Direct Determination rather than Oscillometric Estimation of Systolic Blood Pressure in Patients with Severe Chronic Kidney Disease

<b><i>Introduction:</i></b> Although arterial hypertension is a major concern in patients with chronic kidney disease (CKD), obtaining accurate systolic blood pressure (SBP) measurement is challenging in this population for whom automatic oscillometric devices may yield erroneous results. <b><i>Methods:</i></b> This cross-sectional study was conducted in 89 patients with stages 4, 5, and 5D CKD, for whom we compared SBP values obtained by the recently described systolic foot-to-apex time interval (SFATI) technique which provides direct SBP determination, the standard technique (Korotkoff sounds), and oscillometry. We investigated the effects of age, sex, diabetes, CKD stage, and pulse pressure to explain measurement errors defined as biases or misclassification relative to the SBP thresholds of 110–130-mm Hg. <b><i>Results:</i></b> All 3 techniques showed satisfactory reproducibility for SBP measurement (CCC &#x3e; 0.84 and &#x3e;0.91, respectively, in dialyzed and nondialyzed patients). The mean ± SD from SBP as determined via Korotkoff sounds was 1.7 ± 4.6 mm Hg for SFATI (CCC = 0.98) and 5.9 ± 9.3 mm Hg for oscillometry (CCC = 0.88). Referring to the 110–130-mm Hg SBP range outside which treatment prescription or adaptation is recommended for CKD patients, SFATI underestimated SBP in 3 patients and overestimated it in 1, whereas oscillometry underestimated SBP in 12 patients and overestimated it in 3. Higher pulse pressure was the main explanatory factor for measurement and classification errors. <b><i>Discussion/Conclusion:</i></b> SFATI provides accurate SBP measurements in patients with severe CKD and paves the way for the standardization of automated noninvasive blood pressure measurement devices. Before prescribing or adjusting antihypertensive therapy, physicians should be aware of the risk of misclassification when using oscillometry.

Deep learning-based robust automatic non-invasive measurement of blood pressure using Korotkoff sounds

This paper proposes a method that automatically measures non-invasive blood pressure (BP) based on an auscultatory approach using Korotkoff sounds (K-sounds). There have been methods utilizing K-sounds that were more accurate in general than those using cuff pressure signals only under well-controlled environments, but most were vulnerable to the measurement conditions and to external noise because blood pressure is simply determined based on threshold values in the sound signal. The proposed method enables robust and precise BP measurements by evaluating the probability that each sound pulse is an audible K-sound based on a deep learning using a convolutional neural network (CNN). Instead of classifying sound pulses into two categories, audible K-sounds and others, the proposed CNN model outputs probability values. These values in a Korotkoff cycle are arranged in time order, and the blood pressure is determined. The proposed method was tested with a dataset acquired in practice that occasionally contains considerable noise, which can degrade the performance of the threshold-based methods. The results demonstrate that the proposed method outperforms a previously reported CNN-based classification method using K-sounds. With larger amounts of various types of data, the proposed method can potentially achieve more precise and robust results.

Abstract P171: The Intermediate Korotkoff Sounds: Variation In Sound Proportions In Different Age Groups Of Men And Women In A Healthy Adult Population

There are 5 known Korotkoff sounds which occur during a standard blood pressure (BP) measurement cycle, the first 4 (K1 to K4) having specific acoustic signatures, and the fifth (K5) occurring where sound first becomes absent. The different Korotkoff sound proportions (KSPs) are not well understood. Using bespoke acoustic analysis technology, we compared KSPs (K1P, K2P, K3P, K4P) in normotensive men and women at different ages and described the effect of normalising the cuff deflation rate (CDR) to allow 60 heart beats (CDR 60 ) versus a standard 3mmHg/s (CDR 3mmHg ). At a CDR 3mmHg , men had a higher K2P (36% vs 26%, p=0.006) and lower K3P (27% vs 38%, p=0.002) than women. K3P significantly increased with age in both men (p<0.001) and women (p<0.004). CDR 60 caused a significant drop in K2P (p<0.001) and rise in K3P (p=0.019). These differences may reflect changes in vascular stiffness which may vary with gender, age and CDR. To our knowledge, this phenomenon has never been described before and requires further investigation.

Abstract P192: Is Auscultation Adequate To Estimate Blood Pressure Responses Related To Body Position Changes?

Double-blinded auscultation is the current reference to validate new devices in the sitting position. There are few data to tell whether it should be used for device validation in other body positions, as the Korotkoff sounds can be affected by changes in vascular tone. In this study, we recorded the BP response to orthostatic posture change (standing to supine) in 75 subjects, aged between 21 and 65 years old. Systolic (SBP) and diastolic (DBP) were measured on the left upper arm by auscultation by two independent blinded observers before and 150s after posture change. In case the observers did not agree, i.e. readings differed more than 4 mmHg, the measurement was repeated. Beat-to-beat BP values were measured on the ipsilateral middle finger with Nexfin (BMEYE, The Netherlands). Because Nexfin measurements were not available during upper-arm cuff inflation, the mean of the values in a 30s window prior to auscultation onset was used for the analysis. The distribution of the BP responses to posture change was characterized in terms of median, 10 th and 90 th percentiles (see Table). The response was considered consistent if these percentiles were on the same side of zero. Neither auscultation nor Nexfin detected any consistent posture-related changes in SBP when going from standing to supine. Nexfin detected a consistent decrease in DBP. Auscultation detected no consistent posture-related change. Compared to volume-clamp, auscultation was not able to detect any consistent changes in DBP during orthostatic challenge. Our study suggests that the use of Korotkoff sounds to estimate BP in body positions other than sitting may not be appropriate.

Non-invasive methods for studying the dynamics of blood pressure

The paper summarizes the main methods of automatic non-invasive assessment of the blood pressure (BP) dynamics. The advantages and disadvantages of BP measurement according to Korotkoff sounds and the oscillations in the brachial cuff are discussed. Currently, BP is measured during deflation of the cuff, while the pressure in the cuff should be inflated (by about 20–30 mm Hg) above the systolic BP. The BP level before measurement can be unknown, thereby increases the possibility of raising the pressure in the cuff above the optimum. In connection with this, recently, methods for determining BP during inflation of the cuff have been proposed. The BP value, determined both by Korotkov’s tone and by oscillometry during inflation, differs from that during the deflation of the cuff. The difference varies with age and BP and in a number of cases is clinically significant. The causes and consequences of such differences are discussed. In intensive care units and in operating rooms, continuous BP measurement is necessary. In comparison with the discrete measurement of BP, it allows to detect timely hypotension, to evaluate its duration, which improves the management of the patients. The invasive method of BP detection has known limitations and complications which stimulated the development of devices for non-invasive BP control. Despite the comparisons of the accuracy of such measurement methods, this issue continues to be debated. Thus, the methods of non-invasive control of BP level, discussed in this review, reflect both their advantages and limitations, which dictates the need for further research in this field.