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Biomedical subjects

Hans Gregersen

Publications and source records attributed to Hans Gregersen.

At least 37 records · Page 2Linked to original sources
PubMed2006

In vitro strain measurement in the porcine antrum using ultrasound doppler strain rate imaging.

Strain rate imaging (SRI) enables study of deformation in soft tissues. The aim of this study was to evaluate the accuracy of SRI in measuring strain in the porcine antral wall in vitro. An experimental set-up enabled controlled distension of a porcine stomach in a saline reservoir. Radial strain obtained by SRI was compared with radial strain calculated from B-mode ultrasonography. Circumferential strain obtained by SRI was compared with circumferential strain calculated from sonomicrometry. The agreement between radial strain values measured by SRI and B-mode, along and across several ultrasound (US) beams, using US frequency 6.7 MHz and strain length (SL) = 1.9 mm was = -1.0 +/- 12.1% and 0.5 +/- 13.4%, respectively (mean difference +/- 2SD%) and it was better than with SL 1.2 mm. Compared with sonomicrometry, SRI-determined circumferential strain using 6.7 MHz and SL = 1.9 mm was less accurate, whether averaging along or across several US beams (-9.2 +/- 46.7% and 13.8 +/- 51.2%, respectively). In conclusion, SRI gave accurate measurement of radial strain of the antral wall, but seemed to be less accurate for measurement of circumferential strain for this in vitro set-up.

Animals↗
PubMed2006

Central sensitization in patients with non-cardiac chest pain: a clinical experimental study.

OBJECTIVE: Patients with non-cardiac chest pain (NNCP) suffer from unexplained and often intractable pain which can pose a major clinical problem. The aim of this study was to investigate nociceptive processing in NNCP patients and their response to experimentally acid-induced oesophageal hyperalgesia using a multimodal stimulation protocol. MATERIAL AND METHODS: Ten highly selected patients with NCCP (mean age 43 years, 1 M) were compared with an age- and gender-matched group of 20 healthy subjects. After preconditioning, the distal oesophagus was painfully distended with a balloon using "impedance planimetry". This method assesses the luminal cross-sectional area of the oesophagus based on the electrical impedance of the fluid inside the balloon. The baseline distensions were done before and after pharmacological relaxation of the smooth muscle with 20 mg butylscopolamine. After baseline distensions, a series of up to 10 mechanical stimuli was performed (temporal summation). The stimulations were repeated after sensitization of the oesophagus induced by acid perfusion. The sensory intensities were assessed during the stimulations and the referred pain area was mapped. RESULTS: At baseline distensions, no differences were seen between patients and controls before and after relaxation of the smooth muscles. The patients tolerated fewer repeated distensions than controls (4.8+/-0.5 versus 9.1+/-0.9; p=0.04) and had an increased size of the referred pain areas to the mechanical stimulations (32.9+/-6.2 versus 64.9+/-18.3 cm2; p=0.01). After sensitization with acid, the patients developed hyperalgesia (p<0.001), whereas no significant changes were seen in controls. CONCLUSIONS: NCCP patients showed facilitated central pain mechanisms (temporal summation and visceral hyperalgesia after sensitization). This could be used in the diagnosis and understanding of the symptoms in these patients.

Acids↗
PubMed2006

Pain and mechanical properties of the rectum in patients with active ulcerative colitis.

BACKGROUND: The pain, urgency, and incontinence in ulcerative colitis may be related to changes in viscoelastic properties of the gut wall or to alterations of the sensory pathways. In the present study, we used an advanced rectal probe to study the mechanosensory and smooth muscle properties in patients with active disease. METHODS: Nine patients with ulcerative colitis (mean age 39.5 years) with exacerbation limited to the rectum and sigmoid colon and 17 age-matched healthy subjects were included. The rectum was distended before and after pharmacological relaxation of the smooth muscle until moderate pain was reported, and the cross-sectional area, volume, pressure, tension, and strain were computed. To investigate central integration of a tonic stimulus, the bag was finally distended to the pain threshold; then, the cross-sectional area was held constant for 2 min. RESULTS: The patients were hypersensitive to mechanical stimuli as assessed by the cross-sectional area (F = 21.7; P < 0.001). There were no differences in compliance or stiffness between the 2 groups, but the hypersensitivity was abolished after muscle relaxation. Together with the muscle analysis, this finding demonstrated that the smooth muscles were tonically contracted in the inflamed rectum, resulting in a decreased rectal circumference. The tonic distensions did not evoke central integration of the pain response, indicating that hyperalgesia is more likely related to peripheral factors. CONCLUSIONS: Patients with active ulcerative colitis have hypersensitivity and increased tone of the smooth muscles, which may explain the symptoms. Drugs that affect smooth muscle contraction may be helpful in difficult cases.

