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F Christ

Publications and source records attributed to F Christ.

At least 37 records · Page 2Linked to original sources
PubMed1999

Microvascular fluid filtration capacity (Kf) assessed with cumulative small venous pressure steps and with various degrees of tilt.

UNLABELLED: Orthostatic dysregulation is a frequent phenomenon in pilots experiencing extreme G forces and after prolonged exposures to microgravity in cosmonauts. We used non-invasive venous congestion plethysmography (VCP) to study microcirculatory changes and the ability to activate peripheral and centrally mediated protective mechanisms during various degrees of tilt, which we used as an orthostatic challenge. METHOD: The study, which was approved by the local ethical committee of the Institute of Biomedical Problems, was performed on six healthy 20 - 26 years old male volunteers. We applied 6 - 8 cumulative small venous congestion pressure steps (8 mmHg) to the thigh and determined the fluid filtration capacity (Kf), the linear relationship between cuff pressure (Pcuff) and measured fluid filtration (Jv). We then measured the fluid filtration (Jv) response to varying cumulative degrees of tilt, starting at 0 degrees followed by head down -8 degrees -15 degrees, -30 degrees -15 degrees, -8 degrees, 0 degrees, and then head up 15 degrees, 30 degrees, 70 degrees, 30 degrees, 15 degrees and 0 degrees. Each tilt stage was sustained for 15 minutes. The change in hydrostatic load, at the level of the strain gauge, was determined by measuring the difference in vertical height between the right atrium and mid calf at the level of the gauge. Limb arterial blood flow was measured and lung function tests were performed before and after the small cumulative pressure step protocol, as well as at the end of each tilt step. RESULTS: No significant changes in blood pressure (BP) and heart rate (HR) occurred during the cumulative pressure step protocol. However, an increase in HR was observed during the tilt, but only reached significance at 30 degrees and 70 degrees. The mean Kf value measured with small cumulative pressure steps was 3.25 +/- 0.5 (10(-3) ml.100 ml tissue(-1) mmHg(-1) = KfU), which was significantly (p < 0.005) higher than the value obtained using tilt to increase the hydrostatic load (0.98 +/- 0.2 KfU). One subject had an unchanged Kf value and experienced vaso - vagal syncope following the imposition of 70 degrees tilt, with a heart rate < 35 / min and a systolic blood pressure of 60 mmHg. The measurement of blood flow in the limb showed no significant change during the tilt procedure. The lung function measurements revealed, that only expiratory reserve volume (ERV) did significantly increase during 35 degrees and 70 degrees head up tilt. All other parameters were unchanged. We suggest that the differences in these Kf values can be explained by the activation of both central and peripheral mediated changes in pre- capillary resistance in response to the tilt. We suspect, that the vaso - vagal syncope, experienced by one subject, reflected his inability to activate these protective reflex mechanisms, a situation that could be exacerbated by sub-clinical venous insufficiency. We believe that these results show that VCP is a useful tool for the determination of intolerance to orthostatic stress.

Adult↗
PubMed1999

On the substrate specificity of DNA methyltransferases. adenine-N6 DNA methyltransferases also modify cytosine residues at position N4.

Methylation of DNA is important in many organisms and essential in mammals. Nucleobases can be methylated at the adenine-N6, cytosine-N4, or cytosine-C5 atoms by specific DNA methyltransferases. We show here that the M.EcoRV, M.EcoRI, and Escherichia coli dam methyltransferases as well as the N- and C-terminal domains of the M. FokI enzyme, which were formerly all classified as adenine-N6 DNA methyltransferases, also methylate cytosine residues at position N4. Kinetic analyses demonstrate that the rate of methylation of cytosine residues by M.EcoRV and the M.FokI enzymes is reduced by only 1-2 orders of magnitude in relation to methylation of adenines. This result shows that although these enzymes methylate DNA in a sequence specific manner, they have a low substrate specificity with respect to the target base. This unexpected finding has implications on the mechanism of adenine-N6 DNA methyltransferases. Sequence comparisons suggest that adenine-N6 and cytosine-N4 methyltransferases have changed their reaction specificity at least twice during evolution, a model that becomes much more likely given the partial functional overlap of both enzyme types. In contrast, methylation of adenine residues by the cytosine-N4 methyltransferase M.BamHI was not detectable. On the basis of our results, we suggest that adenine-N6 and cytosine-N4 methyltransferases should be grouped into one enzyme family.

