Comparison of Four Methods for Calculating Diffusing Capacity by the Single Breath Method: Results
The mean percents of predicted values for pulmonary function variables are listed in Table 2, categorized by pulmonary function abnormalities. Mean and SD values for Deo and the mean WP-SD of Deo by the various protocols are listed in Table 3 using the same categorization. The ESP protocol resulted in the largest Deo, followed by the JM and 3PIT methods, with Og resulting in the smallest Deo in most categories. The differences among Deo by various timing methods was significant (p < 0.01) for all paired comparisons in the group with normal patterns of pulmonary function. In other categories, the differences were generally less, and statistical significance was not attained in a number of comparisons. The JM and 3PIT Dcos were not significantly different in moderate to severe obstruction, restriction, or reduced Deo patient groups. The JM was less than ESP Deo in all patient groups except moderate restriction and isolated reduced Deo. The Og remained significantly less than JM, ESP, and 3PIT Dcos in all groups except in the moderate restriction and reduced Deo groups, where Og and 3PIT Dcos were not significantly different. The intrasubject SD of Deo was generally not significantly different among groups (p > 0.01) with the exception of the 3PIT method that gave the least reproducible Deo in the group with mild restriction. buy tavist online
To determine if the Deo differences were related to pulmonary function abnormalities or differences in IT, ET, and LT, stepwise regression analysis was performed on the ratios of Deo by the various protocols (Table 4). The Og/JM and ESP/JM ratios were significantly related to inspiratory time and expiratory time, which is a reasonable finding considering that the timing differences between JM and both Og and ESP Dcos are in both inspiratory and expiratory phases. The Og/ESP ratio was influenced only by the inspiratory time, because expiratory timing is the same in the two protocols. A plot of the differences in Og-JM Deo vs inspiratory time and FEVj is shown in Figure 2. Although FEVj was dropped by backward elimination when inspiratory and expiratory time were in the list of predictors, the Og-JM Deo difference was related to FEVl (R2 = 0.40) due to the inverse hyperbolic relationship between expiratory time and FEVl (Fig 3). Mean values for IT, ET, and LT are listed in Table 5. Note the increase in mean ET, and its percent contribution to total maneuver time with severity of obstruction, and the decrease in mean IT with severity of restriction.
The ratio of Deo using Og, JM, or ESP to the Deo by the 3PIT method was influenced by Deo, TLC, and MI (Table 3) in addition to IT, ET, and LT.
Figure 2. Difference between Deo calculated using Ogilvie (Og) and Jones-Meade (JM) protocols vs inspiratory time (top) and FEV (bottom). Inspiratory time contributed most to explaining the total variance of Og/JM in the stepwise multiple regression analysis, although expiratory time also contributed significantly. FEV, would be expected to be correlated because of the inverse relationship between FEV, and expiratory time.
