14 research outputs found
Abdominal muscle fatigue following exercise in chronic obstructive pulmonary disease
<p>Abstract</p> <p>Background</p> <p>In patients with chronic obstructive pulmonary disease, a restriction on maximum ventilatory capacity contributes to exercise limitation. It has been demonstrated that the diaphragm in COPD is relatively protected from fatigue during exercise. Because of expiratory flow limitation the abdominal muscles are activated early during exercise in COPD. This adds significantly to the work of breathing and may therefore contribute to exercise limitation. In healthy subjects, prior expiratory muscle fatigue has been shown itself to contribute to the development of quadriceps fatigue. It is not known whether fatigue of the abdominal muscles occurs during exercise in COPD.</p> <p>Methods</p> <p>Twitch gastric pressure (TwT10Pga), elicited by magnetic stimulation over the 10<sup>th </sup>thoracic vertebra and twitch transdiaphragmatic pressure (TwPdi), elicited by bilateral anterolateral magnetic phrenic nerve stimulation were measured before and after symptom-limited, incremental cycle ergometry in patients with COPD.</p> <p>Results</p> <p>Twenty-three COPD patients, with a mean (SD) FEV<sub>1 </sub>40.8(23.1)% predicted, achieved a mean peak workload of 53.5(15.9) W. Following exercise, TwT<sub>10</sub>Pga fell from 51.3(27.1) cmH<sub>2</sub>O to 47.4(25.2) cmH<sub>2</sub>O (p = 0.011). TwPdi did not change significantly; pre 17.0(6.4) cmH<sub>2</sub>O post 17.5(5.9) cmH<sub>2</sub>O (p = 0.7). Fatiguers, defined as having a fall TwT10Pga ≥ 10% had significantly worse lung gas transfer, but did not differ in other exercise parameters.</p> <p>Conclusions</p> <p>In patients with COPD, abdominal muscle but not diaphragm fatigue develops following symptom limited incremental cycle ergometry. Further work is needed to establish whether abdominal muscle fatigue is relevant to exercise limitation in COPD, perhaps indirectly through an effect on quadriceps fatigability.</p
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Interactions between metal ions and DNA
84 years elapsed between the announcements of the periodic table and that of the DNA double helix in 1953, and the two have been combined in many ways since then. In this chapter an outline of the fundamentals of DNA structure leads into a range of examples showing how the natural magnesium and potassium ions found in nature can be substituted in a diversity of applications. The dynamic structures found in nature have been studied in the more controlled but artificial environment of the DNA crystal using examples from sodium to platinum and also in a range of DNA-binding metal complexes. While NMR is an essential technique for studying nucleic acid structure and conformation, most of our knowledge of metal ion binding has come from X-ray crystallography. These days the structures studied, and therefore also the diversity of metal binding, go beyond the double helix to triplexes, hairpin loops, junctions and quadruplexes, and the chapter describes briefly how these pieces fit into the DNA jigsaw. In a final section, the roles of metal cations in the crystallisation of new DNA structures are discussed, along with an introduction to the versatility of the periodic table of absorption edges for nucleic acid structure determination