Biomedical subjects

N Obayashi

Publications and source records attributed to N Obayashi.

15 recordsLinked to original sources

PubMed1994

Role of endothelium-derived nitric oxide and adenosine in functional myocardial hyperemia.

To investigate the role of endothelium-derived nitric oxide (EDNO) and adenosine in functional myocardial hyperemia, we examined the effect of NG-nitro-L-arginine (L-NNA) and 8-p-sulfophenyltheophylline (8-SPT) on coronary vasodilation in response to increased myocardial oxygen consumption in pentobarbital sodium-anesthetized dogs. L-NNA significantly attenuated the increase in coronary conductance from 28 +/- 6 to 16 +/- 2% with atrial pacing, from 69 +/- 5 to 36 +/- 6% with isoproterenol, and from 25 +/- 6 to 9 +/- 4% with constriction of the aorta. 8-SPT given alone attenuated the increase in coronary conductance to the same extent as L-NNA. The combined administration of L-NNA and 8-SPT did not further change coronary conductance. These findings suggest that EDNO and adenosine play an important role in functional hyperemia. EDNO-induced functional hyperemia appears to be dependent on adenosine receptor activation.

Adenosine↗

PubMed1994

Effects of nipradilol on venous hemodynamics: evaluation with a Doppler blood flow method.

Nipradilol is a newly synthesized beta-blocker which has a propranolol-like structure and contains a nitrate moiety. To examine the effect of nipradilol on venous blood flow, a single oral dose of nipradilol (6 mg) and propranolol (20 mg) was administered in the same 15 normal volunteers on separate days. Peak flow velocities, flow velocity integrals, and the diameter of the right brachiocephalic vein were measured before and 2 h after drug administration using Doppler echocardiography. These two beta-blockers significantly decreased systolic blood pressure to the same extent as they did heart rate. Nipradilol dilated the venous diameter by 8% and decreased peak flow velocity by 8% during systole and 9% during diastole. The flow velocity integral in one cardiac cycle also decreased significantly by 14%. Propranolol, however, failed to modify these parameters. These results suggest that nipradilol decreased venous return through its nitroglycerin-like direct vasodilating action.

Adult↗

PubMed1993

Morning increase in hemodynamic response to exercise in patients with angina pectoris.

The present study was conducted to determine whether or not there is diurnal variation in the hemodynamic responses to stimuli that increase myocardial oxygen demand, and the effects of such variation on electrocardiograms (ECG). Fifteen patients with angina pectoris, 17 patients with old myocardial infarction, and 8 healthy controls were examined in this study. Graded exercise stress testing was conducted in the supine position, once in the morning and once in the afternoon, using a bicycle ergometer. A standard 12-lead ECG was recorded before, immediately after, and 3, 5, and 10 min after the end of the exercise. The exercise ECG and blood pressure changes were compared among the groups and, within each group, the results after morning and afternoon exercise were compared. Hemodynamic responses, including heart rate, blood pressure, and the pressure-rate product, showed greater increases in the morning than in the afternoon in angina patients and controls, in association with greater depression of the electrocardiographic ST-segment. In contrast, patients with old myocardial infarction exhibited no difference in hemodynamic responses or the ST-pattern from morning to afternoon. The results suggest that diurnal variation of hemodynamic responses to increased oxygen demand may explain, at least partly, why myocardial ischemia of effort angina is more severe in the morning than in the afternoon.

Adult↗

PubMed1993

Effects of oral theophylline on sick sinus syndrome.

