The oxygen costliness of augmented ventilation is increased in patients with chronic obstructive pulmonary disease.

The oxygen costliness of augmented ventilation is increased in patients with chronic obstructive pulmonary disease, either at quiet or during exercise. Thus, if excessive demands are placed onward the respiratory muscles during exercise in these patients, we postulate that the total oxygen consumption ([VOsub2]) may increase relative to the work rate compared to check subjects. The aim of this research was to examine the relationship between [VOsub2] and work rate during exercise in patients with airflow obstruction. A retrospective analysis of data aggregateed over 7 years was actionsed Patients with airflow obstruction (n= 131) were compared and contrasted with those in whom pulmonary function studies (spirometry, lung volumes) were normal (n=199) Severity of airflow obstruction (ie, mild moderate, severe) was determined, using the 95 percent confidence limits for the ratio of [FEVsub1] to FVC Incremental exercise studies were performed upon a cycle ergometer. Resting [VOsub2] was not significantly different across the disposes with airflow obstruction measured either directly or normalized for dead body weight. The [VO.sub.2] max was significantly reduc in the patients with austere airflow obstruction, compared with the normal form into groups as well as the patients with mild and moderate airflow obstruction. No differences were noted in the acclivity [i]or[/i] declivity of [VO.sub.2] Plotted against work rate in the patients with airflow obstruction (regardless of the severity of the obstruction) and individuals in whom originates of pulmonary function tests were normal. In addition, when inflection for sex was taken into account, there was essentially no difference in the oblique directions for either male or female enthralls across all groups. Stepwise, linear regression failed to demonstrate any variable or variables that were earnestly related to slope. We postulate that the maintenance of a normal inclination of [VO.sub.2] on work rate in patients with airflow obstruction, in whom the oxygen price and work of breathing is likely increased, may mask a significant reduction in nonrespiratory [VOsub2] (for example, to exercising skeletal muscles).

ANOVA=analysis of variance; CL=confidence limit; IBW=ideal material substance weight; [VO.sub.2] Max=maximum oxygen consumption; [VOsub2] di=diaphragmatic [VOsub2]; [VOsub2] resp=oxygen consumption of the respiratory pump

An increase in the oxygen outlay of augmented ventilation has been well documented in patients with chronic obstructive pulmonary disease (COPD) either at ease or during exercise.[1-4] This may in part be explained by way of the increased mechanical loads and reduc efficiency of the respiratory muscles induced particularly on dynamic hyperinflation,[5-7] coupled during exercise, with a disproportionate increase in ventilation for a given work rate.[3] An increased demand on the respiratory pump in patients with COPD has been well documented through Levison and Cherniack,[3] who reported that the oxygen consumption of the respiratory cross-question ([VO.sub.2] resp), expressed as a percentage of the total [VOsub2] during exercise, was considerably higher in patients with COPD compared with normal make submissives For example, at a minute ventilation of 30 L/min, [VOsub2] resp accounted for 379 percent of the total [VOsub2] in the patients with COPD compared with merely 12.9 percent in normal subjects[3]

The authors intimateed that the [VO.sub.2] available to nonrespiratory muscles and the other tissues would be commensurately curtailed. It has been reported lately by Donahoe and coworkers[4] that a significant correlation was set between parameters of increasing airflow obstruction ([FEVsub1]) and hyperinflation (RV/TLC) and the oxygen preciousness of augmented ventilation in patients with COPD Similar correlations were observ in normal enthralls subjected to inspiratory resistive loads and hyperinflation.[6] Thus, single might hypothesize that the significantly increased demands through the respiratory pump in patients with censorious degrees of airflow obstruction and hyperinflation would manifest as an increase in the total [VOsub2] during exercise relative to the work rate, particularly if the increment in [VOsub2] resp was disproportionately great.

small in number studies have specifically examined the relationship between [VOsub2] and work rate during exercise in patients with airflow obstruction.[3,8-10] Filley[8] and Levison and Cherniack[3] reported no differences in the [VO.sub.2]/work rate relationship in patients with COPD compared with normal enthralls Jones et al[9] found that, while the [VO.sub.2]/work rate relationship in patients with COPD was similar to that obtained in normal make submissives the regression line was displaced upward above the line for normal make subordinates By contrast, Hatzfeld and coworkers[10] reported a 35 percent increase in the [VO.sub.2]/work rate relationship in patients with COPD compared with normal make subordinates In these studies, the number of patients studied were relatively small and no attempt was made to stratify patients according to step of airflow limitation. The aim of this consideration was to retrospectively examine the relationship between [Vsub2] and work rate during exercise in a large cohort of patients with varying steps of airflow obstruction, and to compare and contrast these patients with those in whom originates of pulmonary function tests were normal.

...