Adult↗
PubMed2006

The Giome project.

Explore the source record for details and available documents.

Databases, Factual↗
PubMed2006

Balloon-distension studies in the gastrointestinal tract: current role.

Balloon distension is a commonly used technique in visceral organs. Research studies take advantage of this technique for studying organ physiology, e.g. for studying the force-deformation relationship and mechanosensitive receptors in the gastrointestinal wall. Balloon distension is also used for diagnostic purposes, e.g. in the diagnostics of non-cardiac chest pain and for treatment of diseases such as bleeding esophageal varices caused by liver disease and lower esophageal sphincter occlusion caused by achalasia. Balloon distension can be carried out with concomitant measurements of pressure, volume and cross-sectional area alone or in combination. Furthermore, balloon-distension techniques can be combined with various imaging techniques such as B-mode ultrasonography and MRI to obtain three-dimensional geometric data about the three-dimensional surface with subsequent calculation of the tension or stress in the gastrointestinal organs. This article describes balloon-distension techniques, in particular new developments of the impedance planimetric technique including methods for studying gastrointestinal muscle function.

Catheterization↗
PubMed2005

An experimental study of viscero-visceral hyperalgesia using an ultrasound-based multimodal sensory testing approach.

Widespread visceral hypersensitivity and the overlap of symptom complexes observed in functional gastrointestinal disorders may be related to central sensitization and neuroplastic changes. A multimodal and multi-segmental model was developed to evaluate viscero-visceral hyperalgesia induced by experimental esophageal sensitization in healthy volunteers. Twelve healthy subjects were studied using a double-blinded, placebo-controlled design. The sensitivity to mechanical and heat stimulations was assessed in the proximal esophagus, duodenum and rectum before and after perfusion of the distal esophagus with acid or saline. A special-designed probe was used allowing cross-sectional ultrasound imaging during mechanical and heat stimulation of the esophagus and duodenum. Another probe was used for mechanical stimulation of the rectum. The referred somatic pain areas to gut pain stimulations were also assessed. Following acid perfusion 11 of 12 volunteers showed increased sensitivity to one or more stimulation modalities. An overall increased sensitivity to mechanical stretch in the three gut segments was seen (P=0.0001). Posthoc analysis showed that this was mainly due to increased sensitivity in the rectum (P<0.001). No changes were seen to thermal stimulations (all P-values>0.4). The somatic referred pain area to duodenal stimulations increased (P=0.04), while it was unaffected to esophageal and rectal stimulations (P>0.3). The present method demonstrated a new approach to assess multimodal sensitivity to experimental sensitization of the esophagus and related viscero-visceral hyperalgesia. Central mechanisms can explain the remote hyperalgesia to mechanical visceral stimulation and the increase in referred pain areas. The present method may be used to explore pathophysiology and pharmacological interventions in patients with visceral hypersensitivity.

Abdominal Pain↗
PubMed2005

Time-dependent viscoelastic properties along rat small intestine.

