Higher Fb Research Articles

How does cervical spinal cord injury impact the cardiopulmonary response to exercise?

We compared cardiopulmonary responses to arm-ergometry in individuals with cervical spinal cord injury (C-SCI) and able-bodied controls. We hypothesized that individuals with C-SCI would have higher respiratory frequency (fb) but lower tidal volume (VT) at a given work rate and dynamically hyperinflate during exercise, whereas able-bodied individuals would not. Participants completed pulmonary function testing, an arm-ergometry test to exhaustion, and a sub-maximal exercise test consisting of four-minute stages at 20, 40, 60, and 80% peak work rate. Able-bodied individuals completed a further sub-maximal test with absolute work rate matched to C-SCI. During work rate matched sub-maximal exercise, C-SCI had smaller VT (main effect p < 0.001) compensated by an increased fb (main effect p = 0.009). C-SCI had increased end-expiratory lung volume at 80% peak work rate vs. rest (p < 0.003), whereas able-bodied did not. In conclusion, during arm-ergometry, individuals with C-SCI exhibit altered ventilatory patterns characterized by reduced VT, higher fb, and dynamic hyperinflation that may contribute to the observed reduced aerobic exercise capacity.

Ventilatory adaptation during eccentric cycling in patients with severe COPD: Potential implications for exercise training

IntroductionEccentric (ECC) cycling is viewed as an alternative to concentric (CON) cycling for exercise training in patients with severe COPD as it induces a much lower ventilatory demand for a given mechanical load than CON cycling. However, a more hyperpneic breathing pattern (i.e., higher fB and lower tidal volume (VT)) during ECC than during CON has been reported in healthy subjects. Research questionDo patients with severe COPD develop a more hyperpneic breathing pattern during ECC than during CON cycling, and is it associated with differences in dynamic hyperinflation, ventilatory efficiency and cardiometabolic adaptation? MethodsFourteen patients with severe COPD performed incremental CON and ECC cardiopulmonary exercise tests (CPET). Several physiological parameters including VT, fB, inspiratory capacity (IC) and oxygen consumption (V̇O2) were recorded at each workload increment during CPET. ResultsAt the highest identical minute ventilation (V̇E) achieved during ECC and CON (28.6 ± 4.6 L.min−1), VT was lower (1010 ± 218 vs. 1100 ± 233 mL; p = 0.02), fB was higher (29.0 ± 5.1 vs. 27.0 ± 5.5 min−1; p = 0.03), IC(% baseline) was lower (84 ± 10 vs. 78 ± 9; p < 0.01) and markers of ventilatory efficiency were poorer during ECC than during CON. Similar results were found at the highest identical V̇O2 achieved during ECC and CON. ConclusionThe finding of a more hyperpneic ventilatory pattern during ECC cycling together with a lower IC and a poorer ventilatory efficiency suggests that ECC exercise training should be decided with caution in patients with severe COPD.

Comment on Krasnov et al. ''Temperature dependence of lifetime...'', C. Appl. Phys. 2015

In a recent paper [V.A. Krasnov et al., Curr. Appl. Phys. 15 (2015) 504–510], Krasnov et al., derived an equation for the recombination lifetime (τ0) dependency on the temperature and applied voltage of the wide band gap P+–n GaP junctions. They stared with Sah–Noyce–Shockley (SNS) theory based on the Shockley–Read–Hall (SRH) recombination in the Space Charge Region (SCR). However, they used a rather simplified version of the recombination mechanism to derive the recombination lifetime. This comment is to correct the derived Eq. (4) in [V.A. Krasnov et al., Curr. Appl. Phys. 15 (2015) 504–510] which neglects the pre-exponential (dependent on (Eg−2∆µ)−1/2 and also exponential factor (exp(qV/nkT)–1) in the SNS theory. Also, the presence of different trap levels and uncompensated defect density (NB) within the band gap was ignored and the rise in τ0 under higher FB was related to narrowed SCR and gradually increased nonequilibrium charge carriers that no more recombine and cause increased τ0. This is incorrect. This overestimation occur by ignoring the variation in the ideality factor under bias and temperature. Also by calculating the recombination rate for the different trap levels and densities. The thermal sensitivity of τ0 is corrected to be due to the presence of shallow levels in the bandgap.

