Non-invasive blood pressure as an application of electrical impedance: a short review

Electrical bioimpedance (EBI) has gained importance as a diagnostic technique in medicine to determine the electrical properties of tissues. For example, it has been used in tissue characterization, cancer detection, and electromyography. Some of the characteristics of EBI are its low cost, the absence of irradiation during the measurement process, and its non-invasive nature. In this sense, there is interest in developing medical equipment that performs non-invasive measurements of blood pressure (BP). Electrical Impedance Plethysmography (EIP) is a technique commonly used to extract the waveform associated with BP. In this short review, we will cover research articles published in peer-reviewed journals during the last decades, and show developments in the area of EIP, with a brief discussion of relevant results and current challenges.

Bioimpedance plethysmography with capacitive electrodes and sole force sensors: comparative trial

Foot impedance plethysmography was implemented using two types of electrodes (dry and capacitive) and sole force sensors. The latter are commonly used for assessing diabetic foot ulcers (DFU). For impedance plethysmography, a tetrapolar configuration has been used with three different plantar setups: four skin contact electrodes, four capacitive contact electrodes and two Force Sensing Resistors (FSRs). In this work, FSRs have been considered as possible capacitive electrodes because the top substrate contains interdigitating conductive electrodes and a semiconductive polymer. All the measurements have been performed using a 1 mA/10 kHz excitation current and have been tried under the feet of a standing person to detect impedance plethysmography signals. Contact electrodes allow a good cardiac pulse signal while capacitive contact through the socks features mains interferences. Force sensing resistors with their force-dependent resistance in parallel to the capacitive coupling, were not able to detect cardiac pulse. But promising results can be anticipated from these findings provided higher frequencies are used and larger sensor areas to help detect altered skin states in diabetic foot.

Gravity-Induced Lower-Leg Swelling Can Be Ameliorated by Ingestion of α-Glucosyl Hesperidin Beverage

The most likely cause of lower-leg swelling is prolonged sitting, which sometimes induces deep vein thrombosis, also known as, economy class syndrome. We aimed to clarify the influence of intake of 4G-α-glucopyranosyl hesperidin (G-Hsp) beverage on the lower-leg swelling caused by 6 h of sitting in six healthy women. All subjects ingested 100 mL of G-Hsp or Placebo beverages with 100 mL of mineral water after 10 min of rest in a chair. Subsequently, subjects were requested to sit in the chair in a relaxed position for 6 h with two breaks to walk for urination. Calf water content measured by impedance plethysmography, calf circumference, and calf skin temperature by infrared thermography were measured, along with assessment of calf swelling sensation on a visual analog scale. Increase in ankle % circumference was significantly less after the G-Hsp ingestion (101.8 ± 1.5%) than after placebo (103.3 ± 0.8%; P = 0.004). A significant difference was found between percent circumference after the G-Hsp and the placebo, that is, the calf swelling after the placebo was significantly larger (P = 0.043). A gradual increase in skin temperature at the lower limb was observed after G-Hsp ingestion, while there was no change after placebo. Gravity-induced calf and ankle swelling resulted by prolonged sitting can be ameliorated by oral ingestion of hesperidin-derived G-Hsp through production of nitric oxide. It might be helpful in preventing economy-class syndrome caused by enforced sitting for a long duration.

Bio-Impedance Measurement Optimization for High-Resolution Carotid Pulse Sensing

Continuous hemodynamic monitoring is important for long-term cardiovascular healthcare, especially in hypertension. The impedance plethysmography (IPG) based carotid pulse sensing is a non-invasive diagnosis technique for measuring pulse signals and further evaluating the arterial conditions of the patient such as continuous blood pressure (BP) monitoring. To reach the high-resolution IPG-based carotid pulse detection for cardiovascular applications, this study provides an optimized measurement parameter in response to obvious pulsation from the carotid artery. The influence of the frequency of excitation current, electrode cross-sectional area, electrode arrangements, and physiological site of carotid arteries on IPG measurement resolution was thoroughly investigated for optimized parameters. In this study, the IPG system was implemented and installed on the subject’s neck above the carotid artery to evaluate the measurement parameters. The measurement results within 6 subjects obtained the arterial impedance variation of 2137 mΩ using the optimized measurement conditions, including excitation frequency of 50 kHz, a smaller area of 2 cm2, electrode spacing of 4 cm and 1.7 cm for excitation and sensing functions, and location on the left side of the neck. The significance of this study demonstrates an optimized measurement methodology of IPG-based carotid pulse sensing that greatly improves the measurement quality in cardiovascular monitoring.

