Simple mechanical-chemical systemic pressure-control device

An implantable mechanical-chemical device was constructed to act as a feedback mechanism in controlling the blood pressure. It consisted of a balloon connected to a rubber catheter ending in a slit valve. Flow-pressure curves were derived fromin vitro testings for three valve thresholds (120, 140 and 170 mmHg). Five fast-acting hypotensive drugs subsequently filled the device during 40 noradrenaline infusions in 25 dogs, with the balloon in the abdominal aorta and the catheter in the inferior vena cava. The results were as follows: (i) Following a short initial increase in systolic aortic pressure, significantly lower (p<0·001) than in control experiments, the device prevented any pressure rise above its threshold. (ii) The time needed for pressure lowering at the device's threshold depended on the drug used being 3·34±0·84 (mean ± s.e. in minutes) for sodium nitroprusside, 5·99±0·96 for phentolamin, 11·63±2·97 for hydralazine, 14·54±2·43 for a-methyl-dopa and 23·32±2·07 for diazoxide.     

Isolated aorta setup for hemodynamic studies

A setup consisting of a high-performance hydraulic pump connected to the ascending part of an isolated aorta, including all major distal branches, each loaded with calibrated artificial resistors, was developed. The system was used to study total aortic compliance of the baboon as a function of mean aortic pressure (n=5). The aorta loaded with the resistors was mounted in a custom-designed sink table, such that it was submersed in physiological saline maintained at 37°C. Mean distending pressure in the entire aortic compliance from pressure and flow waves generated by the pump. Total aortic compliance as a function of mean pressure was fitted with a logarithmic function: Ln (Compliance)=A+B * P. The value of A(±SE) was: 1.565±0.319 and B: −0.020±0.003 (P<0.001). The results were compared with previously published results (also using the same three-element Windkessel fit) obtained in three of the same animalsin vivo. Thein vivo data were A: 1.095±0.235 and B: −0.019±0.003.In vitro data had a significantly higher value of A thanin vivo (P=0.017), implying a significantly higher aortic compliancein vitro thanin vivo. Occlusion of the proximal descending aorta was performed at a low distending pressure (55 mm Hg) to determine the proximal complicance. It was found (n=4) that 46±11% (SD) of the total arterial compliance is to be attributed to the ascending and proximal descending aorta. This work was supported in part by Grant RG 86/0066 from the scientific affairs division of Nato.     

In vivo experiments with a pH-ISFET electrode

The_{in vivo} stability and pH sensitivity of 19 intravascular pH electrodes for continuous monitoring have been investigated. The sensors were mounted in indwelling vascular catheters (7F) which were inserted into the arteries of seven anaesthetised and mechanically ventilated dogs. Variations in arterial pH, ranging from 6·82 to 7·72, were obtained by infusion of sodium bicarbonate and hydrochloric acid and by hyper/ hypoventilation with various volume fractions of carbon dioxide in the inspiratory gas mixture. The pH sensor output potential was compared within vitro pH determinations of arterial blood samples. After an initial stabilisation period following their introduction into the arterial blood, the electrodes showed an average long-term drift of 2·3 mVh⁻¹. When this drift was taken into account, a typical pH sensitivity of 50 mV per pH was found. The relationship between the electrode potentials and thein vitro pH values was linear and in almost all cases the correlation coefficient (r) was above 0·9. The electrodes responded rapidly enough to reflect breath-to-breath oscillations in pH.     

Wave-velocity in the proximal aorta

The wave velocity in the ascending aorta has been measured by 2 methods; (1) from the transit-time of the wave front between 2 points (the wave-front velocity) and (2) from the mean value of the phase shift of the harmonic components of both pressure waves (mean phase velocity). Close agreement was found between values obtained by both methods. With mean arterial pressure (M.A.P.) in the range 90–120 mm Hg the velocities recorded were (1) wave-front velocity, 4·04±(S.E.M.)0·14 m/s; (2) mean phase velocity, 3·98±0·12 m/s. With an electromagnetic flow probe on the ascending aorta the velocity was 3·98±0·09 m/s. Mean phase velocities were based on the values at frequencies above 2 Hz as wave reflection causes a large increase in measured phase-velocity below this frequency. Decrease in M.A.P. below 100 mm Hg produced no significant change in wave-velocity; above 100 mm Hg there was an increase in velocity to 5·6 m/s with a M.A.P. of 160 mm Hg. The wave-velocity in the ascending aorta is somewhat lower than that in the thoracic aorta.     

