Uncertain (human) Science, Bricks and Walls

My blood pressure has been up-and-down for years. Usually, when it’s measured in the surgery it’s up, but at home it’s down. A consultant physician told me in 1994 I had white-coat (labile) hypertension, and not to worry about it. There’s no denying that in the surgery the level of “up-ness” merits the adjective hypertensive (i.e. over 140/90). A few years ago a different consultant physician decided to I needed 24-hour ambulatory blood pressure monitoring. On the basis of this he decided I required treatment. Since then I’ve been on medication without any problems.

When I went for a regular checkup this morning, the nurse frowned. “Your blood pressure is a bit up” she said. “I’ll check it again in a minute.” She did so, and again a minute after that. Everything she did was in accordance with NICE guidelines. “Yes. It’s definitely a bit up.” She showed me the reading on the monitor. It was 150/95. She told me that I had to come back again in two weeks to have it checked again. If it were still elevated, I would have to see the pharmacist for advice about my medication.

The problem is when I measure my blood pressure at home with an up-to-date, top of the range electronic sphygmomanometer, my blood pressure is consistently within normal limits. It varies between 120/80 to 150/87. It seems to me that the discrepancy between the readings in the surgery and the readings at home confirm that I have labile hypertension. But the matter is further complicated a very interesting observation two weeks ago. I had to see my G.P. about my carpal tunnel syndrome. I wasn’t expecting to have my blood pressure checked, but right at the end of the consultation he checked my blood pressure. I was surprised to see that it was 135/85. I went to the surgery not expecting to have my blood pressure measured, and so wasn’t worried about it. This strongly suggests to me that my blood pressure is elevated if I know in advance I’m going to the surgery to have my blood pressure measured. In other words my anxiety about having it measured puts the reading up.

All this raises doubts in my mind about what’s really going on here. The NICE guidelines are as you might expect clear and unambiguous. They ring with certainty as far as the diagnosis and management of hypertension are concerned. Regular readings either in the clinic, or ambulatory (24-hour monitoring), or at home greater than 150/90 require treatment.

The problem is that if you look elsewhere there is little agreement as to what constitutes labile hypertension, how to define it, what levels of elevation are necessary to diagnose it, or indeed, what long-term risks it carries. Of course, the point of monitoring blood pressure is to reduce morbidity and mortality from strokes and heart attacks (see for example Mann, S. (2009) The Clinical Spectrum of Labile Hypertension: A Management Dilemma. The Journal of Clinical Hypertension, 11, 491-4967). But this lack of clarity about labile hypertension means that I am in danger of becoming fodder for pharma. Is the pharmacist the practice nurse wants me to see for medication advice really going to offer an impartial view? What about the fee the NHS pays her or his employer (Boots the Chemist)? What about exhorting me to make life-style changes. Yes, I know I’m moderately obese, and could probably benefit from reducing my red wine intake, but I do walk four or five miles most days.

What really interests me is the way that my perspective is invalidated by the nurse. I’ve made the point about the discrepancy between surgery and home blood pressure measurements repeatedly, but although it is never voiced, I have the feeling that with the weight and authority of NICE guidelines behind her, I am being foolish and silly to doubt her advice. But the fact is that my blood pressure is without exception ‘normal’ when measured at home. The nurse checks my blood pressure once a month. It takes ten minutes or so. That’s ten minutes out of the 282,400 minutes there are in a month. That’s 0.000035% or my life, per month. Indeed, it’s not even the surgery; it’s the fact that I am expecting my blood pressure to be measured. The vast majority of my time is spent at home oblivious and aware of my blood pressure. I’m simply not concerned about it in my natural habitat.

This, surely, is a very human form of Heisenberg’s uncertainty principle. (I understand that the formula at the head of this piece is the mathematical statement for the simplest instance of Heisenberg’s principle.) The very act of making an observation changes this human system. My expectations and anxieties when I go to have my blood pressure checked, my interaction with the nurse (charming though she is) operate in such a way as to make the reading different from might have been had this human system remained unobserved. It makes me deeply suspicious of the one-size fits all approach that typifies NICE guidelines. Yes folks, I’m just another brick in the wall fortifying pharma’s profits.