Biomedical subjects

P Liu

Publications and source records attributed to P Liu.

At least 289 records · Page 16Linked to original sources

PubMed1995

Photoacoustic ultrasound (PAUS)--reconstruction tomography.

The theoretical underpinnings of photoacoustic ultrasound (PAUS) reconstruction tomography are presented. A formal relationship between PAUS signals and the heterogeneous distribution of optical absorption within the object being investigated is developed. Based on this theory, a reconstruction approach, analogous to that used in x-ray computed tomography, is suggested. Initial experimental results suggest that this approach produces "reasonable" reconstructions for absorbers distributed within a narrow plane embedded within a highly scattering medium.

Acoustics↗

PubMed1995

Expression of tumour necrosis factor alpha and accumulation of fibronectin in coronary artery restenotic lesions retrieved by atherectomy.

BACKGROUND: The formation of coronary artery neointima experimentally induced in piglets after cardiac transplantation is related to an immune-inflammatory reaction associated with increased expression of T cells and inflammatory mediators (tumour necrosis factor alpha and interleukin 1 beta) and upregulation of fibronectin. In vivo blockade of tumour necrosis factor alpha in rabbits after cardiac transplantation results in reduced neointimal formation. The objective of this study was to investigate the hypothesis that coronary restenosis after atherectomy or percutaneous balloon angioplasty is associated with a similar inflammatory cascade initiated by mechanical injury. METHODS: Specimens taken at coronary atherectomy were analysed from 16 patients. Nine had had the procedure performed twice, firstly, to remove a primary lesion, and secondly, to remove a restenotic lesion. Seven had percutaneous balloon angioplasty after removal of restenotic tissue. Coronary atherectomy specimens were analysed by immunohistochemistry for the presence of T cells, macrophages, major histocompatibility complex II, interleukin 1 beta, tumour necrosis factor alpha, fibronectin, and the receptor for hyaluronan mediated motility. RESULTS: The groups were clinically and angiographically similar with equivalent lumens before and after atherectomy. Restenotic lesions had increased expression of tumour necrosis factor alpha and fibronectin compared with the primary lesions (P < 0.05 for both). There was also a trend towards a greater number of T cells and increased expression of interleukin 1 beta. CONCLUSIONS: Restenosis is associated with increased expression of tumour necrosis factor alpha and fibronectin, suggesting that an immune-inflammatory reaction probably contributes to neointimal formation and may represent a form of wound healing and repair secondary to mechanical injury.

Angioplasty, Balloon, Coronary↗

PubMed1995

Clinical variability in two pairs of identical twins with the Charcot-Marie-Tooth disease type 1A duplication.

We report two pairs of male homozygotic twins in two unrelated families with the Charcot-Marie-Tooth disease type 1A duplication. Homozygosity was supported by DNA analysis. There was remarkable congruity of conduction velocities between the left and right side of each twin and between twin brothers. The similarity and symmetry of the electrophysiologic deficit contrast with the variable and asymmetric clinical presentations. Variability of clinical expression in these patients with identical mutations suggests the action of stochastic factors or environmental modulation of disease severity.

Adult↗

PubMed1995

Cardiovascular effects of varying G-suit pressure and coverage during +1 Gz positive pressure breathing.

With the continued evolution of anti-G suits, used to counter the cardiovascular dysfunction arising from +1 Gz hypoxia protection positive pressure breathing (PPB), it was hypothesized that full-coverage anti-G-suits would offer equal protection while using lower inflation pressures than the traditional 4:1 ratio. Nine experienced subjects were exposed to 2 min of 70 mm Hg PPB while wearing either the COMBAT EDGE (CE) and Tactical Life Support System (TLSS) garments with the G-suit inflated to 4 x breathing pressure, and the Advanced Tactical Anti-G-Suit (ATAGS) at 4, 3, 2, and 1 x the breathing pressure. All subjects were measured with impedance cardiography (IC), and six were measured simultaneously with both IC and the Cardioscint nuclear probe. IC-estimated stroke volume, relative left ventricular (LV) end-diastolic volume, LV ejection fraction, and peak filling rate were depressed most in the CE and ATAGS 1 conditions (p < 0.001). Heart rate and mean arterial blood pressure changes were highest and lowest, respectively, using the CE and ATAGS 1 garments (p < 0.001). There were no differences in these variables between the TLSS and ATAGS 2-4 conditions. Thus, protection against the PPB-induced fall in LV preload and cardiovascular function may still be adequately afforded by lower G-suit inflation pressures when using full-coverage anti-G suits during PPB intended for high altitude-protection.

Blood Pressure↗

PubMed1995

Repeated radial keratotomy.

