Sphygmomanometer
A sphygmomanometer is a medical instrument used to measure blood pressure, consisting of an inflatable cuff that wraps around the upper arm, a pressure gauge to display the reading, and a bulb or pump with a valve to control inflation and deflation.[1] It enables the non-invasive assessment of arterial pressure, typically through the auscultatory method where a healthcare provider listens for Korotkoff sounds using a stethoscope as the cuff pressure is gradually released.[2] This device is essential for diagnosing conditions like hypertension, monitoring cardiovascular health, and guiding treatments in clinical settings worldwide.[3] The development of the sphygmomanometer began in the late 19th century, with Austrian physician Samuel Siegfried Karl von Basch inventing the first non-invasive version in 1881, using a water-filled bag connected to a manometer to estimate systolic pressure by compressing a peripheral artery.[4] In 1896, Italian physician Scipione Riva-Rocci significantly improved the design by introducing a more accurate mercury-filled manometer and an upper-arm cuff, which became the foundation for modern blood pressure measurement.[4] The auscultatory technique was later refined in 1905 by Russian physician Nikolai Korotkoff, who described the characteristic sounds produced by turbulent blood flow during cuff deflation, allowing for precise determination of both systolic and diastolic pressures.[5] Traditionally, mercury sphygmomanometers served as the gold standard due to their high accuracy and reliability, but they have been largely phased out since the early 2000s because of mercury's toxicity and environmental hazards, prompting international bans and regulations.[6] Common alternatives include aneroid devices, which use a dial gauge instead of mercury and require regular calibration to maintain accuracy within 4 mmHg, and oscillometric digital sphygmomanometers, which automatically detect pressure oscillations for automated readings without auscultation.[7] These modern variants are widely used in primary care, hospitals, and home monitoring, though validation against reference standards remains crucial to ensure clinical precision.[8]Etymology and History
Etymology
The term sphygmomanometer derives from the Greek sphygmos, meaning "pulse" or "throbbing," combined with manometer, a device for measuring pressure.[9] The prefix sphygmo- specifically denotes the arterial pulse, while manometer originates from the Greek roots manos ("thin" or "rare," referring to the sparse liquid column used in early pressure gauges) and metron ("measure").[10] This composite term thus describes an instrument for measuring pulse-related pressure, particularly arterial blood pressure.[9] The word was coined in German around 1881 by Austrian physician Samuel Siegfried Karl Ritter von Basch, who invented the first clinically viable non-invasive device for assessing arterial tension.[9][4] Its first documented English usage appeared in 1882.[9] In 1896, Italian physician Scipione Riva-Rocci employed the term in his seminal publication on an enhanced mercury sphygmomanometer, contributing to its widespread adoption in medical literature.[4]Historical Development
The sphygmomanometer's development began in 1881 when Austrian physician Samuel Siegfried Karl von Basch invented the first non-invasive device, using a water-filled bag connected to a manometer to estimate systolic pressure by compressing a peripheral artery. This early design, while innovative, was limited in accuracy and ease of use.[4][11] The first practical sphygmomanometer was invented in 1896 by Italian physician Scipione Riva-Rocci, who developed a mercury-based device consisting of an inflatable cuff connected to a mercury manometer, allowing for noninvasive measurement of systolic blood pressure.[4] This innovation marked a significant advancement over earlier rudimentary designs, such as those using water-filled bulbs, by providing a more accurate and reproducible method for clinical use.[12] In 1905, Russian surgeon Nikolai Korotkoff introduced the auscultatory technique, observing characteristic sounds produced by blood flow through the brachial artery during cuff deflation, which enabled the measurement of both systolic and diastolic pressures.[13] Korotkoff's discovery, initially reported in a brief dissertation while serving in the Russo-Japanese War, transformed Riva-Rocci's device into a complete tool for assessing full blood pressure profiles.[14] Aneroid sphygmomanometers, which replaced mercury columns with a mechanical dial gauge for pressure indication, emerged as a portable alternative in the early 20th century and gained use in field and ambulatory settings due to their compactness. However, mercury devices remained the gold standard in clinical practice for accuracy until phased out starting in the 2000s because of toxicity risks.[15][16] Environmental and health concerns over mercury exposure led to regulatory bans on mercury sphygmomanometers starting in the 2000s, including the European Union's Mercury Directive of 2007, which restricted their sale and use in professional and consumer applications.[17] Digital sphygmomanometers began emerging in the 1970s with the integration of electronic sensors and automated inflation systems, evolving into oscillometric devices that detect pressure oscillations in the cuff to estimate blood pressure without auscultation.[18] Key developments in the 1980s included patents for refined oscillometric algorithms, such as those improving systolic and diastolic detection accuracy, which facilitated the transition to fully automated, user-friendly models prevalent in home and clinical monitoring today.[19]Measurement Principles
