A novel approach to bioelectrical impedance plethysmography for the assessment of arterial and venous circulatory problems in the forearm

Peripheral vascular disease (PVD) and/or peripheral arterial disease (PAD) are sicknesses known to inadequate delivery of either arterial or venous blood towards the extremities. Such sickness may trigger complications owing to the lack of transport of oxygen and nutrients, thus causing hypoxic events that may eventually prompt to ischaemic tissue or even the loss of the compromised limb. One of the most prominent indicators of prosperous health is blood volume and flow. The basic information within these health parameters may show cardiovascular problems or the advance of further complications related to other diseases like diabetes. In clinical setting, there effective methods to measure these parameters like Doppler ultrasound, photoplethysmography or venous occlusion plethysmography. These methods take measurements from either single vessels and/or small volume of tissue. However, it is difficult to establish a relation between the obstruction of arterial and/or venous circulation and the amount of blood received by the tissue. Bioelectrical impedance plethysmography (iPG) measures blood changes by driving a small amount of AC current into the body and after measuring the potential created by fluids flowing through tissue. This technique apart from taking measures within defined volumes of tissue, it is easy to use as only needs four electrodes on the skin. Hence, a bespoken bioelectrical impedance device including hardware and software was built ready to measure changes in blood volume/flow in the upper limbs. The system was assessed in an in-vivo controlled environment with 8 participants. The blood flow towards their left arms was altered by constricting the upper arm with a cuff at three levels: 1) below venous pressure 2) amongst venous and arterial pressure and 3) during total occlusion. Simultaneously, measurements from various instruments like ECG, Doppler ultrasound, laser Doppler flowmetry and PPG were taken and compared to the measurements obtained from the iPG instrument and defining its correlation with the impedimetric signal. The results from the experiments showed that the bioelectrical impedance signal changed in basal and arterial pulses showing specific characteristics for each kind of occlusion. The data indicated that it is possible to differentiate between a venous and arterial occlusion by examining both components of the impedance signal. The impedance during venous occlusion dropped in average 0.658±0.230% from the baseline. On the other hand, during arterial occlusion the base impedance dropped in a higher rate approximately 1.13±04.82%, indicating a differentiator during both type of blood flow disruption. Furthermore, the impedance plethysmography waveform morphology also reshaped during these occlusive periods. The whole waveform during artificial venous obstruction increased in magnitude, the systolic peak rose 31.80%, the dicrotic notch 47.73% and the diastolic point 31.92%, where the value of the latter was higher than the dicrotic notch point. In contrast, in the time of partial arterial occlusion the waveform also increased in size at all these points, but its shape was altered. The impedance magnitude at the diastolic point went below the ones at the dicrotic notch. These fluctuations provided additional further information that it might be possible to differentiate amongst venous and arterial occlusions. By consolidating the data obtained by the iPG device, it is possible to produce an index ratio between the basal impedance and these three reference points which may help to identify early circulatory problems in the arterial and/or venous systems

A system to monitor segmental intracellular, interstitial, and intravascular volume and circulatory changes during acute hemodialysis

This paper describes a new combined impedance plethysmographic (IPG) and electrical bioimpedance spectroscopic (BIS) instrument and software that allows noninvasive real-time measurement of segmental blood flow and changes in intracellular, interstitial, and intravascular volumes during various fluid management procedures. The impedance device can be operated either as a fixed frequency IPG for the quantification of segmental blood flow and hemodynamics or as a multi-frequency BIS for the recording of intracellular and extracellular resistances at 40 discrete input frequencies. The extracellular volume is then deconvoluted to obtain its intra-vascular and interstitial component volumes as functions of elapsed time. The purpose of this paper is to describe this instrumentation and to demonstrate the information that can be obtained by using it to monitor segmental compartment volumes and circulatory responses of end stage renal disease patients during acute hemodialysis. Such information may prove valuable in the diagnosis and management of rapid changes in the body fluid balance and various clinical treatments

