Scope and nature of sudden cardiac death before age 40 in Ontario: a report from the cardiac death advisory committee of the office of the chief coroner.

BACKGROUND: Understanding sudden cardiac death in the young may inform prevention strategies. OBJECTIVE: To determine the scope and nature of sudden death in a geographically defined population. METHODS: We performed a retrospective population-based cohort study in Ontario, Canada, of all sudden cardiac death cases involving persons aged 2-40 years identified from the 2008 comprehensive Coroner database. Of 1741 Coroner's cases, 376 were considered potential sudden cardiac death cases and underwent review. RESULTS: There were 174 cases of adjudicated sudden cardiac death from a population of 6,602,680 persons aged 2-40 years. Structural heart disease was present in 126 cases (72%), 78% of which was unrecognized. There was no identifiable cause of death in 48 cases (28%), representing primary arrhythmia syndromes. The majority of decedents were men (76%) over the age of 18 (90%). The overall incidence of sudden cardiac death increased with age from 0.7/100,000 (2-18 years) to 2.4/100,000 (19-29 years) to 5.3/100,000 (30-40 years) person-years. Persons experiencing sudden cardiac death before age 30 were more likely to have a primary arrhythmia syndrome (odds ratio 2.97; P<.001). The majority of events occurred in the home (72%); 33% of the events in children/adolescents and 9% of the events in adults occurred during reported moderate or vigorous exercise (P = .002). There were no pediatric deaths during organized competitive sports. CONCLUSIONS: The incidence of sudden cardiac death increases with age, typically occurring in a man at rest in the home with unrecognized underlying heart disease or a primary arrhythmia syndrome. Prevention strategies should consider targeting identification of unrecognized structural heart disease and primary arrhythmia syndromes.

Effects of autonomic blockade on nonlinear heart rate dynamics.

INTRODUCTION: Analysis of nonlinear heart rate (HR) dynamics may provide greater insight into neurocardiac influences during exercise and disease than traditional HR variability. However, the physiological basis of nonlinear HR dynamics has not been investigated in individuals with spinal cord injury (SCI). The purpose of this study was to compare the effects of autonomic blockade in SCI and able-bodied participants. METHODS: Five participants (42 +/- 13 years) with SCI (C4-C7, AIS B-D, 13 +/- 13 years post-injury) and four able-bodied controls (33 +/- 8 years) underwent beta(1)-adrenergic and vagal blockade in the supine and cardiovascular stress positions. Cardiovascular stress consisted of 40 degrees tilt plus sustained isometric jaw contraction and cold water submersion of the right hand. RESULTS: In both SCI and able-bodied participants, vagal blockade significantly increased HR (p < 0.05) and resulted in significant reductions in sample entropy and correlation dimension in the supine and cardiovascular stress positions (p < 0.05). During the cardiovascular stress position, baseline sample entropy (p < 0.05) and correlation dimension (p < 0.05) were lower in participants with SCI. Nonlinear measures were also significantly correlated with HR (p < 0.05). CONCLUSION: The results suggest that vagal modulations are a primary modulator of nonlinear HR signals in both SCI and able-bodied participants, while the role of the beta(1)-adrenergic system remains less defined. Further study is required to elucidate the role of the autonomic nervous system in nonlinear HR dynamics in both SCI and able-bodied populations.

Body weight-supported treadmill training for patients with hip fracture: a feasibility study.

UNLABELLED: Giangregorio LM, Thabane L, deBeer J, Farrauto L, McCartney N, Adachi JD, Papaioannou A. Body weight-supported treadmill training for patients with hip fracture: a feasibility study. OBJECTIVE: To determine the feasibility of body weight-supported treadmill training (BWSTT) as a strategy for improving independent ambulation among patients who had sustained a hip fracture. DESIGN: Nonrandomized controlled trial. SETTING: Inpatient rehabilitation. PARTICIPANTS: Patients with a stable hip fracture and at least 50% weight-bearing. INTERVENTION: BWSTT in lieu of standard walking exercises throughout stay in rehabilitation. MAIN OUTCOMES MEASURES: Feasibility outcomes included the number of patients agreeing to participate in treadmill walking, the number who returned for follow-up assessments, compliance, and the number of adverse events. Secondary outcomes included the Lower Extremity Functional Scale, the Timed Up & Go test, a 2-minute walk test, and the Falls Self-Efficacy Scale. Univariate regression was used to assess the group effect on score changes from baseline to discharge and from baseline to follow-up. RESULTS: Among 41 potentially eligible patients, 21 (51%) agreed to participate and 14 returned for follow-up assessments. The recruitment goal of 12 patients agreeing to BWSTT was achieved; however, retention by 3-month follow-up was 67%. The average compliance was 3 sessions a week; however, several patients were below average. No adverse events of BWSTT were reported. There were no significant differences between groups with respect to secondary outcomes. CONCLUSIONS: BWSTT may be a feasible method for retraining gait among patients with hip fracture. However, future studies evaluating its efficacy need rigorous methods for ensuring compliance and retention.

