BTPS Correction for Ceramic Flow Sensor: Experiments

Figure 5 shows the relationship of the percent difference in FEVi between room air and heated-humidified air vs the exit air temperature at 1 s using data from experiments 1 through 4. A least squares linear fit to these data is shown in the figure and the correlation coefficient was 0.91. Since there were only a few data points at the lowest temperatures, a second linear fit was made using only data with temperatures greater than 20°C. The correlation coefficient in this analysis was only reduced to 0.89. If the relationship shown in Figure 5 is used to derive a dynamic BTPS correction factor, then the equivalent FEVi accuracy would be within ±2 percent when a dynamic BTPS correction factor is used. Similar results were obtained for FEV05.
The results for experiment 5 (six subjects) are shown in Table 1 and Figure 1. Table 1 shows the FVC, FEVi, and FEVe values obtained using a dry rolling sealed spirometer with the corresponding values using the flow sensor or flow spirometer. Buy inhalers online Link The FEVe measurements from the dry rolling seal spirometer were used in comparisons with the flow sensor FEVg. Since the FVC maneuver was terminated after approximately 6 s of exhalation, the flow sensor FVC was approximately an FEV6. The tests using the flow sensor were conducted after those using the volume spirometer with only a brief (<15 min) rest period. Table 2 shows the number of test sessions (at least three self-administered FVC maneuvers) for each of the six subjects. These repeated tests were used to derive the results shown in Figure 1. One flow spirometer malfunctioned and only 15 test sessions were obtained for subject 6.
As can be seen in Table 1, the volume and flow spirometer values of FEVi and FEV6 are not statistically different (p>0.14), with mean differences of 0.10 and 0.13 L, respectively. The two subjects with the largest FVCs (cases 2 and 3) appear to contribute the most to these differences.
Figure 1 shows the average FVCs and FEVis for repeated testing sessions vs maneuver order. The FVC and FEVi values obtained (unfilled symbols) clearly show a maneuver order effect: the second and third maneuvers provide significantly larger values than the first maneuver when a constant BTPS correction factor is used. When an adjustment to the BTPS correction factor is made, based on the exit air temperature (filled symbols), the maneuver order effect is still present but is reduced and the resulting values are within ± 3 percent. The standard errors of the mean or standard deviations are not shown in Figure 1 because they were extremely small, due to the large number of repeated examinations (N=268).


Figure 5. Percent difference in FEVi between room air and heated-humidified air vs exit temperature at 1 s after the start of exhalation.

Table 1—FVC, FEVj, and FEVe Results Using Both a Dry Rolling Seal Spirometer (VS) and a Flow Spirometer (FS) in Six Subjects

Subject FVC (VS), L FEV6 (VS), L FEV6 (FS), L A FEV6, L FEV! (VS), L FEV, (FS), L A FEVi, L
1 3.72 3.67 3.64 0.03 2.89 2.86 0.03
2 4.26 4.03 3.58 0.45 3.37 3.02 0.35
3 5.09 5.01 4.75 0.26 4.41 4.19 0.26
4 3.41 3.17 3.08 0.09 2.53 2.49 0.04
5 2.71 2.50 2.46 0.04 1.06 1.91 0.03
6 2.54 2.31 2.39 0.08 1.24 1.31 -0.07
Mean 0.13t Mean o.iot
SD 0.17 SD 0.14

Table 2—Number of Repeated Examinations for Six Different Subjects

Subject 1 2 3 4 5 6 Total
N 90 43 31 54 35 15 268
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