1,721,116 research outputs found
Physiological effects of heart rate variability biofeedback during laboratory induced congnitive stress
No full textIncludes bibliographical references.Heart rate variability (HRV) biofeedback is effective in reducing stress as well as managing chronic disease. It facilitates easy manipulation of HRV, and, therefore, potentially provides a valuable intervention for altering the activity of the autonomic nervous system. The aim of this thesis was to examine the effects of a single 10 minute episode of HRV biofeedback on measures of HRV and EEG during and immediately after the intervention, measures of HRV and cognitive performance during laboratory induced cognitive stress and subjective feelings of anxiety and relaxation states after testing. Eighteen healthy male volunteers (34 ± 6 years) exposed to work-related stress, were randomised into an HRV biofeedback intervention (BIO) and a comparative intervention group (COM)
Physiological evaluation of sleep surfaces in healthy volunteers and patients with acute-upon-chronic lower back pain
Full text linkStudies have documented that the use of a lumbar support while in the sitting position results in reduced back and leg pain, centralisation of pain and reduced erector spinae muscle activity in patients with lower back pain (LBP). While the positive effects of a lumbar support in sitting have been studied, few researchers have attempted to document the value of such a support in the supine position. Since many patients with LBP suffer from insomnia and nocturnal discomfort, it may be possible that the use of a foam surface overlay could positively influence their symptoms. Several foam surface overlays are currently used as a popular form of management for patients presenting with LBP. These include the convoluted foam surface ("egg box'' shape), which to my knowledge has not been scientifically studied and the lumbar body support, the value of which has only recently been reported. That study found that patients with chronic LBP have decreased electromyographic (EMG) activity of the erector spinae muscles, lower heart rates (HR) and decreased perception of discomfort (ROD) when lying on this locally designed, triple density, contoured, lumbar body support system (LBS) compared with a conventional flat innerspring mattress (CM). Accordingly the aim of this thesis was to measure the EMG activity, heart rate response, perception of comfort and pattern of pressure distribution after lying on a variety of different surfaces, thus endeavouring to determine a mechanism of action of the LBS. In the first study of this thesis, ten patients with LBP were exposed to a random order, 30 minute period on three sleep surfaces: Lumbar body support on top of a conventional mattress (LBS+ CM), 60 mm convoluted foam surface on top of a conventional mattress (CFS + CM), and a conventional mattress (CM) alone. Each patient acted as his/her own control. Recordings of EMG activity, HR and ROD were measured for each patient. Average HR over the 30 minute period was lower after acute exposure to the LBS+ CM (60 ± 11 b/min) compared to the CM (66 ± 10 b/min, p < 0.05; LBS+ CM vs. CM). Although average HR response to the LBS+ CM was lower compared to CFS + CM (64 ± 9 b/min), this difference was not significant. ROD reported after acute exposure to the LBS+ CM was improved (1.9 ± 0.7 units), compared to the CFS+ CM (3.9 ± 1.0 units) and CM (4.7 ± 2.2 units; p < 0.05). Average EMG activity was lower after 30 minutes on the LBS + CM (2.68 ± 1.1 mv) compared to the CFS+ CM (4.46 ± 2.7 mv) and CM (4.19 ± 2.4 mv; p < 0.05). These results suggest that patients with LBP have reduced EMG activity and HR measurements with lower ROD when lying on a LBS + CM compared with a CM and CFS + CM. The second series of experiments involved a further ten patients with lower back pain, who were required to lie supine in random order on the LBS + CM, on a polystyrene mould (PM) (identical to the shape of the LBS) and on a CM. Recordings of EMG activity, HR and ROD were measured for each patient. Average HR over the 30 minute period was lower on the LBS + CM (60 ± 7 b/min) vs. PM + CM (66 ± 10 b/min) and CM (68 ± 9 b/min; p < 0.01 ). Average ROD was improved when patients lay on the LBS+ CM (1.8 ± 0.6 units) vs. PM + CM (5. 