Basic Principles
Blood pressure is defined as the force exerted by circulating blood against the walls of arteries, expressed in millimeters of mercury (mmHg) as the standard unit of measurement.[1] This pressure varies cyclically with the cardiac cycle, resulting in two key values: systolic pressure, which represents the peak force during ventricular contraction when blood is ejected into the arteries, and diastolic pressure, which indicates the minimum force during ventricular relaxation when the heart refills.[1] These measurements provide insight into cardiovascular health, as deviations can signal conditions like hypertension or hypotension.[6] Sphygmomanometers employ an indirect method to assess blood pressure by using an inflatable cuff placed around the upper arm to temporarily occlude the brachial artery, the major vessel supplying the arm.[1] When the cuff is inflated to a pressure exceeding systolic levels, it fully compresses the artery, halting blood flow and creating a state of ischemia distal to the cuff.[6] As the cuff deflates gradually, blood flow resumes in a pulsatile manner driven by the heartbeat, generating detectable pressure oscillations or waves within the cuff that correspond to the underlying arterial pressure dynamics.[1] This pulsatile resumption reflects the intermittent nature of arterial blood flow, allowing estimation of systolic and diastolic pressures without direct vascular invasion.[6] The cuff's inflation mechanism relies on the pressure-volume relationship of the enclosed air, governed by Boyle's law, which states that for a fixed amount of gas at constant temperature, the pressure P is inversely proportional to the volume V: P_1 V_1 = P_2 V_2 where subscripts denote initial and final states.[20] In practice, squeezing the inflation bulb decreases the cuff's internal volume (V_2 < V_1), thereby increasing pressure (P_2 > P_1) to achieve occlusion, while deflation reverses this process to release the compression controllably.[20] This gas law ensures precise control over cuff pressure, essential for reliable arterial compression.[6] Physiologically, effective blood pressure measurement presupposes adequate arterial compliance—the elasticity of arterial walls that allows expansion under pressure—and the propagation of pulse waves from the heart through the arterial system.[6] Arterial compliance enables the vessels to distend during systole and recoil during diastole, modulating the amplitude and velocity of pulse waves.[6] Reduced compliance, as seen in aging or atherosclerosis, can amplify systolic pressures and alter wave propagation, potentially affecting measurement accuracy by increasing wave reflection and stiffness.[1] These factors underscore the interplay between vascular physiology and the mechanical principles of sphygmomanometry.[6]Korotkoff Sounds and Auscultatory Method
In 1905, Russian surgeon Nikolai Korotkoff introduced the auscultatory method for measuring arterial blood pressure, revolutionizing non-invasive sphygmomanometry by identifying audible sounds produced during cuff deflation over the brachial artery.[13][21] This technique relies on listening through a stethoscope placed over the brachial artery, positioned proximal and medial to the antecubital fossa and below the cuff's lower edge, to detect pulsatile sounds that indicate systolic and diastolic pressures.[22] The Korotkoff sounds arise from the transition of blood flow from laminar to turbulent patterns within the partially occluded artery during cuff deflation.[14] In laminar flow, blood moves smoothly in parallel layers, producing no audible vibrations, whereas turbulent flow—triggered by high-velocity jets through the narrowing—creates vibrations in the arterial wall and surrounding tissues that propagate as detectable sounds via the stethoscope.[23][14] The auscultatory method identifies five distinct phases of Korotkoff sounds, each corresponding to changes in arterial flow dynamics. Phase I marks the onset of clear, repetitive tapping sounds for at least two beats, signifying systolic blood pressure as blood first pulses through the cuff-compressed artery.[14] Phase II follows with a softening or murmur-like quality to the sounds as flow becomes more consistent.[14] In Phase III, the sounds intensify and become crisper, reflecting stronger pulsatile flow.[14] Phase IV features muffled, low-intensity sounds, sometimes used as an estimate of diastolic pressure in specific clinical contexts like pediatrics or hypotension.[14] Phase V, the standard indicator of diastolic pressure, occurs when all sounds abruptly disappear, corresponding to fully restored laminar flow below the cuff.[14] A potential pitfall in the auscultatory method is the auscultatory gap, a temporary disappearance of Korotkoff sounds often spanning 20-40 mmHg below the systolic pressure in hypertensive patients due to transient equalization of pressures or reduced flow turbulence.[24] This phenomenon can lead to underestimation of systolic pressure if undetected.[22] To avoid it, inflate the cuff 20-40 mmHg above the point where the radial pulse disappears during initial palpation, and consider elevating the arm overhead to minimize the gap's occurrence.[22][24]Types
