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Biomedical subjects

A J Peters

Publications and source records attributed to A J Peters.

At least 19 recordsLinked to original sources
PubMed2004

Changes in chemical signature and host specificity from larval retrieval to full social integration in the myrmecophilous butterfly Maculinea rebeli.

The ant social parasite, Maculinea rebeli shows high levels of host specificity at a regional scale. While 68-88% of caterpillars in the field are adopted by nonhost Myrmica ants, 95-100% of the butterflies emerge from the natural host M. schencki the following year. While retrieval of preadoption caterpillars is specific to the genus Myrmica, it does not explain differential survival with different Myrmica species. We present survival data with host and nonhost Myrmica species suggesting that, with nonhosts (M. sabuleti and M. rubra), survival depends on the physiological state of the colony. We also compared the similarities of the epicuticular surface hydrocarbon signatures of caterpillars that were reared by host and nonhost Myrmica for 3 weeks with those from tending workers. Counterintuitively, the hydrocarbons of postadoption caterpillars were more similar (78%, 73%) to the ant colony profiles of the nonhost species than were caterpillars reared in colonies of M. schencki (42% similarity). However, caterpillars from M. schencki nests that were then isolated for 4 additional days showed unchanged chemical profiles, whereas the similarities of those from nonhost colonies fell to 52 and 56%, respectively. Six compounds, presumably newly synthesized, were detected on the isolated caterpillars that could not have been acquired from M. sabuleti and M. rubra (nor occurred on preadoption caterpillars), five of which were found on the natural host M. schencki. These new compounds may relate to the high rank the caterpillars attain within the hierarchy of M. schencki societies. The same compounds would identify the caterpillars as intruders in non-schencki colonies, where their synthesis appeared to be largely suppressed. The ability to synthesize or suppress additional compounds once adopted explains the pattern of mortalities found among fully integrated caterpillars in Myrmica colonies of different species and physiological states.

Animals↗
PubMed2001

Americium binding to humic acid.

The binding of americium (Am) by peat humic acid (PHA) has been investigated at Am concentrations between 10(-1) and 10(-7) M at pH approximately 2.6 in the presence and absence of Cu as a competing ion. Cu-PHA binding was also investigated in order to derive independent binding constants for use in modeling the competitive binding studies. Humic ion-binding model VI was used to compare the acquired data with previously published binding data and to investigate the importance of high-affinity binding sites in metal-PHA binding. Am was not observed to bind to high-affinity, low-concentration binding sites. The model VI parameter deltaLK2 takes into accountthe small number of strong sites in PHA and was found to be important for Cu-PHA binding but not for Am-PHA binding, regardless of whether Cu was present. Analysis of the PHA sample revealed that it contained a considerable quantity of Fe not removed by the extraction procedure, much of which is believed to be present as Fe(III). Model VI was then used to investigate the possible importance of the presence of Fe(III) in the Am-PHA binding experiments. When Fe(III) was assumed to be present, improved descriptions of the data by model VI were obtained by assuming that all of the metals [Am, Cu, and Fe(III)] undergo strong binding. This highlights the importance of Fe(III) competition in metal-PHA binding studies and possible shortcomings in the extraction procedure used to extract PHA.

Americium↗
PubMed2001

Organochlorine pesticide residues in archived UK soil.

Archived background soils ("Broadbalk', 1944-1986) and sludge-amended soils ("Luddington", 1968-1990), collected from long-term agricultural experiments in the UK, were analyzed for a range of organochlorine (OC) pesticides to establish trends over time. Concentrations typically ranged from 0.1 to 10 ng/g of soil (dry weight), with gamma-hexachlorocyclohexane (gamma-HCH), dieldrin, and p,p'-DDE consistently having the highest concentrations. The trends in the Broadbalk background soils are largely consistent with usage patterns, with peak concentrations occurring in the 1960s for DDTs and between the 1960s and the 1980s for the other OCs. In the Luddington control and sludge-amended soils, several of the OCs show a significant decline in concentrations from the late 1960s to 1990, with half-lives ranging from approximately 7 years (alpha-HCH) to approximately 25 years (dieldrin). The sludge-amended plot received 125 tonnes of sludge per ha in 1968, which was mixed in to a depth of 15 cm. It appears that the sludge treatment had little effect on concentrations in the soil, with no significant difference between control soil and sludge-amended soil for most compounds, except for HCB, p,p'-DDE, and dieldrin. Enantiomeric fractions (EFs) of some chiral pesticides (alpha-HCH, cis- and trans-chlordane, and o,p'-DDT) were determined in the Luddington soils. Results reveal that enantioselective degradation of OC pesticides is occurring in these soils for trans-chlordane (TC) and cis-chlordane (CC). However, the depletion over time is not statistically significant, and there is no statistically significant difference between EFs in the control soil and sludge-amended soil. This indicates that enantioselective microbial degradation was not consistent over time and that the addition of sludge to soil did not significantly alter the enantiomeric preference of the microbial community.