38 cases 59 eyes received repeated radial keratotomy in which the secondary incisions were performed along the scars of old incisions. The average follow-up after the reoperation was 13 months. Before reoperation, the mean spherical equivalent of the refraction was -3.78D and the mean keratometry was 40.15D. 13 months after the reoperation, the mean spherical equivalent of the refraction decreased by 2.30D, and the mean keratometry decreased by 2.04D. After the reoperation, the mean uncorrected visual acuity increased by 5 lines. There was no relationship between the therapeutic effect of the reoperation and the degree of initial myopia or pre-reoperative keratometry. The repeated radial keratotomy can decrease the degree of astigmatism and its complications are few.

Adult↗

PubMed1995

[Refractory periods of cardiac tissues and the filtering properties of the atrioventricular node in the isolated rabbit heart].

It is generally believed that the atrioventricular node (AVN) possesses filtering properties (FP) capable of preventing excess atrial impulses or earlier atrial premature beat from reaching the ventricle. In the present study, the refractory periods (RP) of cardiac tissues and the FP of the AVN were investigated in isolated rabbit hearts (n = 18). It was found that: (1) The relative RP of AVN was the longest at shorter basic cycle lengths (BCL) (200-300 ms) while the relative RP of His-Purkinje system (HPS) was the longest at longer BCL (600, 700 ms). (2) The effective RP of AVN was shorter than the functional RP of the atrium in most cases (16/18) at any BCL. (3) During rapid atrial pacing at cycle length of 140 ms in 7 cases, AVN maintained 1:1 conduction. (4) The atrioventricular nodal conduction curve was smooth at BCL from 200 to 700 ms. The present results suggest that AVN in the isolated perfused rabbit heart do not have the FP and any dual atrioventricular pathways in a physiological sense.

Animals↗

PubMed1995

Activation of Kupffer cells and neutrophils for reactive oxygen formation is responsible for endotoxin-enhanced liver injury after hepatic ischemia.

The potential role of reactive oxygen species generated by Kupffer cells and neutrophils was investigated in a model of endotoxin-enhanced liver injury after hepatic ischemia. Male Fischer rats were subjected to 20 min ischemia and reperfusion of up to 24 h; .5 mg/kg Salmonella enteritidis endotoxin was injected at 30 min of reperfusion. The animals developed severe liver injury resulting in 50% hepatocellular necrosis at 24 h. Isolated Kupffer cells and neutrophils from the postischemic liver generated 10-fold more superoxide than cells from control livers. Treatment with gadolinium chloride (GdCl3) selectively reduced the capacity of Kupffer cells to generate superoxide by 65% and attenuated liver injury by 73% at 4 h and 58-69% at 24 h. Monoclonal antibodies against neutrophil adhesion molecules (CD11/CD18) had no effect on the early injury but reduced hepatocellular necrosis by 90-95% at 24 h. The antioxidant Trolox and the iron-chelator deferoxamine attenuated liver injury by 71 and 80%, respectively. It is concluded that Kupffer cells are mainly responsible for the initial injury, and neutrophils are the dominant cytotoxic cell type during the later phase. Reactive oxygen generated by both cell types is critical for this pathogenesis.

Animals↗

PubMed1995

[Stability of refraction in post-operative two years of radial keratotomy].

In order to study the stability of the refraction after radial keratotomy, we took 123 cases (245) eyes who all had continuous follow-up records in two postoperative years to observe their dynamic changes. The mean preoperative spherical equivalent refraction was -6.74 D, and the mean keratometry was 44.32 D. The mean spherical equivalent refraction which was reduced after the surgery at one week, one month, three months, six months, one year and two years was 6.77 D, 5.74 D, 5.14 D, 5.09 D, 5.14 D and 5.27 D, respectively. The decrease of the spherical equivalent refraction in our cases showed that the maximum range of myopic drop was at one week after surgery. But the myopia obviously rose again in the postoperative three months. Statistical analyses showed that the differences between one week and one month and between one week and three months after surgery were significant (P < 0.01). There were little changes in the course of postoperative six months to two years, being not significant statistically (P > 0.05).

Follow-Up Studies↗

PubMed1994

Genetically modified keratinocytes transplanted to wounds reconstitute the epidermis.