Mercury Sphygmomanometers
Mercury sphygmomanometers feature a U-shaped glass tube partially filled with mercury, forming a manometer that directly measures pressure through the hydrostatic balance of the liquid column, with the tube calibrated in millimeters of mercury (mmHg) and connected to an inflatable cuff via rubber tubing.[25][26] These devices offer high accuracy due to their direct measurement of hydrostatic pressure without mechanical intermediaries, making them the gold standard for blood pressure validation in clinical research and device calibration until environmental regulations prompted their decline.[27][25][28] However, mercury's toxicity poses significant health risks, including neurological and renal damage from spills or vapor inhalation, alongside environmental hazards from improper disposal leading to bioaccumulation.[29][30][31] The glass components are also fragile, prone to breakage that exacerbates mercury exposure.[32] Regulatory efforts, including World Health Organization recommendations aligned with the Minamata Convention's 2020 phase-out target for mercury-added products, have led to their widespread replacement in many countries as of 2025, though some continued use and exemptions persist globally to mitigate these risks.[33][34][35] In clinical settings, mercury sphygmomanometers remain valued as reference standards for calibrating alternative devices, such as aneroid models checked every six months against them to ensure measurement reliability.[36][25][37]Aneroid Sphygmomanometers
Aneroid sphygmomanometers employ a mechanical pressure-sensing mechanism, such as a Bourdon tube or diaphragm gauge, to translate cuff pressure into needle movement on a circular dial without relying on liquid columns.[38][39] The Bourdon tube, a curved, flattened metal tube sealed at one end, straightens proportionally to the internal pressure increase, driving a geared linkage that rotates the indicator needle across the dial face.[38] Alternatively, a diaphragm variant uses a flexible membrane that deflects under pressure to actuate the needle via similar mechanical linkage, offering robustness in compact designs.[40] These devices excel in portability and durability, making them suitable for clinical, field, or home use, as their solid-state construction avoids breakage risks associated with glass components and eliminates mercury toxicity concerns.[41][42] Available in handheld models for mobile applications or wall-mounted versions for stationary setups, they provide a lightweight alternative weighing typically under 1 kg.[43] However, aneroid gauges are prone to mechanical drift from factors like shock, vibration, or temperature fluctuations, necessitating calibration every 6-12 months to maintain accuracy within ±3 mmHg, and they generally offer lower precision compared to mercury standards.[44][45] Calibration involves connecting the aneroid gauge to a reference mercury manometer via a Y-connector and verifying readings at multiple pressures (e.g., 0, 100, 200 mmHg) by pumping air through the system, adjusting the zero point or internal mechanism as needed to align discrepancies unique to the elastic deformation in Bourdon or diaphragm elements.[46][40]Digital Sphygmomanometers
Digital sphygmomanometers are electronic devices that automate blood pressure measurement through the oscillometric technique, utilizing pressure transducers to detect subtle oscillations in cuff pressure caused by arterial pulsations. These devices typically incorporate a microcontroller to process signals from the transducer, which converts mechanical pressure variations into electrical signals for analysis. The system computes systolic, diastolic, and mean arterial pressure (MAP) values using proprietary algorithms that interpret the oscillometric waveform, enabling a fully automated readout without the need for auscultation.[47][48] The core of the oscillometric principle lies in the detection of pressure pulses within the cuff as it deflates from above systolic pressure to below diastolic pressure. These oscillations arise from the expansion and contraction of the artery against the cuff, with their amplitude peaking at the MAP, where the cuff pressure equals the mean intra-arterial pressure. Algorithms then estimate systolic pressure at a point where the oscillation amplitude is typically 50-70% of the maximum (above MAP), and diastolic pressure at around 50-80% of the maximum (below MAP), though exact ratios vary by device manufacturer and physiological factors such as arterial compliance. This method allows for rapid computation, often within seconds, and supports variants like upper-arm or wrist-mounted models for home or clinical use.