The venous pump of the human foot

Pressures in the flexor digitorum muscle, posterior tibial and anterior tibial muscles and subcutaneous pressure in the lower leg were recorded in 18 volunteers with a non-infusion technique. The venous plexus of the sole of the foot was compressed by a pneumatic foot pump. Activation of this device creates oscillations of intramuscular and subcutaneous interstitial fluid hydrostatic pressure in the lower leg. The mechanism for this is explained by intermittent passive muscle stretch. The interstitial fluid pressure decreased following active muscle contractions during venous stasis of the limb, but not following activation of the pneumatic pump. Although the pneumatic foot pump may on theoretical grounds be useful in early treatment of postoperative and post-traumatic oedema of the leg, complementary studies are necessary to establish its effectiveness.     

Pulmonary oedema at necropsy: a combined pathological and radiological method of study.

Fixation of lungs at necropsy by inflation with formaldehyde vapour was used in a combined radiological and pathological study of pulmonary oedema. Pulmonary oedema was found in 79% of lungs examined. The earliest phases affect the interstitial tissue with oedematous connective tissue planes and distension of pulmonary lymphatics. These changes may be associated with reduction in the compliance of the lung. Alveolar filling is a late stage in the accumulation of oedema fluid in the lungs.     

Impression technique for the assessment of oedema: comparison with a new tactile sensor that measures physical properties of tissue

To measure tissue oedema, the impression technique and a new tactile sensor technique are compared and evaluated in a silicone rubber model and in an in vivo rat testis model. The principles of the two techniques differ in that the impression technique evaluates interstitial fluid flow FT and peak force F(0) when tissue is compressed, whereas the tactile sensor evaluates the hardness/softness or change in resonance frequency Δf when a vibrating rod is attached to tissue. Both techniques can detect changes in silicone hardness/softness or in hormone-induced changes of testes, interstitial fluid. Although both F(0) and FT are significantly correlated to Δf in the experiments, it is concluded that F(0) is the most promising impression parameter to give valuable information about the hardness of living tissue as compared with Δf. The comparison indicates that the impression technique in the most easy, to interpret, non-invasive tool to assess tissue oedema so far developed.     

Cross-calibration of eight-polar bioelectrical impedance analysis versus dual-energy X-ray absorptiometry for the assessment of total and appendicular body composition in healthy subjects aged 21-82 years

Aim: To calibrate eight-polar bioelectrical impedance analysis (BIA) against dual-energy X-ray absorptiometry (DXA) for the assessment of total and appendicular body composition in healthy adults. Research design: A cross-sectional study was carried out. Subjects: Sixty-eight females and 42 males aged 21-82 years participated in the study. Methods: Whole-body fat-free mass (FFM) and appendicular lean tissue mass (LTM) were measured by DXA; resistance ( R ) of arms, trunk and legs was measured by eight-polar BIA at frequencies of 5, 50, 250 and 500 kHz; whole-body resistance was calculated as the sum R of arms, trunk and legs. Results: The resistance index (RI), i.e. the height 2 /resistance ratio, was the best predictor of FFM and appendicular LTM. As compared with weight (Wt), RI at 500 kHz explained 35% more variance of FFM ( vs 0.57), 45% more variance of LTM arm ( vs 0.48) and 36% more variance of LTM leg ( vs 0.50) ( p < 0.0001 for all). The contribution of age to the unexplained variance of FFM and appendicular LTM was nil or negligible and the RI &#50 sex interactions were either not significant or not important on practical grounds. The percent root mean square error of the estimate was 6% for FFM and 8% for LTM arm and LTM leg. Conclusion: Eight-polar BIA offers accurate estimates of total and appendicular body composition. The attractive hypothesis that eight-polar BIA is influenced minimally by age and sex should be tested on larger samples including younger individuals.     