Normal and retrovirally transfected keratinocyte suspensions expressing either the beta-galactosidase gene or the human growth hormone (hGH) gene were transplanted into chamber-enclosed skin full-thickness wounds of Yorkshire pigs. Immunostaining of sequential skin biopsies obtained for 4 weeks after transplantation showed survival of the transplanted keratinocytes as well as expression of beta-galactosidase. Transfected keratinocytes were first seen in the neodermal portions of the wounds, then in the regenerating basal epidermal layer, and finally in the terminally differentiating cells of the stratum spinosum. When keratinocytes transfected with the hGH gene were transplanted into similar wounds, hGH was detected for 10 days in wound fluid. In contrast, hGH was detected in vitro for 47 days. Wounds transplanted with either transfected or normal keratinocytes restored the epithelial barrier function significantly faster than nontransplanted controls (P < 0.05). The study confirms the successful transplantation of keratinocyte suspensions, their reconstitution of the epidermis, and their acceleration of repair. Further, this apparently normal incorporation of genetically engineered transplanted keratinocytes expressing either beta-galactosidase or hGH suggests the possibility of introducing other genes expressing therapeutic proteins into wounds to favorably affect healing. Wound fluid detection of the expressed peptide provided early demonstration of successful transfer of the hGH gene.

Animals↗

PubMed1994

Assignment of xeroderma pigmentosum group C (XPC) gene to chromosome 3p25.

The human gene XPC (formerly designated XPCC), which corrects the repair deficiency of xeroderma pigmentosum (XP) group C cells, was mapped to 3p25. A cDNA probe for Southern blot hybridization and diagnostic PCR analyses of hybrid clone panels informative for human chromosomes in general and portions of chromosome 3 in particular produced the initial results. Fluorescence in situ hybridization utilizing both a yeast artificial chromosome DNA containing the gene and XPC cDNA as probes provided verification and specific regional assignment. A conflicting assignment of XPC to chromosome 5 is discussed in light of inadequacies in the exclusive use of microcell-mediated chromosome transfer for gene mapping.

Animals↗

PubMed1994

Detection of fusion transcripts generated by the inversion 16 chromosome in acute myelogenous leukemia.

Pericentric inversion of chromosome 16 [inv(16)(p13q22)] and the related t(16;16)(p13;q22) are seen in a subset of acute myelogenous leukemia (AML) phenotypically and prognostically differing from other cases. We have recently shown that inv(16) results in fusion of CBFB/PEBP2B, a gene encoded at 16q22 to MYH11, a smooth muscle myosin heavy chain gene encoded at 16p13. Chimeric transcripts consisting of upstream CBFB fused to downstream MYH11 coding sequences result from this fusion. In this study we have examined a series of 37 of these cases using reverse transcriptase-polymerase chain reaction (RT-PCR) to detect expression of a hybrid CBFB/MYH11 transcript. Chimeric cDNAs were detected in all but 1 of 37 leukemias with typical inv(16) or t(16;16). Such chimeric products were not seen in a case with inv(16)(p13q24) (ie, a variant q arm breakpoint) or any of 10 cases of AML without these chromosomal changes. Four different chimeric transcripts were found, representing differing fusion points within MYH11 spliced to position 495 of CBFB. Primer sets are described for efficient amplification of these different cDNA forms. Amplification of cDNA showed that all but 17 codons of the CBFB coding sequence are included in the abnormal transcripts. RT-PCR was shown to be highly sensitive and potentially useful for detection of leukemic cells during morphologic remission.

Base Sequence↗

PubMed1994

Iron overload cardiomyopathies: new insights into an old disease.

Iron overload cardiomyopathy is an old disease that has evolved from a rare undiagnosable and untreatable condition to a now much more common, diagnosable, and potentially treatable condition. Pathologically it is due to a direct free iron effect on the myocytes, and not due to interstitial infiltration. This also implies that the disease process is reversible if the tissue iron concentration can be controlled. The advent of magnetic resonance imaging and future genetic identification can identify the population at risk. Chelation therapy, including newer forms of oral chelators, likely will be more commonly available to benefit an ever increasing number and spectrum of the population. Further active research will be needed to improve our pathophysiological understanding and clinical treatment of this increasingly common condition.

Cardiomyopathies↗

PubMed1994

Localized scleroderma: imaging features.

Localized scleroderma is distinct from the diffuse form of scleroderma and does not show Raynaud's phenomenon and visceral involvement. The imaging features in 23 patients ranging from 2 to 17 years of age (mean 11.1 years) were reviewed. Leg length discrepancy and muscle atrophy were the most common findings (five patients), with two patients also showing modelling deformity of the fibula. One patient with lower extremity involvement showed abnormal bone marrow signals on MR. Disabling joint contracture requiring orthopedic intervention was noted in one patient. In two patients with "en coup de sabre" facial deformity, CT and MR scans revealed intracranial calcifications and white matter abnormality in the ipsilateral frontal lobes, with one also showing migrational abnormality. In a third patient, CT revealed white matter abnormality in the ipsilateral parietal lobe. In one patient with progressive facial hemiatrophy, CT and MR scans showed the underlying hypoplastic left maxillary antrum and cheek. Imaging studies of areas of clinical concern revealed positive findings in half our patients.

