共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Arakawa K. Kambara T. Segawa F. Ando T. Kawada M. Ohno 《Medical & biological engineering & computing》1993,31(1):S67-S72
The authors examined the usefulness of sodium chloride as a nondiffusible indicator during the first passage through dogs'
lungs, before and after increased-permeability pulmonary oedema produced by an intravenous injection of alloxan. With an injection
of a mixture of ice-cold 3 per cent sodium chloride and indocyanine green dye (a nondiffusible reference indicator), the authors
simultaneously recorded three dilution curves from the aortic root: dye dilution, thermal and blood electrical conductivity
dilution curves in six dogs. The mean transit time of sodium chloride in the conductivity dilution curve was significantly
different from, but fairly equal to, that of indocyanine green dye (6·2±1·4 s (mean±SD) against 6·5±1·4s(p<0.01) in the baseline
period, and 7·6±1·9 s against 8·4±2·1 s (p<0·01) in the oedema period, respectively). The calculated extravascular lung thermal
volume with the thermal and conductivity dilution method (Y, ml kg−1) correlated well with the gravimetrically determined extravascular lung mass in a total of 12 dogs, including six other dogs
without intervention (x, g kg−1) (y=0·72x±3·03, r=0·96). The authors conclude that sodium chloride is useful as a nondiffusible indicator in the first passage
through the lungs, and that the thermal and conductivity dilution method is also useful for measuring extravascular lung water
mass. 相似文献
2.
N. J. H. Raat G. E. C. Wetzels J. G. R. De Mey 《Pflügers Archiv : European journal of physiology》1998,436(2):262-269
We evaluated the relationship between intracellular calcium concentration ([Ca2+]i) and vasoconstriction during the presence of exogenous noradrenaline (NA) and sympathetic nerve stimulation. An imaging technique
was used to determine calcium/tension relationships in isolated rat mesenteric resistance arteries that had been mounted for
recording of isometric tension development and loaded with Fura-2/AM. Experiments were performed after depletion of vasodilator
neuropeptides and in the continuous presence of 1 μM propranolol, 3 μM indomethacin, and 30 μM nitro-l-arginine. NA (10 μM) was shown first to induce a further increase in tension, but not [Ca2+]i, during the contraction induced by 125 mM K+. Subsequently, calcium/tension relationships were determined during stimulation with graded increases in extracellular [K+] (5.9–125 mM K+), cumulative administration of NA (0.2–10 μM) and electrical field stimulation of perivascular nerves (EFS, 1–16 Hz). A basal
calcium/tension relationship without the calcium-sensitizing property of NA was constructed using a cumulative concentration/response
curve of 5.9–125 mM K+ in arteries after prior exposure to the irreversible α-adrenoceptor antagonist phenoxybenzamine (POB). K+ series before and during α-blockade were also studied using the combination of the α1-antagonist prazosin and α2-antagonist yohimbine yielding comparable results as with POB. Calcium/tension curves obtained in the presence of NA, K+ and during EFS all were shifted to the left compared with the basal condition and all showed a similar slope indicating that
neurogenically released NA is equally capable of inducing calcium sensitization in smooth muscle of mesenteric resistance
arteries as exogenously applied NA. In the presence of exogenous and endogenous NA we not only observed an elevated contractile
response for a given increase in [Ca2+]i, but also an attenuated rise in [Ca2+]i for a given intensity of stimulation. This suggests that the agonist-induced calcium-sensitization is accompanied by a reduction
of the rise in [Ca2+]i.
Received: 24 October 1997 / Received after revision: 26 January 1998 / Accepted: 26 February 1998 相似文献
3.
