Biomedical subjects

H Gregersen

Publications and source records attributed to H Gregersen.

At least 37 records · Page 2Linked to original sources

PubMed1996

Unexplained chest pain: the hypersensitive, hyperreactive, and poorly compliant esophagus.

OBJECTIVE: To determine whether neuromuscular dysfunction of the esophagus causes chest pain in patients in whom no disease is found on cardiac work-up, upper gastrointestinal endoscopy, esophageal manometry, and 24-hour pH studies. DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: 24 consecutive patients and 12 healthy controls. MEASUREMENTS: A new technique, impedance planimetry, was used to measure the sensory, motor, and biomechanical properties of the human esophagus. The impendance planimeter, which consists of a probe with four ring electrodes, three pressure sensors, and a balloon, simultaneously measures intraluminal pressure and cross-sectional areas. This allows calculation of the biomechanical variables of the esophageal wall. RESULTS: Stepwise balloon distentions from 5 to 50 cm H2O induced a first sensation at a mean pressure (+/- SD) of 15 +/- 9 cm H2O in patients and 30 +/- 11 cm H2O in controls (P < 0.001). Moderate discomfort and pain were reported by 20 of 24 patients (83%) at 26 +/- 9 cm H2O and at 36 +/- 9 cm H2O, respectively, but by none of the controls (P < 0.001). Typical chest pain was reproduced in 20 of 24 patients (83%). In patients, the reactivity of the esophagus to balloon distention was greater (P = 0.01), the pressure elastic modulus was higher (P = 0.02), and the tension-strain association showed that the esophageal wall was less distensible (P = 0.02). Distention excited tertiary contractions and secondary peristalsis at a lower threshold of pressure (P = 0.05) and with a higher motility index in patients than in controls (P = 0.04). CONCLUSION: In patients with chest pain and normal cardiac and esophageal evaluations, impedance planimetry of the esophagus reproduces pain and is associated with a 50% lower sensory threshold for pain, a 50% lower threshold for reactive contractions, and reduced esophageal compliance.

Adult↗

PubMed1996

Systemic treatment with epidermal growth factor in the rat. Biomechanical properties of the growing small intestine.

Prolonged treatment with epidermal growth factor (EGF) in the rat provides an experimental model to growth of the gastrointestinal tract. We treated female Wistar rats for 0 (n = 15), 1 (n = 8), 2 (n = 8), and 4 (n = 8) weeks with subcutaneous EGF (i50 micrograms.kg-1.day-1). Segments were taken from locations at 10, 50 and 90% along the length of the small intestine, weighed, the wall thickness was measured and the luminal cross-sectional area and passive biomechanical properties were assessed using impedance planimetry. In addition, the wall composition was evaluated on histological sections. The weight of the total small intestine and of the three segments (measured in mg.cm-1) increased with the duration of the EGF treatment due to mucosal and muscular growth. After 1 week of treatment the wall thickness increased. After 2 weeks of treatment the cross-sectional area began to increase. The circumferential stress-strain distributions revealed translation of the curves to the right in the graphs implying reduced wall stiffness during EGF treatment. In conclusion EGF treatment for 1 to 4 weeks caused a time-dependent increase in intestinal weight. The growth was characterized by increased wall thickness, increased cross-sectional area and reduced wall stiffness.

Animals↗

PubMed1996

Discrimination between artefacts and contractions in pressure signals from the gastrointestinal tract by pattern recognition method.

A pattern recognition algorithm has been developed to discriminate between artefacts and contractions in interdigestive motility recorded by a pressure catheter with four channels from the human duodenum. A learning and a test set, both containing natural and induced artefacts, such as respiration and body movement, are obtained from five volunteers. The event classes were phase I, II and III contractions of the interdigestive motility complex and artefacts from respiration, cough, calibration signals and movements. Length, area, amplitude, inter-event interval, up- and downstroke, and correlation to other pressure channels and to respiration, are applied to classify the events. The sensitivity of the computer scoring increases with the number of applied features. When all the features are applied, the sensitivity of the Bayes' classifier against the visually scored contractions and artefacts is 0.96 with a specificity of 0.69.

