Detecting absolute human knee angle and angular velocity using accelerometers and rate gyroscopes

Knee joint angle and angular velocity were calculated in real time during standing up and sitting down. Two small modules comprising rate gyroscopes and accelerometers were attached to the thigh and shank of two able-bodied volunteers and one T₅ ASIA(A) paraplegic assisted by functional electrical stimulation (FES). The offset and drift of the rate gyroscopes was compensated for by auto-resetting and auto-nulling algorithms. The tilt of the limb segments was calculated by combining the signals of the accelerometer and the rate gyroscope. The joint angle was calculated as the difference in tilt of the segments. The modules were also tested on a two-dimensional model. The mean differences between the rate gyroscope-accelerometer system and the reference goniometer for the model, able-bodied and paraplegic standing trials were 2.1°, 2.4° and 2.3° respectively for knee angle and 2.3° s⁻¹, 5.0° s⁻¹ and 11.8° s⁻¹ respectively for knee velocity. The rate gyroscope-accelerometer system was more accurate than using the accelerometer as a tilt meter, possibly due to the greater bandwidth of the rate gyroscope-accelerometer system.     

Biomechanical and Microstructural Properties of Common Carotid Arteries from Fibulin-5 Null Mice

Alteration in the mechanical properties of arteries occurs with aging and disease, and arterial stiffening is a key risk factor for subsequent cardiovascular events. Arterial stiffening is associated with the loss of functional elastic fibers and increased collagen content in the wall of large arteries. Arterial mechanical properties are controlled largely by the turnover and reorganization of key structural proteins and cells, a process termed growth and remodeling. Fibulin-5 (fbln5) is a microfibrillar protein that binds tropoelastin, interacts with integrins, and localizes to elastin fibers; tropoelastin and microfibrillar proteins constitute functional elastic fibers. We performed biaxial mechanical testing and confocal imaging of common carotid arteries (CCAs) from fibulin-5 null mice (fbln5 ^−/−) and littermate controls (fbln5 ^+/+) to characterize the mechanical behavior and microstructural content of these arteries; mechanical testing data were fit to a four-fiber family constitutive model. We found that CCAs from fbln5 ^−/− mice exhibited lower in vivo axial stretch and lower in vivo stresses while maintaining a similar compliance over physiological pressures compared to littermate controls. Specifically, for fbln5 ^−/− the axial stretch λ = 1.41 ± 0.07, the circumferential stress σ _θ  = 101 ± 32 kPa, and the axial stress σ _z  = 74 ± 28 kPa; for fbln5 ^+/+ λ = 1.64 ± 0.03, σ _θ  = 194 ± 38 kPa, and σ _z  = 159 ± 29 kPa. Structurally, CCAs from fbln5 ^−/− mice lack distinct functional elastic fibers defined by the lamellar structure of alternating layers of smooth muscle cells and elastin sheets. These data suggest that structural differences in fbln5 ^−/− arteries correlate with significant differences in mechanical properties. Despite these significant differences fbln5 ^−/− CCAs exhibited nearly normal levels of cyclic strain over the cardiac cycle.     

Measuring orientation of human body segments using miniature gyroscopes and accelerometers

In the medical field, there is a need for small ambulatory sensor systems for measuring the kinematics of body segments. Current methods for ambulatory measurement of body orientation have limited accuracy when the body moves. The aim of the paper was to develop and validate a method for accurate measurement of the orientation of human body segments using an inertial measurement unit (IMU). An IMU containing three single-axis accelerometers and three single-axis micromachined gyroscopes was assembled in a rectangular box, sized 20×20×30 mm. The presented orientation estimation algorithm continuously corrected orientation estimates obtained by mathematical integration of the 3D angular velocity measured using the gyroscopes. The correction was performed using an inclination estimate continuously obtained using the signal of the 3D accelerometer. This reduces the integration drift that originates from errors in the angular velocity signal. In addition, the gyroscope offset was continuously recalibrated. The method was realised using a Kalman filter that took into account the spectra of the signals involved as well as a fluctuating gyroscope offset. The method was tested for movements of the pelvis, trunk and forearm. Although the problem of integration drift around the global vertical continuously increased in the order of 0.5°s ⁻¹, the inclination estimate was accurate within 3° RMS. It was shown that the gyroscope offset could be estimated continuously during a trial. Using an initial offset error of 1 rads ⁻¹, after 2 min the offset error was roughly 5% of the original offset error. Using the Kalman filter described, an accurate and robust system for ambulatory motion recording can be realised.     

