In this Issue
October 2016; volume 121, issue 4
- Using devices to upregulate nonnutritive swallowing in typically developing infants
Sensory stimuli—a pacifier and a vibrator placed over the laryngeal area on the neck—were used to determine whether they could upregulate reflexive swallowing in typically developing infants. Both increased reflexive swallowing, although the vibrator did not alter respiratory rate in typical infants. Because vibration would not interfere with oral feeding, further research is needed to determine whether the novel vibratory device might enhance swallowing during feeding in infants with oral feeding difficulties.
- Whey protein with potassium bicarbonate supplement attenuates the reduction in muscle oxidative capacity during 19 days of bed rest
Reduced muscle oxidative capacity and capillary rarefaction may be critical factors in disuse-induced muscle weakness in spaceflight or bed rest. Here we show that 19 days of bed rest induced a reduction in the fiber oxidative capacity, irrespective of muscle (soleus and vastus lateralis muscle) or fiber type, without significant capillary loss, that was in part attenuated by a whey protein plus potassium bicarbonate-enriched diet.
- Contractile properties of motor units and expression of myosin heavy chain isoforms in rat fast-type muscle after volitional weight-lifting training
At the early stage of resistance exercise, modifications to motor unit muscle fiber contractile force, speed, and fatigue resistance occur before any significant transition in the muscle myosin heavy chain isoform and upregulation of Ca2+-handling proteins can be detected.
- Attenuation of exercise effect on inflammatory responses via novel role of TLR4/PI3K/Akt signaling in rat splenocytes
The spleen is an important innate/adaptive immunity organ. To our knowledge, this is the first study to illustrate that exercise attenuates immune responses via a novel regulatory activity in the spleen. Our study demonstrates science-based evidence to support exercise exerting potent anti-inflammatory activity by suppressing toll-like receptor 4 (TLR4) and phospho-NF-κB while promoting the activation of phosphoinositide 3-kinase (PI3K)/Akt expression, consequently leading to decreased LPS-induced proinflammatory molecules. These observations provide novel insights for better understanding of the immunomodulatory effects of exercise.
- Improved single muscle fiber quality in the oldest-old
This is the first study to report single muscle fiber strength, speed, and power in the oldest-old. These data suggest an improvement in myocellular quality with age that is more pronounced in the fast-twitch muscle fibers. The improved quality of these remaining muscle fibers suggests a “survival of the fittest” phenomenon that is in contrast to the classic aging skeletal muscle dogma.
- Healthy aging does not compromise the augmentation of cardiac function during heat stress
Previous studies suggest that healthy aged humans are unable to maintain stroke volume during heat stress. We hypothesized that this is due to an inappropriate augmentation of cardiac function during heat stress. Contrary to our hypothesis, stroke volume was maintained during heat stress in healthy aged adults and was accompanied by a leftward shift of the Frank-Starling relation. These results suggest that cardiac function is appropriately augmented during heat stress in healthy aged humans.
- Athletic training affects the uniformity of muscle and tendon adaptation during adolescence
This study demonstrates for the first time that athletic training during adolescence can disrupt the uniformity of muscle and tendon adaptation. The resultant imbalance of muscle strength and tendon stiffness increases the demand on the tendon. This could have potential implications for the risk of overuse injury, which is a major problem in specific sport disciplines.
- A structure-function analysis of the left ventricle
Our model of oxygen transport through left ventricular cardiac tissue shows that oxygen demands are easily satisfied at rest, but only just satisfied during simulated heavy exercise. We also find that cardiac mitochondria likely operate close to their functional limits during heavy exercise. However, the cardiac myofibrils retain a reserve capacity for tension development, which possibly protects the left ventricle from excessive force loads during health and compensates for impaired function during disease.
- Continuous positive airway pressure treatment does not normalize the prolonged reflex inhibition to inspiratory loading in obstructive sleep apnea
Patients with severe obstructive sleep apnea have an abnormal prolongation of the inhibitory reflex to inspiratory muscle loading. However, in this study we found that treatment with continuous positive airway pressure at night does not reverse the abnormality. The explanation for the failure of the reflex to return to normal is unknown.
- Effect of irradiation on Akt signaling in atrophying skeletal muscle
Despite important clinical and physiological significance there is currently limited information on how irradiation interacts with skeletal muscle unloading. Our study examined the independent and combined effects of acute irradiation exposure and short-term unloading on muscle Akt signaling. We report that an acute dose of irradiation is sufficient to alter unloading-induced regulation of Akt signaling.
- Computational fluid dynamics upper airway effective compliance, critical closing pressure, and obstructive sleep apnea severity in obese adolescent girls
This study applied an engineering tool, computational fluid dynamics, to noninvasively estimate the pharyngeal air pressure field based on dynamic MR images acquired during relaxed wakeful tidal breathing. The slope of cross-sectional area vs. airway pressure was defined as the “effective compliance” and was often negative, which is attributed to strong activation of airway dilators during inspiration. Effective compliance in the nasopharynx was more negative in girls with obstructive sleep apnea syndrome and correlated with Pcrit.