OBJECTIVES: We sought to determine the effect of theophylline on cardiac pauses in sick sinus syndrome. BACKGROUND: Sick sinus syndrome, a relatively benign condition, is usually treated with pacemaker implantation without any proved effectiveness. Thus, an appropriate pharmacologic therapy would be useful. METHODS: Theophylline (200 to 400 mg/day for 1 month) was initially administered orally to 17 patients with sick sinus syndrome, which is manifested by sinus pauses of > 2.5 s. Eleven of the 17 patients subsequently received theophylline for an additional 8 to 37 months. Twenty-four-hour Holter recordings were obtained before treatment, at the end of 1 month of treatment and then at 6-month intervals. RESULTS: Theophylline decreased the frequency of sinus pauses from 256 +/- 230 to 23 +/- 62 pauses per 24 h and decreased the duration of the longest pauses from 4.7 +/- 1.8 to 2.2 +/- 0.97 s after 1 month of treatment. Subjective symptoms associated with cardiac pauses disappeared in 16 of 17 patients. Ventricular premature beats increased in frequency but did not last longer than two beats. Three patients experienced adverse effects. Nine of the 11 patients receiving long-term treatment had a good outcome, but 2 patients required a pacemaker because of the reappearance of long sinus pauses. CONCLUSIONS: The results suggest that oral theophylline may be beneficial for the treatment of patients with sick sinus syndrome.

Administration, Oral↗

PubMed1993

Relationship between pressure-rate product and myocardial oxygen consumption of normal and hypertrophic right ventricles in open-chest dogs.

There are few reports on the relationship between right ventricular performance and its myocardial oxygen consumption (RVMVO2). The present study was conducted to investigate the relationship between RVMVO2 and the mechanical performance of normal and hypertrophic right ventricles in open-chest dogs. Right ventricular hypertrophy (RVH) was induced by producing chronic right ventricular pressure overload by banding the pulmonary arteries of 8 puppies for 6 months. The experiment was performed under basal conditions and after increasing the RVMVO2 in the eight dogs with RVH as well as in 20 normal dogs. The RVMVO2 showed significant positive relationships with right coronary (RCA) flow, right ventricular systolic pressure, and right ventricular pressure-rate product (PRP) in both the normal right ventricle and RVH hearts. However, the slope between the PRP and RVMVO2 was significantly steeper in the normal right ventricle (RV) than in the hypertrophic RV. When the PRP was normalized for the thickness of the right ventricular free wall, the slope of the two regression lines merged into a single line of fit. These results suggest that the pressure-rate product can be used to predict myocardial oxygen demand not only in the normal RV but also in well-compensated, hypertrophic RV. Isoproterenol induced smaller increases in cardiac output in the dogs with RVH than in those with normal RV. It also appears that the cardiac output of the hypertrophic RV is less sensitive to beta-adrenoceptor stimulation than that of the normal RV.

Animals↗

PubMed1993

Effects of inosine on adenosine-induced coronary vasodilation in the open chest dog.

The effects of inosine (CAS 58-63-9) on adenosine-induced coronary vasodilation were studied in open-chest dogs. Inosine and hypoxanthine were infused into the coronary artery at a rate to obtain respective calculated coronary plasma concentrations of 10(-5) mol/l, and the dose-coronary flow response of adenosine was recorded with and without inosine or hypoxanthine infusion. When the maximum coronary dilation was obtained, 10 ml of 2 x 10(-3) mol/l 8-phenyltheophylline (8-PT) solution was injected into the femoral vein. Additionally, adenosine deaminase activity was measured in vitro in the presence of various concentrations of either inosine or hypoxanthine. It was found that inosine, but not hypoxanthine, intensified the coronary vasodilatory effect of adenosine, which was abolished by 8-PT injection: EC50 of adenosine was reduced from 10(-5.43) mol/l to 10(-5.90) mol/l by inosine. Inosine and hypoxanthine did not affect adenosine deaminase activity at concentrations of 10(-4) mol/l or less. These findings indicate that inosine intensifies the coronary vasoactivity of adenosine, independent of inhibition of adenosine deaminase activity.

Adenosine↗

PubMed1993

[A case of an idiopathic enlargement of the right atrium, lacking in prominent right atrium contour and mimicking left pericardial defect on the chest X ray].