A quantitative analysis of the effect of cycle length on arrhythmogenicity in hypokalaemic Langendorff-perfused murine hearts

The clinically established proarrhythmic effect of bradycardia and antiarrhythmic effect of lidocaine (10 μM) were reproduced in hypokalaemic (3.0 mM K⁺) Langendorff-perfused murine hearts paced over a range (80–180 ms) of baseline cycle lengths (BCLs). Action potential durations (at 90% repolarization, APD₉₀s), transmural conduction times and ventricular effective refractory periods (VERPs) were then determined from monophasic action potential records obtained during a programmed electrical stimulation procedure in which extrasystolic stimuli were interposed following regular stimuli at successively decreasing coupling intervals. A novel graphical analysis of epicardial and endocardial, local and transmural relationships between APD₉₀, corrected for transmural conduction time where appropriate, and VERP yielded predictions in precise agreement with the arrhythmogenic findings obtained over the entire range of BCLs studied. Thus, in normokalaemic (5.2 mM K⁺) hearts a statistical analysis confirmed that all four relationships were described by straight lines of gradients not significantly (P > 0.05) different from unity that passed through the origin and thus subtended constant critical angles, θ with the abscissa (45.8° ± 0.9°, 46.6° ± 0.5°, 47.6° ± 0.5° and 44.9° ± 0.8°, respectively). Hypokalaemia shifted all points to the left of these reference lines, significantly (P < 0.05) increasing θ at BCLs of 80–120 ms where arrhythmic activity was not observed (∼63°, ∼54°, ∼55° and ∼58°, respectively) and further significantly (P < 0.05) increasing θ at BCLs of 140–180 ms where arrhythmic activity was observed (∼68°, ∼60°, ∼61° and ∼65°, respectively). In contrast, the antiarrhythmic effect of lidocaine treatment was accompanied by a significant (P < 0.05) disruption of this linear relationship and decreases in θ in both normokalaemic (∼40°, ∼33°, ∼39° and ∼41°, respectively) and hypokalaemic (∼40°, ∼44°, ∼50° and ∼48°, respectively) hearts. This extended a previous approach that had correlated alterations in transmural repolarization gradients with arrhythmogenicity in murine models of the congenital long QT syndrome type 3 and hypokalaemia at a single BCL. Thus, the analysis in terms of APD₉₀ and VERP provided a more sensitive indication of the effect of lidocaine than one only considering transmural repolarization gradients and may be particularly applicable in physiological and pharmacological situations in which these parameters diverge.     

Infestation status of gnathiid isopod juveniles parasitic on Dusky grouper (<Emphasis Type="Italic">Epinephelus marginatus</Emphasis>) from the northeast Mediterranean Sea

This is the first detailed documented record of Gnathiid isopod praniza larvae infestating dusky grouper, (Epinephelus marginatus Lowe 1834) in the northeast Mediterranean Sea (36°36′N–36°07′E, 35°52′N–36°25′E). Fish were sampled monthly from Iskenderun Bay during a 3-year period from 2000 to 2003 [N = 468, W ± SD (range) = 503.69 ± 342.35 g (177–2,832 g), TL ± SD (range) = 32.39 ± 9.22 cm (16.1–67.0 cm), W _total = 0.213L _total ^2.19, r _total ² = 0.85]. Juveniles of the Gnathia sp. were only extracted from the epithelium of the buccal cavity. The monthly and seasonal patterns in infestation rates (mean prevalence, P = 27.35% and mean intensity, MI ± SD = 21.35 ± 16.19), and the relationship between length–weight and infested/non-infested fish were calculated. This study suggests that gnathiid parasite has no effect on the growth and general health condition of infested fish, although high intensities were observed in fish.     