Arterial Parameters in Type-2 Diabetes and Healthy Subjects by using Impedance Plethysmography: A Case-control Study

Introduction: A reduced blood supply to lower limb, due to arterial disease, is a common cause of foot ulceration in patients with Diabetes Mellitus (DM). Impedance Plethysmography (IPG) is based on the measurement of changes in the electrical resistance (impedance) caused by blood volume changes. Aim: To compare parameters of type-2 diabetic subjects with those of healthy subjects along with different age group and to associate with Blood Flow Index (BFI), Fasting Blood Sugar (FBS), Post-Prandial Blood Sugar (PP2BS) and Body Mass Index (BMI). Materials and Methods: This case-control study was conducted at Government Medical College and in UHTC, Bhavnagar, Gujarat, India, from May 2012 to August 2013 on 100 healthy subjects and 100 type-2 diabetic subjects. IPG arterial parameters like BFI, Pulse Arrival Time (PAT), Pulse Termination Time (PTT), Differential Pulse Arrival Time (DPAT), Z0 (Basal impedance) recorded. The data were analysed by unpaired t-test and ANOVA test. Results: This study had 200 subjects of age more than 30 years. The diabetic subjects included 56 males and 44 females whereas the healthy subjects included 67 males and 33 females. There was bilateral significant reduction of BFI, PAT at knee, ankle and calf segment among diabetics group in males and females; and a bilateral significant reduction of PTT at ankle segment among diabetic males and females. DPAT value increased at knee, calf and ankle segment on both sides in male and female; except right ankle segment in diabetic group in females as compared to healthy subjects. Z0 increased at knee, ankle and calf segment in diabetic group on both side in males and females. BFI decreased with an increase in the duration of diabetes. The effect of FBS, PP2BS and BMI in diabetic subjects suggested a negative association with BFI. Conclusion: There was decrease in BFI, PAT, PTT and increase in DPAT in the knee, calf and ankle region of diabetic subjects. BFI negatively correlated with FBS, PP2BS and BMI among diabetics and decreased with increased duration of DM

Segmental volume and circulatory changes that occur in humans and Rhesus monkeys during 4 hour, −6 degree head down tilt

Nonhuman primates are often used to investigate physiologic processes that occur in man during aerospace/cardiovascular orthostatic research. Few studies have compared nonhuman primates and man under identical test conditions to assess the degree of similarity between the two species. Impedance plethysmography was used to measure calf, thigh, pelvic, thoracic, upper arm, and lower arm volume changes in eight rhesus (Macacca Mulatta) monkeys and twelve human subjects during four hour exposures to −6 degree head down tilt (HDT).

Electrical impedance plethysmography versus tonometry to measure the pulse wave velocity in peripheral arteries in young healthy volunteers: a pilot study

The leading cause of health loss and deaths worldwide are cardiovascular diseases. A predictor of cardiovascular diseases and events is the arterial stiffness. The pulse wave velocity (PWV) can be used to estimate arterial stiffness non-invasively. The tonometer is considered as the gold standard for measuring PWV. This approach requires manual probe fixation above the artery and depends on the skills of the operator. Electrical impedance plethysmography (IPG) is an interesting alternative using skin surface sensing electrodes, that is miniaturizable, cost-effective and allows measurement of deeper arteries. The aim of this pilot study was to explore if IPG can be a suitable technique to measure pulse wave velocity in legs as an alternative for the tonometer technique. The PWV was estimated by differences in the ECG-gated pulse arrival times (PAT) at the a. femoralis, a. popliteal, a. tibialis dorsalis and a. dorsalis pedis in nine healthy young adults using IPG and the SphygmoCor tonometer as a reference. The estimated PWV results from bioimpedance and the tonometer were fairly in agreement, and the beat-to-beat variability in PAT was similar. This pilot study indicates that the use of IPG may be a good alternative for estimating PWV in the legs.