bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Mechanisms Responsible for Lack of Reproducible Induction of Atrioventricular Nodal Reentrant Tachycardia
Authors: ADA STRICKBERGER S. , DAOUD EMILE G. , NIEBAUER MARK J. , HASSE CAROL , MAN K. CHIN , MORADY FRED 
Published: May 2007

Lack of AVNRT Induction. Introduction: AV nodal reentrant tachycardia (AVNRT) is not always reproducibly inducible. The purpose of this study was to determine the mechanisms responsible for the lack of reproducible induction of AVNRT. Methods and Results: The induction of AVNRT was assessed with atrial burst pacing, and with atrial and ventricular programmed stimulation, each with one and two extrastimuli, in 103 patients with AVNRT. The stimulation protocol was repeated 10 times in the baseline state, during isoproterenol infusion, and after atropine administration, or until AVNRT was induced in 7 of 10 attempts. The mechanisms responsible for < 7 of 10 inductions were classified as: (1) the inability to achieve critical AH prolongation; (2) fast pathway block; and (3) slow pathway block. The induction endpoint was achieved in 90 patients: 55 in the baseline state, 34 during isoproterenol infusion, and 1 after atropine. Tbe mechanism of noninducibility in the baseline state (n = 48) was the inability to achieve a critical AH interval in 20%, fast pathway block in 49%, and slow pathway block in 31% (P = 0.02). During isoproterenol administration (n = 14) and after atropine administration (n = 13), the three mechanisms were equally responsible for nonreproducible induction of AVNRT. Conclusions: The induction of AVNRT is poorly reproducible in approximately 10% of patients. In the baseline state, the most common reason for the inability to reproducibly induce AVNRT is fast pathway block. In the presence of isoproterenol or atropine, each of the three mechanisms was equally responsible for noninducibility of AVNRT.
Effect of Graded Increases in Parasympathetic Tone on Heart Rate Variability
Authors: GOLDBERGER JEFFREY J. , KIM YOU‐HO , AHMED MIRZA W. , KADISH ALAN H. 
Published: May 2007

Parasympathetic Effects on Heart Rate Variability. Introduction: Time‐ and frequency‐domain measurements of heart rate variability have been used as indices of parasympathetic tone. However, studies of the effect of parasympathetic stimulation on these indices in humans have yielded conflicting results. Methods and Results: This study evaluated the effects of parasympathetic stimulation on heart rate variability. Twelve normal subjects (7 males, 5 females; age 24.8 ± 3.4 years) were evaluated in the Clinical Research Center. Five‐minute ECG recordings were obtained at baseline and during graded phenylephrine infusions (0.3 and 0.6 μg/kg per min). Recordings were made during spontaneous respiration and when breathing was timed with a metronome at 15 cycles/min. Heart rate variability analysis was performed using standard time‐ and frequency‐domain parameters. Graded phenylephrine infusion resulted in a progressive increase in blood pressure and RR interval but no consistent changes in heart rate variability for the group. The results during normal versus metronome breathing were similar. Stepwise linear regression analysis revealed that the phenylephrine‐induced changes in heart rate variability were inversely correlated with the baseline heart rate variability and not related to the baseline KR interval or the phenylephrine‐induced change in RR interval. Conclusion: These findings suggest that the respiratory variation in “parasympathetic effect” typically observed at the sinus node can be either increased or decreased by parasympathetic stimulation, depending on the initial level of parasympathetic tone and the intensity of stimulation. This resolves the previously conflicting data. Thus, evaluation of parasympathetic tone using heart rate variability techniques should be cautiously undertaken.
Pathological Findings Following Slow Pathway Ablation for AV Nodal Reentrant Tachycardia
Authors: OLGIN JEFFREY E. , URSELL PHILIP , KAO ANN K. , LESH MICHAEL D. 
Published: May 2007

