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Biomedical subjects

H Miyahara

Publications and source records attributed to H Miyahara.

At least 91 records · Page 5Linked to original sources
PubMed1990

A mathematical model of atrioventricular conduction block using the excitability recovery curve of the myocardial cell.

A simple mathematical model of AV conduction block was constructed on the basis of single-cell electrophysiological experiments concerning the rate-dependent property of excitability of the AV nodal cells (the excitability recovery curve, ERC). This ERC was analogous to the phase response curve (PRC) of cardiac pacemaker cells, which the authors had previously used to construct a model of modulated parasystole. Computer simulation was used to reproduce the ERC. The single-cell ERC was then extended to the entire AV node, and this curve was used to formulate a mathematical model of AV conduction block as a nonlinear, first-order difference equation of the successive PR intervals of the ECG. This model predicted a variety of ECG patterns of AV conduction block: normal rhythm, first-degree block, and several second-degree blocks of complex Wenckebach periodicity in relation to the sinus rate and the shape of the ERC. By assuming this model it was possible to identify the underlying ERC of actual ECGs with complex Wenckebach periodicity.

Animals↗
PubMed1990

Morphological study of normal and tumor cells in the head and neck region using irradiated collagen gel embedding technique: morphological study using collagen gel.

Fourteen specimens of normal, benign, or malignant tumor cells from the head and neck region were subjected for culture using 0.2% of irradiated collagen gel embedding technique. Re-differentiation of glands within the gel in serum-free medium was observed. There were marked differences in the growth patterns within the gel between normal or benign and malignant cells. Four normal glands and 5 out of 6 benign tumors showed branch-like growth patterns. On the other hand, malignant tumors showed no branch-like pattern, or could not grow at all. The results showed that the collagen gel technique could be useful for the differential diagnosis of malignancy in head and neck tumors.

Cell Differentiation↗
PubMed1990

Two cases of pilomatrix carcinoma.

We report two cases of pilomatrix carcinoma. Wide surgical excision, radiation, and chemotherapy were required for the first patient. The tumor eventually revealed the characteristics of a carcinoma, both clinically and histopathologically, as it recurred. In the second case, although the tumor exhibited the histology of pilomatricoma in the central part of the lesion, there were numerous outgrowing irregular nests of basaloid tumor cells with cellular atypia and frequent mitoses; these are the characteristic features of the pilomatrix carcinoma in its early stages.

Adult↗
PubMed1990

Inhibition by FK506 of established lesions of collagen-induced arthritis in rats.

We investigated the superior potency of the immunosuppressive agent FK506 on collagen-induced arthritis in rats. In our initial studies, we demonstrated that only one shot administration of FK506 at a dose of 10 mg/kg on the same day as type II collagen immunization suppressed the incidence of arthritis completely as well as humoral and delayed-type hypersensitivity (DTH) skin test responses to type II collagen. Yet no major side effects were observed in the rats treated with such a high dose of FK506. Additional studies demonstrated that pretreatment with FK506 on day -7 or day -3 was effective in suppressing the severity of arthritis and immune responses to type II collagen. The immunosuppressive effect of a single high-dose administration of FK506 continued for at least 1 week in this animal model of arthritis. A single administration of FK506 at a dose of 10 mg/kg on day 12 or 15, after the clinical onset of arthritis, was also effective in suppressing the severity of arthritis and immune response to type II collagen. We conclude that FK506, in this model, possesses an important, curative action when applied therapeutically. The outlook of FK506 treatment in clinical autoimmunity is promising at present.

Animals↗
PubMed1990

[Three dimensional culture of human salivary gland using irradiated collagen gel embedding technique].

Embedding culture was performed on normal salivary gland cells from five subjects using 0.2% irradiated collagen gel. Collagen was collected from rat tail tendon and gelatinized at the final concentration of 0.2%. D-MEM added BSA (5mg/ml), insulin (10 micrograms/ml) and EGF (5 micrograms/ml) was used as a serum-free medium. Within the collagen gel, the cells were found to grow in a branch-like pattern, and then to form a lot of radial duct-like structures containing alcian blue positive secretions. Immunohistochemical observation of myoepithelial cells with monoclonal antibody from human mammalian cancer suggested that these cells play an important role in the process of glandular ducts formation. Salivary gland cells being able to grow in collagen gel in a very similar fashion to in-vivo condition, the present collagen gel embedding culture is useful for morphological or functional studies on salivary gland cells.

