Thursday, August 25, 2011

AMBULATORY BP MONITORING TO DIAGNOSE HYPERTENSION

For many years, we have thought that the diagnosis of hypertension is probably one of the easiest in medicine. Fix on a blood pressure cuff ( and we like the hardy mercury column syphynomanometer ), pump it up, lower the BP column slowly ( 1 millimeter per second ), and listen for thefirst pulsatile ( systolic) BP sound and then the loss of the pulsatile ( diastolic ) BP sound. There we have it, your BP is 120/80 mmHg. That seems simple enough.
The whole problem is that BP varies, and responds to the environment. It a stressful environment, the BP may rise, and in a calm and peaceful environment, the BP may fall. This is obviously because, the circulatory system, must increase its cardiac output for the human to have sufficient cardiac output to manage a stressful situation. Blood pressure is a function of cardiac output., so when cardiac output rises, BP rises, thereby increasing the circulation and so allowing more circulation ( more oxygen and nutirents being circulated ) to cope with the stress. So BP is also determined by circulation. Anxiety is the most common cause of a falsely elevated BP at a physician's clinic. We have a name for this - "white collar" hypertension.
Because of this fact, many hypertensives may be overdiagnosed, if the physician just takes a spot reading, and initiates treatment. That spot reading, in a stressful physician clinic, may be an "anxiety " reading. This fact, two devices have been brought into the market two near device.


The first is a professional device, called the 24 hrs ambulatory monitoring. This is usually uused by the professionals. The BP cuff is fixed on to the patient for 24 hours, and the BP cuff is pumped up automatically at regular intervals ( say every 2 hours ) and the BP is recorded digitally and stored in the optical hard disc which is attached to the cuff ( as shown in the image on the left ). With the BP cuff on, the patient can go about his normal activity ( a bit uncomfortable ), and all the BP for the whole day is stored. After 24 hours the recording is returned and analysed in a main computer, and a 24 hour tracing is printed out, showing us the patients BP for the last 24 hours. This is better obviously than a spot clinic check, but it is still not the best, as there is still an element of stress during that 24 hours, and it is not a pleasant device to carry around, as it does limit your activity, and also the regular pumping up of the cuff can be a nuisance, especially at night when you want to sleep. Imagine sleeping with something strap to your arm, which pumps up ( say 4 hourly ) through the night.

Then we have the home BP monitoring unit, which is very popular. Patients buy them ( they are quite affordable ), and keep at home. When they feel a headache or any usual symptom, they fix on the cuff and presses a button which pumps up the machine and records the BP digitally, with a monitor to display the number. See image on left. A popular brand in Malaysia is Omron. Nowadays, it is not unusual to have a patient come to the clinic with their daily BP recording for the last month.



This article is in some ways prompted by a clinical study by the National Institute of Health Research, UK, studying the cost effectiveness of ambulatory BP monitoring in the diagnosis of hypertension. The researches found that 24 hrs ambulatory BP monitoring was the the most cost effective way of diagnsosing hypertension and have been able to save cost. They found that the traditional two clinic visits, to confirm hypertension, still tend to over-diagnose hypertension by almost 25% resulting in 25% of patients being treated. 24hr BP monitoring tend to cost more upfront due to the cost of the device and also the cost of generating the report. This initial cost is off set by the cost savings from treating 25% less patients.
While this may be true for UK, I must say that my own preference will be for properly coached and properly supervise home BP monitoring using one of those home monitoring device. For those hypertensives without target organ damage, I would spend time explaining to them how to take their BP at home. I usually like a 3 times a day regime, where they take their BP using one of those digital devices, after 5-10 mins rest ( exhaling and inhaling deeply ), This should be repeated at 7.30am, 6pm and 10.30pm. The BP should be recorded and the average calculated, and recorded. They are all advise that should they take it during a crisis or stress, it is bound to be elevated. I find this a good means of managing hypertension. It also gets the patient to care for himself/herself, and increases compliance. Of course, the digital BP machines need calibration and adjustments yearly or two yearly.
The NICE recommendation may be good for UK, where patient understanding and compliance may be good. I find the BP cuff inflation and deflation a nuisance. Of course 24 hr Ambulatory BP monitoring requires a medical center referral, and the additional cost, and it is also not infallible.
It is true that in our local population, there is a high percentage of "white collar" hypoertension as we are subjected to more and more stress from the 21st century demands. In my practice, I seem to see matbe a 40-50% incidence of "white collar" hypertension. Once proven, these patients can be help with just regular assurances, relaxation techniques, green veges and fruits and no added salt diet. Simple and cheap.
Of course all these patients have no target organ damage.

1 comment:

Pilot Medical said...

Thanks for the post. It was really helpful to solve my confusion.

Occupational Medicine