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.     

Extracellular bicarbonate and non-bicarbonate buffering against lactic acid during and after exercise

Defense of extracellular pH constancy against lactic acidosis can be estimated from changes (Δ) in lactic acid ([La]), [HCO₃⁻], pH and PCO₂ in blood plasma because it is equilibrated with the interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 13 untrained (UT) and 21 endurance-trained (TR) males to find out if acute and chronic exercise influence the defense. During exercise the capacity of non-bicarbonate buffers (β_nbi = −Δ[La] · ΔpH⁻¹ − Δ[HCO₃⁻] · ΔpH⁻¹) available for the extracellular fluid (mainly hemoglobin, dissolved proteins and phosphates) amounted to 32 ± 2(SEM) and 20 ± 2 mmol l⁻¹ in UT and TR, respectively (P < 0.02). During recovery β_nbi decreased to 14 (UT) and 12 (TR) mmol l⁻¹ (both P < 0.001) corresponding to values previously found at rest by in vivo CO₂ titration. Bicarbonate buffering (β_bi) amounted to 44–48 mmol l⁻¹ during and after exercise. The large exercise β_nbi seems to be mainly caused by an increasing concentration of all buffers due to shrinking of the extracellular volume, exchange of small amounts of HCO₃⁻ or H⁺ with cells and delayed HCO₃⁻ equilibration between plasma and interstitial fluid. Increase of [HCO₃⁻] during titration by these mechanisms augments total β and thus the calculated β_nbi more than β_bi because it reduces ΔpH and Δ[HCO₃⁻] at constant Δ[La]. The smaller rise in exercise β_nbi in TR than UT may be caused by an increased extracellular volume and an improved exchange of La⁻, HCO₃⁻ and H⁺ between trained muscles and blood.     

Causes of differences in exercise-induced changes of base excess and blood lactate

It has been concluded from comparisons of base excess (BE) and lactic acid (La) concentration changes in blood during exercise-induced acidosis that more H⁺ than La⁻ leave the muscle and enter interstitial fluid and blood. To examine this, we performed incremental cycle tests in 13 untrained males and measured acid–base status and [La] in arterialized blood, plasma, and red cells until 21 min after exhaustion. The decrease of actual BE (−ΔABE) was 2.2 ± 0.5 (SEM) mmol l⁻¹ larger than the increase of [La]_blood at exhaustion, and the difference rose to 4.8 ± 0.5 mmol l⁻¹ during the first minutes of recovery. The decrease of standard BE (SBE), a measure of mean BE of interstitial fluid (if) and blood, however, was smaller than the increase of [La] in the corresponding volume (Δ[La]_if+blood) during exercise and only slightly larger during recovery. The discrepancy between −ΔABE and Δ[La]_blood mainly results from the Donnan effect hindering the rise of [La]_erythrocyte to equal values like [La]_plasma. The changing Donnan effect during acidosis causes that Cl⁻ from the interstitial fluid enter plasma and erythrocytes in exchange for HCO₃⁻. A corresponding amount of La⁻ remains outside the blood. SBE is not influenced by ion shifts among these compartments and therefore is a rather exact measure of acid movements across tissue cell membranes, but changes have been compared previously to Δ[La]_blood instead to Δ[La]_if+blood. When performing correct comparisons and considering Cl⁻/HCO₃⁻ exchange between erythrocytes and extracellular fluid, neither the use of ΔABE nor of ΔSBE provides evidence for differences in H⁺ and La⁻ transport across the tissue cell membranes.     

Changes in the countercurrent system in the renal papilla: diuresis increases pH and HCO 3 − gradients between collecting duct and vasa recta

This study was designed to elucidate the acid-base balance local to the collecting duct urine (CD) and vasa recta blood (VR) in the rat renal papilla in diuresis. The pH changes were measured in both a furosemide-induced and a volume-load-induced diuresis, whereas the PCO₂ (i.e., CO₂ tension) and HCO₃ ⁻ concentration were measured only in a furosemide-induced diuresis. In an antidiuresis, the pH of the VR was more acidic than that of the systemic arterial blood (ΔpH = 0.44–0.73). Additionally, the pH of the ascending VR was significantly lower than that of the descending VR (ΔpH = 0.14–0.16). In diuresis, the pH of the CD decreased (ΔpH = 0.81–0.97), while the pH of the descending and the ascending VR increased; however, the increase was only significant in the ascending VR (ΔpH = 0.23–0.30). Consequently, the significant difference in the pH gradient between the descending and the ascending VR was eliminated. The PCO₂ values in the CD and the ascending VR were not different from those in antidiuresis, while the HCO₃ ⁻ concentration in the CD and the ascending VR, respectively, decreased and increased significantly. Thus, in diuresis, the decrease in the pH of the CD and the increase in the pH of the ascending VR result, respectively, from the decrease and the increase in the HCO₃ ⁻ concentration, with no changes in the PCO₂ values. Received: 5 February 1996/Received after revision and accepted: 20 May 1996     

