Analyzing the radial pulse waveform: narrowing the gap between blood pressure and outcomes

Pulse wave response characteristics for thickness and hardness of the cover layer in pulse sensors to measure radial artery pulse

Background

Piezo-resistive pressure sensors are widely used for measuring pulse waves of the radial artery. Pulse sensors are generally fabricated with a cover layer because pressure sensors without a cover layer are fragile when they come into direct contact with the skin near the radial artery. However, no study has evaluated the dynamic pulse wave response of pulse sensors depending on the thickness and hardness of the cover layer. This study analyzed the dynamic pulse wave response according to the thickness and hardness of the cover layer and suggests an appropriate thickness and hardness for the design of pulse sensors with semiconductor device-based pressure sensors.

Methods

Pulse sensors with 6 different cover layers with various thicknesses (0.8 mm, 1 mm, 2 mm) and hardnesses (Shore type A; 30, 43, 49, 71) were fabricated. Experiments for evaluating the dynamic pulse responses of the fabricated sensors were performed using a pulse simulator to transmit the same pulse wave to each of the sensors. To evaluate the dynamic responses of the fabricated pulse sensors, experiments with the pulse sensors were conducted using a simulator that artificially generated a constant pulse wave. The pulse wave simulator consisted of a motorized cam device that generated the artificial radial pulse waveform by adjusting the stroke of the cylindrical air pump and an air tube that conveyed the pulse to the artificial wrist.

Results

The amplitude of the measured pulse pressure decreased with increasing thickness and hardness of the cover layer. Normalized waveform analysis showed that the thickness rather than the hardness of the cover layer contributed more to waveform distortion. Analysis of the channel distribution of the pulse sensor with respect to the applied constant dynamic pressure showed that the material of the cover layer had a large effect.

Conclusions

In this study, in-line array pulse sensors with various cover layers were fabricated, the dynamic pulse wave responses according to the thickness and the hardness of the cover layer were analyzed, and an appropriate thickness and hardness for the cover layer were suggested. The dynamic pulse wave responses of pulse sensors revealed in this study will contribute to the fabrication of improved pulse sensors and pulse wave analyses.

Arterial Stiffness, Kidney Function, and Chronic Kidney Disease Progression

Arterial stiffness can nowadays be measured easily and noninvasively around the globe. Although well established as an independent predictor of cardiovascular events, less is known about the role of arterial stiffness in the progressive loss of kidney function once chronic kidney disease (CKD) is established. In addition to measures of arterial stiffness, a number of devices now noninvasively record the pulse profile from sites such as the radial artery and, using internal algorithms, are able to estimate central pressure profiles. Although these devices have generated much data on the prediction of cardiovascular events, e.g. measures of arterial stiffness, there is much less known about the predictive utility of these measures in CKD progression. In this review, we cover approaches to arterial stiffness as measured by pulse wave velocity and discuss measures of the systolic and diastolic contour of the pulse waveform vis-à-vis their relationship to declines in kidney function over time. We restrict our coverage to studies that have longitudinal data, but we also include a table of studies, which, to our knowledge, have only published cross-sectional data at this time.

Central blood pressure and chronic kidney disease progression

Hypertension, diabetes, and proteinuria are well-recognized risk factors for progressive kidney function loss. However, despite excellent antihypertensive and antidiabetic drug therapies, which also often lower urinary protein excretion, there remains a significant reservoir of patients with chronic kidney disease who are at high risk for progression to end-stage kidney disease. This has led to the search for less traditional cardiovascular risk factors that will help stratify patients at risk for more rapid kidney disease progression. Among these are noninvasive estimates of vascular structure and function. Arterial stiffness, manifested by the pulse wave velocity in the aorta, has been established in a number of studies as a significant risk factor for kidney disease progression and cardiovascular endpoints. Much less well studied in chronic kidney disease are measures of central arterial pressures. In this paper we cover the physiology behind the generation of the central pulse wave contour and the studies available using these approaches and conclude with some speculations on the rationale for why measurements of central pressure may be informative for the study of chronic kidney disease progression.

Blood pressure level and kidney disease progression: do we really need to go to 130/80 mm Hg?

Current guidelines recommend a blood pressure goal of less than 130/80 mm Hg in patients with chronic kidney disease. Considerable epidemiologic observational data, post hoc analyses of clinical trials, and meta-analyses support this goal, particularly in patients with proteinuria. Although prospective clinical trials have not shown a clear benefit, recent data indicate that a longer duration of follow-up may be needed to assess the effects of different blood pressure goals. While we await the results of several ongoing and planned studies in this area, the current recommendations of a blood pressure goal less than 130/80 mm Hg appear reasonable.

Aortic pulse pressure is associated with carotid IMT in chronic kidney disease: report from Chronic Renal Insufficiency Cohort

BACKGROUND

Patients with chronic kidney disease (CKD) have a disproportionate risk of cardiovascular disease. This study was designed to assess the association between two noninvasive measures of cardiovascular risk, pulse wave analysis (PWA), and carotid intima-media thickness (IMT), in a cohort of CKD patients enrolled in the Chronic Renal Insufficiency Cohort (CRIC) study.

METHODS

Three hundred and sixty-seven subjects with CKD enrolled in the CRIC study at the University of Pennsylvania site (mean age 59.9 years, blood pressure 129/74 mm Hg, estimated glomerular filtration rate 48 ml/min/1.73 m2, IMT 0.8 mm) had both carotid IMT and PWA measurements. Carotid ultrasound was also used to determine the presence of plaque. PWA was used to determine augmentation index (AI), amplification ratio (AMPR), aortic pulse pressure (C_PP), and central aortic systolic pressure (C_SP).