Heart rate variability and nonlinear analysis of heart rate dynamics following single and multiple Wingate bouts.

Sprint interval training involves short bouts of high-intensity exercise and has produced training responses similar to those of endurance training. The effects of multiple supramaximal exercise bouts on neurocardiac modulation have not been examined. Therefore, we investigated the recovery of heart rate (HR) variability and nonlinear HR dynamics in 10 young (20.1 +/- 1.2 years) healthy males following single (1) and multiple (4) Wingate tests. HR variability was assessed with time and frequency domain measures, whereas nonlinear HR dynamics were determined by assessing the complexity (sample entropy) and fractal nature (detrended fluctuation analysis) of the HR time series. Responses were determined at pre-exercise baseline and at 3 time points during recovery from exercise: Post1 (5-20 min), Post2 (45-60 min), and Post3 (105-120 min). Following a single Wingate test, all temporal and spectral HR measures had returned to baseline by 1 h of recovery. In contrast, these measures were different from baseline at 2 h following multiple Wingate tests. Fractal HR properties were altered (p < 0.05) at Post1 following a single Wingate test and at Post1 and Post2 following multiple Wingate tests. HR complexity was reduced (p < 0.001) throughout the 2-h recovery following both exercise conditions. In conclusion, Wingate tests result in alterations in cardiac autonomic control, with multiple Wingate tests resulting in larger, more prolonged alterations. Based on the results of the single Wingate test, nonlinear measures, such as HR complexity, may be more sensitive in detecting subtle alterations in neurocardiac behaviour, compared with traditional measures of HR variability.

Cardiovascular reactivity to psychophysiological stressors: association with hypotensive effects of isometric handgrip training.

BACKGROUND: Isometric handgrip (IHG) training has been found to have hypotensive effects in normotensive and hypertensive samples. Mechanisms responsible for the reductions in arterial blood pressure have been suggested, but remain equivocal. OBJECTIVE: To investigate whether cardiovascular reactivity to cold pressor and serial subtraction stressors are associated with changes in resting systolic blood pressure found with IHG training. METHODS: After completion of an 8 week IHG training program and a 6 month detraining washout period, 17 healthy older participants (66 +/- 2 years) completed cold pressor (2 min at 4 +/- 1 degrees C) and serial subtraction (2 min) stressor tasks to assess cardiovascular reactivity. RESULTS: Compared with baseline, cold pressor and serial subtraction stressor significantly increased systolic blood pressure, diastolic blood pressure, and heart rate (P < 0.001). Heart rate reactivity was significantly different between the cold pressor and serial subtraction tasks (P < 0.001). Residualized reductions in systolic blood pressure from IHG training were strongly correlated with serial subtraction task reactivity scores [Systolic blood pressure: r(16) = -0.58, diastolic blood pressure: r(16) = -0.66, heart rate: r(16) = -0.53, P < 0.05], but not with cold pressor reactivity [r(16) < 0.14, P > 0.50]. CONCLUSION: The association between serial subtraction task reactivity and hypotensive effects of IHG training may hint at myocardial mediating mechanisms behind IHG training attenuations and may provide a method for identifying patients who stand to benefit from IHG training.

Isometric handgrip exercise improves acute neurocardiac regulation.

