Can Diastolic Blood Pressure Be Higher Than Systolic Blood Pressure?
No, diastolic blood pressure cannot physiologically be higher than systolic blood pressure in living humans. This would represent a measurement error, equipment malfunction, or improper technique rather than a true physiological state.
Physiological Basis
Systolic blood pressure (SBP) represents the peak arterial pressure during ventricular contraction, while diastolic blood pressure (DBP) represents the minimum arterial pressure during ventricular relaxation 1.
By definition, systolic pressure must always exceed diastolic pressure because it reflects the maximum force generated during cardiac ejection, whereas diastolic pressure reflects the residual pressure when the heart is filling 2, 3.
The difference between systolic and diastolic pressure is called pulse pressure, which reflects arterial stiffness and left ventricular ejection characteristics 3, 4. A negative pulse pressure (diastolic > systolic) is physiologically impossible in a functioning cardiovascular system.
When This Appears to Occur: Measurement Errors
If you observe diastolic readings higher than systolic readings, consider these common causes:
Incorrect cuff size: Using a cuff that is too small or too large for the patient's arm circumference can produce spurious readings 1. The bladder width should be approximately 40% of arm circumference, and bladder length should encircle 80-100% of the arm 1.
Improper arm positioning: If the arm is not at heart level (mid-sternal or fourth intercostal space when sitting), readings can be inaccurate by 2 mm Hg for every inch above or below heart level 1. An arm hanging below heart level produces falsely elevated readings 1.
Equipment malfunction: Automated devices may produce erroneous readings, particularly in patients with arrhythmias or significant peripheral vascular disease 1.
Auscultatory gap: This phenomenon can cause underestimation of systolic pressure if the observer begins inflating the cuff at too low a pressure 1.
Patient factors: Muscle tension from holding the arm up (rather than having it supported) can alter readings through isometric exercise effects 1.
Clinical Action When Encountered
Repeat the measurement immediately using proper technique: patient seated with back supported, legs uncrossed, arm supported at heart level, and appropriate cuff size 1.
Verify equipment function and consider using a different device or manual auscultation if automated readings seem implausible 1.
Average at least 2 readings taken on at least 2 separate occasions before making any clinical decisions about blood pressure classification 1, 5.
Document the measurement conditions and any factors that may have contributed to the aberrant reading 1.
Normal Blood Pressure Relationships
In healthy individuals and those with hypertension, systolic pressure always exceeds diastolic pressure, with the gap (pulse pressure) typically ranging from 40-60 mm Hg in younger adults 3, 4.
With aging, systolic pressure increases progressively while diastolic pressure may plateau or even decrease after age 60, leading to widened pulse pressure due to arterial stiffening 2, 3, 4. However, systolic still remains higher than diastolic.
Even in isolated diastolic hypertension (most common in younger adults), systolic pressure remains elevated above diastolic pressure, defined as SBP <140 mm Hg with DBP ≥90 mm Hg 5.