Adult↗

PubMed1996

Impedance planimetric characterization of the distal oesophagus in the Goettingen minipig.

Regional differences in biomechanical properties of the oesophagus were studied in 15 healthy Goettingen minipigs by means of impedance planimetry. The investigation was performed during anaesthesia by stepwise pressure-induced balloon distensions with concomitant measurement of pressure and luminal cross-sectional area (CSA) in the oesophagus 5 and 10 cm above the gastro-oesophageal junction. The circumferential wall tension, circumferential strain and incremental elastic modulus were computed from the measurements of pressure and CSA at steady-state conditions. Probably due to the anaesthesia, only scant peristalsis was recorded and the CSA always reached steady state during the balloon distensions. The CSAs were highest in the distal oesophagus (P < 0.001). At the highest induced pressure, the CSAs were 605 +/- 32 and 453 +/- 29 mm2 (mean +/- SEM) for the locations 5 and 10 cm from the gastro-oesophageal junction. The tension-strain distributions were non-linear and the curve obtained 5 cm above the gastro-oesophageal junction was shifted to the right when compared with the curve obtained from 10 cm above this junction. Fitting of the function tension = exp(a+b strain) to the data gave determination coefficients higher than 0.97 and P values lower than 0.001 for both measuring points. The constant a differed between the two locations in the oesophagus (P < 0.05). In conclusion, the pressure-CSA and the tension-strain distributions differed between the two measuring points suggesting that the elastic properties are different.

Anesthesia, General↗

PubMed1996

Porcine coronary artery pharmacodynamics in vitro evaluated by a new intravascular technique: relation to axial stretch.

A new intravascular balloon catheter-based technique, impedance planimetry and the wire-mounted isometric tension technique commonly employed to study vessel pharmacodynamics in vitro, were compared. Porcine left anterior descendent coronary artery reactivity to nifedipine was assessed and the influence of 20% axial stretch was investigated. There were no histological differences between segments where the impedance planimetry balloon had been inflated and untouched segments. EC50 values differed significantly between the three procedures applied: The isometric method (n = 7): 2.54 +/- 0.44.10(-9) M; nonstretched arteries by the impedance planimetric method (n = 7): 1.99 +/- 0.40.10(-8) M; arteries 20% axially stretched (n = 7): 2.00 +/- 1.36.10(-7)M (isometric and nonstretched: p < 0.05; isometric and stretched: p < 0.001; nonstretched and stretched: p < 0.05). Maximal relaxant responses to nifedipine were 91.8 +/- 2.1% (isometric method), 105.1 +/- 2.3% (nonstretched), and 104.9 +/- 7.7% (stretched) (ANOVA, p = 0.11). In stretched arteries, the initial 12-min response to an increased dose of nifedipine was more rapid than the response of nonstretched arteries at a concentration of 1.10(-7) M (p = 0.038) and had a nonsignificant tendency toward a more rapid response at other concentrations. Resting tone could not be demonstrated and time control experiments showed no change in the maximal vessel response to potassium with any of the three methods. A new method in the evaluation of artery pharmacodynamics in vitro was presented. The study demonstrated that axial stretching of an artery has impact on the pharmacodynamic reactivity to nifedipine in porcine coronary arteries. Further studies are needed to evaluate the impact of the method on endothelial function.

Animals↗

PubMed1996

Elastic properties in the circumferential direction in isolated rat small intestine.

