Biomedical subjects

R J Peters

Publications and source records attributed to R J Peters.

At least 55 records · Page 3Linked to original sources

PubMed1997

Activation of a retroviral membrane fusion protein: soluble receptor-induced liposome binding of the ALSV envelope glycoprotein.

It is not known how membrane fusion proteins that function at neutral pH, for example the human immunodeficiency virus envelope (Env) glycoprotein and intracellular fusion machines, are activated for target bilayer binding. We have addressed this question using a soluble oligomeric form of an avian retroviral Env glycoprotein (API) and soluble forms of its receptor. Binding of soluble receptor to API induces API to bind to liposomes composed of phosphatidylcholine and cholesterol at neutral pH. Liposome binding only occurs at fusion permissive temperatures (T > 20 degrees C), is complete between 2 to 5 min at 37 degrees C, and is stable to high salt, carbonate, and urea. Liposome binding is mediated by the ectodomain of the transmembrane subunit of API, and a mutant with a Val to Glu substitution in the Env fusion peptide (located in the ectodomain of the transmembrane subunit) shows significantly reduced liposome binding. Moreover, under conditions of equivalent binding to API, a mutant receptor that does not support infection (Zingler, K., and J.A.T. Young. 1996. J. Virol. 70:7510-7516) does not induce significant liposome binding. Our results indicate that a highly specific interaction between an avian retroviral Env and its receptor activates the retroviral glycoprotein for target bilayer binding at neutral pH in much the same way as low pH activates the influenza hemagglutinin. Our findings are discussed in terms of the mechanisms of viral and cellular fusion proteins that function at neutral pH.

3T3 Cells↗

PubMed1997

Pharmacological modulation of the human collateral vascular resistance in acute and chronic coronary occlusion assessed by intracoronary blood flow velocity analysis in an angioplasty model.

BACKGROUND: The pharmacological responsiveness of the coronary collateral circulation in humans has been studied only by indirect means. METHODS AND RESULTS: Patients with one-vessel disease and recruitable (n = 14) or spontaneously visible (n = 24) collateral vessels were studied during coronary angioplasty. Collateral flow in the recipient coronary artery was determined with a 0.014-in Doppler guide wire during balloon coronary occlusion and expressed as the diastolic blood flow velocity integral (dVi). Collateral blood flow velocity, mean aortic pressure (Pao), and coronary wedge pressure (Pw) were used to calculate the collateral vascular resistance index: Rcoll = (Pao-Pw)/ dVi (mm Hg/cm) and the peripheral vascular resistance index of the recipient coronary artery: R4 = Pw/dVi (mm Hg/cm). Adenosine (12 to 18 micrograms) and nitroglycerin (0.2 mg) were injected as a bolus in the donor coronary artery during subsequent balloon inflations to assess their effect on these hemodynamic variables. The administration of adenosine or nitroglycerin in patients with recruitable collateral vessels did not induce a change in dVi and Pw/Pao ratio. In patients with spontaneously visible collateral vessels, dVi increased from 8.0 +/- 4.5 to 10.8 +/- 8.0 cm (P = .01) after adenosine and from 7.4 +/- 4.5 to 10.3 +/- 6.9 cm (P = .003) after nitroglycerin. The Pw/Pao ratio remained unchanged after adenosine and nitroglycerin. Rcoll decreased from 10.3 +/- 9.5 to 8.6 +/- 8.5 mm Hg/cm (P = .01) after adenosine and from 11.6 +/- 10.4 to 8.3 +/- 8.9 mm Hg/cm (P < .001) after nitroglycerin. R4 decreased from 7.7 +/- 5.5 to 5.9 +/- 5.1 mm Hg/cm (P < .001) after adenosine and from 8.4 +/- 6.6 to 7.1 +/- 7.2 mm Hg/cm (P = .01) after nitroglycerin. CONCLUSIONS: Coronary collateral blood flow can be increased with adenosine and nitroglycerin in patients with one-vessel disease and spontaneously visible collateral vessels, which is in contrast to patients with recruitable collateral vessels. This effect is the result of a reduction in the collateral vascular resistance and peripheral vascular resistance of the recipient coronary artery.

