Influence of expiratory flow-limitation during exercise on systemic oxygen delivery in humans

Abstract

To determine the effects of exercise with expiratory flow-limitation (EFL) on systemic O(2) delivery, seven normal subjects performed incremental exercise with and without EFL at approximately 0.8 l s(-1) (imposed by a Starling resistor in the expiratory line) to determine maximal power output under control (W'(max,c)) and EFL (W'(max,e)) conditions. W'(max,e) was 62.5% of W'(max,c), and EFL exercise caused a significant fall in the ventilatory threshold. In a third test, after exercising at W'(max,e) without EFL for 4 min, EFL was imposed; exercise continued for 4 more minutes or until exhaustion. O(2) consumption (V'(O)(2)) was measured breath-by-breath for the last 90 s of control, and for the first 90 s of EFL exercise. Assuming that the arterio-mixed venous O(2) content remained constant immediately after EFL imposition, we used V'(O)(2) as a measure of cardiac output (Q'(c)). Q'(c) was also calculated by the pulse contour method with blood pressure measured continuously by a photo-plethysmographic device. Both sets of data showed a decrease of Q'(c) due to a decrease in stroke volume by 10% (p < 0.001 for V'(O)(2)) with EFL and remained decreased for the full 90 s. Concurrently, arterial O(2) saturation decreased by 5%, abdominal, pleural and alveolar pressures increased, and duty cycle decreased by 43%. We conclude that this combination of events led to a decrease in venous return secondary to high expiratory pressures, and a decreased duty cycle which decreased O(2) delivery to working muscles by approximately 15%.

Chest wall volume regulation during exercise in COPD patients with GOLD stages II to IV

“…Greater activation of abdominal muscles allowed GOLD stage II patients to dynamically hyperinflate much less than GOLD stages III and IV and probably led those patients to stop exercise from leg discomfort rather than dyspnoea (table 2). High expiratory pressures during exercise in patients with COPD [10,11,26] and healthy subjects [27,28] can cause adverse circulatory events that ultimately may impair exercise performance. Under this condition, high expiratory pressures during exercise in patients with GOLD stage II might have caused adverse circulatory effects that ultimately impaired exercise performance resulting in similar peak exercise tolerance in GOLD stages II and III (table 2).…”

The major limitation to exercise performance in COPD is dynamic hyperinflation

“…24) as well as sharp decreases in dynamic lung compliance. DH, particularly if it is accompanied by excessive expiratory muscle activity, also has the potential to adversely effect cardiocirculatory function, and thus ventilatory/locomotor muscle interactions, during exercise in COPD (1,23). When impairment of cardiac output (and oxygen transport) is coupled with severely compromised ventilatory muscle function, the development of inspiratory muscle fatigue is possible.…”

Last Word on Point:Counterpoint: The major limitation to exercise performance in COPD is 1) inadequate energy supply to the respiratory and locomotor muscles, 2) lower limb muscle dysfunction, 3) dynamic hyperinflation

“…We are also pleased that West and Wagner (5) agree with our Point: Counterpoint figure showing that the initiating event in exercise limitation is expiratory flow limitation; this sets in motion a train of events that severely impairs ventilatory pump function (2), including a reduction in cardiac output and energy supplies to working muscles (1). Scano (5), an author on this paper, asks "how does.…”