Extracellular pH defense against lactic acid in normoxia and hypoxia before and after a Himalayan expedition

The extracellular pH defense against the lactic acidosis resulting from exercise can be estimated from the ratios −Δ[La] · ΔpH⁻¹ (where Δ[La] is change in lactic acid concentration and ΔpH is change in pH) and Δ[HCO₃ ⁻] · ΔpH⁻¹ (where Δ[HCO₃ ⁻] is change in bicarbonate concentration) in blood plasma. The difference between −Δ[La] · ΔpH⁻¹ and Δ[HCO₃ ⁻] · ΔpH⁻¹ yields the capacity of available non-bicarbonate buffers (mainly hemoglobin). In turn, Δ[HCO₃ ⁻] · ΔpH⁻¹ can be separated into a pure bicarbonate buffering (as calculated at constant carbon dioxide tension) and a hyperventilation effect. These quantities were measured in 12 mountaineers during incremental exercise tests before, and 7–8 days (group 1) or 11–12 days (group 2) after their return from a Himalayan expedition (2800–7600 m altitude) under conditions of normoxia and acute hypoxia. In normoxia −Δ[La] · ΔpH⁻¹ amounted to [mean (SEM)] 92 (6) mmol · l⁻¹ before altitude, of which 19 (4), 48 (1) and 25 (3) mmol · l⁻¹ were due to hyperventilation, bicarbonate and non-bicarbonate buffering, respectively. After altitude −Δ[La] · ΔpH⁻¹ was increased to 128 (12) mmol · l⁻¹ (P < 0.01) in group 1 and decreased to 72 (5) mmol · l⁻¹ in group 2 (P < 0.05), resulting mainly from apparent large changes of non-bicarbonate buffer capacity, which amounted to 49 (14) mmol · l⁻¹ in group 1 and to 10 (2) mmol · l⁻¹ in group 2. In acute hypoxia the apparent increase in non-bicarbonate buffers of group 1 was even larger [140 (18) mmol · l⁻¹]. Since the hemoglobin mass was only modestly elevated after descent, other factors must play a role. It is proposed here that the transport of La⁻ and H⁺ across cell membranes is differently influenced by high-altitude acclimatization. Accepted: 14 September 2000     

Extracellular pH defense against lactic acid in untrained and trained altitude residents

The assumption that buffering at altitude is deteriorated by bicarbonate (bi) reduction was investigated. Extracellular pH defense against lactic acidosis was estimated from changes (Δ) in lactic acid ([La]), [HCO₃ ⁻], pH and PCO₂ in plasma, which equilibrates with interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 10 untrained (UT) and 11 endurance-trained (TR) highlanders (2,600 m). During exercise the capacity of non-bicarbonate buffers (β _nbi = −Δ[La] · ΔpH⁻¹ − Δ[HCO₃ ⁻] · ΔpH⁻¹) amounted to 40 ± 2 (SEM) and 28 ± 2 mmol l⁻¹ in UT and TR, respectively (P < 0.01). During recovery β _nbi decreased to 20 (UT) and 16 (TR) mmol l⁻¹ (P < 0.001) corresponding to values expected from hemoglobin, dissolved protein and phosphate concentrations related to extracellular fluid (ecf). This was accompanied by a larger decrease of base excess after than during exercise for a given Δ[La]. β _bi amounted to 37–41 mmol l⁻¹ being lower than at sea level. The large exercise β _nbi was mainly caused by increasing concentrations of buffers due to temporary shrinking of ecf. Tr has lower β _nbi in spite of an increased Hb mass mainly because of an expanded ecf compared to UT. In highlanders β _nbi is higher than in lowlanders because of larger Hb mass and reduced ecf and counteracts the decrease in [HCO₃ ⁻]. The amount of bicarbonate is probably reduced by reduction of the ecf at altitude but this is compensated by lower maximal [La] and more effective hyperventilation resulting in attenuated exercise acidosis at exhaustion.     

