Potassium and ventilation during positive and negative work inpatients with chronic obstructive pulmonary disease

Abstract

In patients with chronic obstructive pulmonary disease (COPD), reduced ventilatory reserves limit exercise tolerance. In these patients, the ventilatory requirements of eccentric exercise (negative work, Wneg) are lower than those of concentric exercise (positive work, Wpos) at similar workloads. In this study, we investigated the relationship between plasma potassium levels and ventilation during Wpos and Wneg in these patients. Twelve patients with stable COPD [mean (SD) FEV1 46% (16) of predicted] performed Wpos and Wneg on a cycle ergometer (6 min of exercise; interval > or = 1 h) in a randomized order at a constant workload of 50% of the individual maximum (positive) work capacity. Minute ventilation (VE) and arterial plasma potassium concentration ([K+]a) were measured at rest, and at 1-min intervals during exercise and during 3 min of recovery. VE increased less during Wneg than during Wpos [6 (range 3-26) vs. 18 (range 8-28) 1 min-1; P < 0.01]. VE during Wneg was reduced in proportion to VCO2. The increase in [K+]a during Wpos and Wneg [0.45 (range 0.26-0.75) and 0.34 (range 0.1-0.97) mM] did not differ significantly. VE was closely correlated with VCO2 during both types of exercise. VE was also closely correlated with [K+]a, but the slope of the relationship between [K+]a and VE was steeper during Wpos than during Wneg [39.1 (range 15.2-88.6) vs. 18.3 (range 7.2-37.3) 1 min-1 mM-1; P = 0.012]. In contrast, the slope of the relationship between VCO2 and VE was similar during both types of exercise [27.8 (range 19.2-37.1) vs. 32.1 (range 19.8-48.4)]. Thus, for a given increase in [K+]a, the increase in VE was significantly less during Wneg. In patients with COPD, potassium did not explain the difference in exercise ventilation between Wneg and Wpos, and may not play a significant role in the control of breathing during low-intensity exercise.

Discontinuation of Furosemide Decreases Paco2 in Patients With COPD

“…Consequently, stopping furosemide treatment might increase serum plasma levels and thus stimulate ventilation. However, our group has brought forward experimental evidence that serum potassium levels are not very relevant in the control of breathing of COPD patients, 28 confirming the work of others in resting normal subjects. 29 At the start of the study, we had established that serum potassium levels were within the normal range.…”

Eccentric exercise in adults with cardiorespiratory disease: a systematic review

“… CABG: coronary artery bypass graft; CAD: coronary artery disease; CHF: chronic heart failure; CON: concentric; COPD: chronic obstructive pulmonary disease; ECC: eccentric; FEV1: forced expiratory volume in one second; LVEF: left ventricular ejection fraction; NT-proBNP: N-terminal prohormone of brain natriuretic peptide; NYHA: New York Heart Association; PTCA: percutaneous transluminal coronary angioplasty; RCT: randomised controlled trial; SpO 2 : pulse oximetry oxygen saturation. a Articles contained the same sample population b Rooyackers et al 23,24 combined as same trial. …”

“… CON: concentric; ECC: eccentric; HR: heart rate; r/min: revolutions per minute; RPE: rating of perceived exertion; SpO 2 : pulse oximetry oxygen saturation; VO 2 : oxygen uptake. a Studies contained the same sample population. b Rooyackers et al 22,23 combined as same trial. …”

“…26 Three of these trials 11,23–25 set the revolutions per minute at 60; two 12,27 set it at 15 and 20, referencing studies in healthy subjects which found that slower velocity contractions resulted in decreased muscle damage. 28 With revolutions set, trials used participant’s results from an initial concentric exercise test, that determined first ventilatory threshold, 12,27 peak oxygen uptake, 13,26,29 or maximum work rate 11,23–25 to set their target intensity. All trials increased exercise intensity during the programme but not in a standardised way.…”

“…Four of the seven trials were randomised controlled trials. One trial 22 was quasi-randomised and allocated participants according to age, weight, body mass index and strength; one trial 23,24 used a single-group, crossover design; and one trial 25 was a single group prepost design with a single session comparison of eccentric and concentric exercise. Tables 1 and 2 summarise details of the included trials and highlight their similarities in terms of the context, content and setting of the eccentric exercise programmes.…”