Blood pressure (BP) measurement is a common and imperative component of physical examinations in children and adults. Although the prevalence of hypertension in children is lower than that in adults, its early detection is crucial for preventing later complications. Before recognizing the BP as normal or high, we must ensure its accurate measurement. BP in children can be affected by several factors such as measurement technique, emotional state, and activity level. The accommodation effect and measurement device type are 2 critical factors for BP measurement accuracy in children. The accommodation effect refers to the fact that BP usually decreases as measurements are repeated. Therefore, multiple BP measurements are recommended before the diagnosis of elevated BP [1]. There are several methods for measuring BP, including the mercury sphygmomanometer (MS). First introduced more than 110 years ago, the MS has been the gold standard method for obtaining BP and diagnosing hypertension in children. However, because of environmental issues related to mercury toxicity, the MS will no longer be used. This review article describes several BP measurement methods and speculates on what may replace MS in children.

Blood circulation in the body is caused by the continuous pumping action of the heart, which creates a pulsating flow when it drains blood from the left ventricle to the aorta. The systolic BP (SBP) is defined as the maximum pressure exerted against the inner walls of the blood vessels when the left ventricle contracts, while the diastolic BP (DBP) is defined as the force exerted during relaxation and dilation of the heart [10]. A noninvasive auscultatory method that easily measures arterial BP using a stethoscope and the bladder of the BP cuff was developed about 110 years ago by Nikolai Korotkoff [11]. Despite efforts to establish a superior BP measurement method, the auscultation method by Korotkoff remains the gold standard. Initially, Korotkoff described 4 sound phases, to which a fifth phase was added later. The pressure at the first audible sound during the slow loosening of the inflated cuff (Korotkoff phase I) was recorded as the SBP, while the pressure at the moment all sounds (Korotkoff phase V) disappear was recorded as the DBP. A sphygmomanometer and stethoscope are required to measure arterial BP using Korotkoff’s auscultatory method.

bladder (cuff) through a rubber tube and consists of a pressure gauge or mercury column. The auscultation method using an MS is the gold standard for recording BP. An MS usually does not require calibration since the density of mercury cannot be changed, although periodic maintenance is necessary, such as filter cleaning [12]. Due to environmental and personal health concerns, international efforts have been made to discard healthcare sources of mercury in the thermometer and sphygmomanometer and replace them with less toxic alternatives [13,14]. Therefore, the clinical standard of auscultatory methods using mercury columns has given way to oscillometric devices in recent adult guidelines [15]. However, the MS is considered the standard device for BP measurement in epidemiological surveys in adults [16]. Moreover, in children, it should be noted that the BP table for the diagnosis of hypertension was made based on values using an MS [2,17]. There is a need for a method that can replace MS for measuring BP and diagnosing hypertension in children and adolescents.

Oscillometric devices have the advantage of eliminating human observer errors since they all provide a digital readout of the BP. Unlike the auscultatory method, oscillometry calculates a person’s SBP and DBP, and each manufacturer of oscillometric devices uses its own algorithm for the calculation by examining the reflected oscillating pulse wave that is generated inside the deflating bladder [10,12]. A typical oscillometric device automatically inflates the cuff and then gradually deflates it to a pressure below the diastolic pressure. The oscillations begin above the systolic pressure and continue below the diastolic pressure so the SBP and DBP can only be estimated indirectly according to some empirically derived algorithms. Even a child’s small movements can affect oscillometric pulses, which are essential to determining an accurate BP; therefore, it is challenging to measure BP in children who cry, shiver, or move.

The empirical nature of oscillometry requires validation of each model’s accuracy [26]. Although many devices are marketed by different manufacturers, less than 15% pass validation studies. This issue is crucial in children, in whom few devices have been successfully validated using an established protocol [27]. Recent studies described models that have been validated in children, and we can read a device’s user manual to see whether validation was performed and what protocol was used [27]. Oscillometric devices are convenient because their measurements are fully automated, they do not require training, and they have good interrater reliability. However, their accuracy in children remains uncertain. Each method mentioned above has advantages and disadvantages (Table 2).

