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Biomedical subjects

J Davis

Publications and source records attributed to J Davis.

At least 397 records · Page 22Linked to original sources
PubMed1986

Use-dependent effects of lidocaine on conduction in canine myocardium: application of the modulated receptor hypothesis in vivo.

Lidocaine is a commonly used antiarrhythmic drug that causes use-dependent blockade of sodium channels in vitro and reduces conduction velocity in vitro and in vivo. According to the modulated receptor hypothesis of antiarrhythmic drug action, lidocaine has a low affinity for rested sodium channels but a high affinity for open and inactivated channels. In the present experiments, we characterized use-dependent conduction slowing and recovery from slowing by lidocaine in anesthetized dogs. The His-to-ventricular conduction interval was used as the indicator of conduction velocity. We found that prolongation of conduction time was greater as the stimulation frequency was increased. Moreover, on abruptly changing the stimulation frequency, a new steady-state conduction time was approached in two to three depolarizations. On discontinuation of stimulation, the conduction time of progressively less premature extrastimuli shortened exponentially with a terminal phase time constant of 152 +/- 115 msec. These effects by lidocaine were enhanced during acidosis and enhancement was reversed by correction of the acidosis. It is concluded that the effects in vivo of lidocaine on conduction under several conditions of rate, rhythm, and pH are similar to its effects on the maximum upstroke velocity of the action potential in vitro. Although these experiments were not designed to validate the modulated receptor hypothesis, it appears that the modulated receptor hypothesis can predict the effects of lidocaine on conduction in vivo.

Animals↗
PubMed1986

Ablation of cardiac tissues by an electrode catheter technique for treatment of ectopic supraventricular tachycardia in adults.

Five patients with chronic or recurrent ectopic supraventricular tachycardias unresponsive to drugs underwent programmed stimulation, endocardial mapping, and attempted catheter ablation of the arrhythmia focus. For attempted ablation, an intracardiac electrode catheter was positioned near the exit point of the tachycardia and served as the cathode while a chest wall patch served as the anode. In two patients with tachycardia originating near the coronary sinus, discharges of 200 or 400 J each were delivered to two electrodes at the earliest area of endocardial activation. These two patients with incessant tachycardia remain free of tachycardia for 17 and 11 months, respectively. In one patient with tachycardia originating from the right atrial appendage, both catheter and surgical ablation proved unsuccessful in that a new focus of atrial tachycardia supervened. This patient subsequently underwent successful catheter ablation of the atrioventricular junction. Two patients with junctional tachycardia underwent catheter ablation of the atrioventricular junction. Complete atrioventricular block followed atrioventricular junctional ablation and these patients required permanent cardiac pacing. The junctional tachycardia was replaced by sinus rhythm with episodes of unsustained atrial tachycardia. However, after 13 +/- 5 months follow-up, neither of the patients require antiarrhythmic drugs. Catheter ablation can be effective for atrial foci near the coronary sinus os, and can be performed with preservation of atrioventricular conduction. Arrhythmia ablation is possible in those with atrioventricular junctional tachycardia but requires the sacrifice of atrioventricular conduction. After ablation, other automatic atrial foci may become operative and complicate use of dual-chamber pacemakers.

Adolescent↗
PubMed1986

Non-Hodgkin's lymphoma after treatment of Hodgkin's disease: association with Epstein-Barr virus.

Non-Hodgkin's lymphoma occurs infrequently as a late complication of obscure cause after treatment of Hodgkin's disease. We investigated the possible role of Epstein-Barr virus in the pathogenesis of such secondary malignancies of B-cell lineage. Two patients, aged 25 and 43 years, developed high-grade non-Hodgkin's lymphomas 12 and 8 years after radiation therapy for Hodgkin's disease. Serologic profiles in these patients showed evidence of acute and past Epstein-Barr virus infections, respectively. Molecular hybridization analysis showed the presence of multiple cellular equivalents of virus genome in tumor specimens from each patient. Our findings suggest that Epstein-Barr virus may play an integral role in the pathogenesis of non-Hodgkin's lymphoma of B-cell lineage that develops after treatment of Hodgkin's disease.

Adolescent↗
PubMed1986

Anti-DNA antibodies react with DNA expressed on the surface of monocytes and B lymphocytes.

