Blood shifts between body compartments during submaximal exercise with induced expiratory flow limitation in healthy humans

Abstract

 External expiratory flow limitation (EFLe) can be applied in healthy subjects to mimic the effects of chronic obstructive pulmonary disease (COPD) and safely study the mechanisms of exercise intolerance associated with the disease. At maximal exercise intensity with EFLe, exercise intolerance results from high expiratory pressures altering the respiratory pump mechanism and limiting venous return. We used double body plethysmography to quantify blood shifting between the trunk and the extremities and examine whether the same effects occur with EFLe at submaximal exercise intensity, where the increase in expiratory pressures is milder. Our data show that during submaximal exercise, EFLe amplifies the respiratory pump mechanism, each breath producing greater blood displacements between the trunk and the extremities, with a prevailing effect from lower inspiratory intra-thoracic pressure progressively drawing blood into the trunk. These results help better understand the hemodynamic effects of respiratory pressures during submaximal exercise with expiratory flow restriction.

A game of chest: Where does blood volume shift?

“…Recently, Stucky et al. (2022) built on these maximal exercise findings by conducting a complex and technically challenging study using EFLe during submaximal exercise (∼40% $${\dot V_{{{\rm{O}}_{\rm{2}}}{\rm{max}}}}$$). The study aimed to emulate lower intensity exercise similar to that typically experienced by patients with COPD and determine how the accompanying respiratory pressure swings influence the displacement of blood between the trunk and extremities.…”

“…However, Stucky et al. (2022) speculate that any expiratory‐phase venous return limitation may be overcompensated for by lower inspiratory‐phase intrathoracic pressure enhancing blood flow into the thorax. It was also postulated that, because peak abdominal pressure significantly decreased from expiration to inspiration throughout exercise for the EFLe group, there was a significant window of time during inspiration favoring venous return.…”

“…Hyperinflation is an additional consequence of EFLe, developing in 50% of total runs in Stucky et al. (2022), which might lead to increased inspiratory muscle blood flow as a result of a higher inspiratory muscle metabolic demand. Hyperinflation results in a higher operational lung volume in which there is an increased ratio of inspiratory effort to lung volume displacement.…”

Expiratory flow limitation during exercise: why does it ‘suck’ so much?

“…In this issue of The Journal of Physiology , Stucky et al. (2023) pursued this intriguing hypothesis with an experimental and measurement protocol that allowed for indirect measurement of fluid shifts in healthy men using double plethysmography and externally imposed EFL during submaximal exercise to mimic a ventilation that can be achieved by COPD patients. They report a net movement of fluid into the thorax, which was more related to the negative oesophageal pressure during inspiration than to the greater gastric pressure during expiration, which is in contrast with their prior work.…”

“…The findings of Stucky et al. (2023) suggest that for us to arrive at an answer, we must first turn the lens on ourselves and ask: is it me that ‘sucks’? Or am I just a ‘blowhard’?…”