Isometric handgrip (IHG) training (>6 weeks) has been shown to reduce resting arterial blood pressure (ABP) and improve cardiac autonomic modulation. However, the effects of a single bout of IHG on acute neurocardiac regulation remain unknown. The purpose of this study was to examine the effect of IHG exercise on nonlinear heart rate dynamics and cardiac vagal activity. Nonlinear dynamics were assessed by sample entropy, detrended fluctuation analysis (alpha(1)), and correlation dimension techniques. The 4-second exercise test was used to calculate the cardiac vagal index (CVI), an indirect measure of cardiac vagal activity. In a randomized crossover design, 18 older (70 +/- 5 years of age) subjects completed IHG exercise (four 2-min isometric contractions at 30% MVC) and a time-matched control condition. Following a single bout of bilateral IHG, there was a small reduction in systolic blood pressure (125 +/- 2 to 122 +/- 1 mmHg, P < 0.01), in addition to, a significant decrease in alpha(1) (1.42 +/- 0.12 to 1.22 +/- 0.10, P < 0.05), an increase in sample entropy (1.28 +/- 0.03 to 1.40 +/- 0.05, P < 0.001), and an increase in the CVI (1.24 +/- 0.03 to 1.29 +/- 0.03, P < 0.01). These results suggest improvements in acute cardiac autonomic modulation following a single bout of IHG. This may be mechanistically linked to the observed reductions in ABP seen in previous IHG training studies. Alternatively, these acute effects may have clinical applications and require further investigation.

Effects of short-term training on heart rate dynamics in individuals with spinal cord injury.

Increased risk of cardiovascular diseases and autonomic dysregulation are common health concerns in individuals with spinal cord injury (SCI). Two therapies that may help improve cardiovascular control are body-weight supported treadmill training (BWSTT) and head-up tilt training (HUTT). The purpose of this study was to examine the effects of short-term BWSTT and HUTT on cardiac autonomic function. Seven participants (6 male, 37.1+/-7.7 years) with SCI (C5-T10, ASIA A-C; 5.0+/-4.4 years post-injury) completed the study protocol. In this randomized cross-over design, participants were required to complete 4 weeks of thrice-weekly BWSTT and HUTT (i.e. 12 sessions each), separated by a 4 week detraining period. Cardiac autonomic function was assessed at rest, before and after, each 4 week training period using linear and non-linear measures (sample entropy and detrended fluctuation analysis (alpha(1))) of heart rate dynamics. Participants completed equivalent amounts of time performing BWSTT and HUTT (453.7+/-27.3 min vs. 471.6+/-19.7 min, p=0.24). There were no significant differences in linear heart rate variability following BWSTT or HUTT (p>0.05). In contrast, there was a significant change in sample entropy following BWSTT (1.05+/-0.14 to 1.42+/-0.12, p<0.05). Due to the bi-directional pattern of alpha(1) values, distance scores were calculated (|1-alpha(1)|) and demonstrated a significant reduction following BWSTT (0.54+/-0.06 to 0.26+/-0.05, p=0.001). In conclusion, 4 weeks of BWSTT but not HUTT training are sufficient to increase sample entropy and reduce the fractal scaling distance score in participants with SCI.

The hypotensive effects of isometric handgrip training using an inexpensive spring handgrip training device.

PURPOSE: Research has demonstrated the efficacy of isometric handgrip (IHG) training to attenuate resting blood pressure. These studies have relied on the use of programmable digital handgrips for training. This study aimed to determine the effectiveness of simple, inexpensive spring-loaded handgrip devices in producing hypotensive effects. METHODS: The study was a randomized controlled trial of 49 normotensive participants (66.4 +/- 0.9 years; 57% women). Participants in the exercise group (n = 25) trained and had blood pressure measured twice weekly for 8 weeks. Control participants (n = 24) completed weekly blood pressure measurements. Pre- and posttraining measurements were each assessed over 3 visits. Statistical analysis of the pre-post data involved analyses of variance and hierarchical linear modeling was used to examine changes over time. RESULTS: Following 8 weeks, IHG participants demonstrated significant reductions in resting blood pressure. Systolic and diastolic blood pressures were reduced from 122 +/- 3 mm Hg to 112 +/- 3 mm Hg (P < .001) and from 70 +/- 1 mm Hg to 67 +/- 1 mm Hg (P < .05), respectively. Hierarchical linear modeling analysis also revealed a significant cross-level (ie, group / time) interaction, with an estimated reduction in systolic blood pressure of 5.4 mm Hg (P < .001) over the training period in the IHG group. CONCLUSIONS: In agreement with previous studies, IHG training reduced resting arterial pressure following 8 weeks of training. Hypotensive effects linked to IHG training may be achieved using simple, inexpensive spring handgrip training devices and may provide a convenient and affordable therapeutic alternative or adjunctive therapy for lowering blood pressure.

Effect of aerobic vs combined aerobic-strength training on 1-year, post-cardiac rehabilitation outcomes in women after a cardiac event.