Agriculture↗
PubMed2001

In vitro bleeding test with PFA-100-aspects of controlling individual acetylsalicylic acid induced platelet inhibition in patients with cardiovascular disease.

OBJECTIVES: This study investigated the usefulness and practicability of a platelet function analyzer (PFA-100(TM), DADE-Behring, Germany) to determine individual platelet inhibition in patients treated with acetylsalicylic acid (ASA). BACKGROUND: Patients with coronary artery disease (CAD) routinely and during angioplasty (PTCA) receive standard doses of ASA to avoid acute coronary syndromes and abrupt vessel closures without information of the individual efficacy of platelet inhibition. METHODS: With the PFA-100(TM) a standardized bleeding time is measured. Whole-blood anticoagulated with 3.2% sodium citrate is aspirated through a capillary ( solidus in circle 200 microm) and through an aperture ( solidus in circle 147 microm). The time until occlusion of the aperture (closure time, CT) by a stable platelet plug induced by shear stress, collagen and epinephrine (COLL/EPI-CT) or shear stress, collagen and adenosine 5'-diphosphate (COLL/ADP-CT) is determined. To examine the usefulness of the PFA-100(TM) as a rapid bedside test and the individual effect of ASA, closure time was measured in healthy individuals (n=17), in patients with stable CAD (n=19) and in patients undergoing PTCA (n=8). RESULTS: Patients with stable CAD and regular medication with 100 mg ASA per day for at least 3 month showed shorter COLL/ADP-CT in comparison to healthy individuals who took only one single dose of 100 mg ASA. Of the patients with CAD 63% had a COLL/EPI-CT within normal range suggesting a low or no response to ASA. Also only 50% of the patients undergoing PTCA reached the expected COLL/EPI-CT>300 s after an additive single dose of 500 mg ASA intravenously. Neither heparin, phenprocoumon, sex nor different blood sampling methods seem to influence the measurements relevantly. CONCLUSIONS: This pilot study indicates that with the PFA-100(TM) test device a simple and quick measurement of an in vitro bleeding time is possible. It is able to detect an increase in the bleeding time after a single dose of ASA 100 mg in healthy subjects, reflecting a sensitive detection of ASA induced changes in platelet inhibition respective activation. Differences in the individual response to ASA could be observed in healthy subjects, patients with stable CAD and patients undergoing PTCA. Further studies should validate the PFA-100(TM) with standard methods to determine ASA response in patients with cardiovascular disease and investigate implications for treatment and outcome in this patient group.

Adult↗
PubMed2001

Angiographic progression of coronary artery disease in patients with end-stage renal disease.