Novel concepts for non-invasive telemonitoring in chronic heart failure

Background: The morbidity and mortality from chronic heart failure (HF) remains alarmingly high, in part due to failure to apply substantial disease modifying strategies to halt disease progression. Telemonitoring has been proposed as a potential disease management strategy to deal with the burden posed by HF. While treatment decisions guided by invasive telemonitoring data have shown early promise, it is unclear whether non-invasively derived surrogates of haemodynamics could be reliable enough to guide therapeutic interventions.Aims: The principal aim of this thesis is to investigate whether non-invasive “smart technologies” could accurately detect and track subtle changes in surrogates of cardiovascular haemodynamics in response to challenges posed by activities of daily living and non-adherence to therapy. Methodology: A series of prospective clinical studies were conducted in stable patients with chronic heart failure, on optimum tolerated guideline directed therapy for heart failure. Studies were performed under clinically adapted conditions to mimic the patient’s own habitat.Results: Significant systemic haemodynamic perturbations were detected non-invasively with variations in environmental temperature. Additionally, music, which modulates the sympathetic tone, led to modest changes in systemic blood pressure and heart rate, although the changes did not reach statistical significance. Non-adherence to cardiovascular therapy led to striking adverse changes in systemic haemodynamics. Smart technologies demonstrated a remarkable consistency in detecting haemodynamic perturbations.Conclusion: Non-invasive detection and tracking of changes in haemodynamics is feasible with smart technologies. The results need to be validated in larger multicenter clinical trials, with particular emphasis on using the data to guide therapeutic decisions

Combined use of laser Doppler flowmetry and skin thermometry for functional diagnostics of intradermal finger vessels

We introduce a noninvasive diagnostic approach for functional monitoring of blood microflows in capillaries and thermoregulatory vessels within the skin. The measuring system is based on the combined use of laser Doppler flowmetry and skin contact thermometry. The obtained results suggest that monitoring of blood microcirculation during the occlusion, performed in conjunction with the skin temperature measurements in the thermally stabilized medium, has a great potential for quantitative assessment of angiospatic dysfunctions of the peripheral blood vessels. The indices of blood flow reserve and temperature response were measured and used as the primarily parameters of the functional diagnostics of the peripheral vessels of skin. Utilizing these parameters, a simple phenomenological model has been suggested to identify patients with angiospastic violations in the vascular system

The non-invasive assessment of the ischaemic limb, with particular reference to thermography.

Skin temperature (Tsk) has long been used in assessing limb circulation, and in recent years thermography has been used as an accurate way of measuring Tsk. However, apart from the general proposition that Tsk must be related to that of the blood, the precise relationship between the blood supply to a limb and its Tsk remains poorly understood. Without this knowledge full use cannot be made of thermography in the assessment of the limb with peripheral vascular disease. The purpose of these studies was to provide a scientific basis for the use of thermography on limbs. Previous work had indicated that Tsk was related to skin blood flow in the hand and foot, but not in the forearm or calf. This work has been confirmed and extended by studies on normal subjects at different ambient temperatures, and on subjects with a peripheral A-V fistula. I have shown that Tsk over the forearm and calf is related to the core temperature of the limb, i.e. to the arterial inflow. An attempt was then made to see if these findings could be used to interpret the abnormal thermograms found in a group of patients with intermittent claudication, and in a group with more severe peripheral vascular disease. In claudicants the regression line relating mean calf Tsk to total blood flow was parallel to, but higher than that in normal subjects, i.e. for the same blood flow, claudicants' Tsk was higher than in normal subjects. The reasons for this difference are not apparent. Thermograms in patients with more severe limb ischaemia were often difficult to interpret because of the confusion introduced by other pathologies. Thermography is a useful adjunct in the assessment of the ischaemic limb, but is unlikely to replace more conventional methods of investigation

Overview of biofluids and flow sensing techniques applied in clinical practice

This review summarizes the current knowledge on biofluids and the main flow sensing techniques applied in healthcare today. Since the very beginning of the history of medicine, one of the most important assets for evaluating various human diseases has been the analysis of the conditions of the biofluids within the human body. Hence, extensive research on sensors intended to evaluate the flow of many of these fluids in different tissues and organs has been published and, indeed, continues to be published very frequently. The purpose of this review is to provide researchers interested in venturing into biofluid flow sensing with a concise description of the physiological characteristics of the most important body fluids that are likely to be altered by diverse medical conditions. Similarly, a reported compilation of well-established sensors and techniques currently applied in healthcare regarding flow sensing is aimed at serving as a starting point for understanding the theoretical principles involved in the existing methodologies, allowing researchers to determine the most suitable approach to adopt according to their own objectives in this broad field.This research was supported by the Consejo Nacional de Ciencia y Tecnología (CONACYT) of México through Ph.D. grant 472102 and by the Ministerio de Economía y Competitividad through grant FIS2017-89850R.Peer ReviewedPostprint (author's final draft

Skeletal Muscle Tissue Saturation Changes Measured Using Near Infrared Spectroscopy During Exercise Are Associated With Post-Occlusive Reactive Hyperaemia

