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Biomedical subjects

A M Drewes

Publications and source records attributed to A M Drewes.

At least 19 recordsLinked to original sources
PubMed2007

A new method for evaluation of intestinal muscle contraction properties: studies in normal subjects and in patients with systemic sclerosis.

Systemic sclerosis is a connective tissue disease that involves the gastrointestinal (GI) tract. Seventy-five per cent of systemic sclerosis patients experience symptoms arising from oesophagus. The intestine has less frequently been subject for studies than the oesophagus. When the small intestine becomes involved, nausea, vomiting, bloating, diarrhoea and malabsorption may occur. Previous studies have shown decreased and abnormal intestinal motility, dilatation and a stiffer wall. The aim was to study muscle mechanics in systemic sclerosis patients using novel analysis of intestinal muscle contraction force-velocity and power. A volume-controlled duodenal ramp-distension protocol was used in nine patients and eight healthy controls. The wall stretch ratio, tension, shortening velocity and muscle power were computed from pressure and cross-sectional area data recorded by an impedance planimetry system. The tension-stretch ratio relation obtained in patients was shifted to the left, indicating a stiffer wall. The in vivo tension-shortening velocity relationship was quantified using Hill's equation. The maximum preload tension (tension at zero velocity) was lower in the patients than in the healthy controls (P < 0.001). The muscle power was lowest in the patients. An association was found between the duration of the disease and the maximum stretch ratio (P < 0.05). The study represents the first data with application of in vivo muscle force-velocity relations in patients with gastrointestinal diseases. Systemic sclerosis patients had increased stiffness and impaired muscle dynamics of the duodenum. Decreased muscle function and increased wall stiffness may explain the GI symptoms reported in this patient group.

Algorithms↗
PubMed2006

Cortical changes to experimental sensitization of the human esophagus.

Topographical organization in the neocortex shows experience-dependent plasticity. We hypothesized that experimental sensitization of the esophagus results in changes of the topographical distribution of the evoked potentials and the corresponding dipole source activities to painful stimulation. An endoscopic method was used to deliver 35 electrical stimuli at the pain threshold to a fixed area of the mucosa in 10 healthy volunteer men and women. The stimulations were repeated after 30 min (reproducibility experiment), and after 60 min following perfusion of 200 ml 0.1 N hydrochloric acid (sensitization experiment). During stimulation the electroencephalogram was recorded from 64 surface electrodes. The sensitization resulted in a decrease in the pain threshold (F=6.2; P=0.004). The topographic distribution of the evoked potentials showed reproducible negative (N1, N2) and positive (P1, P2) components. After acid perfusion a reduced latency and a change in localization was seen for the P1 subdivided into frontal and occipital components (F=29.5, P<0.001; F=53.7, P<0.001). Furthermore the sensitization resulted in a reduction of the latency for P2 (F=6.2, P=0.009). The source analysis showed consistent dipolar activity in the bilateral opercular-insular cortex before and after acid perfusion. For the anterior cingulate dipole there was a reduction in latency (P=0.03) and a posterior shift (P=0.0002) following acid perfusion. The findings indicate that short-term sensitization of the esophagus results in central neuroplastic changes involving the cingulate gyrus, which also showed pathological activation in functional diseases of the gut, thus reflecting the importance of this region in visceral pain and hyperalgesia.

Adult↗
PubMed2006

Sensation and distribution of stress and deformation in the human oesophagus.

Evaluation of the distribution of stresses and strains in relation to distension-induced sensation in the human oesophagus is valuable for understanding oesophageal biomechanics and mechano-sensation. In 12 healthy volunteers a specially designed oesophageal bag containing an endoscopic ultrasound probe was inflated to the moderate pain level. Ultrasound images, bag pressure and perceived sensation were recorded before and after pharmacological relaxation of the smooth muscle with butylscopolamine. The oesophagus was assumed to be circular and thick-walled. Distension induced a tensile circumferential stretch, radial compression and longitudinal shortening. Both circumferential strain and stress were highest at the mucosal surface and decreased throughout the wall. The stiffness increased throughout the wall and was highest at the outer surface (P < 0.001). The decrease in stiffness in response to butylscopolamine was non-significant. The infused volume (P = 0.012) and circumferential stress (P < 0.001) were most closely associated with the distension-induced sensation (adjusted R2 = 0.88). The perceived sensation was highly individual but was unaffected by butylscopolamine (P > 0.08). The present study provides a method for computation of the stress-strain distribution throughout the wall and the mechano-sensory interaction in the human oesophagus. In the future, this may be useful for understanding of mechanoreceptor responses and generation of symptoms in visceral organs in health and in disease.