Recently, as the tools for BP measurement have diversified and the mobile market has evolved, a method using a mobile application for BP measurement has emerged. Instead of wrapping the bladder cuff around the arm and pumping air into it, a user simply places a finger on the smartphone to measure BP and checks the results through the mobile application. When the patient puts a finger on the smartphone camera sensor, the sensor emits a 940-nm light-emitting diode, the light of which reaches the photodetector after passing through the finger [30]. This photoplethysmography (PPG) signal detects changes in blood flow corresponding to the patient’s natural pulsation, and SBP and DBP can be measured according to the algorithm of each application. In 2020, traditional BP using an arterial catheter and BP using a smartphone were simultaneously measured and analyzed in 50 adults to determine the accuracy of “BP measured by applying the PPG signal obtained from the smartphone to the dedicated app (OptiBP)” [36]. The difference between the 2 values showed only the difference of SBP -0.7±7.7 mmHg, DBP -0.4±4.5 mmHg, and mean BP -0.6±5.2 mmHg, confirming the accuracy of mobile application-based BP. Another study compared the BP of senior nursing students (aged over 18 years) using a traditional automated BP cuff versus that using PPG signals in Apple iOS health applications. The article reported that DBP was significantly overestimated by the mobile application at SBP 122.94 mmHg/DBP 76.62 mmHg in the traditional method and SBP 125.72 mmHg/DBP 81.86 mmHg in the mobile method [37]. No studies have examined smartphone-based PPG using BP measurements in children. However, in a study comparing BP with standard ABPM using pulse transit time, a cuffless BP measurement method, the mean SBP and DBP of 30 patients aged 10–18 years with primary hypertension or a high normal BP were evaluated. As a result, the cuffless device showed a significantly higher BP (standard vs. cuffless device: SBP 123.47±14.91 mmHg and 127.48±15.98 mmHg, P<0.001; DBP 66.88±11.86 mmHg and 68.52±12.36 mmHg, P<0.001).38) More research in pediatric populations is needed, and a certified validation protocol for each manufacturer’s device and algorithm should be developed. The World Health Organization technical specification for an automated noninvasive BP measuring device with a cuff showed concern that BP measurements using smartphone application are in the early stages of research and development and may lead to wrong clinical decision due to the absence of validation protocols and inaccuracy of measurements and expressed the expectation that it improves hypertension diagnostics by increasing interest and ease of BP measurement [30]. It is currently in the early stage of research, and we expect that the subject will be expanded to children and adolescents in the future. If the problem of low accuracy is improved, it will be possible to improve the quality of medical care and reduce medical costs for vulnerable populations.

A recent study of Korean adults compared the accuracy and errors of BP measured by 2 types of non-MS devices in an epidemiologic survey [39]. The researchers alternatively used an MS and 2 electronic devices and calculated the BP measurement differences, defined as BP measured by MS minus BP obtained by 2 electronic devices. The concordance correlation coefficients were not significantly different for SBP (mean differences: -0.52 and -0.62 mmHg, P=0.76; concordance correlation coefficients: 0.97 and 0.94), but the concordance correlation coefficient for DBP were significantly different among manufacturers (mean differences: -0.78 and 6.23 mmHg, P<0.01; concordance correlation coefficients: 0.95 and 0.76) [39]. In 2018, a similarly designed study of the Korean National Health and Nutrition Examination Survey Program was conducted in children over 10 years of age to determine which BP measurement device is most suitable for replacing MS in future surveys. A direct comparison among the 3 devices under well-controlled BP measurement protocols suggested significant differences among manufacturers in children and adolescents as seen in adults, especially for DBP (unpublished data). Two recent guidelines for hypertension in children recommended that oscillometric devices may be used for BP screening in children, and if they detect hypertension, the values must be confirmed using the auscultatory method. They emphasize that at least 3 BP measurements obtained at rest by manual auscultation are essential when diagnosing a child or adolescent with hypertension [2,17,40]. ABPM may also help diagnose hypertension in cases of elevated manual auscultatory BP values [3,5].

In conclusion, although oscillometric devices have become widely used in children, they have not yet completely replaced MS or other auscultatory methods, especially for confirming hypertension in children. The aneroid or hydrid auscultatory device can be a good alternative to MS, and hybrid devices have the advantage that they usually do not require regular calibration of aneroid devices. There is a need for further discussion about a BP measurement device that can replace mercury, and it can be said that the mobile application-based BP measurement has very high development potential because of its convenience and accessibility, even though it is still in the early stages of research.