Electrocardiogram sources in a 2-dimensional anisotropic activation model

This paper develops a model of 2-dimensional anisotropic cardiac tissue which permits the examination of the electrical sources arising from excitation at a point. The specific results depend on the anisotropy parameters and two cases are considered in detail. For assumed equal anisotropicity ratios in the interstitial and intracellular space the isochrones are (asymptotically) confocal ellipses and the total double layer source is (asymptotically) uniform. Surface fields are calculated and plotted for this condition. (For nonequal anisotropy ratios the total double layer source is necessarily nonuniform). When the preparation is very thin so that all fibres are essentially in contact with the extracellular medium the isochrones are (asymptotically) confocal ellipses but the total double-layer sources are now nonuniform. The sources for this case are determined and the fields at the surface of the cardiac tissue evaluated and plotted. The aforementioned ‘thin’ and ‘thick’ tissue preparations are contrasted with each other and the effects of anisotropicity in cardiac tissue discussed.     

Enhanced slow caudad fluid shifts in orthostatic intolerance after 24-h bed-rest

To evaluate mechanisms of late orthostatic intolerance, slow fluid shifts along the body axis were studied during deconditioning by 24-h bed-rest and during 13-min upright tilts before and after this manoeuvre. In 11 healthy male subjects the fluid volumes of a thorax and a calf segment (impedance plethysmography) as well as tissue thickness at the forehead and the tibia (miniature ultrasonic plethysmograph) were recorded. Cardiovascular performance was monitored by recording heart rate (electrocardiogram), brachial and finger arterial pressure (by the Riva Rocci method and by the Finapres technique) as well as stroke volume (by impedance cardiography). Bed-rest led to a cephalad fluid shift with a mean interstitial leg dehydration of 2.2 ml·-100 ml^–1 with no changes in body mass and plasma volume. No syncope during the tilt occurred before bed-rest, while after bed-rest 8 subjects fainted between min 2.1 and 9.0 of the tilt. Bed-rest resulted in an augmented initial heart rate response to tilting which was similar in all subjects. In later orthostasis, bed-rest caused two- to threefold faster caudad fluid shifts with higher calf filtration rates in fainters (prior to hypotension) than in nonfainters. Through bed-rest the estimated extravasation within 10 min into general lower body tissue spaces increased by 192 ml in (late) fainters as opposed to only 23 ml in nonfainters. It was concluded that contributing factors to orthostatic intolerance may be slow transcapillary fluid shifts which are easily underestimated and whose quantity and time course call for further investigation after various deconditioning manoeuvres. In particular, the postflight fluid shifts in astronauts who will have markedly dehydrated legs, may impose a circulatory stress which needs to be evaluated. In general, the filtration rate in relevant areas appears to be an integrative and easily determined parameter, reflecting hormonal and neurogenic vascular as well as local interstitial control of the Starling forces.     

The membranous layer of superficial fascia: evidence for its widespread distribution in the body

A discrete membranous layer, “stratum membranosum”, in human subcutaneous tissue is classically described as confined to the lower anterior abdominal wall and perineum and referred to as Scarpa’s and Colles’ fasciae, respectively. Evidence for its existence elsewhere in the body is scanty and therefore the present study was undertaken. Dissection of six embalmed adult cadavers, along with ultrasound imaging on four living subjects, were carried out to determine the existence, topography, and thickness of the membranous layer of superficial fascia in different regions of the body. In all six cadavers, a continuous layer of fibrous membrane in the superficial fascia was found consistently in all the dissected regions of the body and was also confirmed by ultrasonography. The arrangement and thickness of this membranous layer varied according to body region, body surface, and gender. It was thicker in the lower than in the upper extremity, on the posterior than anterior aspect of the body, and in females than in males. The mean thickness of the membranous layer ranged from 39 to 189 μm, being thickest in the leg and thinnest over the dorsum of the hand. The membranous layer was observed to have two or even three components in regions such as the breast, back, thigh, and arm and was seen to split, forming special compartments around subcutaneous major veins of upper and lower extremities, with fibrous septa extending to attach to the vessel wall. Functionally, the membranous superficial fascia may play a role in the integrity of the skin and support for subcutaneous structures particularly veins, by ensuring their patency. Understanding the topographic anatomy of this fascial layer may help explain body-contour deformities and provide the anatomic basis for surgical correction.     

