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1 Fondazione Don Gnocchi, I-50020 Pozzolatico; 6 Clinica Medica III, Università di Firenze, I-50134 Firenze; 2 Centro di Bioingegneria, Fondazione Don Gnocchi e Politecnico, I-20148 Milano; 3 Dipartimento di Bioingegneria, Politecnico di Milano, 32 I-20133 Milano, Italy; 4 University of Geneva, CH-1211 Geneva, Switzerland; 5 Westmead Hospital, NSW-2145 Sydney, Australia; 7 Meakins-Christie Laboratories, Montreal Chest Institute, McGill University Health Centre, Montreal, Quebec, Canada H2X 2P4; and 8 Department of Respiratory Medicine, Institute of Tuberculosis and Lung Diseases, 01-138 Warsaw, Poland
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 ~1. We measured volume at the mouth (Vm), esophageal,
gastric and transdiaphragmatic (Pdi) pressures, maximal exercise power
(
max) and the difference (
) 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 (di). Four subjects
hyperinflated and two did not. EFL limited performance equally to 65%
max with Borg = 9-10 in both. At EFL
max, inspiratory time (TI) was
0.66s ± 0.08, expiratory time (TE) 2.12 ± 0.26 s, Pmus ~40 cmH2O and VL-Vm = 488.7 ± 74.1 ml. From
PA and VL, we calculated compressed gas volume
(VC) = 163.0 ± 4.6 ml. The difference,
VL-Vm-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 Borg.
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.
dyspnea; respiratory muscles; dynamic hyperinflation; ventilation; blood volume shifts
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