Uphill Walking as Exercise for COPD Patients

This study is designed to provide preliminary information regarding how to improve pulmonary rehabilitation for persons with chronic obstructive pulmonary disease (COPD). Pulmonary rehabilitation is an exercise program for COPD patients that is recommended and benefits some, but not all, patients. The question being studied in this trial is whether walking on an incline might be better than walking on faster on a flat surface in training muscles so that patients might be less short of breath with exercise.

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality and presents an important healthcare problem, especially for Veterans. Prevalence of COPD in the Veteran population ranges from 33%-43%, a higher prevalence than among the general population of the United States. COPD patients experience diminished exercise capacity. A significant portion of this limitation in exercise capacity is due to dynamic hyperinflation and dyspnea. Humans demonstrate a coupled relationship between walking and breathing. The investigators' preliminary data indicates that patients with COPD demonstrate an abnormal coupling pattern compared to those without COPD, using one stride for one breath, even at speeds outside of their self-selected walking pace. Current pulmonary rehabilitation relies on increasing intensity of exercise through accelerated walking. Based on coupling patterns in patients with COPD, increasing speed leads to an increase in respiratory rate, dynamic hyperinflation, and dyspnea, thus limiting exercise time. The goal of this proposed project is to investigate, in Veteran COPD patients, the effect of walking faster vs. walking on a slope on dynamic hyperinflation and dyspnea, oxygen uptake and dead space, and walking and breathing coupling. The investigators hypothesize that walking on a slope will alter breathing and walking coupling, lower respiratory rates, and reduce dynamic hyperinflation and associated dyspnea. The investigators predict that walking on a slope will permit an increase in oxygen uptake and a decrease in dead space in patients with COPD as compared to accelerated walking speeds. These hypotheses will be tested through three aims: 1) Identify differences in dynamic hyperinflation and dyspnea; 2) Compare differences in respiratory rate, oxygen uptake, and lung dead space; 3) Determine the complexity of walking and breathing coupling ratios. In this cross-sectional study, Veterans with COPD will be recruited and screened using a cardiopulmonary exercise test. A total of 25 eligible Veterans will be enrolled through stratified sampling of disease severity. The time course of work rate will be calculated from the cardiopulmonary exercise test. The speed and slope that corresponds to 60% of peak work rate will be used. An additional constant work rate test will be given using increases in speed with a level treadmill to determine the speed that elicits oxygen uptake comparable to the sloped walking test. Subjects will be asked to perform two experimental trials (walking faster vs. walking on a slope) at 60% peak work rate. Measures of dynamic hyperinflation, dyspnea, oxygen uptake, dead space, and coupling will be recorded during all walking trials. Possible covariates will also be collected. The investigators anticipate that dynamic hyperinflation and dyspnea will be reduced in patients with COPD due to slower walking and slower respiratory rates during sloped walking as compared to faster level walking. It is expected that this will be influenced by the complexity in breathing and walking coupling ratios. The investigators' multidisciplinary team will provide combined expertise from several disciplines and is uniquely qualified to complete the aims proposed. Results from this feasibility and acceptability study will set the stage for a rigorous, well-powered, full Merit award outcome study evaluating the effectiveness of a slope-based training regimen as part of rehabilitation.

Subjects will walk on treadmill at slope and speed to equal 60% of their peak work rate as determined on baseline cardiopulmonary exercise test.

Subjects will be prepared for data collection by wearing a form-fitting suit (i.e., wrestling singlet) and obtaining height and body weight. Retro-reflective markers will be placed bilaterally on anatomical locations of the feet, legs, and hips. be outfitted with the portable metabolic cart and oximeter as in the previous visit. One of two treadmill trials will be performed: 1) at the speed and 2) at the slope +speed determined in the previous visit. Trial order will be randomized among subjects and across visits 3 & 4. For each trial, subjects will be asked to walk on a treadmill for up to 6 minutes. Speed or slope will be increased every 30 seconds and they will be asked to walk for one minute at that speed or

Perceived dyspnea: Breathlessness will be measured based on a 0 to 10-point Borg scale at the end of the treadmill trials. 0 on scale is no breathlessness and 10 is maximal breathlessness

Dynamic hyperinflation will be assessed by inspiratory capacity through pre- and post-walking trial resting spirometry. Dynamic hyperinflation will be considered to be present when inspiratory capacity values decrease after walking trials when compared to resting values.

Respiratory rate will be analyzed using motion capture markers on the chest. With custom computer code, the markers will be identified to model a sphere. The volume of the sphere will be recorded over time. As the volume increases and decreases, respiratory flow will be identified, and respiratory rate can be calculated.

The laboratory is equipped with a 17-camera, digital motion capture system (Motion Analysis Corp., Santa Rosa, CA; 120Hz) to allow for collection of three-dimensional marker positions in real time. The marker position data will be analyzed using custom MATLAB code. Data will be plotted to detect spikes and outliers. Spikes and data points greater than three standard deviations from the mean will be removed. A cubic spline will be used to interpolate the removed data points. All marker data are then normalized to the unit vector for comparison. Coupling is often quantified as frequency coupling. Frequency coupling refers to how many heel strikes occur within a single cycle of respiration (one inhalation to the next); it is usually counted in integer or half-integer ratios, measured using discrete relative phase. The range of ratios and the percentage of time each ratio is utilized will be recorded.

Heart rate and pulmonary gas exchange analysis will be recorded on a breath-by-breath basis. This will provide an accurate measure of pulmonary gas exchange, including oxygen uptake, i.e. VO2, . Steady-state VO2 while walking will be averaged and normalized to standing metabolic rate.

Dead space: Tidal volume and expired carbon dioxide will be measured using the same equipment as oxygen uptake above. Partial pressure of arterial carbon dioxide will be measured using a transcutaneous sensor.

Inclusion Criteria: Veterans from all sex/gender, race, and ethnicity will be recruited All subjects will undergo post-bronchodilator spirometry and be clinically stable All subjects must have documented FEV1/FVC ratio of <0.7, and between 30% to 80% FEV1% predicted If subjects have non-qualifying spirometry, they will not be screened further Subjects with qualifying spirometry will be screened further Potential subjects must have a BMI of less than 35 kg/m2 and must be free from co-morbidities that may affect walking patterns e.g., peripheral arterial disease, diabetes, low back pain Exclusion Criteria: Confounding effects such as neurological, musculoskeletal, or metabolic disease Subjects taking medications that alter mood or metabolic demand will be excluded All potential subjects must be cleared for participation by a physician after undergoing a cardiopulmonary exercise test Require an O2 mask during rest or activity