Measuring local haemodynamics in skeletal muscle has the potential to provide valuable insight into the oxygen delivery to tissue, especially during high demand situations such as exercise. The aim of this study was to compare the skeletal muscle microvascular response during post-occlusive reactive hyperaemia (PORH) with the response to exercise, each measured using near-infrared spectroscopy (NIRS) and to establish if associations exist between muscle measures and exercise capacity or sex. Participants were from a population-based cohort study, the Southall and Brent Revisited (SABRE) study. Skeletal muscle measures included changes in tissue saturation index at the onset of exercise (∆TSIBL-INC) and across the whole of exercise (∆TSIBL-EE), time to 50%, 95% and 100% PORH, rate of PORH recovery, area under the curve (AUC) and total oxygenated Haemoglobin (oxy-Hb) change during PORH. Exercise capacity was measured using a 6-min stepper test (6MST). Analysis was by multiple linear regression. In total, 558 participants completed the 6MST with NIRS measures of TSI (mean age±SD: 73 ± 7years, 59% male). A sub-set of 149 participants also undertook the arterial occlusion. Time to 100% PORH, recovery rate, AUC and ∆oxy-Hb were all associated with ∆TSIBL-EE (β-coefficient (95%CI): 0.05 (0.01, 0.09), p = 0.012; -47 (-85, -9.9), p = 0.014; 1.7 (0.62, 2.8), p = 0.002; 0.04 (0.002.0.108), p = 0.041, respectively). Time to 95% & 100% PORH, AUC and ∆oxy-Hb were all associated with ∆TSIBL-INC (β-coefficient (95%CI): -0.07 (-0.12,-0.02), p = 0.02; -0.03 (-0.05, -0.003), p = 0.028; 0.85 (0.18, 1.5), p = 0.013 & 0.05 (0.02, 0.09), p = 0.001, respectively). AUC and ∆Oxy-Hb were associated with steps achieved (β-coefficient (95%CI): 18.0 (2.3, 33.7), p = 0.025; 0.86 (0.10, 1.6), p = 0.027). ∆TSIBL-EE was associated with steps and highest VO2 (1.7 (0.49, 2.9), p = 0.006; 7.7 (3.2, 12.3), p = 0.001). ∆TSIBL-INC was associated with steps and VO2 but this difference was attenuated towards the null after adjustment for age, sex and ethnicity. ∆TSIBL-EE was greater in women (3.4 (0.4, 8.9) versus 2.1 (0.3, 7.4), p = 0.017) and ∆TSIBL-INC was lower in women versus men (2.4 (0.2, 10.2) versus 3.2 (0.2, 18.2), p = 0.016). These Local microvascular NIRS-measures are associated with exercise capacity in older adults and several measures can detect differences in microvascular reactivity between a community-based sample of men and women

Plasma nitrite reserve and vascular function before and after handgrip training in patients with heart failure

There is a direct relationship between vascular health and physical function. The controllers of this relationship are unclear, but appear to involve biomechanical and biochemical influences on the vascular wall. Purpose: The purpose of this dissertation was twofold: (1) to explore the relationship between vascular health and physical function in three populations (elderly, young and chronic heart failure patients); and (2) to determine the modifying role of physical activity, inactivity and exercise training on controllers of this relationship. Methods: Four projects were designed to address 3 key issues in exercise vascular biology, including the influence of the pattern of blood flow on the vasculature; the effects of exercise training with blood flow restriction vascular function; and the influence of exercise training on vascular function in individuals with known disease. Results: Projects 1 and 2 indicate an increase in oscillatory shear within the vasculature with aging. This appears to be associated with lower physical function. Those individuals who maintain a higher amount of daily physical activity have more favorable blood flow pattern and higher vascular function. Project 3 indicates that localized exercise training with blood flow restriction dissociates vascular and muscle gains leading to enhanced muscular strength but diminished vascular function. The controller involved in the lower vascular function may be reduced shear stress during exercise. The controller that contributes to greater muscle strength during blood flow restriction remains unknown. Project 4 concludes that localized exercise training significantly improves vascular function and muscular strength in heart failure patients, although the gains are less than in age-matched individuals. The underlying controllers are unclear but may involve localized increases in shear stress and reduced oxidative stress. However, the benefits of exercise training are transient with vascular function returning to pre-training levels within 4 weeks after cessation of the training stimulus. Conclusion: These projects confirm a direct relationship between vascular health and physical function. This relationship is modifiable with physical activity levels and exercise training. It appears that intermittent shear stress, as seen with acute exercise, and oxidative stress serve as important stewards of the relationship between vascular and physical function