BACKGROUND: Patients with end-stage renal disease have an increased risk of developing coronary artery disease (CAD). The cardiovascular mortality of dialysis patients is 10-15 times higher compared with the general population. The aim of our study was to evaluate the morphological progression of coronary arteriosclerosis in this cardiovascular high-risk group by visual assessment and quantitative coronary angiography. Methods and results. In 26 patients with chronic renal failure (age, 47+/-11 years; 15 male; duration of dialysis, 23+/-25 months) the severity of CAD and degree of coronary stenoses were assessed in two coronary angiograms after a mean follow-up interval of 30+/-15 months (12-60). Baseline angiography revealed CAD in 13/22 patients (59%). The second angiography was performed as screening procedure prior to renal transplantation (n=20) and/or as follow-up angiography after coronary angioplasty (n=10). Visual assessment showed a progression defined by the development of haemodynamically relevant stenosis of >50% luminal diameter in 13 patients. Quantitative angiographic evaluation was performed in a total of 45 segments showing >25% narrowing at the second angiogram. A progression (>15% luminal reduction) was found in 17 of 45 segments, a new lesion (initial luminal diameter <20%) was detected in nine segments, resulting in progression or new lesion in 16 patients (62%). Patients with or without progression did not differ in age, duration of dialysis treatment, number of cardiovascular risk factors, or serum total cholesterol and fibrinogen levels. After percutaneous transluminal coronary angioplasty (PTCA) a restenosis was seen in seven of 16 primarily successfully dilated segments. After the second angiography, myocardial revascularization was performed in eight patients (1 PTCA, 7 coronary artery bypass graft). CONCLUSIONS: Patients with end-stage renal disease have a high prevalence of CAD. In line with the clinical course, CAD patients on maintenance dialysis undergo rapid angiographic progression of CAD, which results in a high rate of subsequent myocardial revascularizations.

Adult↗
PubMed2000

Intra-abdominal sound pressure levels during impulse noise exposure in sheep.

Ambient sound pressure levels (SPLs) created with intense blasts were compared with SPLs recorded in the abdomen of euthanized sheep. Hydrophones were placed in the abdominal cavity at locations referred to as proximal, medial, and distal with respect to a shock tube that created 169-dB peak SPL (pSPL). No differences in pSPL, duration, or rise time were found between recordings in air and at the intra-abdominal proximal position. Significant differences were noted in these variables when recordings in air were compared with recordings made at the medial and distal locations. Intra-abdominal pSPL varied by 20 dB depending on recording location.

Abdomen↗
PubMed1999

Congenital asplenia detected in a 60 year old patient with septicemia.

A 60 year-old female who had never been seriously ill, was brought to the emergency ward after she had been found somnolent at home. She developed renal failure, meningitis, respiratory distress and disseminated intravascular coagulation. Overwhelming septicemia was evident, and streptococcus pneumoniae was isolated from blood and cerebrospinal fluid. Surprisingly, peripheral blood smears showed numerous Howell-Jolly-bodies, indicating severe impairment of splenic function. On abdominal ultrasound, CT-scan, and scintigraphy no spleen could be detected. There was no history of abdominal surgery. Apparently, congenital asplenia, which was not noticed until the age of 60, was responsible for the patient's life-threatening septicemia. We suggest that, in cases of severe septicemia, the examination of a blood smear is useful to detect functional (or congenital) asplenia.

Bacteremia↗
PubMed1999

[Large pseudoaneurysm of the left ventricle after posterolateral wall infarct].

Pseudoaneurysms of the left ventricle are rare complications after acute myocardial infarction. We report on a 69 year old patient with a large false aneurysm located in the posterolateral ventricular wall. It became clinically apparent during an episode of severe left heart failure. Echocardiography and left ventriculography allowed an accurate determination of localization and dimension of the pseudoaneurysm; coronary angiography revealed a proximal occlusion of the left circumflex coronary artery. Because of the high risk of rupture, a rapid surgical repair of the false aneurysm was indicated.

Aged↗
PubMed1999

[Influence of pulmonary hemodynamics on right ventricular ejection fraction in chronic obstructive pulmonary disease].

