Arteriolar Elasticity Measurement in the Fingertip Based on Photoplethysmographic Volume-Oscillometry: A New Approach to the Assessment of Vasomotor Functions in the Microvasculature.

Purpose: Dysfunction of vasomotor reactions due to arteriolar smooth muscle causes serious adverse events, such as loss of hemodynamic coherence. This in turn can increase risks of cardiovascular-related diseases. A noninvasive and quantitative evaluation of microvascular disorder is therefore very important for early diagnosis and treatment.

A new noninvasive technique for heat-flux-based deep body thermometry together with possible estimation of thermal resistance of the skin tissue.

A new noninvasive core-thermometry technique, based on the use of two heat flux sensors with different very low thermal resistances, is proposed. Thermodynamically derived equations, using a pair of skin temperatures and heat fluxes detected from the sensors, can give the estimated deep body temperature (DBT) together with thermal resistance of the skin tissue itself. The validity and accuracy of this method are firstly investigated through in vitro experiments using a tissue phantom model and, secondly, as in vivo comparisons with sublingual (T) or rectal temperature (T) measurements in 9 volunteers, attaching the sensors around the upper sternum or the nape.

Peripheral arterial elasticity changes derived by volume-oscillometry in reaction to hyperemia as a possible assessment of flow-mediated vasodilatation.

The flow-mediated dilation (FMD) test is commonly utilized and is the only technique for the assessment of vascular endothelial cell function. With this test, the augmentation of a brachial artery diameter following reactive hyperemia is measured precisely using ultrasonography by a skilled operator. This is a hospital-only test, and would be more useful if conveniently performed at home.

Volume elastic modulus with exponential function of transmural pressure as a valid stiffness measure derived by photoplethysmographic volume-oscillometry in human finger and radial arteries: potential for arteriosclerosis screening.

Noninvasive and convenient measurement of vascular stiffness is of considerable importance for early detection and treatment of arteriosclerosis. Volume elastic modulus ([Formula: see text]) is one of representative measures reflecting effective vascular elasticity that is strongly dependent upon blood pressure (BP) or transmural pressure ([Formula: see text] = mean BP - (externally applied pressure)). However, its nonlinear nature in terms of functional form has not been fully investigated in human vasculature.

Cuffless blood pressure estimation based on haemodynamic principles: progress towards mobile healthcare.

Background: Although cuff-sphygmomanometry is used worldwide in medical and healthcare fields, it is a fact that the use of an occlusive cuff to obtain blood pressure () is troublesome and inconvenient. There have therefore been on-going efforts to devise methods that do not require the use of a cuff, almost all being based on the measurement of pulse wave velocity or pulse transit time, but so far few significant developments have been made, especially regarding measurement accuracy. We have previously reported a smartphone-based cuffless method using a linear multiple regression calibration model comprising of obtained with a cuff-sphygmomanometer as an objective variable and modified normalized pulse volume (: a measure of vasoconstrictive activity in a finger) and pulse rate () as explanatory variables.

NIR spectroscopic determination of urine components in spot urine: preliminary investigation towards optical point-of-care test.

Presently, there is no convenient method to measure 24-h urinary Na excretion, which is an important index of daily Na intake, and 24-h urine collection involves a complex process. However, the Na-to-creatinine ratio (NCR) in spot urine has the potential to evaluate 24-h Na excretion and is useful for point-of-care testing. Thus, this study aimed to realize a near-infrared spectroscopic system to assess NCR in spot urine: (1) We attempted to estimate Na concentration using fewer than 10 wavelengths; (2) we calculated NCR using creatinine concentrations from our previous report and verified the NCR predictability.

Side-scattered finger-photoplethysmography: experimental investigations toward practical noninvasive measurement of blood glucose.

