Search PubMed⌕ Search

Biomedical subjects

H van Langen

Publications and source records attributed to H van Langen.

34 records · Page 2Linked to original sources
PubMed1997

Decreased ankle/brachial indices in relation to morbidity and mortality in patients with peripheral arterial disease.

To determine the relationship between ankle/brachial indices (ABIs) and morbidity and mortality in patients with peripheral arterial disease (PAD), a historical cohort study was performed. A total of 154 patients who had undergone noninvasive arterial assessment of the lower extremities in 1989 and 1990 were selected for this purpose. Selection criteria were age > 40 years at the time of investigation, a resting ABI < 0.90 and the availability of an ABI after exercise or arterial occlusion. Mortality and vascular events were recorded after an average follow-up period of 6 years. A vascular event was defined as an intervention because of PAD, the occurrence of a nonfatal myocardial infarction or stroke, a transient ischaemic attack or a coronary artery bypass graft (CABG) or percutaneous transluminal coronary angioplasty (PTCA) procedure. During the period studied, 44 patients died and 111 patients suffered a vascular event. The relative risk for mortality was 3.1 per 0.50 decrease of the ABI at rest (95% confidence interval (CI) 1.1-8.7, p = 0.03) and 2.4 per 0.50 decrease of the ABI after exercise or arterial occlusion (95% CI 0.9-6.4, p = 0.08). The relative risk for mortality or the occurrence of a vascular event was 3.3 per 0.50 decrease of the resting ABI (95% CI 1.7-6.3, p < 0.001) and 2.5 per 0.50 decrease of the ABI after exercise or occlusion (95% CI 1.5-4.4, p < 0.001). After standardization, the prognostic power of the two types of ABIs was equivalent. The cumulative survival after 5 years was 63% for patients with resting ABIs < 0.50, 71% for patients with ABIs 0.50-0.69 and 91% for those with ABIs of 0.70-0.89. There were obvious differences between the mean initial ABIs of patients who suffered a vascular event and/or died and those of survivors, who did not suffer an event. A relatively simple measurement like the determination of the resting ABI can give valuable information about the prognosis for vascular related morbidity and mortality. This can be of help in the approach of patients with PAD and assist in therapeutical decision making. Determination of the ABI after exercise or occlusion has no additional value for this purpose.

Adult↗
PubMed1997

D-dimer determination to assess regression of deep venous thrombosis.

A number of studies evaluating deep venous thrombosis (DVT) have demonstrated that plasma levels of thrombotic and fibrinolytic parameters change during treatment, but the relationship between thrombus regression and evolution of these markers remains unknown. The objective of the present study was to correlate levels of D-Dimer (DD) with thrombus regression as assessed by duplex scanning. From 44 patients treated for acute DVT, DD were determined at diagnosis and at the end of initial heparin therapy of at least 5 days. Thrombus regression was measured by repeated duplex scanning at diagnosis and after 1 and 3 months. DD significantly decreased during heparin treatment as compared with values at presentation. DD levels were significantly higher in the group of patients without normalization of the DVT after 3 months (p = 0.003). A ninefold excess tendency was seen for DD levels > 1200 ng/ml at the end of initial treatment to be associated with poor resolution of the DVT [odds ratio 9.0, 0.95 confidence interval (CI) 2.3-35.4]. When the patients with an established malignancy were excluded, the differences were even more significant (p = 0.0004 for DD levels after initial treatment and an odds ratio of 17.5, 0.95 CI 3.3-92.5). These results suggest that increased DD levels after the initial phase of treatment are related to poor resolution of DVT after 3 months. These findings contribute to further insight into the process of thrombus regression. Furthermore high DD levels might help to identify the patients with a poor prognosis and could be useful to judge the efficacy of anticoagulant treatment.

Adult↗
PubMed1996

[Low stimulation impedance in pacemaker patients with cardiac diseases. The Thera Pacemaker Study Group].