The aim was to study the passive biomechanical wall properties in the isolated duodenum, jejunum and ileum of the rat. The organ bath contained a Krebs-Ringer solution with 10(-2) M MgCl2 to abolish smooth muscle contractile activity. Stepwise inflation of an intraluminal balloon, in which the cross-sectional area (CSA) was measured, provided the distension stimulus. The circumferential wall stress-strain distributions were computed from steady-state values of these measurements and the unstressed wall thickness was measured in order to evaluate the passive elastic properties. The CSAs measured increased from duodenum to jejunum and to ileum (P < 0.001). At the highest applied pressure load the CSA was 16.64 +/- 0.46 mm2 for the duodenum, 18.70 +/- 0.53 mm2 for the jejunum and 21.73 +/- 0.49 mm2 for the ileum. The wall thickness was 0.19 +/- 0.01, 0.25 +/- 0.01 and 0.28 +/- 0.02 mm, in duodenum, jejunum and ileum, respectively (P < 0.01). All segments showed stress-strain distributions that were exponential by nature. Applying the function Y = exp (a + bX) gave a median determination coefficient of 0.98 (quartiles 0.96-0.99). The duodenum was significantly stiffer than the two other segments. The values of a and b were 2.03 +/- 0.11 and 14.82 +/- 1.81, 1.39 +/- 0.20 and 13.15 +/- 1.42, and 1.13 +/- 0.13 and 10.69 +/- 0.65 for the duodenum, jejunum and ileum, respectively. The a differed between the duodenum and the other segments (P < 0.001). whereas the b differed only between the duodenum and ileum (P < 0.005). In conclusion, differences in the luminal CSA, wall thickness and elastic properties were found between the duodenum, jejunum and ileum.

Animals↗

PubMed1996

Biomechanics of the gastrointestinal tract.

As the function of the gastrointestinal tract is to a large degree mechanical, it has become increasingly popular to acquire distensibility data in motility research based on various parameters. Hence it is important to know on which geometrical and mechanical assumptions the various parameters are based. Currently, compliance and tone derived from pressure-volume curves are by far the most often used parameters. However, pressure-volume relations obtained in tubular organs must be carefully interpreted as they provide no direct measure of luminal cross-sectional area and other variables useful in plane stress and strain analysis. Thus, erroneous conclusions concerning tissue distensibility may be deduced. Other parameters, such as wall tension, stress and strain, give more useful information about mechanical behaviour. Distensibility data procure significance in fluid mechanics and in the study of tone, peristaltic reflexes, and mechanoreceptor kinematics. Such data are needed for the determination of the interaction between stimulus, electrical responses in neurons and the mechanical behaviour of the gut. Furthermore, from a clinical perspective, investigation of visco-elastic properties is important because GI diseases are associated with growth and remodelling. For example, prestenotic dilatation, increased collagen synthesis, dysmotility and altered distensibility are common features of obstructive diseases. The purpose of this review is to discuss the physiological and clinical importance of acquiring biomechanical data, distensibility parameters and interpretation of these results and their associated errors. We will also discuss some aspects of the relationship between morphology, growth and biomechanics. Finally, we will outline a number of techniques to study the mechanical properties of the GI tract.

Biomechanical Phenomena↗

PubMed1996

Pressure-cross-sectional area relations and elasticity in the rabbit oesophagus in vivo.

The aim was to assess the luminal cross-sectional area (CSA) and the passive elastic properties of the oesophageal body under luminal pressure loading in anaesthetized rabbits. Stepwise inflation of a luminal balloon, in which the CSA and pressure were measured by means of impedance planimetry and perfused low-compliance manometry, provided the distension stimulus. The parameters of elasticity were computed from steady state values of these measurements. The steady state pressure-CSA and pressure-radius relations were nonlinear. At the lowest and highest luminal pressure load of 1 and 10 kPa, the steady state CSAs were 39 +/- 3 and 91 +/- 4 mm2, respectively. The circumferential tension-strain distribution was nonlinear and showed an exponential behaviour that fitted well to the function tension = a.e(b.strain). Differentiation of the function yielded the wall stiffness which also showed an exponential behaviour.

Animals↗

PubMed1996

Regional differences exist in elastic wall properties in the ureter.

According to classical mechanical theory, the passive elastic properties of a distensible tube are important for the resistance to flow. The aim was to study luminal dimensions under pressure loading and the tension-strain distribution of the ureter in anaesthetized pigs by means of impedance planimetry. Stepwise inflation of an intraluminal balloon in which the cross-sectional area (CSA) and pressure were measured provided the distension stimulus in the ureteropelvine junction, in the midureter and in the intramural part of the ureter at the ureterovesical junction. The circumferential tension-strain distributions were computed from steady state values of these measurements. The CSA always reached equilibrium within the two-minute distension period. The steady state pressure-CSA curves were nonlinear and differed between the three measuring points (p < 0.001). The most pronounced difference was found between the ureteropelvine junction and the two other measuring points. At the lowest applied pressure of 1 kPa the steady state CSA was 15.4 +/- 1.1, 16.6 +/- 1.1, and 19.9 +/- 19.9 mm2 in the intramural part, middle part and ureteropelvine junction, respectively. At the maximum pressure the figures were 41.9 +/- 2.9, 47.0 +/- 2.7, and 73.1 +/- 8.2 mm2 for the three locations, respectively. The circumferential tension-strain distributions were nonlinear with an exponential-like behaviour. The tension-strain curve obtained from the ureteropelvine junction was translated to the right compared to the curves obtained from the two other measuring points (p < 0.05) indicating that the ureteropelvine junction was more compliant than the two other locations.

