CHAPTER 1
Evidence and scientific rationale for ambulatory blood pressure monitoring (ABPM)

Diurnal BP variation and the concept of “perfect 24‐hour BP control”

Blood pressure (BP) always varies over time, including beat‐by‐beat, trigger‐induced, orthostatic, diurnal, day‐by‐day, weekly, seasonal, and age‐related variations. Of these different BP variability components, circadian rhythm is the central component of individual BP variability, and there is a large body of accumulating evidence highlighting the importance of this parameter.

Basic circadian rhythm forms the basis of individual diurnal BP variation (Figure 1.1) [1] . The circadian rhythm of BP is physiologically determined partly by the intrinsic rhythm of central and peripheral clock genes, which regulate the neurohumoral factor and cardiovascular systems, and partly by the sleep‐wake behavioral pattern, and is associated with various pathological conditions.

In addition to different patterns of circadian rhythm, short‐term BP variability such as morning blood pressure surge (MBPS), physical or psychological stress‐induced daytime BP, and nighttime BP surge triggered by hypoxic episodes in obstructive sleep apnea, arousal, rapid‐eye‐movement sleep, and nocturnal behavior (e.g. nocturia) modulates the circadian rhythm of BP, resulting in the different individual diurnal BP variation.

It is well‐known that elevated 24‐hour BP is a more important cardiovascular risk factor than office BP. In addition, disrupted circadian rhythm and exaggerated forms of short‐term BP variability (e.g. MBPS) are associated with an increased risk of cardiovascular events [2] . We hypothesized that “perfect 24‐hour BP control,” which includes lowering the average 24‐hour BP (quantity of BP control), maintaining adequate circadian rhythm, and stabilizing BP variability (quality of BP control), is the ideal goal (Figure 02) [3] . In particular, control of 24‐hour BP to <130/80 mmHg is important to minimize organ damage, independent of any regional differences in the risk of cardiovascular disease (Figure 1.2) [4] .

Figure 1.1 Components of nocturnal hypertension and determinants—nocturnal dipping status and surge in blood pressure. BP, blood pressure; CHF, chronic heart failure; CKD, chronic kidney disease; OSA, obstructive sleep apnea; REM, rapid eye movement.

Source: Kario. Hypertension. 2018; 71: 997–1009 [1] .

Figure 1.2 Regional differences in the impact of 24‐hour blood pressure control on cardiovascular remodeling and target organ damage (n = 596). IMT, intima‐media thickness; LVMI, left ventricular mass index; NS, not statistically significant.

Source: Created based on data from Yano et al. Am J Hypertens. 2011; 24: 437–443 [4] .

Nocturnal hypertension and nocturnal BP dipping status

Nocturnal BP dipping status

Different patterns of the circadian rhythm of BP can be determined using ambulatory BP monitoring (ABPM). Population‐based and clinical studies using ABPM have shown that nighttime BP is a better predictor of cardiovascular diseases than daytime BP [5, 6]. Nocturnal hypertension (where nighttime BP is high) and a non‐dipper/riser pattern (where nighttime BP is higher than daytime BP, even if office and 24‐hour BP readings are within the normal range) both increase the risk of target organ damage and subsequent cardiovascular events [7–10].

In healthy subjects, nighttime BP falls by 10–20% from daytime BP (normal dipper pattern). Patients with hypertension who do not have target organ damage also show the dipper pattern. However, those with organ damage tend to exhibit a non‐dipper pattern with diminished nighttime BP fall. Recent guidelines on the management of hypertension defined four different dipping patterns of nighttime BP: dipper, non‐dipper, riser, and extreme dipper based on the magnitude of the nighttime BP fall (Figure 1.3) [7, 8]. The terms “riser” and “extreme dipper” patterns describe the extremes on a continuum of circadian BP variability and represent the most pathologically relevant forms of disrupted circadian BP rhythm [11] .

