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PubMed1988

Computer models for designing hypertension experiments and studying concepts.

This paper demonstrates how computer models along with animal experiments have been used to work out the conceptual bases of hypertensive mechanisms, especially the following: (1) The renal-fluid volume pressure control mechanism has a feed-back gain for pressure control of infinity. Therefore, the chronic level to which the arterial pressure is controlled can be changed only by altering this pressure control mechanism. (2) An increase in total peripheral resistance is not sufficient by itself to cause hypertension. The only resistances in the circulatory system that, when increased, will cause hypertension are those along a restricted axis from the root of the aorta to Bowman's capsule in the kidneys. (3) Autoregulation in the peripheral vascular beds does not increase the arterial pressure in hypertension. However, autoregulation can convert high cardiac output hypertension into high peripheral resistance hypertension. (4) In a computer simulation that cannot yet be performed in animals, a simulated hypertension caused by a combination of increased renal afferent and efferent arteriolar resistances has characteristics that match almost exactly those of essential hypertension.

Animals↗
PubMed2005

Clip reconstruction for a case of peripheral posterior inferior cerebellar artery aneurysm: case report.

The authors report an unusual surgical treatment for an aneurysm on the left peripheral posterior inferior cerebellar artery (PICA). The computed tomographic scan showed subarachnoid haemorrhage and a haematoma in the left cerebellar region close to the fourth ventricle. The 3D CT angiography demonstrated an aneurysm on the left peripheral PICA which was confirmed on four-vessel angiography. The aneurysm was approached through a posterior suboccipital craniotomy and the PICA was reconstructed with multiple clips. The literature concerning peripheral PICA aneurysms and their treatment is reviewed and discussed.

Aged↗
PubMed2004

Multidetector row computed tomographic angiography of the abdominal aorta and lower limbs arteries. A new diagnostic tool in patients with peripheral arterial occlusive disease.

AIM: The aim of this study is to evaluate the accuracy of multidetector row CT angiography (MDCTA) of the abdominal aorta and lower extremities arteries in patients with peripheral arterial occlusive disease who did not receive any prior treatment whether interventional or surgical. METHODS: Twenty-two patients with peripheral vascular occlusive disease (16 male, 6 female, age range 44-85 years) underwent MDCTA of the abdominal aorta and lower extremities. Digital subtraction angiography (DSA) of the same districts was performed within 3 months. Images were blindly interpreted by 2 interventional radiologists and compared with the results of digital subtraction angiography. RESULTS: Sensitivity and specificity of MDCTA were 92% and 94%, respectively, with positive and negative predictive values of 93% and 95%. Overall diagnostic accuracy was 93%. Normal arterial segments and 100% occlusions were correctly identified in all cases by MDCTA. Moderately stenotic segments interpretation in the calves appeared to be more controversial, but no statistical difference in accuracy in this district was noted with respect to accuracy in more proximal arteries. CONCLUSION: MDCTA of the abdominal aorta and lower extremities is a feasible, accurate imaging modality in clinical practice when compared to DSA.

Adult↗
PubMed1996

Simulators for anesthesia.

Two commercially available complete anesthetic simulators were studied in the United States. Although there are some differences between the two systems, each consists of an adult manikin allowing some direct anesthetic interventions, a system of producing physiologic signals to any commercial monitoring system, and the ability to interface with an anesthetic machine and ventilator. In addition, both simulators model the responses to a variety of drugs used by anesthetists. With their associated computer controls, it is possible to mimic a number of recognized anesthetic critical situations and to record the responses made by the anesthetist and determine the effects on the "patient." In use, one system is devoted principally to teaching crisis resource management to anesthetists. The other system is used more generally to teach anesthetists how to approach a variety of problems. In our opinion, each system could be used in either of these ways. Both systems are capable of development into valuable teaching tools for anesthetists and for others involved in critical care. There is potential for the training of paramedics or nurses involved in anesthetic and recovery room care and intensive care. Other options include the investigation of critical events and the development and subsequent testing of clinical management protocols. Anesthetists are familiar with the use of manikins in the teaching of airway management and basic and advanced life support. Newer manikins can be used to practice skills in intravascular cannulation; some can be used with monitoring equipment and defibrillators to provide more realistic teaching. Computer programs, especially those for personal computers (PCs), can also be used to simulate the pharmacophysiologic behavior of patients in a variety of states. Now available are combined systems using manikins controlled by computer, with interfaces to anesthetic machines, ventilators, and monitoring equipment. Two systems are commercially available in the United States. In this report, we briefly describe their technical specifications and how we saw them being used.

