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

KEY POINTS: 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.

ABSTRACT: External expiratory flow limitation (EFLe) can be applied in healthy subjects to mimic the effects of COPD during exercise. At maximal exercise intensity, EFLe leads to exercise intolerance due to respiratory pump dysfunction limiting venous return. We quantified blood shifts between body compartments to determine whether such effects can be observed during submaximal exercise, when the load on the respiratory system is milder. Ten healthy men (25.2±3.2 y, 177.3±5.4 cm, 67.4±5.8 kg) exercised at 100 W (∼40 % VO2 max) while breathing spontaneously (CTRL) or with EFLe. We measured respiratory dynamics with optoelectronic plethysmography, esophageal (Pes) and gastric (Pga) pressures with balloon catheters, and blood shifting between body compartments with double body plethysmography. During exercise, EFLe resulted in (1) greater intra-breath blood shifts between the trunk and the extremities (518±221 (EFLe) vs 224±60 ml (CTRL); P<0.001) associated with lower Pes during inspiration (r = 0.53, P<0.001) and higher Pga during expiration (r = 0.29, P<0.024) and (2) a progressive pooling of blood into the trunk over time (∼700 ml after 3 min exercise; P<0.05), explained by a predominant effect of lower inspiratory Pes (r = 0.54; P<0.001) over that of increased Pga. It follows that during submaximal exercise, EFLe amplifies the respiratory pump mechanism, with a prevailing contribution from lower inspiratory Pes over increased expiratory Pga, drawing blood into the trunk. Whether these results can be replicated in COPD patients remains to be determined. Abstract figure legend Quantification of blood shifting between the trunk and the extremities by double plethysmography (total body and optoelectronic plethysmography). The volume of blood shifted (Vbs) from the extremities to the trunk and intra-breath Vbs amplitude (swings) significantly increase during submaximal exercise with externally applied expiratory flow limitation (EFLe). This article is protected by copyright. All rights reserved.