Adult↗
PubMed2005

Cerebral processing of painful oesophageal stimulation: a study based on independent component analysis of the EEG.

BACKGROUND AND AIMS: Independent component analysis (ICA) of the electroencephalogram (EEG) overcomes many of the classical problems in EEG analysis. We used ICA to determine the brain responses to painful stimulation of the oesophagus. METHODS: Twelve subjects with a median age of 41 years were included. With a nasal endoscope, two series of 35 electrical stimuli at the pain threshold were given to the distal oesophagus and the EEG was subjected to ICA. The sessions were separated by 30 minutes. For each component head models, event related images, spectral perturbation, coherence analysis, and dipoles were extracted. The most valid components were found according to time/frequency information and reliability in both experiments. RESULTS: Reliable components with the most valid dipoles were found in the thalamus, insula, cingulate gyrus, and sensory cortex. Time locked activities were consistent with upstream activation of these areas, and cross coherence analysis of the sources demonstrated dynamic links in the beta(14-25 Hz) and gamma(25-50 Hz) bands between the suggested networks of neurones. The thalamic components were time and phase locked intermittently, starting around 50 ms. In the cingulate gyrus, the posterior areas were always firstly activated, followed by the middle and anterior regions. Components with dipoles in the sensory cortex were localised in several regions of the somatosensory area. CONCLUSIONS: The method gives new information relating to the localisation and dynamics between neuronal networks in the brain to pain evoked from the human oesophagus, and should be used to increase our understanding of clinical pain.

Adult↗
PubMed2005

Multimodal pain stimulations in patients with grade B oesophagitis.

AIM: To obtain a better understanding of nociceptive processing in patients with oesophagitis. PATIENTS AND METHODS: Eleven patients with grade B oesophagitis were compared with an age and sex matched group of 16 healthy subjects. A probe was positioned in the lower part of the oesophagus. After preconditioning of the tissue, painful mechanical stimuli were applied as distensions with a bag using an impedance planimetric method. Distensions were done before and after pharmacological impairment of distension induced smooth muscle contractions. Thermal stimulation was performed by recirculating water at 1 and 60 degrees C in the bag. The area under the temperature curve (AUC) represented caloric load. The referred pain area (being a proxy for the central pain mechanisms) to the mechanical stimuli was drawn at maximum pain intensities. RESULTS: Patients were hyposensitive to mechanical stimuli, as assessed by the distending volume (F=8.1, p=0.005). After relaxation of smooth muscle with butylscopolamine, the difference between the two groups was more evident (F=27.4, p<0.001). AUC for cold stimulation was 1048.6 (242.7) degrees Cxs in controls and 889.8 (202.6) degrees Cxs in patients (p=0.5). For heat stimuli, AUC values were 323.3 (104.1) and 81.3 (32.3) degrees Cxs in controls and patients, respectively (p=0.04). The referred pain area to the mechanical stimulations was larger and more widespread in patients (49.3 (6.2) cm2 compared with controls 23.9 (7) cm2; p=0.02). CONCLUSIONS: The data indicate that peripheral sensitisation of heat sensitive receptors and pathways combined with facilitation of central pain mechanisms may explain the symptoms in patients with oesophagitis.

Adult↗
PubMed2005

A new technique for evaluating sphincter function in visceral organs: application of the functional lumen imaging probe (FLIP) for the evaluation of the oesophago-gastric junction.

