Circulatory effects of expiratory flow-limited exercise, dynamic hyperinflation and expiratory muscle pressure

CORRESPONDENCE: P. T. Macklem, PO Box 250, Lansdowne, ON, K0E 1L0 Canada. Fax: 39 0223999000. E-mail: ptm01{at}hotmail.com This article reviews recent research in normal subjects exercising with and without expiratory flow limitation at 1 L·s –1 imposed by a Starling resistor in the expiratory line, and in patients with chronic obstructive pulmonary disease (COPD), using optoelectronic plethysmography to measure respiratory kinematics, combined with mouth, pleural and abdominal pressure measurements, to assess work of breathing and respiratory muscle performance. In normal subjects, flow-limited exercise resulted in the following: 1) Impaired exercise performance due to intolerable dyspnoea; 2) hypercapnia; 3) excessive respiratory muscle recruitment; 4) blood shifts from trunk to extremities; 5) a 10% reduction in cardiac output and a 5% reduction in arterial oxygen saturation, decreasing energy supplies to working respiratory and locomotor muscles. In both normal subjects and in COPD patients, dynamic hyperinflation did not always occur. Those patients that hyperinflated had worse lung function and less work of breathing, but better exercise performance than the others, in whom expiratory muscle recruitment prevented dynamic hyperinflation at the cost of increased work of breathing and excessive oxygen cost of breathing. This established an early competition between respiratory and locomotor muscles for available energy supplies. Dynamic hyperinflation is a better exercise strategy in chronic obstructive pulmonary disease than expiratory muscle recruitment, but the benefit it confers is small. KEYWORDS: Chronic obstructive pulmonary disease, hypercapnia, respiratory muscles, ventilatory pump, work of breathing