Cuffless blood pressure estimation using only a smartphone.

Cuffless blood pressure (BP) measurement is an all-inclusive term for a method that aims to measure BP without using a cuff. Recent cuffless technology has made it possible to estimate BP with reasonable accuracy. However, mainstream methods require an electrocardiogram and photoplethysmogram measurements, and frequent calibration procedures using a cuff sphygmomanometer. We therefore developed a far simpler cuffless method, using only heart rate (HR) and modified normalized pulse volume (mNPV) that can be measured using a smartphone, based on the knowledge that ln BP = ln cardiac output (CO) + ln total peripheral resistance (TPR), where CO and TPR are correlated with HR and mNPV, respectively. Here, we show that mean arterial pressure (MAP), systolic BP (SBP), and diastolic BP (DBP) could be estimated using the exponential transformation of linear polynomial equation, (a × ln HR) + (b × ln mNPV) + constant, using only a smartphone, with an accuracy of R > 0.70. This implies that our cuffless method could convert a large number of smartphones or smart watches into simplified sphygmomanometers.

Oscillometric sphygmomanometers: a critical appraisal of current technology.

AIM: Blood pressure (BP), a key vital sign, monitors general health. Oscillometric devices are increasingly used for measurement, although their accuracy continues to be critically debated. A functional block diagram is used to review the components that affect accuracy. METHODS: A block diagram is presented covering the components from cuff to algorithm. The oscillometric waveform is described, considering factors that can alter its shape. Methods used to assess accuracy, including the potential use of simulators, are described. RESULTS AND DISCUSSION: The block diagram focuses attention on cuff, amplifier, signal processing and algorithm. The importance of correct cuff size is emphasized. Accuracy can be affected by the extraction of the oscillometric pulses and the interpolation to compensate for higher deflation rates. Modern electronic amplifiers are assumed to be stable and do not drift, an assumption largely untested. Crucial to accuracy is the algorithm, but there is no standard algorithm and limited theoretical basis, leading to significant measurement errors in groups of patients, even by approved devices. The causes are not well understood, but differences in oscillometric waveform shape between patient groups have been observed and may explain auscultatory-oscillometric differences. The ability of theoretical models to explain the effects of arterial stiffness on BP measurements is discussed. Validation remains statistical though steps have been taken to improve it. CONCLUSION: The indirect nature of BP measurement poses particularly problems for ensuring accuracy. Critical assessment has done much to improve standards, but a solid theoretical understanding of the technique has not been formulated and further work is required.

A perfect replacement for the mercury sphygmomanometer: the case of the hybrid blood pressure monitor.

This study validated a hybrid mercury-free device as a replacement of the mercury sphygmomanometer for professional use, and also as a standard for future validations. A validation study was performed according to the European Society of Hypertension International Protocol 2010 (ESH-IP) in 33 subjects using simultaneous blood pressure (BP) measurements. A total of six BP measurements were taken per participant simultaneously by a supervisor (S; hybrid auscultatory device Nissei DM3000) and two observers (A and B; mercury sphygmomanometers). ESH-IP analysis (99 BP readings): mean device-observer systolic/diastolic BP difference 0.2±2.0/0.1±2.0 mm Hg; systolic BP differences ≤5/10/15 mm Hg in 97/99/99 readings, respectively (diastolic 98/99/99). All 33 subjects had 2 of 3 BP differences ≤5 mm Hg and none without a difference ≤5 mm Hg. Further analysis (198 BP readings): mean differences S-A 0.1±2.4/0.2±2.4 mm Hg (systolic/diastolic), S-B 0.3±2.1/0.2±2.2, A-B 0.2±2.4/0.0±2.3; differences ≤2 mm Hg S-A in 88/84% (systolic/diastolic), S-B 87/85%, A-B 87/86% and ≤4 mm Hg S-A 95/96%, S-B 95/96%, A-B 95/98%. In conclusion, a hybrid mercury-free auscultatory BP monitor comfortably passed the ESH-IP 2010 requirements and has the same level of accuracy as the mercury sphygmomanometer. This device appears to be a reliable alternative to the mercury sphygmomanometer for professional use and also as a standard for future validations.

Scipione Riva-Rocci and the men behind the mercury sphygmomanometer.