Mechanics of porcine coronary arteriesex vivo employing impedance planimetry: A new intravascular technique

Our objective was to evaluate methodological aspects of impedance planimetry, a new balloon catheter-based technique, for the investigation of coronary artery mechanical wall properties. We used a four ring-electrode electrical impedance measuring system that was located inside a balloon. Two of the electrodes were used for excitation and connected to a generator producing a constant alternating current of 250 mA at 5 kHz. The other two electrodes for detection were placed midway between the excitation electrodes. The balloon was distended with electrically conducting fluid through an infusion channel. The vessel cross-sectional area (CSA) was measured according to the field gradient principle by measuring the impedance of the fluid inside the balloon. Impedance planimetry was applied in the three major branches of the coronary arteries of seven extracted porcine hearts to assess luminal CSAs in response to internal pressurization. The biomechanical wall properties were evaluated by computing the strain [(r−r ₀)·r ₀ ⁻¹, wherer is the vessels inner radius computed as (CSA · π⁻¹)^? andr ₀ is the radius of the vessel at a minimal distension pressure], the tension [(r·dP), wheredP is the transmural pressure difference], and the pressure elastic modulus (ΔP·r·Δr ⁻¹). We found thatin vitro testing demonstrated that impedance planimetry was accurate and reproducible. The technique has controllable sources of crror. Measurements were performed with consecutively increasing pressures in the range 1–25 kPa (8–188 mmHg, 0.01–0.25 atm). The CSAs increased nonlinearly and were significantly larger in the left anterior descendent coronary artery (LAD) (1 kPa, mean 5.0 mm²; 25 kPa, mean 21.8 mm²) than in both the left circumflex (Cx) (4.5–16.0 mm²) and the right coronary artery (RCA) (2.8–15.6 mm²) (analysis of variance,P<0.001 for both). The circumferential wall tension-strain relation showed exponential behavior. For a given strain, tension values for LAD were significantly lower than those of Cx (P<0.01). The pressure elastic modulus-strain relation also was exponential, and values for Cx were significantly lower than values for LAD (P<0.001) and RCA (P<0.05). Impedance planimetry was applied to the study of coronary artery biomechanicsex vivo. The LAD had the largest CSA, and the Cx was the least compliant. Methodological aspects of anin vivo introduction of the method require additional evaluation.     

Automatic online numerical analysis of prolonged recording of gastro-oesophageal acid reflux

An automatic numerical amplitude analyser was designed for use in conjunction with a measuring system for the recording of acid reflux at the distal end of the oesophagus. The analyser is described, and its use is discussed in the light of the results of stability and reliability studies carried out by way of 12 hin vitro andin vivo recordings. The apparatus has proved stable with an electrode drift of 0–0·2 pH units over 12 h. The analyser permits calculation of the temporal distribution of the pH values within various preselected intervals, expressed as percentages of the total time of recording. The accuracy of the analysis was tested on a simulated pH curve, and, within the frequency range 0·1–5 Hz, deviation was less than 1% for all analytical areas. By repeated analyses of the samein vivo studies, the coefficient of variation was calculated at 0·0001–0·10.     

Inhibition of histamine release from basophil leucocytes of asthmatic patients treated with corticosteroids

We studied the protective effect of corticosteroids in asthmatic patients bothin vivo andin vitro. Steroid treatment of patients inhibitied thein vivo response to bronchial challenge with the specific allergen as shown by the substantial rise in allergen-threshold. It also produced inhibition of thein vitro elicited release of histamine and slow-reacting substance of anaphylaxis from blood leucocytes. This effect was apparent within 24 h of starting treatment with prednisolone in a daily dose of 30 mg, and reached a maximum after 48 h. In addition, in peripheral venous blood basophil count and total leucocyte histamine content were reduced, eosinophils disappeared and neutrophils increased.     