Adult↗
PubMed2006

Intramolecular Diels-Alder reactions of ester linked 1,3,9-decatrienes: cis/trans selectivity in thermal and Lewis acid promoted reactions of ethylene-tethered and benzo-tethered systems.

High cis (i.e., endo) diastereoselectivities are witnessed in heat-promoted intramolecular Diels-Alder (IMDA) reactions of ethylene-tethered hexadienyl acrylates. The cis stereoselectivity is improved by promotion with Et2AlCl. The first examples of Et2AlCl catalyzed intramolecular Diels-Alder reactions of ester-activated dienophiles are reported. In contrast, the corresponding benzo-tethered hexadienyl acrylates undergo moderately trans (i.e., exo) selective IMDA reactions. Very high trans stereoselection is obtained upon promotion with ATPH. The outcomes of these reactions are essentially insensitive to dienophile (C10) geometry and substitution. DFT (B3LYP/6-31+G(d)) computed cis/trans product distributions-based on Boltzmann transition structure populations-are in good agreement with the experimental results. These computational investigations provide useful insights into the origins of stereoselection in these systems. The stereoselectivity exhibited by the ethylene-tethered hexadienyl acrylates is ascribed to stabilizing secondary orbital interactions at play in the cis-transition structures (TSs). In the benzo-tethered series, this effect is overridden by stabilizing pi-conjugative interactions, between the benzo moiety and the 1,3-diene component, which are stronger in trans TSs, compared to the cis TSs. The computed TS geometries generally exhibit advanced peripheral bond forming asynchronicity, with the tether carbonyl group in conjugation with the dienophile. Such TS features significantly weaken the stereodirecting influence of terminal dienophile substituents.

Acids↗
PubMed2003

Impact of CT angiography on endovascular therapy.

In the last ten years, computed tomography (CT) angiography has evolved from an experimental diagnostic tool to the preferred imaging study for a variety of disease processes. At the same time, endovascular surgery has become the first-line therapy for several types of peripheral vascular disease. With the recent introduction of multidetector computed tomography, CT angiography of the entire peripheral vascular system is possible in mere seconds. This imaging modality has become critical for the pre-procedure planning and post-procedure follow-up of several endovascular procedures, including endovascular aneurysm repair, lower extremity revascularization, and renal artery revascularization. A thorough knowledge of the current applications of CT angiography with respect to the peripheral vasculature is essential for the endovascular specialist.

Angiography↗
PubMed1983

Spectral analysis of Doppler ultrasonic flow signals by a personal computer.

This paper describes a method of performing spectral analysis on Doppler acoustical signals from peripheral blood vessels with the use of an Apple II plus personal computer. Digitization is accomplished with a commercially available analog-to-digital converter. The data are transformed with a fast Fourier technique, and the resultant information is plotted by an inexpensive X-Y plotter and/or on a television receiver.

Blood Vessels↗
PubMed1993

Extraskeletal mesenchymal chondrosarcoma.

Among seven patients with extraskeletal mesenchymal chondrosarcoma (EMC), three children (aged 3-6 years) developed EMC in a central location and four adults (aged 38-54 years) developed EMC in both central and peripheral sites. Conventional radiography and tomography and computed tomography (CT) depicted EMC as a soft-tissue mass with ring, arc, stippled, and highly opaque calcifications in four patients. Contrast-enhanced CT showed lobulation and peripheral tumoral enhancement, sometimes with central low-attenuation areas. On magnetic resonance (MR) images, EMC was a lobulated mass with high signal intensity on T2-weighted images and enhancement with low-signal-intensity focal areas on contrast-enhanced T1-weighted images. All adults developed recurrences and/or metastases and died. Of the three children, two were living and free of disease at the end of the study and the third child died of chemotherapeutic-induced leukemia. Although imaging features of EMC are nonspecific, its chondroid-type calcifications and foci of low signal intensity within enhancing lobules may reflect its dual histopathologic morphologic characteristics of differentiated cartilage islands interspersed within vascular undifferentiated mesenchyme.