Analysis of Variance↗

PubMed1996

In vivo assessment of luminal cross-sectional areas and circumferential tension-strain relations of the porcine aorta.

UNLABELLED: The objectives were to measure the pressure--cross-sectional area relations and intrinsic stiffness of the porcine aorta in vivo. METHODS: Measurements were made in 12 pigs, weight 30, 50 or 75 kg, proximal and distal to the bifurcation of the renal arteries, using an electrical impedance system which was located inside a balloon mounted on a catheter. Vessel cross-sectional area (CSA) was assessed by measuring impedance of the fluid inside the balloon during distension. RESULTS: In vitro testing demonstrated the accuracy and reproducibility of impedance planimetry. In vivo steady-state CSA values showed non-linear relationship with rising distension pressures. Mean CSA values rose with increasing weight of the pigs. the suprarenal aorta was larger than the infrarenal only in 75 kg pigs (p < 0.05). At three measurements the within-subject variation was 0.89% and the between-subject variation 99.11%. Nitroglycerine infusion produced only minor, insignificant CSA increase, indicating negligible tone in the abdominal aorta. All segments showed circumferential wall strain-tension relations with exponential behaviour uninfluenced by weight class or site in the aorta. CONCLUSION: Information of vascular mechanics in vivo is obtainable by catheterization of the abdominal aorta.

Analysis of Variance↗

PubMed1995

[Chronic lymphocytic and myeloid leukemia in the same patient].

A patient with chronic lymphocytic leukemia (CLL) treated with chlorambucil and prednisone developed chronic myelocytic leukemia (CML) five years later. An association between the two chronic leukemias has only rarely been reported. In the majority of cases the CLL preceded CML after which the malignancies coexisted morphologically in bone marrow and peripheral blood. In this case we report a suppression of CLL related symptoms and blood findings after the emergence of CML. However, immunophenotypic studies demonstrated a minor remaining population of CLL cells in the peripheral blood.

Aged↗

PubMed1995

Passive elastic wall properties in isolated guinea pig small intestine.

The aim was to study and compare the passive biomechanical wall properties in the isolated duodenum and distal ileum of the guinea pig in vitro. The organ bath contained a Krebs-Ringer solution with 10(-2) M MgCl2 to abolish smooth muscle contractile activity. Stepwise inflation of an intraluminal balloon, in which the cross-sectional area (CSA) was measured, provided the distension stimulus. The circumferential wall tension-strain distributions and wall stiffness-strain relations were computed from steady-state values of these measurements in order to evaluate the passive elastic properties. The CSA always reached equilibrium within the 2-min distension period. The CSAs obtained in the distal ileum were higher than those in the duodenum (P < 0.001). The basal CSA was 17.31 +/- 1.14 mm2 and 12.96 +/- 0.42 mm2 for the distal ileum and the duodenum, respectively (P < 0.01). At a maximum pressure of 6 kPa, the CSA of the ileum was 56.63 +/- 1.81 mm2 and 36.86 +/- 1.76 mm2 for the duodenum (P < 0.01). The circumferential wall tension-strain distributions showed an exponential behavior that accorded well with the equation Y = exp(a+bX) with determination coefficients of 0.96 +/- 0.01 and 0.99 +/- 0.00 in the duodenal segments in the distal ileal segments, respectively. The values of a (intercept with the y-axis) were 0.54 +/- 0.11 and -0.35 +/- 0.19 for the duodenal and ileal segments, respectively (P < 0.001). The slope of the curves (b values) were 4.34 +/- 0.35 in the duodenal and 5.23 +/- 0.37 in the ileal segments (0.1 > P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

A new combined high-frequency ultrasound-impedance planimetry measuring system for the quantification of organ wall biomechanics in vivo.