Adenine↗
PubMed1999

Photocross-linking of the homing endonuclease PI-SceI to its recognition sequence.

PI-SceI is an intein-encoded protein that belongs to the LAGLIDADG family of homing endonucleases. According to the crystal structure and mutational studies, this endonuclease consists of two domains, one responsible for protein splicing, the other for DNA cleavage, and both presumably for DNA binding. To define the DNA binding site of PI-SceI, photocross-linking was used to identify amino acid residues in contact with DNA. Sixty-three double-stranded oligodeoxynucleotides comprising the minimal recognition sequence and containing single 5-iodopyrimidine substitutions in almost all positions of the recognition sequence were synthesized and irradiated in the presence of PI-SceI with a helium/cadmium laser (325 nm). The best cross-linking yield (approximately 30%) was obtained with an oligodeoxynucleotide with a 5-iododeoxyuridine at position +9 in the bottom strand. The subsequent analysis showed that cross-linking had occurred with amino acid His-333, 6 amino acids after the second LAGLIDADG motif. With the H333A variant of PI-SceI or in the presence of excess unmodified oligodeoxynucleotide, no cross-linking was observed, indicating the specificity of the cross-linking reaction. Chemical modification of His residues in PI-SceI by diethylpyrocarbonate leads to a substantial reduction in the binding and cleavage activity of PI-SceI. This inactivation can be suppressed by substrate binding. This result further supports the finding that at least one His residue is in close contact to the DNA. Based on these and published results, conclusions are drawn regarding the DNA binding site of PI-SceI.

Base Sequence↗
PubMed1999

[Preoperative changes in fluid filtration capacity in patients undergoing vascular surgery].

UNLABELLED: Patients undergoing major vascular surgery frequently require a substantial intraoperative fluid replacement to assure hemodynamic stability, which is in excess of the expected fluid requirements due to starving, blood and insensible losses. This leads to a positive fluid balance which can not be readily explained. METHOD: We have used venous congestion plethysmography (VCP) a non-invasive method for measurement of microvascular parameters in limbs to investigate the changes in microvascular permeability (FFK) and the balance of Starling forces of patients undergoing surgery for unilateral femoral artery reconstruction (FEM) under epidural anaesthesia or abdominal aortic aneurysm repair (AAA) under general anaesthesia. The control group consisted of patients scheduled for inguinal hernia repair or hand surgery under general anaesthesia. All patients were measured 24 hours pre-operatively, immediately after the induction of anaesthesia or completion of epidural anaesthesia and on the 1st, 5th and 10th postoperative day. The perioperative patient management followed a standard protocol and all patients with vascular disease were invasively monitored using indwelling arterial lines and central venous catheters. Continuous infusion of Ringers lactate and 6% Dextran 60 was sustained during the induction period. Each patient gave informed consent. RESULTS: Preoperatively we found no significant difference in the mean FFK-values of controls (4.1 +/- 0.4, ml.min-1 100 ml tissue-1 mmHg-1 x 10(-3) = FFKU), the AAA (3.6 +/- 0.3 FFKU) and FEM (4.2 +/- 0.3 FFKU). After induction of anaesthesia the mean FFK value in the controls fell to 3.5 +/- 0.5 FFKU (p = 0.07), whereas in the AAA patients we observed a significant increase to 4.7 +/- 0.2 FFKU (p < 0.005) and after epidural anaesthesia in FEM to 5.5 +/- 0.4 FFKU (p < 0.001) respectively. Those post anaesthetic FFK values where significantly higher in FEM and AAA than in the controls (p < 0.02). In AAA we found a significant positive correlation between the increase in FFK and the intraoperative fluid balance (r2 = 0.69, p < 0.01). No such correlation was found in controls and FEM. The postoperative values of FFK where unchanged in the control group, whereas a further increase was seen in both patient groups with vascular disease, with a maximum in AAA on the 1st postoperative day (to 5.4 +/- 0.4 FFKU mean both legs) and the 5th postoperative day in FEM (to 7.3 +/- 1.7 non-ischemic leg, 7.1 +/- 1.2 ischemic leg FFKU). In both groups normal FFK values where found on the 10th day after the operation. CONCLUSION: The data presented suggests an increase in extravascular fluid loss in patients undergoing vascular surgery, which becomes evident after the induction of general anaesthesia or completion of epidural anaesthesia. The positive correlation with the intraoperative fluid requirements may partially explain the often reported large intraoperative fluid requirements of patients undergoing AAA repair. The fact that the maximum change in fluid filtration capacity is found postoperatively may be explained by the additional effect of an ischemia/reperfusion injury in response to both the clamping an declamping of the artery and the increase in arterial blood flow to the limb due to the successful reconstruction of the blood vessel.

