Expiratory flow limitation relates to symptoms during COPD exacerbations requiring hospital admission

Figures & data

Table 1 Baseline characteristics of COPD patients at hospital admission

Total (males)	29 (22)
Age (years)	63 (8.3)
BMI (kg/m^2)	23.2 (3.5)
Smoking history (years)	54.2 (23.5)
Duration of admission (days)	5 (1)
FEV1 (L)	0.76 (0.31)
FEV1 (% predicted)	31.03 (12.7)
FVC (L)	1.7 (0.5)
FVC (% predicted)	56.2 (15.2)
FEV1/FVC	0.44 (0.1)

Note: Data presented as mean (standard deviation) unless otherwise stated.

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; COPD, Chronic obstructive pulmonary disease.

Table 2 Physiological measurements and symptom (Borg) scores at admission and discharge in COPD patients with and without EFL on admission

	Units	EFL at admission (n=9)			No EFL at admission (n=20)			Between groups (admission)
		Admission	Discharge	P	Admission	Discharge	P	P
FEV1	L	0.69 (0.31)	0.74 (0.18)	0.5	0.78 (0.33)	0.82 (0.38)	0.6	0.4
FVC	L	1.50 (0.54)	1.54 (0.33)	0.6	1.79 (0.47)	1.75 (0.50)	0.4	0.2
FEV1/FVC		0.46 (0.10)	0.48 (0.09)	0.5	0.43 (0.09)	0.46 (0.10)	0.4	0.5
Rrs	cmH2O·s·L^−1	8.79 (2.55)	7.73 (2.37)	0.3	5.94 (2.80)	5.61 (2.12)	0.2	0.01
Rrsinsp	cmH2 O·s·L^−1	7.67 (2.17)	7.05 (1.75)	0.2	5.67 (2.67)	5.34 (1.71)	0.4	0.003
Rrsexp	cmH2O·s·L^−1	9.00 (2.74)	8.02 (2.74)	0.3	6.09 (2.84)	5.74 (2.29)	0.2	0.01
Xrs	cmH2O·s·L^−1	−7.37 (2.27)	−4.41 (1.92)	0.008	−3.05 (1.42)	−3.19 (1.72)	0.5	<0.001
Xrsinsp	cmH2O·s·L^−1	−3.73 (0.79)	−2.90 (0.87)	0.01	−2.22 (0.93)	−2.46 (1.29)	0.3	0.001
Xrsexp	CmH2O·s·L^−1	−8.70 (3.19)	−5.12 (2.33)	0.008	−3.55 (1.76)	−3.66 (2.00)	0.5	<0.001
ΔXrs	CmH2O·s·L^−1	4.97 (2.64)	2.21 (1.51)	0.008	1.32 (1.03)	1.19 (0.98)	0.3	<0.001
Borg		6.44 (1.01)	4.83 (1.87)	0.01	6.11 (1.00)	4.55 (1.47)	0.007	0.4

Note: Data presented as mean (standard deviation).

Abbreviations: EFL, expiratory flow limitation (defined by EFL index >2.8 cmH₂O·s·L⁻¹); FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; Rrs, mean respiratory system resistance; Rrs_insp, Rrs during inspiration; Rrs_exp, Rrs during expiration; Xrs, mean respiratory system reactance; Xrs_insp, Xrs during inspiration; Xrs_exp, Xrs during expiration; ΔXrs, Xrs_insp–Xrs_exp; COPD, Chronic obstructive pulmonary disease.

Figure 1 Daily tracking in subjects with and without flow-limited breathing at recruitment.

Notes: (A and A’) EFL index; (B and B’) symptom (Borg) score; (C and C’) Rrs_insp; (D and D’) FEV₁/FVC.
Abbreviations: EFL, expiratory flow limitation (defined by EFL index >2.8 cmH₂O·s·L⁻¹); Rrs_insp, mean respiratory system resistance during inspiration; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; Xrs, mean respiratory system reactance; ΔXrs, Xrs during inspiration – Xrs during expiration.

Table 3 Mixed-effect analysis. Predictors of symptom (Borg) scores during recovery from COPD exacerbations

Outcome	Predictor	Units	β-coefficient (± SE)	P
EFL at admission
Borg score	FEV1/FVC		−1.56 (1.14)	0.2
	FVC	L	−0.20 (0.47)	0.7
	Rrsinsp	cmH2O·s·L^−1	−0.24 (0.11)	0.04
	ΔXrs	cmH2O·s·L^−1	0.26 (0.09)	0.01
No EFL at admission
Borg score	FEV1/FVC		−3.79 (1.76)	0.03
	FVC	L	−0.33 (0.38)	0.4
	Rrsinsp	cmH2O·s·L^−1	0.08 (0.09)	0.4
	ΔXrs	cmH2O·s·L^−1	−0.07 (0.17)	0.7

Notes: Separate models were run for each group. All predictors entered into the models are shown. Effect sizes of significant predictors are independent of the other predictors in the model.

Abbreviations: SE, standard error; EFL, expiratory flow limitation (defined by EFL index >2.8 cmH₂O·s·L⁻¹); FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; Rrs_insp, mean respiratory system resistance during inspiration; Xrs, mean respiratory system reactance; ΔXrs, Xrs during inspiration – Xrs during expiration; COPD, Chronic obstructive pulmonary disease.