Figure 3. Relationship between expiratoiy time (vertical axis) and FEV, (horizontal axis). Note the hyperbolic increase in expiratory times when FEV, is reduced.
Table 3—Single-Breath Diffusing Capacity of the Lungs for Carbon Monoxide (Deo) Calculated by Different Methods
Pulmonary Function Category | Og(i) | ЗРГГ (2) | JM(3) | ESP (4) | ||||
Mean | WP-SD | Mean | WP-SD | Mean | WP-SD | Mean | WP-SD | |
Normal n = 7 | 6.7±6.5(2,3,4) | 0.7 ±0.5 (…) | 27.7 ±6.8 (1,3,4) | 0.7 ±0.5 (…) | 28.2±6.7(1,2,4) | 0.8 ±0.6 (…) | 28.9 ±6.9 (1,2,3) | 0.8 ±0.6(-) |
Mild obstruction n = 52 | 22.8±7.4(2,3,4) | 0.6 ±0.5 (…) | 23.5±7.9(1,3,4) | 0.7 ±0.5M) | 24.1±7.9(1,2,4) | 0.6 ±0.5 (…) | 24.6 ±8.0 (1.2,3) | 0.6 ±0.4 (-.2,-) |
Moderate obstruction n = 36 | 20.7 ±6.1 (2,3,4) | 0.6 ±0.4 (…) | 21.5±6.6(l,-,4) | 0.7 ±0.5 (…) | 21.6±6.4(1»”»4) | 0.7 ±0.4 (…) | 22.2 ±6.6 (1,2,3) | 0.7 ±0.4 (…) |
Severe obstruction n = 25 | 15.6±5.4(2,3,4) | 0.5±0.5(…) | 16.2 ±5.7 (1»“»4) | 0.6 ±0.5 (…) | 15.9 ±5.7 (l,-,4) | 0.6 ±0.5 (…) | 16.6 + 5.7 d.2,3) | 0.6 ±0.5 (…) |
Mild restriction n = 54 | 16.2 ±5.8 (2,3,4) | 0.5±0.5(2,3,-) | 16.8 ±6.1 d,-,4) | 0.7 ±0.6 (1,3,4) | 16.9±6.1(1,”,4) | 0.6 ±0.5 (1,2,-) | 17.3 ±6.1 (1.2,3) | 0.6±0.5(-.2.-) |
Moderate restriction n = 9 | 13.3 ±4.3 (-.3,4) | 0.5 ±0.5 (…) | 14.0±4.7(-) | 0.7 ±0.7(._) | 13.8 ±4.4(1,-) | 0.4 ±0.5 (…) | 14.2 ±4.7 (1.-) | 0.5 ±0.6 (…) |
Reduced Deo n = 5 | 20.1 ±3.9 (•*3,4) | 0.8±0.5(…) | 20.5±4.2(–4) | 0.7 ±0.5 (…) | 20.9±3.8(1,“) | 1.0±0.6(…) | 21.5 ±4.3 (1,2,-) | 0.9 ±0.5 (…) |
Reduced FVC, FEV, n = 31 | 22.8±5.9(2,3,4) | 0.6 ±0.5 (2,-) | 23.6 ±6.1 (1,3,4) | 0.8 ±0.5 (1,-) | 24.0 ±6.2 (1,2,4) | 0.7±0.6(…) | 24.4±6.2(1.2,3) | 0.7 ±0.6 (…) |
Table 4—Stepwise Regression Analysis
Og/JM = 1.034 – 0.029 (IT) + 0.026 (ET) – 0.005 (LT) R!=0.75, n = 334 |
Og/ESP = 0.992-0.032 (IT) R*=0.53, n = 334 |
Or/3PIT= 1.038-0.120 (Deo)+ 0.102 (TLC)-0.022 (IT)-0.027 (ET)-0.122 (Ml)R2 = 0.38, n = 334 |
]M/ESP= 1.005 – 0.029(ET)-0.007 (IT) R2 = 0.34, n = 334 |
J M/3PIT = 1.056 – 0.128(Dco) – 0.057(ET) + 0.117(TLC) – 0.150 (MI)R2 = 0.42, n = 334 |
ESP/3PIT = 1.036 – 0.132(Dco) + 0.126(TLC) – 0.160 (MI) – 0.028 (ET) + 0.013(IT)R2=0.41, n = 334 |
Table 5— Timing Components of Total Maneuver Time
LT | IT | ET | ||
Normal n = 71 | 7.7:(76% | ±0.4±4%) | 2.02±0.4 (20% ±4%) | 0.4±0.1 (4% ± 1%) |
Mild obstruction n = 52 | 7.5:(76% | ±0.5±6%) | 1.9±0.6 (19% ±5%) | 0.5±0.2(5% ±2%) |
Moderate obstruction n = 36 | 7.3:(73% | ±0.5±6%) | 2.0±0.5 (20% ±5%) | 0.7±0.2 (7% ±2%) |
Severe obstruction n = 25 | 6.8:(68% | ±0.6±7%) | 2.0±0.4 (19% ±4%) | 1.3±0.7 (13% ±6%) |
Mild restriction n = 54 | 7.5:(76% | ±0.4±5%) | 1.7±0.5 (18% ±5%) | 0.6 ±0.3 (6% ± 3%) |
Moderate restriction n = 9 | 7.6:(79% | ±0.4±4%) | 1.4±0.4 (15% ±4%) | 0.6±0.1(6%±1%) |
Reduced Deo n = 5 | 7.8:(17% | ±0.3±2%) | 1.8±0.2 (18% ±2%) | 0.5±0.1 (5% ± 1%) |
Reduced FVC, FEV, n = 31 | 7.6:(77% | ±0.4±5%) | 1.8±0.5 (18% ±4%) | 0.5 ±0.2 (5% ±1%) |