Semimetal to semiconductor transition in Bi/TiO2 core/shell nanowires.

We demonstrate the full thermoelectric and structural characterization of individual bismuth-based (Bi-based) core/shell nanowires. The influence of strain on the temperature dependence of the electrical conductivity, the absolute Seebeck coefficient and the thermal conductivity of bismuth/titanium dioxide (Bi/TiO2) nanowires with different diameters is investigated and compared to bismuth (Bi) and bismuth/tellurium (Bi/Te) nanowires and bismuth bulk. Scattering at surfaces, crystal defects and interfaces between the core and the shell reduces the electrical conductivity to less than 5% and the thermal conductivity to less than 25% to 50% of the bulk value at room temperature. On behalf of a compressive strain, Bi/TiO2 core/shell nanowires show a decreasing electrical conductivity with decreasing temperature opposed to that of Bi and Bi/Te nanowires. We find that the compressive strain induced by the TiO2 shell can lead to a band opening of bismuth increasing the absolute Seebeck coefficient by 10% to 30% compared to bulk at room temperature. In the semiconducting state, the activation energy is determined to |41.3 ± 0.2| meV. We show that if the strain exceeds the elastic limit the semimetallic state is recovered due to the lattice relaxation.

Effects of resistance training protocols on nonlinear analysis of heart rate variability in metabolic syndrome.

Despite the various standard non-linear measurements used in autonomic modulation (AM) assessments usually being applied to long time-series, such analyses can sometimes be applied to shorter term series. To overcome this disadvantage, chaotic global methods were formulated by putting together heart rate variability (HRV) linear methods. Chaos provides information about vegetative function control related to cardiovascular risks. Applying this method can be useful to investigate the complexity of the health condition after resistance training protocols, as a therapeutic intervention in AM in metabolic syndrome individuals (MetS). This study aimed to compare the effects of two resistance training programs (conventional vs functional) in MetS using nonlinear analysis of AM. MetS subjects (n=50) of both sexes aged 40 to 60 years were randomly divided into two programs; a group of 12 people served as a control group. Both groups performed 30 sessions of training. AM was assessed in the chaos domain by chaotic global techniques. The main results showed that both resistance training, functional and conventional, increased chaos when compared to the control group, respectively, observed by chaotic forward parameter (CFP)1 (13.9±17.9 vs 12.8±14.4 vs -2.23±7.96; P≤0.05) and CFP3 (15.4±19.8 vs 21.9±13.2 vs -4.82±11.4; P≤0.05). In addition, 30 sessions of both resistance programs increased chaos, and non-linear analysis enabled discrimination of AM after interventions when compared to the control group.

Effects of resistance training protocols on nonlinear analysis of heart rate variability in metabolic syndrome

Despite the various standard non-linear measurements used in autonomic modulation (AM) assessments usually being applied to long time-series, such analyses can sometimes be applied to shorter term series. To overcome this disadvantage, chaotic global methods were formulated by putting together heart rate variability (HRV) linear methods. Chaos provides information about vegetative function control related to cardiovascular risks. Applying this method can be useful to investigate the complexity of the health condition after resistance training protocols, as a therapeutic intervention in AM in metabolic syndrome individuals (MetS). This study aimed to compare the effects of two resistance training programs (conventional vs functional) in MetS using nonlinear analysis of AM. MetS subjects (n=50) of both sexes aged 40 to 60 years were randomly divided into two programs; a group of 12 people served as a control group. Both groups performed 30 sessions of training. AM was assessed in the chaos domain by chaotic global techniques. The main results showed that both resistance training, functional and conventional, increased chaos when compared to the control group, respectively, observed by chaotic forward parameter (CFP)1 (13.9±17.9 vs 12.8±14.4 vs -2.23±7.96; P≤0.05) and CFP3 (15.4±19.8 vs 21.9±13.2 vs -4.82±11.4; P≤0.05). In addition, 30 sessions of both resistance programs increased chaos, and non-linear analysis enabled discrimination of AM after interventions when compared to the control group.

Quantification of dyspnoea using descriptors: development and initial testing of the Dyspnoea-12.