OBJECTIVE: To compare the effect and sustainability of 6 months combined aerobic/strength training vs aerobic training alone on quality of life in women after coronary artery by-pass graft surgery or myocardial infarction. DESIGN: Prospective, 2-group, randomized controlled trial. PARTICIPANTS: Ninety-two women who were 8-10 weeks post-coronary artery by-pass graft surgery or myocardial infarction, able to attend supervised exercise, and fluent in English. METHODS: The aerobic training alone group had supervised exercise twice a week for 6 months. The aerobic/strength training group received aerobic training plus upper and lower body resistance exercises. The amount of active exercise time was matched between groups. The primary outcome, quality of life, was measured by the MOS SF-36; secondary outcomes were self-efficacy, strength and exercise capacity. RESULTS: After 6 months of supervised exercise training both groups showed statistically significant improvements in physical quality of life (p = 0.0002), peak VO2 (19% in aerobic/strength training vs 22% in aerobic training alone), strength (p < 0.0001) and self-efficacy for stair climbing (p = 0.0024), lifting (p < 0.0001) and walking (p = 0.0012). However, by 1-year follow-up there was a statistically significant difference in physical quality of life in favor of the aerobic/strength training group (p = 0.05). CONCLUSION: Women with coronary artery disease stand to benefit from both aerobic training alone and aerobic/strength training. However, continued improvement in physical quality of life may be achieved through combined strength and aerobic training.

Effects of isometric handgrip training among people medicated for hypertension: a multilevel analysis.

OBJECTIVE: To examine the longitudinal effects of isometric handgrip (IHG) exercise training on blood pressure using hierarchical linear modeling. METHODS: Data from 43 participants who were medicated for hypertension at the time of training were amalgamated from three previous investigations. In each study, IHG training was completed 3 days/week for 8 weeks at 30% of maximal voluntary contraction and resting blood pressure was assessed at twice-weekly intervals throughout. RESULTS: Hierarchical linear modeling analysis revealed a linear pattern of blood pressure decline over time with estimated reductions of 5.7 and 3 mmHg reductions in systolic and diastolic pressure, respectively. Participants with higher initial systolic pressure showed greater rates of blood pressure decline (r=-0.67), inferring that individuals with higher blood pressure stand to achieve greater benefits from this method of training. CONCLUSIONS: These results provide further evidence that IHG training lowers resting blood pressure among persons medicated for hypertension.

Isometric handgrip training improves local flow-mediated dilation in medicated hypertensives.

Bilateral isometric handgrip (IHG) training lowers resting arterial blood pressure (BP) in medicated hypertensives. Numerous mechanisms have been suggested, but have yet to be investigated. One such mechanism is that of improved systemic endothelial-dependent vasodilation. The purpose of this investigation was twofold: (1) to determine if bilateral IHG training had any beneficial effects on endothelial-dependent vasodilation, and (2) to see if improved systemic endothelial-dependent vasodilation was responsible for lowering BP. Sixteen participants performed four, 2 min IHG contractions at 30% of their maximal voluntary effort, using either a bilateral (n = 7) or a unilateral IHG protocol (n = 9), three times per week for 8 weeks. Brachial artery (BA) flow-mediated dilation (FMD, an index of endothelial-dependent vasodilation, measured in both arms) was assessed pre- and post-training. Following bilateral IHG training, BA FMD improved in both arms (normalized to peak shear rate 0.005 +/- 0.001 to 0.02 +/- 0.002 s(-1), P < 0.01). Following unilateral IHG training, BA FMD improved in the trained arm only (normalized 0.009 +/- 0.002 to 0.02 +/- 0.005 s(-1), P < 0.01). These findings suggest that although IHG training improves endothelial-dependent vasodilation, the improvements only occur locally in the trained limbs. This suggests that enhanced systemic endothelial-dependent vasodilation is not the mechanism responsible for the observed post-IHG training reductions in BP in medicated hypertensives.

Isometric handgrip training does not improve flow-mediated dilation in subjects with normal blood pressure.