BACKGROUND AND AIM OF THE STUDY: As increasing impedance of the pacing impulse decreases pacing current, high pacing impedance lowers pacing current and subsequently prolongs pacemaker longevity. The present assumption of a standard 500 ohms impedance disregards interindividual differences. In the present study, the interindividual range of pacing impedance was assessed at implantation. Additionally clinical parameters of patients with low pacing impedance were compared to those of patients with high values. PATIENTS AND METHODS: The same lead and the same pacemaker (CapSure VDD; Thera VDD; Medtronic) were implanted in 126 patients (79 men, 47 women, mean age 65 +/- 16 years). Patients with an impedance below or similar to the median were compared to patients with an impedance above the median in respect to clinical (age, gender, arterial hypertension, cardiac diseases such as coronary heart disease, valvular heart disease, cardiomyopathy) and electrical parameters (pacing threshold at 0.5 ms pulse duration, R-wave amplitude). RESULTS: Mean impedance was 687 +/- 121 ohms with a range from 333 to 1040 ohms and a median of 670 ohms. 64 patients had an impedance < or = 670 ohms and 62 patients > 670 ohms. Mean age, gender and the occurrence of arterial hypertension were similar in the two groups. Cardiac diseases occurred significantly (P < 0.01) more often in patients with lower (n = 23) than with higher impedance (n = 9). Intraoperative pacing thresholds and R-wave amplitudes were not different between the two groups. CONCLUSIONS: The range of pacing impedance was 707 ohms for the studied lead. Under consideration of permanent pacing with 2.5 V pulse amplitude and 0.5 ms pulse duration this would vary expected longevity of the implanted pacemaker from 7.8 to 9.3 years. Patients with lower impedance more often had cardiac diseases than patients with higher impedance.

Adult↗
PubMed1996

[Intermittent atrial fibrillation/flutter: contraindication for implantation of a dual chamber pacemaker?].

UNLABELLED: The programming of dualchamber pacemakers to DDD(R) mode is not recommended in patients with paroxysmal atrial fibrillation/flutter, because the pacemaker detects atrial fibrillation/flutter and paces the ventricle up to the pacemaker's upper tracking rate. Some newer pacemakers have the feature to switch automatically from DDD(R) to DDIR mode at the onset of atrial tachyarrhythmias. The aim of the study was to assess how many patients who received such a new DDDR pacemaker with automatic mode switch can be programmed to DDD(R) mode during follow-up. The dual-chamber pacemaker Thera DR (Medtronic) was implanted for clinical evaluation in 142 patients (65 +/- 16 years, male n = 86; female n = 56). Paroxysmal atrial fibrillation/flutter was present in 54 patients, with an additional 2nd or 3rd degree AV-block in 13 and no high-degree AV block in 22 cases; an AV node ablation was performed in 19 patients. Pacemakers were programmed to DDD(R) mode at discharge in 52 of 53, at month 1 in 44 of 46, and at month 3 in 28 of 30 cases. In respect to the programming to DDD(R) mode there were no statistically significant differences to patients without paroxysmal atrial fibrillation/flutter. CONCLUSION: Paroxysmal atrial fibrillation/flutter was present in 38% of the studied patients. During follow up more than 90% of the patients were paced in the DDD(R) mode.

Aged↗
PubMed1996

[Comparison of active and passive fixation of steroid emitting atrial electrodes].

