Serum LDH and exercise capacity in COPD

M.A. Spruit, H.J. Pennings, J.D. Does, G.M. Möller, P.P. Janssen, and E.F.M. Wouters

Online repository

Pulmonary function

Post-bronchodilator forced expiratory volume in the first second (FEV1) has been calculatedfrom the flow-volume curve using spirometry. Carbon monoxide transfer factor of the lung (DLCO) was determined usingthe single breath method. Lung function parameterswere expressed as a percentage of reference values (1).

Dyspnea

Self-perceived dyspnea in relation to physical disability has been assessed by using the MRC dyspnea scale (2). COPD patients had to grade their self-perceived dyspnea by using pre-defined statements, e.g. 1: “I only get breathless with strenuousexercise.”; 2: "I get short of breath when hurrying on thelevel or up a slight hill."; 3: "I walk slower than peopleof the same age on the level because of breathlessness or haveto stop for breath when walking at my own pace on the level."; 4: "I stop for breath after walking 100yards or after afew minutes on the level."; and 5: "I am too breathless to leavethe house or breathless when dressing or undressing.”.

Body composition

Body composition was assessed by using single-frequency bioelectrical impedance assessment after overnight fasting (3). Fat-free mass was calculated by using validated COPD-specific equations (4). Body mass index and fat-free mass index have been calculated by dividing body weight or fat-free mass by the squared height, respectively.

Exercise capacity

Functional exercise capacity has been assessed by using a 6-minute walking distance (6MWD) test (5) and were expressed in percentage (%) predicted (6). 6MWD test was performed in a 125-meter corridor and encouragement was standardized. The test was performed twice on two separate days. The largest distance was used in the analyses.

Serum lactate dehydrogenase activity

Serum LDH activity has been measured in serum by an enzymatic rate method, using pyruvate as substrate (7). The test is optimized according to the recommendations of the German Society for Clinical Chemistry. The reduction of pyruvate to L-lactate with concurrent oxidation of β-NADH is measured at 340 nm. Serum LDH activity is expressed in micromoles of pyrovate converted per minute (U) per litre of serum at 37 °C. Serum LDH activity >480 U/l has been defined as abnormal.

Statistics

All statistics were done using GraphPad Prism 4.03 and SPSS 14.0. Obtained values have been tested for normality and are presented as mean (standard deviation, SD). Patients were stratified by serum LDH activity. Differences between patients with a normal or increased serum LDH activity been assessed by using an unpaired t-test.A priori, a two-sided level of significance was set at p ≤ 0.05 (8).

References online repository

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8.Altman DG, Gore SM, Gardner MJ, Pocock SJ. Statistical guidelines for contributors to medical journals. Br Med J (Clin Res Ed) 1983;286(6376):1489-93.