Search PubMed⌕ Search

Biomedical subjects

L M Akkermans

Publications and source records attributed to L M Akkermans.

144 records · Page 8Linked to original sources
PubMed1983

Electrode-oxygen consumption and its effects on tissue-oxygen tension. A study by mass spectrometry.

A theory for the mechanism of electrical bone stimulation proposes that passage of an electric current reduces the local PO2 and raises the pH near the cathode, thereby creating a favorable environment for osteogenesis. To study the effects of electric current passage on the PO2, PCO2 and pH in the vicinity of the electrodes in vivo, a wire electrode spiralled around the catheter of a clinical mass spectrometer was placed in dog muscle. Electrodes were made of stainless steel or platinum. With a cathode located in the tissue, a 20-microA direct constant current caused a drop in PO2 of 5-10 mmHg and a drop in PCO2 of 2-6 mmHg, both reaching plateaus again within five to 20 minutes. The time required to reach this new equilibrium was shorter for platinum than for stainless steel. When the electric current was turned off, PO2 and PCO2 reversed to their original values. Because of the high buffer capacity of tissue, it is highly unlikely that 20-microA current would induce a change in pH.

Animals↗
PubMed1979

Lower esophageal sphincter function after highly selective vagotomy.

We evaluate whether highly selective vagotomy (HSV) might disturb functional integrity of the lower esophageal sphincter (LES). Special interest was directed to changes in position of the LES in relation to the diaphragm, LES pressure, and pH reflux pattern. The conditions of 20 patients were evaluated by manometric studies and by 12-hour overnight pH measurements before and 14 days after HSV; five of them were also studied one year after HSV. The results indicate: (1) There is a slight elongation of the LES in the early postoperative phase, which seems to disappear after one year. (2) The position of the diaphragm as measured manometrically by the pressure inversion point descends in relation to the LES 14 days after HSV, and it does not seem to return to its original position after one year. (3) There is no significant change in LES pressure after HSV. (4) There is no increase in reflux after HSV.

Adult↗
PubMed1975

Effects of aldrin-transdiol on neuromuscular facilitation and depression.

The effects of aldrin-transdiol, one of the active metabolites of the insecticide dieldrin, on evoked transmitter release, neuromuscular facilitation and neuromuscular depression have been studied in frog sartorius nerve-muscle preparations. Conventional techniques of intracellular recordings were used. Aldrin-transdiol caused a marked increase in end-plate potential amplitude under conditions of low quantal content, i.e., in Mg2+-blocked junctions. The increase in end-plate potential amplitude was less pronounced in curarized junctions, in which the transmitter release was not impaired. Concomitant with the increase in end-plate potential size there was a marked enhancement of facilitation during short trains of stimuli applied to the motor nerve. The decay of facilitation was, however, not seriously affected by aldrin-transdiol. These effects may be explained in terms of the known 'calcium hypothesis' by assuring that aldrin-transdiol increases the amount of calcium which enters the nerve terminal during the nerve impulse. The increase in end-plate potential amplitude and in facilitation by aldrin-transdiol was transient. At later stages of poisoning, end-plate potential and facilitation decreased below control level and neuromuscular depression was significantly enhanced. This latter effect may be the result of a direct inhibitory effect of aldrin-transdiol on transmitter mobilization. As far as the fall in end-plate potential amplitude is concerned the known suppressive action of aldrin-transdiol on the chemical sensitivity of the postsynaptic membrane and on the nerve action potential probably plays a part as well. Finally, neuromuscular transmission was completely blocked by aldrin-transdiol.

Aldrin↗
PubMed1975

Excitatory and depressant effects of dieldrin and aldrin-transdiol in the spinal cord of the toad (Xenopus laevis).

An investigation was made into the action of the insecticide dieldrin and one of its metabolites, aldrin-transdio, on the isolated spinal cord of the toad, Xenopus laevis. Conventional electrophysiological techniques were used for stimulating and recording of dorsal and ventral spinal roots. An augmentation of polysynaptic reflex activity along with a marked reduction of orthodromic postsynaptic inhibition could be demonstrated in preparations isolated from dieldrin-poisoned animals. However, application of dieldrin to the isolated spinal cord failed to produce any significant effect. Application of aldrin-transdiol, on the other hand, caused a potentiation of spinal reflex activity and an increase in spontaneous activity of ventral and dorsal roots. Aldrin-transdiol also produced a marked reduction of spinal inhibitory mechanisms. The excitatory effects of aldrin-transdiol were followed by a strong depressant action on spinal excitability.