Non‐dipper patterns of BP and pulse rate

O'Brien et al. first demonstrated that an abnormal, non‐dipping pattern of nighttime BP, with a <10% reduction in nocturnal BP compared with daytime BP, is associated with advanced organ damage [12] . The magnitude of the nighttime BP fall tends to diminish with advancing age. Shimada et al. first demonstrated that a non‐dipper pattern of nighttime BP in elderly patients with hypertension was associated with advanced silent cerebral disease (such as silent cerebral infarcts and deep white matter lesions) detected using brain magnetic resonance imaging (MRI) [13] .

Figure 1.3 Four different dipping status of nighttime blood pressure (BP) in hypertensive patients.

Source: Created based on data from Kario et al. Hypertension. 2001; 38: 852–857 [8] .

Non‐dipping of the pulse rate pattern is also associated with poor cardiovascular prognosis, and synergistically increases the risk associated with a non‐dipper pattern of nighttime BP fall. In a prospective study of elderly patients with hypertension, those with a non‐dipper pulse rate pattern showed a increase in cardiovascular events compared with a dipping pattern, independent of BP. In addition, non‐dippers of both nighttime BP and nighttime pulse rate were found to have the worst cardiovascular prognosis, showing a synergistic 7.9‐fold increase in the risk of cardiovascular events compared to those with a dipping profile for both parameters (Figure 1.4) [14] .

Riser pattern of BP and cardiovascular disease risk

The “riser” pattern is defined as higher BP during nighttime vs. daytime BP (i.e. no nocturnal BP fall), and the term “extreme dippers” refers to patients with an exaggerated nighttime BP fall (≥20%) compared with the daytime BP reading [7] . Some authors use the term “reverse dipper” or “inverted dipper” instead of “risers,” but these refer to the same lack of nocturnal BP fall.

A study in elderly patients with hypertension was the first to demonstrate that both extreme forms of disrupted circadian BP pattern (i.e. riser and extreme dipper) were associated with advanced silent cerebral disease evaluated on brain MRI (Figure 1.5) and were significantly associated with the occurrence of stroke (Figure 1.6) [8] . In particular, the riser pattern appears to have a particularly poor prognosis with respect to stroke and cardiac events (Figure 1.7) [15] .

Figure 1.4 Cardiovascular (CV) prognosis in non‐dippers of blood pressure (BP) and pulse rate (PR) (JMS‐ABPM study wave 1).

Source: Kabutoya et al. Am J Hypertens. 2010; 23: 749–755 [14] .

Figure 1.5 Silent cerebral infarcts detected by brain magnetic resonance imaging and nighttime blood pressure dipping in elderly patients with hypertension (JMS ABPM study wave 1). Green area indicates single infarct per person.

Source: Kario et al. Hypertension. 2001; 38: 852–857 [8] .

The multicenter, prospective, practitioner‐based, Japan Ambulatory Blood Pressure Monitoring Prospective (JAMP) study used the same ABPM device across all study centers to investigate the impact of nocturnal hypertension and nighttime BP dipping patterns on the occurrence of cardiovascular events, including heart failure (HF), in patients with hypertension (Figure 1.8) [16] . The results showed that both higher nighttime BP values and a riser pattern were significantly associated with the risk of developing atherosclerotic cardiovascular disease. The multivariable‐adjusted hazard ratio (HR) value for the risk of atherosclerotic cardiovascular disease associated with a 20 mmHg increase in nighttime systolic blood pressure (SBP) was 1.21 (95% confidence interval [CI] 1.03–1.41; p = 0.017) [16] .

Figure 1.6 Nighttime blood pressure dipping status and stroke prognosis in older patients with sustained hypertension.

Source: Kario et al. Hypertension. 2001; 38: 852–857 [8] .

Figure 1.7 Fatal and non‐fatal cardiovascular events in patients with a riser vs. non‐riser pattern.

Source: Kario and Shimada Clin Exp Hypertens. 2004; 26: 177–189 [15] .

Figure 1.8 Nighttime blood pressure...