[48][49][44] Key advantages of digital sphygmomanometers include their user-friendly design, which automates cuff inflation and deflation via electric pumps, eliminating the need for manual pumping and reducing operator training requirements. Many models feature memory storage for multiple readings, irregular heartbeat detection, and connectivity options for data tracking, making them suitable for self-monitoring by patients. Wrist variants offer portability for on-the-go use, though arm models are generally preferred for accuracy in clinical settings.[44][50] However, these devices have notable disadvantages, including sensitivity to improper cuff positioning or arm movement, which can lead to inaccurate readings if the cuff is not at heart level. Algorithm variability across brands can result in inconsistent estimates of systolic and diastolic pressures, particularly in patients with arrhythmias or stiff arteries, necessitating validation against auscultatory standards for reliable use. Additionally, reliance on batteries and potential electronic failures highlight the importance of regular maintenance.[44][51][49] Emerging cuffless digital sphygmomanometers utilize wearable sensors, such as those based on photoplethysmography (PPG) or applanation tonometry, to estimate blood pressure without an inflatable cuff. These devices process signals like pulse transit time or wave analysis via algorithms, with several models receiving regulatory clearance for over-the-counter use by 2025. However, their accuracy, particularly for absolute values, requires ongoing validation against traditional methods, and they are often calibrated periodically with a cuff-based device.[52][53]Components and Design
Cuff and Inflation System
The cuff of a sphygmomanometer consists of an inflatable rubber bladder encased within a fabric envelope, typically made of durable nylon or polyester to ensure air impermeability and repeated use.[54][55] The bladder, which is the key component for applying pressure, is a flexible, elongated pouch designed to wrap around the upper arm and occlude the brachial artery when inflated.[54] Standard cuff sizes are determined by the dimensions of the bladder, with the adult size featuring a width of approximately 12–13 cm and a length of 24–26 cm to accommodate typical arm circumferences.[44] Proper selection requires measuring the mid-upper arm circumference and choosing a cuff where the bladder length covers at least 80% of that circumference, ideally 75%–100%, to ensure even pressure distribution and accurate readings.[44][56] The inflation system in manual sphygmomanometers employs a hand-operated rubber bulb connected to the cuff via tubing, incorporating a one-way valve to allow air intake during squeezing while preventing backflow.[57] In digital models, an electric motor drives an automatic pump to inflate the cuff, enabling consistent and controlled pressure buildup without manual effort.[58] During measurement, the inflation system increases cuff pressure beyond the systolic blood pressure level to fully occlude arterial blood flow, after which gradual deflation via a release valve allows pulsatile flow to resume, facilitating pressure detection.[44] Cuff materials must meet durability standards, such as those outlined in ANSI/AAMI SP9 for non-automated devices, ensuring resistance to wear from repeated inflation cycles; many modern cuffs are latex-free to minimize allergy risks.[59][60] Using an inappropriately small cuff can lead to overestimation of systolic blood pressure by 10–20 mmHg due to uneven pressure application and increased resistance on the artery.[61][62]Manometer and Display Mechanisms
The manometer in a sphygmomanometer serves as the primary mechanism for indicating cuff pressure, converting the mechanical force from the inflated bladder into a readable format that allows clinicians to determine systolic and diastolic blood pressures. Different types of manometers employ distinct principles to achieve this: mercury-based systems use a liquid column, aneroid devices rely on mechanical deflection, and digital models process signals electronically for numerical display. These mechanisms ensure accurate pressure visualization, typically calibrated to atmospheric pressure as the baseline zero point.