G. Lose H. Colstrup K. Saksager J. K. Kristensen 《Medical & biological engineering & computing》1986,24(5):488-492
A probe for measurement of related values of cross-sectional area (CA) and pressure in a biological tube has been developed
to study passive and active closure forces in the female urethra. CA is measured in the range 0·13–1·00 cm2 by the field gradient technique. The system is able to produce an arbitrarily chosen CA in the urethra in about 50 ms. Pressure
is measured in the range 0–150 cm H2O (0–14·7 kPa) by a microtransducer. The risetime of the pressure measuring system is 2·5 ms. Pressure needed for inflation
and deflation of the balloon ranges from 2 to −5 cm H2O (0·2 to −0·5 kPa). The hysteresis of the balloon is approximately 1 cm H2O (0·1 kPa). The method permits estimation of urethral distensibility (rigidity/compliance), the real (noninstrumented) urethral
closure pressure and urethral hysteresis. Furthermore, evaluation of the urethral closure function in terms of isometric contraction,
isotonic contraction, muscular work and power can be performed. 相似文献
4.
R. W. Grunewald M. Oppermann G. A. Müller 《Pflügers Archiv : European journal of physiology》1997,434(6):815-821
Organic osmolytes such as betaine and glycerophosphorylcholine (GPC) are of major importance concerning volume regulation
of inner and outer medullary epithelial cells. Recently we demonstrated that the intracellular betaine content in rabbit kidney
cells derived from the outer medullary thick ascending limb of Henle’s loop (TALH) is osmotically regulated by betaine synthesis.
In this context it was our purpose to characterize the uptake of choline, a precursor of betaine and GPC. We found TALH cells
to possess a specific choline transport system with a maximum velocity (V
max) of 71 ± 12 pmol ·μl–1 cell water · min–1 and an apparent affinity (K
m) of 155 ± 19 μmol · l–1. The uptake of choline was sodium independent and not electrogenic, but it was significantly reduced by the removement of
chloride from the incubation medium. After long-term adaptation of TALH cells to a hyperosmotic medium (600 mosmol · l–1, osmolarity adjusted with NaCl or urea) a significant higher choline uptake rate was observed (V
max: 166 ± 9 (NaCl), 96 ± 12 (urea) pmol ·μl–1 cell water · min–1). Our results suggest that the uptake of choline is due to higher intracellular requirements of choline under hypertonic
conditions. Finally, an increase in the V
max of the choline transport system may enable sufficient synthesis of betaine and GPC.
Received: 7 April 1997 / Received after revision: 2 June 1997 / Accepted: 3 June 1997 相似文献
5.
Ma H Huang X Li Q Guan Y Yuan F Zhang Y 《The journal of physiological sciences : JPS》2011,61(4):337-342
Previous studies have confirmed that tea polyphenols possess a broad spectrum of biological functions such as anti-oxidative,
anti-bacterial, anti-tumor, anti-inflammatory, anti-viral and cardiovascular protection activities, as well as anti-cerebral
ischemia-reperfusion injury properties. But the effect of tea polyphenols on ischemia/reperfusion heart has not been well
elucidated. The aim of this study was to investigate the protective effect of theaflavin (TF1) and its underlying mechanism.
Young male Sprague-Dawley (SD) rats were randomly divided into five groups: (1) the control group; (2) TF1 group; (3) glibenclamide + TF1
group; (4) 5-hydroxydecanoate (5-HD) + TF1 group; and (5) atractyloside + TF1 group. The Langendorff technique was used to
record cardiac function in isolated rat heart before and after 30 min of global ischemia followed by 60 min of reperfusion.