Adult↗
PubMed1999

[Localized Castleman disease. Diagnostic difficulties in a surgically treatable disease].

Castleman's disease is a rare cause for a retroperitoneal mass. The disorder can be classified into two histopathological groups: the hyalin-vascular and plasma-cell types. The former type, particularly in its localized form, is often asymptomatic and benign, the surgical therapy may cure the patient. The latter type is frequently associated with systemic manifestations and an uncertain prognosis. We present a case in which the diagnosis of localized Castleman's disease proved to be extremely difficult. In these cases, the correct diagnosis, however, is indispensable, as these patients can be cured by radical surgical tumor excision.

Adult↗
PubMed1998

Attenuation of the near-infrared and red photoplethysmographic signal by different depth of tissues.

Photoplethysmography enables non-invasive investigation of the volume pulse in the microvasculature of patients. We previously have shown that time-discrete analysis enables identification of highly reproducible characteristics of the volume pulse in absolute values. The method would be of particular interest, if the perfusion of deeper tissue layers like the skeletal muscle can be assessed. The aim of the current study was to investigate the attenuation of the photoplethysmographic signal by different tissues and up to which depth of tissue a time-discrete analysis of the photoplethysmographic signal would be possible. For the recordings we used the time-discrete near-infra-red photoplethysmography (NIRP), a reflection photoplethysmograph measuring at wavelengths of 840 nm and 640 nm. In an in vitro circuit filled with bovine blood we generated a typical and exactly reproducible volume pulse. On a platform the NIRP sensor probe was placed above the artificial vessel and recordings of the volume pulse were obtained by varying the sensor-vessel-distance with increasing layers of water, blood-agar or bovine skeletal muscle tissue. - The amplitude of the NIR signal was attenuated to 50% by each layer of 2.01 mm of water, 1.42 mm of blood-agar and 1.05 mm of bovine skeletal muscle tissue. A time-discrete analysis could be performed up to a depth of 15 mm of water, 6 mm of blood-agar and 5 mm of bovine skeletal muscle tissue. - As the photoplethysmographic curve is strongly attenuated even by a few millimetres of water we suggest that the NIRP signal mirrors the perfusion of the superficial tissue layer and mainly originates from the subpapillary capacious plexus. - We conclude that with the equipment used in this study volume pulsations in deeper layers of tissue like skeletal musculature can not be assessed.

Agar↗
PubMed1998

Changes in the arteriolar volume pulse of the finger during various degrees of tilt using near infra-red and red photoplethysmography.