Adult↗
PubMedDate not supplied

CT of calcified chronic aortic dissection simulating atherosclerotic aneurysm.

Calcification along the outermost aspect of the aorta usually means atherosclerotic aneurysm. On occasion, however, this peripheral type calcification is seen in chronic aortic dissection and leads to a misdiagnosis. Conventional chest roentgenography and CT of 50 cases of chronic dissection proven by angiography were reviewed. Four of these cases (8%) showed calcification in the outermost wall of the affected portion of the aorta. Two cases were Stanford type A and the other two cases were type B. In type A cases chest roentgenography showed calcification in the wall of the dilated ascending aorta closely mimicking aneurysm. In type B cases, calcification was in the outer wall of a localized hump in the descending aorta. Computed tomography clearly demonstrated that this peripheral calcification was located in the outermost wall of the false lumen. Review of the pathologic literature shows sporadic reports of such phenomenon and a theory of endothelialization of the false lumen. It is presumed that the endothelialized false lumen may develop atheromatous changes much more rapidly than the true lumen since two of four cases showed calcification only in the wall of the false lumen with the intimal flap and the wall of the true lumen remaining noncalcified.

Aged↗
PubMed1991

Haemoperitoneum secondary to spontaneous rupture of hepatocellular carcinoma: CT diagnosis.

In Western countries, haemoperitoneum following rupture of hepatocellular carcinoma (HCC) is unusual. Three patients are presented in whom massive intraperitoneal haemorrhage secondary to spontaneous rupture of HCC was diagnosed by computed tomography (CT). CT demonstrated a peripheral hepatic tumour and free intraperitoneal fluid with areas of high-attenuation, representing acute blood-clot, close to the tumour in every case. In our opinion, CT is a valuable imaging modality in the diagnosis of ruptured HCC.

Aged↗
PubMed1999

The influence of eye solutions on blinking and ocular comfort at rest and during work at video display terminals.

The aim of this work was to study blink frequency changes and levels of ocular discomfort during work at a video display terminal, and the effects on these parameters of augmented or reduced humidification of the ocular surface. Blink rate was measured from recordings of the electrical signal evoked by the contraction of the orbicularis oculi muscle. Blink rate and interblink intervals were analyzed at rest and during performance of a task with a computer (playing a card game) for 10 or 30 min in steady environmental conditions and during application of a continuous stream of air to the face. In two separate sessions, the effect of pretreatment with humidifying ocular solutions of different elastoviscosity (balanced salt solution or elastoviscous 0.1% Hylan A solution) was assayed. At the end of each experimental period, the subjects marked the level of ocular discomfort experienced on a 0-10 cm visual analogue scale. The blink frequency at rest (12.4+/-1.2 blinks min-1) was reduced significantly (to 10.3+/-1.1 blinks min-1) by pretreatment with elastoviscous eyedrops both with and without air applied to the face. This effect was not obtained with balanced salt solution. During performance of the visual task for 10 or 30 min, basal blink rate decreased significantly, to about 40% of the control value. Neither application of an air jet on the face nor application of eye solutions of different viscosity modified this reduced blink rate.A low degree of ocular discomfort developed after performance of the visual task that was enhanced by air application to the face. This discomfort was reduced by pretreatment with ocular solutions, the elastoviscous eye solution being more efficient than the balanced salt solution. Interblink interval duration was also more regular after treatment with the elastoviscous solution. These data suggest that blink rate at rest is maintained in part by activation of sensory receptors of the cornea and conjunctiva, which are stimulated by desiccation of the ocular surface. Reduction of eye blink frequency elicited by the performance of a visual task with a computer appears to depend on central neural mechanisms that are quite independent of peripheral sensory inputs. The reduction of blink frequency consecutive to computer use was associated with a sensation of discomfort that was attenuated more effectively by elastoviscous eyedrops than by regular balanced salt solution.

Adult↗
PubMed2005

[Tumor microembolism presenting as characteristic patterns of pulmonary perfusion on lung scanning: a case report].