UNLABELLED: Steroid-eluting screw-in leads (CapSure Fix 4068, Medtronic; n = 14) were compared to the same lead as a J-shaped tined electrode (CapSure SP 4524, Medtronic; n = 27, implanted in the atrium in patients receiving dual-chamber pacemakers. Follow-up were at discharge and after 1 month. Implantation (screw-in lead: 84 +/- 18 min; tined lead: 81 +/-29 min) and fluoroscopy times (screw-in lead: 7.3 +/- 4.9 min; tined lead 9.2 +/- 7.0 min) were similar in the two groups. At implant, P-wave amplitudes were similar with 4.8 +/- 1.6 mV (screw-in lead) and 4.0 +/- 2.6 mV (tinted lead), respectively. Compared to tined leads, the screw-in leads had higher pacing thresholds at 0.5 ms pulse duration (screw-in lead: 0.74 +/- 0.32 V; tined lead: 0.55 +/- 0.15 V; p = 0.02) as well as higher impedance (screw-in lead: 566 +/- 93 ohms; tined lead: 470 +/- 99 ohms; p = 0.01). Pulse duration thresholds at 2.5 V pulse amplitude were neither different at discharge (screw-in lead: 0.07 +/- 0.04 ms; tined lead: 0.06 +/- 0.05 ms) nor after 1 month (screw-in lead: 0.09 +/- 0.04 ms; tined lead: 0.06 +/- 0.06 ms). P-wave amplitudes > or = mV were observed at discharge in 14/14 (screw-in lead) 21/27 patients (tined lead), respectively, and after 1 month in 13/14 (screw-in lead) and 22/27 (tined lead) patients, respectively. Impedance of the screw-in lead was significantly higher with 693 +/- 84 ohms at discharge and 691 +/- 79 ohms after 1 month compared to the tined lead with 520 +/- 81 and 574 +/- 62 ohms (p = 0.001). No lead dislodgment was reported during follow-up. CONCLUSIONS: For the studied steroid-eluting leads active and passive fixation had neither at implantation nor during 1-month follow up any influence on P-wave amplitude. At similar pulse duration thresholds, impedance of the screw-in lead was significantly higher than for the tined lead. Higher impedance additionally reduces pacing current, if similar pacing impulses are delivered.

Administration, Topical↗
PubMed1994

Ultrasound determination of the effect of progestogens on the endometrium in postmenopausal women receiving hormone replacement therapy.

Progestogen challenge tests were performed in 81 postmenopausal women receiving hormone replacement therapy (HRT) with progestogen addition as required. The number of tests carried out totalled 159. The effect of progestogen use on endometrial thickness was determined by vaginosonography. The endometrial shedding caused by progestogen was correlated with the withdrawal bleeding pattern. As expected, in the majority of cases (145 out of 159), progestogen brought about endometrial shedding. In most but not all cases, shedding was attended by withdrawal bleeding. The intensity and the duration of withdrawal bleeding were positively correlated with endometrial shedding. No correlation was found between endometrial shedding and the onset of withdrawal bleeding.

Adult↗
PubMed1993

Dynamic response of a neonatal catheter-manometer system in situ.

OBJECTIVE: The purpose of this study was to develop, validate, and apply a flush-pulse method to determine the dynamic response of a neonatal catheter-manometer system (CMS) in situ. METHODS: In the flush-pulse method, the opened fast-flush valve of the CMS is closed; as a result, the fluid column in the CMS is impacted. This procedure can be done without affecting the net flow of infusion fluid. We validated the method in laboratory conditions by comparing 14 paired results obtained with this method to the results obtained using a generally accepted step-response method. The measurable values are the resonance frequency (fr) and the damping coefficient (delta). The analysis of the flush-pulse method in situ is complicated by the patient's blood pressure wave. A remedy for this problem that is based on the first derivative of the pressure signal has been developed. The flush-pulse method is applied 14 times in situ. RESULTS: In laboratory settings, the fr ranged from 12.5 to 64.0 Hz and delta ranged from 0.14 to 0.32. The correlation coefficient was 0.99 for fr and 0.91 for delta. We found four overdamped systems in situ (delta > 1). In other systems fr values between 8.5 and 41.0 Hz and delta values between 0.16 and 0.72 were observed. The dynamic response in situ appeared to deteriorate with time due to routine intensive care procedures. CONCLUSIONS: The flush-pulse method proved to be a valid test for determining the dynamic response. The results obtained in situ emphasize the need for a regular evaluation of the dynamic response of the neonatal CMS in order to assess the shape of the pressure wave.

Blood Pressure↗
PubMed1992

Monitoring of oestrogen replacement therapy by vaginosonography of the endometrium.