Isometric HG (handgrip) training lowers resting arterial BP (blood pressure), yet the mechanisms are elusive. In the present study, we investigated improved systemic endothelial function as a mechanism of arterial BP modification following isometric HG training in normotensive individuals. This study employed a within-subject repeated measures design primarily to assess improvements in BA FMD (brachial artery flow-mediated dilation; an index of endothelium-dependent vasodilation), with the non-exercising limb acting as an internal control. Eleven subjects performed four 2-min unilateral isometric HG contractions at 30% of maximal effort, three times per week for 8 weeks. Pre-, mid- and post-training resting ABP and BA FMD (exercised arm and non-exercised arm) were measured via automated brachial oscillometry and ultrasound respectively. BA FMD (normalized to the peak shear rate experienced in response to the reactive hyperaemic stimulus) remained unchanged [exercised arm, 0.029+/-0.003 to 0.026+/-0.003 to 0.029+/-0.004%/s(-1) (pre- to mid- to post-training respectively); non-exercised arm, 0.023+/-0.003 to 0.023+/-0.003 to 0.024+/-0.003%/s(-1) (pre- to mid- to post-training respectively); P=0.22]. In conclusion, improved systemic endothelial function is unlikely to be responsible for lowering arterial BP in this population.

Isometric handgrip training improves local flow-mediated dilation in medicated hypertensives.

Bilateral isometric handgrip (IHG) training lowers resting arterial blood pressure (BP) in medicated hypertensives. Numerous mechanisms have been suggested, but have yet to be investigated. One such mechanism is that of improved systemic endothelial-dependent vasodilation. The purpose of this investigation was twofold: (1) to determine if Bilateral IHG training had any beneficial effects on endothelial-dependent vasodilation, and (2) to see if improved systemic endothelial-dependent vasodilation was responsible for lowering BP. Sixteen participants performed four, 2 min IHG contractions at 30% of their maximal voluntary effort, using either a Bilateral (n = 7) or a Unilateral IHG protocol (n = 9), three times per week for 8 weeks. Brachial artery (BA) flow-mediated dilation (FMD, an index of endothelial-dependent vasodilation, measured in both arms) was assessed pre-and post-training. Following Bilateral IHG training, BA FMD improved in both arms (normalized to peak shear rate, 0.005 +/- 0.001 to 0.02 +/- 0.002 s(-1), P < 0.01). Following Unilateral IHG training, BA FMD improved in the trained arm only (normalized: 0.009 +/- 0.002 to 0.02 +/- 0.005 s(-1), P < 0.01). These findings suggest that although IHG training improves endothelial-dependent vasodilation, the improvements occur only locally in the trained limbs. This suggests that enhanced systemic endothelial-dependent vasodilation is not the mechanism responsible for the observed post-IHG training reductions in BP in medicated hypertensives.

The effect of body weight-supported treadmill training on muscle morphology in an individual with chronic, motor-complete spinal cord injury: A case study.

OBJECTIVE: The purpose of this pilot study was to examine the effects of 4 months of thrice-weekly body weight-supported treadmill training (BWSTT) on skeletal muscle morphology in a woman (age 27 y) with chronic, motor-complete (ASIA B) spinal cord injury (SCI). METHODS: The participant performed passive thrice-weekly BWSTT for 4 months (48 total sessions) with manual assistance from therapists. Muscle biopsies of the vastus lateralis were taken prior to the beginning of the training program as well as following the completion of 4 months of training. Histochemical analysis was utilized to evaluate changes in muscle fiber size and type following training. RESULTS: At baseline, vastus lateralis muscle biopsies showed evidence of fiber atrophy and fiber type redistribution typical of persons with SCI, with mean fiber areas (and % distributions) of type I, type IIa and type IIx fibers being 3474 microm2 (1.3%), 3146 microm2 (30.8%) and 1284 microm2 (68.0%), respectively. Following training, there were increases in treadmill walking speed (pre: 1.0km/h; post: 2.5km/h) and distance walked/session (pre: 500m; post: 1875m). Vastus lateralis mean fiber area increased by 27.1% and type I fiber % distribution increased to 24.6%, whereas type IIa and type IIx fiber % distributions both decreased following training. CONCLUSION: These data indicate that 4 months of thrice-weekly BWSTT improved muscle morphology in an individual with chronic, motor-complete SCI.

Can body weight supported treadmill training increase bone mass and reverse muscle atrophy in individuals with chronic incomplete spinal cord injury?

