Blood pressure variability
Blood pressure variability is a topic that has been with us for years. This concept stems from a clinician’s observation that measuring blood pressure in a patient three times within one or two minute intervals can yield results that can be very different. Such differences are not only of academic importance, they are of practical importance, because these differences can be larger than the effects of any antihypertensive drug.
Therefore blood pressure variability can be viewed as blood pressure as it varies over short periods of time. Former studies have focused on finding the mechanisms of these variations. However, even after blocking or inhibiting essential blood pressure regulation systems such as orthosympathetic nerves, blood pressure variation remains. The topic has recently gained new life because a study in the UK has approached it from a different angle (1). Investigators have looked at the difference between blood pressures measured at various visits with the physician and this was done over years. Variability in this study is no longer the variation between readings done within a few minutes, but between readings over months and years (intravisit variation). This study has shown that variability defined in that way correlates with stroke incidence. The higher the variability, the higher the stroke incidence.
Investigators also looked at the effect of drugs on such variability. Ace-inhibitors and beta-blockers increased such variability, while diuretics and amlodipine decreased it. Interestingly, beta-blockers with a vasodilating capacity decreased variability in contrast with other beta-blockers. This study and the new approach to variability, that should be confirmed in other studies, gives us another prognostic factor that may have well have a place within the regular risk factors.
Another topic in research in hypertension is a completely new approach to resistant hypertension. Resistant hypertension is not highly prevalent but causes great problems in the patients (and their physicians) who are facing such a condition. Before starting whatever treatment in patients with such resistant hypertension, one should investigate a number of essential points. First, one needs to be sure that blood pressure in this patient indeed is resistant to any type of treatment. It is important to eliminate secondary causes of high blood pressure and among those, renal artery stenosis. Second, it is highly important to have a 24-hour blood pressure recording done, as many of the so-called resistant hypertensive patients are in reality white-coat hypertensives; meaning that these patients show very high blood pressures at the consultation the pressures are much lower, often even normal in the regular situations of life. The majority of the so-called resistant hypertension seen in out-patient clinics, belong to this category. Finally one should check that the patient is compliant to his antihypertensive drug therapy. The latter is also highly prevalent as many patients need at least triple therapy but are reluctant to take their drugs on a regular basis.
When it is proven that indeed the high blood pressure is resistant, one is in absolute need to find another solution which is suggested in a recent study. In this work, an Australian group of researchers have investigated the effect of denervation of the renal nerves by a laser technique using a catheter introduced in both renal arteries. Such technique did not cause important side effects in this study although of course, one needs to remember that it is an invasive procedure very comparable as that used for renal artery angiography (2).
This study has given very attractive results. There is a rather quick decrease in systolic and diastolic blood pressure seen already at the first month after procedure and it further augments during the one-year follow-up : on average, there was a 30 mmHg decrease in systolic blood pressure and almost 20 mmHg decrease in diastolic pressure after one year. Such results are very encouraging and should be further explored in terms of blood pressure decrease in and of itself, but also regarding the safety and effects on the wall of the renal artery. There are also very stimulating studies on the mechanisms of such blood pressure decreasing (2). Initially the hypothesis was that blood pressure decrease was directly linked to vasodilation of the renal arteries and decrease in the activity of the renin-angiotensin system. However, further very innovative investigations by Blankestijn and Rupp (3) made clear that interruption of afferent nerve activity from the renal arteries to the brain might be involved. Here also, studies should be continued, not only to see the clinical effect, but also the basic mechanisms.
In this document two new areas of research are described as discussed during the 2010 ESC meeting in Stockholm. Blood pressure variability (defined as the variation between visits) is linked to stroke and thus, to long-term prognosis. On the other hand, renal denervation gives realistic hope to control blood pressure in patients with severe and resistant hypertension.