[6] In mercury sphygmomanometers, pressure from the cuff is transmitted through a tube to a reservoir of mercury, causing the liquid to rise in a vertical glass column; the height of the mercury column is directly proportional to the applied pressure, expressed in millimeters of mercury (mmHg), due to mercury's high density of 13.6 times that of water. This design provides a linear, continuous scale for precise readings, historically considered the gold standard for accuracy in non-invasive blood pressure measurement. The column must be zeroed at atmospheric pressure before use, achieved by ensuring the mercury level aligns with the zero mark when the system is open to air, preventing baseline drift from contamination or temperature variations. Scale graduations are standardized at 2 mmHg intervals to facilitate reliable interpretation across clinical settings.30352-9/fulltext)[6] Aneroid sphygmomanometers utilize a sealed, flexible metal bellows (diaphragm) connected to the cuff via tubing; as pressure increases, the bellows expands, mechanically rotating a series of gears and levers that deflect a needle across a circular dial calibrated in mmHg. This needle deflection offers a compact, portable alternative to mercury columns, with the dial's pointer returning to zero when pressure is released to atmospheric levels, a process verified by visual inspection prior to measurement. Like mercury models, aneroid scales feature 2 mmHg graduations for consistency, though regular calibration is essential to counteract potential mechanical wear. Ergonomic enhancements, such as wide visibility angles on the dial face and anti-parallax designs (e.g., mirrored scales to minimize reading errors from off-axis viewing), improve accuracy and usability in varied clinical environments.[44][63][64] Digital sphygmomanometers integrate an electronic pressure transducer (often piezoresistive) that converts cuff pressure into an electrical signal, processed by a microcontroller to display numerical values for systolic, diastolic, and mean arterial pressures directly on a liquid crystal display (LCD) screen. These displays provide clear, backlit illumination in many models to ensure readability in low-light conditions, enhancing accessibility for home or nighttime use. Advanced features include error codes or symbols, such as indicators for irregular heartbeats detected via oscillometric analysis (e.g., rhythms deviating more than 25% from the average), alerting users to potential arrhythmias like atrial fibrillation. Zeroing occurs automatically upon device activation, referencing atmospheric pressure through the transducer, with scales effectively graduating in 1-2 mmHg increments for high-resolution output. The cuff integrates seamlessly with this system via tubing, transmitting pressure without mechanical intermediaries.[65][66][67][68]Operation
Manual Operation Procedure
The manual operation of a sphygmomanometer involves the auscultatory method, where a healthcare provider uses a stethoscope to listen for Korotkoff sounds while controlling cuff inflation and deflation manually.[1] This technique requires precise steps to ensure accurate blood pressure readings, typically performed with a mercury or aneroid manometer.[69]Preparation and Patient Positioning
Before measurement, the patient should rest quietly in a seated position for at least 5 minutes in a quiet environment, with their back supported, feet flat on the floor, and legs uncrossed.[1] The arm to be measured must be supported on a flat surface at heart level, approximately halfway between the shoulder and elbow, to avoid hydrostatic pressure errors.[70] Patients should avoid caffeine, exercise, smoking, or alcohol for at least 30 minutes prior, and empty their bladder if needed, as these factors can elevate readings.[69] Explain the procedure to the patient to reduce anxiety and obtain informed consent.[1]Cuff Application
Select an appropriately sized cuff based on arm circumference: the bladder should encircle 80-100% of the arm, with a width of 40% of the circumference, to prevent over- or underestimation of pressure by up to 30 mmHg.[69] Place the cuff directly on bare skin, 2-3 cm above the antecubital fossa, with the artery marker aligned over the brachial artery; ensure it is snug but allows two fingers to fit under the edge for proper fit.[70] Avoid placing the cuff over clothing, as this can cause inaccuracies of 10-50 mmHg.[1]Estimating Systolic Pressure and Inflation
Locate the radial pulse at the wrist and palpate it while slowly inflating the cuff until the pulse disappears; note this pressure as a rough estimate of systolic blood pressure, then add 20-30 mmHg for the maximum inflation level.[69] Fully inflate the cuff to this level using the rubber bulb and valve, typically reaching 160-200 mmHg for adults, while placing the stethoscope bell over the brachial artery in the antecubital fossa.[70] This palpatory method helps avoid excessive inflation, which could discomfort the patient or miss an auscultatory gap—a temporary disappearance of sounds between 40-80 mmHg above true systolic pressure.[1]Deflation, Auscultation, and Reading
Close the valve and deflate the cuff at a steady rate of 2-3 mmHg per second, auscultating continuously for Korotkoff sounds: record systolic pressure at the onset of Phase 1 (clear tapping sounds) and diastolic pressure at Phase 5 (complete disappearance of sounds).[69] If sounds persist to 0 mmHg, use Phase 4 (muffled sounds) for diastolic in certain cases, such as in children or pregnancy.[1] Fully deflate the cuff to 0 mmHg between readings to allow arterial reperfusion, and wait 1-2 minutes before repeating for at least two or three measurements, averaging the values for the final reading in mmHg.[70] Initially measure in both arms to identify discrepancies greater than 10 mmHg, using the higher reading for subsequent assessments.[69]Precautions and Best Practices