The aim of this study was to discover a simple/convenient geometrical arrangement of radiation sources and detector to acquire finger-photoplethysmograms (PPGs) with wavelength regions of blood glucose (BGL) absorption, toward practical noninvasive BGL measurement. First, we compared PPGs with three wavelengths: 808 nm (without water absorption), 1160 nm (with weak water absorption), and 1600 nm (with nearly peak BGL absorption and strong water absorption), while the source-detector spacing was successively increased circumferentially around a fingertip. In 10 healthy subjects, we observed clear cardiac-related pulsatile components of PPG signals at 808 and 1160 nm in any incident positions with more than 15 dB of signal-to-noise ratio ( S / N ), but reliable PPG detections at 1600 nm with more than 10 dB of S / N was only possible when the source-detector distance was less than 3 mm around the fingertip circumference.

Measurement of electrocardiograms in a bath through tap water utilizing capacitive coupling electrodes placed outside the bathtub wall.

Background: Taking a bath sometimes poses a risk for subjects with chronic cardiopulmonary disorders, due to the thermal effect and water pressure on his/her body. The ECG measurement would be helpful for the early recognition of abnormal cardiac beats and respiratory conditions. This paper describes a new attempt to improve on previous bathtub ECG measurement techniques that had electrodes placed inside the bathtub that were intrusive to the subjects' bathing experience.

Advanced Volume-Compensation Method for Indirect Finger Arterial Pressure Determination: Comparison with Brachial Sphygmomanometry.

Objective: The so-called volume-compensation method (VCM) allows noninvasive instantaneous arterial blood pressure (BP) measurement in human fingers. The VCM is mostly carried out with photoplethysmography (PPG) to detect arterial volume pulsations. However, measurement errors may occur due to movement of the PPG sensors relative to skin and underlying vasculature.

Integrating Sphere Finger-Photoplethysmography: Preliminary Investigation towards Practical Non-Invasive Measurement of Blood Constituents.

The aim of this study was to compare conventional photoplethysmography (PPG) in a finger with PPG using an integrating sphere (ISPPG) to enhance scattered light collection. Two representative wavelengths were used; 1160 nm, a window through the absorption spectra of water and alcohol, and 1600 nm around where water absorption is high and there is an absorption peak of blood glucose. Simultaneous transmission-type measurements were made with conventional PPG and with ISPPG for each wavelength in the tips of index fingers of both hands in a total of 10 healthy young male and female volunteers (21.

Potential for health screening using long-term cardiovascular parameters measured by finger volume-oscillometry: pilot comparative evaluation in regular and sleep-deprived activities.

We explored the potential of health screening based on the long-term measurement of cardiovascular parameters using the finger volume-oscillometric technique. An automated instrument made simultaneous measurements of key cardiovascular parameters, including blood pressure, pulse pressure, heart rate, normalized pulse volume as an index of α-adrenalin-mediated sympathetic activity, and finger arterial elasticity. These were derived from finger photo-plethysmographic signals during application of cuff pressure.

Development of a network system combined with ambulatory and non-conscious physiological measurements for supporting challenged kids - a new proposal of a gait monitoring system for use in rehabilitation.

Various physiological measurement techniques have been developed to support healthcare and daily living of adult including elderly. However, in light of the rapid growth of the declining birth rate, promotion in care and life support for children are not enough. Especially in rehabilitation for disabled children, i.

Comparison between red, green and blue light reflection photoplethysmography for heart rate monitoring during motion.

Reflection photoplethysmography (PPG) using 530 nm (green) wavelength light has the potential to be a superior method for monitoring heart rate (HR) during normal daily life due to its relative freedom from artifacts. However, little is known about the accuracy of pulse rate (PR) measured by 530 nm light PPG during motion. Therefore, we compared the HR measured by electrocadiography (ECG) as a reference with PR measured by 530, 645 (red), and 470 nm (blue) wavelength light PPG during baseline and while performing hand waving in 12 participants.

[Applicability of the two-compartment coaxial cylindrical model for ambulatory measuring of cardiac output with spot-electrodes].

The principle of ambulatory cardiac output (CO) measuring technique is introduced in this paper. Experimental studies about the applicability of the two-compartment coaxial cylindrical model for ambulatory measurement of cardiac output with spot-electrodes have been carried out with using our newly-developed multi-channel impedance mapping system. The key factors using a spot-electrode array instead of a conventional band-electrode array for non-invasive CO) measurement are elaborated.