Interstitial colloid osmotic and hydrostatic pressures in human subcutaneous tissue during early stages of heart failure

Subcutaneous oedema is a common finding in heart failure. However, some patients have reduced cardiac pump function without oedema. The aim of this study was to investigate whether local mechanisms in subcutaneous tissue contribute to oedema prevention. A reduction in interstitial colloid osmotic pressure (pii) and a rise in interstitial fluid hydrostatic pressure (Pi) will both counteract a rise in capillary filtration caused by heart failure. Cardiac catheterization was done in 22 angina pectoris patients without visible oedema. Two days later pii was measured with a wick method and Pi was measured with a wick-in-needle method. Both parameters were measured in subcutaneous tissue on thorax at heart level and on the ankle. Plasma volume was determined by 125I-albumin and extracellular volume measured with 35SO4. Parameters of cardiac pump function ranged from normal to clearly pathological values. Mean pii was 13.0 mmHg on thorax and 8.3 mmHg on the ankle. Pi averaged -2.1 mmHg on thorax and -1.5 mmHg on the ankle. Statistically significant (P less than 0.05) correlations were found between pii on thorax and left ventricular end diastolic pressure (rs -0.40) and pii on thorax and cardiac index (rs 0.42). Pi was positively correlated to right atrial pressure (rs 0.50). Body fluid volumes were normal or moderately reduced. The study shows that a reduction in cardiac pump function is associated with a reduction in pii and a rise in Pi. These changes may help to prevent oedema formation in the early stages of heart failure.     

Cross-calibration of eight-polar bioelectrical impedance analysis versus dual-energy X-ray absorptiometry for the assessment of total and appendicular body composition in healthy subjects aged 21-82 years

AIM: To calibrate eight-polar bioelectrical impedance analysis (BIA) against dual-energy X-ray absorptiometry (DXA) for the assessment of total and appendicular body composition in healthy adults. RESEARCH DESIGN: A cross-sectional study was carried out. SUBJECTS: Sixty-eight females and 42 males aged 21-82 years participated in the study. METHODS: Whole-body fat-free mass (FFM) and appendicular lean tissue mass (LTM) were measured by DXA; resistance (R) of arms, trunk and legs was measured by eight-polar BIA at frequencies of 5, 50, 250 and 500 kHz; whole-body resistance was calculated as the sum R of arms, trunk and legs. RESULTS: The resistance index (RI), i.e. the height(2)/resistance ratio, was the best predictor of FFM and appendicular LTM. As compared with weight (Wt), RI at 500 kHz explained 35% more variance of FFM (vs 0.57), 45% more variance of LTM(arm) (vs 0.48) and 36% more variance of LTM(leg) (vs 0.50) (p < 0.0001 for all). The contribution of age to the unexplained variance of FFM and appendicular LTM was nil or negligible and the RI x sex interactions were either not significant or not important on practical grounds. The percent root mean square error of the estimate was 6% for FFM and 8% for LTM(arm) and LTM(leg). CONCLUSION: Eight-polar BIA offers accurate estimates of total and appendicular body composition. The attractive hypothesis that eight-polar BIA is influenced minimally by age and sex should be tested on larger samples including younger individuals.     

Noninvasive method for the assessment of subcutaneous oedema

A well defined step compression was applied over an area of the skin and maintained for a fixed time. The resistive force of the tissue, which was continuously recorded, decreased with time as a function of the translocation of fluid volume to the surrounding areas. The rate of decrease was proportional to the fluid mobility. Measurements on ten normal subjects and 14 oedematous patients showed marked differences in the pattern of fluid translocation. Flow rate and total volume flow under compression were calculated and found to vary with the degree of oedema. This noninvasive technique can measure the degree of oedema, which provides important information for diagnosis and treatment.     