1. Photoplethysmography is a widely used non invasive technique for the measurement of peripheral oxygen saturation. A more detailed analysis of the volume pulse (VP) can indicate alterations in peripheral vascular tone, due to sympathetic stimulation, stress, pain and temperature. - 2. In six healthy male volunteers we investigated changes in the VP resulting from vasoconstriction and vasodilatation induced by varies degrees of tilt. Subjects were subjected 0 degrees tilt followed by head down -8 degrees -15 degrees, -30 degrees -15 degrees, -8 degrees, 0 degrees, 15 degrees, 30 degrees , 70 degrees, 30 degrees, 15 degrees and 0 degrees. Each tilt stage was sustained for 15 minutes. Both VP - and haemodynamic changes were continuously recorded 30s before and then for 210 s after the imposition of each tilt step. We used a new computer driven soft and hardware for the analysis of the VP. 3. The VP signal was obtained with a sensor emitting 840 nm (NIR) and 640 nm (RED) light into finger tip with a sample rate of 128 Hz. All data was normalised to the initial mean value obtained at 0 degrees tilt. The signal strength parameters amplitude, and area under the curve and the first derivative of the amplitude (flux) as well as time discrete parameters, time of first maximum (Tmax), dicrote wave (Td), volume pulse decrease (Tdec) and fundamental arterial oscillation Tag = Td - Tmax were measured. 4. HR increased significantly during 30 degrees and 70 degrees tilt, but no change in the other hemodynamic parameters was observed. Amplitude, area under the curve and flux of both the Red and the NIR signal increased following head down tilt. A significant decrease of those parameters was found during foot down tilt. 5. No significant changes were found in the time discrete values, neither within each tilt step nor when compared to the initial mean value at 0 degrees tilt. 6. This study reveals that signal strength related parameters such as area under the curve, amplitude and flux reflect changes in vascular tone. Time discrete parameters however did not depict these changes and appear unsuitable for data analysis when using this specific hardware applied in the current study.

Adult↗
PubMed1998

Human calf precapillary resistance decreases in response to small cumulative increases in venous congestion pressure.

1. We studied human lower limbs to test the hypothesis that the application of small cumulative venous congestion pressure steps is associated with a reduction in precapillary resistance. 2. Strain gauge plethysmography was performed on twenty-one young subjects (22.7 +/- 0.6 years). At each of the small cumulative pressure steps, limb blood flow was estimated from the initial slope of the volume response to transient (10 s duration) elevations of venous congestion pressure to 90 mmHg, after which the congestion pressure was returned to the previous value. The blood flow at each pressure was also expressed as a percentage of the initial control value. Peak tibial arterial blood flux was assessed, in four of the subjects, using colour duplex ultrasonography and the same congestion pressure protocol. 3. We used Darcy's Law to predict the limb arterial blood flow and blood flux at each venous congestion pressure, assuming that both mean arterial blood pressure and precapillary resistance remained constant. 4. The mean +/- S.E.M. control arterial blood flow at the lowest venous congestion pressure, 4.8 +/- 0.1 mmHg, was 2.77 +/- 0.18 ml min-1 (100 ml)-1. At the highest venous congestion pressure, 59.2 +/- 0.2 mmHg, arterial blood flow was 2.45 +/- 0.35 ml min-1 (100 ml)-1 (121.6 +/- 16.9% of the initial value). This did not differ significantly from the initial control value, but was significantly greater than the predicted value of 0.77 +/- 0.13 ml min-1 (100 ml)-1 (28.6 +/- 2.1% of the initial value) calculated assuming constant resistance and sustained mean arterial pressure. The tibial arterial peak blood flux at 58.3 mmHg venous congestion pressure was 102.2 +/- 2.3% of the control value, which was significantly greater than the predicted 17.2 +/- 1.3% of control, calculated for this pressure, assuming constant resistance and sustained mean arterial pressure. 5. Our data show that lower limb arterial blood flow is sustained when venous congestion pressure is raised using small cumulative steps, even at congestion pressures approaching mean arterial blood pressure. These data support the notion that precapillary resistance is influenced by signals generated at the microvascular and post microvascular levels and transmitted via the endothelium.

Adult↗
PubMed1998

[Changes in fluid filtration capacity and blood flow after tourniquet in knee operations with spinal anesthesia].

