Effect of resistive load on the inspiratory work and power of breathing during exertion

Resistive loads are used to train respiratory muscles in athletes and in rehabilitation of people with pulmonary disease or spinal injuries [1–3]. Other studies use external resistive load detection as a tool to study dyspnoea sensitivity [4]. Resistive work is dependent on ventilation, and different exercise modes, for example walking and cycling place different metabolic demands on the body. A measure of the work performed during breathing can be derived from the product of the volume and pressure change generated during the respiratory cycle. The mechanical work of breathing which includes the elastic and resistive components, defined per litre of ventilation in resting healthy subjects is around 0.3560.1 JL21 while the power generated is around 2.460.7 W [5]. The power generated is thus influenced by respiratory rate and volume of air moved. Measuring these parameters often involve using invasive techniques and require an estimate of chest wall compliance [6]. At rest the inspiratory work of breathing is consistently larger than expiratory work. However this changes with exercise when expiration also becomes an active process. Measuring work only during the inspiratory phase of the respiratory cycle provides a simple index of the muscle-driven work irrespective of the expiratory phase. This study aims to use a new non-invasive method to measure the resistive work of breathing and the subsequent power generated (WRI and PRI respectively) while breathing against added resistive loads and explore this relationship with ventilation during sub-maximal exercise, sitting, walking or cycling. This study while observational is unique in that the loading was applied in ‘‘real-time’’ using a servo-controlled variable orifice pneumotachograph allowing both resistive inspiratory work and power to be assessed simultaneously