The aim was to develop a method for the quantification of the stress-strain distribution of tubular organs in vivo using the porcine duodenum as an experimental model. We placed four electrodes for impedance planimetry and a 20 MHz ultrasound transducer inside an inflatable balloon mounted on a 6 mm-diameter probe for intraluminal use. By means of the ultrasound transducer and the impedance planimetric system, we measured the wall thickness and luminal cross-sectional area of the duodenum. We calculated the luminal radius on the basis of the latter. We validated ultrasonic measurements of wall thicknesses by comparing the former to microscopic measurements of the wall thickness of unstrained duodenal specimens in vitro. Also, we tested whether the magnitude of the applied balloon pressure affected ultrasonic measurements in vitro. The luminal and the outer radius increased non-linearly by a factor of three, rising steeply at low balloon pressures, moderately at higher pressures. The wall thickness decreased as an almost linear function of the applied balloon pressure, resulting in a 50% decrease. The stress-strain distribution calculated on the basis of the balloon pressures, the wall thicknesses and the luminal radii were non-linear. The wall reached a maximum circumferential strain of 1.71 at 6 kPa, corresponding to a stress of 64.8 kPa. Our system enabled us to quantify the stress-strain distribution of the porcine duodenum in vivo, and it may become a valuable tool for future biomechanical investigations of tubular organs in health and disease.

Animals↗

PubMed1995

Epidermal growth factor attenuates the sclerotherapy-induced biomechanical properties of the oesophagus. An experimental study in minipigs.

BACKGROUND: The effect of epidermal growth factor (EGF) on the biomechanical properties of the oesophagus subjected to sclerotherapy was studied in Goettingen minipigs by means of impedance planimetry. METHODS: Seventeen animals underwent three sessions of weekly endoscopic sclerotherapy. During these 3 weeks and for the subsequent 2 weeks they were treated with either EGF or placebo. After another 3 weeks an impedance planimetric study was done. Ten healthy non-sclerosed pigs were studied as controls. Impedance planimetry was performed by stepwise pressure-induced balloon inflation for analysis of oesophageal cross-sectional area 5 and 10 cm above the gastro-oesophageal junction (GEJ). RESULTS: Systemic treatment with EGF (total daily dose of 30 micrograms/kg/day, administered subcutaneously) for 3 to 7 days per week combined with a weekly paravenous injection of 20-40 micrograms/kg attenuated the oesophageal damage caused by sclerotherapy, implying less pronounced narrowing 5 cm above and less dilation 10 cm above the GEJ. CONCLUSION: These observations suggest a potential therapeutic role for EGF in attenuating sclerotherapy-induced oesophageal injury.

Animals↗

PubMed1994

Elastic wall properties and collagen content in the ureter: an experimental study in pigs.

We used an impedance planimetric method to look at elastic wall properties of ureter in ten anaesthetized pigs. A balloon was stepwise inflated and deflated in the ureteropelvine junction, in the mid-ureter, and in the intramural part of the ureter at the ureterovesical junction with pressures up to 70 cmH2O, while the pressure and balloon cross-sectional area (Bcsa) were measured simultaneously. The elastic wall parameters were calculated from these measurements. At sacrifice, tissue samples were collected for analysis of collagen content of the ureteral wall. A non-linear clockwise relation (hysteresis loops) between Bcsa and balloon pressure was demonstrated. At maximal inflation of the balloon, the Bcsa, wall tension, and compliance were 35.28 +/- 3.52, 38.44 +/- 3.23, and 61.36 +/- 8.09 mm2, 230.71 +/- 12.82, 242.38 +/- 10.49, and 302.17 +/- 20.03 cmH2O x m, and 0.167 +/- 0.047, 0.124 +/- 0.002, and 0.182 +/- 0.040 mm2 x cmH2O-1 in the intramural part of the ureter, middle part, and ureteropelvine junction, respectively. The collagen content was 0.3249 +/- 0.0077, 0.3301 +/- 0.0066, and 0.3457 +/- 0.0060 mg x mg-1 dry defatted weight in the intramural part, in the middle, and in the ureteropelvine junction, respectively. The collagen content of the ureteropelvine junction was significantly higher than that of the middle of ureter (P < 0.02) and than that of the intramural part (P < 0.05). No significant correlations were found between the elastic parameters at maximal inflation of the balloon and the collagen content (P < 0.10). In conclusion the elastic wall properties were significantly different in the three ureteral segments and the collagen content of the ureteropelvine junction differed from that of the two distal locations. However, no relationship between the wall properties and the collagen content was found.