Comparative NMR studies of diffusional water permeability of red blood cells from different species. X. Camel ( Camelus dromedarius ) and alpaca ( Lama pacos )

The diffusional water permeability (P _d) of camel and alpaca red blood cells (RBCs) was measured by a doping nuclear magnetic resonance (NMR) technique on control cells and following inhibition withp-chloromercuribenzene sulphonate (PCMBS). The values ofP _d were, in the case of alpaca RBC≈4.6×10⁻³ cm/s at 25°C, 5.4×10⁻³ cm/s at 30°C, 6.6×10⁻³ cm/s at 37°C and 7.7×10⁻³ cm/s at 42°C. In case of camel RBC the values ofP _d where ≈4.2×10⁻³ cm/s and 9.0×10⁻³ cm/s at 42°C. Systematic studies on the effects of PCMBS on water diffusion in camel RBC indicated that the maximal inhibition was reached in 45 min with 1–2 mm PCMBS. The values of maximal inhibition were around 47% at 25°C and 68% at 30°C for alpaca RBC and around 62% at 25°C and 56% at 37°C for camel RBC. The basal permeability to water of alpaca RBC was estimated at around 2.6×10⁻³ cm/s at 25°C, 1.7×10⁻³ cm/s at 30°C and of camel RBC as 1.8×10⁻³ cm/s at 25°C and 3.0×10⁻³ cm/s at 37°C. The values of the activation energy of water diffusion (E _{a, d}) were around 23 kJ/mol for camel and 34 kJ/mol for alpaca RBC. This suggests that in addition to the number of transport channels other features of the pathways might be important for defining the temperature dependence of the water permeability.     

Comparative Nuclear Magnetic Resonance Studies of Diffusional Water Permeability of Red Blood Cells from Different Species. XII. Dog (<Emphasis Type="BoldItalic">Canis familiaris</Emphasis>) and Cat (<Emphasis Type="BoldItalic">Felis domestica</Emphasis>)

The diffusional water permeability (P _d ) of dog and cat red blood cell (RBC) membrane has been monitored by a doping nuclear magnetic resonance (NMR) technique on control cells and following inhibition with p-chloromercuribenzene sulphonate (PCMBS). The values of P _d were in the case of cat RBC ∼3.0 × 10⁻³ cm/s at 15 °C, 3.5 × 10⁻³ cm/s at 20 °C, 4.2 × 10⁻³ cm/s at 25 °C, 4.4 × 10⁻³ cm/s at 30 °C and 5.9 × 10⁻³ cm/s at 38 °C. In case of dog RBC the values of P _d were higher ∼3.8 × 10⁻³ cm/s at 15 °C, 4.6 × 10⁻³ cm/s at 20 °C, 5.0 × 10⁻³ cm/s at 25 °C, 5.9 × 10⁻³ cm/s at 30 °C and 7.9 × 10⁻³ cm/s at 37 °C. Systematic studies of the effect of PCMBS on water diffusion indicated that in the case of dog RBCs the maximal inhibition was reached in 15–30 min with 1 mm PCMBS, whereas in the case of cat RBCs in 60 min with 1 mm PCMBS or in 30 min with 2 mm PCMBS. The values of maximal inhibition in the case of cat RBC were in the range of 55–60% at 15 °C, 60–68% at 20 °C and 25 °C, 50–60% at 30 °C and 50–55% at 37 °C. In the case of dog RBC the corresponding values were higher, 75–80% at 15 °C, 70–80% at 20 °C and 25 °C, 65–70% at 30 °C and 55–60% at 37 °C. The basal permeability to water was estimated to be ∼1 × 10⁻³ cm/s −2 × 10⁻³ cm/s in the range of temperatures of 25–37 °C. The activation energy of water diffusion E _a,d was ∼19 kJ/mol for the dog RBC and ∼23 kJ/mol for the cat RBC. After incubation with PCMBS the values of E _a,d increased, reaching 40 kJ/mol in conditions of maximal inhibition of water exchange. The membrane polypeptide electrophoretic pattern of dog and cat RBCs has been compared with its human counterpart. Dog and cat RBCs contained higher amounts of spectrin (band 1 and 2) and lower amounts of bands 4.4, 4.2, band 5 and band 7 compared to human RBCs. Band 4.9 was decreased only in the cat RBCs, whereas band 6 was decreased only in the dog RBCs. Correspondence and offprint requests to: Gheorghe Benga, Department of Cell and Molecular Biology, ‘Iuliu Haţieganu’ University of Medicine and Pharmacy, 6 Pasteur St, 3400 Cluj-Napoca, Romania. Tel:/Fax: 40–64–194373; e-mail: GBenga@personal.ro; gbenga@umfcluj.ro     

