Table 2

Twin studies in pulmonary function

Reference	Location and year	Pairs of twins		Lung function indices	Intrapair correlation (difference)		Comments
Reference	Location and year	MZ	DZ	Lung function indices	MZ	DZ	Comments
Man and Zamel34	Canada, 1976	10		6	VC (l)	(0.30)	(0.55)^3-150	Difference seems larger for the geometry of larger airways than for smaller ones
					Vmax₆₀(l/s)	(0.37)	(1.23)^3-150
					Vmax₄₀(l/s)	(0.30)	(0.63)
Hubert et al 32	USA, 1982	127		141	FVC	0.66^3-151	0.08	Correlation in FVC between DZ twins was not significantly different from zero
Hubert et al 32	USA, 1982	127		141	FEV₁	0.62^3-151	0.25^3-151
Redlineet al 33	USA, 1987	256		158	FVC	0.76^3-151	0.39^3-151	Adjusted for body size and smoking
					FEV₁	0.71^3-151	0.16
					FEF_25–75%	0.52^3-151	0.21
					FEV₁/FVC	0.55^3-151	0.18
					FEF_25–75%/FVC	0.53^3-151	0.21
Ghioet al 36	USA, 1989	47		27	FVC (l)	(0.28)	(0.36)	Differences between MZ and DZ were not significant after adjusting for height
					FEV₁(l)	(0.26)	(0.34)
					FEF_25–75%(l/s)	(0.58)	(0.77)

MZ = monozygotic twins; DZ = dizygotic twins; VC = vital capacity; FEV₁ = forced expiratory volume in one second; FVC = forced vital capacity; FEF_25–75% = forced expiratory flow between 25% and 75% of the vital capacity; Vmax₄₀, Vmax₆₀ = maximal expiratory flow rate at 40% and 60% of vital capacity.
↵3-150 p<0.05, difference between MZ and DZ.
↵3-151 p<0.05, difference from zero.