Ventilatory strategies in the six-minute walk test in older patients receiving a three-week rehabilitation programme after cardiac surgery through median sternotomy

Abstract

Although the six-minute walk test (6MWT) is widely used in cardiac rehabilitation, little is known about the ventilatory strategies adopted by older patients who have recently undergone median sternotomy, in order to meet the increased metabolic demand in the 6MWT. Using a portable gas-analyser we assessed the breathing patterns in the 6MWT before and after a 3-week rehabilitation programme in 84 older patients, 58 men and 26 women, mean age 71 years (standard deviation (SD) 6 years), who had undergone median sternotomy. After rehabilitation, patients increased end-test ventilation (33.1 l (SD 9.8) vs. 30.9 l (SD 8.4), p < 0.001) by increasing tidal volume (1.158 l (SD 0.298) vs. 1.065 l (SD 0.255), p < 0.001), while breathing frequency remained unchanged (29.9 bpm (SD 5.4) vs. 30.2 bpm (SD 5.8), p = 0.621). As a consequence, the ventilatory equivalent for CO2, was significantly improved (39.9 (SD 5.3) vs. 43.5 (SD 7.4), p < 0.001). Furthermore, the improvement in ventilatory efficiency was significantly (p < 0.001) correlated with the improvement in the distance walked on the 6MWT. Older patients who have undergone median sternotomy meet the increased metabolic demand on the 6MWT after cardiac rehabilitation by increasing tidal volume. Accordingly, we should consider including as a routine specific exercises for inspiratory muscle training in current rehabilitation programmes to reduce inspiratory muscle effort and further improve ventilatory efficiency.