An In-Shoe Laser Doppler Sensor for Assessing Plantar Blood Flow in the Diabetic Foot

An in-shoe laser Doppler sensor for assessing plantar blood flow in the diabetic foot. Jonathan Edwin Cobb Plantar ulceration is a complication of the diabetic foot prevalent in adults with type 11 diabetes mellitus. Although neuropathy, microvascular disease and biornechanical factors are all implicated, the mechanism by which the tissue becomes pre-disposed to damage remains unclear. Recent theories suggest that the nutritional supply to the tissue is compromised, either by increased flow through the arteriovenous anastomoses ('capillary steal' theory) or through changes in the micro vascu I ature (haemodynamic hypothesis). Clinical data to support these ideas has been limited to assessment of the unclad foot under rest conditions. A limitation of previous studies has been the exclusion of static and dynamic tissue loading, despite extensive evidence that these biornechanical factors are essential in the development of plantar ulceration. The present study has overcome these problems by allowing assessment of plantar blood flow, in-shoe, during standing and walking. The system comprises a laser Doppler blood flux sensor operating at 780nm, load sensor, measurement shoe, instrumentation, and analysis software. In-vitro calibration was performed using standard techniques. An in-vivo study of a small group of diabetic subjects indicated differences in the blood flux response between diabetic neuropaths, diabetics with vascular complications and a control group. For example, following a loading period of 120s, relative increases in response from rest to peak were: Control (150% to 259%), Vascular (-70% to 242%), Neuropathic (109%-174%) and recovery times to 50% of the peak response were: Control (33s to 45s), Vascular (43s to >120s), Neuropathic (>120s). Dynamic re-perfusion rates (arbitrary units per millisecond) obtained for the swing phase of gait were: Control (6.1 a. u/ms to 7.9 a. u/ms), Vascular (4 a. u/ms to 6.2 a. u/ms), Neuropathic (2.3 a. u/ms to 4.5 a. u/ms)

Differences between risk factors for falling in homebound diabetics and non-diabetics

The purpose of this study was to identify the differences in fall risk factors between diabetic and non-diabetic homebound adults in a population identified at high risk for falls. The sample compared 210 non-diabetic homebound adults to 74 diabetic homebound adults. Five research hypotheses supported this study. It was hypothesized that, 1) incidence and severity of somatosensory changes in the feet of diabetics surpassed that of non-diabetics; 2) incidence of lower leg and foot pain in diabetics surpassed that of non-diabetics; 3) deficits in sensory integration would be greater in diabetics than non-diabetics; 4) balance deficits were more evident in diabetics and non-diabetics; and 5) fear of falling was more prominent in diabetics than in non-diabetics. An one-way ANOVA showed a significant difference in sensation between groups, with diabetics reporting less sensation than non-diabetics in all age categories. A small effect size limited external validity. No other significant differences emerged for the other fall risk factors. Gender and age category failed to influence differences between diagnostic groups

Low-frequency oscillations of the cardiovascular system in diabetics during temperature exposure

