Thomas A. Dillard, MD FCCP; Steven ...

Thomas A. Dillard, MD FCCP; Steven Piantadosi, MD Ph.D.;[unkeyable] and Krishnan R Rajagopal, MD FCCP

Patients with chronic airflow obstruction (CAO) ofttimes develop impairment of respiratory muscle function. We hypothesized that inspiratory muscle force as assessed by resting, peak inspiratory urgency (PIP) may be an important determinant of maximum exercise capacity in patients with CAO. Twenty ambulatory male patients (mean age, 56 [+ or -] 3 years [[+ or -] SE[) with CAO ([FEVsub1] 172 [+ or -] 021 L) comprised the studied population. Oxygen consumption at incremental revolution of time ergometry to tolerance ([Vo.sub.2]max, 180 [+ or -] 020 L/min) serv as the conditioned variable for regression vs measures of resting pulmonary function. Significant correlations with [Vo.sub.2]max included power output in watts (r=0951) Vemax (r=0858) Dsb (r=0841) PIP (r=0816) age (r= -0809) [FEVsub1] (r=0763) and FVC (r=0663) The [FEVsub1] Dsb and PIP each recorded into a multiple linear regression relationship describing [Vo.sub.2]max. Also, when paired with Vemax as independent variables in multiple regression, PIP and Dsb each improved description of [Vo.sub.2]max across Vemax alone (p<0.05), whereas [FEVsub1] and FVC did not (p>005) We deduce that factors other than ventilatory capacity also have a quantitative meaning on [Vo.sub.2]max and that PIP constitutes a determinant of maximum exercise capacity in patients with CAO.

Patients with CAO frequently have reduced exercise capacity as a accrue of reduced ventilatory reserves or impairment of gas exchange (or both)[12] Previous studies have examined quantitative relationships between about resting measures of pulmonary function and [Vo.sub.2]max in attempts to correlate exercise performance with specific foibles in the respiratory system.[3-8] Variables previously examined as determinants of [Vo.sub.2]max in earlier studies of patients with CAO include expiratory spirometric data and diffusing capacity (D)[3-8]

In addition to reduc expiratory airflow and impaired gas transfer, patients with CAO are also susceptible to reduction of inspiratory muscle strength[910] We hypothesized that inspiratory hardness may be a determinant of exercise capacity in patients with CAO and that consideration of resting PIP may improve the description of exercise performance given by dint of measures of expiratory airflow and gas transfer.

Quantitative testing of inspiratory muscle power has previously been applied to other clinical puzzles including prediction of the likelihood of fortunate weaning from mechanical ventilation.[11] We regard PIP as a standard clinical variable which should be evaluated as a determinant of other outcomes

The main objective of the not away study was to describe [Vo.sub.2]max in patients with CAO in bounds of resting pulmonary function parameters. In addition, we sought to compare PIP with other univariate descriptors of [Vo.sub.2]max and to determine whether PIP could add to other measures of pulmonary function in multivariate description of [Vo.sub.2]max.

This approach could lead to refinement of prediction formulae for [Vo.sub.2]max and also to greater confidence in accepting observ measurements of exercise capacity for decision-making in clinical situations similar as resection of lung cancer[12] and disability evaluation.[13] In addition, to the length that PIP may determine exercise capacity, this variable may be control to improvement with therapy as it is as respiratory muscle training or other rules Thus, the study could provide support for greater evolution and application of treatments which have potential to improve the functional capability of patients with CAO. [TABULAR DATA OMITTED]

MATERIALS AND METHODS

For the drifts of this study, we defined CAO as clinically stable primary pulmonary disease with the following characteristics: (1) ratio of [FEVsub1]/FVC les than 070; (2) TLC greater than 80 percent of predicted; and (3) change in [FEVsub1] after bronchodilator inhalation les than 15 percent

In addition, we defined VLE as (1) [f.sub.c]max les than 2 SD below predicted maximum; (2) primary symptom at maximal exercise consisting of dyspnea without other limiting symptom; and (3) exercise ventilation exceeding 80 percent of the 12-second MVV[1415]

With regard to the criteria for VLE the [f.sub.c]max criterion exclud the possibility that age-dependent [f.sub.c]max may have limited exercise. Patients with ischemic change, paroxysmal arrhythmia, or [f.sub.c]max plateau in succession the exercise ECG were also exclud The dyspnea criterion accounted for the count uponed limiting symptom in the studied population and exclud the predominance of other symptoms that can limit exercise, including angina, claudication, and joint pain. The ventilation criterion provided a minimum requirement for objective ventilatory effort.

Twenty ambulatory male outpatients, each of whom fulfilled the study's definitions of CAO and VLE provided previously, comprised the studied population (Table 1) No expose had a history of prior acute or chronic ventilatory failure or cardiac disease.