Aldrin↗
PubMedDate not supplied

Psychoneurogastroenterology: interrelations in stress-induced colonic motility and behavior.

Individual differences in behavioral and physiological response patterns to stress may contribute to vulnerability for stress-related illnesses such as functional gastrointestinal disorders. Animal models could give clues about specific individual determinants of intestinal reactivity to stress and stress-induced sensitization. Rats fitted with permanent electrodes on the proximal colon were exposed to a single session of foot shocks (10 x 6 s in 15 min, preshocked) or no shocks (control). Two weeks later, the preshocked group showed a significantly greater colonic spike burst response to a novel shock-prod stressor in the home cage than controls. The increase in burst frequency was positively correlated with the duration of active burying of the threatening prod in both experimental groups, but not with other behavioral components. Basal colonic burst frequency at rest was negatively correlated with the increase in burst frequency due to shock-prod stress in both groups, but the degree of sensitization in preshocked rats vs. controls was of similar magnitude in rats with low and high basal colonic burst frequency. The results indicate that colonic responsivity to stress is related to both basal motility status and individual coping strategies.

Animals↗
PubMedDate not supplied

Myo-electrical and motor activity of the stomach in the first days after abdominal surgery: evaluation by electrogastrography and impedance gastrography.

The electrical and motor activities of the stomach were studied in the early postoperative phase after abdominal surgery by means of surface recording techniques: electrogastrography (EGG) and impedance gastrography (IGG). EGG and IGG recordings were made pre-operatively and on the first and second postoperative days. Physical signs and symptoms related to gastrointestinal motility were assessed. Two patient groups were studied; a group of patients undergoing cholecystectomy (n = 9) was compared with a group with major colonic surgery (n = 14). After colonic surgery, resumption of a normal oral diet was later and nausea and vomiting were seen more frequently than after cholecystectomy. Other physical signs concerning intestinal motility did not differ between the groups. Gastric myo-electrical activity (0.04-0.06 Hz), recorded electrogastrographically, tended to decrease in the postoperative phase in both groups, and return to pre-operative values later in the colonic surgery group. However, none of the differences reached statistical significance. Abnormal gastric activity (tachyarrhythmia) was observed in one pre-operative patient but in 6 patients (2 cholecystectomy, 4 colonic surgery) after operation. IGG variables were not significantly affected by the operation and were not significantly different between the groups. No correlation between the symptoms nausea and vomiting in the postoperative phase and the incidence of tachyarrhythmias could be demonstrated in this study. It is concluded that antral myo-electrical and motor activity, measured with non-invasive techniques (EGG and IGG), are not grossly abnormal on the first and second postoperative day after abdominal surgery. It is further concluded that abnormal gastric frequencies do not appear to play a major role in the genesis of postoperative nausea and vomiting.

Cholecystectomy↗
PubMedDate not supplied

Gastric compliance, sensation, and the relaxation response to a nitric oxide donor in health and reflux oesophagitis.