It is becoming increasingly apparent that nuclear antigens can be expressed on the surfaces of certain cells. We provide evidence that anti-DNA antibodies are reactive with DNA on the surface of monocytes and B lymphocytes. The DNA isolated from monocytes sedimented in a 17.8S position, corresponding to a molecular weight of 4.6 X 10(6); it was mainly double-stranded with many short single stranded regions. In one patient with active systemic lupus erythematosus experiments indicated that anti-DNA antibodies had interacted in vivo with the cell surface DNA on monocytes. The functional significance, if any, of these findings remains to be determined.

Antigen-Antibody Reactions↗
PubMed1986

Genital rhabdomyosarcoma: current management and review of the literature.

Rhabdomyosarcoma is the most common soft tissue sarcoma in childhood and 20 per cent of these cancers involve the pelvis or genitourinary system. Radical pelvic surgery, such as exenteration, was considered at one time to be the standard treatment for this cancer which carried a very poor prognosis. Over the past 15 years, a combined modality approach to treating rhabdomyosarcoma, using chemotherapy, radiotherapy, and less radical surgery, has evolved and survival rates have improved. This paper presents a case of rhabdomyosarcoma involving the perineum which was treated by combination chemotherapy of Vincristine, Actinomycin-D, and Cytoxan, followed by wide local excision, interstitial and external beam radiotherapy, and postoperative chemotherapy. The literature on pelvic rhabdomyosarcoma is reviewed and the current approach to treating this cancer using multimodal therapy is discussed.

Adolescent↗
PubMed1985

A method for determination of antibody-dependent cellular cytotoxicity (ADCC) of human peripheral mononuclear cells.

A method is described for measuring antibody-dependent cellular cytotoxicity (ADCC) of mononuclear cells from human peripheral blood using an established murine cell line and commercially prepared antisera. The test utilizes a standard 51Cr release technique. The ADCC activity of mononuclear cells obtained from 10 healthy human volunteers was measured at 4 different effector: target cell ratios. A linear relationship between %51Cr release (ADCC) and the number of effector cells was observed.

Animals↗
PubMed1985

Characterization of west nile virus persistent infections in genetically resistant and susceptible mouse cells. II. Generation of temperature-sensitive mutants.

Long-term persistent infections were established with the flavivirus, West Nile virus (WNV), strain E101, in embryofibroblast cultures derived from susceptible C3H/HE and congenic-resistant C3H/RV mice. Cultures were initially maintained by weekly subculture at 37 degrees, but at passage 6 sister cultures were shifted to 32 degrees. Virus progeny titers were observed to increase after the shift to 32 degrees indicating the possible presence of temperature-sensitive mutants. Temperature-sensitive mutants were found to arise in cultures of both susceptible and resistant cells. However, only in the resistant cultures did temperature-sensitive virus become the majority population. Temperature-sensitive mutants did not appear to be essential for either initiation or maintenance of WNV-persistant infections. The resistant cells appear to provide an environment which is advantageous for the amplification of temperature-sensitive mutants.

Animals↗
PubMed1985

Meeting community service needs of discharged psychiatric patients.

There is a growing recognition that the chronically mentally ill are a heterogeneous population with a multiplicity and diversity of needs. But inadequate information concerning the extent of the population service needs and the degree to which aftercare services meets these needs has contributed to the minimization of the problem. This article reports on the extent to which aftercare services meets the needs of discharged patients. Most discharged patients had a need for basic maintenance aftercare services such as individual counseling, chemotherapy, and financial assistance. However, there was also a high need for more rehabilitative services such as socialization services, social and vocational rehabilitation, and supportive residential services. Although almost half had their basic service needs met by aftercare services, few had their rehabilitative ones met.

Adolescent↗
PubMed1985

Comparative monocular contributions to brightness in relation to abnormal stereothreshold.

This study was designed to compare brightness contributions of the two monocular inputs to the binocular visual system at three different levels of luminance adaptation in two groups of 15 subjects each. The only known difference between these groups was stereothreshold, 50 to 70 sec arc in one group vs. 40 sec arc or less in the other group. The group with elevated threshold was found to have a significantly larger average difference (13.5%, p less than 0.002) in monocular brightness contributions, between the right and left eyes, when compared to the group with lower stereothresholds (4% mismatch). The results also indicate that neither group showed a significant variation in mismatch as adapting luminance was altered by a factor of four times (0.6 log units). Finally, no clear relation was found between eye dominance and the eye requiring higher illuminance to attain the dichoptic brightness match.

Depth Perception↗