Ageing effects on knee and ankle joint angles at key events and phases of the gait cycle

The objective of this research was to determine whether joint angles at critical gait events and during major energy generation/absorption phases of the gait cycle would reliably discriminate age-related degeneration during unobstructed walking. The gaits of 24 healthy adults (12 young and 12 elderly) were analysed using the PEAK Motus motion analysis system. The elderly participants showed significantly greater single (60.3% versus 62.3%, p < 0.01) and double ( p < 0.05) support times, reduced knee flexion (47.7° versus 43.0°, p < 0.05) and ankle plantarflexion (16.8° compared to 3.3°, p = 0.053) at toe off, reduced knee flexion during push-off and reduced ankle dorsiflexion (16.8° compared to 22.0°, p < 0.05) during the swing phase. The plantarflexing ankle joint motion during the stance to swing phase transition (A₂) for the young group (31.3°) was about twice ( p < 0.05) that of the elderly (16.9°). Reduced knee extension range of motion suggests that the elderly favoured a flexed-knee gait to assist in weight acceptance. Reduced dorsiflexion by the elderly in the swing phase implies greater risk of toe contact with obstacles. Overall, the results suggest that joint angle measures at critical events/phases in the gait cycle provide a useful indication of age-related degeneration in the control of lower limb trajectories during unobstructed walking.     

Comparative Cell Shape and Diffusional Water Permeability of Red Blood Cells from Indian Elephant (Elephas maximus) and Man (Homo sapiens)

Red blood cells (RBC) from an Indian elephant (Elephas maximus) were studied by light microscopy (LM), scanning electron microscopy (SEM) and a new nuclear magnetic resonance (NMR) ‘imaging’ method based on the translational diffusion of water, NMR q-space analysis. Also, the transmembrane diffusional permeability, P _d of water in RBC was measured by using a Mn²⁺-doping NMR technique, taking human RBC as a reference. The main diameter of the elephant RBC was measured as 9.3 ± 0.7 μm by LM, 9.3 ± 0.7 μm by ‘shrinkage-corrected’ SEM, and 9.3 ± 0.4 μm by q-space anlaysis. The value is ∼1.4 μm larger than that for the human RBC. The values of P _d were, in the case of elephant RBC, 3.2 × 10⁻³ cm/s at 25 °C, 3.9 × 10⁻³ cm/s at 30 °C, 5.2 × 10⁻³ cm/s at 37 °C and 6.5 × 10⁻³ cm/s at 42 °C; all values were significantly lower than the corresponding values of P _d for human RBC, namely 4.3 × 10⁻³ cm/s at 25 °C, 5.2 × 10⁻³ cm/s at 30 °C, 6.1 × 10⁻³ cm/s at 37 °C, 7.8 × 10⁻³ cm/s at 42°C. The maximal inhibition of P _d (56%) was reached in 30 min at 37 °C with 2 mm p-chloromercuribenzene sulphonate (PCMBS) for both species of RBC. The basal permeability to water at 37 °C was estimated to be 2.3 × 10⁻³ cm/s for elephant and 2.6 × 10⁻³ cm/s for human RBC. The values of the activation energy for water permeability (E _a,d ) was significantly higher for elephant RBC (31.9 kJ/mol) than for human RBC (25.9 kJ/mol). This indicated that features other than the number of transporters per cell are likely to be important in defining the differences in water permeability in the RBC from the two species.     

Comparative Cell Shape and Diffusional Water Permeability of Red Blood Cells from Indian Elephant ( Elephas maximus ) and Man ( Homo sapiens )