Adenosine↗

PubMed1997

Prediction of restenosis after coronary balloon angioplasty. Results of PICTURE (Post-IntraCoronary Treatment Ultrasound Result Evaluation), a prospective multicenter intracoronary ultrasound imaging study.

BACKGROUND: Intracoronary ultrasound (ICUS) imaging is potentially suitable to identify lesions at high risk of restenosis after percutaneous transluminal coronary angioplasty (PTCA), but it has not been studied systematically. METHODS AND RESULTS: We recruited 200 patients in whom ICUS studies were performed after successful PTCA and related their ICUS parameters to 6-month follow-up quantitative coronary angiography. This was performed in 164 patients (82%), yielding 170 lesions for analysis. The overall incidence of a > or = 50% diameter stenosis at follow-up (categorical restenosis) was 29.4%. Quantitative ICUS parameters were weakly but significantly related to follow-up minimal luminal diameter on quantitative coronary angiography (lumen area: R2 = .36, P = .0001; vessel area: R2 = .29, P = .0002; plaque area: R2 = -.18, P = .021; percent obstruction: R2 = -.15, P = .05), but categorical restenosis was not significantly related to these parameters (P = .63, .77, .38, and .08, respectively). There were no significant predictors of restenosis in ICUS parameters of plaque morphology: eccentric versus concentric (P = 1.0), plaque type (hard, soft, or calcific, P = .98), or the number of calcified quadrants (P = .41). There were no significant predictors of restenosis in two predefined types of vessel-wall disruptions: (1) rupture: presence (P = .79), depth (partial versus complete, P = .85), or extent in quadrants (P = .6), and (2) dissection: presence (P = .31), depth (P = .82), or extent (P = .38). CONCLUSIONS: Qualitative ICUS parameters after PTCA did not predict restenosis. A larger lumen and vessel area and a smaller plaque area by ICUS were associated with a larger angiographic minimal lumen diameter at follow-up, but these parameters were not significantly related to categorical restenosis.

Aged↗

PubMed1997

Environmental and human monitoring of Americium-241 utilizing extraction chromatography and alpha-spectrometry.

Recent developments in extraction chromatography have simplified the separation of americium from complex matrices in preparation for alpha-spectroscopy relative to traditional methods. Here we present results of procedures developed/adapted for water, air, and bioassay samples with less than 1 g of inorganic residue. Prior analytical methods required the use of a complex, multistage procedure for separation of americium from these matrices. The newer, simplified procedure requires only a single 2 mL extraction chromatographic separation for isolation of Am and lanthanides from other components of the sample. This method has been implemented on an extensive variety of "real" environmental and bioassay samples from the Los Alamos area, and consistently reliable and accurate results with appropriate detection limits have been obtained. The new method increases analytical throughput by a factor of approximately 2 and decreases environmental hazards from acid and mixed-waste generation relative to the prior technique. Analytical accuracy, reproducibility, and reliability are also significantly improved over the more complex and laborious method used previously.

Americium↗

PubMed1997

Angioplasty of chronic total coronary occlusions with the use of six French guiding catheters.

The efficacy of 6 French guiding catheters for angioplasty of chronic total coronary occlusions was evaluated in 61 consecutive patients. The duration of the occlusion was determined angiographically, or estimated from an index clinical event. Endpoints were procedural success, defined as recanalization with less than 50% residual stenosis without major complications; and the need to change to larger-sized guiding catheters. Recanalization was attempted in 62 chronic total occlusions; 35 were located in the left anterior descending coronary artery, 18 in the right coronary artery, and 9 in the left circumflex coronary artery. The mean duration of the occlusion was 6.0 +/- 6.6 months; the range was 2-39 months. Lesion morphology included abrupt or diffuse occlusion (55%), a side branch originating at the occlusion (47%), and bridging collaterals (23%). Death, urgent coronary bypass surgery, or myocardial infarction did not occur. Recanalization was successful in 51 of the 62 total occlusions (82%); 49 were completed successfully with a 6 French guiding catheter, and 2 were successful after changing to a larger-sized guiding catheter (which was required for peripheral vessel tortuosity in one patient, and to obtain better back-up support in another). Three other attempts remained unsuccessful after a changing. A total of 12 Palmaz-Schatz stents were implanted in 11 patients for an unsatisfactory result or type C dissection, using the same 6 French guiding catheters. These preliminary findings indicate that 6 French guiding catheters are both effective and safe for angioplasty of chronic total occlusions.