RATIONALE: Dyspnoea is a debilitating and distressing symptom that is reflected in different verbal descriptors. Evidence suggests that dyspnoea, like pain perception, consists of sensory quality and affective components. The objective of this study was to develop an instrument that measures overall dyspnoea severity using descriptors that reflect its different aspects. METHODS: 81 dyspnoea descriptors were administered to 123 patients with chronic obstructive pulmonary disease (COPD), 129 with interstitial lung disease and 106 with chronic heart failure. These were reduced to 34 items using hierarchical methods. Rasch analysis informed decisions regarding further item removal and fit to the unidimensional model. Principal component analysis (PCA) explored the underlying structure of the final item set. Validity and reliability of the new instrument were further assessed in a separate group of 53 patients with COPD. RESULTS: After removal of items with hierarchical methods (n = 47) and items that failed to fit the Rasch model (n = 22), 12 were retained. The "Dyspnoea-12" had good internal reliability (Cronbach's alpha = 0.9) and fit to the Rasch model (chi(2) p = 0.08). Items patterned into two groups called "physical"(n = 7) and "affective"(n = 5). In the separate validation study, Dyspnoea-12 correlated with the Hospital Anxiety and Depression Scale (anxiety r = 0.51; depression r = 0.44, p<0.001, respectively), 6-minute walk distance (r = -0.38, p<0.01) and MRC (Medical Research Council) grade (r = 0.48, p<0.01), and had good stability over time (intraclass correlation coefficient = 0.9, p<0.001). CONCLUSION: Dyspnoea-12 fulfills modern psychometric requirements for measurement. It provides a global score of breathlessness severity that incorporates both "physical" and "affective" aspects, and can measure dyspnoea in a variety of diseases.

Time course of air hunger mirrors the biphasic ventilatory response to hypoxia.

Determining response dynamics of hypoxic air hunger may provide information of use in clinical practice and will improve understanding of basic dyspnea mechanisms. It is hypothesized that air hunger arises from projection of reflex brain stem ventilatory drive ("corollary discharge") to forebrain centers. If perceptual response dynamics are unmodified by events between brain stem and cortical awareness, this hypothesis predicts that air hunger will exactly track ventilatory response. Thus, during sustained hypoxia, initial increase in air hunger would be followed by a progressive decline reflecting biphasic reflex ventilatory drive. To test this prediction, we applied a sharp-onset 20-min step of normocapnic hypoxia and compared dynamic response characteristics of air hunger with that of ventilation in 10 healthy subjects. Air hunger was measured during mechanical ventilation (minute ventilation = 9 +/- 1.4 l/min; end-tidal Pco(2) = 37 +/- 2 Torr; end-tidal Po(2) = 45 +/- 7 Torr); ventilatory response was measured during separate free-breathing trials in the same subjects. Discomfort caused by "urge to breathe" was rated every 30 s on a visual analog scale. Both ventilatory and air hunger responses were modeled as delayed double exponentials corresponding to a simple linear first-order response but with a separate first-order adaptation. These models provided adequate fits to both ventilatory and air hunger data (r(2) = 0.88 and 0.66). Mean time constant and time-to-peak response for the average perceptual response (0.36 min(-1) and 3.3 min, respectively) closely matched corresponding values for the average ventilatory response (0.39 min(-1) and 3.1 min). Air hunger response to sustained hypoxia tracked ventilatory drive with a delay of approximately 30 s. Our data provide further support for the corollary discharge hypothesis for air hunger.

Hypoxic and hypercapnic drives to breathe generate equivalent levels of air hunger in humans.

Anecdotal observations suggest that hypoxia does not elicit dyspnea. An opposing view is that any stimulus to medullary respiratory centers generates dyspnea via "corollary discharge" to higher centers; absence of dyspnea during low inspired Po(2) may result from increased ventilation and hypocapnia. We hypothesized that, with fixed ventilation, hypoxia and hypercapnia generate equal dyspnea when matched by ventilatory drive. Steady-state levels of hypoxic normocapnia (end-tidal Po(2) = 60-40 Torr) and hypercapnic hyperoxia (end-tidal Pco(2) = 40-50 Torr) were induced in naive subjects when they were free breathing and during fixed mechanical ventilation. In a separate experiment, normocapnic hypoxia and normoxic hypercapnia, "matched" by ventilation in free-breathing trials, were presented to experienced subjects breathing with constrained rate and tidal volume. "Air hunger" was rated every 30 s on a visual analog scale. Air hunger-Pet(O(2)) curves rose sharply at Pet(O(2)) <50 Torr. Air hunger was not different between matched stimuli (P > 0.05). Hypercapnia had unpleasant nonrespiratory effects but was otherwise perceptually indistinguishable from hypoxia. We conclude that hypoxia and hypercapnia have equal potency for air hunger when matched by ventilatory drive. Air hunger may, therefore, arise via brain stem respiratory drive.

Repeated exercise paired with "imperceptible" dead space loading does not alter VE of subsequent exercise in humans.

