During the first and last threshold pressure trials of the training period, we continuously measured inspiratory flow and pressure (Pm) at the mouth. Breath by breath flow-time and pressure-time signals and inspiratory flow-volume and pressure-volume curves were recorded on a chart (Fig 2). This allowed measurement of respiratory frequency (f) and inspired minute ventilation (Vi). The Ti/Ttot was determined from the pressure-time trace. (Flow-time measurements underestimate the period of muscle contraction because they do not include the time spent attempting to inspire against a closed valve). Tidal volume (Vt) was calculated from Vi and f.
By dividing Vt by Ti mean inspiratory flow was determined. Planimetry of the pressure-volume and pressure-time recordings yielded the external work/minute /PmdVi and pressure-time integrals Pmdt, respectively. Mean mouth pressure (Pm) during the period of inspiratory flow was calculated from /PmdVi divided by Vi (use of /Pmdt divided by H would underestimate Pm required to open the valve as it would include the period of inspiratory pressure less than threshold when the valve was closed). All measurements were made from one minute segments of the record in the third, eighth and thirteenth minute of each 15-minute trial. Link
Trainees attended the hospital three times weekly for six weeks and commenced threshold pressure training at the SIP determined as described above. At each visit up to three patients performed two, 15-minute trials under the close supervision of the same physiotherapist (JCN). Training pressure was increased when the patient had successfully completed two 15-minute sessions. Pressure could be adjusted in 0.8 cm H,0 intervals. A mouth valve and nose peg were used to ensure that all air was inspired at threshold pressure. The patients were given their own valves and asked to train in the same way at home on the other four days of the week.
Figure 2. Pressure-volume and flow-volume curves (left panel) with pressure-time and flow-time curves (right panel) obtained from a patient during threshold pressure training. Ti is inspiratory time; Te, expiratory time.
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