Animals↗
PubMed1990

[Multiple primary malignancies in patients with head and neck cancer].

From July, 1978 to December, 1985, 1,138 cases of malignancies of the head and neck were treated at the authors' hospital, and up to June, 1986, 132 patients with multiple primary malignancies were detected. In all cases, the incidence rate of a multiple primary malignancy was 11.6%. In 45 (33.0%) of these head and neck cancer cases, the multiple cancer was detected simultaneously, and as for the other cases (66.7%), they were discovered metachronously. In patients with a cancer of the mesopharynx, the incidence rate of a multiple primary malignancy was the highest (25.8%), whereas in those with a cancer of the parotid gland and in those with a cancer of the hypopharynx, the incidence rates were 20.0% and 14.9%, respectively. In most patients the second malignancy occurred in the same head and neck region, and in the rest, the second malignancy was a gastric cancer, a lung cancer, or an esophageal cancer in that descending order. Of the 45 synchronous cancer cases, ten were a thyroid cancer, most being latent. In head and neck malignancies, the authors stress the importance of a precise investigation prior to start of therapy and of maintaining follow-up investigations after therapy.

Adult↗
PubMed1989

[Clinical analysis of supraglottic cancer].

We treated 159 cases of supraglottic cancer including 53 cases of transglottic type from July, 1978 to December, 1984. The mean age was 65 years and man to woman ratio was fifth. Of those patients 15 were classified as T1, 36 as T2, 56 as T3 and 52 as T4 and 113 as N0, 22 as N1, 14 as N2 and 10 as N3. Stage classifications were stage I in 13, stage II in 21, stage III in 50 and stage IV in 75. Treatment modalities were divided radiation in 25, operation only in 105, pre-or post-operative radiation in 29. Multiple primary malignancies were detected in 18 cases (11.3%). Until December, 1986, 52 patients died. Cause of death were original cancer (33 cases, 63.5%), additional malignancies (5 cases, 9.6%), intercurrent disease (12 cases, 23.1%) and others. Deaths of original cancer were attributable to the metastasis to the cervical lymph node and/or distant metastasis, mainly to the lung. Metastatic lymph nodes at the initial treatment were found in 66.7% of patients who died of supraglottic and/or transglottic cancer. In order to improve survival rates, early diagnosis and radical dissection of positive lymph nodes are seemed to be important.

Aged↗
PubMed1989

Inhibitory actions of adenosine differ between ear and mesenteric arteries in the rabbit.

In isolated ear and mesenteric arteries of rabbit, adenosine inhibited nerve-mediated contractions to a similar extent. However, the amplitude of the excitatory junction potentials evoked by perivascular nerve stimulation was increased by adenosine in the ear artery and decreased in the mesenteric artery. Outflows of noradrenaline and its metabolite, 3,4-dihydroxyphenylglycol, evoked by perivascular nerve stimulation were increased and decreased by adenosine in the ear and mesenteric arteries, respectively. Adenosine hyperpolarized the smooth muscle cells, by increasing potassium conductance of the membrane, with no relation to the endothelial cells. The hyperpolarizing action of adenosine was stronger in the ear artery than in the mesenteric artery. The inhibition of the nerve-mediated contraction by adenosine may be mainly due to postjunctional events in the ear artery and prejunctional events in the mesenteric artery.

Action Potentials↗
PubMed1989

A computer-based model of parasystolic activity modulated by ventricular activation in the open-chest dog.

The modulated parasystole hypothesis proposed by Moe has been suggested as a common mechanism of a wide variety of arrhythmias. To represent the arrhythmic patterns defined by the model as an actual ECG trace, a "hybrid" experimental system was devised. The system consisted of the intact canine heart connected to a microcomputer that operated as the modulated parasystolic pacemaker. An intrinsic cycle length of the "ectopic" pacemaker was modulated by the phase-dependent effect of the activity of the intact heart in situ. Discharges in the "ectopic" pacemaker were transmitted to the right ventricle. The result was that the theoretically defined patterns of the ectopic activity were represented as real ECG traces. Some published examples of intermittent parasystole that had been attributed to other complex mechanisms were accurately reproduced when the estimated phase response curves were set in the "ectopic" pacemaker. A wide variety of clinical eCG tracings of ventricular arrhythmias may be reproduced by this hybrid experimental model.

Animals↗
PubMed1989

Limb allografts in rats immunosuppressed with FK506. I. Reversal of rejection and indefinite survival.