Abstract. Diabetes is a metabolic disorder characterized by elevated blood glucose levels. The disease, therefore, reflects an imbalance in blood glucose and is a result of the body’s inability to produce enough or to use the produced insulin efficiently. The impairments in temperature regulation during exposure to thermal stress have been linked to diabetes in recent years. During extreme heat events, diabetics have been reported to be particularly vulnerable, leading to high rates of hospitalizations and deaths. As climate change leads to higher global average temperatures, this area of research has attracted special interest. This thesis was carried out as part of a research group at the Centre for Environmental and Respiratory Health Research (CERH), where an experimental study was conducted to investigate how advanced type 2 diabetes affects the neurological, cardiovascular, and metabolic responses in cold and warm environments. The aim of this thesis is to study cardiovascular system responses such as low-frequency oscillations of blood pressure, heart rate, and tissue blood flow during heat exposure. The thesis’s first part focuses on the cardiovascular system and its function, and how it is changing in diabetes. Also, human thermoregulation is discussed, and a general overview of the studied cardiovascular signals is presented. The second part describes the methods used to analyze the signals. All the signal processing is done in the Matlab environment. The third part of the thesis presents the results. The results of this thesis showed that, in general, all calculated mean parameters were lower in diabetics. Also, the change in the intervention was generally dampened in diabetics, which suggests that the thermoregulatory response is different between diabetic and control groups. Overall, the results suggest that there is a difference between diabetics and controls in the parameters of studied signals, and the difference is reflected in the time-domain parameters as well as in the amplitude and power parameters of the frequency-domain.Sydän- ja verenkiertojärjestelmän matalataajuinen värähtely diabeetikoilla lämpötila-altistuksen aikana. Tiivistelmä. Diabetes on aineenvaihduntasairaus, jolle on ominaista kohonnut veren glukoosipitoisuus. Sairaus kuvastaa siis veren glukoosipitoisuuden epätasapainoa ja se johtuu siitä, että elimistö ei pysty tuottamaan riittävästi tai käyttämään tuottamaansa insuliinia tehokkaasti. Lämpötilan säätelyn heikkeneminen lämpöstressille altistumisen aikana on viime vuosina yhdistetty diabetekseen. Äärimmäisten helleilmiöiden aikana diabeetikoiden on raportoitu olevan erityisen alttiita, mikä johtaa suuriin sairaalahoito- ja kuolemantapauksiin. Koska ilmastonmuutos johtaa maailmanlaajuisesti korkeampiin keskilämpötiloihin, tämä tutkimusalue on herättänyt erityistä kiinnostusta. Tämä diplomityö tehtiin osana Ympäristöterveyden ja keuhkosairauksien tutkimuskeskuksen (CERH) tutkimusryhmää, jossa tehtiin kokeellinen tutkimus, jossa selvitettiin, miten pitkälle edennyt tyypin 2 diabetes vaikuttaa neurologisiin, kardiovaskulaarisiin ja metabolisiin vasteisiin kylmässä ja lämpimässä ympäristössä. Tämän diplomityön tavoitteena on tutkia sydän- ja verenkiertoelimistön vasteita kuten verenpaineen, sykkeen ja kudosverenkierron matalataajuista värähtelyä lämpöaltistuksessa. Diplomityön ensimmäisessä osassa keskitytään sydän- ja verisuonijärjestelmään ja sen toimintaan sekä siihen, miten se muuttuu diabeteksessa. Lisäksi käsitellään ihmisen lämmönsäätelyä ja esitetään yleiskatsaus tutkituista sydän- ja verisuonisignaaleista. Toisessa osassa kuvataan signaalien analysointiin käytetyt menetelmät. Kaikki signaalinkäsittely tehdään Matlab-ympäristössä. Työn kolmannessa osassa esitellään tulokset. Tämän diplomityön tulokset osoittivat, että yleisesti ottaen kaikki lasketut keskimääräiset parametrit olivat alhaisempia diabetesta sairastavilla. Myös lämpötila-altistuksen muutokset olivat yleisesti ottaen vaimeampia diabetesta sairastavilla, mikä viittaa siihen, että lämmönsäätelyvaste on erilainen diabetesta sairastavilla ja kontrolliryhmän välillä. Kaiken kaikkiaan tulokset viittaavat siihen, että diabetesta sairastavien ja kontrolliryhmän välillä on eroja tutkittujen signaalien parametreissa, ja ero näkyy aika-alueparametreissa sekä taajuusalueen amplitudi- ja tehoparametreissa

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

The Venoarteriolar Reflex Significantly Reduces Contralateral Perfusion as Part of the Lower Limb Circulatory Homeostasis in vivo

Perfusion at microvascular level involves the contribution of both local and central regulators, under a complex vascular signaling frame. The venoarteriolar reflex (VAR) is one of such regulatory responses, of particular relevance in the lower limb to prevent edema. Although known for quite some time, many of the complex interactions involving all of these regulatory mechanisms still need clarification. Our objective was to look deeper into VAR through modern photoplethymography (PPG). Twelve healthy subjects (both sexes, 26.0 ± 5.0 y.o.) were enrolled in this study after informed written consent. Subjects were submitted to a leg lowering maneuver while lying supine to evoke the VAR, involving three phases–10 min baseline register, both legs extended, 10 min challenge, with one randomly chosen leg (test) pending 50 cm below heart level, while the contralateral (control) remained in place, and 10 minutes recovery, resuming the initial position. PPG signals were collected from both feet and treated by the wavelet transform (WT) revealing six spectral bands in frequency intervals comprising the cardiac [1.6–0.7 Hz], respiratory [0.4–0.26 Hz], myogenic [0.26–0.1 Hz], neurogenic/sympathetic [0.1–0.045 Hz], endothelial NO-dependent (NOd) [0.045–0.015 Hz], and NO-independent (NOi) [0.015–0.007 Hz] activities. For the first time, this approach revealed that, with VAR, perfusion significantly decreased in both limbs, although the change was more pronounced in the test foot. Here, a significant decrease in myogenic, neurogenic and NOd, were noted, while the control foot recorded a decrease in neurogenic and an increase in NOd. These results confirm the utility of WT spectral analysis for flowmotion. Further, it strongly suggests that VAR results from a complex cooperation between local myogenic-endothelial responses, where a central neurogenic reflex might also be involved