Red blood cells (RBC) from an Indian elephant (Elephas maximus) were studied by light microscopy (LM), scanning electron microscopy (SEM) and a new nuclear magnetic resonance (NMR) ‘imaging’ method based on the translational diffusion of water, NMR q-space analysis. Also, the transmembrane diffusional permeability, P _d of water in RBC was measured by using a Mn²⁺-doping NMR technique, taking human RBC as a reference. The main diameter of the elephant RBC was measured as 9.3 ± 0.7 μm by LM, 9.3 ± 0.7 μm by ‘shrinkage-corrected’ SEM, and 9.3 ± 0.4 μm by q-space anlaysis. The value is ∼1.4 μm larger than that for the human RBC. The values of P _d were, in the case of elephant RBC, 3.2 × 10⁻³ cm/s at 25 °C, 3.9 × 10⁻³ cm/s at 30 °C, 5.2 × 10⁻³ cm/s at 37 °C and 6.5 × 10⁻³ cm/s at 42 °C; all values were significantly lower than the corresponding values of P _d for human RBC, namely 4.3 × 10⁻³ cm/s at 25 °C, 5.2 × 10⁻³ cm/s at 30 °C, 6.1 × 10⁻³ cm/s at 37 °C, 7.8 × 10⁻³ cm/s at 42°C. The maximal inhibition of P _d (56%) was reached in 30 min at 37 °C with 2 mm p-chloromercuribenzene sulphonate (PCMBS) for both species of RBC. The basal permeability to water at 37 °C was estimated to be 2.3 × 10⁻³ cm/s for elephant and 2.6 × 10⁻³ cm/s for human RBC. The values of the activation energy for water permeability (E _a,d ) was significantly higher for elephant RBC (31.9 kJ/mol) than for human RBC (25.9 kJ/mol). This indicated that features other than the number of transporters per cell are likely to be important in defining the differences in water permeability in the RBC from the two species.     

Comparative Nuclear Magnetic Resonance Studies of Diffusional Water Permeability of Red Blood Cells from Different Species. XI. Horses Introduced to Australia and European Horses ( Equus caballus )

The diffusional water permeability (P _d) of red blood cells (RBCs) from horses introduced to Australia and from European horses was measured by a Mn²⁺ doping nuclear magnetic resonance (NMR) technique. The values of P _d were ∼3.5 × 10⁻³ cm/s at 25°C, 4.1 × 10⁻³ cm/s at 30°C, 5.6 × 10⁻³ cm/s at 37°C and 6.3 × 10⁻³ cm/s at 42°C with no significant differences between the two strains of horse. Systematic studies on the effect of p-chloromercuribenzene sulphonate (PCMBS) on water diffusion indicated that the maximal inhibition (60%) was reached in 60 min at 22°C with 1 mm PCMBS. The basal permeability to water was estimated at 1.2 × 10⁻³ cm/s at 25°C, 1.7 × 10⁻³ cm/s at 30°C, 2.0 × 10⁻³ cm/s at 37°C and 2.7 × 10⁻³ cm/s at 42°C. The activation energy (E _a,d) of water diffusion was ∼25 kJ/mol and increased to ∼39 kJ/mol after incubation with PCMBS, in conditions of maximal inhibition of water diffusion. The membrane protein electrophoretic pattern of horse RBCs was compared with its human counterpart. The horse RBC membranes had lower amounts of the proteins migrating as bands 4.1 and 4.2 and higher amounts of the protein migrating as band 4.9, and band 6 (glyceraldehyde-3-phosphate dehydrogenase) was undetectable. A noteworthy feature was the appearance of considerable differences in protein migration distances in the region of bands 7 and 9, between horse and human membranes.     

Toward an optimum prosthetic trileaflet aortic-valve design

The paper presents an optimum leaflet valve design, for a given valve size, satisfying the design criteria of: (1) minimal stress concentration in the leaflets; (2) optimal cusp shape to effect a smooth washout upon valve closure and to provide minimal meridional surface contact between leaflets, so as to minimise haemolysis and prevent adjacent leaflets from sticking to each other; (3) the pressure difference across the leaflet, at valve opening, not exceeding a limiting value (specified, in this paper to be 1–4 mm Hg); and (4) to guarantee an adequate working life (of, say, 1–2×10⁵ hours). The valve leaflet is characterised as a shell surface with two principal radii of curvature R₁, R₂ and subtending angles θ₁, θ₂. These constitute the shape parameters of the valve design. The first two criteria, outlined above provide the following values of the shape parameters: θ₁=150°, θ₂=93°, R₁=θ·89R, R₂=θ·87R. The advocated leaflet material is Avcothan-51, selected on the basis of its biological compatibility. For this material, whose static and fatigue properties are available, the leaflet thickness is determined (for given valve size) in order to satisfy the third and fourth criteria (listed in the above paragraph) ensuring a valve opening leaflet pressure differential of 1–4 mm Hg and a prescribed lifetime T₁ (of, say, 1–2×10⁵ hours, the equivalent of 12–24 years).     

