Blood Pressure

A HealthKit blood-pressure correlation groups systolic and diastolic quantity samples into one reading. In 120/80 mmHg, 120 is the pressure during contraction and 80 is the pressure between contractions. The correlation supplies the relationship; its components supply the values. Apple documents this grouping.

The research snapshot contained 39 systolic and 39 diastolic rows, on 17 reporting days in January and April, within the October 2025–September 2026 window. Systolic values spanned 110–140 mmHg and diastolic values 66–88 mmHg. The component articles show their independent distributions.

The database has no correlation-object or membership table. This is unsupported storage for correlation analysis, not evidence that HealthKit contained zero blood-pressure correlations. A timestamp/end/source join returned 59 candidate combinations: duplicate keys make that join many-to-many. It cannot recover 39 verified readings, and it cannot support paired pulse-pressure values.

These records came from an automation source and a tracking app. Their median positive gaps were about 24 hours and 155 seconds respectively, with repeated timestamps and an approximately 79-day gap in the automation source. These are logging patterns, not a continuous sampling schedule or a recommended cuff protocol.

No component records appeared during the July–September focus quarter. Missing days should remain missing. A weekly average built from a single recorded day does not represent a monitored week.

Clock time cannot recover posture, resting duration or cuff technique. Preserve the measurement conditions when comparing paired readings.

Pulse pressure is systolic minus diastolic from the same verified reading. Do not subtract the closest components merely because they are nearby in time. Daily median comparisons can describe day-level relationships; they do not recreate HealthKit correlation membership.

Use both numbers and standardized repeated measurements. A normal adult AHA category requires systolic below 120 and diastolic below 80 mmHg. Either component can place a reading in a higher category. The American Heart Association’s home-monitoring guidance explains measurement technique, categories and when urgent care is needed. A single imported entry does not establish a diagnosis or treatment target.

See Systolic Blood Pressure and Diastolic Blood Pressure for component ranges, outliers and recording limitations.

Retain original correlation membership when the export supports it, plus both component UUIDs, units, source provenance and timestamps. Validate one-to-one pairing before deriving pulse pressure, category counts or paired trends. If linkage was not stored, document that limitation explicitly and present components separately. An Apple Watch heart-rate or rhythm feature does not replace a cuff blood-pressure measurement.