AIM: To measure the time-dependent (viscoelastic) behavior in the change of the small intestinal opening angle and to test how well the behavior could be described by the Kelvin model for a standard linear solid. METHODS: Segments from the duodenum, jejunum, and ileum were harvested from 10 female Wistar rats and the luminal diameter, wall thickness, and opening angle over time (theta(t)) were measured from rings cut from these segments. RESULTS: Morphometric variations were found along the small intestine with an increase in luminal area and a decrease in wall thickness from the duodenum to the ileum. The opening angle obtained after 60 min was highest in the duodenum (220.8+/-12.9 degrees) and decreased along the length of the intestine to 143.9+/-8.9 degrees in the jejunum and 151.4+/-9.4 degrees in the ileum. The change of opening angle as a function of time, fitted well to the Kelvin model using the equation theta(t)/theta(o) = [-eta exp (-lambda t)] after the ring was cut. The computed creep rate lambda did not differ between the segments. Compared to constant calculated from pig aorta and coronary artery, it showed that alpha agreed well (within 5%), eta was three times larger than that for vascular tissue, and lambda ranged +/-40% from the value of the pig coronary artery and was a third of the value of pig aorta. CONCLUSION: The change of opening angle over time for all the small intestine segments fits well to the standard linear spring-dashpot model. This viscoelastic constant of the rat small intestine is fairly homogenous along its length. The data obtained from this study add to a base set of biomechanical data on the small intestine and provide a reference state for comparison to other tissues, diseased intestinal tissue or intestinal tissue exposed to drugs or chemicals.

Animals↗
PubMed2005

Sensory-motor responses to mechanical stimulation of the esophagus after sensitization with acid.

AIM: Sensitization most likely plays an important role in chronic pain disorders, and such sensitization can be mimicked by experimental acid perfusion of the esophagus. The current study systematically investigated the sensory and motor responses of the esophagus to controlled mechanical stimuli before and after sensitization. METHODS: Thirty healthy subjects were included. Distension of the distal esophagus with a balloon was performed before and after perfusion with 0.1 mol/L hydrochloric acid for 30 min. An impedance planimetry system was used to measure cross-sectional area, volume, pressure, and tension during the distensions. A new model allowed evaluation of the phasic contractions by the tension during contractions as a function of the initial muscle length before the contraction (comparable to the Frank-Starling law for the heart). Length-tension diagrams were used to evaluate the muscle tone before and after relaxation of the smooth muscle with butylscopolamine. RESULTS: The sensitization resulted in allodynia and hyperalgesia to the distension volumes, and the degree of sensitization was related to the infused volume of acid. Furthermore, a nearly 50% increase in the evoked referred pain was seen after sensitization. The mechanical analysis demonstrated hyper-reactivity of the esophagus following acid perfusion, with an increased number and force of the phasic contractions, but the muscle tone did not change. CONCLUSION: Acid perfusion of the esophagus sensitizes the sensory pathways and facilitates secondary contractions. The new model can be used to study abnormal sensory-motor mechanisms in visceral organs.

Adult↗
PubMed2005

Three-dimensional geometry analysis of the stomach in type II diabetic GK rats.

AIMS/HYPOTHESIS: The stomach is affected in more than half of all diabetic patients. The present study aims to investigate 3D geometry, 3D tension distribution and the elasticity in the stomach and its non-glandular and glandular regions in five non-diabetic and five Goto-Kakizaki (GK) rats (type 2 diabetic model). METHODS: The stomachs were distended in vitro using a pressure range from 0 to 8 cm H2O. Gastric compliance curves, the surface principal radii of curvature, the surface tension, and circumferential and longitudinal deformation-pressure curves were calculated based on 3D non-diabetic and the diabetic stomach models. RESULTS: Diabetes lowered the gastric compliance in the non-glandular stomach and the whole stomach (P<0.02). The radii of curvature and tension distribution were non-homogeneous in both the diabetic and the non-diabetic stomach due to the complex geometry. Furthermore, diabetes increased the circumferential stiffness in the non-glandular part (P<0.001). CONCLUSIONS: The diabetic stomach exhibited lower material compliance not only in the proximal stomach but also in the entire stomach. The biomechanical properties differed between regions and in different directions in both the non-diabetic and the diabetic stomach. The changes due to diabetes may contribute to the delayed gastric emptying and the symptoms in diabetic patients.

Animals↗
PubMed2005

Novel method for measurement of medium size arterial lumen area with an impedance catheter: in vivo validation.