7 ± 2.5 units) and CM (4.1 ± 1.8 units; p < 0.05). Furthermore, average EMG activity was significantly reduced after lying on the LBS + CM (2.5 ± 1.0 mv) vs. PM + CM (4.3 ± 1.9 mv) and CM (4.6 ± 1.8 mv; p < 0.01 ). The findings of this study mirror our initial findings. The elevated EMG activity, heart rate and perception of discomfort after lying on a PM suggests that it could be a combination of both the correct density and the correct contour features that is important in reducing muscle spasm in patients with acute-upon-chronic lower back pain. Average HR over the 30 minute period was lower after acute exposure to the LBS+ CM (60 ± 11 b/min) compared to the CM (66 ± 10 b/min, p < 0.05; LBS+ CM vs. CM). Although average HR response to the LBS+ CM was lower compared to CFS + CM (64 ± 9 b/min), this difference was not significant. ROD reported after acute exposure to the LBS+ CM was improved (1.9 ± 0.7 units), compared to the CFS+ CM (3.9 ± 1.0 units) and CM (4.7 ± 2.2 units; p < 0.05). Average EMG activity was lower after 30 minutes on the LBS + CM (2.68 ± 1.1 mv) compared to the CFS+ CM (4.46 ± 2.7 mv) and CM (4.19 ± 2.4 mv; p < 0.05). These results suggest that patients with LBP have reduced EMG activity and HR measurements with lower ROD when lying on a LBS + CM compared with a CM and CFS + CM. The second series of experiments involved a further ten patients with lower back pain, who were required to lie supine in random order on the LBS + CM, on a polystyrene mould (PM) (identical to the shape of the LBS) and on a CM. Recordings of EMG activity, HR and ROD were measured for each patient. Average HR over the 30 minute period was lower on the LBS + CM (60 ± 7 b/min) vs. PM + CM (66 ± 10 b/min) and CM (68 ± 9 b/min; p < 0.01 ). Average ROD was improved when patients lay on the LBS+ CM (1.8 ± 0.6 units) vs. PM + CM (5. 7 ± 2.5 units) and CM (4.1 ± 1.8 units; p < 0.05). Furthermore, average EMG activity was significantly reduced after lying on the LBS + CM (2.5 ± 1.0 mv) vs. PM + CM (4.3 ± 1.9 mv) and CM (4.6 ± 1.8 mv; p < 0.01 ). The findings of this study mirror our initial findings. The elevated EMG activity, heart rate and perception of discomfort after lying on a PM suggests that it could be a combination of both the correct density and the correct contour features that is important in reducing muscle spasm in patients with acute-upon-chronic lower back pain. body support is altered and pressures are more equally distributed when compared to the pressure distribution of the other surfaces measured, without increases in pressure at any point on the body. Similar average and peak pressure results were obtained for the 90 mm CFS + CM and LBS. Since these results were not mirrored by the 60 mm CFS, the thickness of a foam surface possibly plays a role in reducing pressure. The data of these three separate studies could have implications in the adjunctive treatment of i)low back pain and ii) pressure sores. Firstly, the results of this thesis suggest that the use of a 60 mm foam overlay may not be the optimum form of management for patients presenting with paraspinal muscular spasm. Further, it is postulated, that the density and contour features of the lumbar body support are likely to play a role in reducing EMG activity and heart rate, while improving perception of comfort compared to the flat surfaces (CM and 60 mm CFS), which offer little support to the lumbar region of these patients. X Secondly, either the LBS or 90 mm CFS are likely to reduce the incidence of pressure sores in patients required to lie supine for prolonged periods, due to the reduction in peak and average pressures. In view of the contoured surface, it is unlikely that pressure sores could develop in patients lying on the LBS. This hypothesis needs to be confirmed in longer term studies in patients who are severely debilitated or paraplegic, as they are often most at risk for the development of pressure sores
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Exercise training in patients with peripheral vascular disease
No full textBibliography: leaves 91-98.Patients with peripheral vascular disease (PVD) suffer from the symptom of intermittent claudication and are walking intolerant. However, it is not clear what contributes to walking intolerance in patients with PVD
The effects of amlodipine on exercise performance in mild to moderate essential hypertensives
Full text linkThe effect of the long acting dihydropyridine calcium channel antagonist, amlodipine, on the exercise performance of hypertensive patients is not known. The aim of this study was to determine the effects of amlodipine on maximal (MAX), prolonged submaximal (PSX) and on skeletal muscle function (SMF) in patients with mild hypertension. In a double-blind randomised crossover trial, ten physically active hypertensive patients performed i) graded exercise to exhaustion for determination of maximal oxygen consumption (VO₂ₘₐₓ), peak heart rate (HR) and systolic blood pressure (SBP); ii) PSX at 75% VO₂ₘₐₓ to determine, cardiorespiratory responses, cardiac output (Q), blood lactate [La], free fatty acid [FFA], glucose [G] concentrations and ratings of perceived