To prevent hyperplasia and carcinoma of the endometrium during oestrogen replacement therapy (ORT), the addition of progestogens once a month is considered mandatory. However, there is no sound scientific basis for this assumption. As the addition of progestogens has several disadvantages, it is important to minimize the frequency of progestogen addition. Vaginosonography is a rather new technique which has not yet been used for monitoring ORT. In this study the increase in endometrial thickness, as measured by vaginosonography, was taken as an indicator of stimulation of the endometrium by oestrogens. Oestrogen treatment was started in post-menopausal women with little endometrium (thickness less than 3 mm). As long as there was virtually no increase during oestrogen treatment, no progestogen was added, but where considerable growth occurred (greater than 3 mm) progestogen was administered. By means of vaginosonography the growth of the endometrium can be monitored precisely on an individual basis. It is thus possible to distinguish women with a slow growing endometrium from those with an endometrium that grows fast. In this way it will perhaps become possible to minimize progestogen addition during ERT by tailoring dosage to individual requirements.

Endometrial Neoplasms↗
PubMed1992

[Endometrial growth in continuous, estrogen substitution monotherapy with Estraderm TTS (0.05 mg/die) in 31 postmenopausal females].

To prevent hyperplasia and carcinoma of the endometrium during Estrogen Replacement Therapy (ERT), addition of progestogens once a month is considered mandatory. There is, however, no good scientific basis for this assumption. Since the addition of progestogens has several disadvantages, it is important to minimise the frequency of progestogen addition. Vaginosonography is a rather new technique, which has not yet been used for monitoring ERT. This study uses the growth of the endometrium, as it was measured by vaginosonography, as a parameter for stimulation of the endometrium by estrogens. ERT with Estraderm 50 twice a week was started in postmenopausal women. The endometrial thickness at the beginning was less than 3 millimeters. During estrogen treatment the endometrial thickness was determined every 6 to 10 weeks. As long as there was little or no increase during the estrogen treatment, no progestogen was added. Where there was a considerable growth, progestogen was added. With the use of vaginosonography, it is possible, to distinguish "fast growers" (women whose endometrium responded fast) from "slow growers".

Administration, Cutaneous↗
PubMed1989

The fidelity of response by 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene in time-resolved fluorescence anisotropy measurements on lipid vesicles. Effects of unsaturation, headgroup and cholesterol on orientational order and reorientational dynamics.

Time-resolved fluorescence anisotropy measurements on 1-[4-(tri-methylammonio)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) molecules in lipid vesicles of palmitoyloleoylphosphatidylcholine (POPC), PC extracted from egg yolk (EggPC), dioleoyl-PC (DOPC), dilinoleoyl-PC (DLPC), phosphatidylglycerol extracted from egg yolk (EggPG), dioleoyl-PG (DOPG), sulfoquinovosyldiacylglycerol (SQDG) and digalactosyl-DG (DGDG) with and without cholesterol are presented. The observed intensity decay curves are analyzed simultaneously in terms of the Brownian rotational diffusion model. The analysis thus yields the isotropic fluorescence decay, the initial anisotropy r (0), the order parameters mean value of P2 and mean value of P4 as well as the diffusion coefficient of the long molecular axis. It is shown that increasing unsaturation in the acyl chains of the PC lipids results in an increase in the rotational diffusion rates of the probes and a decrease in the order parameter mean value of P2. However, the value of mean value of P4 remains unchanged. The corresponding orientational distribution function of the probes is bimodal, with fractions lying preferentially parallel and perpendicular to the local vesicle surface. Surprisingly, the fraction of probe molecules lying with their long axes parallel to the bilayer surface increases with increasing unsaturation with a concomitant narrowing in the width of the distribution of the fraction lying perpendicular to it. As expected, cholesterol is found to increase the order parameters in all the systems and to suppress the tendency of the molecules to lie parallel to the bilayer surface. Furthermore, the rotational diffusion coefficients of the probes is found to increase in all the systems except for DLPC. Interestingly, the effects of unsaturation on the reorientational dynamics of TMA-DPH molecules in the vesicle systems are opposite to those found in the corresponding planar multibilayers (Deinum et al. 1988), whereas the same cholesterol effect is observed for the two systems. Nevertheless, the TMA-DPH molecules exhibit higher diffusion coefficients in the vesicle than in the planar multibilayer systems. In addition, a unimodal distribution of the probe molecules is found in the multibilayer systems. The differences between the two systems are ascribed to the differences in the radius of curvature and the hydration of the bilayers. Lastly we rationalize the bimodal distribution of the TMA-DPH molecules in the vesicles in terms of their observed partition between the lipid and aqueous phases.