On the edema-preventing effect of the calf muscle pump

Summary During motionless standing an increased hydrostatic pressure leads to increased transcapillary fluid filtration into the interstitial space of the tissues of the lower extremities. The resulting changes in calf volume were measured using a mercury-in-silastic strain gauge. Following a change in body posture from lying to standing or sitting a two-stage change in calf volume was observed. A fast initial filling of the capacitance vessels was followed by a slow but continuous increase in calf volume during motionless standing and sitting with the legs dependent passively. The mean rates of this slow increase were about 0.17%·min⁻¹ during standing and 0.12%·min⁻¹ during sitting, respectively. During cycle ergometer exercise the plethysmographic recordings were highly influenced by movement artifacts. These artifacts, however, were removed from the recordings by low-pass filtering. As a result the slow volume changes, i.e. changes of the extravascular fluid were selected from the recorded signal. Contrary to the increases during standing and sitting the calf volumes of all 30 subjects decreased during cycle ergometer exercise. The mean decrease during 18 min of cycling (2–20 min) was −1.6% at 50 W work load and −1.9% at 100 W, respectively. This difference was statistically significant (p≤0.01). The factors which may counteract the development of an interstitial edema, even during quiet standing and sitting, are discussed in detail. During cycling, however, three factors are most likely to contribute to the observed reduction in calf volume: (1) The decrease in venous pressure, which in turn reduces the effective filtration pressure. (2) An increased lymph flow, which removes fluid and osmotically active colloid proteins from the interstitial space. (3) An increase in muscle tissue pressure, which counteracts the intravascular pressure during the muscle contraction thus playing an important role as an edema-preventing factor, which has not been considered to date.     

Non-invasive estimation of myocardial infarction by means of a heart-model-based imaging approach: A simulation study

In the study, a new myocardial infarction (MI) estimation method was developed for estimating Ml in the three-dimensional myocardium by means of a heart-model-based inverse approach. The site and size of Ml are estimated from body surface electrocardiograms by minimising multiple objective functions of the measured body surface potential maps (BSPMs) and the heart-model-generated BSPMs. Computer simulations were conducted to evaluate the performance of the developed method, using a single-site Ml and dual-site Ml protocols. The simulation results show that, for the single-site Ml, the averaged spatial distance (SD) between the weighting centres of the ‘true’ and estimated Mls, and the averaged relative error (RE) between the numbers of the ‘true’ and estimated infarcted units are 3.0±0.6/3.6±0.6 mm and 0.11±0.02/0.14±0.02, respectively, when 5μV/10μV Gaussian white noise was added to the body surface potentials. For the dual-site Ml, the averaged SD between the weighting centres of the ‘true’ and estimated Mls, and the averaged RE between the numbers of the ‘trus’ and estimated infarcted units are 3.8±0.7/3.9±0.7 mm and 0.12±0.02/0.14±0.03, respectively, when 5μV/10μV Gaussian white noise was added to the body surface potentials. The simulation results suggest the feasibility of applying the heart-model-based imaging approach to the estimation of myocardial infarction from body surface potentials.     

Fractal dynamics of polarized bioelectrodes

This study is concerned with mathematical modelling of the fundamental relationship which exists between the current density and the overpotential across the metalsolution interface in the linear range using methods of system theory enhanced by ‘fractal’ concepts. A primer for both 1/f-type scaling and ‘anomalous’ relaxation/dispersion concepts is provided, followed by a brief review of the research history pertinent to the metal electrode polarization dynamics. Next, the ‘fractal relaxation systems’ approach is introduced to characterize, systems which attenuate with a fractional power-low dependence on frequency through a ‘scaling exponent’. The ‘singularity structure’ which is a scaling, rational system function is proposed to expand fractal systems in terms of basic subsystems individually representing elementary exponential relaxations and collectively exhibiting scaling properties. We stress that the ‘singularity structure’ carries scaling information identical to the conventional ‘distribution of relaxation times’ function. ‘Structure scale’ and ‘view scale’ concepts are presented in the due course to streamline the analysis of scaling phenomena in general and the polarization impedance in particular. System theory-wise, the notable result is that the fractional power function attenuation, or equivalently, the logarithmic nature of the distribution function translates into the ‘self-similar’ pattern replication of the system singularities in the s-plane. The singularity arrangement is governed by a recursive rule solely based on the knowledge of the fractional power factor or the scaling exponent.     

