Question

Discuss how the HR-VO2 relationship may be altered by pulmonary diseases and cardiovascular diseases. Also, what other conditions might affect the HR-VO2 relationship.

Answer 1

Ans) Patients with chronic obstructive pulmonary disease (COPD) present with reduced exercise capacity due to a combination of factors including impaired cardiopulmonary responses, leading to inadequate pulmonary oxygen (O2) uptake and delivery to active skeletal muscle, derangements in the intracellular biochemical reactions in relation to mitochondrial oxygen consumption (VO2) and/or mechanical abnormalities.

- Following the onset of constant workload exercise, the O2 uptake increase (ie, on-kinetics) in COPD patient, which can be characterized by the time required for VO2 to achieve steady state in response to physical stress, is slowed when compared to apparently healthy matched controls. From a clinical context, O2 uptake on-kinetics has been shown to have even better prognostic value than peak VO2 in chronic disease populations.6,7 Moreover, recent studies have shown that, like O2 uptake on-kinetics, heart rate (HR) on-kinetics, are also slower in COPD patients.1,8 Some investigators1,8,9 have postulated that slower O2 uptake and HR on-kinetics10 may reflect the adjustment of both oxygen delivery and muscle metabolism during physical exercise as well as exercise performance/functional capacity in these patients.

Additionally, forced expiratory volume in 1 second (FEV1), a measurement that quantifies the degree of airway obstruction, is often used to diagnose and quantify COPD severity.12 Moreover, the rate of decline in FEV1 is a good marker of disease progression and mortality, however, it does not adequately reflect systemic manifestations that contribute to reduced exercise performance in COPD.

- Active muscle mass involved during exercise is highly associated with VO2max and this relationship may explain partially age-related decline in VO2max. However, the influence of muscle mass on aerobic capacity in elderly athletes may be less, compared to younger athletes. Furthermore, central factors, such as the loss of HR and maximal cardiac output with aging clearly contribute to the reductions in aerobic capacity.