Impact of Chest Wall Restriction on Cardiac Output and Exercising Muscle Oxygenation

Abstract

Restrictive pulmonary diseases (RPD) encompass diseases whereby the lungs are prevented from being able to fully expand. One way that these diseases can manifest is through increased chest wall stiffness. A common symptom that presents in individuals with RPD is reduced exercise capacity. This is commonly thought to be due to reduced ventilation and increased sensations of breathlessness. Chest wall restriction (CWR) is a strategy that mimics RPD by constricting the chest wall. A subsequent result of CWR is that it decreases the amount of blood that is pumped by the heart (cardiac output, CO). When CO is limited, it is possible that the amount of blood being delivered to the exercising muscles may also be reduced, which would have an adverse effect on exercise tolerance. Whether exercising muscle blood flow is affected by a limitation to CO in submaximal exercise is unclear, and therefore the effects of CWR on muscle oxygenation are unknown. As CWR mimics RPD, the CO response to exercise may also be blunted in these individuals. This could lower blood flow to the exercising muscle and be an additional mechanism by which exercise capacity is lowered in RPD. Therefore, we tested whether exercising muscle oxygenation is lowered by a CWR-mediated blunting of CO. Twelve individuals completed exercise cycling tests under normal and CWR conditions. When CWR was applied, exercising CO was lower than what was seen under normal conditions. When CWR was removed during exercise, CO was restored to control levels. In addition, the removal of CWR resulted in an improvement to exercising muscle oxygenation, while no change was seen under control conditions. We interpreted these findings to be consistent with lowered muscle oxygenation with CWR due to a reduced CO, indicating that blood flow to the muscle was reduced. Furthermore, there is potential for this mechanism to exist in individuals with RPD, contributing to their experienced exercise intolerance. However, this remains to be tested.