The parameters of cardiac function, including left ventricular developing pressure (LVDP), left ventricular end-diastolic
pressure (LVEDP), maximal differentials of LVDP (±LVdP/dt
max) and coronary flow (CF), were measured. The results showed: (1) compared with the control group, TF1 (10, 20, 40 μmol/l)
displayed a better recovery of cardiac function after ischemia/reperfusion in a concentration-dependent manner. At 60 min
of reperfusion, LVDP, ±LVdP/dt
max and CF in the TF1 group were much higher than those in the control group, whereas left ventricular end-diastolic pressure
(LVEDP) in the TF1 group was lower than that in the control group (P < 0.01). (2) Pretreatment with glibenclamide (10 μmol/l), a KATP antagonist, completely abolished the cardioprotective effects of TF1 (20 μmol/l). Also, most of the effects of TF1 (20 μmol/l)
on cardiac function after 60 min of reperfusion were reversed by 5-HD (100 μmol/l), a selective mitochondria KATP antagonist. (3) Atractyloside (20 μmol/l), a mitochondrial permeability transition pore (mPTP) opener, administered at the
beginning of 15 min of reperfusion completely abolished the cardioprotection of TF1 (20 μmol/l). The results indicate that
TF1 protects the rat heart against ischemia/reperfusion injury through the opening of KATP channels, particularly on the mitochondrial membrane, and inhibits mPTP opening. 相似文献
6.
P. Linder J. Trzewik M. Rüffer G. M. Artmann I. Digel R. Kurz A. Rothermel A. Robitzki A. Temiz Artmann 《Medical & biological engineering & computing》2010,48(1):59-65
The CellDrum technology (The term ‘CellDrum technology’ includes a couple of slightly different technological setups for measuring
lateral mechanical tension in various types of cell monolayers or 3D-tissue constructs) was designed to quantify the contraction
rate and mechanical tension of self-exciting cardiac myocytes. Cells were grown either within flexible, circular collagen
gels or as monolayer on top of respective 1-μm thin silicone membranes. Membrane and cells were bulged outwards by air pressure.
This biaxial strain distribution is rather similar the beating, blood-filled heart. The setup allowed presetting the mechanical
residual stress level externally by adjusting the centre deflection, thus, mimicking hypertension in vitro. Tension was measured
as oscillating differential pressure change between chamber and environment. A 0.5-mm thick collagen-cardiac myocyte tissue
construct induced after 2 days of culturing (initial cell density 2 × 104 cells/ml), a mechanical tension of 1.62 ± 0.17 μN/mm2. Mechanical load is an important growth regulator in the developing heart, and the orientation and alignment of cardiomyocytes
is stress sensitive. Therefore, it was necessary to develop the CellDrum technology with its biaxial stress–strain distribution
and defined mechanical boundary conditions. Cells were exposed to strain in two directions, radially and circumferentially,
which is similar to biaxial loading in real heart tissues. Thus, from a biomechanical point of view, the system is preferable
to previous setups based on uniaxial stretching. 相似文献
7.
Prof. R. Burattini P. Reale P. Borgdorff N. Westerhof 《Medical & biological engineering & computing》1987,25(3):269-276
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, Rc, and total arterial compliance, C). The resistance regulation was represented by a second-order system with static gain GR, a damping factor σ and an undamped natural frequency ωn. The resistance gain, GR, and the windkessel parameters were obtained from measurements of aortic and venous pressures and cardiac output in two steady
states. The parameters σ and ωn 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, Rc=(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: GR=(4·14±2·38) 10−3 min ml−1, ωn = 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. 相似文献
8.
Effects of prolonged high-altitude exposure on peripheral adrenergic receptors in young healthy volunteers 总被引:4,自引:0,他引:4
Fischetti F Fabris B Zaccaria M Biagi A Calci M Candido R Bortoletto M Caretta R 《European journal of applied physiology》2000,82(5-6):439-445
The regulation of adrenergic receptors during hypoxia is complex, and the results of published reports have not been consistent.