UNLABELLED: An increased microvascular water permeability has been reported after ischemia/reperfusion both in animal models and in human studies. We studied the changes in fluid filtration capacity (FFK) after ischemia/reperfusion due to tourniquet in patients undergoing arthroscopy of the knee. METHOD: Healthy male volunteers (n = 24, mean age 46.9 +/- 3.5) were studied prior to, 1 and 6 hours after arthroscopy of the knee, during which a tourniquet was applied to the thigh. FFK, isovolumetric venous pressure (Pvi) and arterial blood flow in the limb was measured in both legs (tourniquet leg and control leg) using computer assisted venous congestion plethysmography. Venous blood samples were obtained from a cubital vein prior to and from the femoral vein 2 mins after deflation of the tourniquet cuff. 12 patients received preoperatively an infusion of 6% Dextran (D) and 12 patients 500 ml of electrolyte solution (VE) an. RESULTS: The mean duration of the tourniquet was (D) 56.0 +/- 6.9 min and (VE) 53.9 +/- 4.2 min which resulted in a significant increase in venous lactate concentration from (D) 1.4 +/- 0.1 mmol.l-1 to 2.7 +/- 0.3 mmol.l-1 and (VE) 1.3 +/- 0.1 mmol.l-1 to 2.7 +/- 0.3 mmol.l-1 (p < 0.001). A significant decrease in pH from (D) 7.39 +/- 0.01 to 7.32 +/- 0.01 (p < 0.001) and from (VE) 7.39 +/- 0.01 to 7.32 +/- 0.01 (p < 0.001) was also seen. Preoperatively no significant differences in the FFK values of the tourniquet leg (D = 5.3 (4.8-10.7) ml. x 10(-3) min-1.100 ml tissue-1 mmHg-1 = FFKU) and the control leg (5.2 (4.7-8.6 FFKU)) were observed. The maximum FFK value in D was seen 1 hour after ischemia/reperfusion in both, the tourniquet leg (7.5 (4.6-14.2 FFKU) and the control leg (7.8 (5.5-9.4 FFKU). In VE however the maximal FFK value were measured 6 hours after ischemia/reperfusion with an increase in the tourniquet leg from 5.2 (4.2-6.2 FFKU) to 8.1 (3.7-10.4 FFKU) and the control leg from 6.1 (3.6-7.0 FFKU) to 7.3 (6.1-8.3 FFKU) (Median (Range). One-way ANOVA). There were no significant differences in the FFK values between D and VE except for a lower Pvi in VE at the third measurement. No significant changes in the arterial blood flow were seen perioperatively as well as between the operated and non-operated leg. CONCLUSION: A tourniquet of < 1 hour does impair tissue oxygenation as indicated by the increase in lactate and the decrease in pH. The duration of the tourniquet was however to short to have caused sufficient microvascular damage result in a more pronounced increase in fluid filtration capacity.

Anesthesia, Spinal↗
PubMed1998

[Significance of CT in the detection of regional lymph node metastases in colorectal carcinoma].

PURPOSE: For preoperative staging of colorectal cancer a CT scan is frequently performed. This report examines the sensitivity of CT for regional lymph node metastasis of colorectal cancer using different criteria. MATERIALS AND METHODS: Preoperative CT scans of 153 patients with colorectal cancer were analyzed using different criteria for N1. The results were then compared to the postoperative histological findings. RESULTS: For N1 = lymph nodes (LN) > 1 cm the sensitivity was 47%. For N1 = LN > 1 cm or an increased number of LN < 1 cm the sensitivity was 71%. In patients with a primary tumor seen on CT, sensitivity rose to 87%. DISCUSSION: Evidence of regional nodal metastatic disease is only relevant for rectal cancer, colon polyps, and for locally excised tumors when considering present surgical concepts for the treatment of colorectal cancer. In these cases CT analysis using the broadened criteria for N1 proposes a valuable argument regarding possible preoperative radiotherapy or an operative revision.

Aged↗
PubMed1998

Increased microvascular water permeability in patients with septic shock, assessed with venous congestion plethysmography (VCP).

