• 2
    Apr
  • Quantitation of Emphysema by Computed Tomography Using a “Density Mask” Program: RESULTS

The CT “density mask” results for both lungs are summarized in Table 1, which shows mean lung density, total CT lung volume, total volume of emphy­sema, and percentage oflung with emphysema. There was good correlation between the mean lung density and each of the following: total CT lung volume, total CT volume of emphysema and percentage oflung with  emphysema (all absolute r values = 0.66 to 0.67, pCO.OOl). The correlation between mean lung density and percentage lung involvement with emphysema by CT is shown in Figure 2. The total CT lung volume showed significant correlation with total volume of emphysema (r = 0.50, p<0.001) and with percentage oflung with emphysema (r = 0.43, p<0.001). As ex­pected, there was a very high correlation (r = 0.983, p<0.001) between the total volume of emphysema and the percentage oflung involved by emphysema.

The distribution of the CT extent of emphysema expressed as percentage of total lung volume among the 85 subjects is shown in Table 1. Twenty-five patients had minimal or no emphysema on CT (<0.5 percent of total lung volume), 14 had “mild” emphy­sema (>=5 percent and <10 percent), and 18 had “moderate or severe” emphysema affecting more than 10 percent of the total lung volume on CT.

FIGURE 2. Relationship between

FIGURE 2. Relationship between mean lung density on CT and the percentage of lung involvement by emphysema on the CT density mask program. There was a significant correlation (r= —0.67, p<0.001). However, there was overlap in mean lung density between cases without emphysema and cases with significant emphysema.

The pulmonary function data are summarized in Table 2. Mean values for FEVly FVC, and FEV^C are close to normal but there was mild reduction in flow rates at low lung volumes (FEF25-75% and FEF50%), suggesting a mild degree of airflow obstruction. Mean values for Dsb and Dsb/VA also were slightly reduced. However, there were several patients with abnormalities in FEVb flow rates, lung volumes and diffusing capacity, as indicated by the SD and range in results. In the 18 patients who had lung volumes by both helium dilution and plethysmogra¬phy, there was good correlation between the two determinations, with r=0.90 for TLC. However, as expected in the presence of airflow obstruction and emphysema, plethysmographic TLC was slightly higher than helium TLC (mean ± SD = 6.73 ± 1.27 L vs 6.25 ±1.33 L, p<0.005). The pulmonary function results were related to the extent of emphysema by comparing them in the five groups of patients divided as described previously according to the percentage oflung involved with emphysema (Table 3). There was no significant difference in age among the five groups (p>0.20). Pulmonary function tests assessing airflow (FEVi, FEF50%) and diffusing capacity (Dsb and Dsb/VA) were significantly lower in the groups with increasing extent of emphysema than in the group with less than 0.5 percent emphysema (p<0.001). viagra plus

Table 1—CT Density Mask Results

Mean ± SD

Range

Mean density (HU)

-794.0
±

45.0

-652, -884

CT lung volume cm1

4,566.0
±

1,328.0

1,941, 7,573

Volume of
emphysema cm3

352.6
±

563.3

0.1,3,274

Overall percent
of emphysema

6.52
±

9.80

0, 54.3

<0.50%
(n
= 25)

0.17
±

0.13

0.50-0.99%
(n = ll)

0.69
±

0.14

1.00-4.99%
(n
= 17)

2.7
±

1.4

5.00-9.99%
(n
= 14)

7.7±

1.6

>10.00%
(n
= 18)

21.

11.6

Table 4 compares linear regression coefficients for various lung function tests with the CT total lung volume, mean lung density and percentage of emphy¬sema. The mean lung density showed a significant correlation with indices of airflow (FEVb FEV1/FVC, FEF25-75%, FEF50%), with lung density decreasing with decrease in flow rates. There was a good correlation between lung density and lung volumes whether measured by helium dilution or by plethysmography, with lung density decreasing with increasing lung volume. However, mean lung density was not significantly correlated with vital capacity. As expected, the CT total lung volume showed a significant correlation with flow rates, and helium dilution and plethysmo¬graphic lung volumes, being higher in subjects with lower flow rates and higher in subjects with higher volumes. The highest correlation of total CT lung volume was with helium dilution FRC expressed in liters (r = 0.81 pCO.OOl) (Fig 3). Total CT lung volume was not significantly correlated with either Dsb or Dsb/VA.

Ficuisı 3. Relationship between

FIGURE 3. Relationship between total lung volume on CT and helium dilution FRC. There was a significant correlation between the two (r= -0.81, pCO.OOl).

Table 2—Pulmonary Function Data in the 85 Patients

Mean± SD

Range

Age, yrs

64.0 ±7.8

40-78

Male/female ratio

52/33

FEV„
%
predicted

82.6 ±23.2

26-135

FVC,
%
predicted

97.2 ±17.5

61-164

FEV,/FVC
%
predicted

85.3 ±17.8

37-113

FEF^,
%
predicted

61.7 ±38.0

12-197

FEFjjq
%
predicted

60.9 ±37.3

9-200

Helium FRC
%
predicted*

113.5±24.3

64-166

Helium RV
%
predicted*

112.6 ±30.5

56-208

Helium RV/TLC
%
predicted*

110.6 ±28.6

70-185

Helium TLC
%
predicted*

104.6 ±15.5

67-138

Plethysmographic
FRC
%
predicted!

