An Overview of the Expanded Definition and Classification of Hypertension Part 2/5

Blood Pressure as a Biomarker for Hypertension

The concept of elevated BP as a disease marker for hypertension, rather than its cause, is supported by multiple lines of evidence suggesting that the risk for renovascular and CV sequelae may be higher than expected in the presence of normal or near-normal BP in some patients, or, conversely, lower than expected in the presence of above-normal BP in others. This view is based, in part, on the physiologically dynamic nature of BP, in which tissue perfusion is matched with metabolic demands in a complex, ever-changing manner that depends on the coordinated activity of numerous mechanisms involved in hemostasis, including the sympathetic nervous system, the renin-angiotensin system, and the vasodilatory system (eg, prostaglandins and nitric oxide).[4] According to this perspective, optimal BP can vary among individuals and within the same person, depending on hemodynamic circumstances. Sporadic BP elevations may occur in individuals who have no evidence of early CVD.[2] Conversely, because adverse CV and renal outcomes increase across all BP values, hypertension-related morbidity and mortality can occur even at BP levels considered normal by conventional standards. The significant proportions of myocardial infarctions and strokes that occur in patients who have only slight BP elevation, or even normal BP, adds weight to this argument.[7]

Perhaps the most convincing evidence against using BP thresholds to define hypertension is that there is no threshold of BP above 115/70 mm Hg that identifies CV risk -- that is, risk is linear and doubles for each 20/10 mm Hg increase in BP.[2] As a consequence of the dynamic nature of BP, it may be more clinically relevant to use BP patterns, rather than discrete BP thresholds as measured in the clinic, when assessing CV risk in an individual patient. Thus, the HWG places particular attention on ambulatory BP and the contribution of systolic BP (SBP) and pulse pressure (the difference between SBP and diastolic BP [DBP]) to risk, because these are widely considered to be more accurate markers of CV risk than is office DBP, particularly in older patients.[5,8]