Breakdown of lung framework and an increase in pores of Kohn as initial events of emphysema and a cause of reduction in diffusing capacity

Figures & data

Figure 1 Images (H&E) of the lung showing 4 μm thick (A) and 300 μm thick (B–F) sections at ×40 magnification (A and B) and ×100 magnification (C–F).

Notes: The polyhedral complex of alveoli is composed of a framework (C, arrows) and an alveolar wall. We designated the face of the alveolar polyhedron as the FU (D–F, white dashed lines). We categorized FUs into four types based on their morphological characteristics: 1) FUs without an alveolar wall (white dashed lines with an asterisk in D), 2) FUs with fragments of an alveolar wall (white dashed lines in E), 3) FUs with an intact alveolar wall with pores of Kohn (white dashed lines with a single dagger in D and white dashed lines in F), and 4) FUs with an intact alveolar wall without pores of Kohn (white dashed lines with a double dagger in D). The framework is thicker than the cut edges of the alveolar wall (E, arrowheads). The area of each pore and the sum of the area of all pores seen in one FU were evaluated by the percentage area of the FU (F, solid black line tracing and arrows). The black and white scale bars indicate 200 μm.
Abbreviations: FU, framework unit; H&E, hematoxylin and eosin.

Table 1 Characteristics of the cases

Characteristic	Pathological emphysema		P-value*	CT emphysema		P-value*
	Negative n=15	Positive n=10		Negative n=17	Positive n=8
Age, years	65.0 (54.0, 70.0)	66.0 (60.8, 76.3)	0.345	66.0 (57.5, 75.5)	63.0 (60.3, 69.0)	0.382
Sex
Male	6	8	0.099	8	6	0.234
Female	9	2		9	2
Smoking history
Nonsmoker	14	5	0.023	13	6	1
Smoker	1	5		4	2
Number of cigarettes smoked, pack-year	0.0 (0.0, 0.0)	15.0 (0.0, 50.6)	0.022	0.0 (0.0, 15.0)	0.0 (0.0, 27.0)	0.938
Dissected lobe
Upper lobe	11	8	1	17	8	0.129
Lower lobe	4	2		6	0
Pulmonary function test	n=13	n=10		n=15	n=8
VC, %	113.1 (98.4, 123.6)	105.3 (101.1, 124.5)	0.620	114.3 (105.9, 131.6)	103.6 (98.6, 106.6)	0.049
FVC, %	111.1 (96.4, 123.8)	104.8 (98.5, 123.9)	0.577	111.6 (106.5, 132.8)	102.3 (94.2, 105.9)	0.039
FEV1, %	108.2 (91.7, 132.9)	93.1 (81.3, 137.3)	0.292	118.1 (94.5, 145.7)	91.4 (77.6, 101.3)	0.008
FEV1/FVC, %	79.4 (75.3, 82.3)	68.6 (62.2, 73.1)	0.002	78.4 (69.6, 81.1)	67.8 (61.9, 75.1)	0.071
FRC, %	113.1 (105.7, 136.8)	98.2 (82.9, 117.0)	0.063	113.1 (105.6, 132.4)	91.2 (83.6, 110.7)	0.066
RV, %	105.7 (91.1, 108.8)	109.0 (97.7, 121.7)	0.352	105.7 (89.4, 118.6)	108.9 (95.1, 111.6)	0.651
TLC, %	107.0 (95.8, 117.8)	102.8 (97.2, 109.8)	0.664	107.8 (102.5, 121.1)	98.2 (96.9, 98.2)	0.100
DLCO, %	90.6 (80.7, 97.8)	68.9 (60.4, 80.7)	0.006	90.5 (76.6, 94.3)	65.8 (59.8, 77.0)	0.008
DLCO/VA, %	93.2 (81.9, 102.4)	69.3 (53.3, 77.8)	0.002	84.9 (75.7, 97.1)	64.0 (48.4, 81.0)	0.011
CV, L	0.41 (0.24, 0.64)	0.74 (0.54, 0.94)	0.041	0.41 (0.21, 0.71)	0.67 (0.55, 0.79)	0.081
Airflow limitation
Negative	11	3	0.013	10	4	0.657
Positive	2	7		5	4

Notes: The quantitative data were expressed as median (IQR).

* Fisher’s exact test and Wilcoxon’s rank-sum test were performed for categorical and quantitative variables, respectively.

Abbreviations: CT, computed tomography; CV, closing volume; DLCO, diffusing capacity of the lung for carbon monoxide; DLCO/VA, DLCO per unit alveolar volume; FEV₁, forced expiratory volume in 1 second; FRC, functional residual volume; FVC, forced vital capacity; IQR, interquartile range; RV, residual volume; TLC, total lung capacity; VC, vital capacity.