BACKGROUND/AIMS: The gastric fundus affects afferent control of lower oesophageal sphincter function. Nitric oxide is an important relaxant of the fundus. We postulated that gastric distensibility, compliance and nitric oxide sensitivity may be altered in patients with gastro-oesophageal reflux disease (GERD). METHODS: 9 patients with erosive oesophagitis (6 males; median age 55 years) and 16 healthy controls (9 males; median age 36 years) were studied fasting with a gastric barostat. Minimal distending pressure (MDP) and gastric compliance (Deltav/Deltap) were determined by increasing intrabag pressure in 2-mm Hg increments. The pressures required to produce initial sensation and maximum tolerated sensation were recorded. With the intrabag pressure set at MDP +2 mm Hg, 500 microg sublingual glyceryl trinitrate was administered and the percentage change in intrabag volume from initial volume recorded. RESULTS: The MDP was significantly greater in patients than controls (7.5 vs. 6.7 mm Hg median; p = 0.02). Gastric compliance was similar in both groups (57.8 vs. 67.2 ml/mm Hg; p = 0.4). There was no difference between groups in the pressure at first intragastric sensation (11.2 vs. 10.3 mm Hg above MDP; p = 0.5) or in the maximal tolerated pressure (15.8 vs. 14.3 mm Hg above MDP; p = 0.2). The proportional change in gastric volume from baseline in response to glyceryl trinitrate was smaller in patients than controls (66 (3-200) vs. 120 (26-1,053)%; p = 0.02). CONCLUSIONS: Gastric MDP may be altered in GERD, but gastric compliance and sensitivity to distension are normal. Major gastric relaxation occurs in response to a nitric oxide donor, but this appears to be diminished in patients with GERD. Upper gut nitrinergic mechanisms may be altered in oesophageal reflux disease.

Administration, Sublingual↗
PubMedDate not supplied

Bioresorption of ceramic strontium-85-labeled calcium phosphate implants in dog femora. A pilot study to quantitate bioresorption of ceramic implants of hydroxyapatite and tricalcium orthophosphate in vivo.

Ceramic hydroxyapatite and tricalcium orthophosphate were radioactively labeled with their strontium-85 analogs. Porous blocks of these materials (dimensions 2.5 X 1.25 X 0.5 cm) were implanted into surgically created defects in dog femora. The fate of the implants was studied by roentgenography, radioactivity measurements, histology, and microradiography. The radioactivity over the implant site was followed for 22 weeks. Implants were retrieved after 20-25 and 50-55 weeks. Hydroxyapatite implants were not affected by biodegradation processes, while tricalcium orthophosphate implants were subject to extensive bioresorption (25%-30% in 22 weeks). Resorption debris from tricalcium orthophosphate implants was found in mononuclear phagocytes and multinuclear osteoclastlike cells. The supposition is that tricalcium orthophosphate is transformed into hydroxyapatite in a physiologic environment. Labeling of ceramic calcium phosphate implants with strontium-85 analogs offers an adequate technique to quantitate bioresorption in vivo.

Animals↗
PubMedDate not supplied

Long-term study of large ceramic implants (porous hydroxyapatite) in dog femora.

Blocks of porous ceramic hydroxyapatite (dimensions, 2.5 X 1.25 X 0.5 cm; sintering temperature, 1300 degrees; macroporosity, 56%; average pore size 0.18 mm2) were implanted into surgically created defects in dog femora. The implants were retrieved up to 3.5 years after implantation. The implants were 3.5 years after implantation. The implants were firmly attached to the bone. Histologic evaluation suggests that optimal contact between bone and implant should be provided to accelerate bone ingrowth. Bone growth in the pores reached a maximum level after 35 weeks, at which time about one-third of the pore space was filled with bone. When measuring the relative surface areas of bone and ceramic on histologic slides, no change in ceramic mass could be detected, indicating that hydroxyapatite ceramics are not affected by biodegradation processes. The implants effectively provided a scaffold for bone growth bridging a larger bone defect.

Animals↗
PubMedDate not supplied

Interactions of serotonin with multiple receptors and neurotransmitters in the guinea-pig isolated colon.

The motor effects of 5-hydroxytryptamine (5-HT; serotonin) on the guinea-pig isolated proximal colon were studied and analyzed. A classical organ bath setup was used to measure the longitudinal muscle responses isotonically. 5-Hydroxytryptamine induced concentration-dependent contractions which were preceded by relaxations at low concentrations. By means of the neurotoxin, tetrodotoxin, the muscarinic cholinoceptor antagonist, atropine, and selective 5-HT receptor antagonists, it was shown that the contractions to 5-HT are mediated by 5-HT2A receptors, localized on the smooth muscle, and by 5-HT3 and 5-HT4 receptors, localized on cholinergic nerves. The relaxation was abolished by tetrodotoxin and appeared to be mediated by two 5-HT receptor subtypes; the pharmacological profile of the high affinity 5-HT receptor resembled that of 5-HT2C receptors though it displayed also pronounced differences. Subsequently, it was shown that nitric oxide is the mediator released by lower concentrations of 5-HT, while, at higher concentrations, adenosine triphosphate could be involved as an end neurotransmitter as well. No evidence for a peptidergic neurotransmitter, such as vasoactive intestinal polypeptide, was obtained. Results with two 5-HT analogues confirmed the presence of a dual 5-HT receptor system (high and low affinity) regulating each the release of a different neurotransmitter (nitric oxide and adenosine triphosphate, respectively). The above described results stress the important role of 5-HT as a neurotransmitter involved in gastrointestinal motility.

