139 Actual blood supply index (IK)
The actual blood supply index (IK) is a simple indicator used to assess the state of the cardiovascular system. It is calculated with the Starr formula, which estimates stroke volume from blood pressure and age. In the 1950s, Isaac Starr tested this simple method against measured stroke volume. The application compares the result with age-dependent reference values: a value below the age norm suggests that the cardiovascular system performs worse than expected for age (signs of accelerated ageing), while a value above it suggests better-than-expected function. The index is a quick screening estimate, not a direct measurement.
The Starr formula
Stroke volume (mL) ≈ 100 + 0.5 × pulse pressure − 0.6 × diastolic pressure − 0.6 × age
(Pulse pressure = systolic − diastolic pressure, in mmHg; age in years.) The formula captures two facts: a wider pulse pressure usually accompanies a larger stroke volume, and stroke volume tends to decrease with age and higher diastolic pressure. It is less accurate in individuals with stiff arteries, arrhythmias, valve disease or heart failure, in whom stroke volume should be measured directly.
Age-dependent reference values used in this application
| Age (years) | Reference range |
|---|---|
| 1–10 | 144–89 |
| 10–20 | 89–73 |
| 20–30 | 73–65 |
| 30–40 | 65–57 |
| 40–50 | 57–52 |
| 50–60 | 52–44 |
| 60–70 | 44–46 |
| 70–80 | 46–47 |
| 80–90 | 47–48 |
These are the conventional reference values of the method used by the application.
Interpretation
Below the age norm
The circulation performs worse than expected for age: possible reduced stroke volume, arterial stiffness, hypertension or reduced physical fitness. Cardiovascular risk factors should be reviewed.
Above the age norm
Function better than expected for age; such people generally tolerate physical stress, surgery and illness better.
The index is a convenient screening tool, but an abnormal value should be followed by measurement of blood pressure over time and, if needed, echocardiography.
References
- Starr I. Clinical tests of the simple method of estimating cardiac stroke volume from blood pressure and age. Circulation. 1954;9.
- Vincent JL. Understanding cardiac output. Crit Care. 2008;12(4):174. doi:10.1186/cc6975
This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.
Published on 14 May 2024