Right ventricular dysfunction is common in patients with chronic obstructive pulmonary disease. Right ventricular function might be influenced by the afterload, which depends on pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR). To evaluate the influence of the right ventricular afterload on right ventricular performance, we investigated 30 patients with chronic obstructive pulmonary disease without clinical signs or history of left heart failure or coronary heart disease. The study includes lung function tests, analysis of blood gases and right heart catheterisation. RV function was assessed by a thermodilution technique using a pulmonary artery catheter equipped with a rapid response thermistor (produced by Baxter, USA). There are 9 patients with normal, 12 with latent and 9 with fixed pulmonary hypertension. Median RVEF was measured to be 33.3% (19-44%). There was a significant correlation between RVEF and PAP (r = -0.66; p < 0.0001) and RVEF and PVR (r = -0.54; p < 0.0018). RVEF was not directly influenced by lungfunction or pulmonary capillary wedge pressure (PCWP). Under treadmill exercise RVEF and cardiac index increased without a change of PCWP. A low RVEF at rest seems to be a predictive value for a reduced exercise capacity. A reduced RVEF has a predictive value of pulmonary hypertension with a sensitivity of 66% in patients with unstable and 89% in patients with lasting pulmonary hypertension. In a subgroup of 6 cases treadmill exercise led to a RVEF decrease. These patients showed no difference in afterload, blood gases or lung function-tests compared with the total group. In conclusion, right ventricular ejection fraction seems to be influenced by PVR and PAP which determinate the right ventricular afterload. The validity of the method depends on the severity of pulmonary hypertension, and hence measurement of RVEF might not provide a reliable estimation of pulmonary arterial pressure in patients suffering from mild to moderate pulmonary hypertension.

Female↗
PubMed1998

[Angina pectoris in "coronary steal syndrome" caused by a coronary fistula in the left ventricle].

HISTORY AND CLINICAL FINDINGS: A 55-year-old female patient reported left-sided chest pain at rest as well as during exercise, which recurred during the last three years before admission. Cardiovascular risk factors included hypercholesterolemia and smoking. The physical examination of the patient was unremarkable. INVESTIGATIONS: The ECG at rest showed T-wave inversions in leads I, aVL, V3-V6 and ergometric exercise testing resulted in angina pectoris and descending ST-segments in leads V3-V6. Stress thallium 201 scintigraphy demonstrated a reversible perfusion deficit of the the anterior wall at peak exercise. The left ventricular angiogram and echocardiogram revealed normal end-diastolic dimensions and regular systolic contractions without signs of left ventricular hypertrophy. Selective coronary arteriography excluded hemodynamically relevant stenosis of the coronary arteries. A coronary artery fistula originating from a large, ectatic first diagonal branch with drainage into the left ventricle was observed. TREATMENT AND COURSE: Because the patient rejected interventional therapy she was treated conservatively and follow-up investigations 3 and 4 years after arteriography revealed unchanged clinical symptomatology. CONCLUSION: In this case a "coronary steal" phenomenon caused by the coronary fistula induced myocardial ischemia. Therefore if present congenital coronary anomalies have to be considered in patients with chest pain and normal coronary angiogram.

Angina Pectoris↗
PubMed1998

[Assessment of the anti-ischemic effect in patients with therapy refractory angina pectoris in end-stage coronary heart disease--results of chronic intermittent urokinase therapy].

Patients with refractory angina pectoris and end-stage coronary artery disease represent an increasing clinical problem. Numbers of these patients will increase in the future for improved survival due to effective secondary prevention of coronary artery disease. Next to the evaluation of clinical symptoms non-invasive objective parameters of myocardial ischemia are of major relevance before initiation of alternative treatment modalities and for verification of antiischemic effectiveness. Based on our own experience it can be shown that in these patients testing which is mainly based on the patients physical exercise capacity is only of limited value due to the early occurrence of clinical symptoms. Furthermore diffuse perfusion abnormalities reduce the sensitivity of electrocardiographic and scintigraphic detection of ischemic changes. In contrast indirect measures of ischemia relating to the systolic or diastolic function of the left ventricle like doppler-echocardiography and radionuclide ventriculography seem to be promising approaches. This is confirmed by the results from the application of long-term intermittent urokinase therapy. Long-term intermittent urokinase therapy leads to an absolute enhancement of myocardial perfusion, which makes this approach superior to other medical interventions which are mainly based on a reduction of cardiac work-load.

Angina Pectoris↗
PubMed1997

Effect of abdominal vibroacoustic stimulation on sound and acceleration levels at the head of the fetal sheep.

