In: COPD12 Oct 2014
The RM endurance was measured using a 2-min incremental threshold loading test. Section A of Figure 1 illustrates the weighted plunger and inspiratory port with an orifice of 6.6 cm2. Increased weights on the plunger required increased pressure to open the inspiratory port when the stopper was in place. Inspired minute ventilation and Vt were measured using the turbine flow transducer shown in Section B of Figure 1. Inspiratory pressures were measured at the mouth with a ± 100 cm H,0 differential pressure transducer (model 45-32; Validyne Co., Northridge, CA). Peak inspiratory mouth pressure with each breath and Pmean were recorded. The Pmean was obtained on line by passing the mouth pressure signal through a second-order low pass filter with a time constant of 20 s. All signals (time, volume, pressure) were recorded on a strip chart (Gould Instruments, Ballain Villiers, France).
For the 2-min incremental test, subjects began at a low load (50 to 100 g) and weights were added every 2 min until the subject could not continue. Only weights which subjects could tolerate for the full 2 min were included in calculating the maximum results. The average Ppk (generated over six breaths), Vt, Vi, Ti and Ttot were recorded for each weight. The maximum values of Ppk (as %MIP), Pmean and max load were taken as measures of respiratory muscle endurance.
The subjects were monitored with ear eximetry (Biox IV, Bioximetry Technology, Inc), wore nose clips and were seated during the test. Each normal subject and COPD patient was tested three times in the morning on separate days, one week between tests.
An analysis of variance for repeated measures and a Bonferroni multiple comparison procedure were used to examine statistical interactions, differences between visits and differences between groups. Evidence of group differences led to multiple comparison procedures to learn which visits were contributing to the differences. The Bonferroni procedure was chosen as most appropriate for a small number of comparisons. All values are reported as mean ± SD in tables and figures.
Figure 1. Diagram of threshold loading device.
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