Fat energy use and plasma lipid changes associated with exercise intensity and temperature

Summary The effect of 60 min of exercise at two intensities (50 and 60% ) and temperatures (0 and 22° C) on changes (A) in plasma lipids {triglycerides (TG), glycerol (GLY), total cholesterol (TC), and HDL-cholesterol (HDL-C)} was examined. Subjects were 10 men aged 27±7 years ( , % fat=12.2%±7.1%). and respiratory exchange ratio results indicated that total energy and fat energy use were similar at the two temperatures. Changes in plasma volume (%ΔPV) were different (P<0.05) at the two temperatures (22° C: −2.3% vs 0° C: 1.1%). Combining the data at each temperature revealed that the increases in concentrations were greater (P<0.05) at 22° C (ΔTG=0.22, ΔGLY=0.20, ΔTC=0.14, ΔHDL-C=0.05 mmol 1⁻¹) vs 0° C (ΔTG=0.10, ΔGLY=0.12, ΔTC=0.05, ΔHDL-C=0.02 mmol 1⁻¹). Combining the data for each intensity revealed that the increases in concentration were greater (P<0.05) at 60% for ΔTG and ΔHDL-C. The 60% C bout produced greater changes (P<0.05) than all other bouts for ΔTC and ΔHDL-C (0.21 and 0.08 mmol 1⁻¹, respectively). Only ΔTG and ΔGLY were greater at 22° C when adjusted for %ΔPV. These metabolic and plasma lipid results indicate that cold exposure does not act synergistically with exercise to further stimulate fat metabolism.     

Thermodynamic parameters of binding of mouse 2G3 antitheophylline monoclonal antibodies with theophylline

Binding of 2G3 mouse antitheophylline monoclonal antibodies (affinity constant K_aff=2*10¹⁰ liter/mol) with theophylline is studied using isothermal titration microcalorimetry. Thermodynamic parameters of the binding are: enthalpy change ΔH=−0.23 kcal/mol; Gibbs free energy change ΔG=−16.42 kcal/mol; entropy change ΔS=−0.054 kcal/(mol×K). Regression analysis shows a two-site kinetic binding model. A great contribution of entropy component into free energy change of 2G3 antibodies with theophylline is indicative of an entropy-dependent process. The entropy-dependent nature of the binding presumably determines the binding kinetics. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 123, No. 4, pp. 442–445, April, 1997     

In situ measurements of skeletal muscle power output using new capacitive strain gauge

Experiments are described in which a fatigue index is determined for the latissimus dorsi muscle of sheep in situ, using capacitive strain gauges. Parallel experiments for invasive and non-invasive measurements are conducted, measuring global contraction and relaxation rates and shortening duration for paced muscle. The results show that, above one pulse per burst (5V, 100 μs pulsewidth), contraction rates (62±11 mm s⁻¹) and relaxation rates (50±7 mm s⁻¹) are constant for unloaded muscle. For one animal, fatigue testing with a 2.5 kg load at six pulses per burst shows shortening rates increasing to a maximum (80 mm s⁻¹) after 30 s and reducing to 5 mm s⁻¹ after 150 s. The decrease in shortening amplitude is used as a fatigue index, log displacement against time. Power output is load dependent, measuring 4.7 Wkg⁻¹ with a 2.5 kg load. There is good agreement between the invasive and non-invasive measurements, thus providing a method for monitoring changes in muscle parameters non-invasively during future pacing transformation.     