Animals↗
PubMedDate not supplied

[Effect of increasing protein ingestion on the nitrogen balance of mechanically ventilated critically ill patients receiving total parenteral nutrition].

The amount of protein recommended to minimise N loss in critically ill patients receiving total parenteral nutrition (TPN) varies in the literature. Therefore, we studied the effect of increased protein intake on the N balance, administering TPN with either 1.2 g protein/kg/day (low N diet) or 1.8 g protein/kg/day (high N diet). Fifteen mechanically ventilated critically ill patients were studied in a surgical intensive care unit. After at least two days of standard TPN, patients were randomly assigned to either the low or the high N diet. Ten patients were studied on the low N diet and 11 on the high N diet; 6 patients were studied on both diets. Nonprotein energy was supplied according to estimated energy requirements. For five consecutive days, the N balance was measured daily. Total urinary nitrogen (TUN) was analysed using the Kjeldahl method. There was no difference in N balance between the groups. On the low N diet, N balance was -0.113 +/- 0.088 and on the high N diet -0.113 +/- 0.109 g N/kg/day. In patients studied twice, N balance was -0.087 +/- 0.054 and -0.050 +/- 0.060 g N/kd/day respectively. Results of a previous pilot study showed that in 20 similar patients the N balance became 80% less negative (from -5.7 +/- 5.1 to -1.1 +/- 8.2 g N/day) when protein intake was increased from 0.9 to 1.5 g/kg/day. Since these results are consistent with other studies, we conclude that the optimal range of protein supply in this type of critically ill patients is approximately 1.1-1.5 g protein/kg/day.

Adolescent↗
PubMedDate not supplied

Effect of bile salts on in vitro gallbladder motility: preliminary study.

Impaired postprandial gallbladder emptying may be an important factor in cholesterol crystals precipitation and subsequent gallstone formation. We previously found strongly increased bile salt concentrations in gallbladder bile of gallstone patients with weak (< 50% fasting volume) postprandial gallbladder contraction compared to patients with strong (> 50%) postprandial contraction. Therefore, we studied potential effects of various conjugated and unconjugated bile salts with different relative hydrophobicity on in vitro contractility of gallbladder muscle strips obtained at cholecystectomy. Strips were incubated 5 min with bile salt at concentrations of 10(-8)-10(-4)M. The effect of 10(-3)M acetylcholine was measured and related to preincubation control value. Bile salts used were, in order of increasing hydrophobicity: tauroursodeoxy-, ursodeoxy-, tauro-, taurodeoxy- and deoxycholate. Ursodeoxy- and tauroursodeoxycholate did not significantly reduce gallbladder contractility. Taurocholate significantly reduced contractility at concentrations of 10(-6) M and higher, taurodeoxycholate at 10(-7) M and higher and deoxycholate at 10(-5) M and higher. Contractility induced by acetylcholine 10(-3) M at a bile salt concentration of 10(-4) M was 66.0 +/- 11.7% (taurocholate), 50.2 +/- 6.2% (deoxycholate) and 44.8 +/- 11.5% (taurodeoxycholate) of control. The effect of bile salts correlated with their relative hydrophobicity (r = -0.97; p < 0.01). Suppressing effects on gallbladder muscle strip contractility were long lasting and remained after rinsing. Results show that bile salts in the physiological dose range inhibit in vitro gallbladder contraction. If this mechanism exists in vivo, it may have important implications for gallbladder motility regulation.

Acetylcholine↗