In the present study blood cell adrenoceptor characteristics at sea level (SL) before and after prolonged exposure to high
altitude (HA) were measured in seven trained young male lowlanders. Sympathoadrenal activity and clinical haemodynamic parameters
were also evaluated before departure (SLB), after 1 week (HA1) and 4 weeks (HA4) at HA and 1 week after return to sea level
(SLA). As compared to pre-departure sea level values, urinary norepinephrine excretion increased significantly during altitude
exposure [SLB: 10.26 (3.04) μg · 3 h−1; HA1: 23.2 (4.19) μg · 3 h−1; HA4: 20.3 (8.68) μg · 3 h−1] and fell to pre-ascent values 1 week after return to sea level [SLA: 9 (2.91) μg · 3 h−1]. In contrast, mean urinary epinephrine levels did not increase over time at HA. Both systolic and diastolic blood pressures,
as well as heart rate, were increased during HA exposure. The circadian blood pressure and heart rate rhythms were preserved
during all phases of altitude exposure. Mean maximal binding (B
max) of the α2-adrenoceptor antagonist [3H]rauwolscine to platelet membranes was significantly reduced (P < 0.001) after exposure to chronic hypoxia [SLB: 172.6 (48.5) fmol · mg−1 protein versus SLA: 136.8 (56.1) fmol · mg−1 protein] without change in the dissociation constant (K
D). Neither the lymphomonocyte β2-adrenoceptor B
max [SLB: 38.5 (13.6) fmol · mg−1 protein, versus SLA: 32.4 (12.1) fmol · mg−1 protein] nor the K
D for [3H]dihydroalprenolol was affected by chronic hypoxia. Cyclic AMP (adenosine 3′,5′-cyclic monophoshate) generation in lymphomonocytes
by maximal isoproterenol stimulation was not modified after prolonged HA exposure. In conclusion, the down-regulation of α2-adrenoceptors appears to be an important component of the adrenergic system response to HA exposure.
Accepted: 20 April 2000 相似文献
9.
A new method is presented to quantify changes in permeability of the endothelial glycocalyx to small solutes and fluid flow
using techniques of indicator dilution. Following infusion of a bolus of fluorescent solutes (either FITC or FITC conjugated
Dextran70) into the rat mesenteric circulation, its transient dispersion through post-capillary venules was recorded and analyzed
offline. To represent dispersion of solute as a function of radial position in a microvessel, a virtual transit time (VTT)
was calculated from the first moment of fluorescence intensity–time curves. Computer simulations and subsequent in vivo measurements showed that the radial gradient of VTT within the glycocalyx layer (ΔVTT/Δr) may be related to the hydraulic resistance within the layer along the axial direction in a post-capillary venule and the
effective diffusion coefficient within the glycocalyx. Modeling the inflammatory process by superfusion of the mesentery with
10−7 M fMLP, ΔVTT/Δr was found to decrease significantly from 0.23 ± 0.08 SD s/μm to 0.18 ± 0.09 SD s/μm. Computer simulations demonstrated that ΔVTT/Δr is principally determined by three independent variables: glycocalyx thickness (δ), hydraulic resistivity (K
r) and effective diffusion coefficient of the solute (D
eff) within the glycocalyx. Based upon these simulations, the measured 20% decrease in ΔVTT/Δr at the endothelial cell surface corresponds to a 20% increase in D
eff over a broad range in K
r, assuming a constant thickness δ. The absolute magnitude of D
eff required to match ΔVTT/Δr between in vivo measurements and simulations was found to be on the order of 2.5 × 10−3 × D
free, where D
free is the diffusion coefficient of FITC in aqueous media. Thus the present method may provide a useful tool for elucidating
structural and molecular alterations in the glycocalyx as occur with ischemia, metabolic and inflammatory events. 相似文献
10.
Kim SH Bae YM Sung DJ Park SW Woo NS Kim B Cho SI 《Pflügers Archiv : European journal of physiology》2007,454(6):891-902
Clinical doses of ketamine typically increase blood pressure, heart rate, and cardiac output. However, the precise mechanism
by which ketamine produces these cardiovascular effects remains unclear. The voltage-gated K+ (KV) channel is the major regulator of resting membrane potential (E
m) and vascular tone in many arteries. Therefore, we sought to evaluate the effects of ketamine on KV currents using the standard whole-cell patch clamp recordings in single myocytes, enzymatically dispersed from rat mesenteric
arteries. Ketamine [(±)-racemic mixture] inhibited KV currents reversibly and concentration dependently with a K
d
of 566.7 ± 32.3 μM and Hill coefficient of 0.75 ± 0.03. The inhibition of KV currents by ketamine was voltage independent, and the time courses of channel activation and inactivation were little affected.
