Assessment ofrespiratory function inpatients with chronic obstructive airways disease

Thereproducibility ofsome respiratory function tests andasimple self-paced walking test wereassessed in13patients withstable chronic obstructive airways disease by makingobservations on sixoccasions attwotothree weekly intervals. Thecoefficients of variation ofthevarious tests were asfollows: forced expiratory volume inonesecond, -4=14-8%; forced vital capacity, i--11.%; transfer factor (single breath carbon monoxide), +15%; total lungcapacity, +88% byhelium dilution and±8-3%bybodyplethysmography; increase inheart rateandminute ventilation foran increase inoxygen uptake of051min-1, ±19.4% and+16-3%; distance covered ina 12-minute walking test,+8-2%.The12-minute distance increased significantly overthefirst three studies. Theconsiderable variations intheresult of these tests insubjects withapparently stable clinical states andwithout changes intreatment should beconsidered whenassessing theresults ofchanges intreatment. Although there havebeenmanylong-term studies ofrespiratory function inpatients withchronic obstructive airways disease (Bates etal,1971), there islittle information onthevariability ofthe results ofrespiratory function tests overa short termwhentheclinical condition isstable. This information isnecessary toallowtheevaluation oftheeffects ofchanges intreatment. Inthe present study wehaveassessed thereproducibility oftheresults ofsomecommonly usedrespiratory function tests andofthe12-minute walking test described byMcGavinetal(1976). We havealso studied therelationship oftheresults ofthewalk- ingtest totheresults oftheother tests. Methods andsubjects Thirteen patients werestudied whohadchronic bronchitis asdefined bytheMedical Research Council Working Party(1965) orradiological em- physema asdescribed byLawsandHeard(1962). Allpatients weremen witha meanageof554 years(range 47-64), andnonehadevidence of ischaemic heartdisease orotherserious illness. Nonehadreversible bronchoconstriction-that is,