exertion (RPE), and iii) tests of isometric SMF including maximal voluntary contraction (MVC) and time to fatigue (TTF) during repetitve isometric MVC's. Tests were performed following two week ingestion of amlodipine (5 mg daily) or placebo seperated by a two week washout period. Resting SBP was decreased following ingestion of amlodipine (142 ± 13 vs l33 ± 12 mmHg; vs placebo: [mean± SD]; P<0.05). However, VO₂ₘₐₓ ( 31 ± 5 vs 33 ± 5 mlO₂.kg.min⁻¹ ; amlodipine vs placebo), peak heart rate ( 167 ± 12 vs 165 ± l6b.min⁻¹;amlodipine vs placebo)and peak SBP(l8l ±21 vs 170± 16mmHg; amlodipine vs placebo) were not reduced following ingestion of amlodipine. Submaximal cycling time. VO₂, Q, BP, HR, ventilation, RPE, [FFA], [La] and [G] during PSX were unaltered following ingestion of amlodipine. Similarly ingestion of amlodipine did not alter tests of isometric SMF. These data suggest that: i) ingestion of amlodipine lowers resting SBP but does not alter the normal haemodynamic response during exercise; ii) MAX, PSX exercise performance and SMF are unaltered following ingestion of amlodipine in athletic hypertensive patients. These findings suggest that the regulatory mechanisms which maintain haemodynamic homeostasis during maximal and submaximal exercise are not influenced by ingestion of amlodipine in athletic hypertensive patients
Comparative effects of calcium channel antagonism and beta-1 selective blockade on exercise performance in physically active hypertensive patients
Full text linkThe current recommendations by the American Heart Association for health promotion are that all persons should partake in regular physical activity in order to reduce the risk of cardiovascular disease. Regular physical exercise reduces blood pressure and is an important component of the management of hypertension. It is therefore important that patients with hypertension participate in habitual physical exercise. Many hypertensive patients who exercise will require anti-hypertensive medication. However, some antihypertensive agents cause fatigue during exercise. In order for patients to gain the full benefits of an active lifestyle, it is important that the prescribed antihypertensive agent does not prevent them performing and enjoying sustained exercise. It has been well documented that β-blockers cause premature fatigue during physical exercise. The effects on exercise performance of other first line antihypertensive medications, such as calcium channel antagonists have not been extensively investigated. In particular, the effects of these agents on prolonged submaximal exercise endurance have not been well studied. The object of this thesis was to compare the effects of isradipine, a dihydropyridine calcium channel antagonist, to those of atenolol, a β₁-selective antagonist, on maximal and submaximal exercise performance and on short duration high-intensity exercise in physically active hypertensive patients. The study design was a crossover trial where drug treatments were double blinded and randomised. Physically active volunteers with mild to moderate hypertension were recruited. 11 subjects performed i) progressive exercise to exhaustion for determination of maximal oxygen consumption (VO₂max), maximal work load and cardiorespiratory responses to maximal exercise, ii) prolonged submaximal exercise for determination of exercise endurance, cardiorespiratory responses and ratings of perceived exertion (APE), and iii) short duration, high intensity exercise consisting of a 30 second maximal exercise test (Wingate test) to determine skeletal muscle power output, following 4 weeks ingestion of isradipine (2.5mg bd), atenolol (50mg bd) or placebo. Diastolic blood pressure at rest was reduced by both atenolol and isradipine, but was lowered to a greater extent by atenolol (83.3 vs 89.0 vs 96.1 mmHg, atenolol vs isradipine vs placebo, p<.0005). Systolic blood pressure at rest tended to be similarly reduced by both agents, but was significantly reduced during maximal and submaximal exercise by atenolol only (p<.001, atenolol vs isradipine, placebo). Heart rate at rest and during maximal and submaximal exercise was decreased by atenolol only (p<.0005, atenolol vs isradipine, placebo). Maximal exercise performance was reduced after atenolol ingestion compared to placebo but not after isradipine ingestion. Peak workload achieved during the maximal exercise test was decreased after atenolol but unchanged after isradipine ingestion (214 vs 243 W, atenolol vs placebo, p<.01). Similarly, VO₂max was reduced after atenolol compared to placebo but was unchanged after isradipine ingestion (33.6 vs 36.4, 33.6 vs 36.1 mlO₂/kg/min, atenolol vs placebo, atenolol vs isradipine, p<.05). Both atenolol and isradipine