The role of muscle pump in the development of cardiovascular drift

This study examined the role of muscle pump in the development of cardiovascular drift (CV_drift) during cycling. Twelve healthy males (23.4 ± 0.5 years, mean ± SE) exercised for 90 min with 40 and 80 pedal revolutions per minute (rpm) at the same oxygen consumption, in two separate days. CV_drift was developed in both conditions as indicated by the drop in stroke volume (SV) and the rise in heart rate (HR) from the 20th min onwards (ΔSV = −16.2 ± 2.0 and −17.1 ± 1.0 ml beat⁻¹; ΔHR = 18.3 ± 2.0 and 17.5 ± 3.0 beats min⁻¹ for 40 and 80 rpm, respectively, P < 0.05) but without difference between conditions. Mean cardiac output (CO₂ rebreathing) was 14.7 ± 0.3 l min⁻¹ and 15.0 ± 0.3 l min⁻¹, and mean arterial pressure was 100.0 ± 1.0 mmHg and 96.7 ± 0.8 mmHg for 40 and 80 rpm, respectively, without significant changes over time, and without difference between conditions. Electromyographic activity (iEMG) was lower throughout exercise with 80 rpm (35.6 ± 1.2% and 11.0 ± 1.0% for 40 and 80 rpm, respectively). Similarly, total hemoglobin, determined with near-infrared spectroscopy (NIRS) was 58.0 ± 0.8 (AU) for 40 rpm and 53.0 ± 1.4 (arbitrary units) for 80 rpm, from 30th min onwards (P < 0.05), an indication of lower leg blood volume during the faster pedal rate condition. Thermal status (rectal and mean skin temperature), blood and plasma volume changes, blood lactate concentration, muscle oxygenation (NIRS signal) and the rate of perceived exertion were similar in the two trials. It seems that muscle pump is not an important factor for the development of CV_drift during cycling, at least under the present experimental conditions.     

Effects of biomedical sterilization processes on performance characteristics of MEMS pressure sensors

The effects of steam and gamma sterilization on the performance of bulk-micromachined pressure sensors were investigated using a variable pressure setup. Commercially available piezoresistive MEMS (microelectromechanical systems) pressure sensor die were characterized prior and subsequent to sterilization over a 0–500 Torr pressure range. The effects of sterilization were examined as changes in sensor output voltage (ΔV) at various applied pressures. For steam sterilization, ΔV decreased with applied pressure ranging from +0.27 mV at 100 Torr to −0.14 mV at 500 Torr. In contrast, the corresponding values for gamma-sterilized sensors were lower, decreasing from +0.01 mV 100 Torr to −0.06 mV at 500 Torr. The increased variation in ΔV for the steam-sterilized sensors was attributed to the formation of an oxide film, which was confirmed using energy dispersive X-ray (EDX) spectroscopy. Statistical analysis revealed that the effect of both sterilization procedures on sensor performance was insignificant.     

Biomechanical topography of human ankle cartilage

The material properties of normal cadaveric human cartilage in the ankle mortice (tibiotalar articulation) were evaluated to determine a possible etiologic mechanism of cartilage injury of the ankle when an obvious traumatic episode is not present. Using an automated indentation apparatus and the biphasic creep indentation methodology, creep indentation experiments were performed in five sites in the distal tibia, one site in the distal fibula, and eight sites in the proximal talus of 14 human ankles (seven pairs). Results showed significant differences in the mechanical properties of specific human ankle cartilage regions. Topographically, tibial cartilage is stiffer (1. 19 MPa) than talar cartilage (1.06 MPa). Cartilage in the anterior medial portion of the tibia has the largest aggregate modulus (H _A =1.34 MPa), whereas the softest tissue was found to be in the posterior lateral (0.92 MPa) and the posterior medial (0.92 MPa) regions of the talus. The posterior lateral ridge of the talus was the thickest (1.45 mm) and the distal fibula was the thinnest (0.95 mm) articular cartilage. The largest Poisson's ratio was found in the distal fibula (0.08). The lowest and highest permeability were found in the anterior lateral regions of the astragalus (0.80 × 10⁻¹⁵ m⁴N⁻¹sec⁻¹) and the posterior medial region of the tibia (1.79 × 10⁻¹⁵ m⁴N⁻¹sec⁻¹), respectively. The anterior and posterior regions of the lateral and medial sites of the tibia were found to be 18–37% stiffer than the anatomically corresponding sites in the talus. The biomechanical results may explain clinically observed talar dome osteochondral lesions when no obvious traumatic event is present. Cartilage lesions in a repetitive overuse process in the ankle joint may be related to a disparity of mechanical properties between the articulating surfaces of the tibial and talar regions.     

Thermodynamic parameters of binding of mouse 2G3 antitheophylline monoclonal antibodies to theophylline

The binding of 2G3 mouse antitheophylline monoclonal antibodies (affinity constant K_aff=2×10¹⁰ liter/mol) to theophylline is studied using isothermal titration microcalorimetry. Thermodynamic parameters of the binding are: enthalpy change ΔH=−0.23 kcal/mol; Gibbs free energy change ΔG=−16.42 kcal/mol; entropy change ΔS=0.054 kcal/(mol×K). Regression analysis shows a two-site kinetic binding model. A great contribution of entropy component to the free energy change of 2G3 antibody binding to theophylline is indicative of an entropy-dependent process. The entropy-dependent nature of the binding presumably determines the binding kinetics. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 11, pp. 570–573, November, 1997     

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.     