The history of the blood pressure (BP) concept and measurements is described. Many scientists were involved. Among them, major triumphs were achieved by William Harvey during the early 1600s who announced that there is a finite amount of blood that circulated the body in one direction only. In the mid-1700s, Reverend Stephen Hales reported the first invasive measurement in horses and smaller animals. Poiseuille introduced in the early 1800s the mercury hydrodynometer and the mmHg units. Karl von-Vierordt described in 1855 that with enough pressure, the arterial pulse could be obliterated. He also created the sphygmograph, a pulse recorder usable for routine non-invasive monitoring on humans. In 1881, von Basch created the sphygmomanometer and the first non-invasive BP measurements. However, in 1896, Scipione Riva-Rocci developed further the mercury sphygmomanometer, almost as we know it today. The sphygmomanometer could only be used to determine the systolic BP. Observing the pulse disappearance via palpitation would only allow the measuring physician to observe the point when the artery was fully constricted. Nikolai Korotkoff was the first to observe the sounds made by the constriction of the artery in 1905.

Has conventional sphygmomanometry ended with the banning of mercury?

The banning of mercury from clinical practice will lead to the inevitable demise of traditional clinical sphygmomanometry. There are differences in approach to this important issue between European countries on the one hand, which generally have accepted that the mercury sphygmomanometer must be replaced with alternative devices, and the U.S. on the other, where the view is that the mercury sphygmomanometer should remain as the mainstay of blood pressure measurement. The availability of alternative devices for the mercury sphygmomanometer is improving but the problem of independent validation is a serious issue, which is being addressed by the European Society of Hypertension Working Party on Blood Pressure Monitoring, which has drafted an International Protocol for validating blood pressure measuring devices. The removal of the mercury sphygmomanometer from clinical practice has other implications, which merit careful consideration; the advent of automated devices must lead inevitably to the disappearance of the traditional clinical auscultatory technique of blood pressure measurement, and with the disappearance of mercury it will be argued that the Système International(SI) unit of measurement -- the kilopascal -- should replace the millimetre of mercury.

Computer-controlled pneumatic pressure algometry--a new technique for quantitative sensory testing.

Hand-held pressure algometry usually assesses pressure-pain detection thresholds and provides little information on pressure-pain stimulus-response function. In this article, a cuff pressure algometry for advanced pressure-pain function evaluation is proposed. The experimental set-up consisted of a pneumatic tourniquet cuff, a computer-controlled air compressor and an electronic visual analogue scale (VAS) for constant pain intensity rating. Twelve healthy volunteers were included in the study. In the first part, hand-held algometry and cuff algometry were performed over the gastrocnemius muscle with constant compression rate. In the second part, the cuff algometry was performed with different compression rates to evaluate the influence of the compression rate on pain thresholds and other psychophysical data. Pressure-pain detection threshold (PDT), pain tolerance threshold (PTT), pain intensity, PDT-PTT time and other psychophysical variables were evaluated.Pressure-pain detection thresholds recorded over the gastrocnemius muscle with a hand-held and with a cuff algometer, were 482 +/- 19 kPa and 26 +/- 1.6 kPa, respectively. Pressure and pain intensities were correlated during cuff algometry. During increasing cuff compression, the subjective pain tolerance limit on VAS was 5.6 +/- 0.95 cm. There was a direct correlation between the number of compressions, the compression rate and pain thresholds. The cuff algometry technique is appropriate for pressure-pain stimulus-response studies. Cuff algometry allowed quantification of psychophysical response to the change of stimulus configuration.

[Application of the sphygmogram in evaluation of pilots' cardiovascular function in resting condition].

With the purpose of exploring a new method for aerospace medical monitoring, a newly developed method--sphygmogram was used in 169 pilots. The results showed that these pilots could be divided into three types by the features of their resting sphygmogram. Among them, with respect to their cardiovascular function, 71 (about 42%) were "completely normal", 79 were "essentially normal", and 19 had some changes in cardiovascular function. It is considered that the status of cardiovascular function of the pilots can be distinguished with the newly developed method of sphygmogram. It suggests that it is important to make dynamic observations of pilots' cardiovascular function and strengthen the medical care for those who show certain changes in their cardiovascular function as revealed by the sphygmogram.