Table 2 Comparison of FUs and pores of Kohn between groups with and without emphysema

Variables	Pathological emphysema		P-value*	CT emphysema		P-value*
	Negative n=15	Positive n=10		Negative n=17	Positive n=8
Number of FUs without an alveolar wall	16.4 (14.4, 22.8)	13.3 (7.7, 17.0)	0.017	16.0 (13.7, 21.4)	12.9 (7.0, 20.6)	0.180
Number of FUs with fragments of an alveolar wall	1.0 (0.5, 1.6)	1.3 (0.3, 3.7)	0.760	1.0 (0.6, 1.8)	0.4 (0.0, 4.0)	0.414
Number of FUs with an intact alveolar wall with pores	5.2 (3.6, 5.8)	4.1 (3.1, 5.3)	0.317	4.3 (3.8, 5.8)	4.3 (2.4, 5.6)	0.540
Number of FUs with an intact alveolar wall without pores	0.0 (0.0, 0.3)	0.0 (0.0, 0.5)	0.927	0.0 (0.0, 0.2)	0.0 (0.0, 0.6)	0.974
Number of pores in FUs	5.0 (3.7, 7.5)	8.0 (4.6, 10.4)	0.088	5.7 (4.2, 7.9)	6.4 (3.4, 12.0)	0.600
Area percentage of one pore, not log-transformed, %	0.5 (0.2, 0.7)	0.4 (0.2, 1.0)	0.912	0.3 (0.2, 0.5)	0.8 (0.5, 1.1)	0.012
Area percentage of all pores, not log-transformed, %	1.6 (0.9, 3.2)	2.2 (0.9, 7.6)	0.471	1.2 (0.9, 2.5)	3.9 (2.1, 9.7)	0.014

Notes: The quantitative data were expressed as median (IQR).

* Wilcoxon’s rank-sum test was performed.

Abbreviations: CT, computed tomography; FU, framework unit; IQR, interquartile range.

Table 3 Bivariable and multivariable regression analysis on DLCO

Variables	Bivariable	P-value	Multivariable	P-value
	Estimate (95% CI)		Estimate (95% CI)
Number of FUs without an alveolar wall	1.6 (0.4, 2.8)	0.010	1.3 (0.3, 2.4)	0.013
Age, years	−0.3 (−1.1, 0.6)	0.494
Number of cigarettes smoked, pack-year	0.1 (−0.1, 0.4)	0.312	0.3 (0.1, 0.6)	0.004
Pathological emphysema
Negative	Reference	–	Reference	–
Positive	−18.1 (−31.4, −4.8)	0.010	−15.9 (−29.4, −2.5)	0.022
CT emphysema
Negative	Reference	–	Reference	–
Positive	−19.1 (−32.9, −5.4)	0.009	−4.6 (−17.2, 8.1)	0.456

Abbreviations: CI, confidential interval; CT, computed tomography; DLCO, diffusing capacity of the lung for carbon monoxide; FU, framework unit.

Table 4 Bivariable and multivariable regression analysis on DLCO/VA

Variables	Bivariable	P-value	Multivariable	P-value
	Estimate (95% CI)		Estimate (95% CI)
Number of FUs without alveolar wall	2.6 (1.5, 3.6)	<0.001	1.8 (0.8, 2.8)	0.001
Number of pores in FUs	−2.1 (−4.0, −0.3)	0.026
Percent area of all pores, log-transformed	−10.0 (−18.0, −2.0)	0.016
Age, years	−0.4 (−1.4, 0.5)	0.366
Number of cigarettes smoked, pack-year	−0.1 (−0.5, 0.2)	0.385
Pathological emphysema
Negative	Reference	–	Reference	–
Positive	−26.1 (−39.6, −12.6)	<0.001	−11.3 (−23.7, 1.0)	0.070
CT emphysema
Negative	Reference	–	Reference	–
Positive	−22.5 (−38.2, −6.8)	0.007	−10.3 (−22.1, 1.5)	0.083

Abbreviations: CI, confidential interval; CT, computed tomography; DLCO/VA, diffusing capacity of the lung for carbon monoxide per unit alveolar volume; FU, framework unit.

Table 5 Bivariable and multivariable regression analysis on RV

Variables	Bivariable	P-value	Multivariable	P-value
	Estimate (95% CI)		Estimate (95% CI)
Number of pores in FUs	1.9 (0.2, 3.6)	0.034
Percent area of one pore, log-transformed	26.4 (0.7, 52.1)	0.045
Percent area of all pores, log-transformed	8.0 (0.3, 15.7)	0.041	7.9 (1.5, 14.3)	0.017
Age, years	0.02 (−0.9, 0.9)	0.961
Number of cigarettes smoked, pack-year	0.4 (0.1, 0.6)	0.008	0.4 (0.1, 0.6)	0.004
Pathological emphysema
Negative	Reference	–
Positive	7.5 (−8.7, 23.8)	0.347
CT emphysema
Negative	Reference	–
Positive	−1.3 (−18.6, 16.0)	0.878

Abbreviations: CI, confidential interval; CT, computed tomography; FU, framework unit; RV, residual volume.

Figure 2 Schemas (A–D) and images of an ordinary H&E slide (A′–D′) and an H&E thick section (A″–D″) on possible progression of pulmonary emphysema.

Notes: Images A′ and B′ are at ×50 magnification. Images A″ are B″ are at ×80 magnification. Images C′, C″, D′, and D″ are at ×30 magnification. According to our results, the morphological progression of pulmonary emphysema is proposed as follows: alveoli with a few tiny pores of Kohn in the normal state (A–A″) starts to show an increase in the number and size of pores of Kohn, resulting in vulnerability of the alveoli (B–B″); the framework structure and alveoli merge and break down because of mechanical stress and/or inflammation, inducing traction of lung tissue (C–C″); and remodeling of acini resulting in enlarged air spaces of emphysema (D–D″). The pathological slide of images A′–D′ and the thick sections of image A″–D″ were processed from the same tissue block of an identical case. The black and white bars indicate 200 μm.
Abbreviation: H&E, hematoxylin and eosin.