Dynamic model of the short-term regulation of arterial pressure in the cat

The purpose of this study was to characterise the dynamics of the short-term control of arterial pressure in the cat with the aid of a model consisting of a nonlinear negative-feedback control system. The arterial system was described by a three element windkessel model (peripheral resistance, R, aortic characteristic impedance, R_c, and total arterial compliance, C). The resistance regulation was represented by a second-order system with static gain G_R, a damping factor σ and an undamped natural frequency ω_n. The resistance gain, G_R, and the windkessel parameters were obtained from measurements of aortic and venous pressures and cardiac output in two steady states. The parameters σ and ω_n were estimated from mean pressure and mean flow during the transient from control to the new steady state. Pressure reductions averaged 10 per cent and resistance changes averaged 12 per cent. Average windkessel model parameters in the control condition were: C=(25·9±6·1) 10⁻⁶ g⁻¹ cm⁴ s², R_c=(2·51±0·53) 10³ g cm⁻⁴ s⁻¹, R=(40·9±9·8) 10³ g cm⁻⁴ s⁻¹. Average estimates of parameters of the resistance regulator were: G_R=(4·14±2·38) 10⁻³ min ml⁻¹, ω_n = 1·0 ± 1·0 rad s⁻¹, σ=0·41±0·19. A satisfactory fit was found between model predicted and measured pressure. The results suggest that the dynamic short-term control of pressure is underdamped and oscillatory. The amplitude of these oscillations is affected by arterial compliance, suggesting an interaction between the arterial system and short-term resistance regulation.     

Relationship between the curvature constant parameter of the power-duration curve and muscle cross-sectional area of the thigh for cycle ergometry in humans

For high-intensity cycle ergometer exercise, the relationship between power output (P) and its tolerable duration (t) has been well characterized by the hyperbolic relationship: (P–θ _F)·t=W′, where θ_F has been termed the "critical power" or "fatigue threshold". The curvature constant (W′) reflects a constant amount of work which can be performed above θ_F, and it may be regarded as a muscle energy store. The relationship of this energy store to muscle mass is not known. Therefore, the purpose of this study was to determine the relationships among W′, accumulated peak oxygen deficit (accumulated peak O₂-deficit), and muscle cross-sectional area (CSA) of the thigh for high-intensity cycle ergometry in humans. A group of 17 healthy male subjects (aged 21–41 years) participated in this study. The θ_F and W′ of the P-t hyperbolic relationship and the accumulated peak O₂-deficit was calculated by standard procedures. The CSA of muscle, fat and bone in the right thigh were measured using ultrasonography. The mean (SD) of θ_F, W′, accumulated peak O₂-deficit, and muscle CSA of the thigh were 200.0 (17.8) W, 12.60 (2.94) kJ, 2.29 (0.41) l, and 185.3 (22.6) cm², respectively. The muscle CSA of the thigh was positively correlated with W′ (r=0.59, P<0.01) and with accumulated peak O₂-deficit (r=0.54, P<0.05). The relationship between W′ and accumulated peak O₂-deficit also showed a positive correlation (r=0.63, P<0.005). Our results indicated that W′ derived from the P-t hyperbolic curve as anaerobic working capacity is related to the CSA of muscle. Electronic Publication     

Estimation of the retainer height biomechanical contribution in posterior resin-bonded fixed partial dentures: a structural-thermal coupled finite element analysis

This study determines the RBFPD (resin-bonded fixed partial dentures) biomechanical aspects to retainer height using structural-thermal coupled finite element (FE) analysis under normal (37°C) and high (51°C) oral temperatures. Three RBFPD FE models with different retainer heights (100, 75, and 50% of the distance from 2 mm above the CE (cementum-enamel) junction to the occlusal surface) were created using image processing, contour stacking, and mapping mesh procedures. After FE model validation, the maximum first principal and von Mises stresses in the remaining tooth (σ_T) and prosthesis (σ_P), were recorded for all models under structural-thermal coupled analyses. The simulation results showed that the σ_T and σ_p values decreased with greater retainer height as a result of the increasing prosthesis stiffness and maximizing bonding area between the enamel and retainer at normal oral temperature (37°C). However, no significant stress differences were found according to the retainer height varying dimensions at high (51°C) temperatures. The RBFPD retainer height biomechanical response is dominated by the structural analysis result (at 37°C) and it is recommended that the prosthesis retainer have as great a height as possible to decrease the stress values.     