A New Method of Screening for Diabetic Neuropathy using Laser Doppler and Photoplethysmography

의과대학/박사The purpose of this study is to suggest a simple, new method of screening for diabetic neuropathy. We measured blood volume changes by photoplethysmography (PPG) and blood perfusion by laser Doppler (LD) in the index fingers and big toes in 40 control subjects and in 50 (19 mild, 17 moderate, and 14 severe based on the nerve conduction velocity (NCV) test) and 35 diabetic patients with and without neuropathy, respectively. According to the results of PPG and LD measurements, the toe to finger ratios obtained from the neuropathic group were significantly higher than those from the control (p<0.001) and the non-neuropathic groups (p<0.001). Based on the NCV, the sensitivity of the LD method (92.0%) was higher than that of the PPG method (84.0%) for both left and right sides. Although specificity of the LD (92.8%) was also higher than the PPG (84.3%) bilaterally, the PPG showed better reproducibility (5.5% versus 9.5%) and a significant ratio increase with severity, while the LD did not. Our suggested PPG method using the toe to finger ratio is reliable, simple, economical, and accurate, and could become a new effective screening tool for the early detection of diabetic neuropathy.ope

Role of multipoint contact photoplethysmography in assessing changes in blood flow in the plantar aspect of the contralateral foot following amputation in patients with type 2 diabetes mellitus

BACKGROUND: Accurate and reliable assessment of blood flow over the foot in diabetics is imperative in identifying areas of the foot at risk for ulceration. Hence there is a need to explore methods that are direct indicators of microvascular changes and local blood flow over the foot. OBJECTIVES: 1. The primary objective of this study was to determine peak amplitudes and peak times using photoplethysmography waveforms as a measure of change in blood flow in the plantar aspect of the contralateral foot in diabetic patients following amputation. 2. The secondary objectives included: • Comparison of changes in blood flow over the plantar aspect of the foot in diabetic patients with age and gender matched normal subjects. • Mapping of variations in blood flow over the plantar aspect of the foot and identify areas of early microvascular changes in the foot. METHODS: The study included patients with diabetes mellitus who had undergone any form of amputation of one limb as the cases and normal healthy individuals without diabetes as controls. Reflectance type photoplethysmograph sensors were used over six regions of the foot namely hallux, medial forefoot, middle forefoot, lateral forefoot, lateral midfoot and heel to assess the photoplethysmograph waveform pattern in three different positions i.e., supine, sitting and standing. Data was acquired through an indigenous data acquisition system and routed to a laptop for recording and further analysis. Toe pressures were also measured for both groups to serve as a baseline indicator of blood flow to the lower limb. RESULTS AND CONCLUSION: The peak amplitudes were higher in diabetics when compared to non-diabetics. All three regions of the forefoot showed statistically significant increase in the peak amplitude when compared to controls. The hallux was found to have the maximum peak amplitude in both groups indicating maximum local blood flow. There was also a significant change in the peak amplitude on assuming a sitting position from supine position. Even when toe pressures were unable to detect changes in blood flow between the two groups, photoplethysmograph waveforms showed significant difference between the two groups. Therefore, the results of this study laid the foundations for exploring the use of photoplethysmography in the clinical setting for detecting early, subclinical changes in the foot of diabetics

Cutaneous vascular haemodynamics in diabetes mellitus.

