18 research outputs found
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Acute cardiovascular responses to slow and deep breathing
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonSlow and deep breathing (SDB) has long been regarded as a nonpharmacological method for dealing with several physiological and emotional imbalances, and widely used for relaxation purposes. There is, however, limited understanding of the putative mechanisms by which SDB acutely impacts the cardiovascular and autonomic systems to elicit chronic adaptations. The present thesis explored how the manipulation of breathing pattern and intrathoracic pressure during SDB could further the understanding of the regulatory mechanisms that underpin the acute cardiovascular response to SDB. This thesis makes an original contribution to the existing knowledge by reporting a previously undescribed inversion of normal within-breath (inspiration vs. expiration) left ventricular stroke volume (LVSV) pattern for breathing frequencies < 8 breaths∙min-1. This finding might reflect the influence of a lag between enhanced right atrial filling and right ventricular stroke volume during inspiration, and its expression in left ventricular stroke volume; this lag results from the time required for blood to transit the pulmonary circulation. Furthermore, blood pressure variability (BPV) was reduced significantly at the lowest breathing frequencies, likely due to the involvement of baroreflex mediated responses. The pattern of responses was consistent with the buffering of respiratory-driven fluctuations in left ventricular cardiac output (Q̇) and arterial blood pressure (ABP) by within breath fluctuations in heart rate (fc), i.e., respiratory sinus arrhythmia (RSA) (Chapter 4). Chapter 5 demonstrated that magnifying negative intrathoracic pressure with inspiratory loading during SDB increased inspiratory pressure-driven fluctuations in LVSV and fc, and enhanced Q̇, independently of changes in VT and fR. The data support an important contribution to the amplification of RSA, during SDB, of previously underappreciated reflex, and/or ‘myogenic’, cardiac response mechanisms. The findings in Chapter 6 confirmed that inspiratory loading during SDB amplified the effects observed with un-loaded SDB (reported in chapter 5). In contrast, expiratory loading increased ABP and attenuated RSA, LVSV and Q̇ during SDB. A lower RSA for higher ABP, supports the presence of a formerly underappreciated contribution of sinoatrial node stretch to RSA, and throws into question the clinical benefits of expiratory resisted SDB, particularly in hypertensive populations. In conclusion, the findings of the present thesis provide novel information regarding the mechanisms contributing to acute cardiovascular response to SDB. These new insights may contribute to the development of more effective SDB interventions, geared towards maximising the perturbation to the cardiovascular control systems
Interactions between sympathetic baroreflex sensitivity and vascular transduction in males and females
The control of muscle sympathetic nerve activity (MSNA) via the baroreflex is an important mechanism of blood pressure control. Spontaneous sympathetic baroreflex sensitivity (BRS) is a tool used to examine how well the baroreflex buffers beat-to-beat changes in arterial pressure. Due to the lack of research around the baroreflex control of MSNA, it is unknown if an individual's sympathetic BRS reflects the end organ response and thus is indicative of how effective they are at regulating their blood pressure. It was hypothesised that poor baroreflex sensitivity was compensated for by enhanced vascular transduction, and vice versa. Given that sex differences are known to exist in regulatory mechanisms involved in cardiovascular control, these interactions were explored and contrasted in young males and females. In order to further our understanding of the regulatory mechanism of the sympathetic baroreflex, MSNA, blood pressure and superficial femoral artery (SFA) blood flow were measured to i) examine the stability and repeatability of measures of spontaneous sympathetic BRS, ii) examine whether vascular transduction, quantified on a beat-to-beat basis using two different approaches, were different between males and females, iii) examine the relationship between sympathetic BRS and vascular transduction, and iv) examine sympathetic BRS and vascular transduction during physiological stressors that drive increases in MSNA. Here I present evidence of sex differences in sympathetic baroreflex function in healthy young adults. Spontaneous sympathetic BRS was moderately stable in the same recording period and also when examined on different days. Recording periods of at least 5 min should be used when quantifying BRS as shorter durations can overestimate BRS values. Using the Fairfax method, sympathetic vascular transduction was significantly lower in males when compared with females. In contrast, the Briant method did not reveal sex differences in vascular transduction between males and females. Sympathetic BRS and vascular transduction was negatively correlated under resting conditions. This means that individuals with high sympathetic BRS have less effective vascular transduction during spontaneous changes in blood pressure. However, this was only apparent in young males; there was no relationship observed in females. Furthermore, resting MSNA did not predict sympathetic BRS or vascular transduction in either males or females. Finally, vascular transduction was significantly greater in males when quantified as the relationship between MSNA and leg vascular conductance during isometric handgrip and the cold pressor test. Sympathetic BRS was not different between males and females during the cold pressor test but was reset to a higher blood pressure range. Collectively, the studies conducted in this thesis provide insight into the dynamic nature of the baroreflex control of arterial pressure at rest, and during increases in muscle vasoconstrictor drive. Whilst this thesis provides evidence of sex differences in sympathetic BRS and vascular transduction, it also highlights the differences between the various approaches available for quantifying vascular transduction. The method chosen can have a profound effect on the findings regarding sex differences and the interaction vascular transduction has with sympathetic BRS
Neural plasticity in obstructive sleep apnoea and in memory formation
Neural plasticity is the brain's ability to build new neural connection throughout life to adapt for several factors. The work in this thesis is built on two kinds of neural plasticity, respiratory long-term facilitation (rLTF) and memory formation.