Variability of impedivity in normal and pathological breast tissue

The impedivity of six groups of breast tissue is measured between 0.488 kHz and 1 MHz using a hand-held probe, ensuring a constant geometry factor, and a microcomputer-controlled impedance spectroscopy system. 120 spectra are collected in excised tissue samples from 64 patients undergoing breast surgery. Each spectrum consists of 12 frequency points. The mean m, the standard deviation s, and the ‘reduced standard error’ (ε=s/(m N)) of the magnitude and the phase angle of the impedivity are calculated at each frequency for all groups of tissues. The variability at low frequency (f<10 kHz) is attributed to the dispersion in measurement errors. This contributed to the choice of 32 kHz as the lower limit of measurement frequency in the constructed electrical impedance tomograph. The collected data also show that frequencies larger than 1 MHz are needed for the bio-electrical characterisation of breast tissue. In the frequency range used in electrical impedance tomography the reduced standard error of impedivity in breast tissue is about 0.1 or less. The lowest dispersions are observed in the adipose tissue, carcinoma and fibro-adenoma.     

Estimation of non-cardiogenic pulmonary oedema using dual-frequency electrical impedance

The study investigates the effects of non-cardiogenic oedema, especially the accumulation of protein in extracellular fluid, on thoracic impedance and proposes a new method of oedema measurement based on an impedance ratio from a dual-frequency measurement. In vitro measurements in a cell containing an albumin-in-saline solution yield a resistance increase when the albumin concentration increases. Subsequently, 13 patients having acute respiratory failure are measured. The single-frequency Z₀ measurements and the proposed impedance ratio are compared with extravascular lung water (EVLW) determined by the double indicator dilution method. The single-frequency measurement correlates poorly with EVLW (r=−0.24, p=0.56). In some patients, a total thoracic impedance increase is found with increasing EVLW. The correlation between the impedance ratio and EVLW is r=−0.79 (p<0.0005). The ratio decreases as EVLW increases. Thus, when oedema is measured using bio-impedance, cardiogenic and noncardiogenic oedema yield different results. It is well recognised that cardiogenic oedema decreases total thoracic impedance. In non-cardiogenic oedema, however, protein accumulation causes an impedance increase. The decrease in the impedance ratio as EVLW increases can be explained by the accumulation of albumin in the extracellular compartment.     

Influence of temperature on the distribution of blood in humans as assessed by electrical impedance

This study investigated whether ambient temperature influences the distribution of blood as indicated by electrical impedance. In ten supine humans, the room temperature was raised from 14 to 35°C. Skin temperature and blood flow on the thorax increased by 3.6 (SD 0.3)°C and 84 (SD 40)%, respectively, and by 9.8 (SD 1)°C and 115 (SD 45)%, respectively, on the extremities (P < 0.05). Cardiac output remained unchanged, ear temperature and heart rate became elevated, and the oesophageal temperature and mean arterial pressure decreased (P < 0.05). At five discrete frequencies (1.5, 5, 50, 100, 200 kHz) thoracic impedance was increased by 1.2 (SD 1) to 1.5 (SD 1) Ω (P < 0.05). In contrast, total body impedance was reduced by 16.4 (SD 5) Ω and leg impedance was reduced by 4.0 (SD 2) Ω, while an index of intracellular water within the thorax (the difference between the admittances at 100 kHz and 1.5 kHz) was decreased by 10 (SD 1) · 10⁻⁴ S (P < 0.05). The results would suggest that total body impedance is dominated by the impedance of the extremities. The increase in thoracic impedance and a decrease in leg impedance (as in total body impedance) could be explained by a redistribution of blood from the thorax to the extremities during heating. Such a translocation of blood was confirmed by a reduced impedance based index of intracellular water within the thorax. Accepted: 4 June 1999     

Reliability and accuracy of segmental bioelectrical impedance analysis for assessing muscle and fat mass in older Europeans: a comparison with dual-energy X-ray absorptiometry