Pathology of Slow Pathway Ablation. Introduction: AV nodal reentrant tachycardia is routinely cured using radiofrequency catheter ablation techniques. However, there remains controversy as to whether the reentrant circuit for this tachycardia exists solely in the AV node or whether perinodal atrial tissues are vital to the circuit. In addition, the effects of radiofrequency ablation of the slow pathway of AV nodal reentrant tachycardia on the AV node are not known. We examined an autopsy specimen to determine the anatomical location and extent of AV nodal damage of radiofrequency slow pathway ablation for cure of AV nodal reentrant tachycardia. Methods and Results: A 64‐year‐old woman with confirmed AV nodal reentrant tachycardia underwent a successful “slow pathway” AV modification with a single radiofrequency application. Five months after the procedure, the patient died from a spontaneous intracranial hemorrhage. Postmortem gross pathological examination of the heart was performed. The heart was then sectioned and stained for histologic examination. On gross examination, a pale lesion 0.5 cm in diameter was seen on the endocardial surface adjacent to the tricuspid annulus. approximately 0.85 cm anterior to the coronary sinus os and 1.15 cm from the apex of the triangle of Koch where the AV node resides. Histologic examination revealed a right atrial lesion composed of connective tissue and fat. The compact AV node and surrounding transitional cells were unaffected histologically, with normal atrial cells lying between the AV node and the lesion. Conclusion: Ablation of the slow pathway to cure AV nodal reentrant tachycardia does not produce any gross or histologic damage to the AV node, suggesting that the AV nodal reentrant circuit does not exist in its entirety in the AV node.
Unusual Resetting Patterns in Response to Single Atrial Extrastimuli During AV Junctional Reentrant Tachycardia
Authors: TRITTO MASSIMO , CALABRESE PIETRO 
Published: May 2007

Unusual Resetting Patterns in AV Junctional Reentry. Introduction: Two unusual resetting patterns were observed in two patients with slow‐fast AV junctional reentrant tachycardia (AVJRT) submitted to an electrophysiologic study. Methods and Results: After AVJRT induction, resetting was evaluated by introducing single extrastimuli at progressively shorter coupling intervals from the high right atrium (HRA) and the proximal coronary sinus (CS). An alteration in the return cycle length duration allowed demonstration of resetting. In the first patient, during an AVJRT with a large excitable gap, properly timed extrastimuli delivered both from the HRA and CS simultaneously reset the tachycardia and advanced the H electrogram of the preceding tachycardia beat. In the second patient, both HRA and CS stimulation apparently failed to reset AVJRT (return cycle length unchanged), but, at critical coupling intervals, the cycle length duration of the tachycardia beat following the return cycle was consistently shortened. Conclusions: During slow‐fast AVJRT, single atrial stimulation from sites remote to the reentrant circuit may result in unusual resetting patterns. Further studies are required to evidence the full spectrum of resetting in AVJRT.
Unequal Atrial Stretch in dogs Increases Dispersion of Refractoriness Conducive to developing Atrial Fibrillation
Authors: SATOH TAKASHI , ZIPES DOUGLAS P. 
Published: May 2007

Atrial Stretch Precipitates Atrial Fibrillation. Introduction: We have shown previously that acute atrial dilation prolonged atrial refractoriness. We hypothesized that this increase in refractoriness might be heterogeneous and could create an electrophysiologic substrate leading to atrial fibrillation. The purpose of the present study was to test that hypothesis. Methods and Results: We studied 23 anesthetized open chest dogs. Bipolar plunge electrodes were placed in the medial free wall of the right atrium (thin region) and in the lower crista terminalis of the right atrium (thick region). Two bipolar plunge electrodes were also placed in the left ventricular apex to stimulate and record. Atrial effective refractory period (ERP) was measured in a group of nine dogs using the atrial extrastimulus method (A1A2) in two ways: during atrial pacing (AP) and during simultaneous atrioventricular (AV) pacing that achieved an AV interval of 0 msec (AV = 0). One liter/hour of normal saline was infused intravenously to elevate right atrial pressure and produce right atrial stretch. Atrial ERPs were measured before and after the normal saline infusion. To compare the extent of atrial stretch produced by volume overload, two pairs of sonomicrometer transducers were implanted in the thick and thin regions in a separate group of six dogs. The area encompassed by sonomicrometers was measured before and after saline infusion. The inducibility of atrial fibrillation was compared before and after saline infusion using rapid AP in another group of five dogs. Atrial pressure during sinus rhythm increased from 5.1 ± 0.96 mmHg to 6.3 ± 0.93 mmHg after normal saline infusion (P < 0.01). ERP increased in the thin free wall from 151 ± 14.3 to 172 ± 14.7 msec (AV = 0), and from 149 ± 12.0 to 170 ± 14.3 msec (AP). ERP increased in the thick crista terminalis from 134 ± 9.9 to 147 ± 10.2 msec (AV = 0), and from 133 ± 7.9 to 146 ± 9.8 msec (AP) (P < 0.01). The increase in ERP in the thin free wall exceeded that in the thick crista terminalis (P < 0.01), increasing the dispersion of atrial ERP. After 500‐mL saline infusion for 30 minutes, the increase of area in the thin region was 12.8%± 3.7%, and that in the thick was 3.5%± 3.2%. The increase of the area in the thin region after 1000 mL for 1 hour was 18.8%± 6.2%. and that in the thick region was 6.3%± 5.1% (P < 0.01). Atrial fibrillation was not induced in any dog before saline infusion, hut induced in all five dogs after saline infusion. Conclusions: Atrial ERP in the thin right atrial free wall exceeds the ERP of the thick cristaterminalis, and an increase in atrial pressure produced by saline infusion exaggerates this ditterence by stretching thin segments of the atrial myocardium more than it stretches thick regions. Thus, atrial stretch, by increasing the dispersion of atrial ERP, may be conducive to the development of atrial fibrillation.
Leucocytozoon in the Avian Order Columbiformes, with a Description of L. marchouxi Mathis and Leǵer 1910 from the Mourning Dove
Authors: LEVINE NORMAN D. 
Published: May 2007

