Blunted Nocturnal Decline in Blood Pressure

Abstract

Blood pressure normally declines 10%–20% from daytime to sleep. Patients with less than a 10% reduction in daytime blood pressure are referred to as nondippers. A blunted nocturnal decline in blood pressure may be due to diminished sodium excretory capacity, alteration in the autonomic nervous system, or other factors. Secondary hypertension should be considered as a possibility. Target organ damage appears to be more common in nondippers, however, poor reproducibility of nondipping status raises the question as to the appropriate duration of monitoring to establish a diagnosis. Nondippers tend to have a greater reduction in nocturnal blood pressure with nonpharmacologic and pharmacologic treatment.

Ambulatory blood pressure (BP) has changed many concepts about BP. BP is not a static measurement. ¹ The diurnal variation in BP is a prominent feature of a normal 24‐hour ambulatory BP tracing. With sleep, BP normally declines 10%–20%. ² In the Allied Irish Bank Study ³ (n=815), the average nocturnal decline in BP was 18/17 mm Hg. Supine position and sleep explains 65%–75% of the nocturnal decline in BP. ⁴ Prior to awakening and standing, the sympathetic nervous system is activated and BP rises.

MECHANISMS

Nondippers refer to patients whose BP does not decline during sleep (Figure 1). The mechanism may be due to a redistribution of retained volume during sleep due to reduced sodium renal excretory capacity or an alteration in the autonomic nervous system. ² , ⁵ , ⁶ Impaired nocturnal melatonin secretion has also been reported. ⁷

Figure 1.

Ambulatory blood pressure testing. Compare the blood pressure during the daytime and nighttime. What is abnormal?

DEFINITIONS

Nondippers who have no decline in systolic or diastolic BP or an increase in BP are called inverted or reverse dippers (Figure 2). ⁸ , ⁹ In a rural Japanese population of 1542 residents, ≥40 years of age, the prevalence of nondippers and inverted dippers using the definitions shown in Figure 2 was 16% (Figure 3), however, different definitions of nondipper status will result in different prevalences. ¹⁰ Furthermore, arbitrary sleep times, rather than true sleep periods, influence the designation of dipper vs. nondipper. ¹¹ Secondary hypertension may be suggested by a blunted nocturnal decline in BP. Common causes of nondipping are displayed in the Table. Autonomic dysfunction is associated with increased BP at night and daytime hypotension.

Figure 2.

Definitions of dipping patterns. Modified from Am J Hypertens. 1997;10:1201–1207. ⁸

Figure 3.

Patterns of blood pressure. Derived from Am J Hypertens. 1997;10:1201–1207. ⁸

Table.

Causes of Nondipping

Autonomic dysfunction

Cardiac transplantation

Cushing's syndrome

Diabetes

High‐dose corticosteroids

Licorice intoxication

Obstructive sleep apnea

Pheochromocytoma

Preeclampsia/toxemia

Primary aldosteronism

Renal disease

TARGET ORGAN DAMAGE

The consequence of BP not declining during sleep is a greater 24‐hour BP for a similar level of daytime BP. Cardiovascular morbidity is increased, ¹² which is associated with more silent lacunar infarctions, myocardial ischemia, left ventricular hypertrophy, and microalbuminuria. ¹³ , ¹⁴ Using magnetic resonance imaging in a population of 575 older Japanese subjects, the rate of multiple silent cerebral infarcts was 41% in nondippers (n=185) and 49% in reverse dippers (n=63), compared to 29% in dippers (n=230). Also, stroke incidence was more common in reverse dippers than dippers (22% vs. 6.1%). ⁹ Among the reverse dippers, intracranial hemorrhage was a more common type of stroke than the other groups (29% vs. 7.7% of strokes, p=0.04).

REPRODUCIBILITY

Reproducibility of the nocturnal decline in BP is poor. ¹⁵ , ¹⁶ , ¹⁷ , ¹⁸ Based on two 24‐hour ambulatory BP measurements 1 week apart, a week‐to‐week concordance for the categorization of nondipper status was only 14.5% of 69 patients for systolic BP (Week 1=37% and Week 2=32%) and 12% for diastolic BP (Week 1=25% and Week 2=19%). ¹⁹ Body and arm position can both significantly influence the nocturnal ambulatory BP. ²⁰ Also, increased movement during sleep, as assessed by wrist actigraphy, is associated with nondipper status. ²¹ Sleep disturbance during ambulatory BP monitoring potentially contributes to a diminished nocturnal BP. ²² , ²³ With an inflation interval of 10 minutes, the duration of stage 4 (deep) sleep shortens and is associated with an increase in nocturnal waking time without an effect on the frequency of awakenings. ²² If a nondipping pattern is confirmed in two 24‐hour periods, more cardiovascular abnormalities are present. ²⁴

TREATMENT

Like sodium restriction, diuretics can restore a nocturnal BP decline in nondippers. ²⁵ BP decreased to a greater extent in nondippers compared to dippers using a chronotherapeutic verapamil as an antihypertensive given at night ²⁶ ; however, the incidence of cardiovascular events was not reduced during the early morning hours in these patients. Similar results were observed using arotinolol, an α‐β adrenergic blocker. ²⁷

CONCLUSION

A blunted nocturnal decline in BP in some patients appears to increase vascular risk when data on groups are considered, however, for individual patients, interpretation is confounded by poor reproducibility.