Читать книгу What Doctors Don’t Tell You - Lynne McTaggart, Lynne McTaggart - Страница 12

Your problems can start even when your doctor brandishes his blood-pressure cuff to record your blood pressure. Professor William White, chief of Hypertension and Vascular Diseases at the University of Connecticut, refers to this gizmo, known in medicalese as the ‘sphygmomanometer’, as ‘medicine’s crudest investigation’. Blood pressure, he says, can vary tremendously – as much as 30 mm Hg over the course of any day.⁵ In fact, the time it’s most likely to rise is in your doctor’s surgery, when you’re waiting to have the test – a phenomenon known as ‘white-coat hypertension’. A recent study comparing blood-pressure readings taken at home, at work and at the doctor’s surgery found that the most inaccurate were those performed in the doctor’s surgery.⁶ Such an artificially high test reading at the doctor’s surgery can launch a patient onto a lifetime of blood-pressure medication.⁷ The latest studies into blood pressure and hypertension have concluded that true high blood pressure is more related to average levels over 24 hours and also the degree of fluctuation between day and night than any particular or casually-made blood-pressure readings.⁸

These days, your doctor is more likely to give you a home-monitoring device or even to strap you up with a portable electronic device, which will measure your blood pressure at pre-set intervals over 24 hours. This is now thought to be the more accurate way of assessing your average blood pressure, although there is still a great deal of evidence that this system, called ‘ambulatory monitoring’, likewise doesn’t provide accurate enough information for doctors to decide whether a patient needs treatment for high blood pressure.⁹

Even the World Health Organization recommends that ambulatory monitoring is best conducted with multiple readings over six months. But because no one has yet bothered to do proper large-scale scientific studies, no one can agree over how long you should go on doing the ambulatory monitoring before making a diagnosis, or what actually constitutes high blood pressure over this period, or even how much blood pressure should be lowered by to make it ‘normal’.¹⁰

The values used today are still hypothetical, gleaned from studies of populations with normal blood pressure.¹¹ With home-monitoring systems, accuracy also remains a large problem. Only about a fifth of self-recording devices evaluated in recent studies have met acceptable criteria.¹²

In the US, the Food and Drug Administration mandates that any hypertension medication must be shown to lower blood pressure over 24 hours through ambulatory monitoring. Nevertheless, neither doctors nor drug companies really understand which reading – morning average, evening average, ambulatory reading, difference between day and night, degree of variation – shows that things are finally under control. Furthermore, many patients have different degrees of variability, depending on the nature of the stress they confront on the job.¹³ Older patients also have more exaggerated differences in day and night readings – the significance of which is anyone’s guess.¹⁴

A task force of participants at the 1999 Consensus Conference on ABP monitoring, sponsored by the International Society of Hypertension, recommended against using ambulatory monitoring for routine screening purposes.¹⁵ The latest recommendations are that patients use ambulatory monitoring for initial diagnoses of hypertension, and self-monitoring for long-term follow-up.¹⁶

Even the variation between the arms influences a blood-pressure reading. One doctor from City General Hospital in Staffordshire, England discovered a variation of more than 8 mm Hg in systolic blood pressure between the two arms of nearly a quarter of his patients. In one case, the difference was 20 mm Hg.¹⁷

Things are just as confusing for pregnant women and children. Doctors and health-care workers can’t even agree over how to record the second beat of blood pressure (called the diastole), which measures when blood fills up the heart,¹⁸ or whether certain sounds accurately reflect diastolic pressure. This was even the subject of a heated debate at a world congress of hypertension in pregnancy in Italy, calling for an ‘international consensus’ on how to record blood pressure in pregnant women. In fact, some researchers have claimed that doctors have been using the wrong type of blood-pressure test on pregnant women: obstetricians and midwives prefer the blood-pressure gauge called Korotkoff phase 4, but research shows that phase 5 testing is far more reliable – the reverse of the prevailing view. In one test, virtually nobody agreed on the reading from a K4 test, while everyone was in agreement on the K5 test.¹⁹ As for children, the latest recommendations are that they, too, have ambulatory monitoring.²⁰

This potential for different interpretations in readings can cause problems for you if your blood pressure is being monitored by several people who may have had different training in how to read the cuffs.