This study evaluates the impact of 12 months of body weight supported treadmill training (BWSTT) on muscle and bone in individuals with spinal cord injury (SCI). Fourteen individuals who sustained an incomplete SCI at least 12 months before the study were recruited to participate in BWSTT 3 times/week for a total of 144 sessions. Thirteen individuals completed the study. The average age of subjects was 29 y, average time post-injury was 7.70 y (range: 1-24 y). Areal bone densities of the proximal and distal femur, proximal tibia, spine, and whole body were measured using dual-energy X-ray absorptiometry. Muscle cross-sectional area (CSA), volumetric bone density, and bone geometry at mid-femur and proximal tibia were measured using computed tomography. Serum osteocalcin and urinary deoxypyridinoline were measured at baseline and after 6 and 12 months of training. All other measures were made before and after training. Participants experienced significant increases in whole-body lean mass, from 45.9 +/- 8.7 kg to 47.8 +/- 8.9 kg (mean +/- SD; p < 0.003). Muscle CSAs increased by an average of 4.9% and 8.2% at the thigh and lower leg sites, respectively. No significant changes occurred in bone density or bone geometry at any site, or in bone biochemical markers. Whole-body bone density exhibited a small but statistically significant decrease (p < 0.006). BWSTT may therefore be a promising intervention for increasing muscle mass. Although 12 months of BWSTT did not increase bone density in individuals with chronic incomplete SCI, it did not appear to decrease bone density at fracture-prone sites.

Acute vascular responses to isometric handgrip exercise and effects of training in persons medicated for hypertension.

Previous work from our laboratory demonstrated that isometric handgrip (IHG) training improved local, endothelium-dependent vasodilation in medicated hypertensives [McGowan CL (PhD Thesis), 2006; McGowan et al. Physiologist 47: 285, 2004]. We investigated whether changes in the capacity of smooth muscle to dilate (regardless of endothelial factors) influenced this training-induced change, and we examined the acute vascular responses to a single bout of IHG. Seventeen subjects performed four 2-min unilateral IHG contractions at 30% of maximal voluntary effort, three times a week for 8 wk. Pre- and posttraining, brachial artery flow-mediated dilation (FMD, an index of endothelium-dependent vasodilation) and nitroglycerin-mediated maximal vasodilation (an index of endothelium-independent vasodilation) were measured in the exercised arm by using ultrasound before and immediately after acute IHG exercise. IHG training resulted in improved resting brachial FMD (P < 0.01) and no change in nitroglycerin-mediated maximal vasodilation. Pre- and posttraining, brachial artery FMD decreased following an acute bout of IHG exercise (normalized to peak shear rate, pre-, before IHG exercise: 0.01 +/- 0.002, after IHG exercise: 0.008 +/- 0.002%/s(-1); post-, before IHG exercise: 0.020 +/- 0.003, after IHG exercise: 0.010 +/- 0.003%/s(-1); P < 0.01). Posttraining, resting brachial artery FMD improved yet nitroglycerin-mediated maximal vasodilation was unchanged in persons medicated for hypertension. This suggests that the training-induced improvements in the resting brachial artery FMD were not due to underlying changes in the forearm vasculature. Acute IHG exercise attenuated brachial artery FMD, and although this impairment may be interpreted as hazardous to medicated hypertensives with already dysfunctional endothelium, the effects appear transient as repeated exposure to the IHG stimulus improved resting endothelium-dependent vasodilation.

Bone loss and muscle atrophy in spinal cord injury: epidemiology, fracture prediction, and rehabilitation strategies.

Individuals with spinal cord injury (SCI) often experience bone loss and muscle atrophy. Muscle atrophy can result in reduced metabolic rate and increase the risk of metabolic disorders. Sublesional osteoporosis predisposes individuals with SCI to an increased risk of low-trauma fracture. Fractures in people with SCI have been reported during transfers from bed to chair, and while being turned in bed. The bone loss and muscle atrophy that occur after SCI are substantial and may be influenced by factors such as completeness of injury or time postinjury. A number of interventions, including standing, electrically stimulated cycling or resistance training, and walking exercises have been explored with the aim of reducing bone loss and/or increasing bone mass and muscle mass in individuals with SCI. Exercise with electrical stimulation appears to increase muscle mass and/or prevent atrophy, but studies investigating its effect on bone are conflicting. Several methodological limitations in exercise studies with individuals with SCI to date limit our ability to confirm the utility of exercise for improving skeletal status. The impact of standing or walking exercises on muscle and bone has not been well established. Future research should carefully consider the study design, skeletal measurement sites, and the measurement techniques used in order to facilitate sound conclusions.

Reproducibility of heart rate variability and blood pressure variability in individuals with spinal cord injury.