Induction and decay of short-term heat acclimation

The purpose of this work was to investigate adaptation and decay from short-term (5-day) heat acclimation (STHA). Ten moderately trained males (mean ± SD age 28 ± 7 years; body mass 74.6 ± 4.4 kg; [(V)\dot]_{\textO 2\textpeak} \dot{V}_{{{\text{O}}_{ 2{\text{peak}}} }} 4.26 ± 0.37 l min⁻¹) underwent heat acclimation (Acc) for 90-min on 5-days consecutively (T _a = 39.5°C, 60% RH), under controlled hyperthermia (rectal temperature 38.5°C). Participants completed a heat stress test (HST) 1 week before acclimation (Acc), then on the 2nd and 8th day (1 week) following Acc (T _a = 35°C, 60% RH). Seven participants completed HSTs 2 and 3 weeks after Acc. HST consisted of 90-min cycling at 40% peak power output before an incremental performance test. Rectal temperature at rest (37.1 ± 0.4°C) was not lowered by Acc (95% CI −0.3 to 0.2°C), after 90-min exercise (38.6 ± 0.5°C) it reduced 0.3°C (−0.5 to −0.1°C) and remained at this level 1 week later (−0.5 to −0.1°C), but not two (0.1°C −0.4 to 0.5°C; n = 7) or 3 weeks. Similarly, heart rate after 90-min exercise (146 ± 21 b min⁻¹) was reduced (−13: −6 to −20 b min⁻¹) and remained at this level after 1 week (−13: −6 to −20 b min⁻¹) but not two (−9: 6 to −23 b min⁻¹; n = 7) or 3 weeks. Performance (746 s) increased 106 s: 59 to 152 s after Acc and remained higher after one (76 s: 31 to 122) but not two (15 s: −88 to 142 s; n = 7) or 3 weeks. Therefore, STHA (5-day) induced adaptations permitting increased heat loss and this persisted 1 week but not 2 weeks following Acc.     

Effects of different after-loads and knee angles on maximal explosive power of the lower limbs in humans

Maximal explosive power during two-leg jumps was measured on four sedentary subjects [mean age 43.0 (SD 10.3) years, mean height 1.74 (SD 0.04) m, mean body mass 73.5 (SD 1.3) kg] using a sledge apparatus with which both force and speed could be directly measured. Different after-loads were obtained by positioning the sledge at five different angles (SA, α) in respect to the horizontal so that m · g · sin α (where m is the sum of body mass and the mass of the sledge seat, g the acceleration due to gravity) decreased (on average) from 78% body mass at 30° to 27% body mass at 10°, thus simulating conditions of low gravity. The subjects were asked to jump maximally, without counter movement, starting from 70°, 90°, 110°, and 140° of knee angle (KA); the protocol being repeated at 10°, 15°, 20°, 25° and 30° SA. The average (W˙ _mean ⁺) power output during concentric exercise (CE) was found to decrease when the starting KA was increased, but to be unaffected by SA (i.e. by the after-load, the simulated low g). The higher values of W˙ _mean ⁺ were recorded at 90° KA [15.01 (SD 1.46) W · kg⁻¹, average for all subjects at all SA]. The subjects were also asked to perform counter movement (CMJ) and rebound jumps (RE) at the same SA as for CE. In CMJ and RE maximal power outputs were also found to be unaffected by the SA; W˙ _mean ⁺ amounted to 16.03 (SD 0.28) W · kg⁻¹ in CMJ and 16.88 (SD 0.36) W · kg⁻¹ in RE (average for all subjects at all SA). In CE, CMJ and RE, the instantaneous force at the onset of the positive speed phase (F _i) was found to increase linearly with SA (i.e. with increasing m · g · sin α), and the difference between F _i in CMJ or RE and F _i in CE (F _i in CMJ minus F _i in CE and F _i in RE minus F _i in CE) was unaffected by SA. This indicated that both maximal power and the elastic recoil were unaffected by simulated low g ranging from 1.71 m · s⁻² (at 10° SA) to 4.91 m · s⁻² (at 30° SA). Accepted: 9 March 2000     

