Ergogenic value of oxygen supplementation in chronic obstructive pulmonary disease

Abstract

Patients with COPD exhibit limited exercise endurance time compared to healthy age-matched individuals. Oxygen supplementation is often applied to improve endurance time during pulmonary rehabilitation in patients with COPD and thus a comprehensive understanding of the mechanisms leading to improved endurance is desirable. This review analyses data from two studies by our research group investigating the effect of oxygen supplementation on cerebrovascular, systemic, respiratory and locomotor muscle oxygen availability on the same cohort of individuals with advanced COPD, and the mechanisms associated with improved endurance time in hyperoxia, which was essentially doubled (at the same power output). In hyperoxia at isotime (the time at which patients became exhausted in normoxia) exercise was associated with greater respiratory and locomotor muscle (but not frontal cortex) oxygen delivery (despite lower cardiac output), lower lactate concentration and less tachypnoea. Frontal cortex oxygen saturation was higher, and respiratory drive lower. Hence, improved endurance in hyperoxia appears to be facilitated by several factors: increased oxygen availability to the respiratory and locomotor muscles, less metabolic acidosis, and lower respiratory drive. At exhaustion in both normoxia and hyperoxia, only cardiac output and breathing pattern were not different between conditions. However, minute ventilation in hyperoxia exceeded the critical level of ventilatory constraints (V_E/MVV > 75-80%). Lactate remained lower and respiratory and locomotor muscle oxygen delivery greater in hyperoxia, suggesting greater muscle oxygen availability improving muscle function. Taken together, these findings suggest that central haemodynamic and ventilatory limitations and not contracting muscle conditions dictate endurance time in COPD during exercise in hyperoxia.

Keywords: COPD; Exercise tolerance; Oxygen supplementation.

Fig. 1

Percentage improvement in submaximal exercise endurance time during hyperoxia compared to normoxia in patients with COPD. Fractions of inspired oxygen concentration (FIO₂) and peak work rate (PWR) are shown for each study. The study by Somfay et al. 2001, shows data from the same patients exercising at different FIO₂

Fig. 2

Frontal cortex cerebrovascular oxygenation and haemodynamic responses: (a) blood flow, (b) oxygen delivery and (c) fractional oxygen saturation (St,O₂%) at rest and at exhaustion while breathing room air (closed symbols), or 100% oxygen (open symbols). Values are means (SEM) for n = 12 [5]. *p < 0.05 compared with room air at the same time point of exercise; ¶p < 0.05 compared with exhaustion in room air

Fig. 3

Breathing pattern responses: (a) time of inspiration (T_I), (b) time of expiration (T_E), (c) breathing frequency (f), (d) minute ventilation (V_E), (e) tidal volume (V_T), (f) breathing reserve (V_E/MVV), all recorded at rest, at isotime and at exhaustion while breathing room air (closed symbols) or 100% oxygen (open symbols). Values are means (SEM) for n = 10 [4, 5]. Isotime data are those obtained on 100% oxygen at the same time as at exhaustion on room air. *p < 0.05 compared with room air at the same time point of exercise; ¶p < 0.05 compared with exhaustion in room air. Significant differences between data at isotime or exhaustion and rest are not indicated on the figure. Dotted line on Fig. 3f denotes the level of critical ventilatory constraints

Fig. 4

Central haemodynamic responses: (a) cardiac output, (b) systemic arterial oxygen content (Ca,O₂), (c) systemic oxygen delivery, (d) lactate concentration, recorded at rest, at isotime and at exhaustion while breathing room air (closed symbols) or 100% oxygen (open symbols). Values are means (SEM) for n = 10 [4, 5]. Isotime data are those obtained on 100% oxygen at the same time as at exhaustion on room air. *p < 0.05 compared with room air at the same time point of exercise; ¶p < 0.05 compared with exhaustion in room air. Significant differences between data at isotime or exhaustion and rest are not indicated here

Fig. 5

Quadriceps and respiratory muscle haemodynamic responses: (a) quadriceps muscle blood flow; (b) intercostal muscle blood flow; (c) abdominal muscle blood flow; (d) quadriceps muscle oxygen delivery; (e) intercostal muscle oxygen delivery; (f) abdominal muscle oxygen delivery recorded at rest, at the time of exhaustion in room air (isotime), and at exhaustion while subjects breathed 100% oxygen (open symbols), or room air (closed symbols). Values are means (SEM) for n = 10 [4]. Isotime data are those obtained on 100% oxygen at the same time as at exhaustion on room air. *p < 0.05 compared with room air at the same time point of exercise; ¶p < 0.05 compared with exhaustion in room air

Fig. 6

A schematic representation conceptualising the acute physiological responses of patients with COPD during exercise breathing oxygen compared with exercise in room air at isotime (when work completed is the same between normoxia and hyperoxia). t_E expiratory time, DH dynamic hyperinflation, CO cardiac output, O₂DEL oxygen delivery, SVC systemic vascular conductance