Leucocytozoon marchouxi is described from the mourning dove, Zenaidura macroura carolinensis in Illinois. The macrogametocytes are rounded or elliptical, measuring 7 to 11 by 8 to 15 microns (mean, 9 by 12 microns), and stain dark blue with Giemsa stain. The microgametocytes are often distorted or ruptured by the smearing process, but if not badly injured measure 5 to 11 by 8 to 15 microns, (mean, 8 by 11 microns). They stain pale blue with Giemsa stain. Host cell cytoplasm is rarely seen surrounding the microgametocytes, but was found in 26% of cells parasitized by the macrogametocytes. When present it forms a narrow border around part or all of the parasite's periphery, and is not drawn out to form elongate “horns.”The parasite was found in ten birds, of which five were adults, one was a juvenile, and four were nestlings. The infections were relatively light in the adults. The youngest bird in which the protozoon was found was 14 days old.The literature on Leucocytozoon in the avian order Columbiformes is reviewed. All forms with rounded gametocytes so far reported are considered to be L. marchouxi Mathis and Leger, 1910, of which L. turtur Covaleda Ortega and Gallego Berenguer, 1946, is considered a synonym.
The Opalinid Infusorians: Flagellates or Ciliates?
Authors: CORLISS JOHN O. 
Published: May 2007

SUMMARY. The controversial question of the affinities of the enigmatic opalinids is discussed in the light of recent findings and with regard for modern ideas concerning characters of most significance in the phylogeny of various major protozoan groups. Metcalf's “protociliate” hypothesis still retains a high popularity although many of the factors supporting it have been adequately disproven during the past 20 years. The “ciliate‐” and “flagellate‐like” characteristics of the Opalinidae are listed and reviewed.Considered to be one of the most significant of mastigophoran features is the “symmetrigenic” mode of fission, a character generally disregarded in the past. Coupled with nuclear monomorphism and a syngamous reproductive cycle the type of division presents a very strong argument in favor of closer affinities with the zooflagellates than with the ciliates. It is stressed that the opalinids are highly differentiated forms, not likely primitive or ancestral for any major group of protozoa, which have had a long evolutionary history of their own. Grassé's recent erection of a new super‐order in the Zoomastigophora to contain the family Opalinidae is defended and commended.
The Activity of Primaquine‐Pyrimethamine (Daraprim®) Combinations Against Plasmodium relictum in Pigeons
Authors: Parra Galo Soberon y , Reyes Rodolfo Perez 
Published: May 2007