Negative Pressure Transients with Mechanical Heart-Valve Closure: Correlation between In Vitro and In Vivo Results

Negative pressure transients (NPT) recorded in a single closing event of mechanical valves in the mitral position in an in vitro setup are compared with data recorded in the left atrium in vivo with the valves implanted in the mitral position in an animal model. The loading at valve closure (dP/dt__CL) computed from the in vivo ventricular pressure recording (ranging from 700 to 2300 mm Hg/s) agreed with the magnitudes predicted in our earlier in vitro experiments (750-3000 mm Hg/s). The NPT signals and the corresponding power spectral density plots from the in vivo data were in qualitative agreement with those recorded in vitro. The NPT magnitudes were found to be below the vapor pressure for blood in mechanical valves with rigid occluders suggesting a potential for the valve to cavitate in vivo. Our in vivo results also suggest that the valves with flexible occluders are less likely to cavitate. The correlation of the in vitro and in vivo data also suggests that the flexibility of valve housing used in the in vitro studies is not an important factor in the dynamics of mechanical valve closure in vivo. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8790+y     

Effect of SAS 650—Furofenac®) on malondialydehyde production by platelets

The activity of SAS 650, a new anti-inflammatory drug, onex vivo andin vitro MDA production by platelets was compared to that of aspirin. The drug induced dose-dependent inhibition ofin vitro MDA production by rat and guinea-pig platelets and also had good activity after 30 second of incubation in rat platelets, quicker than aspirin.SAS 650 preincubation reduced thein vitro inhibitory effect of ASA, as shown also byex vivo experiments.The results of the present study support the involvement of SAS 650 in the platelet cyclooxygenase pathway.     

The potential use of implanted radiolabelled bovine nasal cartilage in dialysis tubing to evaluate agents affecting cartilage degradationin vivo

Cartilage which undergoes extensive autolysisin vitro (spontaneous or stimulated) is characterized by proteoglycan loss. Experimental conditions and inhibitor profils studies suggest neutral metalloproteinases induce the autolysis.In these preliminary studies we compared the degradation of Na₂ ³⁵SO₄ labeled bovine nasal cartilage (BNC) plugs placed in dialysis tubingin vitro andin vivo. The dialysis tubing was used to exclude large molecules (molecular weights greater than 2000) like proteinases, and proteinase inhibitors (e.g. ₂-macroglobulin) but not potential test agents from the implanted cartilage. Cartilage autolysis occurred with live tissue but not with heat-killed tissue in both thein vitro andin vivo systems. In addition retinoic acid and phenanthroline were effective when placed inside or outside the dialysis tubing. A potentially useful procedure to evaluate agents which affect cartilage degradation is described.     

Efficacy and immunomodulatory actions of ONO‐4641, a novel selective agonist for sphingosine 1‐phosphate receptors 1 and 5, in preclinical models of multiple sclerosis

ONO‐4641 is a next‐generation sphingosine 1‐phosphate (S1P) receptor agonist selective for S1P receptors 1 and 5. The objective of the study was to characterize the immunomodulatory effects of ONO‐4641 using preclinical data. ONO‐4641 was tested in both in‐vitro pharmacological studies as well as in‐vivo models of transient or relapsing–remitting experimental autoimmune encephalomyelitis (EAE). In vitro, ONO‐4641 showed highly potent agonistic activities versus S1P receptors 1 and 5 [half maximal effective concentration (EC₅₀) values of 0·0273 and 0·334 nM, respectively], and had profound S1P receptor 1 down‐regulating effects on the cell membrane. ONO‐4641 decreased peripheral blood lymphocyte counts in rats by inhibiting lymphocyte egress from secondary lymphoid tissues. In a rat experimental autoimmune encephalomyelitis (EAE) model, ONO‐4641 suppressed the onset of disease and inhibited lymphocyte infiltration into the spinal cord in a dose‐dependent manner at doses of 0·03 and 0·1 mg/kg. Furthermore, ONO‐4641 prevented relapse of disease in a non‐obese diabetic mouse model of relapsing‐remitting EAE. These observations suggest that ONO‐4641 may provide therapeutic benefits in the treatment of multiple sclerosis.     

