But we don't have the luxury of measuring this easily and certainly not routinely, so I follow what we know how to measure as long as it's practical.
The same goes for BP at altitude. Can we measure it? Sure. (See the picture below). Is it practical? Probably not, since placing and or wearing a blood pressure cuff in your arm while you are freezing in a tent or while climbing is simply not practical. Wrist monitors are rather inaccurate, so let's forget about using these when we know they generate data that one cannot trust.
|Withings Bluetooth Blood Pressure Monitor|
But let's assume that we had a simple way of measuring blood pressure - as easy as the measurement of heart rate. What would I do with the number?
I think up above 20,000 feet, your blood pressure becomes almost a binary problem. Either you have one, and you are moving along and are conscious, or you are passed out, with a weak pulse, and it's really low. If I see you climbing, that probably means your blood pressure is fine and it will stay so without telling us that other problems are at hand. (Dehydration for instance, will eventually lower your BP, but a much better indicator would be an abnormally high heart rate, a dry tongue, loss of skin turgor, and a recent bout of diarrhea.)
Your BP could be even high due to your exertion, and it won't require any intervention. Of course it could be really high, so high that you spring a leak in one of your cerebral vessels. And if this happens, how can I help you up there by simply measuring your blood pressure?
If your BP is low and you have passed out, knowing the exact number won't really help me up there - unless I am carrying in my backpack the drugs I usually have in the operating room. These will then allow me to pick one from my arsenal of medications in order to help revive you.
In short, just by feeling your pulse, I will know if it's weak (low blood pressure), its rate, and that is probably enough for me to make an accurate assessment as to the causes of your collapse.
In CPR, you learn 3 basic steps to resuscitate somebody: Airway, Breathing, and Circulation. Blood pressure comes in last, and up in the mountain, you should ensure that the climber has a patent airway. You can then administer oxygen knowing that it will reach the climber's lungs. You then need to assess if he/she is breathing in order to get the O2 in and the CO2 out. And finally, you should check the climber's pulse to assess his circulatory status (is the heart pumping blood, and if so, is it able to generate a blood pressure which will move the blood to the O2 starved organs.
In short, just because we can measure something, it does not mean that its useful, and if one is at 24,000 feet, I'm not sure blood pressures are telling me much I can't see clinically.
If you insist on measuring your blood pressure while climbing, WiCis-Sports can do it. But I'd rather know your heart rate, temperature, and SpO2 to make a quick diagnosis.
EKG streaming in the very near future may reveal that many climbers are having arrhythmias and this is why they don't respond to oxygen as quickly as we would want them to. So again, that is more important in my mind than blood pressure.
In short, let's be practical about what we measure for climbers. Just because we can measure something, it does not mean that it is useful. And as most expedition leaders know - just by lookng at a climber, and talking to him, you already have much information as to how his body is tolerating altitude.
Climb safe, be smart, and measure numbers that are really useful.