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Biomedical subjects

D Carroll

Publications and source records attributed to D Carroll.

At least 235 records · Page 13Linked to original sources
PubMed1979

Heart rate changes with exercise and voluntary heart rate acceleration.

The present study examined the relationship between heart rate (HR) changes accompanying isometric and isotonic exercises and HR changes during attempted voluntary HR acceleration. Substantial cardiac accelerations accompanied both types of exertion, with the isotonic exercise attracting the larger magnitude HR changes. Significant HR increases were also observed during attempted voluntary HR acceleration both with and without feedback; however, feedback prompted larger HR increases than instructions alone. The HR changes accompanying both types of exercise reliably predicted the extent of voluntary HR increase but only for the condition in which feedback was available. This occurred in spite of the absence of observable EMG changes during attempted HR acceleration. Changes in respiration rate during voluntary HR increase were highly correlated with changes in HR. A similar co-variation occurred with the isotonic exercise but was absent with the isometric exercise. The results are discussed in terms of the possible mediational mechanisms underlying voluntary HR acceleration.

Adult↗
PubMed1979

Individual differences in visual imaging and the voluntary control of heart rate.

The role of visual imagery in the bidirectional control of heart rate (HR) was explored in 24 subjects. While voluntary HR increases were reliably demonstrated with and without HR feedback, appropriate HR decreases were modest and inconsistent. Changes in respiration rate (RR) generally paralleled the alterations in HR. Eighteen of the subjects reported conventionally using visual imagery to effect HR changes. For these subjects, vividness of visual imagery scores and the extent of HR change showed indications of a direct relationship in the HR increase condition. However, in the HR decrease condition, it was concomitant RR changes which were associated with the vividness and the control of imagery production. The remaining six subjects, who reported not employing visual imagery, demonstrated superior HR acceleration to the imaging subjects. Further, while the imaging subjects did not benefit from the introduction of feedback, the six non-imaging subjects showed reliably greater HR acceleration as a result of feedback introduction.

Adolescent↗
PubMed1978

The behavioural significance of heart rate: the Laceys' hypothesis.

The Laceys' account of the significance of heart rate changes for behaviour is critically evaluated. Two interwoven propositions are discerned in their account: first, the cardiac variations regulate central attentional activities via an afferent feedback mechanism; second, that environmental intake-rejection comprises a basic dimension underlying directional cardiac changes. Examination of pertinent psychophysiological research reveals that the first of these propositions lacks substantive support. The intra-cardiac cycle method has yielded highly equivocal results. Inter-cardiac cycle studies offer only modest correlational support and the two studies which have directly manipulated heart rate found that sensori-motor performance was largely unaffected. Difficulties also surround the other proposition. Consideration of the verbalization, pleasantness-unpleasantness and time estimation studies indicates that the relationship between heart rate and attention is variable and that heart rate is associated with factors other than attentional requirements. While the Laceys have attempted to reconcile such unfavourable evidence, conceptual clarity is frequently sacrificed in the process. It is concluded that the interpretation of cardiac responses must be sought in superordinate variables that account for both heart rate changes that can be related to attention and those that cannot, and that any afferent feedback mechanism, based on heart rate, most likely fulfills functions other than that proposed by the Laceys.

Aorta↗
PubMed1978

Resistance of visna virus to interferon.

Visna is a slow infection of sheep caused by a retrovirus. The persistence of virus despite the immune response of the host is best explained by restricted genetic expression of the virus and consequently prolonged periods of residence inside cells. The purpose of this investigation was to determine whether the restriction in genetic expression of visna virus is mediated by interferon. Sheep interferon induced by polyriboinosinic-polyribocytidylic acid in fetal lambs inhibited the growth of herpes simplex virus, vesicular stomatitis virus, and vaccinia virus, but even highly concentrated interferon did not affect the replication of visna virus in sheep choroid plexus cells. The same results were obtained whether the effects of interferon were assessed in single of multiple cycles of growth and when interferon was added at later times in the growth cycle of the virus. This unusual resistance of visna virus to interferon suggests that restriction of viral expression by the host is probably not mediated in this way.

Animals↗
PubMed1977

Cardiac perception and cardiac control. A review.

The evidence regarding specific cardiac perception and discrimination, and its relationship to voluntary cardiac control, is critically reviewed. Studies are considered in three sections, depending on the method used to assess cardiac perception: questionnaire assessment, discrimination procedures, and heartbeat tracking. The heartbeat tracking procedure would appear to suffer least from interpretative difficulties. Recommendations are made regarding the style of analysis used to assess heartbeat perception in such tracking tasks.

Autonomic Nervous System↗
PubMed1976

Repeating units of Xenopus laevis oocyte-type 5S DNA are heterogeneous in length.

The restriction enzymes Hind III and Hae III cleave Xenopus laevis 5S DNA at one and three sites, respectively, in each repeating unit of approximately 700 base pairs. The cleavage sites for both enzymes have been located within the repeating unit by denaturation mapping of the restriction fragments. The Hind III products and one of the Hae III fragments are variable in length, indicating heterogeneity in the length of the repeating unit in 5S DNA. This length heterogeneity is confined to the major A + T-rich spacer region. Repeating units differ from each other by discrete quanta of approximately 15 base pairs. The A + T-rich spacer has been shown to consist largely of tandem subrepeats of just this size (Brownlee, Cartwright, and Brown, 1974). We suggest that the repeat-length heterogeneity is due to variable numbers of these subrepeats in the spacer regions of the major repeating units.

Adenine↗