The accepted model of autonomic control of heart rate (HR) during dynamic exercise indicates that the initial increase is entirely attributable to the withdrawal of parasympathetic nervous system (PSNS) activity and that subsequent increases in HR are entirely attributable to increases in cardiac sympathetic activity. In the present review, we sought to re-evaluate the model of autonomic neural control of HR in humans during progressive increases in dynamic exercise workload. We analysed data from both new and previously published studies involving baroreflex stimulation and pharmacological blockade of the autonomic nervous system. Results indicate that the PSNS remains functionally active throughout exercise and that increases in HR from rest to maximal exercise result from an increasing workload-related transition from a 4 : 1 vagal-sympathetic balance to a 4 : 1 sympatho-vagal balance. Furthermore, the beat-to-beat autonomic reflex control of HR was found to be dependent on the ability of the PSNS to modulate the HR as it was progressively restrained by increasing workload-related sympathetic nerve activity. In conclusion: (i) increases in exercise workload-related HR are not caused by a total withdrawal of the PSNS followed by an increase in sympathetic tone; (ii) reciprocal antagonism is key to the transition from vagal to sympathetic dominance, and (iii) resetting of the arterial baroreflex causes immediate exercise-onset reflexive increases in HR, which are parasympathetically mediated, followed by slower increases in sympathetic tone as workloads are increased. Abbreviations ABP, arterial blood pressure; ABR, arterial baroreflex; ANS, autonomic nervous system; CBR, carotid baroreflex; CBV, central blood volume; CC, central command; CI, chronotropic incompetence; CNS, central nervous system; CPBR, cardiopulmonary baroreceptors; EPR, exercise pressor reflex; HF, high frequency; HR, heart rate; HRV, heart rate variability; NO, nitric oxide; NP, neck pressure; NS, neck suction; OP, operating point; PAG, periaquaductal grey; PNS, peripheral nervous system; PSNA, parasympathetic nervous activity; PSNS, parasympathetic nervous system; RONS, reactive oxygen/nitrogen species; SNA, sympathetic nervous activity; SNS, sympathetic nervous system.

The technique of microneurography and the assessment of muscle sympathetic nerve activity (MSNA) are used in laboratories throughout the world. The variables used to describe MSNA, and the criteria by which these variables are quantified from the integrated neurogram, vary amongst studies and laboratories and, therefore, can become confusing to those starting to learn the technique. Therefore, the purpose of this educational review is to discuss guidelines and standards for the assessment of sympathetic nervous activity through the collection and analysis of MSNA. This review will reiterate common practices in the collection of MSNA, but will also introduce considerations for the evaluation and physiological inference using MSNA.

Approaches used to remove bacteria from wounds, such as irrigants other than saline solution or high-pressure devices, may not have the best clinical outcome.

The rate of major tendon rupture was 13 times greater for black men in this study population when compared with whites. Interventions among those at a higher risk for injury should be considered.

Caffeine ingestion disrupts post-exercise autonomic recovery because of increased sympathetic nerve activity. The prolonged sympathetic recovery time could subsequently hinder baroreflex function during recovery and disrupt the stability of autonomic function, potentiating a pro-arrhythmogenic state in young adults.

Despite some anecdotal evidence, the racial differences in tendon injuries have received little attention in the literature. We sought to determine the effect of race on major tendon injuries. A search was performed according to the International Classification of Diseases, Ninth Revision, Clinical Modification code 727.65 (rupture of quadriceps tendon), 727.66 (rupture of patellar tendon), and 727.67 (rupture of Achilles tendon) using the U. S. Defense Medical Epidemiology Database (DMED). Multivariate poisson regression was used to estimate the rate of major tendon rupture per 1000 person-years, while controlling for differences in gender, service, rank, and age for each code. We computed rate ratios and 95% confidence intervals using whites as the referent category. The adjusted rate ratio for black service members when compared to white service members was 2.89 (95% CI 2.42, 3.44) for quadriceps tendon tears, 4.52 (95% CI 3.94, 5.19) for patellar tendon tears, and 3.58 (95% CI 3.31, 3.88) for Achilles tendon tears. There appears to be a significant relative predisposition toward lower-extremity major tendon rupture in black U. S. service members when compared to white service members. Investigation of the racial differences in risk factors is warranted.

Arterial stiffness is related to the risk of cardiovascular disease (CVD) and increases with aging. Functional impairment of the arterial wall can occur before structural changes and can be detectable before CVD symptoms. The elastic properties of the carotid arterial wall during the cardiac cycle can be evaluated by standard 2-dimensional (2D) ultrasound longitudinal or circumferential imaging of vascular deformation (strain) using speckle tracking. The purpose of this study was to compare standard 2D ultrasound circumferential and longitudinal images of vascular tissue motion and strain using speckle tracking in young and older individuals. Participants underwent recording of 2D ultrasound circumferential and longitudinal images of the common carotid artery. Circumferential carotid strain (CS) and CS rate were obtained and analyzed via speckle tracking software. Following the strain analysis, the circumferential strain β-stiffness (C-β) was calculated. Conventional longitudinal β-stiffness (L-β) was calculated and non-invasive blood pressure measurements were obtained from carotid artery pressure measurements in a resting supine position using applanation tonometry. C-β was significantly higher than L-β, and the association with age was greater (r = .824 vs. r = .547). CS and CS rate were significantly higher in the young compared to the older group. L-β does not explain as much of the age-dependent differences in the carotid artery compared with C-β. This is possibly due to the inclusion of whole arterial wall motion and deformation observed in the CS image. The ability of C-β to accurately predict the future risk of CVD independent of age still needs further investigation.

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