- Central command does not suppress baroreflex control of cardiac sympathetic nerve activity at the onset of spontaneous motor activity in the decerebrate cat
We examined the effects of spontaneous motor activity on baroreflex-induced decreases in cardiac sympathetic outflow and heart rate, elicited by aortic occlusion, in paralyzed, decerebrate cats. Baroreflex bradycardia was blunted at the onset of spontaneous motor activity, whereas baroreflex inhibition of cardiac sympathetic outflow was not altered at all. The finding implies that central command must attenuate cardiovagal baroreflex sensitivity at the onset of spontaneous motor activity while preserving baroreflex control of cardiac sympathetic outflow.
- Heme oxygenase-1-dependent central cardiorespiratory adaptations to chronic intermittent hypoxia in mice
Oxygen sensitivity of central cardiorespiratory regions including the pre-Bötzinger complex and C1 region are heme oxygenase (HO) dependent and may be altered by chronic intermittent hypoxia (CIH). Induced expression of HO-1 in wild-type mice and decline in hypoxic sensitivity of sighs and sympathetic activity were seen in wild-type and HO-1 null mice following 1 day of CIH that persisted in HO-1 null mice, suggesting HO-1-dependent alterations in oxygen sensitivity in these regions following CIH.
- Assessment of the interaction of hyperbaric N2, CO2, and O2 on psychomotor performance in divers
N2, CO2, and O2 affected cognitive performance differently. Attention, memory, and planning were more affected by N2 than CO2. Motor tasks were nearly unaffected by N2. O2 at 0.925 ATA partially rescued motor and memory reaction time impaired by 0.075-ATA CO2. However, 1.22-ATA O2 with 4.5-ATA N2, 0.075-ATA CO2, and exercise caused incapacitation with amnesia. O2 narcosis or enhanced O2 toxicity is postulated. Perception of narcosis was not correlated with actual scores.
- Gut fermentation seems to promote decompression sickness in humans
This is the first time that the gut microbiota has been shown to affect the risk of decompression sickness in humans: we show that gut bacterial fermentation seems to exacerbate the likelihood of the problem. This confirms results that we obtained in rats in simulated air dives in a chamber. The main interest of this study is to suggest new recommendations on how to prevent decompression sickness by reducing the fermentation rate in the gut.
- FloWave.US: validated, open-source, and flexible software for ultrasound blood flow analysis
We developed FloWave.US, publicly distributed software for automated ultrasound blood flow analysis. The software provides efficient and reliable measures of blood velocity and vessel diameter that are valid with a skeletal muscle flow phantom and independent of the ultrasound scanner. Open-source access to this software reduces barriers to use and enables community improvements and customization of analysis features to advance vascular physiology research.
- Optical coherence tomography in the assessment of acute changes in cutaneous vascular diameter induced by heat stress
This manuscript examines for the first time the utility of optical coherence tomography (OCT) as a novel imaging technique to visualize and quantify changes in the cutaneous microvasculature in response to acute passive heating. We hypothesized that lower body heating would induce detectible microvascular changes in the skin of the forearm. Our findings demonstrate the capacity of OCT to image vascular structures over multiple time points and to quantify these changes using automated techniques.
HIGHLIGHTED TOPIC | Aging and Exercise
- Modeling age-related changes in muscle-tendon dynamics during cyclical contractions in the rat gastrocnemius
The age-related increase in muscle and tendon tissue stiffness and reduction in active force capacity of the muscle compromise elastic energy utilization and positive work production, which may require the recruitment of additional muscle volume potentially contributing to the increased cost of locomotion observed in older individuals.
- Motor unit number and transmission stability in octogenarian world class athletes: Can age-related deficits be outrun?
World champion master athletes in their ninth decade of life had a greater number of surviving motor units, reduced collateral reinnervation, better neuromuscular transmission stability, and a greater amount of excitable muscle mass compared with age-matched controls. The presumed better maintenance of motor units occurs at a time point when motor unit loss is greatest and the loss of muscle mass becomes functionally relevant, potentially maintaining function and attenuating the deleterious effects of sarcopenia.
- Effects of hypervolemia by protein and glucose supplementation during aerobic training on thermal and arterial pressure regulations in hypertensive older men
The incidence of heat illness has rapidly increased in older people during the midsummer. Protein+carbohydrate supplementation during aerobic training reportedly increased plasma volume to enhance thermoregulatory adaptation; however, in hypertensive older people, the symptoms may be worsened by hypervolemia. We demonstrated that in hypertensive older men, protein+glucose supplementation during aerobic training increased plasma volume and thermoregulation, but blood pressure rather decreased. Thus, we find the prescription to be applicable to hypertensive older people to prevent heat illness.
- Resistance or aerobic training decreases blood pressure and improves cardiovascular autonomic control and oxidative stress in hypertensive menopausal rats
Although in a different magnitude, dynamic resistance training (RT) is able to decrease blood pressure in hypertensive menopausal rats compared with aerobic training. Mechanisms related to cardiovascular autonomic control and cardiac oxidative stress were associated to this decrease. Therefore, menopausal individuals with hypertension may be benefitted by not only the osteomuscular benefits of RT but also by improved mechanisms of blood pressure control, which in association with aerobic training may account for cardiovascular risk prevention.