Proceedings of The Physiological Society
Kings College London (2005) J Physiol 565P, C177
Maximum walking time in patients with peripheral artery disease: prediction of baseline and change following exercise training.
Sandercock, Gavin ; Hodges, Lynette ; Bromley, Paul ; Brodie, David ; Das, Saroj ;
1. Research Centre for Health Studies., Buckinghamshire Chilterns University College, Chalfont St Giles, Buckinghamshire, United Kingdom. 2. Imperial College, London, United Kingdom.
Patients with peripheral artery disease (PAD) are characterised by suffering intermittent claudication and have greatly reduced functional capacity and limited ambulation. It is commonly believed that peripheral factors relating to limb blood flow are the major determinants of maximum walking time (MWT) (Green 2002). Data obtained from healthy subjects shows vagal cardiac modulation measured by high frequency spectral power (HF), is related to changes in exercise capacity due to training (Hautala et al. 2003). The purpose of this study was to determine whether cardiopulmonary and heart rate variability measures could predict MWT at baseline and change in walk time (ΔMWT) following exercise training. Twenty eight patients (six women, mean age 59±6) were recruited. Resting HF was derived from a five min ECG recorded in the semi-recumbent position. All patients completed a standard incremental exercise test with two minute stages. Cardiopulmonary measures were made constantly throughout the test (MedGraphics Corporation, CardiO2 CP stress system. St. Paul, Minnesota, USA). Blood pressure, ratings of perceived exertion and ischaemic pain were measured at the end of each stage. Patients were randomly assigned to either a home based (HB) or supervised (SU) exercise group. The exercise group were required to complete two, 30 min sessions of treadmill walking a week. All tests were repeated after 12 weeks. Multiple stepwise regression was performed to determine the best predictors of MWT and ΔMWT. The SU group showed significant increases in MWT (t-test, P < 0.001); there was no increase in the HB group. At baseline, peak oxygen consumption was the only predictor of MWT (R2 = 0.51 and S.E.E = 167.8 s). In the SU group, peak oxygen consumption and high frequency spectral power in log units (HFln) both predicted ΔMWT (R2 = 0.74, S.E.E = 90.9 s). Colinearity diagnostics confirmed the independence of these measures. This study shows that central factors account from much of the variance in MWT in PAD patients. Higher oxygen consumption and greater cardiac vagal modulation (HFln) at baseline were indicators of a greater training response to exercise. This work indicates that those involved in rehabilitation can use baseline measures to guide the intensity of training and thus optimise their programmes. All work conformed to the standards set by the declaration of Helsinki.
Where applicable, experiments conform with Society ethical requirements