A 55-year-old man presented with tumor microembolism manifesting as characteristic patterns of pulmonary perfusion on lung scanning. He had a 2-week history of dyspnea and general fatigue. Echocardiography demonstrated right ventricular enlargement. Computed tomography of the chest was normal. Lung perfusion imaging showed multiple subsegmental peripheral defects, which were characteristic of tumor embolism. Ultrasonography and computed tomography of the abdomen revealed multiple enlargement of the lymph nodes. Upper gastrointestinal panendoscopy showed gastric cancer. At 10 days after admission, he suffered cardiac arrest and died despite resuscitative efforts. Histological examination revealed pulmonary arterial obstruction with tumor cells, and poorly differentiated adenocarcinoma in the stomach and lymph nodes. This case emphasizes the need to include tumor microembolism in the differential diagnosis of dyspnea, even if there is no evidence of an underlying malignant tumor.

Adenocarcinoma↗
PubMed2005

Recognizing extrahepatic collateral vessels that supply hepatocellular carcinoma to avoid complications of transcatheter arterial chemoembolization.

Extrahepatic collateral arteries commonly supply hepatocellular carcinomas if the tumors are large or peripherally located. Because development of these vessels interferes with effective control of the tumor with transcatheter arterial chemoembolization (TACE), radiologists should become familiar with the imaging findings of extrahepatic collateral vessels to detect them at an early stage. The authors observed 2104 such vessels in 860 patients over 5.5 years. The extrahepatic collateral vessels observed originated from the inferior phrenic artery, omental branch, adrenal artery, intercostal artery, cystic artery, internal mammary artery, renal or renal capsular artery, branch of the superior mesenteric artery, gastric artery, and lumbar artery. The authors suspected extrahepatic collateral vessels when (a) a tumor grew exophytically or invaded adjacent organs, (b) a tumor was in contact with the ligaments and bare area of the liver, (c) a hypertrophied extrahepatic collateral vessel was observed on a computed tomographic (CT) scan, (d) a peripheral defect of iodized oil retention within a tumor was seen during chemoembolization or on a follow-up CT scan, (e) a local recurrence developed at the peripheral portion of the treated tumor during follow-up, or (f) a sustained elevation in serum alpha-fetoprotein level was noted despite adequate embolization of the hepatic artery. When both the hepatic artery and extrahepatic collateral vessels supply a tumor, additional extrahepatic collateral vessel chemoembolization should be attempted to increase the therapeutic efficacy of TACE for hepatocellular carcinoma.

Adult↗
PubMed2004

Cardiac output by Modelflow method from intra-arterial and fingertip pulse pressure profiles.

Modelflow, when applied to non-invasive fingertip pulse pressure recordings, is a poor predictor of cardiac output (Q, litre x min(-1)). The use of constants established from the aortic elastic characteristics, which differ from those of finger arteries, may introduce signal distortions, leading to errors in computing Q. We therefore hypothesized that peripheral recording of pulse pressure profiles undermines the measurement of Q with Modelflow, so we compared Modelflow beat-by-beat Q values obtained simultaneously non-invasively from the finger and invasively from the radial artery at rest and during exercise. Seven subjects (age, 24.0 +/- 2.9 years; weight, 81.2 +/- 12.6 kg) rested, then exercised at 50 and 100 W, carrying a catheter with a pressure head in the left radial artery and the photoplethysmographic cuff of a finger pressure device on the third and fourth fingers of the contralateral hand. Pulse pressure from both devices was recorded simultaneously and stored on a PC for subsequent Q computation. The mean values of systolic, diastolic and mean arterial pressure at rest and exercise steady state were significantly ( P < 0.05) lower from the finger than the intra-arterial catheter. The corresponding mean steady-state Q obtained from the finger (Qporta) was significantly ( P < 0.05) higher than that computed from the intra-arterial recordings (Qpia). The line relating beat-by-beat Qporta and Qpia was y =1.55 x -3.02 ( r2 = 0.640). The bias was 1.44 litre x min(-1) and the precision was 2.84 litre x min(-1). The slope of this line was significantly higher than 1, implying a systematic overestimate of Q by Qporta with respect to Qpia. Consistent with the tested hypothesis, these results demonstrate that pulse pressure profiles from the finger provide inaccurate absolute Q values with respect to the radial artery, and therefore cannot be used without correction with a calibration factor calculated previously by measuring Q with an independent method.

Adult↗
PubMed2002

Quantifying the implications of nonlinear cochlear tuning for auditory-filter estimates.