113.7 ±29.1

83-209

Plethysmographic
RV
%
predicted!

133.2 ±40.3

54-280

Plethysmographic
RV/TLC
%
predicted!

124.0 ±36.1

60-255

Plethysmographic
TLC
%
predicted!

112.1 ±16.0

81-155

Dsb
%
predicted

74.8 ±23.3

31-128

DLsb/va
%

predicted

75.2 ±21.7

34-134

The extent of emphysema on CT as indicated by the percentage of emphysema showed a significant negative correlation with flow rates and Dsb and a significant positive correlation with lung volumes as shown in Table 4. The highest correlation was with FEVi/FVC percent predicted. The extent of emphy-sema was significantly correlated with both Dsb and Dsb/VA (Fig 4). Only seven out of 36 patients with less than 1 percent emphysema had Dsb or Dsb/VA < 60 percent of predicted, while in most (13 out of 18) of the patients with > 10 percent emphysema, Dsb and Dsb/VA were reduced below 60 percent of predicted. The limit of 60 percent predicted for Dsb/VA discriminated better than Dsb patients with < 1 percent of emphysema from those with > 10 percent emphysema.
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FIGURE 4. Relationship between

FIGURE 4. Relationship between CT extent of emphysema and results of Dsb. 1bp panel: Dsb percent predicted; bottom panel: Dsb/VA percent predicted. Both showed a significant correlation with the extent of emphysema (r= —0.53, p<0.001).

Table 3—Lung Function Data According to CT Overall Percentage of Emphysema

Range
<0.50

0.50-0.99

1.00-4.99

5.00-9.99

10.00-53.4

%
of Emphysema

Median
0.14

0.65

2.28

8.01

19.61

Number of cases

25

11

17

14

18

Age, yr

62.5 ±8.1

63.0 ±9.3

62.2 ±8.5

64.7 ±7.4

67.6 ±5.1

%
of emphysema

0.17 ±0.13

0.69 ±0.14

2.7±
1.4

7.7±
1.6

21.
11.6

FEV,
%
predicted

94±
18

88±
14

89 ±18

81 ±23

59 ±23

FEV,/FVC
%
predicted

99±9

91 ±8

88±
12

84±
14

61 ±15


fef
jsq
%
predicted

90 ±37

60 ±26

59 ±27

58 ±34

25±
18

Dsb
%
predicted

87 ±20

78 ±24

78 ±24

75 ±18

53±
16

Dsb/va
%
predicted

91 ±20

79 ±16

73 ±19

73 ±18

55±
14

Table 5 shows the number of subjects with abnormal values for Dsb and Dsb/VA as defined by using the lower 95 percent confidence limit of normal from the prediction equations. The table allows us to analyze abnormality in Dsb by reference to the group with < 0.5 percent emphysema on CT. Based on the CT “density mask” diagnosis of emphysema, we found that 14 out of the 18 cases with > 10 percent emphysema and 32 of the 60 cases with > 0.5 percent emphysema had abnormal Dsb values, while only seven of the 25 cases with < 0.5 percent had abnormal Dsb values, a highly significant difference by chi- square (p<0.001). Analysis of the Dsb/VA data sug¬gested that it discriminated better than Dsb between the presence and absence of emphysema on CT. There were only four out of 25 cases with abnormal Dsb/VA in the patients with < 0.5 percent emphysema, while Dsb/VA was abnormal in 35 out of 60 cases with >0.5 percent emphysema, and in 17 out of 18 cases with > 10 percent emphysema (p<0.001 by chi-square analysis).
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Table 4—Correlation Coefficients between CT Scan Data and Lung Function Tests

CT

CT mean

CT
%
of

Total, Volume

Density

Emphysema

r

P

r

P

r

P

FEV,
%
predicted

-0.28

<0.01

0.44

<0.001

-0.56

<0.001

FEV/FVC
%
predicted

-0.49

<0.001

0.85

<0.001

-0.72

<0.001

FEFso
%
predicted

-0.38

<0.001

0.55

<0.001

-0.51

<0.001

Helium FRC
%
predicted

0.61

<0.001

-0.55

<0.001

0.55

<0.001

Helium RV
%
predicted

0.46

<0.001

-0.42

<0.005

0.48

<0.001

Helium TLC
%
predicted

0.49

<0.001

-0.33

<0.01

0.32

<0.01

Dsb
%
predicted

0.04

NS

0.29

<0.005

-0.53

<0.001

Dsb/VA
%
predicted

-0.16

NS

0.36

<0.001

-0.53

<0.001

Table 5—Number of Cases with Abnormal* Diffusing Capacity According to С T Overall Percentage of Emphysema

CT % Emphysema

<0.50

0.50-0.99

1.00-4.99

5.00-9.99

>10.00

n = 25

n — 11

n = 17

n= 14

n = 18

Dsb % predicted

7

4

7

7

14

Dsb/va
% predicted

4

4

8

6

17

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