Validation of normalized pulse volume in the outer ear as a simple measure of sympathetic activity using warm and cold pressor tests: towards applications in ambulatory monitoring.

Normalized pulse volume (NPV) derived from the ear has the potential to be a practical index for monitoring daily life stress. However, ear NPV has not yet been validated. Therefore, we compared NPV derived from an index finger using transmission photoplethysmography as a reference, with NPV derived from a middle finger and four sites of the ear using reflection photoplethysmography during baseline and while performing cold and warm water immersion in ten young and six middle-aged subjects.

Development of a ubiquitous healthcare monitoring system combined with non-conscious and ambulatory physiological measurements and its application to medical care.

The demand for ubiquitous healthcare monitoring has been increasingly raised for prevention of lifestyle-related diseases, acute life support or chronic therapies for inpatients and/or outpatients having chronic disorder and home medical care. From these view points, we developed a non-conscious healthcare monitoring system without any attachment of biological sensors and operations of devices, and an ambulatory postural changes and activities monitoring system. Furthermore in this study, in order to investigate those applicability to the ubiquitous healthcare monitoring, we have developed a new healthcare monitoring system combined with the non-conscious and the ambulatory measurements developed by us.

Adaptive control with self-tuning for non-invasive beat-by-beat blood pressure measurement.

Up to now, we have successfully carried out the non-invasive beat-by-beat measurement of blood pressure (BP) in the root of finger, superficial temporal and radial artery based on the volume-compensation technique with reasonable accuracy. The present study concerns with improvement of control method for this beat-by-beat BP measurement. The measurement system mainly consists of a partial pressurization cuff with a pair of LED and photo-diode for the detection of arterial blood volume, and a digital self-tuning control method.

A novel photoplethysmography technique to derive normalized arterial stiffness as a blood pressure independent measure in the finger vascular bed.

Stiffening of the small artery may be the earliest sign of arteriosclerosis. However, there is no adequate method for directly assessing small arterial stiffness. In this study, the finger arterial elasticity index (FEI) was defined as the parameter n which denotes the curvilinearity of an exponential model of pressure (P)-volume (V(a)) relationship (V(a) = a - b exp (-nP)).

[Optimal electrode array for ambulatory measuring of cardiac output based on the electrical impedance method].

Principle of ambulatory cardiac output (CO) measuring technique is introduced in this paper. A lot of experimental studies of the current distribution on the thorax under the condition that the current injection electrodes were adhered to different positions were carried out by using a developed multi-channel impedance mapping system. The static impedance contour maps (Zo-map) and its pulsatile component contour maps (deltaZ-map) under different measuring conditions were analyzed, and the applicability of a two-compartment coaxial cylindrical model using a spot-electrode array instead of the conventional band-electrode array for ambulatory CO measurement, as well as the optimal spot-electrode array, were discussed.

Observation of capillary flow in human skin during tissue compression using CCD video-microscopy.

Recent technological advances of the CCD video-camera have made microscopes more compact and greatly improved their sensitivity. We newly designed a compact capillaroscopy which was composed with a CCD video-probe equipped a contact-type objective lens and illuminator. In the present study, we evaluated usefulness of the instrument for a bed-side human capillaroscopy to observe the capillary flow in various dermal regions.

[An instantaneous blood pressure measuring system at the wrist based on the volume-compensation method].

An instantaneous blood pressure measuring system at the wrist based on the volume-compensation method is developed, and the characteristics and accuracy of the system is evaluated. The radial artery at the wrist is used as the detecting object, and a pad-type cuff as well as a newly designed electro- pneumatic converter is used in the system. Also, the comparative experiments between the system and the invasive blood measuring device (direct method) indicated that, the results obtained from the two methods are well correlated not only in rest condition, but also in a stressful condition.

In the Spotlight: BioInstrumentation.

This paper discussed physiological measurement instrumentation for ambulatory/wearable physiological monitoring, cardio-pulmonary monitoring, activity monitoring, and biochemical monitoring. Future aspects also were discussed.