SUMMARY. As part of an extended series of experiments, various combinations of primaquine‐pyrimethamine were tested against pigeons infected with Plasmodium relictum.(a) Rapid clearance of blood forms was observed, although each component had been reduced to one‐half of its previously established MED (minimal effective dose) for such clearance when administered alone.(b) Primaquine‐pyrimethamine was followed by unprecedented delays in relapse after drug withdrawal. Such delays had not been elicited in any previous experiments in the series, employing each component alone, or chloroquine alone, or primaquine‐chloroquine combinations, or pamaquine‐plasmocid‐chloroquine (Premaline N).
Protozoa of Amazonian and Andean Waters of Colombia, South America
Authors: Bovee Eugene C. 
Published: May 2007

SUMMARY. A survey of protozoa in four water samples from Colombia, South America, yielded 84 species identifiable to genus or to species. Three of the collections were from the Amazon River and a tributary in the vicinity of Leticia, at the southern tip of the country. The fourth was taken near the high Andean town of Medellin in central Colombia.All four subphyla are represented. Forty ciliophorans, 26 mastigophorans, 17‐sarcodinians, and one sporozoan are included. Of the ciliophorans all but one are euciliates in three orders. The exception is a suctorean. Two classes, and six orders of mastigophorans are represented; one class, and two orders of sarcodinians; and one class, one subclass, and one order of sporozoans. Eleven suborders, 33 families, and 49 genera are exemplified.Other protozoa seen, but not identified to generic or specific accuracy, are omitted.
A Species of Tetrahymena Parasitic in the Renal Organ of the Slug Deroceras reticulatum
Authors: Kozloff Eugene N. 
Published: May 2007

SUMMARY. A ciliate found in the renal organ of the gray garden slug, Deroceras reticulatum, is referred to Tetrahymena (Paraglaucoma) rostrata (Kahl). In the parasitic phase, the ciliate is evidently not histiophagic. It is readily cultivated in bacterized tissue infusions, and has been established in axenic culture in yeast extract.The number of complete primary ciliary meridians in ciliates of the parasitic phase has been observed to range from 41 to 58; in ciliates from cultures, the number of meridians has been observed to range from 28 to 37. In culture, the form of T. rostrata from D. reticulatum appears to be morphologically identical with a strain (NZ‐4) recovered from soil in New Zealand.
Types and Life Cycles of Centrioles of Flagellates
Authors: Cleveland L. R. 
Published: May 2007

SUMMARY. Two centrioles, an old one and a new one, are always present in the resting cell. From prophase onward two new ones and two old ones are present. Beginning with the resting stage, five types of centriole life cycles are described and compared with one another: In type 1, both centrioles are elongate; in type 2, the old one is long and the new one, which is short, elongates in prophase; in type 3, both are short, both elongate in prophase, and both, except for their anterior tips, degenerate in late telophase; in type 4, both are long but in prophase their distal ends become free of the rest of the centrioles, these ends migrate to center or posterior end of cell, where, after they produce the achromatic figure and it completes its function in nuclear division, they degenerate; in type 5, both are short and neither elongates at any stage of its life cycle.New centrioles are produced by the anterior ends of old ones. In their first generation, centrioles produce only extranuclear organelles (flagella, parabasals, axostyles, etc.); in their second and later generations, they produce only the achromatic figure (gametogenesis in Trichonympha and reorganization in Barbulanympha and Rhynchonympha are exceptions to this rule).The distal ends of centrioles in some types of cycles are surrounded by centrosomes; in others they are not. In one type of centriole life cycle a small central spindle is present in the resting cell in two genera; in the other types this is not the case.
Relation between Multiplication Rate and Temperature in Tetrahymena pyriformis, Strains HS and GL
Authors: Prescott David M. 
Published: May 2007

SUMMARY. The multiplication rate of Tetrahymena pyriformis HS in proteose peptone medium was measured at 12 temperatures between 18.4°C. and 36.6°C. At the temperature optimum, 32.5°C., the generation time is 2.25 hours. The upper lethal temperature lies between 36.6°C. and 38.0°C. Similarly, a study of Tetrahymena pyriformis GL revealed a temperature optimum for multiplication of 29°C. with a generation time of 3.70 hours. The upper lethal temperature falls between 34.6°C. and 35.4°C. At all temperatures employed the HS strain of organisms multiplies more rapidly than strain GL. Under identical conditions, the two strains have distinctly different growth optima, upper lethal temperatures and growth rates.As measured by multiplication rate the readjustment to a sudden change in temperature (from 18.4°C. to 27.7°C.) is completed very rapidly, with an effective lag time of about 1 hour. Such a shift in temperature gives rise to a small degree of division synchrony during the first and second population doublings which follow. Subsequently, all traces of division synchrony are lost.
Le Cortex de la Vacuole Contractile et son Ultrastructure chez les Ciliés
Authors: ROUILLER E. FAURÉ‐FREMIET et CH. 
Published: May 2007