No quantitative method has been implemented routinely in clinical practice to assess the oesophago-gastric junction (OGJ). Using impedance planimetry a functional lumen imaging probe (FLIP) was constructed to measure eight cross-sectional areas (CSA) at 4 mm intervals inside a saline-filled bag. To validate the FLIP technique for profiling the OGJ, polymethylmethacrylate (Perspex) cylinders with different CSAs were measured ten times by the FLIP to assess reproducibility and accuracy. A geometric sphincter phantom was constructed and its geometry was measured with a 360 degrees radial ultrasound (US) mini-probe pulled through it at a rate of 1 mm s(-1). The measurements were compared with FLIP measurements. Safety and technique reproducibility were tested on a volunteer. Reproducibility and accuracy between the ten samples were good. The probe performed well with and without a balloon mounted on it except for the smallest CSA (38.5 mm(2)) where there was a difference of 22% from the actual value at one CSA measurement point. The FLIP imaged the phantom geometry as well as the radial scanning US mini-probe. Pilot studies on a volunteer showed that the probe could be placed in the OGJ and the balloon distensions revealed the geometry of the sphincter at various levels of distension. The technique may be useful in accessing the role of the OGJ in diseases such as gastroesophageal reflux disease (GORD) and achalasia and their treatments with surgical and endoscopic therapies.

Esophageal Sphincter, Lower↗
PubMed2005

Three-dimensional biomechanical properties of the human rectum evaluated with magnetic resonance imaging.

A method to evaluate the three-dimensional (3-D) geometry of the human gastrointestinal wall may be valuable for understanding tissue biomechanics, mechano-sensation and function. In this paper we present a magnetic resonance imaging (MRI) based method to determine rectal geometry and validation of data obtained in three volunteers. A specially designed rectal bag was filled in a stepwise manner while MRI and bag pressure were recorded. 3-D models of curvatures, radii of curvature, tension and stress were generated and the circumferential and longitudinal strains were calculated. The computed bag volumes corresponded to the infused volumes. A pronounced bag elongation and decrease in wall thickness was observed during the bag filling. The spatial distributions of the biomechanical parameters were distinctly different between individuals and non-homogeneous throughout the rectal wall due to its complex geometry. The average tension and stress increased as a function of infused volume and circumferential strain. The present study provides a method for characterizing the complex in vivo 3-D geometry of the human rectum. The non-homogenous spatial curvature distribution suggests that simple estimates of tension based on pressure and volume do not reflect the true 3-D biomechanical properties of the rectum.

Adult↗
PubMed2005

New analysis for the study of the muscle function in the human oesophagus.

The aim was to further develop a method for studying the active and passive tissue properties in the human oesophagus. An impedance planimetric probe with a bag for distension was placed in the distal oesophagus in 14 healthy volunteers. Distension was done at an infusion rate of 25 mL min(-1) with and without the administration of the antimuscarinic drug butylscopolamine. The flow was reversed when moderate pain was experienced by the subject. The total and the passive tension showed an exponential behaviour as function of the change in radius. The active tensions increased until they reached a maximum point. The active tension decreased after the maximum until the distension was stopped shortly after due to the pain. The change in tension during distension-induced contractions (the afterload) was plotted as function of the precontraction radius (the preload). The human oesophagus behaves in a manner known from in vitro studies on muscle strips and exhibits a muscle diagram similar to that in the heart, i.e. the larger the initial muscle length during distension (within limits), the greater the contraction force.

Adult↗
PubMed2004

A comparative study of skills in virtual laparoscopy and endoscopy.

BACKGROUND: The present study was designed to investigate whether there is a correlation between manual skills in laparoscopic procedures and manual skills in flexible endoscopy. METHODS: In a prospective study using laparoscopy and endoscopy simulators (MIST-VR, and GI-Mentor II), 24 consecutive subjects (gastrointestinal surgeons, novice and experienced gastroenterologists, and untrained subjects) were asked to perform laparoscopic and endoscopic tasks. Their performance was assessed by the simulators' software and by observers blinded to the levels of subjects' experience. Performance in experienced vs inexperienced subjects was compared. Score pairs of three parameters--time, errors, and economy of movement--were also compared. RESULTS: Experienced subjects performed significantly better than inexperienced subjects on both tasks in terms of time, errors, and economy of movement (p < 0.05). All three performance parameters in laparoscopy and endoscopy correlated significantly (p < 0.02). CONCLUSION: Both simulators can distinguish between experienced and inexperienced subjects. Observed skills in simulated laparoscopy correlate with skills in simulated flexible endoscopy. This finding may have an impact on the design of training programs involving both procedures.

