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Here is a thorough reference on blood pressure normal values and measurement, drawn from current cardiology and physiology textbooks:
Blood Pressure: Normal Values & Measurement
Normal Values (Adults and Children)
Per the 2017 ACC/AHA Hypertension Guidelines (the current standard in the US):
| Category | Systolic (SBP) | Diastolic (DBP) | |
|---|---|---|---|
| Normal | < 120 mmHg | and | < 80 mmHg |
| Elevated | 120-129 mmHg | and | < 80 mmHg |
| Stage 1 Hypertension | 130-139 mmHg | or | 80-89 mmHg |
| Stage 2 Hypertension | ≥ 140 mmHg | or | ≥ 90 mmHg |
- Children aged 1-12 years: Normal BP is below the 90th percentile for age. Hypertension is defined at the 95th percentile or higher.
- Adolescents ≥ 13 years: Same thresholds as adults (< 120/80 mmHg = normal).
The 2018 ESC/ESH (European) Guidelines set hypertension at ≥ 140/90 mmHg and further categorize:
- Optimal: < 120/80 mmHg
- Normal: 120-129 / 80-84 mmHg
- High-normal: 130-139 / 85-89 mmHg
(Fuster and Hurst's The Heart, 15th Ed.; Symptom to Diagnosis, 4th Ed.)
How Blood Pressure Is Measured
Unit: mmHg (millimeters of mercury) - the pressure required to push a mercury column to that height against gravity. Occasionally expressed as cmH₂O (1 mmHg = 1.36 cmH₂O). (Guyton & Hall Textbook of Medical Physiology)
Auscultatory Method (Most Common)
- The patient should be at rest - do not measure immediately after walking into the room.
- Use the correct cuff size: the inflatable bladder width should be ~40% of arm circumference. An undersized cuff overestimates BP.
- Avoid smoking and caffeine before measurement.
- Inflate the cuff above anticipated SBP, then slowly deflate.
- Korotkoff sounds:
- Phase I (first sound heard) = Systolic BP
- Phase V (sounds disappear) = Diastolic BP
- Note: An auscultatory gap - sounds that disappear and reappear between systolic and diastolic - can cause underestimation of SBP if not recognized.
- Check both arms on initial assessment; a difference of ≤ 20 mmHg between arms is normal (usually slightly higher in the right arm). A larger difference may indicate subclavian stenosis.
(Fuster and Hurst's The Heart, 15th Ed.)
How Many Readings?
Proper categorization requires ≥ 2 readings on ≥ 2 separate occasions, then averaged. Out-of-office measurements (home BP or ambulatory BP monitoring) should confirm elevated office readings before diagnosing hypertension.
Other Methods
- Oscillometric (automated cuff): Most home and hospital devices; detects oscillations in cuff pressure. Convenient but less accurate in arrhythmias.
- Intra-arterial (invasive): Gold standard for continuous beat-to-beat monitoring; used in critical care and major surgery. Requires arterial catheter connected to an electronic pressure transducer.
- High-fidelity electronic transducers: Use capacitance, inductance, or resistance-wire principles to convert pressure to electrical signal; can record up to 500 cycles/sec. (Guyton & Hall)
Key Clinical Points
- BP is a continuous variable - cardiovascular risk rises continuously with increasing BP, without a clear threshold.
- Hypotension is generally SBP < 90 mmHg or DBP < 60 mmHg, but is context-dependent. In shock, a "normal" BP may still represent hypotension relative to the patient's baseline (e.g., a normally hypertensive elderly patient).
- Hypertension prevalence in US adults is ~45% using the 2017 ACC/AHA criteria.
- Sodium intake significantly affects BP over time - populations with minimal sodium consumption show little rise in BP with aging.
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