Adult↗

PubMed1997

Arterial remodeling after balloon angioplasty of the coronary artery: an intravascular ultrasound study. PICTURE Investigators. PostTreatment IntraCoronary Transluminal Ultrasound Result Evaluation.

OBJECTIVE: Before balloon dilation, failure of compensatory enlargement and even arterial shrinkage are frequently observed at the lesion site in response to plaque accumulation. Balloon angioplasty may be regarded as artificial remodeling to enlarge the artery. The prevalence of the different types of arterial wall remodeling after applied stretch by balloon angioplasty is unknown. METHODS AND RESULTS: In 181 patients an intravascular ultrasound study was performed after coronary balloon angioplasty (n = 200 lesions). The vessel area was measured at a proximal and distal reference site and at the lesion site. Subsequently, the relative vessel area [(Vessel area lesion site)/Vessel area reference site) x 100] was calculated. Lesions were classified in three groups on the basis of their relative vessel areas: > or =105%, <105% but >95%, and < or =95%. A relative vessel area > or =105%, indicating enlargement compared with the reference site, was observed in 84 (44%) lesions. A relative vessel area <105% but >95% was observed in 43 (22%) lesions. A relative vessel area < or =95%, indicating "shrinkage" compared with the reference site, was observed in 66 (34%) lesions. CONCLUSIONS: After balloon angioplasty, the vessel area was found to be smaller compared with the reference site in 34% of the lesions. This small vessel area at the lesion site compared with a reference site may be a reflection of insufficient stretch by balloon angioplasty.

Angioplasty, Balloon, Coronary↗

PubMed1997

Clinical, angiographic and hemodynamic predictors of recruitable collateral flow assessed during balloon angioplasty coronary occlusion.

OBJECTIVES: We sought to determine the predictive value of factors influencing coronary collateral vascular responses in humans. BACKGROUND: There is limited information on the factors responsible for coronary collateral vascular development, despite the protective effect of collateral vessels in ischemic syndromes. METHODS: Angiography of the contralateral artery was performed during balloon coronary occlusion in 105 patients with single-vessel disease (left anterior descending coronary artery in 69 patients, left circumflex coronary artery in 4 patients, right coronary artery in 32 patients) and normal left ventricular function. Collateral vessels were graded according to the classification of Rentrop. The relative collateral vascular resistance was calculated in a subgroup of 34 patients by means of aortic pressure, coronary wedge pressure and collateral flow, defined as the transient increase of coronary blood flow velocity of the contralateral artery during balloon coronary occlusion. Ischemia during coronary occlusion was evaluated by the ST segment shift (mV) in a 12-lead electrocardiogram (ECG). RESULTS: A multivariate logistic analysis of clinical and angiographic variables revealed duration of angina (> or = 3 months, p < 0.0001), lesion severity (> or = 75% diameter stenosis, p < 0.0001) and proximal lesion location (p = 0.02) as independent factors positively associated with recruitability of collateral vessels, whereas the use of nitrates exerted an independent negative effect (p = 0.01). The regression equation yielded an overall predictive accuracy of 80%. The presence of recruitable collateral vessels during coronary occlusion resulted in a higher coronary wedge/aortic pressure ratio (mean [+/- SD] 0.35 +/- 0.13 vs. 0.27 +/- 0.12, p < 0.005), a lower relative collateral vascular resistance (6.7 +/- 7.4 vs. 21.3 +/- 10, p < 0.001) and a reduction of ECG signs of ischemia (0.14 +/- 0.19 vs. 0.38 +/- 0.33 mV, p < 0.001). The relative collateral vascular resistance was the best predictor for recruitability of collateral vessels compared with the other variables related to collateral vascular growth (p < 0.05). CONCLUSIONS: Clinical and angiographic variables predict recruitability of collateral vessels with an 80% overall accuracy. These findings are important for risk stratification of patients undergoing interventions for ischemic coronary syndromes.