Measurement of aortic compliance from the transthoracic admittance plethysmogram in the living dog

An attempt was made to measure the compliance and elastic modulus of the thoracic aorta from simultaneous recordings of the transthoracic admittance plethysmogram and intra-aortic pressure in living dogs. Initially, the compliance values determined by this method were correlated with those measured from the volume-pressure relationships in three different silicone-rubber tubes; these two groups of values were consistent with each other within the error range of ±10%. The mean value of the compliance of the thoracic aortae in four normal dogs (13–15 kg) measured by this method was 0·00387±0·00100 ml/mmHg cm. The elastic modulus E and velocity v of the pulse wave were calculated from this value; E=2·71±0·79×10⁵ dN/m² and v=4·52±2·44 m/s. These data were compared with those reported previously by other investigators. Taking simplicity, safety and practicability into consideration, it was concluded that this method would only be useful in clinics for the rough estimation of the elastic properties of the thoracic aorta.     

Apoptotic death of pancreatic cancer cells induced by polyunsaturated fatty acids varies with double bond number and involves an oxidative mechanism

Polyunsaturated fatty acids (PUFAs), reported to be cytotoxic at micromolar concentrations for cancer cells in vitroand in vivo, are currently being tested in clinical trials as anti-cancer agents. This study has shown that seven PUFAs all inhibited the growth in vitroof three pancreatic cancer cell lines and the HL-60 leukaemic cell line. Five PUFAs induced cell death within 20–30 h, but two less potent PUFAs induced death between 50 and 75 h. Apoptosis was demonstrated to be the mode of cell death by light, UV fluorescence, and electron microscopy, together with studies of DNA fragmentation. In a time–course study of PUFA-treated Mia-Pa-Ca-2 cells, apoptosis accounted for an average of 80 per cent of the loss of viability, with ‘secondary necrosis’, a feature of late apoptosis, apparently accounting for the remainder. Correlations were found between the number of fatty acid double bonds and the proportion of cells undergoing apoptosis induced in both Mia-Pa-Ca-2 cells (R=0·88, P=0·0001) and HL-60 cells (R=0·85, P=0·0001) and inversely with the micromolar concentrations of PUFAs required for 50 per cent inhibition of growth (IC₅₀) of Mia-Pa-Ca-2 cells (R=−0·73, P=0·05). Cell death was preceded by progressively increasing lipid peroxidation. The extent of PUFA-induced lipid peroxidation, measured as malondialdehyde (MDA), also correlated with the proportion of apoptosis induced in Mia-Pa-Ca-2 cells (R=0·69, P=0·025) or HL-60 cells (R=0·64, P=0·043), as well as with the number of fatty acid double bonds (R=0·82, P=0·0015). PUFA-induced apoptosis was oxidative, being blocked by both vitamin E acetate and sodium selenite, the latter in a critically time-dependent manner. The cytotoxic effects of exposure to a PUFA and to γ-irradiation simultaneously with, or prior to, the addition of PUFA. © 1998 John Wiley & Sons, Ltd.     

Nonlinear closed-loop control system for intracranial pressure regulation

A nonlinear closed-loop control system with flat pressure-versus-flow characteristics that is aimed at regulating intracranial pressure (ICP) by adjusting the volume of cerebral spinal fluid (CSF) was designed, built, and tested. The control system design allows both the pressure setpoint and hysteresis to be adjusted to overcome the difficulties inherent in differential pressure-activated, fixed resistance, open-loop shunts. A dynamic six-compartment bench-top fluid system, which mimics the cerebral spinal fluid system, was designed, built, and tested. A computer simulation was developed which included the nonlinear on-off controller with hysteresis and a sixth-order, linear, multicompartmental model of the CSF system. The computer model andin vitro system results showed the ability of the system to track and compensate for pressure variations above and below normal as well as for spurious outputs that mimic suchin vivo problems as blood pressure changes, sneezing, or coughing. There was one discrepancy between the simulated andin vitro results. Thein vitro system had a higher rate of increase in pressure due to the more rigid compliance of the materials used, whereas the computer model compliance, based on the basalin vivo compliance of the CSF system, was less rigid. Based on these findings, the controller was modified to account for shortduration, extremely elevated pressures.     