The effects of ketamine on steady-state activation and inactivation curves were also minimal. Use-dependent inhibition was
not observed either. S(+)-ketamine inhibited KV currents with similar potency and efficacy as the racemic mixture. The average resting E
m in rat mesenteric artery myocytes was −44.1 ± 4.2 mV, and both racemic and S(+)-ketamine induced depolarization of E
m (15.8 ± 3.6 and 24.3 ± 5.0 mV at 100 μM, respectively). We conclude that ketamine induces E
m depolarization in vascular myocytes by blocking KV channels in a state-independent manner, which may contribute to the increased vascular tone and blood pressure produced by
this drug under a clinical setting. 相似文献
11.
Marguerite Hatch Robert W. Freel 《Pflügers Archiv : European journal of physiology》1988,411(3):333-338
Electrolyte transport across rabbit caecal epithelium was investigated in vitro using conventional shortcircuiting and radioisotope
techniques. In standard saline the caecum exhibited a relatively high short-circuit current (I
sc=4.4 μEq · cm−2 · h−1) and conductance (6.43 mS · cm−2). Both sodium and chloride were absorbed (J
net
Na
=6.40 andJ
net
Cl
=3.40 μEq · cm−2 · h−1) and potassium was secreted (J
net
K
=−0.5 μEq · cm−2 · h−1). Removal of Na+ abolishedI
sc andJ
net
Cl
whereas removal of Cl− reducedJ
net
Na
to 2.92 μEq · cm−2 · h−1 but did not alterI
sc. In HCO
3
−
free salines containing 10−4 M acetazolamideJ
net
Cl
was abolished andJ
net
Na
andI
sc were reduced to 2.3 and 2.5 μEq · cm−2 · h−1 respectively. A positive residual ion flux (∼ 1 μEq · cm−2 · h−1) was detected in standard and Cl−-free salines but not in Na+-free or HCO
3
−
buffers. Mucosal amiloride (10−3 M) decreased net Na+ and Cl− absorption but did not decreaseI
sc. Mucosal DIDS (10−4 M) decreasedJ
net
Cl
while mucosal bumetanide (10−4 M) did not affect any of the measured parameters. Finally, addition of theophylline (8 mM) stimulated Cl− secretion and increasedI
sc. It is concluded that net sodium absorption by caecal epithelia occurs by both electrogenic and electroneutral mechanisms
whereas net chloride absorption occurs only by an electroneutral process. Coupling of the absorptive fluxes of Na+ and Cl− may result from Na+/H+ and Cl−/HCO
3
−
antiport systems in this tissue. Finally, it is proposed that up to half of theI
sc is due to a Na+-dependent secretion of bicarbonate ion. 相似文献
12.
W. W. Mapleson R. T. Chilcoat B. A. Willis 《Medical & biological engineering & computing》1980,18(6):701-708
A technique is described for analysing small discrete samples of gas (about 100 μl) by injecting them into a stream of carrier
gas being continuously sampled by a ‘respiratory’ mass spectrometer. This involves interrupting the normal respiratory monitoring
use of the mass spectrometer for only 20s per sample. The theory for calculating the composition is given for the case when
the carrier gas is totally different from the discrete sample, and for the case when it is air and the discrete sample may
contain air. Allowance is made for difference of viscosity between sample and carrier and for different response times to
different components of the sample. The method was developed for the analysis of gas bubbles equilibrated with blood. When
tested on a mixture of 1·2% halothane and 5% CO2 in 50/50 N2O/O2, with air as the carrier, the standard deviation between repeat determinations was about 0·5% of the actual concentration
of each component. 相似文献
13.