We have tested the effects of FK506 (FK), a new immunosuppressive agent, on a rat limb allograft model. Histoincompatible BN limb allografts were rejected in untreated F344 hosts within 11 +/- 1 days (mean +/- SD) after operation. A single injection of 2 mg/kg, 10 mg/kg, or 50 mg/kg of FK on the day of limb transplantation (day 0) significantly prolonged graft survival in a dose-dependent manner--i.e., mean limb survival times (MST) based on gross signs of skin rejection were 16 +/- 3 days, 51 +/- 6 days, or 104 +/- 17 days, respectively (P less than 0.01). Delayed treatment with a single injection of 10 mg/kg of FK at when early signs of rejection were visible (day 7 or day 10) reversed the ongoing rejection. The MSTs in these groups were comparable to that of those treated with the same dosage of FK on day 0. The FK-induced unresponsiveness toward limb allografts was donor-specific because limb-allografted. FK-protected rats could not accept the skin grafts from a third-party donor. In the next set of experiments, rats were given a single administration of 10 mg/kg of FK on the day of limb allograft, followed by intermittent injections of 3 mg/kg of FK once a week. This regimen produced complete graft survival for more than 200 days, though Pneumocystis carinii pneumonia occurred in most of the recipients. These results represent the unique effects of FK in preventing or reversing the graft rejection and in inducing indefinite survival in this animal model of composite tissue allografts.

Animals↗
PubMed1989

Reentrant arrhythmias generated by a computer-based model of the modulated parasystole in an open-chest dog.

It has been demonstrated that parasystolic activity of a linear Purkinje bundle can be converted into a form of reentry, termed reflections, as a function of changes in electrotonic interactions between two active segments separated by an inexcitable gap. In this study, we attempted to reproduce arrhythmic patterns based upon the reflection mechanism by utilizing a hybrid experimental model of modulated parasystole. The experimental system consisted of the intact heart of a dog connected to a computer, which operated as an ectopic focus. The "ectopic" discharges were shifted by the phase-dependent effects of the input ventricular activation of the heart and were transmitted to the ventricle with a conduction delay in the circuit. A high level of the electrotonic influence was incorporated in the "ectopic" focus by programming a phase response curve with dominant acceleratory phase. The focus was repeatedly captured and reset by the ventricular activation over a wide range of basic heart rates. This preparation produced heart rate-dependent changes in arrhythmias defined by the reflection model. Appropriate conduction delays in the simulated exit pathway allowed the focus to be captured by the activity that it initiated. This process of reciprocation generated a ventricular tachycardia, which could be either induced or terminated by a timed premature beat. Thus, arrhythmias of reentrant type, including reciprocating tachycardia, can be produced by a computer-based model of the modulated parasystole.

Animals↗
PubMed1989

[Local control after radiation therapy for T1N0M0 glottic carcinoma].

From 1978 through 1984, we had 151 patients with T1N0M0 glottic carcinoma. They were treated by radiotherapy with 4MV x-ray in parallel opposing field of 5 X 5 cm2 or 6 X 6 cm2. The total dose was 60 Gy/30 fractions/6 weeks. The local control rate was 88.1%, the local recurrence being noted in 18 cases (11.9%). Of these 18 cases, 6 underwent partial laryngectomy, and 10 total laryngectomy. The remaining two cases died: one refused further treatment for recurrence and the other died in spite of total laryngectomy due to recurrence after partial laryngectomy. The salvage rate was 94.1%. The cumulative survival rate was 82.6% in Tla, 71.5% in Tlb and 81.1% in 151 T1N0. The tumor response was poor in the presence of lesion occupying the whole length of the vocal cord. Also, in the cases with ulcer formation or thickened vocal cord as seen on laryngogram, local control rate was not good. Better results will be achieved by improving treatment techniques, specially by improving dose-distribution by wedge-filtered technique and method for immobilization in plastic shell during radio-therapy.

Adult↗
PubMed1989

Prolonged limb allograft survival with short-term treatment with FK-506 in rats.

The effect of the new immunosuppressive agent FK-506 on rat limb allograft was investigated across the BN-to-F344 histocompatibility barrier. A 14-day course of FK-treatment at doses of 1 mg/kg per day or more, begun on the day of operation, significantly increased the period of graft survival. Additional studies demonstrated that single treatment with FK only on the day of operation prolonged the graft survival in a dose-dependent manner. These results stress the profound immunosuppressive effect of FK and suggest the possible future application of composite tissue allograft in humans.

Animals↗