OBJECTIVE: To measure the vibratory response of the fetal head and abdominal wall in sheep during vibroacoustic stimulation. METHODS: A piezoresistive accelerometer was attached to the skulls of seven sheep fetuses (128-134 days' gestational age), and a miniature hydrophone was attached to the skin overlying the fetal temporal bone. During fetal preparation and vibroacoustic stimulation procedures, ewes were anesthetized and supine. Vibroacoustic stimulation of the maternal abdomen was produced by each of two clinical devices that differed in spectral content, and an electric toothbrush. RESULTS: The approximate fundamental frequencies (f0) and first overtones (f1), as determined by both recordings of intrauterine sound pressure level and fetal head acceleration, were as follows: fetal acoustic stimulator, 75 and 150 Hz; electronic larynx, 150 and 300 Hz; and electric toothbrush, 25 and 50 Hz, respectively. At fundamental frequencies and first overtones, the ranges of fetal head accelerations (expressed in 1/12-octave bands) were as follows: fetal acoustic stimulator, 10-53 and 25-224 mm/sec2; electronic larynx, 10-53 and 18-114 mm/sec2; and electric toothbrush, 33-792 and 8-116 mm/sec2, respectively. Sound pressure levels exceeded 110 dB in all cases. High sound pressure levels in the uterus were proportional to fetal head vibration levels. CONCLUSION: Vibroacoustic stimulation of the surface of the abdomen of pregnant sheep is accompanied by both acoustic and vibratory exposure of the fetus.

Abdominal Muscles↗
PubMed1997

[Chronic intermittent urokinase therapy: anti-ischemic and hemodynamic effects].

Long-term intermittent urokinase therapy has been developed for patients with severe coronary artery disease and refractory angina pectoris. This therapeutic approach is predominantly effective at the microcirculatory level based on a combination of rheologic and fibrinolytic effects; furthermore, plaque regression seems to be a possible mechanism. Patients with refractory angina pectoris are characterized by severe coronary artery disease without a therapeutic option for conventional revascularization procedures, only slight impairment of left ventricular systolic function and hyperfibrinogenemia, which results in further enhancement of myocardial ischemia due to microcirculatory impairment of blood flow. In this article data on the anti-ischemic effectiveness as well as first results on the impact of this therapeutic approach on hemodynamics are described. A dose-response study, which compared 3 x 50,000 IU with 3 x 500,000 IU urokinase three times a week over a treatment period of 12 weeks demonstrated subjective as well as objective antiischemic effectiveness. Only patients who were treated with 500,000 IU per injection achieved marked increases in exercise capacity, while some patients in the low-dose group presented even with a deterioration of exercise performance. First hemodynamic studies could not show marked changes of systolic parameters, either at rest or during exercise. But a decrease of pulmonary capillary wedge pressure at rest after treatment with 500,000 IU per injection indicates an improvement of diastolic function as a result of enhanced myocardial perfusion. Echocardiographic measurements of transmitral Doppler flow in 21 patients with end-stage coronary artery disease demonstrated normalization of early and late diastolic filling rates in most cases. These changes were accompanied by a reduction of clinical signs of heart failure. Long-term intermittent urokinase therapy is a valuable approach as it not only improves quality of life during the actual treatment period but by the persistence of therapeutic effects following the cessation of therapy.

Angina Pectoris↗
PubMed1997

[Prognostically relevant parameters in patients with coronary heart disease, arterial hypertension and sleep apnea disorders].

Patients with untreated sleep apnea syndrome have a higher cardiovascular mortality. It is not known which mechanisms lead to this increase in mortality and whether it is independent from the often associated coronary heart disease and systemic hypertension. In 48 consecutive patients with coronary heart disease confirmed by angiography, exercise-ECG, Holter-ECG, echocardiography, spirometric tests, analysis of ventricular late potentials, heart rate variability and a test for sleep-disordered breathing with a screening device were performed. Seventeen patients showed disordered breathing during sleep (obstructive sleep apnea) with a desaturation index of > or = 10 (mean desaturation index 17.3 +/- 9.3 vs. 2.6 +/- 3.1 in the patients without sleep-disordered breathing). There are no significant differences in age (58.9 +/- 6.1 vs. 59.7 +/- 7.6 years), body-mass-index (28.6 +/- 3.7 vs. 27.7 +/- 3.3 kg/m2), left ventricular ejection fraction (57.2 +/- 13.6 vs. 64.0 +/- 14.6%), forced expiratory volume in 1 second/vital capacity 95.4 +/- 13.9 vs. 92.9 +/- 11.2% predicted, heart rate variability (standard deviation of the RR-intervals 39.4 +/- 29.4 vs. 37.2 +/- 17.0 ms), the frequency of premature ventricular beats over 24 h and at night, the frequency of multivessel disease (71 vs. 68%), additional hypertension 53 vs. 48%), status postmyocardial infarction (47 vs. 48%) and positive late potential analysis (24 vs. 13%). There were no ST segment depressions during the night. Patients with coronary heart disease and mild sleep-disordered breathing show no significant differences in the investigated parameters compared with patients without obstructive sleep apnea or sleep-disordered breathing.