OBJECTIVES: To investigate microvascular water permeability (filtration capacity, Kf) in patients with septic and non-septic shock using a new non-invasive method for studying microvascular parameters in man. SETTING: Intensive Care Unit of a university hospital. PATIENTS AND METHODS: We investigated 28 patients, presenting with cardio-vascular instability due to either septic shock, or non-septic shock (haemorrhage, multiple trauma, respiratory and/or cardiac failure). INTERVENTIONS: We used standard invasive methods of monitoring (in-dwelling arterial lines and pulmonary artery flotation catheters) in combination with computer assisted venous congestion plethysmography (VCP) measurements, for a parallel assessment of peripheral microcirculatory parameters. RESULTS: On admission to the ICU, patients with septic shock revealed a significantly higher mean value of filtration capacity Kf = 6.1 +/- 0.4 x 10(-3) (mean value +/- standard error of the mean, ml.min-1.100 ml tissue-1.mmHg-1 = KfU) than non-septic patients Kf = 3.5 +/- 0.3 KfU (p < 0.02). The Kf values of the septic patients were significantly higher than those from age-matched patients with peripheral vascular disease (4.1 +/- 0.2 KfU, p < 0.001) and those of healthy controls (4.3 +/- 0.2 KfU, p < 0.001); the Kf values of the non-septic patients, however, were not significantly different. The highest mean Kf value observed during the stay on ICU was Kfmax 11.6 +/- 0.2 KfU in the septic group and 5.7 +/- 0.1 KfU in the non-septic group (p < 0.001). Pvi, a value reflecting the balance of hydrostatic and oncotic forces in the microcirculation, was elevated in both patient groups. On admission, in septic patients Pvi was 39.2 +/- 3.3 mmHg and in non-septic patients 35.1 +/- 2.7 mmHg, these values were not significantly different, but significantly higher than the Pvi value of healthy controls (Pvi 21.5 +/- 0.8) (p < 0.001). A weak, however significant, positive correlation was found between Kf and Pvi in both patient groups. No correlations were found between Kf, as well as Pvi, and cardiac index (CI), oxygen delivery index (DO2I), oxygen consumption index (VO2I) and systemic vascular resistance index (SVRI). CONCLUSIONS: An increase in permeability of microvessels will cause a loss of intravascular fluid and may therefore partially explain the large fluid requirements of patients in shock. It will also favour the development of oedema, which is often found in septic patients. We propose that changes in Kf are useful indices of microvascular malfunction and that VCP allows the non-invasive assessment of these parameters.

Adult↗
PubMed1997

Relationship between venous pressure and tissue volume during venous congestion plethysmography in man.

1. Venous congestion strain-gauge plethysmography enables the non-invasive assessment of arterial blood flow, fluid filtration capacity (Kf), venous pressure (Pv) and isovolumetric venous pressure (Pvi) in man. One of the major assumptions of this technique, that cuff pressure (Pcuff) applied to the limb equals Pv at the level of the strain gauge, was tested in this study. 2. In nine healthy male volunteers (mean age, 29.3 +/- 1.2 years) the saphenous vein was cannulated with an 18-gauge catheter proximal to the medial malleolus. The subjects were supine and Pv was continuously measured during the application of small step (8-10 mmHg) increases in congestion Pcuff (up to 70 mmHg). Pcuff, changes in limb circumference and Pv were recorded by computer for off-line analysis. Since the determination of Kf is influenced by the changes in plasma oncotic pressure, venous blood samples were obtained at the start of the study, when Pcuff was raised to 30 mmHg and again to 65 mmHg and 4 min after deflation of the cuff. 3. The relationship between Pv and Pcuff was linear over the range of 10-70 mmHg (n = 9, 69 measurements, slope 0.91, r = 0.97, P << 0.001). The non-invasively measured calf Pv, based on the intercept of the relationship between the vascular compliance component (Va) and Pcuff, was 8.0 +/- 0.4 mmHg, which was not significantly different from the corrected invasively measured Pv value of 8.8 +/- 0.3 mmHg (P = 0.08). 4. Venous blood lactate and haemoglobin concentrations, as well as colloid osmotic pressure, total protein and albumin concentrations were unchanged throughout the protocol, whereas significant decreases in PO2 and blood glucose concentration were observed when Pcuff reached 65 mmHg. Assuming a constant oxygen consumption, this may suggest a reduction in tissue perfusion. 5. This study demonstrates the close correlation between Pcuff and Pv in the saphenous vein. Since the small congestion Pcuff step protocol does not cause significant increase in plasma oncotic pressure, we conclude that Pv, as well as Kf, can be accurately determined with this venous congestion plethysmography protocol.

