Predictors of Smaller Oxygen Uptake Reserve Above Anaerobic Threshold in Patients with Cardiovascular Diseases

Abstract

Aerobic exercise up to 70 % of peak oxygen uptake (VO2peak) or below anaerobic threshold (VO2AT) is recommended in patients with cardiovascular diseases. However, a VO2AT/VO2peak ratio greater than 0.70 is often observed in such patients at maximal exercise testing. Fifty two cardiovascular patients (60±14 years, m/f 44/8) with their peak respiratory exchange ratio (RER) >1.10 at cardiopulmonary exercise test, indicative of maximal effort, were stratified into 2 groups: VO2AT/VO2peak>0.70 (n=33) and VO2AT/VO2peak<0.70 (n=22). Clinical variables including echocardiographic data were compared, and predictors of VO2AT/VO2peak were evaluated. VO2AT/VO2peak ratio and age were higher in VO2AT/VO2peak>0.70 than VO2AT/VO2peak<0.70 (0.77±0.08 vs. 0.62±0.06, and 64±10 vs. 56±16 years, p<0.01). No differences were observed in gender, current medication, underling diseases, or RER at anaerobic threshold and peak exercise (1.24±0.11 vs. 1.26±0.09, p=0.51). At peak exercise, VO2AT/VO2peak>0.70 had smaller peak heart rates (p=0.02), VO2peak (19.9±5.9 vs. 22.8±54.0 ml/kg/min, p<0.01), minutes ventilation (p<0.01), and work rates (86±28 vs. 106±24 watt, p<0.01). Echocardiography showed higher E wave, slower peak early diastolic mitral annular velocity, and lower ejection fraction in VO2AT/VO2peak>0.70. Multivariate analysis showed that age was positively and left ventricular ejection fraction and VO2peak were negatively associated with VO2AT/VO2peak ratio. Cardiovascular patients with higher age and lower ejection fraction may have smaller oxygen uptake reserve above anaerobic threshold.