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Effects of hyperinflation on the oxygen pulse as a marker of cardiac performance in COPD

¹ Division of Pulmonary, Critical Care and Sleep Medicine, Caritas St Elizabeth's Medical Center, Tufts University School of Medicine, Boston, MA, USA, ² Departamento de Fisiología, Instituto Nacional de Enfermedades Respiratorias, México City, Mexico.

CORRESPONDENCE: V. M. Pinto-Plata, Caritas St Elizabeth's Medical Center, 736 Cambridge, Boston, 02135, MA, USA 02135. Fax: 1 6175627756. E-mail: vpinto{at}copdnet.org

Keywords: Chronic obstructive pulmonary disease, exercise, inspiratory capacity, inspiratory capacity to total lung capacity ratio, oxygen pulse, oxygen uptake

Received: November 13, 2007
Accepted May 29, 2008

A decreased inspiratory capacity (IC)/total lung capacity (TLC) ratio is associated with dynamic hyperinflation and decreased exercise capacity. The present authors hypothesised that static (low IC/TLC) and dynamic hyperinflation impair cardiac function as assessed by oxygen pulse at rest and during cardiopulmonary exercise testing (CPET).

Lung function, body mass index, hand grip strength and CPET parameters were measured (oxygen uptake (mL·kg^–1·min^–1) and oxygen pulse (mL·beat^–1)) in 87 chronic obstructive pulmonary disease (COPD) patients (American Thoracic Society/European Respiratory Society/Global Initiative for Chronic Obstructive Lung Disease stage 3–4) and 46 controls. The patients were divided into those with IC/TLC >25% or 25%.

The IC/TLC ratio at rest and at peak exercise was associated significantly with oxygen pulse. Patients with IC/TLC 25% (n = 45) had significantly lower exercise capacity, peak oxygen pulse, peak minus baseline oxygen pulse, peak IC, peak IC/TLC ratio and % change from baseline to peak IC/TLC ratio compared with patients with IC/TLC >25% and controls. During CPET, the oxygen pulse was lower at iso-work in patients with IC/TLC 25% than in those with IC/TLC >25%.

Resting hyperinflation (inspiratory capacity/total lung capacity) is associated with lower oxygen pulse, peak exercise inspiratory capacity/total lung capacity and exercise capacity in patients with severe chronic obstructive pulmonary disease. The present results support an interaction between hyperinflation and decreased cardiac function that may contribute to exercise limitation in these patients.