Table 1.

Mechanical properties of the lung in normal and diseased states

Parameter	Magnitude in healthy lung	Magnitude during pulmonary disease
Alveolar tissue strain (%)	4% normal tidal breathing [33–35] 12% deep sigh (calculation from excised dog lungs) [36,37]	Inhomogeneity of the diseased lung creates focal stressors that increase alveolar strain [35,38,39]
	0–5% (Linear distension estimate for normal tidal breathing) [33]
	15–40% or higher (for functional residual capacity to TLC) [33]
Noncollagenous lung tissue stiffness (kPa)	0.5 to >3 (mice saline treatment) [26]	3 to >15 (mice bleo treatment) [26]
	1.96 ± 0.13 (human lung tissue) [40]	16.52 ± 2.25 (IPF human lung tissue) [40]
	1.9137 rat lung parenchyma [41]	9-38.5 (IPF human lung tissue) [42]
	3.7 ± 1.3 (human lung tissue) [42]	2.9 ± 0.8 (COPD GOLD IV human lung tissue) [42]
Collagenous Bronchi Stiffness (kPa)	Pseudo-elatic linear modulus in Pig [3]
	Axial 30.31  ±  3.1
	Circumferential
	-Small bronchi 12.5 ± 1.9
	-Trachea 6.0 ± 0.6
	-Large bronchi 6.6 ± 0.9
Shear stress in alveoli (dyn/cm2)	<15 [31]	Several magnitudes higher in alveolar reopening conditions [31]
Respiratory frequency (Hz)	0.20 (normal tidal breathing)	0.44 (cystic fibrosis (CF)) [43]
	0.55 (heavy exercise) [44]
	0.285 [43]
Tidal volume (mL)	410 [43]; 500 [44]	403 (CF) [43]
Surfactant based surface tension (mN/m)		Minimum surface tension:
	Inspiration ∼ 20	ACB > 12 [45]
	Expiration <2 [14]	CF > 15 [46]
	(near zero [15])	ARDS > 20 [15]