Pathophysiology
P-I-18. ABPM and its indications
ABPM（24時間血圧測定）とその適応
ABPM — Ambulatory Blood Pressure Monitoring
- Automatic BP measurement several times a day, usually for 24 hours
- Performed with a portable cuff/monitor worn by the patient during normal daily activity and sleep
What ABPM Detects
- White-coat hypertension — BP high in the medical office but normal at home
- Masked hypertension — BP normal in the office but abnormally high during certain periods of the day
- Disturbed diurnal rhythm — BP is normally lower at night; loss of this fall suggests a severe and progressive form of hypertension
Diurnal Index
- Healthy individuals show a biphasic pattern: BP peaks in the morning and falls in the evening/night
- Diurnal index = (daytime mean BP − nighttime mean BP) / daytime mean BP × 100
- Normal value: 10–20%
- <10% → non-dipper (sleep apnea syndrome, old age)
- >20% → extreme dipper
- <0% → inverse (reverse) dipper
- All deviations represent a cardiovascular risk
Why Diurnal Rhythm Matters
- The night-time dip reflects healthy autonomic regulation
- Its absence or reversal correlates with target-organ damage and higher cardiovascular risk, so ABPM adds prognostic information that single office readings cannot
Diagnostic Thresholds
| Category | Systolic (mmHg) | Diastolic (mmHg) |
|---|---|---|
| ABPM — daytime (awake) | ≥135 | ≥85 |
| ABPM — nighttime (asleep) | ≥120 | ≥70 |
| ABPM — 24-hour | ≥130 | ≥80 |
一問一答
▶What is white-coat hypertension as detected by ABPM?
BP high in the medical office but normal at home.
▶What three main conditions does ABPM detect?
White-coat hypertension, masked hypertension, and disturbed diurnal rhythm.
▶What is ABPM and how is it performed?
Ambulatory blood pressure monitoring — automatic BP measurement several times a day (usually 24 h) using a portable cuff/monitor worn during normal activity and sleep.
▶What is the normal diurnal BP pattern in healthy individuals?
A biphasic pattern: BP peaks in the morning and falls in the evening/night (a night-time dip).
▶What is masked hypertension as detected by ABPM?
BP normal in the office but abnormally high during certain periods of the day.
▶How is the diurnal index calculated?
Diurnal index = (daytime mean BP − nighttime mean BP) / daytime mean BP × 100.
▶What is the normal value of the diurnal index?
10–20%.
▶What is a non-dipper, and what conditions are associated with it?
A diurnal index <10% (insufficient night-time fall); associated with sleep apnea syndrome and old age.
▶What diurnal index defines an extreme dipper?
A diurnal index >20%.
▶What is an inverse (reverse) dipper?
A diurnal index <0%, meaning night-time BP is higher than daytime BP.
▶What is the clinical significance of all deviations from the normal diurnal index?
They represent increased cardiovascular risk.
▶Why does the night-time BP dip matter prognostically?
It reflects healthy autonomic regulation; its absence/reversal correlates with target-organ damage and higher cardiovascular risk.
▶What prognostic advantage does ABPM have over single office readings?
It adds prognostic information (diurnal rhythm, true 24-h burden) that single office readings cannot provide.
▶What are the ABPM daytime (awake) hypertension thresholds?
Systolic ≥135 mmHg or diastolic ≥85 mmHg.
▶What are the ABPM nighttime (asleep) hypertension thresholds?
Systolic ≥120 mmHg or diastolic ≥70 mmHg.
▶What is the ABPM 24-hour hypertension threshold?
Systolic ≥130 mmHg or diastolic ≥80 mmHg.
▶Why are ABPM thresholds lower than office thresholds?
Out-of-office readings are typically lower than office readings, so lower cut-offs are used to define hypertension.
▶Why is a non-dipping pattern common in obstructive sleep apnea?
Recurrent nocturnal sympathetic activation prevents the normal night-time BP fall.
▶What does loss of the normal night-time fall suggest about hypertension severity?
It suggests a severe and progressive form of hypertension.
▶Why is ABPM considered the gold standard for diagnosing true hypertension?
It captures real-life 24-h BP across activity and sleep, distinguishing sustained hypertension from white-coat or masked patterns.