Resting Dead Space Fraction as Related to Clinical Characteristics, Lung Function, and Gas Exchange in Male Patients with Chronic Obstructive Pulmonary Disease

Ming-Lung Chuang,1,2 Benjamin Yung-Thing Hsieh,3 I-Feng Lin4 1Division of Pulmonary Medicine and Department of Internal Medicine, Chung Shan Medical University Hospital, Taichung, Taiwan, 40201, Republic of China; 2School of Medicine, Chung Shan Medical University, Taichung, Taiwan, 40201, Republic of China; 3School of Medicine, National Yang Ming University, Taipei, Taiwan, 11221, Republic of China; 4Institute of Public Health, National Yang Ming University, Taipei, Taiwan, 11221, Republic of ChinaCorrespondence: Ming-Lung ChuangDivision of Pulmonary Medicine and Department of Internal Medicine, Chung Shan Medical University Hospital, #110, Section 1, Chien-Kuo North Road, South District, Taichung, 40201, Taiwan, Republic of ChinaTel +886-4-2473-9595 ext. 34718Email yuan1007@ms36.hinet.netI-Feng LinInstitute of Public Health, National Yang Ming University, 155, Sec 2, LihNong Street, ShiPai, Taipei, Taiwan, 11221, Republic of ChinaEmail iflin@ym.edu.twBackground: Measures of forced expired volume in one second % predicted (FEV1%), residual volume to total lung capacity ratio (RV/TLC) and diffusing capacity for carbon monoxide measurements (DLCO) are the standard lung function test for evaluating patients with chronic obstructive pulmonary disease (COPD). The dead space fraction (VD/VT) has been shown to be a robust marker of gas exchange abnormality. However, the use of VD/VT has gradually become less common. As VD/VT measured at rest (VD/VTR) has been successfully used in non-COPD conditions, it was hypothesized that in COPD the VD/VTR was more sensitive than the standard lung function test in correlation with clinical characteristics and gas exchange. This study aimed to test the hypothesis and to identify the variables relevant to VD/VTR.Methods: A total of 46 male subjects with COPD were enrolled. Clinical characteristics included demographic data, oxygen-cost diagram (OCD), and image studies for pulmonary hypertension. The standard lung function was obtained. To calculate VD/VT, invasive arterial blood gas and pulmonary gas exchange (PGX) were measured. The variables relevant to VD/VTR were analyzed by multiple linear regression.Results: Compared to lung function, VD/VTR was more frequently and significantly related to smoking, carboxyhemoglobin level, pulmonary hypertension and PaCO2 (all p < 0.05) whereas FEV1% was more related to lung function test, PaO2 and OCD score. VD/VTR and FEV1% were highly related to resting gas exchange but RV/TLC and DLCO% were not. Cigarette consumption, the equivalent for CO2 output, arterial oxyhemoglobin saturation, and the product of tidal volume and inspiratory duty cycle were identified as the parameters relevant to VD/VTR with a power of 0.72.Conclusion: Compared to lung function test, VD/VTR is more related to clinical characteristics and is a comprehensive marker of resting gas exchange. Further studies are warranted to provide a noninvasive measurement of VD/VTR.Registration Number: MOST 106– 2314-B-040-025 and CSH-2019-C-30.Keywords: obstructive airway disease, residual volume and total lung capacity ratio, diffusing capacity of lung, dead space and tidal volume ratio, cigarette consumption, carboxyhemoglobin, pulmonary hypertension