Mechanics of porcine coronary arteries<Emphasis Type="Italic">ex vivo</Emphasis> employing impedance planimetry: A new intravascular technique

Our objective was to evaluate methodological aspects of impedance planimetry, a new balloon catheter-based technique, for the investigation of coronary artery mechanical wall properties. We used a four ring-electrode electrical impedance measuring system that was located inside a balloon. Two of the electrodes were used for excitation and connected to a generator producing a constant alternating current of 250 mA at 5 kHz. The other two electrodes for detection were placed midway between the excitation electrodes. The balloon was distended with electrically conducting fluid through an infusion channel. The vessel cross-sectional area (CSA) was measured according to the field gradient principle by measuring the impedance of the fluid inside the balloon. Impedance planimetry was applied in the three major branches of the coronary arteries of seven extracted porcine hearts to assess luminal CSAs in response to internal pressurization. The biomechanical wall properties were evaluated by computing the strain [(r?r ₀)·r ₀ ^?1, wherer is the vessels inner radius computed as (CSA · π^?1)^½ andr ₀ is the radius of the vessel at a minimal distension pressure], the tension [(r·dP), wheredP is the transmural pressure difference], and the pressure elastic modulus (ΔP·r·Δr ^?1). We found thatin vitro testing demonstrated that impedance planimetry was accurate and reproducible. The technique has controllable sources of crror. Measurements were performed with consecutively increasing pressures in the range 1–25 kPa (8–188 mmHg, 0.01–0.25 atm). The CSAs increased nonlinearly and were significantly larger in the left anterior descendent coronary artery (LAD) (1 kPa, mean 5.0 mm²; 25 kPa, mean 21.8 mm²) than in both the left circumflex (Cx) (4.5–16.0 mm²) and the right coronary artery (RCA) (2.8–15.6 mm²) (analysis of variance,P<0.001 for both). The circumferential wall tension-strain relation showed exponential behavior. For a given strain, tension values for LAD were significantly lower than those of Cx (P<0.01). The pressure elastic modulus-strain relation also was exponential, and values for Cx were significantly lower than values for LAD (P<0.001) and RCA (P<0.05). Impedance planimetry was applied to the study of coronary artery biomechanicsex vivo. The LAD had the largest CSA, and the Cx was the least compliant. Methodological aspects of anin vivo introduction of the method require additional evaluation.     

Sida rhomboidea.Roxb aqueous extract down-regulates in vivo expression of vascular cell adhesion molecules in atherogenic rats and inhibits in vitro macrophage differentiation and foam cell formation

The present study evaluates efficacy of Sida rhomboidea.Roxb (SR) leaves extract in ameliorating experimental atherosclerosis using in vitro and in vivo experimental models. Atherogenic (ATH) diet fed rats recorded significant increment in the serum total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), very LDL (VLDL), autoantibody against oxidized LDL (Ox-LDL), markers of LDL oxidation and decrement in high-density lipoprotein (HDL) along with increment in aortic TC and TG. The ex vivo LDL oxidation assay revealed an increased susceptibility of LDL isolated from ATH rats to undergo copper mediated oxidation. These set of changes were minimized by simultaneous co-supplementation of SR extract to ATH diet fed rats. Histopathology of aorta and immunolocalization studies recorded pronounced atheromatous plaque formation, vascular calcification, significant elastin derangements and higher expression of macrophage surface marker (F4/80), vascular cell adhesion molecule-1 (VCAM-1) and p-selectin in ATH rats. Whereas, ATH+SR rats depicted minimal evidence of atheromatous plaque formation, calcium deposition, distortion/defragmentation of elastin and accumulation of macrophages along with lowered expression of VCAM-1 and P-selectin compared to ATH rats. Further, monocyte to macrophage differentiation and in vitro foam cell formation were significantly attenuated in presence of SR extract. In conclusion, SR extract has the potency of controlling experimental atherosclerosis and can be used as promising herbal supplement in combating atherosclerosis.     