Angioplasty, Balloon, Coronary↗

PubMed1997

Comparison of collateral vascular responses in the donor and recipient coronary artery during transient coronary occlusion assessed by intracoronary blood flow velocity analysis in patients.

OBJECTIVES: This study was designed to evaluate the hemodynamic variables of the collateral circulation during acute coronary occlusion. BACKGROUND: There is limited information on the physiology of the collateral circulation in coronary artery disease. METHODS: Angiography of the contralateral donor artery was performed before and during balloon coronary occlusion in 57 patients with one-vessel disease. Recruitable collateral flow was assessed during coronary occlusion by blood flow analysis of the contralateral donor artery (n = 19) or the ipsilateral recipient artery (n = 15), or both (n = 23), using a Doppler catheter or guide wire. Ischemia was evaluated by the ST segment shift (> or = 0.1 mV) on a 12-lead electrocardiogram at 1 min of coronary occlusion. RESULTS: The presence (n = 39), compared with the absence (n = 18), of recruitable collateral vessels was associated with an increase of blood flow velocity in the donor artery (20 +/- 19% vs. 4.8 +/- 5.9% [mean +/- SD], p = 0.003) and the recipient artery (velocity integral 7.2 +/- 5.5 vs. 2.8 +/- 2.2 cm, p = 0.02) related to a reduced relative collateral vascular resistance (9.2 +/- 10 vs. 20 +/- 11, p = 0.003). Collateral flow in the donor artery yielded a similar predictive value for recruitability of collateral vessels as collateral flow determined in the recipient artery or the coronary wedge/aortic pressure ratio (areas under the receiver operating characteristics curves 0.76 +/- 0.07, 0.78 +/- 0.08, 0.77 +/- 0.07, respectively, p = NS). Collateral flow in the recipient artery was a better predictor for ischemia than collateral flow in the donor artery or angiographic grading of collateral vessels (areas 0.90 +/- 0.05, 0.64 +/- 0.10, 0.73 +/- 0.07, respectively, p < 0.05). CONCLUSIONS: Coronary blood flow velocity analysis of the donor and recipient coronary arteries can characterize the dynamics of the collateral circulation during acute coronary occlusion. The protective effect of recruitable collateral vessels relates to an increase of flow in the donor and recipient coronary arteries due to a reduced collateral vascular resistance. This study underscores the importance of physiologic variables for the evaluation of the function of recruitable collateral vessels.

Adult↗

PubMed1997

Does a waiting time for elective coronary angioplasty affect the primary success rate?

OBJECTIVE: To evaluate the effect of the waiting time for elective percutaneous transluminal coronary angioplasty (PTCA) on the primary success rate. SETTING: University hospital in The Netherlands. PATIENTS: A cohort of 817 consecutive patients awaiting elective PTCA. Scheduled PTCA was performed in all 817 patients, involving 1237 coronary lesions. MAIN OUTCOME MEASURES: The relation between procedural success and the duration of the waiting time was evaluated. Major cardiac events, that is, death and myocardial infarction while awaiting PTCA, were documented. Alterations in lesion characteristics during the waiting time were assessed in unsuccessful procedures. RESULTS: Elective PTCA was performed within one to six weeks after acceptance in 388 patients (587 lesions; 47.5%), between six and 12 weeks in 203 patients (308 lesions; 25%), and after more than 12 weeks in 226 patients (342 lesions; 27.5%). The procedural success rates in the defined time intervals were 97%, 99%, and 97% in ACC/AHA type A lesions, 93%, 87% and 90% in type B lesions, and 63%, 55% and 38% in type C lesions respectively; 96% of type C lesions were total coronary occlusions. There was a significant decrease in primary success rate in type C lesions after a waiting time beyond 12 weeks. A reasonable explanation for an unsuccessful angioplasty related to alterations in lesion characteristics during the waiting time was documented in only four of 115 procedures. CONCLUSIONS: The primary success in type A and B lesions is unaffected by the duration of a waiting period for elective PTCA. A waiting time of more than 12 weeks is associated with a lower success rate in patients with total coronary occlusions.