Elastic modulus of prepared canine jejunum,a new vascular graft material

The submucosal connective tissue of the jejunum has been shown to be suitable for use as a vascular graft in preliminary dog studies. To partially characterize the mechanical properties of this new graft material, longitudinal stress (σ)-strain (ε)-data were obtained on 13 specimens of canine jejunum, stripped of its mucosal and external smooth-muscle layers. The ratio of stress to strain is the modulus of elasticity (E). It was found that the stress σ-strain ε-data fitted the expressionγ=K∈ ^α very well. For a typical specimenγ=2.69×10⁶∈^2.33. The modulus of elasticity (E=γ ^1-1/α K ^1/α) was found to increase with increasing stress, ranging from about 2,000 to 9,000 mmHg. For the average specimenE=573γ ^0.57, where σ is in mmHg, (1 mmHg=133.3 Pascals).     

Ex vivo biomechanical behavior of abdominal aortic aneurysm: Assessment using a new mathematical model

Knowledge of the biomechanical behavior of abdominal aortic aneurysm (AAA) as compared to nonaneurysmal aorta may provide information on the natural history of this disease. We have performed uniaxial tensile testing of excised human aneurysmal and nonaneurysmal abdominal aortic specimens. A new mathematical model that conforms to the fibrous structure of the vascular tissue was used to quantify the measured elastic response. We determined for each specimen the yield σ_y and ultimate σ_u strengths, the separate contribution to total tissue stiffness by elastin (E _E) and collagen (E _C) fibers, and a collagen recruitment parameter (A), which is a measure of the tortuosity of the collagen fibers. There was no significant difference in any of these mechanical properties between longitudinal and circumferential AAA specimens, nor inE _E andE _C between longitudinally oriented aneurysmal and normal specimens.A, σ_y, and σ_u were all significantly higher for the normal than for the aneurysmal group:A=0.223±0.046versus A=0.091±0.009 (mean ± SEM;p<0.0005), σ_y versus σ_y (p<0.05), and σ_u versus σ_u (p<0.0005), respectively. Our findings suggest that the AAA tissue is isotropic with respect to these mechanical properties. The observed difference inA between aneurysmal and normal aorta may be due to the complete recruitment and loading of collagen fibers at lower extensions in the former. Our data indicate that AAA rupture may be related to a reduction in tensile strength and that the biomechanical properties of AAA should be considered in assessing the severity of an individual aneurysm.     

Thermoregulatory effects of three different types of head cooling in humans during a mild hyperthermia

Seven healthy young men participated in six trials with three different types of local cooling [cool air breathing (CAB), face skin cooling (FaC), and combined cooling (CoC)] in a warm environment for 90 min while either resting (operative temperature: T ₀ = 40°C, dew point temperature: T _dp = 15°C, air velocity: v _a = 0.3 m·s⁻¹) or exercising on a cycle ergometer with an external work load of 90 W (T ₀ = 36°C, T _dp = 15°C, v _a = 0.3 m·s⁻¹). Cool air (10°C) arrived at the entry point of the hood and/or the mask at a ventilation rate of 12 m · s⁻¹. Oesophageal temperature was not affected by any kind of cooling, while tympanic temperature was decreased at rest by both FaC and CoC [respectively −0.15 (0.06) and −0.09 (0.03)°C, P ≤ 0.05]. Mean skin temperature was decreased by FaC and CoC at rest [respectively −0.31 (0.07) and −0.27 (0.09)°C, P ≤ 0.05] and during exercise [respectively −0.64 (0.15) and −1.04 (0.22)°C, P ≤ 0.01]. CAB had no effect on skin temperatures. CoC and FaC reduced head skin temperature during both rest and work (P < 0.001) with no effect on the skin temperature of the rest of the body, except under CoC with exercise (P < 0.05). CAB did not influence local sweating. FaC, however, decreased the more profuse sweat rates (P ≤ 0.05) at rest, while CoC decreased all sweating rates at rest (P ≤ 0.05) and only the back, head and leg sweating rates during exercise (P ≤ 0.05). These results suggest that head skin cooling causes a reduction in heat strain, while CAB does not. This beneficial influence does not, however, appear to be the result of selective brain cooling. Tympanic temperature seems to be a good index of the core thermal inputs to the hypothalamic regulatory system, since variations in that parameter were associated with similarly directed variations in the sweating outputs. Accepted: 12 April 1999