There is no doubt that the transformation of a cardiac catheter into a conductance catheter that allows reliable and accurate assessment of lumen cross-sectional area (CSA) will provide a powerful diagnostic and treatment tool for the invasive cardiologist. The objective of this study was to develop a method based on the impedance catheter that allows accurate and reproducible measurements of CSA for medium size vessels (e.g., coronary, femoral, and carotid arteries). Two solutions of NaCl (0.5% and 1.5%) with known conductivities were injected directly into the lumen of the artery in eight swine. We showed that the CSA can be determined analytically from two Ohm's law-type algebraic equations that account for the parallel conductance of the current into the surrounding tissue. Excellent agreement was found between the conductance catheter with the proposed two-injection method and B-mode ultrasound (US). The root mean square error for the impedance measurements was 4.8% of the mean US diameter. The repeatability of the technique was assessed with duplicate measurements. The mean of the difference between the two measurements was nearly zero, and the repeatability coefficient was within 2.4% of the mean of the two measurements. The validated method was used to assess the degree of acute vasodilatation of the vessel in response to flow overload.

Animals↗
PubMed2005

Regional surface geometry of the rat stomach based on three-dimensional curvature analysis.

A better understanding of gastric accommodation and gastric perception requires knowledge of regional gastric geometry and local gastric tension throughout the stomach. An analytic method based on medical imaging data was developed in this study to describe the three-dimensional (3D) rat stomach geometry and tension distribution. The surface principal radii of curvatures were simulated and the surface tension was calculated in the glandular and non-glandular region of the stomach at pressures from 0 Pa to 800 Pa. The radii of curvature and tension distribution in the stomach were non-homogeneous. The radii of curvature in the glandular stomach were larger than those in the non-glandular region at pressures less than 100 Pa (P < 0.001). When the pressure increased to more than 200 Pa, the radii of curvature in the non-glandular stomach was larger than in the glandular stomach (P < 0.05). The curvature and tension distribution mapping using medical imaging technology and 3D models can be used to characterize and distinguish the physical behaviour in separate regions of the stomach.

Anatomy, Cross-Sectional↗
PubMed2005

The effect of digestion of collagen and elastin on histomorphometry and the zero-stress state in rat esophagus.

To understand the physiology and pathology of the esophagus, it is necessary to know the mechanical properties and their dependence on the structural components. The aim of this study was to investigate the effect of collagenase and elastase on the morphological and biomechanical properties in the no-load and zero-stress states in the rat esophagus. Twenty tissue rings from each esophagus of seven normal rats were sectioned in an organ bath containing calcium-free Krebs solution with dextran and EGTA. After the rings were photographed in the no-load state, 8 of the 20 rings were separated into mucosa-submucosa and muscle rings and the rings were transferred to four different solutions containing collagenase, elastase, or corresponding control solutions. The rings were cut radially to obtain the zero-stress state and photographed again. The thickness, area, and opening angle were measured from the digitized images. The collagen and elastin area fractions were determined from histological slides with Van Gieson and Weigert's elastic stain. The opening angles and residual strain did not differ in the nonseparated enzyme-treated rings and control rings. However, in the separated mucosa-submucosa ring the opening angle was significantly smaller after treatment than that in control rings (P < 0.01). Collagenase and elastase reduced collagen and elastin in the mucosa-submucosa layer about 40% in the nonseparated wall and 54% in the separated mucosa-submucosa layer (P < 0.01). Collagenase and elastase increased the thickness in the separated mucosa-submucosa layer compared to the control (P < 0.05). Disconnection between the epithelia and the lamina propria was histologically observed after elastase digestion. In conclusion, collagenase and elastase caused the opening angle and the residual strain in the separated mucosa-submucosa layer to decrease. The opening angle of the separated mucosa-submucosa layer depended to some extent on the fraction of collagen and elastin.

Animals↗
PubMed2005

Gender differences in pain and biomechanical responses after acid sensitization of the human esophagus.