Effects of the mycotoxin fumonisin B1 on cell death in human kidney cells and human lung fibroblasts in primary culture

Fumonisins are mycotoxins produced by Fusarium verticillioides. The toxic effects of fumonisin B(1) (FB(1)) at the cellular level consist of a mixture of both necrosis and apoptosis. We studied the effect of FB(1) in human lung fibroblasts (NHLF) and human kidney epithelial cells (RPTEC) in primary culture. Apoptotic and necrotic cell death, collagen and fibronectin secretion were determined mainly after 14 days' exposure. The protein content of NHLF and RPTEC cells was slightly increased after 14 days' exposure to low FB(1) concentrations (0.1 or 1 microm). Caspase-3 activity tended to increase in NHLF and to decrease in RPTEC cells with higher FB(1) concentrations after 14 days' exposure. LDH release was slightly decreased in both cell types after 14 days. Collagen I and III secretion was enhanced in NHLF cells. Collagen III was decreased in RPTEC. Collagen IV was not changed in both cell types. Fibronectin secretion was uninfluenced in RPTEC and interim increased in NHLF. Furthermore LC-MS/MS studies did not give any hints for a metabolism of FB(1). Therefore, the main risk of prolonged FB(1) exposure seems to be altered collagen secretion pattern.

Influence of experimental parameters on the fluorescence response and recovery of the high-performance liquid chromatography analysis of fumonisin B 1

The effect of mobile phase pH, column temperature, extraction method and derivatisation time on the fluorescence response and recovery of fumonisin B 1 in corn was investigated. Column temperature and mobile phase pH were negatively and positively correlated with the fluorescence response, respectively. Use of an Ultraturrax blender for extraction resulted in higher FB 1 recoveries compared to a rotary shaker. In contrast to other reports, maximum fluorescence response occurred after a derivatisation time of 8 min. These results reflect on the absolute requirement for standardisation of the aforementioned parameters.

Selective and transient activation of protein kinase C α by fumonisin B 1, a ceramide synthase inhibitor mycotoxin, in cultured porcine renal cells

Fumonisin B 1 (FB 1), a potent and naturally occurring mycotoxin produced by the fungus Fusarium verticillioides, has been implicated in fatal and debilitating diseases in animals and humans. FB 1 affects a variety of cell signaling proteins including protein kinase C (PKC); a serine/threonine kinase, involved in a number of signal transduction pathways that include cytokine induction, carcinogenesis and apoptosis. The aim of this study was to investigate the short-term temporal and concentration-dependent effects of FB 1 on PKC isoforms present in LLC-PK 1 cells in relation to the FB 1-induced accumulation of sphinganine and sphingosine utilizing various inhibitors and activators. Our studies demonstrated that FB 1 (0.1–1 μM) selectively and transiently activated PKCα at 5 min, without affecting PKC-δ, -ε and -ζ isoforms. At higher FB 1 concentrations and later time points (15–120 min), PKCα membrane concentrations declined to untreated levels. The observed increase in cytosol PKCα protein expression at 15 min was not associated with an increase in its activity or protein biosynthesis. Calphostin C, a PKC inhibitor, abrogated the FB 1-induced translocation of PKCα. Pre-incubation with the PKC activator, phorbol 12-myristate 13-acetate, resulted in an additive effect on membrane translocation of PKCα. Intracellular sphinganine and sphingosine concentrations were unaltered at the time points tested. Myriocin, a specific inhibitor of serine palmitoyltransferase, the first enzyme in de novo sphingolipid biosynthesis, did not prevent the FB 1-induced PKCα cytosol to membrane redistribution. Altering PKCα and its signal transduction pathways may be of importance in the ability of FB 1 to exert its toxicity via apoptosis and/or carcinogenesis.