Aged↗

PubMed1996

Relationship between anterior fontanelle pressure measurements and clinical signs in infantile hydrocephalus.

The treatment of choice in progressive hydrocephalus is drainage of cerebrospinal fluid in order to reduce elevated intracranial pressure (ICP). Defining the right moment for surgical intervention, however, in a hydrocephalic infant on the basis of clinical signs alone can be a difficult task. Clinical signs of raised ICP are known to be unreliable and sometimes even misleading. In the present study, the relationship between long-term anterior fontanelle pressure (AFP) measurements and clinical signs was investigated in 37 infants with hydrocephalus. The decision as to whether to operate or not was based on clinical signs alone; AFP values were not taken into account. There was an overall difference between the non-operated group and the preoperative measurements in the operated group, and also between the preoperative and the postoperative measurements in the latter, in regard to both AFP measurements and clinical signs. Almost all preoperative AFP values were increased. The direct correlation (phi) between most individual clinical signs and AFP levels, however, was low (phi = 0.15-0.41). The clinical sign "tense fontanelle" showed the best correlation with the AFP levels (phi = 0.75). Furthermore, using logistic regression analysis, no combination of clinical signs could be found which reliably predicted the AFP. The relationship between the AFP pressure variables and clinical signs was also examined. The pathological A-waves occurred only in the presence of raised (baseline) AFP, a situation in which considerably more frequent B-waves were observed as well. It was concluded that clinical signs of raised ICP in infantile hydrocephalus are not very reliable and AFP monitoring can therefore provide valuable information on intracranial dynamics in patients with dubious neurological manifestations of progressive hydrocephalus.

Female↗

PubMed1996

In vitro validation of intravascular ultrasound imaging after balloon angioplasty of coronary artery stenoses.

Systematic studies of intravascular ultrasound imaging of in vitro balloon angioplasty on coronary arteries with a greater than 50% diameter stenosis on angiogram have not been performed. We used 23 plasma-perfused postmortem human coronary arteries with an angiographic diameter stenosis of > or = 50%. After balloon dilation the vessels were examined by 30-MHz intravascular ultrasound imaging (IVUS) and the presence of ruptures and dissections was noted. Ruptures were defined as disruptions of the vessel wall in a radial direction, and dissections were defined as disruptions in a circumferential direction. After pressure fixation they were studied by histology. On IVUS, 24 vessel wall disruptions were diagnosed in 14 arteries. On histology, 29 disruptions were diagnosed in 19 arteries. The sensitivity of IVUS for the detection of disruptions was 79%, the specificity was 75%. Total agreement was 79%. Accuracy was better for dissections (total agreement 96%) than for ruptures (total agreement 74%). Shadowing behind calcium and close contact of the catheter to the arterial wall were important sources of error in the IVUS analysis. We conclude that intravascular ultrasound imaging is accurate for the detection of disruptions after balloon angioplasty of angiographically significant coronary artery stenoses.

Angioplasty, Balloon↗

PubMed1996

Reproducibility of quantitative measurements from intracoronary ultrasound images. Beat-to-beat variability and influence of the cardiac cycle.