We employed an associative learning paradigm to test the hypothesis that exercise hyperpnea in humans arises from learned responses forged by prior experience. Twelve subjects undertook a "conditioning" and a "nonconditioning" session on separate days, with order of performance counterbalanced among subjects. In both sessions, subjects performed repeated bouts of 6 min of treadmill exercise, each separated by 5 min of rest. The only difference between sessions was that all the second-to-penultimate runs of the conditioning session were performed with added dead space in the breathing circuit. Cardiorespiratory responses during the first and last runs (the "control" and "test" runs) were compared for each session. Steady-state exercise end-tidal PCO(2) was significantly lower (P = 0.003) during test than during control runs for both sessions (dropping by 1.8 +/- 2 and 1.4 +/- 3 Torr during conditioning and nonconditioning sessions, respectively). This and all other test-control run differences tended to be greater during the first session performed regardless of session type. Our data provide no support for the hypothesis implicating associative learning processes in the ventilatory response to exercise in humans.

Central chemosensitivity and breathing asleep in unilateral medullary lesion patients: comparisons to animal data.

The rostro-ventrolateral medulla (RVLM) is a site of chemosensitivity in animals; such site(s) have not been defined in humans. We studied the effect of unilateral focal lesions in the rostrolateral medulla (RLM) of man, on the ventilatory CO(2) sensitivity and during awake and sleep breathing. Nine patients with RLM lesions (RLM group), and six with lesions elsewhere (non-RLM group) were studied. The ventilatory CO(2) sensitivity was lower in the RLM compared with the non-RLM group (mean (S.D.), RLM, 1.4 (0.9), non-RLM 3.0 (0.6) L min(-1) mmHg(-1)). In both groups resting breathing was normal. During sleep all RLM patients had frequent arousals, four had significant sleep disordered breathing (SDB), only one non-RLM patient had SDB. Our findings in humans resemble those in animals with focal RVLM lesions. This review provides evidence that in humans there is an area of chemosensitivity in the RLM. We propose that in humans, dorsal displacement of the RVLM area of chemosensitivity in animals, arises from development of the olive plus the consequences of the evolution of the cerebellum/inferior peduncle.

Acute partial paralysis alters perceptions of air hunger, work and effort at constant P(CO(2)) and V(E).

Breathing sensations of AIR HUNGER, WORK and EFFORT may depend on projections of central motor discharge (corollary discharge) to the forebrain. Source of motor drive (brainstem or cortex) may determine what is perceived. To test the effect of changing motor discharge at constant ventilation, we induced partial neuromuscular blockade during hypercapnic hyperpnea (31 + or - 9 L min(-1); PET(CO(2))=49 + or - 2 Torr) and during matched volitional hyperpnea (34 + or - 5 L min(-1); PET(CO(2))=41 + or - 1 Torr). Decline of vital capacity was similar between conditions (39%). Ventilation was unchanged with paralysis, indicating increased respiratory motor drive to maintain hyperpnea. Sensations were rated on a seven point ordinal scale. Median EFFORT and WORK increased 3-3.5 points with paralysis during both forms of hyperpnea (P<0.02, Wilcoxon signed rank). Median AIR HUNGER increased 2.5 points with paralysis during hypercapnic (P<0.02) but not during volitional hyperpnea. Data suggests that EFFORT and WORK arise from motor cortex activity (subjects reported engaging volitional control when paralyzed even during hypercapnia) and suggests that AIR HUNGER arises from medullary motor activity.

Simple contrivance "clamps" end-tidal PCO(2) and PO(2) despite rapid changes in ventilation.

The device described in this study uses functionally variable dead space to keep effective alveolar ventilation constant. It is capable of maintaining end-tidal PCO(2) and PO(2) within +/-1 Torr of the set value in the face of increases in breathing above the baseline level. The set level of end-tidal PCO(2) or PO(2) can be independently varied by altering the concentration in fresh gas flow. The device comprises a tee at the mouthpiece, with one inlet providing a limited supply of fresh gas flow and the other providing reinspired alveolar gas when ventilation exceeds fresh gas flow. Because the device does not depend on measurement and correction of end-tidal or arterial gas levels, the response of the device is essentially instantaneous, avoiding the instability of negative feedback systems having significant delay. This contrivance provides a simple means of holding arterial blood gases constant in the face of spontaneous changes in breathing (above a minimum alveolar ventilation), which is useful in respiratory experiments, as well as in functional brain imaging where blood gas changes can confound interpretation by influencing cerebral blood flow.

Unilateral focal lesions in the rostrolateral medulla influence chemosensitivity and breathing measured during wakefulness, sleep, and exercise.