Clinical Competence↗
PubMed2004

Somatosensory changes in the referred pain area in patients with acute cholecystitis before and after treatment with laparoscopic or open cholecystectomy.

BACKGROUND: Visceral pain can lead to hypersensitivity in the referred pain area. In patients with chronic visceral pain this somatic hypersensitivity can persist for years. As 25%-40% of patients continue to have symptoms after cholecystectomy, whereof no explanation for pain can be offered in up to 30%, it could be hypothesized that altered sensory characteristics induced by acute cholecystitis could persist in some patients and thus be responsible for postcholecystectomy pain. The aim of this study was to investigate the somatosensory sensitivity in the referred pain area in patients with acute cholecystitis before and after cholecystectomy. METHODS: Patients with acute cholecystitis were studied before (n = 30) and after (n = 18) treatment. Sensitivity to pinprick, heat, cold, pressure and single and repeated electrical stimulation was studied in the referred pain area and in the control area on the contralateral side of the abdomen. RESULTS: Significant hypersensitivity in the referred pain area was detected in patients with acute cholecystitis. The somatic sensitivity was normalized after cholecystectomy. CONCLUSIONS: Acute cholecystitis leads to hypersensitivity in the referred pain area. Persistent hypersensitivity, as earlier reported after chronic visceral pain, was not seen aftiser cholecystectomy, indicating that this mechanism may not play a major role in patients with postcholecystectomy pain syndrome. The possible role in patients operated on for chronic gallstone pain has still to be investigated.

Abdominal Pain↗
PubMed2004

A new measurement of oesophago-gastric junction competence.

Knowledge of the competence of the oesophago-gastric junction (OGJ) is fundamental to the understanding of gastro-oesophageal reflux disease (GORD), a disorder with a high incidence among the general population. A catheter with a bag 9.5 cms long mounted towards the distal end was swallowed by three volunteers. Using manometry readings and the point of respiratory inversion as a guide the probe was placed in the OGJ. The bag was distended with saline at a fixed rate volume before and after the administration of butylscopolamine to block cholinergic-mediated contractile smooth muscle activity. Using impedance planimetry three cross-sectional areas (CSA) measurements were made between three pairs of electrodes with 4 mm between each electrode on the catheter placed inside the ballon. Using the law of Laplace, CSA and pressure data could be calculated to give wall tension. Tension rose in all volunteers as the radius increased and it was higher towards the proximal end of the OGJ indicating that this measurement can be used to show the distensibility of the OGJ at different degrees of opening. This technique could be useful in identifying changes in the competence of the lower oesophageal sphincter in some patients with GORD.

Biomechanical Phenomena↗
PubMed2003

A comparison of hyperalgesia and neurogenic inflammation induced by melittin and capsaicin in humans.

Melittin (a main compound of bee venom) and capsaicin were injected intradermally in healthy human volunteers: (1) to study secondary mechanical hyperalgesia (static hyperalgesia and dynamic hyperalgesia) around the injection site; and (2) to correlate the sensory changes to the neurogenic inflammation assessed by laser-doppler blood flowmetry. Melittin 50 microg and capsaicin 10 microg induced comparable spontaneous pain and increased blood flow (neurogenic inflammation). Intradermal injection of melittin induced regions of secondary mechanical hyperalgesia around the injection site, however, they were not as large as the hyperalgesia induced by capsaicin. This is the first report studying mechanical hyperalgesia induced by melittin in humans, and the results were in agreement with the previous observations in rats. Melittin seems to be a valuable model to study a possible contribution of neurogenic inflammation to hyperalgesia in humans.

Analysis of Variance↗
PubMed2003

Spatial and temporal profiles of flare and hyperalgesia after intradermal capsaicin.

