Background: Little is known about the mechanistic basis for the exercise intolerance characteristic of patients with\nrespiratory disease; a lack of clearly defined, distinct patient groups limits interpretation of many studies. The purpose\nof this pilot study was to investigate the pulmonary oxygen uptake (V_: O2) response, and its potential determinants, in\npatients with emphysema and idiopathic pulmonary fibrosis (IPF).\nMethods: Following a ramp incremental test for the determination of peak V_: O2 and the gas exchange threshold, six\nemphysema (66 Ã?± 7 years; FEV1, 36 Ã?± 16%), five IPF (65 Ã?± 12 years; FEV1, 82 Ã?± 11%) and ten healthy control participants\n(63 Ã?± 6 years) completed three repeat, heavy-intensity exercise transitions on a cycle ergometer. Throughout each\ntransition, pulmonary gas exchange, heart rate and muscle deoxygenation ([HHb], patients only) were assessed\ncontinuously and subsequently modelled using a mono-exponential with (V_: O2, [HHb]) or without (HR) a time delay.\nResults: The V_: O2 phase II time-constant (Ãâ??) did not differ between IPF and emphysema, with both groups significantly\nslower than healthy controls (Emphysema, 65 Ã?± 11; IPF, 69 Ã?± 7; Control, 31 Ã?± 7 s; P < 0.05). The HR Ãâ?? was slower in\nemphysema relative to IPF, with both groups significantly slower than controls (Emphysema, 87 Ã?± 19; IPF, 119 Ã?± 20;\nControl, 58 Ã?± 11 s; P < 0.05). In contrast, neither the [HHb] Ãâ?? nor [HHb]:O2 ratio differed between patient groups.\nConclusions: The slower V_: O2 kinetics in emphysema and IPF may reflect poorer matching of O2 delivery-to-utilisation.\nOur findings extend our understanding of the exercise dysfunction in patients with respiratory disease and may help to\ninform the development of appropriately targeted rehabilitation strategies.
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