Adult↗
PubMed1997

The growth-associated protein GAP-43 is specifically expressed in tyrosine hydroxylase-positive cells of the rat retina.

In the adult retina, the growth-associated protein GAP-43 is exclusively present in three distinct sublaminae of the inner plexiform layer. During postnatal development, it is transiently expressed in the optic nerve fibers. No conclusions about the GAP-43 expressing cells can be derived from immunohistochemical stainings because GAP-43 protein is rapidly transported into the distal neuronal processes. We have combined immunohistochemistry to study the protein expression of GAP-43 and non-radioactive in situ hybridization to study the cellular expression of GAP-43 in the rat retina. We have found that in the mature retina GAP-43 mRNA is present only in retinal ganglion cells and in a small subset of cells of the inner nuclear layer. During postnatal development, no cells besides retinal ganglion cells and a subpopulation of cells in the inner nuclear layer express GAP-43 mRNA. Double staining experiments with tyrosine hydroxylase (TH) immunohistochemistry and GAP-43 in situ hybridization showed that GAP-43 expressing cells in the inner nuclear layer are immunoreactive for TH. They are most probably dopaminergic amacrine cells. Our results show that GAP-43 expression in the retina is restricted to very few cell types. They suggest that TH-positive cells (probably dopaminergic amacrine cells) retain a higher degree of structural plasticity in the adult retina.

Animals↗
PubMed1997

The effect of passive tilting on microvascular parameters in the human calf: a strain gauge plethysmography study.

1. Cumulative small steps in venous congestion pressure were used to study the effect of passive tilt on vascular parameters in dependent tissues. Using this protocol we have non-invasively assessed venous pressure (Pv,est), isovolumetric cuff pressure (Pv,i), which is the congestion cuff pressure (Pcuff) that has to be exceeded to induce fluid filtration. We have also assessed microvascular filtration capacity (Kf), which is the linear relationship between filtration rate (Jv) and Pcuff, when Pcuff > Pv,i, and is the product of the available exchange vessel surface area and wall conductance. 2. Subjects were passively tilted to increase the venous pressure at the level of the calf by 47.4 +/- 2.4 mmHg (mean +/- S.E.M.). The value of Pv,i increased from 20.6 +/- 1.8 to 48.5 +/- 3.8 mmHg after the imposition of the tilt. This change may reflect the increased colloid osmotic pressure at the microvascular interface that is known to occur in response to this manoeuvre. 3. The pre-tilt value of Kf did not change after the imposition of the passive tilt, the values being 3.2 +/- 0.4 x 10(-3) and 3.6 +/- 0.4 x 10(-3) ml min-1 (100 ml-1) mmHg-1, respectively, (n = 13). 4. These results support the notion that passive postural change alters the pre-capillary resistance, thereby altering the pressure and flow characteristics within the exchange vessels, but does not alter the surface area available for fluid exchange in the calf, contrary to previous findings in the dependent human foot using a single-step venous occlusion protocol.

Adult↗
PubMed1997

[Small-volume resuscitation for hypovolemic shock. Concept, experimental and clinical results].

