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J Nitta

Publications and source records attributed to J Nitta.

61 records · Page 4Linked to original sources
PubMed1983

Measurements of erythrocyte flow velocity by means of grating laser microscope.

The possibility of measuring erythrocyte flow velocity by means of grating laser microscope has been examined in an in vitro test using erythrocytes smeared on glass plates and in vivo using microvessels in the web of a frog foot. Magnified projections of flowing erythrocytes are spatially filtered by a simple glass plate grating and then detected by a photomultiplier. Output signals from the photomultiplier are first electronically filtered so as to yield oscillating burst-like wave signals. Moving erythrocytes resulted in burst-like oscillation in output signals whose wave period (T) changed with their velocities. These results suggest that the velocity (V) of erythrocytes could be given by V = d/MT, where d and M represent the grating constant and the optical magnification, respectively. The requirement for the establishment of this relation was examined by the microscopic observation of smeared erythrocyte preparation. It was shown that the flow velocity of erythrocyte could be measured even when the size of magnified images of erythrocytes strongly exceeded the value of d and even when many erythrocytes existed. A preliminary experiment to confirm the possibility of methodological adaptation was made by measuring the flow velocity in venules of foot web of frogs. Heart rate increased in all six frogs studied when the frog body was warmed. However, the peripheral flow velocity increased only in three frogs, while it remained almost unaffected in the other three. This result suggests that the frog peripheral microcirculation is affected by complicated intrinsic factors.

Animals↗
PubMed1982

White blood cell adhesion to endothelium and rheological behavior in microvessels of overinflated frog's lung.

The flow behaviors of white blood cells (WBCs) in frog's pulmonary microvessels were recorded and analyzed by means of a microscope-TV camera system. When the flow velocity in arterioles was reduced to a level lower than 1 mm/sec by a moderate overinflation of the exposed lung, WBCs rolled on the endothelial surface, frequently came in contact with the capillary orifice and passed it quickly without deformation. The time length which was required for WBCs to pass through the capillary orifice was shorter than the time length for red blood cells. This observation suggested that WBCs were no hinderance to blood delivery from arterioles to the capillary network in the normal and moderate overinflation of the lung. However, when the lung was strongly overinflated and the center line flow velocity was reduced to 0.1 mm/sec, WBCs adhered to the endothelium in ten minutes. The adhering WBCs could not be detached by the recovery of the blood flow. It seemed probable that a large shear stress up to 100 to 200 dynes/cm2 was necessary to pull down the interaction between the adhering WBCs and the endothelium.

Animals↗
PubMedDate not supplied

Role of proximal electrode position in transvenous ventricular defibrillation.

Transvenous defibrillation lead systems have been demonstrated to reduce operative morbidity and mortality associated with implantation of cardioverter-defibrillators. To determine the best position for the proximal electrode in transvenous systems, defibrillation thresholds were compared for three positions in a single-pathway, two-lead system. Two defibrillation lead electrodes were transvenously inserted into seven dogs. The distal electrode was positioned in the right ventricular apex. The proximal electrode was randomized to one of three positions: (1) the superior (cranial) vena cava (SVC) at the junction of the right atrium, (2) the left innominate vein at the junction of the SVC, or (3) the external jugular vein. Biphasic defibrillation thresholds for converting electrically induced ventricular fibrillation were determined for the three positions of the proximal electrode in each dog. The innominate vein position resulted in the lowest defibrillation threshold (555 +/- 123 V) as compared to the SVC (640 +/- 126 V; p = 0.0612) and the jugular vein (709 +/- 117 V; p = 0.0013). Lead impedance gradually increased with increasing distance between the two shocking electrodes: 58.4 +/- 11.4 omega for SVC, 76.2 +/- 13.8 omega for innominate vein, and 94.9 +/- 10.2 omega for jugular vein proximal lead electrode position (p < 0.05 for all pairwise comparisons). In two-electrode transvenous defibrillation lead systems, positioning the proximal electrode in the left innominate vein produced the lowest defibrillation threshold.

Animals↗
PubMedDate not supplied

Long-term follow-up of heart transplant recipients requiring permanent pacemakers.

BACKGROUND: Permanent pacemaker implantation after heart transplantation is contentious. Indications for these devices in this population are uncertain. The goals of this project were to (1) analyze the time course of donor sinus node dysfunction and atrioventricular block after heart transplantation; (2) evaluate which selected parameters (donor age, ischemic time, heart rate before pacer insertion, and number of rejection episodes) might relate to persistent permanent pacing need, and (3) assess pacemaker complications during follow-up. METHODS: A retrospective analysis of pacemaker implantations (22 cases) was performed in 286 consecutive heart transplantations performed between February 1984 and April 1994 at The Methodist Hospital and Baylor College of Medicine, Houston, Texas. RESULTS: Permanent pacemakers were inserted early after transplantation in 19 patients (mean 24 days); 14 pacemakers were for sinus node dysfunction (bradycardia in five, sinus arrest with junctional escape in eight, and optimization of hemodynamics in one). Symptomatic complete heart block prompted insertion late in two patients (3 and 47 months), and symptomatic sinus pause was the indication for late insertion in one. Recipient mean age was 52.4 years, with mean donor age 29.7 years in patients with pacemakers. By 3 months, 13 of 19 patients receiving pacemakers early (mean preinsertion heart rate 58.3 beats/min) became pacer independent with subsequent mean intrinsic heart rate of 97 beats/min. Recipient or donor age, ischemic time, and rejection episodes did not appear related to long-term pacing need early or late after transplantation. CONCLUSIONS: Inferences from these observations include the fact that many patients with early sinus node dysfunction and bradycardia are not pacer dependent at 3 months. However, those with atrioventricular block early appear to require long-term pacing support. However, the possibility that more aggressive and long-term oral chronotropic medication use after transplantation would obviate early permanent pacemaker need is not addressed. Finally, prospective clinical trials are necessary to precisely characterize benefit of permanent pacemakers and define optimal pacing modes after heart transplantation.

Adult↗