ingestion reduced submaximal endurance time compared to placebo (27.8 vs 46.4, 34.4 vs 46.4 min, atenolol vs placebo, isradipine vs placebo, p<.005), and increased rating of perceived exertion (APE) after 30 min of submaximal exercise (p<.05). Submaximal oxygen consumption (VO₂), ventilation, respiratory exchange ratio (REA) and blood lactate, glucose and free fatty acid concentrations were not altered after the ingestion of either agent. Neither agent influenced peak skeletal muscle power, total work done, or rate of fatigue during the Wingate test compared to placebo. The results of these studies indicate that impaired performance and increased RPE during submaximal exercise after ingestion of either atenolol or isradipine is not due to alterations of ventilation, VO₂, RER, or blood lactate, glucose and free fatty acid concentrations during prolonged submaximal exercise. Similarly, reduced submaximal exercise performance after atenolol or isradipine ingestion is not due to factors which would also limit the ability of skeletal muscle to perform short duration, high intensity exercise before a bout of prolonged exercise. This study demonstrates that prolonged submaximal exercise testing can reveal an impairment in exercise performance after ingestion of antihypertensive medication which is not evident during maximal exercise testing. This finding is important as prolonged submaximal exercise is the form of exercise which most hypertensive patients actually perform. Further research is required on the effects of anti-hypertensive medications on submaximal exercise performance before firm recommendations can be made regarding medications most suitable for the physically active hypertensive patient. The results of these and other studies indicate that it is not yet possible to make claims that the calcium channel antagonist agents are without effect on physical exercise performance in physically active hypertensive patients
The effects of an ultra-endurance event on heart rate variability and cognitive performance during induced stress in Ironman triathletes
No full textIncludes abstract.Includes bibliographical references (leaves 55-79).The effects of long-term participation in ultra-endurance exercise on the cardiovascular system have recently been the subject of much interest. It is well known that HRV, a marker of autonomic activity, is enhanced with long-term aerobic exercise training. However, after acute exercise, HRV is reduced, but recovers over time depending on the intensity of the prior bout of exercise. A limitation of previous research is that exercise bouts of only up to 120 minutes have been studied. A modified Stroop Task is a laboratory stressor to assess executive cognitive function by means of reaction time and accuracy. The resting HRV is directly related to these prefrontal neural functions, but the effect of an altered HRV on cognitive function has never been investigated. We determined the effects of an ultra duration (10 – 15 hours) exercise event on parameters of HRV and cognitive function during a Modified Stroop Task, 60 – 200 minutes after the 2007 South African Ironman Triathlon event (3,6km swim; 180 Km cycle; 42,2 Km run). 1 Female and 13 male competing triathletes (IRON; ages 33.7±7.9) and 7 control subjects (CON; 2 female and 5 males aged 42 ±4.5) completed a Modified Stroop Task before and after the event. The individual HRV parameters, heart rate (HR), respiratory frequency (RF), reaction time (RT) and % of mistakes made were recorded via the Biopac MP150WSW System (Goletta, California, USA). Data was transformed by auto regressive analyses (Biomedical signal analysis group, University of Kuopio, Finland) into LF (0.04 - 0.15 Hz) and HF (0.15 - 0.5 Hz) components. Additional calculations included %LF and %HF as well as the central or peak frequencies in both the LF and HF bands
Exercise tolerance and skeletal muscle structure and function in patients with chronic obstructive pulminary disease
No full textBibliography: pages 143-154.Exercise intolerance is well documented in patients with chronic obstructive pulmonary disease (COPD). Historically, this exercise intolerance has been attributed to the central factors of lung damage and subsequent heart failure. However, recent evidence suggests that (i) patients with cardiac and renal failure suffer from skeletal muscle (SM) abnormalities that impair exercise tolerance and (ii) patients with chronic obstructive pulmonary disease (COPD) may have metabolic and functional abnormalities of SM. However, no studies have conducted a detailed investigation of SM structure and function and their relation to exercise tolerance in patients with COPD
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