A system for measurements of micturition urethral cross-sectional areas and pressures

A system for the measurement of urethral urinary stream cross-sectional areas and pressures is described. The system consists of: (1) A 4 French gauge probe with electrodes for the electrical impedance measurement of cross-sectional areas and side-holes for pressure measurements (2) an electrical field generator and impedance detecting section and (3) a side-hole perfusion and pressure measuring part. Thein vitro performance of the system is: linear cross-sectional area measurement in the range of 0–38 mm², independent of the shape of the lumen and with an axial resolution of approximately 7 mm. Measurement of hydrostatic pressures with a time constant of 0·38 s and of closure pressures with a post-occlusion pressure increase rate of 0·85 kPa s⁻¹.In vivo cross-sectional areas are calibrated in a standard made of PVC. The influence of the electrical shunting of the urethral mucosa is shown to permit this, provided that the impedance of the mucosa in the closed urethra is measured in each patient investigated.     

Effects of flezelastine and its enantiomers on LPS-induced IL-1β generationin vitro and LPS-induced pyrexiain vivo

The effects of the novel antiasthmatic/antiallergic compound flezelastine on LPS-induced actions were investigatedin vitro andin vivo. In monocytes, IL-1 generation stimulated by LPS was inhibited dose dependently.In vivo, LPS-induced fever in rats, which is at least partly driven by the release of IL-1, was also inhibited by flezelastine. These findings suggest that flezelastine inhibits IL-1 synthesis and/or releasein vitro andin vivo.     

Modulation of immunologic responses in nontuberculous mycobacterial infections with indomethacin

We have previously reported that impairedin vitro cellular immunity is a common finding in patients with nontuberculous mycobacterioses and that the subnormal responses may be improved by indomethacin. Subsequently, we have studied thein vivo effects of indomethacin on cell-mediated immune functions of four patients withMycobacterium avium-intracellulare infections. Prior to treatment none of the patients had delayed cutaneous reactions to purified protein derivative (PPD) of the tubercle bacillus, and their lymphocytes had subnormalin vitro proliferation responses to tuberculins fromM. tuberculosis andM. avium-intracellulare and to phytohemagglutinin. The administration of indomethacin reconstituted both thein vitro lymphocyte responses and delayed cutaneous hypersensitivity. We propose that the impairment of T-cell dependent immune functions is mediated by a suppressive factor (or factors) that is a metabolic product(s) of the cyclooxygenase pathway of arachidonic acid metabolism. Preferential inhibition of this pathway with indomethacin allows the expression of cell-mediated responses.     

Polyclonal expansion of cervical cytobrush‐derived T cells to investigate HIV‐specific responses in the female genital tract

Human immunodeficiency virus (HIV) ‐specific T‐cell responses are detectable in the female genital tract of HIV‐infected women but little is known about their frequency or the factors that influence their detection. We investigated the feasibility of polyclonal in vitro expansion of cervical cytobrush‐derived T cells to investigate HIV‐specific responses in the female genital tract in HIV‐infected women. Cytobrush‐derived cervical cells were isolated from 22 HIV‐infected women and expanded with anti‐CD3 and recombinant interleukin‐2. Cervical T‐cell lines were investigated for Gag‐specific responses by interferon‐γ ELISPOT and compared with those detected in matched blood samples. Cervical T‐cell lines were established from 16/22 (72·7%) participants. Although the absolute number of CD3^± cells recovered after expansion was positively associated with the number of cells isolated ex vivo (P = 0·01; R = 0·62), we observed a significant negative correlation between fold expansion and ex vivo cell number (P = 0·004; R = ?0·68). We show that both the magnitude (P = 0·002; R = 0·7) and specific Gag regions targeted by cervical T‐cell lines (P < 0·0001; R = 0·5) correlated significantly with those detected in blood. With one exception, cervical interferon‐γ T‐cell responses to Gag were detected only in HIV‐infected women with blood Gag‐specific response > 1000 spot‐forming units/10⁶ cells. We conclude that cervical Gag‐specific T‐cell responses in expanded lines are most easily detectable in women who have corresponding high‐magnitude Gag‐specific T‐cell responses in blood.