Individuals with spinal cord injury (SCI) are prone to orthostatic intolerance and an increased risk of cardiovascular disease. The use of heart rate variability (HRV) and blood pressure variability (BPV) as indices of cardiovascular regulation would be valuable in this population; however, their reproducibility has yet to be tested in those with SCI. The purpose of this study was to examine the day-to-day reproducibility of resting HRV and BPV in individuals with SCI. Ten individuals (age 35.9 +/- 13.2 yrs) with chronic (5.4 +/- 7.7 years post injury) SCI (C4-T12; ASIA A-C) participated. On two occasions within a two-week period, 10-minute supine electrocardiogram and Finapres blood pressure recordings were obtained during spontaneous breathing. Computer software calculated frequency domain measures of HRV and BPV (Low frequency (LF) power, High frequency (HF) power, and LF:HF ratio). Intraclass correlations coefficients (R) were used as an index of day-to-day reproducibility, and analyses were conducted on all participants and only those with tetraplegia. For HRV, measures of heart rate, LF, and LF:HF were found to be highly reproducible (R = 0.82-0.88); however, the reproducibility of HF was found to be poor (all participants: R = 0.53, tetraplegia: R = 0.66). Measures of blood pressure as well as systolic BPV also showed high reproducibility (R = 0.72-0.93). Measures of diastolic BPV were less reproducible but still acceptable (R = 0.71-0.89) with the exception of LF:HF(DBP) (R = 0.51). In conclusion, despite the autonomic dysfunction associated with SCI, measures of HRV and BPV may still be used as reproducible indices of autonomic cardiovascular regulation in this population.

Effects of body weight-supported treadmill training on heart rate variability and blood pressure variability in individuals with spinal cord injury.

Individuals with spinal cord injury are prone to cardiovascular dysfunction and an increased risk of cardiovascular disease. Body weight-supported treadmill training (BWSTT) may enhance ambulation in individuals with incomplete spinal cord injury; however, its effects on cardiovascular regulation have not been investigated. The purpose of this study was to examine the effects of 6-mo of BWSTT on the autonomic regulation of heart rate (HR) and blood pressure (BP) in individuals with incomplete tetraplegia. Eight individuals [age 27.6 yr (SD 5.2)] with spinal cord injury [C4-C5; American Spinal Injury Association B-C; 9.6 yr (SD 7.5) postinjury] participated. Ten-minute HR and finger arterial pressure (Finapres) recordings were collected during 1) supine rest and 2) an orthostatic stress (60 degrees head-up tilt) before and after 6 mo of BWSTT. Frequency domain measures of HR variability [low-frequency (LF) power, high-frequency (HF) power, and LF-to-HF ratio] and BP variability (systolic and diastolic LF power) were used as clinically valuable indexes of neurocardiac and neurovascular control, respectively. There was a significant reduction in HR [61.9 (SD 6.9) vs. 55.7 beats/min (SD 7.7); P=0.05] and LF-to-HF ratio [1.23 (SD 0.47) vs. 0.99 (SD 0.40); P < 0.05] after BWSTT. There was a significant reduction in LF systolic BP [183.1 (SD 46.8) vs. 158.4 mmHg2 (SD 45.2); P < 0.01] but no change in BP. There were no significant effects of training on HR variability or BP variability during 60 degrees head-up tilt. In conclusion, individuals with incomplete tetraplegia retain the ability to make positive changes in cardiovascular autonomic regulation with BWSTT without worsening orthostatic intolerance.

An examination of the mechanisms of exercise-induced change in psychological well-being among people with spinal cord injury.

For individuals with a spinal cord injury (SCI), regular exercise training leads to significant improvements in pain, stress, and depression. The mechanisms by which exercise effects change in these variables are poorly understood. To address this issue, we examined the mediated effects of exercise on the psychological well-being of individuals with SCI according to the relationships described in the Chronic Pain Process Model. Twenty-one individuals with traumatic SCI either participated in a 9-month, twice-weekly exercise program (n = 11), or participated as nonexercising controls (n = 10). Measures of pain, stress, and depression were administered at the baseline and 3, 6, and 9 months into the intervention. Change in pain mediated exercise-induced change in stress, F(4,17) = 7.72, p < 0.01. Change in stress mediated exercise-induced change in depression, F(4,17) = 7.68, p < 0.01. With the identification of these factors as mediators of exercise-related changes in pain and well-being, exercise interventions can be designed that specifically target these mediators and possibly maximize intervention efficacy.