RESULTS

IMT was significantly associated with all PWA-derived measures. However, on multivariable linear regression analysis, only AMPR (regression coefficient -0.072, P = 0.006), C_PP (regression coefficient 0.0025, P < 0.001), and C_SP (regression coefficient 0.0017, P < 0.001) remained significantly associated with IMT. The prevalence of carotid plaque in the cohort was 59%. Of the PWA-derived measures, only C_PP was significantly associated with the presence of carotid plaque (P < 0.001).

CONCLUSIONS

PWA-derived measures are associated with carotid IMT and plaque in the CKD. Of these measures, C_PP was most associated with carotid IMT and plaque.

The message for World Kidney Day 2009: hypertension and kidney disease--a marriage that should be prevented

The prevalence of chronic kidney disease (CKD) continues to increase worldwide as does end-stage renal disease. The most common, but not the only, causes of CKD are hypertension and diabetes. CKD is associated with a significant increase in cardiovascular risk as most patients with CKD die of a cardiovascular cause. Moreover, cardiovascular risk increases proportionally as estimated glomerular filtration rate falls below 60 ml/min. Cardiovascular causes of death in CKD are more prevalent than those from cancer; as a result, the identification and reduction of CKD is a public health priority. High blood pressure is a key pathogenic factor that contributes to the deterioration of kidney function. The presence of kidney disease is a common and underappreciated preexisting medical cause of resistant hypertension. Therefore, treatment of hypertension has become the most important intervention in the management of all forms of CKD. For this reason, the forthcoming World Kidney Day on 12 March 2009 will emphasize the role of hypertension.

The message for World Kidney Day 2009: hypertension and kidney disease: a marriage that should be prevented

The prevalence of chronic kidney disease (CKD) continues to increase worldwide as does end stage renal disease. The most common, but not only, causes of CKD are hypertension and diabetes. CKD is associated with a significant increase in cardiovascular (CV) risk as most patients with CKD die of a CV cause. Moreover, CV risk increases proportionally as estimated glomerular filtration rate falls below 60 mL/min. CV causes of death in CKD are more prevalent than those from cancer; as a result, the identification and reduction of CKD is a public health priority. High blood pressure is a key pathogenic factor that contributes to the deterioration of kidney function. The presence of kidney disease is a common and underappreciated preexisting medical cause of resistant hypertension. Therefore, treatment of hypertension has become the most important intervention in the management of all forms of CKD. For this reason, World Kidney Day on March 12, 2009 will emphasize the role of hypertension.

Effects of salt substitute on pulse wave analysis among individuals at high cardiovascular risk in rural China: a randomized controlled trial

Reduced-sodium, increased-potassium salt substitutes lower blood pressure but may also have direct effects on vascular structure and arterial function. This study aimed to test the effects of long-term salt substitution on indices of these outcomes. The China Salt Substitute Study was a randomized, controlled trial designed to establish the effects of salt substitute (65% sodium chloride, 25% potassium chloride, 10% magnesium sulfate) compared with regular salt (100% sodium chloride) on blood pressure among 600 high-risk individuals living in six rural areas in northern China over a 12-month intervention period. Data on central aortic blood pressure, aortic pressure augmentation (AUG), augmentation index (AIx), the differences of the peak of first and baseline waves (P(1)-P(0)) and pulse wave reflection time (RT) were collected at randomization and at the completion of follow-up in 187 participants using the Sphygmocor pulse wave analysis system. Mean baseline blood pressure was 150.1/91.4 mm Hg, mean age was 58.4 years, 41% were male and three quarters had a history of vascular disease. After 12 months of intervention, there were significant net reductions in peripheral (7.4 mm Hg, P=0.009) and central (6.9 mm Hg, P=0.011) systolic blood pressure levels and central pulse pressure (4.5 mm Hg, P=0.012) and correspondingly there was a significant net reduction in P(1)-P(0) (3.0 mm Hg, P=0.007), borderline significant net reduction in AUG (1.5 mm Hg, P=0.074) and significant net increase in RT (2.59 ms, P=0.001). There were no detectable reductions in peripheral (2.8 mm Hg, P=0.14) or central (2.4 mm Hg, P=0.13) diastolic blood pressure levels or AIx (0.06%, P=0.96). In conclusion, over the 12-month study period the salt substitute significantly reduced not only peripheral and central systolic blood pressure but also reduced arterial stiffness.

The message for World Kidney Day 2009: hypertension and kidney disease--a marriage that should be prevented

The prevalence of chronic kidney disease (CKD) continues to increase worldwide as does end stage renal disease. The most common, but not the only, causes of CKD are hypertension and diabetes. CKD is associated with a significant increase in cardiovascular (CV) risk as most patients with CKD die of a CV cause. Moreover, CV risk increases proportionally as eGFR falls below 60 ml min(-1). CV causes of death in CKD are more prevalent than those from cancer are; as a result, the identification and reduction of CKD is a public health priority. High blood pressure is a key pathogenic factor that contributes to the deterioration of kidney function. The presence of kidney disease is a common and underappreciated pre-existing medical cause of resistant hypertension. Therefore, treatment of hypertension has become the most important intervention in the management of all forms of CKD. For this reason, the forthcoming World Kidney Day on 12 March 2009 will emphasize the role of hypertension.