SYNOPSIS. In various ciliates the contractile vacuole is a permanent organelle, delimited by a differentiated cortex.The cortex is made up of a dense reticulum of anastomosing tubules limited by a smooth membrane, and vesicles. This “spongiome” can be considered as a localized and specialized condensation of the endoplasmic reticulum.
Susceptibility and Resistance of Avian and Mosquito Hosts to Strains of Plasmodium relictum Isolated from Pigeons*
Authors: HUFF CLAY G. , MARCHBANK DOROTHY F. , SHIROISHI TSUGIYE 
Published: May 2007

SYNOPSIS. Two strains (1B and 1P) of Plasmodium relictum isolated from pigeons could be easily passed serially in pigeons by transfer of infected blood. What appeared at first to be a qualitative difference between the infectiousness of gametocytes of strain 1P in pigeons and of gametocytes of the strain after being adapted to canaries (1P1) was found to be only a quantitative difference in their infectivity for mosquitoes. Earlier work had indicated that gametocytes of strain 1P were noninfectious for mosquitoes. The experiments reported here show that Culex tarsalis is highly susceptible to gametocytes of both strains 1B and1P and that Culex pipiens is slightly susceptible to gametocytes of strain 1P.The susceptibility of 72 pigeons (belonging to 24 varieties, plus mongrels and 3 species hybrids) to sporozoites of strain 1P1 was tested; only 5 transient infections lasting no more than two days and 3 subpatent infections were obtained. Similar results were obtained with sporozoites of strain 1B.The two strains are similar in both mosquito and avian hosts except that 1B is more highly infectious for C. pipiens and C. tarsalis than 1P. There is evidence that one or both of these strains may be Plasmodium relictum matutinum, Huff(7). A proposed hypothesis indicates that (1) various species of mosquitoes have different susceptibilities, (2) various species of avian hosts are infectious to different degrees, and (3) that the probability of a mosquito of a given species being infected from a given species of parasite may be expressed by the degree of overlap between the normal curves of susceptibility of the mosquito and infectiousness of the gametocytes in the pertinent avian host. The susceptibilities of pigeons to sporozoites of the two strains of parasites and of mosquitoes to gametocytes produced in pigeons are so low that it can be questioned whether these strains could persist in nature without the presence of other avian hosts on the one hand possessing greater susceptibility than the pigeon to sporozoites and on the other hand contributing more to the infectiousness of the gametocytes than the pigeon does.
Further Nutritional Requirements of Paramecium aurelia
Authors: TARANTOLA V. A. , van WAGTENDONK W. J. 
Published: May 2007

SYNOPSIS. An acetone‐insoluble yeast fraction required for axenic growth of P. aurelia, stock 51, variety 4, sensitive, after fractionation contained at least 3 essential components: (1) one soluble in perchloric acid and completely replaceable by a mixture of ribosides or ribotides; (2) one inactivated after digestion with trypsin, chymotrypsin or papain. Proteose‐Peptone restored activity to this preparation, which suggests a peptide requirement; and (3) one not yet characterized.As for the purine and pyrimidines, these combinations, in decreasing order of activity, supported growth: guanosine + cytidine, guanosine + uridine, guanylic acid + cytidylic acid, and guanylic acid + uridylic acid. Each combination was maximally effective when the molar purine: pyrimidine ratio was ∼ 0.4. On a molar basis, the minimal riboside combinations were ∼ 1.3 × more active than the ribotides.Sparing of the purine and pyrimidine requirement was also investigated. In the presence of limiting amounts of guanylic acid, the following compounds, in decreasing order of activity, had sparing activity: deoxyguanosine, inosine, xanthosine, adenylic acid, and guanine. Adenine, adenosine, and deoxyadenosine were inhibitory under the test conditions. The requirement for cytidylic acid was spared by deoxycytidine, uridine, uridylic acid, deoxyuridine, thymidine, thymine, and uracil, in descending order.