Transcephalic electrical impedance in the study of cerebral circulation in a juvenile pig model

Transcephalic electrical impedance offers a technique for non-invasive, cotside monitoring of neonatal cerebral circulation but the exact nature of the signal is somewhat ambiguous. The impedance signal is examined in an animal project where the ventilator settings are adjusted (20 min⁻¹–10 min⁻¹–40 min⁻¹ for 10 min periods each) to produce circulatory changes. Six juvenile pigs are intubated, and ECG, arterial blood pressure, carotid flow (CF) by electromagnetic flowmeter and impedance are continuously monitored and stored on analogue tape. Cardiac output by thermodilution, blood oxygen (pO₂) and carbon dioxide (pCO₂) tensions are measured. ECG is converted to heart rate, mean blood pressure is integrated, and the high-frequency (1.50–4.00 Hz) component of the impedance signal ΔZ is computed using autoregressive spectral estimation. Stroke volume, peripheral vascular resistance (PVR) and cerebral vascular resistance (CVR) are calculated. pCO₂ and CF increase and pO₂ decreases during hypoventilation. CF correlates positively with cardiac output, stroke volume, ΔZ and pCO₂, and negatively with pO₂ and CVR. ΔZ correlates positively with heart rate and cardiac output, and negatively with PVR and CVR. It is concluded that the impedance signal is related to the amount of blood transmitted to the brain by every beat of the heart, depending on the changes in both the systemic circulation and the cerebral vascular compliance.     

In vivo 4-androstene-3,17-dione and 4-androstene-3β,17β-diol supplementation in young men

To determine if known androgenic hormone precursors for testosterone in the androgen pathway would be readily transformed to testosterone, eight male subjects [mean age 23.8 (SEM 3) years, bodymass 83.1 (SEM 8.7) kg, height 175.6 (SEM 8.5) cm] underwent a randomized, double-blind, cross-over, placebo-controlled oral treatment with 200 mg of 4-androstene-3,17-dione (Δ4), 4-androstene-3β,17β-diol (Δ4Diol), and placebo (PL). The periods of study were separated by 7 days of washout. Blood was drawn at baseline and subsequently every 30 min for 90 min after treatment. Analysis revealed mean area-under-the-curve (AUC) serum Δ4 concentrations to be higher during Δ4 treatment [2177 (SEM 100) nmol · l⁻¹] than Δ4Diol [900 (SEM 96) nmol · l⁻¹] or PL [484 (SEM 82) nmol · l⁻¹; P < 0.0001]. The Δ4 treatment also revealed a significant effect on total testosterone with a mean AUC [1632.5 (SEM 121) nmol · l⁻¹] that was greater than PL [1418.5 (SEM 131) nmol · l⁻¹; P < 0.05] but not significantly different from those observed after Δ4Diol treatment [1602.9 (SEM 119) nmol · l⁻¹; P = 0.77]. Free testosterone concentrations followed a similar pattern where mean AUC for the Δ4 treatment [6114.0 (SEM 600) pmol · l⁻¹] was greater than after PL [4974.6 (SEM 565) pmol · l⁻¹; P < 0.06] but not significantly different from those observed after Δ4Diol [5632.0 (SEM 389) pmol · l⁻¹; P = 0.48]. The appearance and apparent conversion to total and free testosterone over 90 min was stronger for the Δ4 treatment (r = 0.91, P < 0.045) than for Δ4Diol treatment (r = 0.69, NS) and negatively correlated for PL (r = −0.90, P < 0.02). These results would suggest that Δ4, and perhaps Δ4Diol, taken by month are capable of producing in vivo increases in testosterone concentrations in apparently healthy young men as has already been observed in women after treatment with Δ4. Accepted: 26 August 1999     

Streaming potentials during the confined compression creep test of normal and proteoglycan-depleted cartilage

