The MSBC was adapted from the four-minute test described by Freedman (1970). It was determined by asking the patients to breathe humidified air as rapidly and as deeply as possible for three minutes via a low resistance two-way valve and minute ventilation was recorded. Eucapnea was maintained by adding carbon dioxide to the inspired gas at a rate adjusted to maintain the end-tidal level at 5 percent. The patient was informed of the passing of each 30-second interval but was given no other encouragement.
For both the 12 MWD and the MSBC, the patient was allowed a practice trial during the four weeks prior to baseline testing. He then performed the test three times on one day with a minimum of 30 minutes between tests. The best performance was taken as the pretraining value provided there was a matching value within 5 percent; if not, the test was repeated until this situation obtained. The posttraining measurement was made in a similar way but without a practice trial. The mean values and standard deviations for the coefficients of variability of the triplicate baseline values for
12 MWD and MSBC were 2.17±1.77 percent and 3.03±1.83 percent, respectively.
Maximum inspiratory pressure was determined in a body ple-thysmograph at functional residual capacity (MIF-FRC) and residual volume (MIB-RV). Serial inspiratory efforts (minimum number six) were made at each lung volume until performance had reached a plateau and then began to decline. The highest pressure sustainable for one second was taken as MIP. further
Lung volumes (FRC, TLC and RV) were measured in a body plethysmograph in four of the eight patients before and after training.
The patient was then introduced to the training valve. Threshold pressure was initially set at 70 percent of MIP-RV and then decreased by 5 percent intervals until the maximum pressure sustainable for 15 minutes (SIP) was determined. Twenty minutes of rest was allowed between trials.
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