Validity of Breathing Frequency to Monitor Exercise Intensity in Trained Cyclists

This study compared breathing frequency (fB) during a ventilation threshold (VT) test with fB during a simulated 40 km time trial (40TT) to assess whether fB can be used to monitor exercise intensity. Twenty-six male cyclists (mean +/- SD VO2max = 4.42 +/- 0274 l.min-1) performed an incremental VT ergometer test and a simulated 40TT on a set of wind-loaded rollers. During the 40TT, expired gas was collected for 3 min using open circuit spirometry at 10 km intervals. A significant correlation (r = 0.89; p < or = 0.05) was found between the fB threshold (VTf) and the gas exchange VT (VTg) (3.42 +/- 0.08 and 3.31 +/- 0.09 l.min-1, respectively). No differences were found in VO2 at the VTf vs. X VO2 (3.48 +/- 0.08 l.min-1) during the simulated 40TT. However, when fB in br.min-1 calculated from the VT test (32.5 br.min-1), was compared with fB during the 40TT (45.6 br.min-1), there was a significant difference. Ventilation, heart rate and the respiratory exchange ratio were all significantly higher during the 40TT. Although a significant relationship was found between the VT test and the 40TT for VTf measured in l.min-1 of VO2 (r = 0.66; p < or = 0.05), fB in br.min-1 obtained from the incremental test should not be used to identify exercise training intensity. These data suggest that during competition, trained athletes exercise at a higher fB than that determined when being tested, implying that fB in br.min-1 may not be a valid measurement of exercise intensity.

Auditory cortical neurons are sensitive to static and continuously changing interaural phase cues

1. The interaural-phase-difference (IPD) sensitivity of single neurons in the primary auditory (AI) cortex of the anesthetized cat was studied at stimulus frequencies ranging from 120 to 2,500 Hz. Best frequencies of the 43 AI cells sensitive to IPD ranged from 190 to 2,400 Hz. 2. A static IPD was produced when a pair of low-frequency tone bursts, differing from one another only in starting phase, were presented dichotically. The resulting IPD-sensitivity curves, which plot the number of discharges evoked by the binaural signal as a function of IPD, were deeply modulated circular functions. IPD functions were analyzed for their mean vector length (r) and mean interaural phase (phi). Phase sensitivity was relatively independent of best frequency (BF) but highly dependent on stimulus frequency. Regardless of BF or stimulus frequency within the excitatory response area the majority of cells fired maximally when the ipsilateral tone lagged the contralateral signal and fired least when this interaural-phase relationship was reversed. 3. Sensitivity to continuously changing IPD was studied by delivering to the two ears 3-s tones that differed slightly in frequency, resulting in a binaural beat. Approximately 26% of the cells that showed a sensitivity to static changes in IPD also showed a sensitivity to dynamically changing IPD created by this binaural tonal combination. The discharges were highly periodic and tightly synchronized to a particular phase of the binaural beat cycle. High synchrony can be attributed to the fact that cortical neurons typically respond to an excitatory stimulus with but a single spike that is often precisely timed to stimulus onset. A period histogram, binned on the binaural beat frequency (fb), produced an equivalent IPD-sensitivity function for dynamically changing interaural phase. For neurons sensitive to both static and continuously changing interaural phase there was good correspondence between their static (phi s) and dynamic (phi d) mean interaural phases. 4. All cells responding to a dynamically changing stimulus exhibited a linear relationship between mean interaural phase and beat frequency. Most cells responded equally well to binaural beats regardless of the initial direction of phase change. For a fixed duration stimulus, and at relatively low fb, the number of spikes evoked increased with increasing fb, reflecting the increasing number of effective stimulus cycles. At higher fb, AI neurons were unable to follow the rate at which the most effective phase repeated itself during the 3 s of stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)