The concept of small-volume resuscitation, the rapid infusion of a small volume (4 ml/kg BW) of hyperosmolar 7.2-7.5% saline solution for the initial therapy of severe hypovolemia and shock was advocated more than a decade ago. Numerous publications have established that hyperosmolar saline solution can restore arterial blood pressure, cardiac index and oxygen delivery as well as organ perfusion to pre-shock values. Most prehospital studies failed to yield conclusive results with respect to a reduction in overall mortality. A meta-analysis of preclinical studies from North and South America, however, has indicated an increase in survival rate by 5.1% following small-volume resuscitation when compared to standard of care. Moreover, small-volume resuscitation appears to be of specific impact in patients suffering from head injuries with increased ICP and in severest trauma requiring immediate surgical intervention. Results from clinical trials in Austria, Germany and France have demonstrated positive effects of hyperosmolar saline solutions when used for fluid loading or fluid substitution in cardiac bypass and in aortic aneurysm surgery, respectively. A less positive perioperative fluid balance, a better hemodynamic stability and improved pulmonary function were reported. In septic patients oxygen consumption could significantly be augmented. The most important mechanism of action of small-volume resuscitation is the mobilisation of endogenous fluid primarily from oedematous endothelial cells, by which the rectification of shock-narrowed capillaries and the restoration of nutritional blood, flow is efficiently promoted. Moreover, after ischemia reperfusion a reduction in sticking and rolling leukocytes have been found following hyperosmolar saline infusion. Both may be of paramount importance in the long-term preservation of organ function following hypovolemic shock. An increased myocardial contractility in addition to the fluid loading effects of hyperosmolar saline solutions has been suggested as a mechanism of action. This, however, could not be confirmed by pre-load independent measures of myocardial contractility. Some concerns have been raised regarding the use of hyperosmolar saline solutions in patients with a reduced cardiac reserve. A slower speed of infusion and adequate monitoring is recommended for high risk patients. Recently, hyperosmolar saline solutions in combination with artificial oxygen carriers have been proposed to increase tissue oxygen delivery through enhanced O2 content. This interesting perspective, however, requires further studies to confirm the potential indications for such solutions. Many hyperosmolar saline colloid solutions have been investigated in the past years, from which 7.2-7.5% sodium chloride in combination with either 6-10% dextran 60/70 or 6-10% hydroxyethyl starch 200,000 appear to yield the best benefit-risk ratio. This has led to the registration of the solutions in South America, Austria, The Czech Republic, and is soon awaited for North America.

Dextrans↗
PubMed1997

Hyperosmotic-hyperoncotic solutions during abdominal aortic aneurysm (AAA) resection.

A largely positive perioperative fluid balance during both elective and emergency abdominal aortic aneurysm repair (AAA) may put patients at risk of developing left ventricular failure and may thus contribute to morbidity. In the present paper we report on a prospective study using hyperosmotic-hyperonocotic solutions (HHS) infused during clamping of the aorta, for the prevention of declamping shock, and the associated reduction in perioperative fluid requirements. The major aim of this paper was to determine the efficacy of an HHS infusion when given over 20 minutes and to detect possible adverse effects of HHS. For perioperative fluid replacement 12 patients received crystalloid solutions with HHS [250 ml of 7.2% NaCl combined with either 6% Dextran (n = 3), 6% Hydroxyethylstarch (HES, n = 4) or 10% HES (n = 5)]. In 16 controls, crystalloids with 1000 ml of HES 10% were infused. Patients were invasively monitored and hemodynamic parameters frequently assessed during the operation, which were statistically analyzed in relation to the start of the fluid loading during clamping of the aorta. One patient showed an anaphylactoid reaction to HES, otherwise no side effects of HHS were observed during infusion (no hypotension, no pathological EKG changes). Plasma sodium and chloride concentration as well as osmolality rose resulting in an osmotic gradient and a desired intravascular volume expansion. Prior to declamping pulmonary capillary wedge pressure had increased to the desired value of > 13 mmHg and < 18 mmHg. Oxygen delivery was significantly elevated upon HHS and remained so post declamping, whereas no change was observed in controls. During clamping systemic vascular resistance was significantly decreased, but was unchanged in controls. The perioperative fluid balance of patients receiving HHS was 2471.0 +/- 948.6 ml, which was significantly less than + 3386.7 +/- 1247.9 ml of controls (P < 0.01). We suggest that HHS opens new perspectives in perioperative fluid management of both elective and emergency AAA repair, since hemodynamic parameters are improved and the overall fluid balance is less positive, thus decreasing the likelihood of edema formation. Moreover, the previously described positive microcirculatory effects of HHS may be particular beneficial in some high-risk patients.

Aged↗