Intradermal injection of capsaicin induces a region of visual flare (neurogenic inflammation) and regions with modality specific hyperalgesia. Their temporal and spatial profiles have been studied to elucidate the mechanism behind neurogenic inflammation and hyperalgesia. Until today, the flare response has mainly been quantified by visual inspection. However, recent developments of thermography and laser-Doppler flowmetry have facilitated quantitative measurement of the neurogenic inflammation. The purpose of the present study was (1). to measure the temporal and spatial profiles of neurogenic inflammation and hyperalgesia induced by capsaicin by using thermography/laser-Doppler flowmetry and various sensory tests, and (2). to correlate the parameters related to neurogenic inflammation with the areas of secondary hyperalgesia. Eight healthy volunteers were injected intradermally with 250 microg of capsaicin. Five minutes after the injection, temperature and blood flow were measured by thermography and a laser-Doppler flowmetry, and followed by assessment of visual flare and hyperalgesia. Punctate hyperalgesia, stroking hyperalgesia, and heat hyperalgesia were assessed by von Frey hair, cotton swab, and radiant heat stimulator, respectively. This procedure was repeated 30 and 60 min after the injection. A significant increase in blood flow and temperature was detected by laser-Doppler flowmetry and thermography (F=102.08, P<0.001, and F=8.46, P=0.002, respectively). Throughout the experiment, the areas of visual flare, stroking hyperalgesia, and punctate hyperalgesia were covered by the area of significantly increased blood flow detected 5 min after the injection. The intensity of pain to heat stimuli significantly increased over time at the distal site and the proximal site (P<0.05). However, there was no significant difference between the pain intensity to radiant heat stimuli inside/outside the area of punctate hyperalgesia. These results seem to indicate that a possible contribution of neurogenic inflammation to secondary hyperalgesia (especially to radiant heat stimuli) must be reconsidered.

Capsaicin↗
PubMed2003

Controlled mechanical distension of the human oesophagus: sensory and biomechanical findings.

BACKGROUND: The relation between mechanical distension of the gut and the sensory response is poorly understood. The current experimental study aimed to examine the sensory response in the human oesophagus during on-line recording of the luminal pressure, cross-sectional area (CSA) and sensory rating using different distension rates before and during relaxation of the smooth muscle. METHODS: An impedance planimetric probe for bag distension of the oesophagus was used in 13 healthy subjects aged 43 +/- 15 years. Ramp distensions were done with an electromechanical pump using infusion rates of 10, 25 and 50 ml/min, with and without relaxation of the smooth muscle with butylscopolamine. The sensory intensity was measured using a 0-10 visual analogue scale (VAS), with 5 as the pain threshold. The pump was reversed at 8 on the scale, corresponding to medium pain intensity, and the pressure, volume, tension and CSA were evaluated. Finally, three isovolumetric experiments where the CSA was held constant for 2 min at initial VAS ratings of 3, 5 and 7 were performed. RESULTS: A total of 104 distension profiles were investigated. The volume at maximal pain intensity (VAS = 8) increased as a function of the distension rate (P < 0.001), whereas the pressure, tension and CSA were not affected. When the smooth muscle was relaxed, there was a 29% fall in pressure at maximal pain intensity (P = 0.004), a 27% fall in tension (P = 0.003), whereas CSA did not change (P = 0.3). When the pressure was recorded as a function of the sensory intensity, there was an exponential increase after the pain threshold was reached, whereas the stimulus-response functions for tension, volume and CSA were nearly linear. In the isovolumetric experiments the ratings during the three sensory intensities were the same in the individual subjects, but the between-individual pain response was variable, probably reflecting individual differences in adaptation/central integration. CONCLUSIONS: The study allowed us to assess the strain-rate dependency of both perception and biomechanical properties in the oesophagus. It was demonstrated that the pain response was related to the CSA (and hence strain), independently of the contractile state of the muscle and biomechanical behaviour of the tissue. The findings support the fact that the pain-sensitive mechanoreceptors in the human oesophagus depend on circumferential wall stretch rather than on pressure, tension and volume. The model should be used in future studies to investigate whether changes in strain are responsible for the oesophageal sensation in health and disease.

Adult↗
PubMed2002

Sensory-motor responses to volume-controlled duodenal distension.