Adult↗
PubMed1996

Auditory brainstem response in sheep. Part II: Postnatal development.

The auditory brainstem response (ABR) was recorded from 15 chronically instrumented lambs between birth and 7 weeks of age as well as from four adult ewes. Latency changes observed within two days of birth may be related to the dissipation of fluid from the lamb external auditory canal and middle ear cavity. Developmental changes observed in the lambs included an early period of wave latency decrements from 1 to 4 weeks followed by a subsequent increase in wave latencies from 4 to 7 weeks. These changes were significant for the I-IV interwave interval, possibly reflecting the combined effects of increased myelinization and increased neural track length. Responses from 7 week-old lambs were not significantly different from those obtained from the ewes.

Aging↗
PubMed1996

Acceleration of fetal head induced by vibration of maternal abdominal wall in sheep.

OBJECTIVE: The human body is often exposed to significant vibration stress in the workplace, at home, and during recreational activities. The current study was designed to evaluate whether low- to midfrequency vibrations present at the extraabdominal wall would be attenuated across this wall and what the levels of exposure would be once these vibrations reached the fetal head. STUDY DESIGN: Four pregnant sheep were instrumented with acceleration transducers to obtain acceleration levels at the extraabdominal and intraabdominal walls and at the fetal head. Sine-wave vibration stimulation was applied over a frequency range of 3 to 150 Hz at a constant acceleration level of 2.5 m/sec2 (root-mean-square). RESULTS: Vibration of the extraabdominal wall resulted in a frequency-dependent rise in vibration levels at the intraabdominal wall, from 4% to 140% of the input level. At the fetal head a broad peak in response was noted between 6 and 12 Hz, but the overall levels never exceeded 4% of the input level. CONCLUSION: Fetal exposure to localized vibratory stimulation of the maternal abdomen is maximal in the range of 6 to 12 Hz.

Abdominal Muscles↗
PubMed1996

Cocaine does not compromise cerebral or myocardial oxygen delivery in fetal sheep.

Eight time-dated pregnant ewes at 125 days' gestation (145 days = term) underwent surgery for placement of fetal vascular catheters, electrodes for recording fetal behavioural state, and maternal venous catheters. Three days later, fetal cerebral and myocardial blood flow were determined by the coloured microsphere technique under four conditions: (1) during rapid-eye movement (REM) sleep, before fetal cocaine infusion, (2) 30 min after initiation of a cocaine infusion to the fetus at 0.2 mg/kg per min, (3) during REM sleep, before maternal cocaine infusion, and (4) 30 min after initiation of a cocaine infusion to the ewe at 0.3 mg/kg per min. Cocaine infusion directly to the fetal lamb did not cause hypoxaemia or significantly change cerebral or myocardial blood flow or oxygen delivery. Cocaine administered to the ewe led to a drop in fetal oxygen tension from 3.0 +/- 0.5 to 2.5 +/- 0.3 kPa (P < 0.0001) and in fetal oxygen content from 3.8 +/- 0.7 to 2.8 +/- 0.4 mmol O2/L (P < 0.0001). Prior to maternal cocaine administration, fetal cerebral blood flow was 146 +/- 103 mL/100 g per min and during maternal cocaine infusion it went to 184 +/- 147 mL/100 g per min (P = NS) while myocardial blood flow increased from 156 +/- 92 to 333 +/- 178 mL/100 g per min (P < 0.002). This increase in blood flow negated the effects of hypoxaemia so that cerebral oxygen delivery was unaffected while myocardial oxygen delivery increased an average of 67%. It is concluded that cocaine administration to pregnant sheep does not impede fetal cerebral or myocardial oxygen delivery.

Analysis of Variance↗