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. Author manuscript; available in PMC: 2020 Sep 7.
Published in final edited form as: Thorax. 2018 Jul 20;74(2):114–124. doi: 10.1136/thoraxjnl-2018-211881

Table 2.

Association of RV:TLC and health outcomes

Respiratory-related health outcomes
RV:TLC Clinical diagnosis of COPD Respiratory medications Office visits ER visits Hospital admissions ICU admissions Mortality COPD on follow-up
spirometry*
HR IRR IRR IRR IRR IRR HR OR, mixed eff
Binary
Single-lung function model
Model r2 NA 0.01 0.06 0.02 0.03 0.02 NA NA
Abnormal vs normal 1.55
(1.42 to 1.70) p<0.001 		1.12
(1.10 to 1.13) p<0.001 		1.28
(1.26 to 1.30) p<0.001 		1.09
(1.003 to 1.18) p=0.043 		1.48
(1.40 to 1.57) p<0.001 		1.32
(1.12 to 1.56) p=0.001 		1.41
(1.29 to 1.54) p<0.001 		1.30
(1.03 to 1.65) p=0.027
Binary
Multilung function model		 Includes FEV1:FVC, FEV1 and FEF25–75
Model r2 NA 0.01 0.08 0.04 0.05 0.04 NA NA
Abnormal vs normal 1.41
(1.29 to 1.55) p<0.001 		1.07
(1.05 to 1.08) p<0.001 		1.16
(1.14 to 1.18) p<0.001 		0.95
(0.87 to 1.03) p=0.240		 1.34
(1.26 to 1.42) p<0.001 		1.12
(0.95 to 1.33) p=0.190		 1.31
(1.19 to 1.44) p<0.001 		1.30
(1.00 to 1.69) p=0.050
Continuous
Multilung function model		 Includes FEV1:FVC, FEV1 and FEF25–75
Model r2 NA 0.01 0.09 0.04 0.05 0.04 NA NA
RV:TLC (%) 1.033
(1.026 to 1.040) p<0.001 		1.005
(1.004 to 1.006) p<0.001 		1.016
(1.014 to 1.017) p<0.001 		1.007
(1.002 to 1.013) p=0.013 		1.031
(1.027 to 1.035) p<0.001 		1.016
(1.004 to 1.029) p=0.009 		1.019
(1.013 to 1.025) p<0.001 		1.022
(1.003 to 1.041) p=0.021

The association of RV:TLC and respiratory-related healthcare outcomes with a COPD diagnosis was estimated using Cox proportional hazards regression for time to outcomes, Poisson regression for counts of outcome, or mixed effects (mixed eff) logistic regression for binary outcomes with adjustment for age, sex, height and years of follow-up: Healthcare outcomes=β0+β1(age)+β2(sex)+β3(height)+(β4(years of follow-up)+β×(lung function indices). The model coefficients of determination (r2), HR, IRR and OR with 95% CI and p value of the predictors are shown in the table. Significant associations are shown in bold. n=7479 unless noted otherwise.

*

Follow-up spirometry (last available postbronchodilator spirometry) was available for a subgroup of patients (n=1706); models were adjusted for time from index pulmonary function test to such follow-up spirometry instead of years of follow-up.

ER, emergency room; FEF25–75, maximum airflow at mid-lung volume; ICU, intensive care unit; IRR, incident rate ratio; NA, not applicable; RV, residual volume; TLC, total lung capacity.