Blood pressure is one of the most measured health metrics in clinical medicine, and one of the least well understood in terms of what a single reading actually means. Knowing how blood pressure works and why it varies so much makes it considerably easier to use Intentra's blood pressure tracking as a useful tool rather than a source of anxiety.

What blood pressure measures

Blood pressure is expressed as two numbers: systolic over diastolic, measured in millimetres of mercury (mmHg). Systolic pressure (the higher number) reflects the pressure in the arteries when the heart contracts. Diastolic pressure (the lower number) reflects the pressure when the heart is at rest between beats.

A reading of 120/80 mmHg — often described as "ideal" — is a population-level reference, not a fixed individual target. Blood pressure varies continuously throughout the day, responding to every physiological and environmental signal the body receives.

Why blood pressure varies so much

Blood pressure is not a stable number. It responds within seconds to changes in:

Posture. Standing up from sitting causes a brief drop in blood pressure as the cardiovascular system adjusts. Lying down typically produces lower readings than sitting.

Activity. Exercise elevates blood pressure significantly during the session; readings taken within 30 minutes of exercise are higher than resting values.

Caffeine. A single coffee can elevate blood pressure for 1–3 hours in most people, with larger effects in those who don't consume caffeine regularly.

Stress and emotional state. The sympathetic nervous system response to stress — the "fight or flight" mechanism — causes immediate vasoconstriction and elevated blood pressure.

The white coat effect. Approximately 15–25% of people with elevated blood pressure readings in clinical settings have normal blood pressure at home. The act of measurement in a medical context produces a stress response that elevates the reading. This has been well-documented since the 1940s and is one reason home monitoring is increasingly recommended over clinic-only measurement.

Time of day. Blood pressure follows a circadian pattern — typically lowest in the early morning, rising through the morning, and declining again through the evening.

Given all of these sources of variation, a single blood pressure reading is a sample from a highly variable distribution. It has limited diagnostic value on its own. A reading of 140/90 in a single measurement does not mean you have hypertension; a consistent pattern of readings at or above that threshold across multiple measurements in appropriate conditions is what carries clinical meaning.

How to measure accurately at home

  • Rest for 5 minutes in a seated position before measuring
  • Sit with your back supported and feet flat on the floor
  • Place the cuff at heart level
  • Don't talk or move during the measurement
  • Avoid caffeine, exercise, and smoking for 30 minutes before measuring
  • Take two or three readings and use the average

Measuring at the same time of day, under similar conditions, produces more comparable readings across days and weeks.

What the trend tells you

Consistent blood pressure tracking over weeks and months reveals a trend that single readings cannot. A gradual increase in your average readings over several months is more informative — and more actionable — than any single elevated measurement. Intentra's blood pressure view is designed to surface this trend rather than flagging individual readings.

Blood pressure interpretation is a clinical matter. If your readings are consistently elevated, or you experience symptoms like persistent headaches, visual changes, or chest discomfort, consult a qualified health professional rather than relying on self-monitoring alone. Intentra organises and displays information but does not diagnose.