In this thesis the laser Doppler flowmeter and other microvascular methods were used to investigate the skin microcirculation in non-diabetic and diabetic subjects in order to gain a greater understanding of the normal microcirculation and to define abnormalities relevant to the diabetic state. The principle findings were- 1. The normal skin microvascular response to thermal and mechanical injury is a substantial increase in blood flow. In diabetic subjects with and without complications this hyperaemic response was reduced and degree of impairment was found to be greatest in those with the severest complications. 2. In diabetic patients, the diameter of foot skin capillaries was reduced and the basement membrane width was found to increase progressively with increasing severity of complications. These structural changes may partly explain the reduced hyperaemic responses and their relationship with severity of complications. These structural and functional abnormalities may be implicated in the pathogenesis and impaired healing of diabetic foot lesions. 3. In normal subjects, blood flow in the toe pulp fell by 80% when the foot was lowered 50 cm below the heart. Toe blood flow in neuropathic diabetic subjects was three fold higher than in normal subjects, and on lowering the foot this difference was even greater; dependent flow was seven fold higher and the fall in blood flow was only 50%. These findings are compatible with reduced central sympathetic tone and/or peripheral sympathetic nerve failure. 4. In young non-neuropathic diabetic subjects, the more severe stress of sitting still for 50 minutes with the foot 1 meter below heart level, also revealed an increase in toe pulp blood flow. This was associated with elevated capillary pressure, failure in the expected rise in plasma osmotic pressure, and increased foot swelling. These results provide evidence of capillary hypertension and impairment of oedema preventing mechanisms in the dependent foot of diabetic subjects. These abnormalities may be important in initiating structural and functional damage to the skin microcirculation

Analysis of Pulse Transit Time with the Inclusion of a Microvascular Component in Head-up Tilt and Blood Withdrawal Induced Central Hypovolemia

The pulse transit time (PTT) has been investigated as an early noninvasive marker of hypovolemia, reflecting a combination of changes in the pre-ejection period (PEP) and vascular transit time (VTT). The use of photoplethysmography (PPG) has limited the analysis to the macrovascular peripheral circulation by nature of the detection mechanism of the PPG itself. Excluded is the richly innervated microcirculation that may have a significant influence on the vasomotor response to a hypovolemic challenge. Therefore the time required for the blood to travel from the PPG to the microvasculature (VTTm) under a laser Doppler flowmeter (LDF) would provide a more complete understanding of the physiologic response to hypovolemia. The present study sought to assess changes in the components of PTT, including VTTm, in a head-up tilt (HUT) model and in a post hoc analysis of data recorded from a two-unit blood withdrawal (BW) experiment performed by members of this research team. With IRB approval, 10 healthy volunteers were recruited for a 60o HUT test to simulate mild-to-moderate hypovolemia. Monitoring included a 3-lead EKG, Finapres and a PPG and LDF applied to both the finger and ear. Measurements were taken during the pre-tilt phase while the subject was supine and again upon tilting. The data from the BW study were retrospectively analyzed (see Appendix for methodology). Paired t-tests were performed and p-values are given where p \u3c 0.05. During HUT and BW, PEP increased significantly (p \u3c 0.001). While PTT also significantly lengthened with tilting (p = 0.02), no such change was observed with BW. There was no change in heart rate in either experiment. VTT also remained essentially the same after tilting and BW. As expected, VTTm was a significant addition to VTT, however it did not exhibit any significant changes in any region with either hypovolemic challenge. VTT and VTTm of the forehead were significantly different than the finger at baseline and after blood withdrawal. The component values of the ear and finger did not vary significantly. Results confirm previous reports of an increase in PEP in response to a mild-to-moderate hypovolemic insult. Flow through the microcirculation is a significant component of PTT. However, the VTTm did not exhibit a significant response to mild-to-moderate hypovolemia. VTT remained essentially the same in both conditions and PTT was only found to change significantly with tilting. It is interesting to note the lack of change in VTTm with tilting in the finger as well as the ear, even though the arterial network of the finger is more densely innervated by α-adrenergic receptors than other parts of the body. In a comparison with the existing literature, timing of the measurements and testing conditions are believed to significantly influence the results. Though our early timing of the measurements after the hypovolemic challenge might veil the presence of a sympathetic hemodynamic response, it is believed that baseline hydration status of the subject and time spent in the supine position before tilting are the root causes of this discrepancy with other studies