The relation between auditory filters estimated from psychophysical methods and peripheral tuning was evaluated using a computational auditory-nerve (AN) model that included many of the response properties associated with nonlinear cochlear tuning. The phenomenological AN model included the effects of dynamic level-dependent tuning, compression, and suppression on the responses of high-, medium-, and low-spontaneous-rate AN fibers. Signal detection theory was used to evaluate psychophysical performance limits imposed by the random nature of AN discharges and by random-noise stimuli. The power-spectrum model of masking was used to estimate psychophysical auditory filters from predicted AN-model detection thresholds for a tone signal in fixed-level notched-noise maskers. Results demonstrate that the role of suppression in broadening peripheral tuning in response to the noise masker has implications for the interpretation of psychophysical auditory-filter estimates. Specifically, the estimated psychophysical auditory-filter equivalent-rectangular bandwidths (ERBs) that were derived from the nonlinear AN model with suppression always overestimated the ERBs of the low-level peripheral model filters. Further, this effect was larger for an 8-kHz signal than for a 2-kHz signal, suggesting a potential characteristic-frequency (CF) dependent bias in psychophysical estimates of auditory filters due to the increase in strength of cochlear nonlinearity with increases in CF.

Auditory Perception↗
PubMed2005

Weight, fat mass, and central distribution of fat increase when women use depot-medroxyprogesterone acetate for contraception.

OBJECTIVE: To compare longitudinal changes in weight, body fat, and ratio of central to peripheral fat mass among first-time depot-medroxyprogesterone acetate (DMPA) users to women using no hormonal contraception, and to evaluate user characteristics associated with that change. DESIGN: Prospective longitudinal study. SUBJECTS: Healthy women, aged 18-35 y, using DMPA for contraception (n=178) and women using no hormonal contraception (n=145). MEASUREMENTS: Weight, body fat, and the central distribution of fat, measured at 3-month intervals for 30 months, by electronic scale and dual-energy X-ray absorptiometry (DEXA). The ratio of central to peripheral distribution of body fat was computed by dividing the body fat in the conventional DEXA trunk region of interest (ROI) by the ROI's that encompass the arms, hips and legs. RESULTS: Women using DMPA had a significantly greater increase in all measures of fatness than women using no hormonal method of contraception (P<0.03). The observed weight of DMPA users increased from a mean of 69.4 kg (s.d.=16.9) at baseline to 75.5 kg (s.d.=25.0) at 30 months; an increase of 6.1 kg (8.8.%). Fat mass increased from a mean of 25.3 kg (s.d.=12.6 kg) at baseline to 31.4 kg (s.d.=17.8); an increase of 6.1 kg (23.6%) in DMPA users. The ratio of central to peripheral fat mass in DMPA users changed from 0.95 (s.d.=0.155) at baseline to 1.01(s.d.=0.198) at 30 months. In contrast, weight, fat mass and the ratio of central to peripheral fat mass of control participants remained virtually unchanged over the same time period. Women with higher baseline physical activity levels had a smaller increase in body fat (P=0.003) and the fat ratio (P=0.03), but not weight (P=0.48). No other user characteristics including, smoking, past oral contraceptive use or previous pregnancies predicted change in level of fatness. CONCLUSIONS: This study has demonstrated a change in body composition toward greater fatness and toward a central redistribution of fat among DMPA users as compared to controls and provides important information to be used when counseling women regarding contraceptive methods. Given the potential long-term implication of these changes, further study is recommended to determine whether the gains in fatness are reversed following DMPA discontinuation and to examine the role of progestins in the development and maintenance of obesity.

Absorptiometry, Photon↗
PubMedDate not supplied

[Influenza B virus pneumonia after bone marrow transplantation: case report with emphasis to the high resolution computed tomography findings].

Nine year-old male patient, who underwent bone marrow transplantation because of acute myelogenous leukemia, presented with fever and dry cough three days after the procedure. The chest radiograph demonstrated bilateral diffuse reticular infiltrate. The high resolution computed tomography showed peribronchovascular interstitial thickening, peripheral small centrilobular nodules and areas of ground-glass attenuation. The bronchoalveolar lavage demonstrated positive direct fluorescence antibody testing against influenza B virus. Treatment with aerolizated ribavirin was instituted during 10 days and the patient showed clinical-radiological improvement.

Bone Marrow Transplantation↗