OBJECTIVES: The purpose of this study was to determine the variability of quantitative measurements from intracoronary ultrasound images, and the influence of the cardiac cycle on this variability, as a basis for in vivo applications. METHODS: Two observers analysed 30 MHz cross-sectional images from 96 in-vivo coronary arterial sites. By computer-assisted contour tracing we determined lumen area, vessel area, lesion area (vessel area minus lumen area) and percent obstruction (100% x lesion area/vessel area). Intra- and inter-observer and beat-to-beat variability, and systolic to diastolic differences were calculated by paired analysis. RESULTS: Consistent intra- and inter-observer differences (bias) were small (< or = 0.9%). Random variations in the two direct parameters were < or = 21.1%, but for the two derived parameters they were up to 40%. For all four parameters, random inter-observer variability was significantly greater (up to 119% for vessel area: 19.3 vs 8.8%) than intra-observer variability, but consistent variability was similar. Consistent beat-to-beat differences were small (< or = 1.4%), random variations were 8.9% to 17.5%. Random beat-to-beat variability for all four parameters was greater in diastolic than in systolic frames (up to 47.0% difference (11.9 vs 17.5%) for lesion area). Vascular dimensions were significantly greater in systole (2%). We found an error of 0.24 mm (2SD) for intra-observer variability of calculated mean arterial diameters, which is similar to the error described in angiographic studies (0.22 mm). CONCLUSIONS: Quantitative measurements from intracoronary ultrasound images generally reproduce well. It is preferable to use directly measured parameters as opposed to derived parameters, as they are less subject to variability. Variability can be reduced by selecting systolic images.

Adult↗

PubMed1995

[Secondary prevention in patients with a coronary disorder: wider indication for cholesterol-lowering drugs].

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Aged↗

PubMed1995

Assessment of collateral flow during balloon coronary occlusion by intracoronary blood flow velocity analysis.

Coronary blood flow velocity analysis of the contralateral and of the ipsilateral artery can be used to assess collateral flow during controlled balloon coronary occlusion. Coronary blood flow velocity assessment in combination with measurement of aortic pressure and coronary wedge pressure permits expression of the development of the collateral circulation in terms of flow and resistance. The application of both techniques is illustrated in two patients.

Adult↗

PubMed1995

Non-invasive ICP monitoring in infants: the Rotterdam Teletransducer revisited.

Measurement of intracranial pressure (ICP) is important in patients at risk of raised ICP, as in hydrocephalus. Ideally, it should be non-invasive, thus avoiding the risk of infection and other complications: Such is provided by measurement of ICP through the anterior fontanelle. There are several methods of measuring anterior fontanelle pressure (AFP); those most frequently used are based on the applanation principle. An evaluation of AFP measurement devices resulted in the choice of the Rotterdam Teletransducer (RTT) to be used in our study of children with hydrocephalus. The literature contains little information on the accuracy or validation of the AFP measurements using the RTT. Therefore, the physical qualities of the RTT were reassessed, using a specially developed calibration device. The results of this study demonstrate that membrane temperature does not have any effect on the measured pressure. The thermal stabilization time of the RTT was found to be 3 h after switching on. Insufficient thermal stabilization results in a pressure underestimation of up to 3 mmHg. Furthermore, a maximum inaccuracy of 2.6 mmHg, after calibration and readjustment of the transducer, was calculated. Validation of the equipment was achieved by simultaneous AFP/ICP measurements in hydrocephalic patients showing high correlations (r = 0.96-0.98). The discussion suggests a measurement protocol as a means of increasing the reliability of RTT measurements.

Calibration↗

PubMed1995

Value of transcranial Doppler indices in predicting raised ICP in infantile hydrocephalus. A study with review of the literature.

