Cough is one of the most important defensive reflexes. However,
extensive non- productive cough is a harmful mechanism leading
to the damage of human airways. Cough is initiated by activation
of vagal afferents in the airways. The site of their convergence is
particularly the nucleus of the solitary tract (nTS). The secondorder neurons terminate in the pons, medulla and spinal cord and
there is also the cortical and subcortical control of coughing. Upper
airway cough syndrome (UACS) – previously postnasal drip
syndrome - is one of the most common causes of chronic cough
together with asthma and gastroesophageal reflux. The main
mechanisms leading to cough in patients with nasal and sinus
diseases are postnasal drip, direct irritation of nasal mucosa,
inflammation in the lower airways, upper airway inflammation and
the cough reflex sensitization. The cough demonstrated by UACS
patients is probably due to hypersensitivity of the upper airways
sensory nerve or lower airways sensory nerve, or a combination of
both. Further studies are needed to clarify this mechanism.
Obstructive sleep apnoea syndrome (OSAS) is a common disorder associated with upper airway muscle dysfunction. Agents that improve respiratory muscle performance may have considerable therapeutic value. We examined the effects of acute exposure to sustained and intermittent hypoxia on rat pharyngeal dilator muscle function. Additionally, we sought to test the efficacy of antioxidant treatment in ameliorating or preventing hypoxia-related muscle dysfunction. Isometric contractile and endurance properties of isolated rat sternohyoid muscle bundles were examined at 35 °C in vitro. Muscle bundles were exposed to one of four gas treatments: hyperoxia (control), sustained hypoxia (SH), intermittent hypoxia (IH) or hypoxia/reoxygenation (HR), in the absence or presence of the superoxide scavenger – Tempol (10 mM). Stress-frequency relationship was determined in response to electrical stimulation (10-100 Hz in increments of 10-20 Hz, train duration: 300 ms). Muscle performance was also assessed during repetitive muscle stimulation (40 Hz, 300 ms every 2 s for 2.5 min). Compared to control, IH and HR treatments significantly decreased sternohyoid muscle force. The negative inotropic effect of the two gas protocols was similar, but both were of lesser magnitude than the effects of SH. SH, but not IH and HR, increased muscle fatigue. Tempol significantly increased sensitivity to stimulation in all muscle preparations and caused a leftward shift in the stressfrequency relationship of IH and SH treated muscles. Tempol did not ameliorate sternohyoid muscle fatigue during SH. We conclude that Tempol increases upper airway muscle sensitivity to stimulation but only modestly ameliorates respiratory muscle weakness during intermittent and sustained hypoxic conditions in vitro. Respiratory muscle fatigue during sustained hypoxia appears unrelated to oxidative stress., J. R. Skelly, ... [et al.]., and Obsahuje seznam literatury
In this paper, we develop computational procedures to approximate the spectral abscissa of the switched linear system via square coordinate transformations. First, we design iterative algorithms to obtain a sequence of the least μ1 measure. Second, it is shown that this sequence is convergent and its limit can be used to estimate the spectral abscissa. Moreover, the stopping condition of Algorithm 1 is also presented. Finally, an example is carried out to illustrate the effectiveness of the proposed method.
We present a lower and an upper bound for the second smallest eigenvalue of Laplacian matrices in terms of the averaged minimal cut of weighted graphs. This is used to obtain an upper bound for the real parts of the non-maximal eigenvalues of irreducible nonnegative matrices. The result can be applied to Markov chains.