Blood pressure continued

Part two: why do we need such high blood pressure?

So we have seen how blood pressure can be used as an indicator of largely chronic effects, and that it is a very useful measurement to keep track of. But what about the more acute side of medicine? 

I was lucky enough to stay in cardiothoracic critical care in my local hospital for a while as part of a work experience scheme with a consultant anaesthetist (a very underrated speciality, I have decided). While I was there, I noticed that they were measuring blood pressure on almost every patient. None of the people on the ward was there for chronic problems, so why were they bothering to measure the blood pressure? 

The answer is that they needed to see whether the heart was working properly, as almost everyone there had just been in or was about to go into surgery for a heart operation. If the heart is pumping blood around the body, it will push against the outside of the arterial walls, which is what we call blood pressure. If the pressure decreases, it is likely that the heart is not pumping the blood so well, and the patient might need to be looked at in more detail.

But that is a very crude way of getting a very vague answer. What I wanted to know was what the blood pressure actually signified about the heart that the doctors were interested in. When I asked the consultant this, he answered me with another question: why do we need such high blood pressure? I'll admit, I didn't understand the question when he first asked me it. 

My first thought was that some of the organs need high blood pressure, such as the kidneys: in the nephron, blood needs to be at high pressure in order to undergo ultrafiltration. But there are very few bits of the body that are like that, so it doesn't make sense to have the whole system running under unnecessary stress. What could be the advantage of having high pressure in the system? Does it have an advantage in itself? No. The advantage of running any fluid system at high pressure is to make the fluid move fast. That's what really matters: how quickly can the blood transport the necessary nutrients to the organs, and take away the waste products.

Again, I thought I'd got it, that we needed to run at such high pressure in order to move the blood around our body fast enough to work properly. Sadly for me, it turns out that the pressure needed to move the blood around our body is much lower than the average blood pressure. All I'd done was work out the question: why do we have such high blood pressure, when the same blood flow could be achieved with much lower pressure?

Looking at it from a purely physical standpoint, it makes no sense that two different pressures in the same system can provide the same blood flow. Where is the pressure being lost? There must be some kind of resistance that we are artificially providing in order to keep flow lower than its maximum. The pressure could be coming from the organs, or the arteries. We already know that only a few organs need the maximum pressure, so it must be coming from the arteries before the blood reaches the tissue it's going to. That can easily be provided by the muscle layer in the vessels, but I still hadn't worked out why it happened, just how it happened.

Why would the body have adapted to provide more resistance in the vascular system, making more work for the heart? Because it's not a fixed system: the muscles in the arteries can relax, reducing the pressure for various tissues, increasing the flow to those organs. This means when any tissue needs to increase the rate it gets its nutrients, the resistance of the vessels supplying that tissue can drop, which makes the flow spike immediately.

So to answer the question, we need high blood pressure so that blood flow to any part of the body can be increased straight away. That doesn't really explain why they measure blood pressure. That'll be in part three.

GP Work Experience

This is Wallingford Medical practice. It's a building on the side of a small stream in a town just a few miles from a train station which is two stops from my station. To the right of the picture, there's a community hospital, including a maternity ward. My week's work experience was spent mainly in the consultation rooms, but I did get to see the hospital too; thanks to everyone's hospitality, I managed to see pretty much everything.

Work starts early in GP practices; I knew that already in theory, but the reality is coffee and morning discipline. Which I actually enjoyed - getting up to do something you are really looking forward to is a great feeling.

One difference between salary doctors and partners is that partners have to work the hours to finish the work, and salary doctors only have to work the hours they're paid. I was shadowing a partner, so I was in bright and early, and was allowed to sit in on the practice meeting. Practice meetings are great at showing the business side of the general practice, something that is not so prevalent in other areas of the NHS, and it gave me an insight into how everyone worked as a team, despite spending most of their days shut off from each other in their rooms. The other thing I gleaned from the meetings was that no matter how many years you've been a doctor, there's always more to learn. In the practice meeting, two doctors were asking for study leave to go on different courses to learn about more in fields they're interested in, and in another meeting, a consultant physiotherapist came and talked about what she did and how GPs can help (when to refer, what to expect etc.).

Each day is split into morning surgery, then coffee, then visits, then lunch (meetings and paperwork), then afternoon surgery. There is also ward rounds of the hospital (which I got to shadow on the last day) in the morning, to check up on patients in the wards and reissue any drugs that needed a new prescription for.

It's hard to pick a favourite part of GP work, because each patient is so different that it's difficult to generalise. I'll probably post one or two of the cases I thought were the most interesting as individual blog posts, but the thing I noticed the most, in visits and in consultations, and in the hospital, was how much the atmosphere was moulded around the patient. Every person was different - an excited visit from an expecting young mum, a calm talk about testicles with a nervous teenage boy, a veeeerryy sloowww conversation with a depressed woman -  I could go on. 

The relationship with the doctor is also different each time, and that's one of the challenges of general practice, I think, because you don't only have to have gone through umpteen years of medical training and have the responsibility of looking after all of your patients, but also you have to be able to communicate with whoever walks through that door. Communication is different to making friends with, as well. In a lot of cases, it would be easy to let the patient tell you what they think is wrong with them and exactly what drugs they want, write a prescription, and let them go. But often, that's not what's needed, and it can be hard to tell someone that they need nothing at all, or a different treatment, or tests. Cooperation is important, and the needs of the patient come first, but a confident, misinformed person could be more of a danger to themselves than the disease they have.

I'll post more about GP work later, but this post is long enough. Bite sized work experience!