistance and the cardiac output.
The volume of blood is rather self-explanatory: more blood equals more pressure. One may visualize this by imagining the vessels as pipes: the more water you have, the more water push against the tube. Volume of blood in turn has a complex regulation of which the kidneys are the main agent, and will therefore be focused on later.
Peripheral vascular resistance on the other hand is fundamentally a property of the circulatory system, and can be defined as the resistance blood must overcome to flow. Things to keep in mind here are that humans have two main types of vessels: arteries and veins. Blood flows from arteries of decreasing sides to capillaries, wherein exchanges may occur.
This means that large vessels with very thick walls come out of the heart and get increasingly smaller as they go to the tissues, until their walls are thin enough that nutrients may pass. Then they return to the heart through veins that are increasingly large. Veins and arteries vary greatly in composition; arteries have walls that are much more muscular and elastic.
What this means is that arteries are very capable of contraction – they may squeeze so that less blood passes whenever necessary, and even squeezes themselves shut. This is particularly important when you keep in mind that humans have in fact more vessels than the blood can fill at one time. Imagine a system of pipes: we have more pipes than water to fill them, and if we want water to get anywhere, then some pipes have to be opened and closed as needed.
Arteries are the main agent of this control, and not the large arteries such as the Aorta, but rather its tiny terminal branches, called arterioles. Some of you may be familiar to the functioning of circuits in parallel and series – here, the arterioles behave like the former.
It might be counter-intuitive to think this at first, but keep in mind we have few truly large vessels and millions of arterioles. Peripheral vascular resistance is peripheral precisely because of that: the terminal vessels and not the central, large arteries are the ones responsible for it.
Effectively, what this implies is that the second big agent on blood pressure control is whether the tiny arteries in your body are closed or open, and if open, how much. Your body will decide this based on how much nutrition your cells need.
Cardiac output is the third big factor to play a role in blood pressure control, and the one where supposedly the modifications were made. It is not the brain but the heart itself who decides how fast it will beat. Heart cells are muscular cells that have a property that we call “self-excitability”. In simple words, it means that while your usual muscular cell needs to be stimulated to contract, heart cells will do it on their own.
This doesn’t mean that they can’t be stimulated; they are in fact under constant electrical impulse to keep them on track. And while each individual cell can and will contract on their own pace if you just let them there, they work in a manner that they will follow the fastest impulse around. It’s like a bunch of runners: they’ll follow the guy who’s on the lead, regardless of how fast he is. If that guy drops down for some reason, then they’ll start following the second fastest guy.
And who are the fast guys here? Well, we have the Sinoatrial Node, who goes at about 70 beats per minute. Then, we have the Atrioventricular Node, who goes at about 50 beats. The Purkinje fibers come last, at between 25 and 40 beats per minute. So by default, if left to its own devices, the heart will beat at a steady 70.
How do you slow that down? Here’s where the Vagus nerve comes in. The Vagus is a buddy who comes out of the brain stem and he’s responsible for regulating a lot of things, including the heart rhythm. Your brain gets feedback from various receptors around the body about the blood pressure, and if it needs to drop, then it sends a signal of “slow the eff down” through the Vagus.
Therefore, we have two possible reasons that Widowmaker’s heart beats so slow: either the natural pacemakers are down to the Purkinje fibers only, or the Vagus nerve is hyperstimulated.
Of the two, if I were Talon, I’d definitely go with the later, merely because it’s much safer. Stimulating the Vagus through electrical impulse is relatively simple; breaking down the SA and AV nodes, on the other hand, is much riskier. If it goes wrong, you may cause what we call a fibrillation: each muscle cell contracts whenever it wants, and if they’re out of synch, the heart does a thing like a seizure and it doesn’t pump blood at all.
As a curiosity, this is the very reason we shock people: to stop their heart so it can pick up a pace again. A common Hollywood misconception is that we shock people when the ECG does a flat line and goes “beep”. Flat lines are not shockable. A flat line means a still heart, and what the defibrillator does is precisely…stop the heart. If you shock a flat line, you’re only cooking that person’s insides.
