Carditech, California, USA University Of West Bohemia, Czech Republic Wrist Cuff Method Determines Diastolic Pressure in Dual Cuff Blood Pressure System Jiri Jilek Carditech, California, USA Milan Stork University Of West Bohemia, Czech Republic

Abstract Single cuff noninvasive blood pressure (BP) measurements performed manually or automatically are subject to errors. We developed an experimental system that uses two cuffs in order to improve accuracy of noninvasive BP measurement. This study concentrated on a novel determination of diastolic BP using wrist cuff pulse waveforms and arm cuff pressures. The method was compared with the oscillometric method using the British Hypertension Society agreement grading system. The resulting grade was B- “good agreement”. The wrist cuff method may prove to be better than single cuff methods because it is based on physiological principles.

I. INTRODUCTION Manual method for blood pressure (BP) measurement uses a sphygmomanometer and a stethoscope. Systolic and diastolic pressures are determined from Korotkoff sounds and cuff pressures. The systolic pressure (SBP) is the cuff pressure at the point of first appearance of Korotkoff sounds. The diastolic pressure (DBP) is the point of the disappearance of Korotkoff sounds. Automatic BP monitors are fast becoming the most popular method in the hospital, the clinic, and the home. Most BP monitors use single cuff oscillometric method. The method evaluates amplitudes of arterial pulsations in the cuff. The oscillometric method can determine SBP and DBP, but the measurements are not based on physiological principles. The oscillometric method has accuracy problems that have been described in literature.

I. INTRODUCTION (2) We developed an experimental dual cuff system for the determination of blood pressures and hemodynamics that uses an arm cuff and a wrist cuff. The arm cuff functions as an occluding cuff in a manner identical to the manual BP method or an automatic method. The wrist cuff functions as a pulse detector . The system configuration is shown in Figure 1. Figure 1. Dual cuff system

II. METHODS (1) Block diagram of the main module is shown in Figure 2. It consists of two similar circuits for the arm and the wrist cuffs. Cuff pressures and waveforms are digitized in the submodule. Digitized signals are sent via USB to the laptop computer. Windows based software performs data processing, display and storage functions. Figure 2. Block diagram of the dual cuff system module

Wrist cuff (WW) and arm cuff (AW) waveforms are shown in II. METHODS (2) Wrist cuff (WW) and arm cuff (AW) waveforms are shown in Figure 3. ACP is arm cuff pressure. Point of SBP is at the onset of WW waveforms. Point of DBP (W-DBP) is reached when WW amplitudes no longer increase. Figure 3. Pulse waveforms from the wrist and the arm cuffs during gradual arm cuff deflation.

WW amplitudes increase when ACP is higher than the point of DBP. II. METHODS (3) Figure 4 shows WW and AW waveforms near the point of wrist cuff DBP (W-DBP). WW amplitudes increase when ACP is higher than the point of DBP. WW amplitudes at the point of W-DBP no longer increase. The value of ACP at this point is the value of DBP. The AW amplitudes decrease during this segment of ACP gradual decrease. Figure 4. Detailed segment near the point of W-DBP

III. RESULTS Results in Table I show mean values, standard deviations (SD) and ranges for five variables. W-SBP is wrist SBP, W-MAP is wrist MAP, O-MAP is oscillometric MAP, W-DBP is wrist DBP, and O-DBP is oscillometric DBP. Table 1. Mean values, standard deviations and ranges of computed variables N=50

IV. DISCUSSION (1) Because we did not have the opportunity to obtain direct DBP values, we compared the W-DBP method with the O-DBP (oscillometric) method. We used British Hypertension Society (BHS) grading system for comparison of BP devices. The results are shown in Table II. The comparison grade was “good agreement”. The category of differences larger than 9 mmHg and smaller than 15 mmHg had eight values. Seven values had corresponding SBP values higher than 140 mmHg which qualify those tests as hypertension (HTN). Table II. BHS grading of agreement between O-DBP and W-DBP

IV. DISCUSSION (2) Sixteen of the 50 wrist tests had BP values that qualified them as isolated systolic hypertension (ISH) (SBP > 140 and DBP < 90 mmHg). Nine of the 50 oscillometric tests qualified as ISH. Prevalence of ISH is much higher in individuals older than 60 years. All individuals in our ISH group were over 60 years old. Decreased arterial compliance has been associated with ISH and with increased errors in oscillometric BP determination. It is reasonable to conclude that the W-DBP method may be more accurate than the oscillometric method. Another factor in favor of the W-DBP method is the fact that it is based on physiological principle.

V. CONCLUSION The results in this study indicate that the wrist cuff method for the determination of DBP may be sufficiently accurate to replace the oscillometric method. It is, however, prudent to consider our results and conclusions preliminary. Further studies are necessary to validate the results of our study. END