Cholesterol↗
PubMed1989

The membrane fluidity concept revisited by polarized fluorescence spectroscopy on different model membranes containing unsaturated lipids and sterols.

Quantitative analysis of time-resolved anisotropy measurements of DPH or TMA-DPH in lipid vesicles yields more than one mathematically correct solution. The solutions differ with respect to the average orientation and to the reorientational dynamics of the probe molecules in the bilayer. This leads to quite opposite results regarding the effects of cholesterol on membrane fluidity. One solution predicts an increase in fluidity, the other a decrease. Angle-resolved fluorescence depolarization (AFD) measurements of probes in oriented lipid bilayers enable determination of the average orientation of the probes in the bilayer and, if the fluorescence decay function is known, of the reorientational dynamics. Analysis of AFD measurements of DPH and TMA-DPH show that increasing unsaturation leads to a decrease in molecular order and a decrease in reorientational dynamics (= fluidity) of the probes. At temperatures above the phase transition of the lipids, the addition of cholesterol causes an increase in molecular order and an increase in reorientational dynamics (= fluidity). The plant sterol stigmaterol, which is structurally closely related to cholesterol, has different effects than cholesterol. The effects vary with the structure of the surrounding lipids. The membrane fluidity concept as it was originally proposed by Chapman attempts to describe the structural and dynamic properties of lipids in a membrane using one single parameter indicated as 'membrane fluidity'. Our results show that it is necessary to distinguish between structural parameters describing molecular order and motion parameters describing molecular dynamics, thus supporting a similar suggestion by Seelig and Seelig. In order to be useful, the membrane fluidity concept has to be limited to the parameters describing molecular dynamics.

Cholesterol↗
PubMed1989

Order and dynamics in the lamellar L alpha and in the hexagonal HII phase. Dioleoylphosphatidylethanolamine studied with angle-resolved fluorescence depolarization.

Fluorescence depolarization techniques are used to determine the molecular order and reorientational dynamics of the probe molecule TMA-DPH embedded in the lamellar L alpha and the hexagonal HII phases of lipid/water mixtures. The thermotropically induced L alpha----HII phase transition of the lipid DOPE is used to obtain macroscopically aligned samples in the hexagonal HII phase at 45 degrees C from samples prepared in the lamellar L alpha phase at 7 degrees C. The interpretation of angle-resolved fluorescence depolarization experiments on these phases, within the framework of the rotational diffusion model, yields the order parameters (P2) and (P4), and the diffusion constants for the reorientational motions. The reorientational motion rates of the TMA-DPH molecules in the hexagonal HII phase are comparable with those in the lamellar L alpha phase. Furthermore, the lateral diffusion of the probe molecule on the surface of the lipid/water cylinder in the hexagonal phase is found to be considerably slower than the reorientational motion.

Liposomes↗
PubMed1988

Molecular order and dynamics in planar lipid bilayers: effects of unsaturation and sterols.