Throughout the procedure, avoid patient movement, talking, or crossed legs, as these can falsely elevate readings by 2-10 mmHg.[1] Limit inflations to no more than five per session to prevent venous congestion, and ensure the manometer is calibrated and leak-free.[70] If an auscultatory gap is suspected, deflate to 0 mmHg and reinflate after a brief rest.[69] Record readings promptly and notify the provider if values exceed 180/110 mmHg for immediate evaluation.[1]Digital Operation Procedure
The operation of a digital sphygmomanometer begins with proper preparation to ensure accurate readings. The patient should sit comfortably in a chair with back support, feet flat on the floor, and legs uncrossed, resting quietly for at least 3 to 5 minutes beforehand to allow stabilization of blood pressure. The cuff must be applied to a bare upper arm, positioned approximately 1 inch above the elbow bend with the tubing aligned over the brachial artery, ensuring it is snug enough that two fingers can fit under the upper edge but not so tight as to pinch the skin. Unlike manual devices, digital models automatically adjust the inflation pressure limit based on the patient's estimated systolic value to prevent over-inflation.[71][72][44] To initiate measurement, the user simply presses the start button on the device, which triggers automatic cuff inflation to the predetermined pressure. As the cuff deflates gradually, the device employs oscillometric detection to sense arterial pressure oscillations and calculate systolic and diastolic values along with heart rate. Results are typically displayed on the digital screen within 30 to 60 seconds, providing a straightforward readout without the need for auditory interpretation. For enhanced reliability, many models are designed to take and average multiple consecutive readings—often three or more—with a brief interval between them, discarding outliers if necessary.[71][72][44][73] Advanced features in some digital sphygmomanometers include one-touch operation for simplicity and optional voice prompts to guide users through the process, particularly in home-use models. These devices often store readings for later review or transmission to healthcare providers via connected apps. However, user errors such as arm movement, talking, or improper positioning during measurement can introduce motion artifacts, prompting the device to display an "error" message and requiring the procedure to be repeated after repositioning. To minimize inaccuracies, patients should remain still and silent throughout the process, avoiding caffeine, exercise, or tobacco use for at least 30 minutes prior.[72][44][73]Calibration, Validation, and Maintenance
Calibration Procedures
Calibration procedures for sphygmomanometers ensure measurement accuracy and are recommended every 6 months for aneroid devices and annually for mercury devices in clinical use, in accordance with AAMI/ANSI SP10:2002 and ISO 81060 series standards.[74] These procedures involve verifying and adjusting the device's pressure readings against a known reference to maintain tolerances within ±3 mmHg across the operational range.[63] For mercury sphygmomanometers, calibration primarily verifies the mercury column height against a known pressure source, such as a calibrated pressure simulator or reference manometer, as mercury devices rely on gravitational equilibrium and rarely require mechanical adjustment.[75] The process uses tools like a calibration pump to generate controlled pressures; the device is connected via tubing and Y-connectors, then pressurized to test points (e.g., 0, 100, 200, 300 mmHg), with the mercury level compared to the reference for alignment within 1 mmHg.[36] If discrepancies occur due to contamination or tilting, the column is cleaned or leveled, followed by re-verification.[76] Aneroid and digital sphygmomanometers necessitate more frequent adjustments for zero (baseline) and span (full-scale) accuracy, using a reference manometer or pressure simulator as the standard.[40] Essential tools include a calibration pump, manometer with ±0.5 mmHg precision, and connectors for sealed connections. The step-by-step adjustment process is as follows:- Deflate the system fully and confirm the zero reading aligns with the reference (adjust the zero pin or software reset if offset exceeds 2 mmHg).
- Connect the device to the reference via Y-connector and pressurize gradually to test points (e.g., 0, 100, 200 mmHg) using the pump, ensuring deflation rate ≤10 mmHg/second.
- Record and compare readings at each point; deviations prompt span adjustment by calibrating the dial needle (for aneroid) or electronic offset (for digital) per manufacturer guidelines.
- Retest across the full range (up to 300 mmHg) to verify linearity within ±3 mmHg, repeating adjustments as needed.[63][77][78]