In vivo studies on frog mesenteric arterioles (4) indicate that segmental differences in the response of microvessels to physical
and chemical stimuli can be explained simply in terms of the length-tension characteristics of vascular smooth muscle at diferent
points along the vascular tree. Studies on single, isolated arterioles in vitro were initiated to examine more closely the
validity of this explanation for regional response differences. This paper reports some of the results. First-, second-, and
third-order arterioles (18–60 μm i.d.) were dissected from hamster cheek pouches. The vessels were cannulated with a modified
Burg microperfusion system, and their mechanical properties studied using the methods described by Duling and Gore (3). Vessels
were activated in four stages with K+ and norepinephrine. During activation, transmural pressures were adjusted to minimize vascular smooth-muscle shortening.
Active pressure-diameter curves were recorded while adjusting transmural pressure through the range 5 to 400 cm H2O in 5–25 cm steps. Vessel dimensions were measured with a videomicrometer. Passive curves were obtained after equilibration
overnight in Ca2+-free medium. The vessels were then fixed and prepared for histologic sectioning, and measurements of vessel-wall composition
were made. The Laplace relationship was used to construct length-tension diagrams, and the histologic data were used to normalize
the dimensional data to smooth-muscle lengths. Maximum active tension of second-order arterioles (1,170 dynes/cm) was two
times previous values reported by Gore et al. (5). This was due presumably to refinements in techniques and dissection procedures.
Maximum active stress averaged 3.9×10+6 dynes/cm2 for second-order arterioles. This number is identical to data obtained from hog carotid strips by Dillon et al. (2). 相似文献
14.
Louhevaara V Smolander J Aminoff T Korhonen O Shen N 《European journal of applied physiology》2000,82(4):340-344
In occupational work, continuous repetitive and isometric actions performed with the upper extremity primarily cause local
muscle strain and musculoskeletal disorders. They may also have some adverse effects on the cardiorespiratory system, particularly,
through the elevation of blood pressure. The aim of the present study was to compare peak cardiorespiratory responses to fatiguing
dynamic and isometric hand-grip exercise. The subjects were 21 untrained healthy men aged 24–45 years. The dynamic hand-grip
exercise (DHGE) was performed using the left hand-grip muscles at the 57 (SD 4)% level of each individual's maximal voluntary
contraction (MVC) with a frequency of 51 (SD 4) grips · min−l. The isometric hand-grip exercise (IHGE) was done using the right hand at 46 (SD 3)% of the MVC. The endurance time, ventilatory
gas exchange, heart rate (HR) and blood pressure were mea- sured during both kinds of exercise. The mean endurance times for
DHGE and IHGE were different, 170 (SD 62) and 99 (SD 27) s, respectively (P < 0.001). During DHGE the mean peak values of the breathing frequency [20 (SD 6) breaths · min−1] and tidal volume [0.89 (SD 0.34) l] differed significantly (P < 0.01) from peak values obtained during IHGE [15 (SD 5) breaths · min−1, and 1.14 (SD 0.32) l, respectively]. The corresponding peak oxygen consumptions, pulmonary ventilations, HR and systolic
blood pressures did not differ, and were 0.51 (SD 0.06) and 0.46 (SD 0.11) l · min−1, 17.1 (SD 3.0) and 16.7 (SD 4.7) l · min−1, 103 (SD 18) and 102 (SD 17) beats · min−1, and 156 (SD 17) and 161 (SD 17) mmHg, respectively. The endurance times of both DHGE and IHGE were short (<240 s). The results
indicate that the peak responses for the ventilatory gas exchange, HR and blood pressure were similar during fatiguing DHGE
and IHGE, whereas the breathing patterns differed significantly between the two types of exercise. The present findings emphasize
the importance of following ergonomic design principles in occupational settings which aim to reduce the output of force,
particularly in tasks requiring isometric and/or one-sided repetitive muscle actions.
Accepted: 16 February 2000 相似文献
15.