Respiratory LTF: Obstructive sleep apnoea (OSA) is a chronic disorder which is characterised by repeated partial or complete airway obstruction during sleep, which leads to intermittent hypoxia (IH). Chronic IH is strongly linked to the increased blood pressure, pulmonary artery pressure, and oxidative stress associated with OSA. Ironically, IH can induce rLTF which enhances ventilation and maintains airway patency, but the utilisation of this intervention is limited due to the complications of IH. Applying intermittent negative airway pressure (INAP) has shown potential for rLTF. One of our studies looked at the possibility of hypoglossal LTF in humans by INAP. Furthermore, we looked at the effects of prolonged exposure to INAP on the blood pressure, pulmonary artery pressure, and oxidative stress on healthy subjects.
Memory formation: We looked at the effect of experimental sleep fragmentation on the consolidation of episodic memory. On the other hand, we also looked at the effect of targeted memory reactivation (TMR) paradigm during wakefulness or during nap on memory consolidation
Life Sciences Program Tasks and Bibliography for FY 1996
This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1996. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive Internet web page
Life Sciences Program Tasks and Bibliography
This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1995. Additionally, this inaugural edition of the Task Book includes information for FY 1994 programs. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive Internet web pag
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Study of the Term Neonatal Brain Injury with combined Diffuse Optical Tomography and Electroencephalography
This thesis describes the application of combined diffuse optical tomography (DOT) and electroencephalography (EEG) in the investigation of neonatal term brain injury. With hypoxic ischaemic encephalopathy (HIE) and perinatal stroke being the most frequent contributors to brain injury in the term neonatal population, the first part of the thesis focuses on the description and ongoing requirement for their further investigation. In continuation to that, the characteristics and unique properties of both DOT and EEG are described and explored.
The combination of these two modalities was utilised in elucidating the relationship between neuronal activity and cerebral haemodynamics both in physiological processes as well as in disease, by the infant’s cot side. This work differs to previous studies using near-infrared technologies and EEG, as a denser whole head array was used, offering the potential of 3-dimensional image reconstruction of the cortical haemodynamic events in relation to electro-cortical activity. These methods were applied in the study of critically ill infants presenting with seizures in the first few days of life.
The relevant results are presented in three separate chapters of the thesis. Distinct neurophysiological phenomena such as seizures and burst suppression were detected and studied in association to underlying HIE. On the grounds of a pre-existing pilot study of our research group, distinct prolonged de-oxygenated cortical areas were identified following electrical seizure activity. Further exploration of infants with seizures provided limited supporting evidence. The investigation of burst suppression in HIE led to the first ever identification of repeated, waveform, cortical haemodynamic events in response to bursts of electrical activity with some spatial correlation to regions of brain injury. Further analysis of the low frequencies within the diffuse optical signal in cases of perinatal stroke, showed a consistent interhemispheric difference between the healthy and stroke-affected brain regions.
The limitations, prospects and conclusions are presented in the final chapter. The use of simultaneous DOT and EEG offers a unique neuro-monitoring and neuro-investigating tool in the neonatal intensive care environment, which is safe, portable, and cost-effective, Ongoing research is required for the exploration and development of the methodology and its potential diagnostic properties
Life Sciences Program Tasks and Bibliography for FY 1997
This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1997. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive internet web page
Added value of acute multimodal CT-based imaging (MCTI) : a comprehensive analysis
Introduction: MCTI is used to assess acute ischemic stroke (AIS) patients.We postulated that use of MCTI improves patient outcome regardingindependence and mortality.Methods: From the ASTRAL registry, all patients with an AIS and a non-contrast-CT (NCCT), angio-CT (CTA) or perfusion-CT (CTP) within24 h from onset were included. Demographic, clinical, biological, radio-logical, and follow-up caracteristics were collected. Significant predictorsof MCTI use were fitted in a multivariate analysis. Patients undergoingCTA or CTA&CTP were compared with NCCT patients with regards tofavourable outcome (mRS ≤ 2) at 3 months, 12 months mortality, strokemechanism, short-term renal function, use of ancillary diagnostic tests,duration of hospitalization and 12 months stroke recurrence