Determinants of exercise performance in normal men with externally imposed expiratory flow limitation

Abstract

To understand how externally applied expiratory flow limitation (EFL) leads to impaired exercise performance and dyspnea, we studied six healthy males during control incremental exercise to exhaustion (C) and with EFL at approximately 1. We measured volume at the mouth (Vm), esophageal, gastric and transdiaphragmatic (Pdi) pressures, maximal exercise power (W(max)) and the difference (Delta) in Borg scale ratings of breathlessness between C and EFL exercise. Optoelectronic plethysmography measured chest wall and lung volume (VL). From Campbell diagrams, we measured alveolar (PA) and expiratory muscle (Pmus) pressures, and from Pdi and abdominal motion, an index of diaphragmatic power (W(di)). Four subjects hyperinflated and two did not. EFL limited performance equally to 65% W(max) with Borg = 9-10 in both. At EFL W(max), inspiratory time (TI) was 0.66s +/- 0.08, expiratory time (TE) 2.12 +/- 0.26 s, Pmus approximately 40 cmH2O and DeltaVL-DeltaVm = 488.7 +/- 74.1 ml. From PA and VL, we calculated compressed gas volume (VC) = 163.0 +/- 4.6 ml. The difference, DeltaVL-DeltaVm-VC (estimated blood volume shift) was 326 ml +/- 66 or 7.2 ml/cmH2O PA. The high Pmus and long TE mimicked a Valsalva maneuver from which the short TI did not allow recovery. Multiple stepwise linear regression revealed that the difference between C and EFL Pmus accounted for 70.3% of the variance in DeltaBorg. DeltaW(di) added 12.5%. We conclude that high expiratory pressures cause severe dyspnea and the possibility of adverse circulatory events, both of which would impair exercise performance.

Flow limitation and dynamic hyperinflation: key concepts in modern respiratory physiology

“…Studies describing the qualitative change in chest wall volume have used magnetometers to look at the contribution of different chest wall compartments, but these are technically demanding and require considerable subject cooperation [94][95][96]. Recently, a different approach that measures the volume of the chest wall has being applied in healthy subjects [97][98][99], patients in ICU [100] and those with COPD at rest and during exercise [101][102][103]. Optoelectronic plethysmography (OEP) is a noninvasive measurement based on computing the volume of the chest wall from a network of points identified by shining infrared light at a series of reflective markers attached to the ribcage and abdomen [104] (fig.…”

“…Normally, the change in volume at the mouth and those occurring with each breath derived from the chest wall signal are the same at rest (in health and COPD patients). This remains true during exercise in healthy subjects, but not if they breathe through a Starling resistor nor is it the case in many COPD patients [99,101]. In this latter group, the difference between the chest wall volume and that at the mouth reflects the effect of gas compression in the lungs, but also the displacement of blood away from the thorax and into the abdomen.…”

Exercise and dyspnoea in COPD

“…In healthy subjects, this method gives excellent agreement with lung volume measurements derived from recordings at the mouth made at rest and during exercise [37,38]. When healthy subjects exercised to their maximum performance breathing through a Starling resistor circuit, most of them maintained a relatively constant end-expiratory chest wall volume, although some tried to behave as they normally would and reduced EELV, which was an energetically counterproductive strategy [39].…”

Regional Chest Wall Volume Changes During Various Breathing Maneuvers in Normal Men

“…A recent study proposed that two factors induce the difference between V L (SP) and V L (CW): underestimation of V L (CW) by gas compression effects when air is compressed by increasing pleural pressure 15) ; and overestimation of V L (CW) during inspiration and underestimation of V L (CW) during expiration because of the movement of blood from the thorax to the extremities 15) . The relationships between these factors were also investigated in this earlier study.…”