Y. J. Kingma N. G. Durdle J. Lenhart K. L. Bowes M. M. Chambers 《Medical & biological engineering & computing》1983,21(3):351-357
When electrodes are used to measure slowly varying signals such as the slow wave in the gastrointestinal tract (0·01 to 10
Hz) it is necessary that the impedances of the electrodes are low at these frequencies, and the drift must also be low. We
have carried out a programme of (a) electrode surface pretreatment, (b) electrolytic AgCl deposition, (c) impedance measurements,
(d) electrode storage methods and (e) noise and drift measurements. Optimal preplating treatment was found to be roughening
of the cleaned Ag surface. The electrode impedance could be lowered by about an order of magnitude using 50 μm Al2O3 abrasive powder. The impedance measured at fixed frequencies (0·01 to 0·05 Hz etc) plotted against the plating product (mAs
cm−2) showed a sharp minimum at 3 mAs cm−2. This mimimum was very sharp at the very low frequencies. This indicates a critical dependence of impedance on the plating
product. Storage of the electrodes in saturated AgCl solution was found to be better than any other method tried. Electrodes
pretreated as above and optimally plated showed drift voltages of less than 1 μV min−1 and noise voltages of less than 1 μV. The low drift allowed the use of d.c. coupling during slow wave measurement on intestinal
smooth muscle. The waveform in this case approximated the intracellular one closely. The electrode impedance could be described
accurately in the frequency range from 0·01 Hz to 1 kHz by the relationships R=1851×f−0·347Ω and |X|=1190×f−0·356Ω where f=frequency in Hertz. 相似文献
16.
Bishop D 《European journal of applied physiology》2000,82(1-2):91-97
This study was conducted to investigate the relationship between selected physiological variables and 500-m flat-water kayak
(K500) performance. Nine female, high-performance kayak paddlers, mean (SD) age 23 (5) years, participated in this investigation.
Testing was conducted over 6 days and included anthropometric measurements (height, body mass and skinfolds), an incremental
test to determine both peak V˙O2 and the “anaerobic threshold” (Than), and a 2-min, all-out test to calculate accumulated oxygen deficit (AOD). Blood lactate concentrations were measured during
the incremental test and at the completion of both tests. Subjects also completed a K500 race under competition conditions. K500 time was significantly correlated with both peak V˙O2 (r=−0.82, P < 0.05) and the power output achieved at the end of the incremental test (r=−0.75, P < 0.05). However, the variable most strongly correlated with K500 time was Than (r=−0.89, P < 0.05). A stepwise multiple regression, for which r=0.95 and the standard error of estimate=1.6 s, yielded the following equation: K500time(s)=160.60.154×AOD·kg−1−0.250 × Than. In conclusion, the results of this study have demonstrated that although K500 performance is a predominantly aerobic activity, it does require a large anaerobic contribution. The importance of both the
aerobic and anaerobic energy systems is reflected by the K500 time being best predicted by a linear combination of Than and AOD · kg−1. This suggests the need to develop and implement training programmes that develop optimally both of these physiological attributes.
Further research is required to elucidate the most effective means by which to develop both the aerobic and anaerobic energy
systems.
Accepted: 29 December 1999 相似文献
17.
D. J. Hughes L. A. Geddes C. F. Babbs J. D. Bourland V. L. Newhouse 《Medical & biological engineering & computing》1979,17(5):619-622
The attenuation coefficient and the speed of 10 MHz ultrasound were determined in canine blood at 37°C by a differential path-length
technique. Blood specimens with packed-cell volumes (p.c.v) ranging from 0 to 53% were prepared by separating the cells from
the plasma and mixing the two components. The mean attenuation coefficient increased linearly with packed-cell volume, the
least squares regression function being α=0·992+0·039 PCV with a standard error of the estimate=0·255. The speed of 10 MHz
ultrasound c in millimetres per second, increased with packed-cell volume, the regression function for a wave equation model
being 1/c2=0·418+2·09×10−4 (PCV)−1·75×10−5 (PCV)2 with a standard error of the estimate=0·0049 (mm/s)−2. Both the attention coefficient and speed of 10 MHz ultrasound were greater in blood than in plasma to a degree dependent
on the packed-cell volume. 相似文献
18.