Abstract Visceral perception and secondary peristalsis evoked by distension of the duodenum were studied in 10 healthy volunteers. An impedance planimetric probe for cross-sectional area (CSA) measurements inside a balloon and with three pressure channels was used. Balloon distensions were performed in the fed state with or without the administration of the antimuscarinic drug butylscopolamine. A modified questionnaire was used to assess the nonpainful and painful sensations. The total tension (T(total)) and the passive tension (T(passive)) were determined from the distensions without and with the administration of butylscopolamine, respectively. The active tension (T(active)) was T(total) - T(passive). The stepwise balloon distensions induced the first sensation at a volume of 33 +/- 3 mL. After administration of butylscopolamine the first sensation appeared at 42 +/- 1 mL. The perception score (PS) revealed an approximately linear increase as function of volume, CSA, pressure and tension after the first sensation. Butylscopolamine resulted in significant changes in PS score as function of volume, CSA and strain, but not as a function of pressure and tension. The frequency of the secondary peristalsis increased to the highest value (8.2 +/- 0.8 contractions min(-1)) at a volume of 21 mL. Butylscopolamine almost abolished the distension-evoked motility. T(total) and T(passive) increased nonlinearly as a function of volume, whereas T(active) increased up to a distension volume of 33 mL and then decreased at higher volumes. Hence, the conventional length-tension diagrams as known from studies of smooth muscle strips in vitro can be reproduced in the human duodenum in vivo. This new way of studying intestinal sensation and motility may prove to have both basic and clinical importance as both passive tissue structures and the sensorimotor function are tested.

Adult↗
PubMed2001

The relationship between selective sleep deprivation, nocturnal jaw-muscle activity and pain in healthy men.

The relationship between nocturnal jaw-muscle activity and temporomandibular disorders (TMD) is still controversial. The aim of this study was to investigate the effect of selective slow wave sleep (SWS = non-rapid-eye-movement (NREM) stage 3 + 4) deprivation on jaw-muscle activity using a new automatic system. Ten healthy men without signs of symptoms of TMD participated. The subjects slept in the laboratory for six continuous nights including one adjustment night, one baseline night, three nights with experimental sleep deprivation and one recovery night. Polysomnographic recordings of electroencephalography (EEG) and electromyography (EMG) were obtained for recognition of sleep stages and masseter muscle activity. During the three experimental nights, computer-controlled sound stimulation (60--90 dB(A), 1000 Hz) were given as long as the subjects were in SWS. Maximum voluntary occlusal force (MVOF), pain pressure threshold (PPT) and visual analogue scales (VAS) were used to assess the state of the masseter muscles every morning and evening during the study period. The results showed that the time spent in SWS was significantly decreased during the first sleep deprivation night, but there were no significant effects on nocturnal EMG activity (i.e. the numbers of bruxism episodes per hour of sleep, bruxism bursts per episodes bruxism bursts per hour of sleep), MVOF, VAS or PPT. Furthermore, the automatic system only deprived the SWS in five subjects for the following two nights although the sound stimulation was given at the maximum intensity. These results suggest that deprivation of SWS may not interact immediately with nocturnal jaw-muscle activity and jaw-muscle pain.

Adult↗
PubMed2001

Cerebral response to electric stimulation of the colon and abdominal skin in healthy subjects and patients with irritable bowel syndrome.

BACKGROUND: Visceral hyperalgesia may play an important part in the pathophysiology of the irritable bowel syndrome (IBS). We investigated the neuronal afferent pathways in healthy volunteers and IBS patients by recording evoked potentials (EPs) elicited by electrical stimulation of the colon and abdominal skin inside and outside the referred pain area. METHODS: Six healthy subjects and nine IBS patients met the inclusion criteria. Morphology and topography of EPs to painful electrical stimuli were estimated in the rectosigmoid junction and on the skin inside/outside the referred pain areas. RESULTS: The EPs to painful stimuli of the gut showed a shorter latency and a smaller amplitude of the first positive peak (P1) in the IBS group. The controls had a mid-latency frontal positive component after 100 ms, whereas no reliable early activation was seen in the IBS patients. In controls, a single late (>150 ms) positive component was seen, whereas the late component was biphasic in the IBS group. The EPs to painful stimuli of the two skin areas differed in IBS patients, but not in controls. CONCLUSION: Differences in the EPs to electrical painful stimulation of the sigmoid colon and skin inside/outside the experimentally evoked referred pain area were seen comparing healthy subjects and IBS patients. The results indicate altered central nervous system responses.

Abdomen↗