The streaming potential response of cartilage in the confined compression creep configuration was assessed theoretically and measured experimentally in normal and proteoglycan-depleted tissue. The analytical solution, using the linear biphasic continuum model including electrokinetics and assuming homogeneous material properties, predicted that: (i) the peak streaming potentials is ΔV=k_e·Δσ, where k_e is the electrokinetic coefficient and Δσ is the change in compressive stress; (ii) the potential is maintained at 95 to 100% of the peak value of 0<t<0.10τ, where τ is the gel diffusion time constant; and (iii) during short times, 0<t<0.01 τ, 90% of the peak streaming potential occurs over a region extending 23% into the tissue sample. Experimentally, adult bovine cartilage disks, 0.5 mm thick, were subjected to step changes of compressive stress. The measured changes in potential indicated a linear response for changes in stress up to 0.10 MPa. The k_e of normal cartilage, estimated from the short time (0<t<2 sec) change in potential, was −1.65±1.25 mV/MPa. Digestion of cartilage by chondroitinase ABC resulted in an increased (less negative) k_e of −0.75±0.70 mV/MPa and a 33±29% depletion of anionic glycosaminoglycan, whereas digestion with trypsin resulted in a further increase in k_e to +1.64±0.95 mV/MPa and a 98±1% depletion of glycosaminoglycan. The streaming potential measurement may be a useful addition to the widely used confined compression creep test to assess cartilage material properties.     

Effect of specific inspiratory muscle warm-up on intense intermittent run to exhaustion

The effects of inspiratory muscle (IM) warm-up on the maximum dynamic IM function and the maximum repetitions of 20-m shuttle run (Ex) in the Yo-Yo intermittent recovery test were examined. Ten men were recruited to perform identical IM function test and exercise test in three different trials randomly. The control trial was without IM warm-up while the placebo and experimental trials were with IM warm-up by performing two sets of 30 breaths with inspiratory pressure-threshold load equivalent to 15% (IMW_P) and 40% (IMW) maximum inspiratory mouth pressure, respectively. In IMW, maximum dynamic IM functions including the maximal inspiratory pressure at zero flow (P ₀) and maximal rate of P ₀ development (MRPD) were increased compared with control values (P<0.05). The Ex was also augmented [mean (SD)] [19.5% (12.6)] while the slope of the linear relationship of the increase in rating of perceived breathlessness for every 4th exercise interval (RPB/4i) was reduced (P<0.05). In IMW_P, although increase in Ex and reduction in RPB/4i were occurred concomitantly in some subjects, the differences in Ex, RPB/4i and dynamic IM functions between control and IMW_P trials were not statistically significant. For the changes (Δ) in parameters in IMW and IMW_P (n=20), negative correlations were found between Δ RPB/4i and Δ Ex (r=−0.92), ΔP ₀ and Δ RPB/4i (r=−0.48), and Δ MRPD and Δ RPB/4i (r=−0.54). Such findings suggested that the specific IM warm-up in IMW may entail reduction in breathlessness sensation, partly attributable to the enhancement of dynamic IM functions, in subsequent exhaustive intermittent run and, in turn, improve the exercise tolerance.     

Noninvasive measurement of arterial elasticity in various human limbs

Arterial elasticity expressed by such indices as volume elastic modulus E_v and compliance C_a were noninvasively measured in various human limb segments; the upper arms, forearms, fingers, thighs, calves and toes. These indices are defined, respectively, as and C_a=ΔV/ΔP, where ΔP is pulse pressure, mean arterial volume and ΔV its pulsatile variation. ΔP was calculated from systolic P_as and mean P_am arterial pressures determined by volume oscillometric sphygmomanometry using the following equation: and the ΔV were detected by electrical admittance plethysmography at various transmural pressure P_t levels controlled by a compression cuff. The values obtained in these limb segments were compared with each other at P_t levels 0,30 and 60 mm Hg and the differences between them were discussed.     

Electric impedance cuff for the indirect measurement of blood pressure and volume elastic modulus in human limb and finger arteries

A new plethysmograph, the electric impedance cuff, was designed for the indirect measurement of blood pressure, volume elastic modulus E_v and compliance C_a in human limb arteries. This comprises a compression chamber filled with electrolyte solution and a tetrapolar electric impedance plethysmograph whose electrodes are placed inside the chamber; the former for controlling transmural arterial pressure P_t, and the latter for detecting total limb volume V_o, mean arterial volume and its variation ΔV_a. Systolic and mean arterial pressure in the upper arms, forearms and fingers were measured by detecting pulsatile impedance variation during the gradual (3–5 mm Hg per heart beat) increase (or decrease) in chamber pressure by the volume oscillometric technique. Diastolic and pulse pressure ΔP were calculated from these pressure values. Compliance C_a=ΔV/ΔP and volume elastic modulus were recorded at various P_t levels, controlled by the compression pressure. Although this is a kind of impedance plethysmograph, the volume change in a limb segment can be detected by this method without passing electric current through the limb.