Usefulness of sodium chloride as a nondiffusible indicator in the measurement of extravascular lung thermal volume in dogs

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.     

Calcium-contraction relationship in rat mesenteric arterial smooth muscle. Effects of exogenous and neurogenic noradrenaline

 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     

New probe for measurement of related values of cross-sectional area and pressure in a biological tube

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.     

Choline transport and its osmotic regulation in renal cells derived from the rabbit outer medullary thick ascending limb of Henle

 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     

ATP-dependent potassium channels and mitochondrial permeability transition pores play roles in the cardioprotection of theaflavin in young rat

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 K_ATP 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 K_ATP 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 K_ATP channels, particularly on the mitochondrial membrane, and inhibits mPTP opening.     

Contractile tension and beating rates of self-exciting monolayers and 3D-tissue constructs of neonatal rat cardiomyocytes

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.     

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.     

Effects of prolonged high-altitude exposure on peripheral adrenergic receptors in young healthy volunteers

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     

Measurement of Solute Transport in the Endothelial Glycocalyx Using Indicator Dilution Techniques

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.     

Ketamine blocks voltage-gated K+ channels and causes membrane depolarization in rat mesenteric artery myocytes

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⁺ (K_V) 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 K_V currents using the standard whole-cell patch clamp recordings in single myocytes, enzymatically dispersed from rat mesenteric arteries. Ketamine [(±)-racemic mixture] inhibited K_V 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 K_V 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 K_V 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 K_V 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.     

Electrolyte transport across the rabbit caecum in vitro

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.     

Analysis of small discrete samples of gas with a respiratory mass spectrometer

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.     

Mechanics of smooth muscle in isolated single microvessels

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).     

Cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise

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     

Improved Ag/AgCl pressure electrodes

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.     

Physiological predictors of flat-water kayak performance in women

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” (Th_an), 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 Th_an (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 × Th_an. 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 Th_an 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     

Attenuation and speed of 10 MHz ultrasound in canine blood of various packed-cell volumes at 37°C

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.     

<Emphasis Type="Italic">In Vitro</Emphasis> Characterization of a Compliant Biodegradable Scaffold with a Novel Bioreactor System

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.     

Effects of multiple stenoses and post-stenotic dilatation on non-Newtonian blood flow in small arteries

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.     

Effect of pressure on transmural fluid flow in different de-endothelialised arteries

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 L_p 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 L_p 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 L_p values increase at 90 mm Hg, as compared with 50 mm Hg, and with a further increase in transmural pressure the values decrease.