Adaptations. Consequences.
So we have this real complex system focused solely on keeping your blood pressure all right. If you artificially slow down your heart, does your body go “okay”? Hell no. It adapts. Let’s go back to that bit in which I tell you that one of the determiners of blood pressure is cardiac output. And what exactly would that be? Well here goes a formula:
Cardiac Output = Heart Rate x Stroke Volume
Stroke Volume, in turn, is the amount of blood ejected per beat. Basically, “how much blood flows though you equals how fast your heart beats times how much blood gets out per beat”. I’m not going to get into more horrifying formulas, but the idea here is that if your heart beats slower, there are things it can do to compensate, such as beating stronger to eject more blood.
If it’s beating stronger, it tends to go hyperthrophic and grow. You know how your muscles get ripped when you go to the gym? The heart does that, too. The good news here is that this change is reversible if the body conditions are normalized.
Remember I told you how there are three big things affecting blood pressure? Well, there are other things your body can do if it drops drastically – it can mess up with the other two factors as well. Your kidneys will start retaining water so blood volume may increase, and – this is important – your peripheral vascular resistance rises.
This means the tiny arteries start closing up real quick so that the pressure rises. Your body does this strategically though: it prioritizes important organs. You know how when someone gets frostbite, the tips of the fingers are the first ones to go? The same principle applies here. Extremities close up first and what you get as a consequence is cyanosis.
Also known as, going blue.
And this, ladies and gentlemen, is why she’s that nice shade of purple.
Cyanosis happens because oxygen rich blood is red, but oxygen poor blood is blue. When you squeeze the tiny arteries of your body, you lower the amount of blood going through them, and so this blood that is still loses oxygen and goes blue. In real life, it’s not as uniform as a neatly purple lady. Mostly, you’d get a very pale lady with blue lips and fingertips. The farther from the heart and the least essential for life, the bluest.
What Widowmaker being blue tells me is that her compensation mechanisms are not working or have been tampered with. I can see the use of that, if I were a Talon operative: she’d be harder to detect on heat scans, for instance. However, for her to be functional with a blood pressure that low, we’d need some serious changes. How can it be possible? Well, consider this:
Look at that picture for a moment. While you’re sitting nicely in your chair reading this, about 15% of your blood is going to your brain and 25% is going to your intestines. When you’re having heavy exercise, on the other hand, as much as 85% of your blood is going to the muscles.
This goes to show you how much your body is able of adapting and directing the blood flow where it’s needed. Now consider the body in its entirety. Where can Widowmaker lose blood and still keep herself working? Not the brain, of course, and not the muscles either – she needs that to work.
The intestines, on the other hand, provide a promising opportunity. They take about 25% of your blood at rest, but that can be more after you just ate – and that’s why you get sleepy after lunch, the blood is off your brain and down your belly. This is also the reason we tell kids not to swim after lunch: blood is down your tummy and if it’s suddenly requested at your muscles, it will at the very least make you want to throw up.
The way I’d have Widowmaker’s low blood pressure biologically work, then, is that the blood from her gastrointestinal system is pretty much null. Translating that into simple words: she doesn’t eat. She can’t eat. Eating would literally kill her, because her body can’t afford the blood flow to the intestines. She’d live on parenteral nutrition: injections with the nutrients she needs, already broken down to their smallest building blocks – glucose, amino acids, nucleotides.
That makes for interesting character dynamics, of course. It always struck me as odd that her relationship with Talon would be one of loyalty; rather, I tend to see it as one of dependency. She can’t leave them, not because she doesn’t want to but because she lacks the physical autonomy to do so. She needs her very specific shots to keep on living because she can’t just escape and have a barbecue, and that, more than anything, is what makes her go back from her missions.
And that closes the circulatory system, I think. Hopefully this was didactic enough for any curious nerds who took the time to read it!