Segmental determination of muscle and fat mass (MM, FM) attains growing importance for judging effects of training and malnutrition in older people. This study evaluated the reliability and accuracy of segmental bioelectrical impedance analysis (sBIA) for use in older people. In 72 (40 men, 32 women) healthy elderly (mean age 69.0 ± 4.8 years), the MM and FM of right and left arm (RA, LA), right and left leg (RL, LL), and trunk were determined by sBIA (BC-418-MA, Tanita) and dual-energy X-ray absorptiometry (DXA) as a reference method. The sBIA provided in both sexes reliable values for limb and truncal MM and FM, except for MM of RL in women. The accuracy of sBIA displayed sex-specific bias. For MM, accurate values were noted for men’s trunk and women’s limbs (except LA). By contrast, MM was significantly underestimated in men’s limbs by 6–18% and overestimated in women’s LA (13%) and trunk (14%). Estimates of FM were accurate for men’s arms as well as women’s legs and trunk. However, FM was significantly overestimated in men’s legs (34–37%) and trunk (60%), but underestimated in women’s arms (27–35%). The proportional deviations of sBIA estimates from DXA values for limbs and trunk were significantly related to the respective MM or FM. The sBIA tends to underestimate MM in men and to overestimate in women. The reverse occurs for FM. The actual equations of the Tanita device may not completely represent the European older population and should be partly revised.     

Dependence of cardiac strength-interval curves on pacing rate

The purpose of the research is to determine how the pacing rate affects the strength-interval curve in cardiac tissue. Computer simulations are used to calculate the cathodal and anodal strength-interval curves. The tissue is represented by the bidomain model with Beeler-Reuter membrane properties. The strength-interval curves shift to shorter intervals as the pacing rate increases. However, the shape of the strength-interval curve, including the separation into ‘make’ and ‘break’ sections and the presence of a ‘dip’, is insensitive to pacing rate.     

The determination of three subcutaneous adipose tissue compartments in non-insulin-dependent diabetes mellitus women with artificial neural networks and factor analysis.

The optical device LIPOMETER allows for non-invasive, quick, precise and safe determination of subcutaneous fat distribution, so-called subcutaneous adipose tissue topography (SAT-Top). In this paper, we show how the high-dimensional SAT-Top information of women with type-2 diabetes mellitus (non-insulin-dependent diabetes mellitus (NIDDM)) and a healthy control group can be analysed and represented in low-dimensional plots by applying factor analysis and special artificial neural networks. Three top-down sorted subcutaneous adipose tissue compartments are determined (upper trunk, lower trunk, legs). NIDDM women provide significantly higher upper trunk obesity and significantly lower leg obesity ('apple' type), as compared with their healthy control group. Further, we show that the results of the applied networks are very similar to the results of factor analysis.     

Body fluid distribution in man in space and effect of lower body negative pressure treatment

Summary The lack of hydrostatic forces in space eventually produces a fluid deficit within the circulatory system. This deficit may alter the circulatory regulation patterns. The aim of the present study was to determine how much of this fluid deficit is attributable to interstitial fluid losses and to determine the effects of lower body negative pressure (LBNP) treatment on fluid distribution. The body fluid distribution of one subject was assessed before, during, and after weightlessness using two electrical impedance methods: (a) standard quadripole impedance for the segments of upper torso, lower torso, thigh, and calf and (b) an electrical impedance tomography technique (applied potential tomography) for a thigh cross-section. To assess the content of interstitial free fluid a thigh cuff overlying the electrodes for applied potential tomography was inflated to suprasystolic values to ascertain how much fluid can be squeezed out of blood vessels and tissue of skin and muscle. After the first thigh cuff maneuver (CUFF I) the subject performed a cardiovascular stress test with LBNP to mimic the gravity-induced blood shift to the lower part of the body. Then the compression maneuver was repeated (CUFF II). (a) This experimental sequence demonstrated a reduction in interstitial fluid in weightlessness of roughly 40% at the thigh. (b) The CUFF I and LBNP experiment demonstrated a reduced ability to cope with blood pooling in microgravity. (c) The CUFF II experiment suggests that LBNP in microgravity can refill the interstitial spaces and counteract the associated cardiovascular deterioration. The impedance measurements provided estimates of the contribution of different body sections to the observed body weight loss of more than 6 kg. The chest contributed nothing of significance, the lower torso more than 0.5 1, and both calves roughly 1.5 1. The thigh segments of both legs contributed between 1.51 and 2.01 with an interstitial free fluid reduction in muscle and skin by 40%.Abbreviations APT applied potential tomography - AU arbitrary units - LBNP lower-body negative pressure