Sympathetic Neural Responses to Acute Thermal Sensations

The influence of thermal stimuli on the sympathetic nervous system is variable and largely depends on the change in temperature and timing of the stimuli. Core temperature changes yield increased muscle sympathetic nerve activity (MSNA) while changes in skin temperature yield variable MSNA responses. The MSNA responses to acute heating or cooling sensations remains unclear. Twenty-three participants (11 women, 12 men; age 24±1 years, BMI 26±1 kg/m2) underwent a thermal protocol that included four trials each of cool sensation threshold, warm sensation threshold, and heat pain (12 total trials). Continuous blood pressure (finger plethysmography), heart rate (electrocardiography), and MSNA (via microneurography) were recorded throughout all trials. Data was assessed with a Shapiro-Wilk test and log transformations were utilized for non-normal distributed data. T-tests were used to compare physiological data for cool and warm sensation thresholds, and repeated measures ANOVA to compare multiple heat pain data points. MSNA was significantly attenuated during the immediate recovery of cool threshold and warm threshold. MSNA was inhibited during the sensation of heat pain and systolic arterial pressure was reduced during the recovery from heat pain. There were no significant differences between men and women for any variables and responses. These results indicate that acute thermal sensations result in the inhibition of MSNA

Sleep Deprivation and Pain Intensity

Little or poor quality sleep is often reported in patients suffering from acute or chronic pain. Conversely, sleep loss has been known to elevate pain perception; thus a potential bi-direction relationship exists between sleep deprivation and pain. The effect of sleep deprivation on the thermal pain intensity has yet to be determined, furthermore, sex differences in pain have not been examined following sleep deprivation. There is also a higher prevalence of insomnia in women, and reports indicate that sleep quality is diminished and pain sensitivity may be greater during high hormone phases of the menstrual cycle. In Study 1 we examined the effects of 24-hour total sleep deprivation (TSD) on pain intensity during a 2-minute cold pressor test (CPT). We hypothesized that TSD would augment thermal pain intensity during CPT and women would demonstrate an elevated response compare to men. In Study 2 we investigated the effects of menstrual phase on pain intensity during CPT following TSD. We hypothesized that pain intensity would be augmented during the mid-luteal (ML) phase of the menstrual cycle. In Study 1, pain intensity was recorded during CPT in 14 men and 13 women after normal sleep (NS) and TSD. Pain intensity responses during CPT were elevated in both conditions; however, pain intensity was augmented (~ 1.2 a.u.) following TSD. When analyzed for sex differences, pain intensity was not different between men and women in either condition. In Study 2, pain intensity was recorded during CPT in 10 female subjects during the early follicular (EF) and ML phases of the menstrual cycle after TSD. Estradiol and progesterone levels were elevated during the ML phase, however, pain intensity was not different between the two phases. We conclude that TSD significantly augments pain intensity during CPT, but this response is not sex dependent. We further demonstrate that the collective effect of TSD and elevated gonadal hormone concentrations do not result in a differential pain response during the EF and ML phases of the menstrual cycle. Collectively, sleep loss augments pain intensity ratings in men and women and may contribute to sleep loss in painful conditions

Age-associated adaptations in lower limb motor patterns during walking and cycling

Muscular strength and power generating ability decline with advancing age. Older adults adapt their lower limb motor patterns to cope with these declines in muscle function. When mechanical demands approach limits of lower limb muscular capacity, motor patterns must be adapted to produce a desired movement. The term “motor pattern” is used to broadly represent the kinematic and kinetic profile of a person accomplishing a given task. Generally, these adaptations involve higher reliance on stronger proximal muscles to compensate for limitations or weakness of distal muscles. Three studies were conducted to examine factors affecting differences between older and young adults in lower extremity mechanics for walking and cycling. In the first two studies, the effects of physical activity status, walking speed, and step length on lower extremity motor patterns of older and young adults were examined. As walking speed and step length increased, lower extremity muscular effort, as reflected by joint moments and power, increased. Differences in motor patterns between older and young participants, were preserved for multiple speed and step length conditions. In general, older adults showed higher reliance on hip musculature to compensate for lower muscle strength of plantarflexors. Moreover, sedentary and older groups, who had lower leg strength, exhibited similar lower limb motor patterns during walking. Likewise, physically active and young participants, who had higher lower extremity strength, displayed similar lower limb motor patterns. Consistent with the 2008 Physical Activity Guidelines for Americans, these results suggest that adopting and maintaining a physically active life-style can help maintain walking abilities in older adults. When cycling at a submaximal intensities, both older and young participants showed higher reliance on muscles about the knee and had higher rates of energy cost for higher power outputs and cadences. Older adults had higher rates of energy cost and higher co-activation of thigh antagonistic muscles during cycling than young adults. The higher antagonist co-activation likely contributes to older adults higher energy cost. Considering all study outcomes, differences in motor patterns used by older and young adults were more apparent for walking than cycling. The less prominent age-related differences in cycling are likely related to its non-weight bearing characteristic, heavier reliance on hip and knee muscular effort, and the kinematically constrained nature of the cycling task