Cerebral hemodynamic changes in infants with progressive hydrocephalus have been studied with the transcranial Doppler (TCD) technique. Several authors have referred to the correlation between the hemodynamic changes and increased intracranial pressure (ICP). Despite conflicting conclusions on the value of pulsatility index (PI) and resistance index (RI) measurements for monitoring infantile hydrocephalus, these pulsatility indices are the most commonly used for this purpose. Although clinical signs of raised ICP are highly variable and unreliable in infants, assumptions have been made in most of the studies about the presence of elevated ICP on the basis of the patient's clinical state. Few studies have reported on actual ICP values, however, and a direct relationship between ICP and TCD changes has never been adequately demonstrated. In the present study, this relationship was investigated in long-term simultaneous TCD/ICP measurements, in an attempt to develop a noninvasive method of monitoring the effect of ICP on intracranial hemodynamics. Two groups of data sets were established. Group I consisted of pre- and postoperative (shunt implantation) TCD/ICP measurements. Group II were long-term simultaneous TCD/ICP recordings showing significant ICP variations. In most of the postoperative measurements there was a decrease in the average PI and RI values. The correlation between PI or RI and ICP in the long-term simultaneous recordings, however, was generally poor. The risk of obtaining false positive or false negative PI or RI values in short-term measurements was also demonstrated. It can be concluded from our results, besides the wide range of reference values for the Doppler indices and extracranial influences upon them, that the present Doppler indices are inadequate for monitoring the complex intracranial dynamic responses in patients with raised ICP.

Adolescent↗

PubMed1995

Monitoring intracranial dynamics by transcranial Doppler--a new Doppler index: trans systolic time.

Since the introduction of transcranial Doppler sonography (TCD) several investigators have described the relationship between raised intracranial pressure (ICP) and Doppler waveform. This waveform has been expressed by several indices, such as the pulsatility index (PI) and the resistance index (RI). These indices are used to demonstrate the presence of raised ICP. In childhood hydrocephalus this information can be used to indicate the need for shunt implantation. However, PI and RI do prove to have certain disadvantages as both are strongly influenced by the heart rate. Moreover, both indices have a broad range of reference values, especially in children. Therefore, they are not very reliable for detecting insidious changes in the ICP. These drawbacks are due to the fact that these indices are composed of blood flow velocity measurements and do not embody the slope of the TCD waveform itself. An ideal TCD waveform analysis should be performed concerning the time-related changes of the velocities. We present a hydrodynamic model, with its electrical analogue, which shows the effects of raised ICP on the intracranial hemodynamic system. Based on these physical findings we define a new Doppler index, the Trans Systolic Time, reflecting specific changes in the TCD waveform induced by changes in the mean ICP. The applicability of this index, compared with PI and RI, is illustrated by consecutive simultaneous TCD and AFP measurements in three children with hydrocephalus.

Blood Flow Velocity↗

PubMed1995

Contribution of age and intimal lesion morphology to coronary artery wall mechanics in coronary artery disease.

1. Atherosclerotic changes of the coronary vascular wall include localized plaque formation and diffuse hardening, both of which influence tensile strength of the inner vascular wall. Insight into the relation between age, the atherosclerotic process and vessel wall elasticity may contribute to the prevention of secondary vascular wall damage. 2. To evaluate the determinants of coronary artery wall elasticity, we studied a group of 34 patients, aged 54.6 +/- 10.1 years, who underwent balloon angioplasty for coronary artery disease. With the use of 30 MHz intravascular ultrasound, a total of 127 cross-sections of coronary artery segments outside the balloon area were studied. The echographic appearance of the intima was classified as normal intimal thickening, fibrous lesions and calcified lesions. Fibrofatty lesions, which are believed to be rupture prone, were analysed separately. From the lumen area change, measured by semiautomated planimetry from digitized ultrasound images, and simultaneously measured aortic pressure change during the diastolic phase of the cardiac cycle, two elastic parameters were derived, pressure-strain modulus Ep and beta-stiffness. 3. In univariate analysis Ep and beta-stiffness were determined by age, vessel size, intimal composition, severity of lumen obstruction and gender, but not by eccentricity of the lesion or a specific coronary artery. In multivariate linear analysis, increased vessel wall stiffness was independently determined by advanced age, larger vessel size, intimal composition, and to a lesser extent by female gender. Elastic parameters of fibrofatty lesions were not different from other fibrous lesions. 4. Coronary artery wall elasticity is independently determined by age, vessel size and intimal composition.

Adult↗