Blood pressure indicates the force with which blood circulates against the walls of your arteries. It is expressed as two numbers: systolic pressure, the upper number, representing the pressure when your heart beats, and diastolic pressure, the lower number, indicating the pressure when your heart rests between beats. Monitoring these readings accurately provides insights into cardiovascular health and can help identify potential issues. While medical conditions can cause genuinely low blood pressure, numerous non-medical factors can lead to readings that appear falsely low, potentially masking a person’s true blood pressure.
Patient-Specific Influences
The position of your body and recent activities can influence blood pressure measurements, resulting in a falsely low reading. When measuring blood pressure, the arm should be supported at the level of the heart. If the arm is positioned above heart level, gravity can cause the reading to be artificially lower than the actual pressure, potentially by as much as 10-12 mmHg.
Unsupported arms can also lead to lower readings if the arm is relaxed. Rest also plays a role; blood pressure is naturally lower during periods of rest. A reading taken after a period of rest might be lower than usual, which could be misinterpreted as falsely low.
Deep breathing can reduce blood pressure. If deep breathing occurs inadvertently during measurement, it can temporarily lower the reading, not reflective of typical blood pressure. These physiological responses highlight the importance of consistent patient positioning and a calm state before and during a blood pressure check.
Equipment Malfunctions and Issues
Inaccurate blood pressure readings can stem from problems with the monitoring equipment. Using a blood pressure cuff that is too large for the arm is a common issue leading to a falsely low reading. An excessively large cuff may not compress the artery sufficiently, underestimating true blood pressure.
For accurate measurement, the inflatable bladder of the cuff should cover about 80% of the arm’s circumference, with the width being at least 40% of the circumference. Monitors not regularly calibrated can also produce unreliable results. Over time, the accuracy of both home and professional devices can drift, yielding consistently off readings.
A low battery in an automatic blood pressure monitor can compromise its performance, leading to inaccurate measurements that might appear falsely low. Physical damage to the equipment, such as kinks in the tubing, air leaks in the cuff, or other structural compromises, can also disrupt the pressure sensing mechanism and result in incorrect readings. Maintaining equipment in good condition and ensuring proper battery levels are essential for dependable blood pressure monitoring.
Measurement Procedure Mistakes
Errors made during the process of taking a blood pressure reading can skew results, leading to a falsely low outcome. Improper cuff placement is a frequent mistake. Placing the cuff too loosely means it cannot apply adequate pressure, resulting in an artificially low reading. Measuring over clothing also interferes with the cuff’s ability to compress the arm, yielding inaccurate and lower readings.
Deflating the cuff too quickly is another procedural error, particularly with manual devices. Rapid deflation can cause the healthcare provider to miss Korotkoff sounds, underestimating actual blood pressure. Taking multiple readings too quickly without allowing sufficient time for blood flow to normalize between measurements can also result in subsequent readings that are artificially lower.
Movement or talking during the measurement process can also introduce inaccuracies. While talking typically causes blood pressure to rise, it can also interfere with arterial sound detection, potentially leading to misinterpretation or a missed initial sound, contributing to a perceived false low. Remaining still and silent during the measurement ensures the most consistent and accurate results.
Interpreting Readings and Next Steps
Understanding when a blood pressure reading might be falsely low involves recognizing the common errors related to patient factors, equipment, and measurement technique. If a reading seems unusually low, consider whether any of these procedural or equipment issues were present during the measurement. For instance, reflect on arm position, cuff fit, or whether there was talking or movement.
If you suspect a reading is falsely low, retake it after a few minutes of rest, ensuring proper technique and equipment. This includes having your arm correctly supported at heart level, using the appropriately sized cuff directly on bare skin, and remaining still and quiet throughout the process. Taking multiple readings and averaging them can also provide a more reliable representation of your blood pressure.
While this article focuses on non-medical causes of falsely low readings, it is important to distinguish these from genuinely low blood pressure that may indicate an underlying health issue. If you consistently observe low blood pressure readings, especially when accompanied by symptoms such as dizziness, lightheadedness, fainting, or unusual fatigue, it is important to consult a healthcare professional. They can assess your situation, determine if there is a medical cause for low blood pressure, and recommend appropriate next steps.