Acute alcohol ingestion and sympathetic neural responses during orthostatic stress in humans

Acute alcohol consumption has been reported to decrease mean arterial pressure (MAP) during orthostatic challenge, a response that may contribute to alcohol-mediated hypotension and eventually syncope. Muscle sympathetic nerve activity (MSNA) increases during orthostatic stress to help maintain MAP, yet the influence of alcohol on MSNA during orthostatic stress has not been determined. We hypothesized that alcohol ingestion would blunt arterial blood pressure and MSNA responses to progressive lower body negative pressure (LBNP). MAP, MSNA, and heart rate (HR) were recorded during progressive LBNP (-5, -10, -15, -20, -30, and -40 mmHg; 3 min/stage) in 30 subjects(age 24 ± 1 yrs). After an initial progressive LBNP protocol (pre-treatment), subjects were randomly assigned to consume alcohol (0.8g ethanol/kg body mass; n=15) or placebo (n=15) and then repeated the progressive LBNP protocol (post-treatment). Alcohol increased (drug × treatment, P ≤ 0.05) resting HR (59 ± 2 to 65 ± 2 beats/min) and MSNA (13 ± 3 to 19 ± 4 bursts/min) when compared to placebo. While alcohol increased MAP (83 ± 2 to 87 ± 2 mmHg), these increases were also observed with placebo (82 ± 2 to 88 ± 1 mmHg; treatment, P \u3c 0.05; drug × treatment, P \u3e 0.05). During progressive LBNP, a prominent decrease in MAP was observed after alcohol (drug × time × treatment, P \u3c 0.05), but not placebo. There was also a significant attenuated response in forearm vascular resistance (FVR) during progressive LBNP (drug × time × treatment, P \u3c 0.05). MSNA and HR increased during all LBNP protocols, but there were no differences between treatments or groups (drugs). In summary, acute alcohol ingestion induces an attenuation in blood pressure response during an orthostatic challenge, possibly due to the effect that alcohol has on impairing peripheral blood vessel constriction

Effects of pediatric adiposity on heart rate variability

The relationship between obesity and heart rate variability (HRV) has been studied in adults and adolescents, but is not determined in young pediatrics. The purpose of this study was to assess autonomic activity using HRV in a pediatric population. We hypothesized that obese children would have reduced parasympathetic and increased sympathetic activity compared to age-matched subjects. 42 pediatric subjects (ages 3-5) were classified into 3 groups based on body mass index-for-age; normal, overweight and obese. HRV and respiratory rate were recorded during 3 minute baseline, 2 minute isometric handgrip and 3 minute recovery. HRV was analyzed in the time domain [heart rate (HR), RR interval (RRI) and RRI standard deviation (RRISD)] and frequency domain [low frequency (LF), high frequency (HF) and LF/HF ratio] using repeated measures ANOVA. Spearman’s correlations were used to examine the relations between BMI and HRV at rest. Significant condition effects were found between baseline, exercise and recovery, but these responses were not significantly different between the normal, overweight and obese children. BMI was negatively correlated with LF/HF, while BMI was positively correlated with RRISD, LF, HF and nHF. Our data demonstrate that higher BMI in the pediatric population is correlated with higher parasympathetic and lower sympathetic activity. These findings are contrary to HRV responses observed in adults and adolescents, suggesting complex relationships between age, obesity and autonomic control of the heart. The data supports the concept of an age reliance of HRV and a novel relationship between adiposity and body mass index in 3-5 year olds

