In this thesis an attempt has been made to try to dissect out the relative importance of atrial natriuretic peptides (ANP) and the renin-angiotensin-aldosterone system in the control of sodium balance in normal man. At the same time the thesis examines the relevance of ANP in the pathophysiology of essential hypertension and cardiac transplantation and the potential therapeutic value of manipulating the ANP system. The studies described in this thesis were important in suggesting a dominant role of suppression of the renin-angiotensin-aldosterone system in permitting excretion of short term increases in intravenous or oral sodium intake. The permissive effects of suppression of angiotensin II or aldosterone for the excretion of an intravenous sodium load showed clear time differences, with suppression of angiotensin II important immediately but the response to suppression of aldosterone delayed. In contrast, there appears to be only a transient role for changes in circulating levels of ANP in the response to an intravenous sodium load and little evidence that changes in ANP release are important in responding to acute increases in dietary sodium intake in normal subjects. However, the sensing mechanism for ANP release is clearly activated by sustained changes in dietary sodium intake. Studies of prolonged dietary sodium alteration in normal subjects clear evidence for a role of ANP in the medium term regulation of sodium balance and further dietary studies suggested an important role for the ANP system in pathophysiology in essential hypertension and in cardiac transplant recipients.

No description available.

Rapid compensatory reach-to-grasp reactions are prevalent and functionally important responses to instability. The need to react very rapidly (to prevent falling) imposes temporal constraints on acquisition and processing of the visuospatial information (VSI) needed to guide the reaching movement. Previous results suggested that the CNS may deal with these constraints by using VSI stored in memory proactively, prior to perturbation-onset; however, the extent to which online visual control is necessary or sufficient to guide these reactions has not been established. Furthermore, the influence of memory-decay and concurrent cognitive-task on the performance of these reactions has not been examined. This Thesis employed a novel paradigm wherein the participant is stationary and a motor-driven handhold is positioned unpredictably in front of the participant for each trial. Reach-to-grasp reactions were evoked in healthy young and older adults by sudden unpredictable antero-posterior platform translation (barriers deterred stepping reactions). Liquid-crystal goggles were used to occlude vision either before (recall-delay time=0s/2s/5s/10s) or after perturbation-onset to force reliance on either stored- or online-VSI, respectively. Participants performed a spatial- or non-spatial-memory task during the delay-time in a subset of trials. When forced to rely on stored-VSI, all participants showed reduction in reach accuracy; however, a tendency to undershoot the handhold was exacerbated in the older adults. Forced-reliance on online-VSI led to similar delays in all participants; however, the older adults were more likely to reach with the “wrong” arm or raise both arms. Comparison with normal-VSI trials suggests that both sources of VSI are utilized when grasping the movable handhold for support, with stored-VSI predominating during initiation/transport and online-VSI contributing primarily to final target acquisition/prehension. In terms of recall-delay, both age groups showed comparable reduction in medio-lateral endpoint accuracy when delay-time was longest. Moreover, both cognitive tasks had similar (slowing) effects in both age-groups, suggesting these effects were related to generic attentional demands. However, the older-adults also showed a dual-task interference effect (poorer cognitive-task performance) that was specific to the spatial-memory-task. Further research is needed to establish whether interventions aimed to improve visual/cognitive processing speed, visuospatial memory, and/or attention capacity can reduce risk of falling among senior populations.

Individuals with stroke suffer from impaired balance that increases their risk of falling. Controlling reactive balance is essential to maintaining stability. The objective of the first study was to identify the role of pre-perturbation stance asymmetry on limb preference for reactive stepping in healthy young adults. This study demonstrated that steps taken with a pre-loaded limb are short, directed laterally and have a rapid swing time. The objective of the second study was to investigate the challenges of reactive stepping among individuals with stroke. This study demonstrated that participants primarily execute reactive stepping with their non-paretic limb, although those steps are highlighted by delays in timing and increased incidence of multiple stepping compared to healthy controls, even though all participants had very good clinical balance scores. Outcomes from this thesis present the need for improved clinical assessment of reactive balance control to help reduce the incidence of falling following stroke.

Individuals with stroke suffer from impaired balance that increases their risk of falling. Controlling reactive balance is essential to maintaining stability. The objective of the first study was to identify the role of pre-perturbation stance asymmetry on limb preference for reactive stepping in healthy young adults. This study demonstrated that steps taken with a pre-loaded limb are short, directed laterally and have a rapid swing time. The objective of the second study was to investigate the challenges of reactive stepping among individuals with stroke. This study demonstrated that participants primarily execute reactive stepping with their non-paretic limb, although those steps are highlighted by delays in timing and increased incidence of multiple stepping compared to healthy controls, even though all participants had very good clinical balance scores. Outcomes from this thesis present the need for improved clinical assessment of reactive balance control to help reduce the incidence of falling following stroke.

Compensatory balance reactions impose tight temporal constraints to motor responses employed to re–capture stability. Vision is particularly important for compensatory reach–to–grasp reactions as locations of hand hold targets have varying inherent features and locations in 3D space, requiring precise motor commands in order to successfully contact the target. Internalizing a representation of the surrounding environment by creating a visuospatial map is possible means of circumventing temporal lags associated with using online visual feedback when performing compensatory reactions. Hand hold targets are often located in the peripheral visual field. This suggests an importance of mapping from the peripheral visual field and further suggests mapping of peripherally located targets may require the allocation of attentional resources in order to correctly encode their location. The purpose of this thesis was to examine the contribution of peripheral vision and associated attentional requirements of visuospatial mapping for rapid upper limb movements. Study 1 was designed to examine the influence of mapping with peripheral vision for compensatory reach–to–grasp reactions, specifically the influence of timing and location of visual information. Study 2 was designed to examine the potential effect a secondary visual attention task would have on mapping peripheral located targets prior to movement initiation. Overall the results from these studies show support for the ability to map peripherally located targets with peripheral visual feedback, and suggest that this mapping may be an automatic process. Findings from this thesis provide a basic insight into the incorporation of peripheral visual information into intrinsic visuospatial maps that provides a framework for future experiments into the understanding of how visuospatial maps are incorporated into compensatory balance reactions.

Thesis (M.A. in Security Studies)--Naval Postgraduate School, June 2008. / Thesis Advisor(s): Kadhim, Abbas ; Russell, James. "June 2008." Description based on title screen as viewed on August 29, 2008. Includes bibliographical references (p. 93-101). Also available in print.

Thesis (doctoral)--Albert-Ludwigs-Universität Freiburg im Breisgau, 1934. / Includes bibliographical references (p. [61]).

Issued also as thesis, Utrecht.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1957. / Typescript. Abstracted in Dissertation abstracts, v. 17 (1957) no. 7, p. 1484-1485. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [250]-256).