A 47-year-old man was admitted for evaluation of heart murmur in 1982. On admission, two-dimensional echocardiogram showed a giant right atrium with mild tricuspid regurgitation, but a chest X ray showed no prominent right atrium contour. Echocardiographic finding at various postures and chest X ray with artificial pneumothorax indicated little likelihood of left pericardial defect. An angiocardiogram and computed tomography showed the dilated right atrium with clockwise rotation. There was no indication of right atrial overload. Therefore, we made the diagnosis of an idiopathic enlargement of the right atrium. For about 10 years after discharge, we have followed up this patient. He has received no treatment and has been asymptomatic. On the other hand, echocardiography shows that the right atrium has gradually enlarged. Electrocardiogram has clearly revealed only a tall and slender peaked P wave in chest leads for the last 5 years. This may indicate not only an increasing load on the right atrium but also that the enlarged atrium is getting closer to the walls of the chest. We report this case of an idiopathic enlargement of the right atrium lacking in prominent right atrium contour, and mimicking left pericardial defect on chest X ray.

Cardiomegaly↗

PubMed1992

Papillary fibroelastoma in the left ventricular outflow tract.

We report a case of a papillary fibroelastoma originating from the left ventricular endocardium in the outflow tract which was discovered by echocardiography in an asymptomatic patient. Two echocardiographic features were observed: (1) the tumor surface was smooth, and characteristic papillary formation was not detected; and (2) the outline of the mass was clearly defined as a dense echo, with the central, radiolucent, portion surrounded by a highly refractive linear echo at the level of the maximum diameter of the mass. The excised tumor was covered with a gelatinous substance that masked multiple papillae on the surface, but its echolucent center could not be explained by the pathology of the tumor which was solid centrally. Our case indicates that a papillary fibroelastoma may sometimes show echocardiographic findings similar to those of a myxoma, although other investigators have not noted the smooth surface and the echolucent center makes it indistinguishable from a myxoma. Thus, in some cases, it is difficult to distinguish papillary fibroelastoma from myxoma by echocardiography.

Connective Tissue↗

PubMed1992

Fractal dimensions of ductal patterns in the parotid glands of normal subjects and patients with Sjögren syndrome.

RATIONALE AND OBJECTIVES: The sialographic ductal patterns of the parotid glands in patients with Sjögren syndrome were compared with those of normal patients by measuring the fractal dimensions. METHODS: Fractal dimensions were estimated using the modified pixel dilation method. RESULTS: The mean fractal dimension was 1.64 +/- 0.06 for the normal glands and 1.39 +/- 0.10 for the glands with Sjögren syndrome (P < .005). No correlation between the age or sex and fractal dimension was observed for both groups. In Sjögren syndrome, a significant difference in the fractal dimension was observed between the subgroup having punctuate fillings with a diameter less than 1 mm and the subgroup from 1 to 2 mm (P < .001). CONCLUSION: The fractal dimension is useful as a numeric grading of the complexity of the ductal pattern and the progression of parotid disease.

Adult↗

PubMed1991

Interaction between adenosine and beta-adrenoceptors.

Interaction between adenosine and isoproterenol (ISP) on myocardial inotropic action was studied in open-chest dog hearts. The local myocardial force and the left ventricular (LV) dP/dt were measured as indices of myocardial contractility. Isoproterenol [ISP, 9.47 microM (2 micrograms/ml)] was infused into the left circumflex coronary artery at rates of 0.05 ml/min (low dose ISP) or 0.2 ml/min (high dose ISP). Two mM adenosine or 0.5 mM N6-phenylisopropyl-adenosine (PIA) were infused into the coronary artery at rates of 0.2 (4 x 10(-7) mol/min), 0.5 (1 x 10(-6) mol/min) and 10 ml/min (2 x 10(-5) mol/min) in the presence of either a low or a high dose of ISP. Adenosine infusion at a rate of 0.2 ml/min did not modify myocardial contractility in the presence of the both doses of ISP. The larger doses of adenosine, 0.5 ml/min and 10 ml/min, decreased myocardial-developed tension and LVmax dP/dt dose-dependently. However, the dose of adenosine which affected myocardial contractility was inphysiologically high in comparison with the concentration in the ischemic myocardium. PIA, a potent agonist of adenosine A1-receptor, attenuated an increase in myocardial contractility in a dose-dependent manner which was caused by intracoronary ISP infusion. This indicates that A1-adenosine receptors exist, but a functional adenosine-catecholamine antagonism does not play a significant role in the canine left ventricle.

Adenosine↗

PubMed1985