Webb AR Macrie BD Ray AS Russo JE Siegel AM Glucksberg MR Ameer GA 《Annals of biomedical engineering》2007,35(8):1357-1367
The influence of scaffold compliance on blood vessel tissue engineering remains unclear and compliance mismatch issues are
important to an in vivo tissue-engineering approach. We have designed and constructed a modular bioreactor system that is capable of imparting pulsatile
fluid flow while simultaneously measuring vessel distension with fluid pressure changes in real time. The setup uses a pneumatic
PID control system to generate variable fluid pressure profiles via LabVIEW and an LED micrometer to monitor vessel distension
to an accuracy of ±2 μm. The bioreactor was used to measure the compliance of elastomeric poly(1,8-octanediol citrate) (POC)
scaffolds over physiologically relevant pressure ranges. The compliance of POC scaffolds could be adjusted by changing polymerization
conditions resulting in scaffolds with compliance values that ranged from 3.8 ± 0.2 to 15.6 ± 4.6%/mmHg × 10−2, depending on the distension pressures applied. Furthermore, scaffolds that were incubated in phosphate-buffered saline for
4 weeks exhibited a linear increase in compliance (2.6 ± 0.9 to 7.7 ± 1.2%/mmHg × 10−2) and were able to withstand normal physiological blood pressure without bursting. The ability to tailor scaffold compliance
and easily measure vessel compliance in real time in vitro will improve our understanding of the role of scaffold compliance on vascular cell processes. 相似文献
19.
B. Pincombe J. Mazumdar I. Hamilton-Craig 《Medical & biological engineering & computing》1999,37(1):595-599
Fully-developed one-dimensional Casson flow through a single vessel of varying radius is proposed as a model of low Reynolds
number blood flow in small stenosed coronary arteries. A formula for the resistance-to-flow ratio is derived, and results
for yield stresses of τ0=0, 0.005 and 0.01 Nm-2, viscosities of μ=3.45×10−3, 4.00×10−3 and 4.55×10−3 Pa·s and fluxes of 2.73×10−6, ×10−5 and ×10−4 m3s−1 are determined for a segment of 0.45 mm radius and 45 mm length, with 15 mm abnormalities at each end where the radius varies
by up to ±0.225 mm. When τ0=0.005 Nm-2, μ=4×10−3 Pa·s and Q=1, the numerical values of the resistance-to-flow ratio vary from
, when the maximum radii of the two abnormal segments are both 0.675 mm, to
, when the minimum radii are both 0.225 mm. The resistance-to-flow ratio moves closer to unity as yield stress increases or
as blood viscosity or flux decreases, and the magnitude of these alterations is greatest for yield stress and least for flux. 相似文献
20.
P. Dhar G. Jayaraman N. Karmakar S. C. Manchanda 《Medical & biological engineering & computing》1996,34(2):155-159
The effect of pressure on filtration across different de-endothelialised arteries has been studied experimentally and the
existing theoretical model is validated. Segments of different arteries are excised, de-endotheliaslised and cannulated. Bovine
serum albumin Krebs solution is used as perfusate. Transmural water flux is measured by following the movement of an air bubble
in a calibrated capillary, which connects the artery to a pressure reservoir; the pressure of which is varied. The hydraulic
conductivity Lp is calculated from the flux values. Using available experimental parameters in the case of the thoracic and abdominal aorta,
a theoretical model is validated using the experimental results. As the elastic constant for the carotid artery is not available,
the theoretical model is used to calculate the elastic constant at different transmural pressures. The values calculated are
in the range −4·9×10−8 to −5·7×10−9 cm2 dyne−1 between 50 and 135 mm Hg. Both theoretical and experimental results show a decrease in Lp values with an increase in transmural pressure for the thoracic and abdominal aorta, whereas a different trend is observed
in the case of the carotid artery. The Lp values increase at 90 mm Hg, as compared with 50 mm Hg, and with a further increase in transmural pressure the values decrease. 相似文献