Determining the Lactate Threshold in Patients with Severe Chronic Obstructive Pulmonary Disease

Abstract

The degree of the metabolic stress associated with muscular exercise depends on the intensity of the work being performed. Consequently, the gas exchange, acid/base and ventilatory requirements will also be intensity dependent. Low intensity exercise can be performed utilising ATP formed aerobically through oxidative phosphorylation but supplemented from creatine phosphate stores utilisation. When heavy exercise is undertaken, anaerobic glycolysis further supplements the high energy phosphate transformation with the consequent production of lactic acid — which at cellular pH is dissociated virtually entirely into lactate ions (La⁻) and protons (H⁺). The consequent H⁺ is predominantly buffered by bicarbonate ions (HCO₃ ⁻): the resulting carbonic acid yields extra carbon dioxide to be excreted by the lungs in addition to that produced from cellular respiration. The level of oxygen uptake at which lactate increases has been termed the Anaerobic or Lactate Threshold (LT).