Adolescent↗

PubMed1994

Congenital mesoblastic nephroma presenting with hemoperitoneum and shock.

We describe an unusual presentation of a congenital mesoblastic nephroma in a 5-month-old boy. He was in hemodynamic shock in admission. Sonography revealed an echogenic right kidney and hemoperitoneum. Right nephrectomy was performed, and he is well one year later without any further treatment.

Hemoperitoneum↗

PubMed1994

Activation of ras oncogene in livers with cirrhosis.

Activation of cellular oncogenes and inactivation of anti-oncogenes have been postulated as important mechanisms during hepatocarcinogenesis. This study was conducted to detect abnormal levels of several proto-oncogenes (c-jun, c-fos, c-H-ras) and of the p53 and the alpha-fetoprotein gene in the liver during cirrhosis, a pathological process which predisposes to the development of hepatocarcinoma. Liver tissue from 11 patients with cirrhosis of different etiologies, and seven histologically normal liver fragments taken at the periphery of benign liver tumors of metastases were studied. Transcripts of the various oncogenes and of the alpha-fetoprotein gene were detected by in situ hybridization, and the p53 protein was revealed by immunocytochemistry. No overexpression of any of the mRNA tested or of the p53 protein was found in histologically normal liver in contact with benign or metastatic tumors. In contrast, 10 of the 11 specimens with cirrhosis (90.9%) displayed abnormally high levels of c-H-ras transcripts. Five samples with cirrhosis revealed a moderate increase in the level of c-fos mRNA. Only one case and two cases, respectively, exhibited increased levels of c-jun and alpha-fetoprotein mRNA. No cases were positive for the p53 antigen. Liver-cell proliferation, as assessed by immunocytochemistry with the Ki 67 monoclonal antibody, was low in both the group with cirrhosis and the control groups (0.49% and 0.55% positive cells, respectively). These data demonstrate that activation of c-H-ras mRNA is an almost constant finding in hepatocytes of livers with cirrhosis. This gene overexpression is not linked to hepatocellular proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Division↗

PubMed1994

Transport of beta-estradiol in freshly excised human skin in vitro: diffusion and metabolism in each skin layer.

This paper describes an experimental and theoretical evaluation of beta-estradiol (E2) transport in post-surgery fresh human skin in vitro. Necessary auxiliary experimental methods were newly developed for these studies. The experimental fluxes of E2 and the metabolite, estrone (E1), using the dermis, stripped skin, and split-thickness skin were consistent with a model considering the human skin as a three-layer (stratum corneum, viable epidermis, and dermis) membrane with the enzyme activity mainly residing in the basal layer of the viable epidermis. The diffusion and metabolism parameters for each skin layer were determined in the overall transdermal transport of E2. Compared to fresh hairless mouse skin, fresh human skin appears more resistant to the stratum corneum diffusion of E2 and is much less capable of metabolizing E2 to E1. These in vitro results have been extrapolated to the possible in vivo human skin situation with blood vessels directly beneath the viable epidermis providing "sink" conditions a short distance from the dermo-epidermal junction. The model analysis has demonstrated that there would be less metabolism and that a much smaller amount of the transdermal metabolite (E1) would be taken up by the blood capillary due to the shorter dermis path length for permeants in vivo than in the in vitro case using dermatomed split-thickness skin.

Biological Transport↗

PubMed1994

A new phase function approximating to Mie scattering for radiative transport equations.

A new scattering phase function is presented to approximate the accurate phase function from Mie theory. The new phase function demonstrates much better agreement with Mie theory for biomedical media (with the mean cosine of scattering angles g > 0.8) than the Henyey-Greenstein phase function, which has been widely adopted by researchers in the biomedical optics field. Using the new phase function as the integral kernel in the radiative transport equation, an analytical result for the integral term of the equation is obtained for highly aligned beams. This may lead to a semi-analytical solution to the time-dependent radiative transport equation for time-resolved spectroscopy.

Algorithms↗

PubMed1994

An analysis of studies comparing electrical impedance tomography with x-ray videofluoroscopy in the assessment of swallowing.

Electrical impedance tomography can be used to record the conductivity change occurring in the neck during a swallow. X-ray videofluoroscopy provides excellent anatomical detail of the structures involved in swallowing and of the position of the swallowed bolus. The two techniques have been performed simultaneously on seven patients with swallowing problems to establish what produces the peak change in conductivity when a solution of low conductivity is swallowed. The results suggest that the exclusion of air from the larynx and pharynx is the major factor influencing the change in conductivity when a solution of low conductivity is swallowed.

Deglutition↗