OBJECTIVES: The rostrolateral medulla (RLM) has been identified in animals as an important site of chemosensitivity; in humans such site(s) have not been defined. The aim of this study was to investigate the physiological implications of unilateral lesions in the lower brainstem on the control of breathing. METHODS: In 15 patients breathing was measured awake at rest, asleep, during exercise, and during CO(2) stimulation. The lesions were located clinically and by MRI; in nine patients they involved the RLM (RLM group), in six they were in the pons, cerebellum, or medial medulla (Non-RLM group). All RLM group patients, and three non-RLM group patients had ipsilateral Horner's syndrome. RESULTS: Six of the RLM group had a ventilatory sensitivity to inhaled CO(2) (V/P(ET) CO(2)) below normal (group A: V/P(ET) CO(2), mean, 0.87; range 0.3-1.4 l. min(-1)/mm Hg). It was normal in all of the non-RLM group (group B: V/P(ET) CO(2), mean, 3.0; range, 2.6-3.9 min(-1)/mmHg). There was no significant difference in breathing between groups during relaxed wakefulness (V, group A: 7.44 (SD 2.5) l.min(-1); group B: 6.02 (SD 1.3) l.min(-1); P(ET) CO(2), group A: 41.0 (SD 4.2) mm g; group B: 38.3 (SD2.0) mm Hg) or during exercise (V/VO(2): group A: 21 (SD 6. 0) l.min(-1)/l.min(-1); group B: 24 (SD 7.3) l.min(-1)/l.min(-1)). During sleep, all group A had fragmented sleep compared with only one patient in group B (group A: arousals, range 13 to > 60 events/hour); moreover, in group A there was a high incidence of obstructive sleep apnoea associated with hypoxaemia. CONCLUSION: Patients with unilateral RLM lesions require monitoring during sleep to diagnose any sleep apnoea. The finding that unilateral RLM lesions reduce ventilatory sensitivity to inhaled CO(2) is consistent with animal studies. The reduced chemosensitivity had a minimal effect on breathing awake at rest or during exercise.

Corticospinal function in severe brain injury assessed using magnetic stimulation of the motor cortex in man.

We have assessed corticospinal function in 19 post-coma patients severely brain-injured by anoxia or physical trauma. Eleven patients were unresponsive (Category 1) and eight demonstrated minimal, non-verbal responses to simple commands (Category 2). Motor evoked potentials (MEPs) could be elicited in hand and leg muscles in nine Category 1 and all eight Category 2 patients in response to transcranial magnetic stimulation (TMS). In comparison with normal subjects, threshold to TMS was significantly elevated in Category 1 but not in Category 2. Central conduction times were within the normal range except for two patients (one in each category) in whom they were prolonged. The variability in MEP amplitude to constant TMS was not significantly different from normal in either category. The size of MEPs recorded simultaneously in different hand muscles were correlated in all three groups. The presence of H-reflexes in hand muscles was associated with an absence of MEPs or a high threshold to TMS. Variability of MEPs was substantially greater than that of H-reflexes. We conclude that brain injury of a severity that may preclude consciousness and voluntary movement does not invariably predicate a non-functional motor cortex and corticospinal system.

Imagination of dynamic exercise produced ventilatory responses which were more apparent in competitive sportsmen.

1. The cardiorespiratory response to imagination of previously performed treadmill exercise was measured in six competitive sportsmen and six non-athletic males. This was compared with the response to a control task (imaging letters) and a task not involving imagination ('treadmill sound only'). 2. In athletes, imagined exercise produced increases in ventilation which varied within and between subjects. The mean maximal increase (11.71 min-1) was approximately 20% of the ventilatory response to actual exercise. This was primarily due to treadmill speed-related increases in respiratory frequency (mean maximal increase, 14.8 breaths min-1) and resulted in significant reductions in end-tidal PCO2 (mean maximal fall, 7 mmHg). These effects were greater (P < 0.01) than any observed during the control tasks. 3. Changes in heart rate (mean increase, 12 beats min-1) were not significantly different from those observed during the control tasks (P > 0.2). 4. In non-athletes, imagination of exercise produced no changes in cardiorespiratory variables. No significant differences were detected in subjective assessments of movement imagery ability between athletes and non-athletes (P = 0.17). 5. This study demonstrates that ventilatory effects, when observed, are specific to imagination of exercise. The greater likelihood of generating ventilatory responses in highly trained athletes, experienced in 'rhythmic' sports, may be related to awareness of breathing and its role in exercise imagination strategy. A volitional component of the response cannot be discounted.