Effects of Elevated Salinity and Oxidative Stress on the Physiology of the Toxigenic Cyanobacterium Microcystis Aeruginosa

Harmful algal blooms (HABs) are found worldwide, particularly in places where warm, well-lit, and stagnant waters are common. HABs can have negative effects on aquatic plants and wildlife due to the reduction in light availability associated with turbidity, decrease in O2 availability, and the production of secondary metabolites that can harm or even prove lethal. Aquatic ecosystems are regularly being affected by elevated salinity because of recent water management strategies, episodes of drought, and salt water intrusion. This research focused on how salinity levels ranging from 0-10ppt affected physiological attributes such as cellular growth and abundance, cell mortality, toxin release, and oxidative stress in the toxigenic cyanobacterium, Microcystis aeruginosa. It was determined that salinity treatments of 7ppt and above caused a decrease in both cellular growth and abundance, as well as an increase in toxin release due to cell mortality. M. aeruginosa was able to survive in salinities up to 7ppt. A pattern of caspase activity in response to elevated salinity was shown, but whether cellular mortality was due solely to programmed cell death (PCD) was not definitive. A strong antioxidant response, measured through catalase activity, was noted when salinity was enhanced to 7ppt. Above this value, the damaging effects of salinity caused elevated levels of reactive oxygen species (ROS) production and cell death. It was determined that the maximum amount of hydrogen peroxide that M. aeruginosa could withstand without significant impact to growth and abundance was below 250µM. Salinities of 7ppt and above had a negative impact on the physiology of M. aeruginosa, leading to cell death and an increase in microcystin release into the environment. These two factors can lead to fish kills, poor drinking water, and other recreational and commercial problems for an aquatic ecosystem. By determining the precise salinity that HAB cellular mortality is imminent, predictive models can be employed to predict the impacts of salt intrusion and groundwater management

MINDFULNESS, AORTIC WAVE REFLECTION, AND ARTERIAL STIFFNESS

Cardiovascular disease and hypertension are leading causes of death worldwide. The mitigation of high blood pressure is essential in decreasing the prevalence of cardiovascular-related deaths worldwide. Stress and anxiety are known to play a role in augmenting blood pressure in individuals of all ages. This increase in pressure can result in premature stiffening of large arteries in systemic circulation. Mindfulness is an ancient, non-secular practice which aids in stress reduction. Decentering, an aspect of mindfulness, involves accepting thoughts as transient rather than permanent associations. The purpose of this project was to examine the relationship between cardiovascular health and mindfulness practices. In Study 1, we investigated how a one-hour session of mindfulness meditation affected arterial stiffness and other cardiovascular variables. In Study 2, we compared inexperienced meditators’ inherent ability to decenter with their arterial stiffness. We hypothesized that an acute meditation session would improve cardiovascular variables in Study 1. In Study 2, we postulated that individuals who are better able to decenter would have a slower pulse wave velocity and more elastic arteries. Our results from Study 1 suggest that an acute session of meditation can significantly decrease aortic pulsatile load. In Study 2, we concluded that a greater ability to decenter is correlated with slower pulse wave velocity. These new findings support many previous studies that suggest that mindfulness practices are a beneficial lifestyle modification that can positively impact cardiovascular health

Tibial rotation and valgus movement at the knee during cutting and stopping

This study was performed to examine tibial rotation and valgus movement at the knee during dynamic sport-specific movements, a jump stop and a side cut maneuver associated with anterior cruciate ligament (ACL) injury. We aimed to assess whether six male and eight female skilled soccer athletes perform these maneuvers with different magnitudes of valgus movement and tibial rotation at the knee. Nine trials of each maneuver were analyzed for each subject. There was a significant difference between males and females for valgus angle at contact, maximum valgus angle, and maximum external rotation (p\u3c0.05). There was no difference for any dependant variable between jump stop and side cut maneuver, and Sex * Maneuver no interaction. Though there is certainly more than one reason for greater number of ACL injuries in females, not finding a difference in valgus movement between the sexes may indicate that tibial rotation might play a greater role than valgus movement alone