Our aims were to investigate gender differences to multimodal stimulations of the esophagus after experimentally induced sensitization. Thirty healthy age-matched subjects, 13 males and 17 females, were included. Pain evoked by mechanical and thermal stimuli was assessed before and after perfusion of the lower esophagus with 0.1 N hydrochloric acid. Males were more sensitive to the baseline mechanical stimuli (P < 0.01) and tolerated a lower volume of acid (P = 0.04). After acid perfusion, males were more sensitive than females to distensions (cross-sectional area P = 0.001 and volume P = 0.001). Acid perfusion sensitized both males (P = 0.03) and females (P = 0.04) to heat stimulation but not to cold stimulation (males, P = 0.09; females, P = 0.8). The referral areas for pain evoked by mechanical and thermal stimuli were larger in females compared with males both before and after acid perfusion (P = 0.002). In females only the referred pain area increased to heat stimulations (P = 0.02). Acid infusion resulted in a more hyperreactive esophagus (P = 0.03) but the hyperreactivity was not gender-dependent. In conclusion, males were more sensitive to mechanical and chemical esophageal stimuli and showed acid-evoked mechanical hyperalgesia. Females had significantly larger referred pain areas to the stimulations. The differentiated response to peripheral and central pain mechanisms may explain the gender-related differences seen in several gastrointestinal disorders.

Adult↗
PubMed2005

Small intestinal morphometric and biomechanical changes during physiological growth in rats.

Changes in small intestinal geometry, residual strain and stress-strain properties during physiological growth were studied in rats ranging from 1 to 32 weeks of age. Small intestinal mass and dimensions increased many-fold with age, e.g. the weight per unit length increased five-fold with age and the wall cross-sectional area increased four-fold. The opening angle of duodenum obtained at zero-stress state was approximately 220 degrees and 290 degrees during the first and second week after birth and decreased to 170 degrees at other ages (p < 0.005). The opening angle of ileum ranged between 120 degrees and 150 degrees . The residual strain of duodenum at the mucosal surface did not vary with age (p > 0.05) whereas the residual strain of ileum at the mucosal surface decreased with age (p < 0.001). The circumferential and longitudinal stress-strain curves fitted well to a mono-exponential function. At a given circumferential stress, the corresponding strain values increased during the first 8 weeks of age (p < 0.05) where after no further change was observed. Hence, the small intestine became more compliant during early life. At a given longitudinal stress, the corresponding strains of ileum and duodenum became larger during the first 2-4 weeks of age (p < 0.05) where after no further change was observed. The small intestine was stiffer in longitudinal direction compared to the circumferential direction. In conclusion, pronounced morphometric and biomechanical changes were observed in the rat small intestine during physiological growth. Such data may prove useful in the understanding of the functional changes of the digestive tract during early life.

Age Factors↗
PubMed2005

Statistical modeling of the response characteristics of mechanosensitive stimuli in the human esophagus.

UNLABELLED: It is believed that mechanical stimuli of the human gut activate afferents responding to either noxious or normal, physiologic stimuli. They might be able to sensitize without relation to the contractile state of the smooth muscle. The current study aimed to verify the above characteristics by using a statistical model based on correlation analysis. The esophagus was distended with a bag in 32 healthy subjects by using an inflation rate of 25 mL/min. The luminal cross-sectional areas and sensory ratings were determined during the distentions. The stimuli were repeated after relaxation of the smooth muscle with butylscopolamine and after sensitization with hydrochloride acid. A positive correlation between the sensory responses to distention was found in the non-painful and painful ranges, respectively, but correlations between non-painful and painful ratings were nonsignificant. Relaxation of the smooth muscle did not influence the correlations, and sensitization resulted in inter-individual differences and disappearance of the above clustering into painful and non-painful correlations. In conclusion, afferent nerves encoding high-threshold and low-threshold mechanical stimuli of the human esophagus are not correlated and thus probably represent different populations. The response characteristics have no physiologic relationship to the contractile state of the smooth muscle, and sensitization affects all types of afferents. PERSPECTIVES: The article adds information about sensory processing of mechanical gut stimuli in human beings. This might increase our understanding of visceral pain in health and disease and guide the statistical analysis of experimental data obtained in the gastrointestinal tract.

Action Potentials↗