Animals↗

PubMed1994

The effects of dihydralazine, labetalol and magnesium sulphate on the isolated, perfused human placental cotyledon.

OBJECTIVE: To assess the effects of dihydralazine, labetalol and magnesium sulphate on the vascular tone in the isolated, perfused human placental cotyledon. METHODS: In vitro perfusion of the fetal compartment of isolated, human placental cotyledons. RESULTS: None of the drugs affected basal vascular tone. The thromboxane A2-mimic U46619 and endothelin-1 induced a concentration-dependent increment in perfusion pressure, while 5-hydroxytryptamine induced a variable increase, and norepinephrine induced a small, transient increase in perfusion pressure. After preconstriction with U46619, magnesium sulphate (1.5 x 10(-3) to 6 x 10(-3) mol/l) induced a decrease in perfusion pressure, while dihydralazine (10(-6) to 10(-4) mol/l) or labetalol (10(-7) to 10(-4) mol/l) enhanced the perfusion pressure. These effects of dihydralazine and labetalol were unaffected by treatment with indomethacin 10(-6) mol/l, but could be reversed by addition of magnesium sulphate 6 x 10(-3) mol/l. Labetalol 10(-6) to 10(-4) mol/l also caused an increase in the perfusion pressure induced by endothelin-1, but showed no effects after preconstriction with 5-hydroxytryptamine. Pretreatment with labetalol 10(-4) mol/l inhibited the transient increase in perfusion pressure induced by norepinephrine 3 x 10(-5) mol/l. CONCLUSIONS: The present data demonstrated that the commonly used vasodilating agents labetalol and dihydralazine do not produce vasodilatation in the human perfused cotyledon after vasoconstriction induced by agents of suggested importance for maintenance of fetal placental vascular tone, and that high concentrations of these drugs may even enhance vasoconstriction induced by thromboxane and endothelin-1 in this area. Magnesium sulphate may show the potential to reverse such unwanted effects of dihydralazine and labetalol.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1994

Biomechanical properties of the oesophagus damaged by endoscopic sclerotherapy. An impedance planimetric study in minipigs.

BACKGROUND: The aims of the present study were to evaluate, by means of impedance plainmetry, regional differences in biomechanical properties in the normal oesophagus and the oesophagus damaged by sclerotherapy. METHODS: Four minipigs underwent a weekly session of sclerotherapy for 4 weeks. Impedance planimetry was performed before the first session of sclerotherapy and 1 week after the last session of sclerotherapy. Investigations were performed by stepwise pressure-induced balloon distensions with concomitant measurements of pressure and luminal cross-sectional area (CSA) in the oesophagus 5 and 10 cm above the gastro-oesophageal junction (GEJ). RESULTS: The normal oesophagus had significantly larger CSAs 5 cm than 10 cm above the GEJ (P < 0.05). Endoscopic sclerotherapy entailed an inversion (P < 0.05) of the normal oesophageal configuration, with narrowing 5 cm above the GEJ (P < 0.05) and increased CSAs 10 cm above the GEJ (P < 0.05). CONCLUSIONS: Regional differences in CSA occur in the normal oesophagus, and sclerotherapy produces profound changes in the oesophageal configuration.

Animals↗

PubMed1993

[Experimental gastrointestinal motility].

Gastrointestinal motility is a major field of research today; however, despite there being a huge amount of available data in the literature, its exact role as a diagnostic tool has yet to be defined. The purpose of this paper is to describe some of the existing experimental models and methods for conducting motility studies.

Animals↗