Angle-resolved fluorescence depolarization experiments were carried out on 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) molecules embedded in macroscopically oriented multilayers of saturated [dimyristoylphosphatidylcholine (DMPC)] and unsaturated [palmitoyloleoylphosphatidylcholine (POPC), dioleoylphosphatidylcholine (DOPC), dilineoylphosphatidylcholine (DLPC), plant digalactosyldiglyceride (DGDG)] lipids with and without cholesterol. In all the lipid systems studied the order parameter (P2) of TMA-DPH molecules was found to be higher than that for DPH. Considerations of the order parameter (P4), however, indicate that DPH molecules have a heterogeneous distribution in bilayers of unsaturated lipids, with a significant fraction of the molecules lying with their long axes parallel to the bilayer planes. Both the DPH and TMA-DPH molecules exhibit a decrease in the molecular order as well as a decrease in their rates of motion on increasing the unsaturation of the hydrocarbon chains. The addition of cholesterol tends to reverse this effect, with an increase in both the order and dynamics. Bilayers of DOPC, however, exhibit a somewhat different result. It is suggested that the discrepancies between these observations and findings with lipid vesicle systems simply reflect the effects of curvature on the behavior of the probe molecules. The results indicate that the concept of membrane fluidity must be used with great caution.

Fatty Acids, Unsaturated↗
PubMedDate not supplied

DDD(R) pacing with automatic mode switch in patients with paroxysmal atrial fibrillation following AV nodal ablation.

Optimal pacing in patients with paroxysmal atrial fibrillation/flutter following AV node ablation remains to be determined because VVIR pacing cannot restore AV synchronization and conventional DDD(R) pacing cannot properly cope with atrial tachyarrhythmias. The objective of the present investigation was to study the clinical outcome of 16 of these patients who received a new DDDR pacemaker with an automatic mode switch (Thera DR; Medtronic) immediately after AV node ablation. Arrhythmia-related symptoms before ablation were palpitations in 12, dizziness in 10, exercise intolerance in 8, and syncope in 6 patients. Pacing modes at hospital discharge were DDDR (n = 14) and DDD (n = 2) with an activated mode switch in all patients. After 1 month 12 patients were symptom free. Clinical events occurred in 4 patients (palpitations in 2, dizziness in 1, chest pain in 1, and fatigue in 1), which could be relieved in 3 patients. At discharge as well as at the 1-month follow-up, Holter ECG recorded a total of 12 episodes of atrial fibrillation in 5 patients, which were correctly detected by the pacemaker and followed by mode switching. At the 3-month follow-up (n = 14), 12 patients were symptom free and 2 continued to report symptoms which could not be resolved. All patients remained on an automatic mode switch in either the DDDR (n = 12) or DDD (n = 2) mode. There were no hints of inappropriate mode switching or reports of pacemaker syndrome, and there were no new symptoms related to automatic mode switching. The patients studied were highly symptomatic before implantation due to paroxysmal atrial fibrillation/flutter. After the first follow-up, 81% of the patients reported no symptoms. Paroxysmal atrial fibrillation/flutter combined with a high-degree AV-block seems no longer to be a contraindication for AV-synchronous pacing.

Atrial Fibrillation↗
PubMedDate not supplied

Two years of smoking cessation does not reduce arterial wall thickness and stiffness.

BACKGROUND: Smoking cessation rapidly reduces cardiovascular risk. The pathophysiological mechanisms involved are still being debated. We measured structural and functional arterial wall properties of the femoral and carotid arteries after smoking cessation to investigate their possible role in cardiovascular risk reduction. METHODS: Out of 127 smokers, 33 proved to stop smoking for two years. They were compared with 50 nonsmokers and 55 persistent smokers in a prospective study. Cross-sectional compliance and distensibility coefficients as well as intima-media thickness of both carotid arteries and of the right common femoral artery were measured ultrasonographically at baseline and 3, 6, 12 and 24 months after smoking cessation. The nonsmoking and persistent smokers group were measured twice at an interval of 24 months. RESULTS: Persistent smoking and two years of smoking cessation did not affect cross-sectional compliance and distensibility coefficients. Although at baseline intimal-medial layers were thicker in smokers, the change over time in intima-media thickness did not differ significantly between all three groups. CONCLUSION: Two years of smoking cessation was not accompanied by a slower progression or a regression in intima-media thickness nor by an improved cross-sectional compliance or distensiblity coefficient. Nevertheless, smoking cessation should be recommended as it reduces cardiovascular risk rapidly after smoking cessation.

Adult↗