Peak expiratory flow rate as a surrogate for forced expiratory volume in 1 second in COPD severity classification in Thailand

Figures & data

Table 1 Baseline characteristics of all COPD patients

Variables	COPD (n=300)
Age (years)	70.4±9.4
Male sex	195 (65.0)
Height (cm)	156.4±8.6
BMI (kg/m^2)	20.4±3.9
Post-bronchodilator spirometry
% predicted FEV1	51.4±20.1
Ratio of FEV1/FVC (%)	50.4±10.4
Severity stages by GOLD classification
I	30 (10.0)
II	114 (38.0)
III	116 (38.7)
IV	40 (13.3)

Note: Data are presented in number (%), mean ± standard deviation.

Abbreviations: BMI, body mass index; FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; GOLD, Global initiative for chronic Obstructive Lung Disease.

Figure 1 Correlation between FEV₁ and PEFR in patients with COPD.

Notes: (A) Correlation between % predicted FEV₁ and % predicted PEFR (r=0.76, P<0.001); (B) correlation between absolute value of FEV₁ and PEFR (r=0.87, P<0.001).
Abbreviations: FEV₁, forced expiratory volume in 1 second; PEFR, peak expiratory flow rate.

Table 2 Comparison between % predicted FEV₁ and % predicted PEFR in each category of airflow limitation

Category of airflow limitation (%)	% predicted FEV1	% predicted PEFR	% FEV1−% PEFR mean difference (95% CI)	P-value
≥80 (n=30)	90.8±15.9	82.9±17.6	7.9 (−0.6, 16.4)	0.068
50–<80 (n=114)	61.9±8.3	62.2±17.3	−0.3 (−3.1, 2.6)	0.855
30–<50 (n=116)	39.9±5.5	42.7±11.9	−2.7 (−4.7, −0.8)	0.007
0–<30 (n=40)	25.0±4.3	29.3±9.5	−4.3 (−7.3, −1.3)	0.006
All categories (n=300)	51.4±20.1	52.3±21.1	−0.9 (−2.6, 0.7)	0.076

Notes: Data are presented in mean ± standard deviation, confidence interval (CI). Bold text denotes statistical significance.

Abbreviations: FEV₁, forced expiratory volume in 1 second; PEFR, peak expiratory flow rate.

Figure 2 Histogram showing the near-normal distribution of differences between % predicted FEV₁ and PEFR in COPD patients.

Abbreviations: FEV₁, forced expiratory volume in 1 second; PEFR, peak expiratory flow rate.

Figure 3 Bland–Altman plot highlighting magnitude of difference between % predicted FEV₁ and PEFR.

Note: Horizontal dashed lines represent the mean bias and its 95% confidence limits. Abbreviations: FEV₁, forced expiratory volume in 1 second; PEFR, peak expiratory flow rate.

Table 3 Concordance between categorization of severity of airflow limitation based on % predicted FEV₁ and % predicted PEFR in COPD patients

	% predicted FEV1
		0–<30	30–<50	50–<80	≥80
% predicted PEFR	0–<30	19 (63.4)	20 (17.5)	–	–
	30–<50	10 (33.3)	67 (58.8)	29 (25.0)	1 (2.5)
	50–<80	1 (3.3)	24 (21.1)	71 (61.2)	17 (42.5)
	≥80	–	3 (2.6)	16 (13.8)	22 (55.0)

Notes: Data are presented in number (%). Bold text indicates concordance between categorization of severity of airflow limitation based on % predicted FEV₁ and % predicted PEFR.

Abbreviations: FEV₁, forced expiratory volume in 1 second; PEFR, peak expiratory flow rate.