Validation of a Simplified, Portable Cardiopulmonary Gas Exchange System for Submaximal Exercise Testing

ABSTRACT

Shape Medical Systems, Inc. has developed a new miniaturized, simplified system for non-invasive cardiopulmonary gas exchange quantification and has targeted their system for submaximal clinical exercise testing in order to abbreviate testing in an expanding clinical market during a climate of escalating health care costs. The focus of the present study was to compare this new device to a validated, standardized system for measures of cardiopulmonary gas exchange. Eighteen healthy adults (10 male/8 female, age 29±7 yr, BMI 23.8±2.4 kg/m2) were brought to the laboratory and instrumented with both measurement systems via in-series pneumotachs. Additionally, the Shape system included a pulse oximeter for heart rate (HR) and oxygen saturation (SaO2), while the standard system included separate 12-lead ECG and oximetry devices. The protocol included 2-min resting breathing, followed by 3-min at each of 3 workloads (50, 70, 125 watts) on a cycle ergometer. Data were collected breath-by-breath and averaged the last 30-sec of each workload. After a 15-min rest period, the pneumotach order was reversed and the study repeated. Since gas exchange data were similar (p>0.05) within a given metabolic testing system between sessions the data were pooled for comparing the Shape and Standard systems. There were no differences (p>0.05) between the systems for oxygen consumption-VO2, carbon dioxide production-VCO2, ventilation-VE, end tidal CO2-PetCO2, tidal volume-VT, respiratory rate-fb, and HR at rest or any work load. SaO2 was slightly, but significantly lower using the Shape embedded oximeter (p<0.05, averaging ~1% across workloads). There were significant correlation coefficients (p<0.001) between the systems for VO2 (r=0.991), VCO2 (r=0.986), VE (r=0.995) and PetCO2 (r=0.953). Bland Altman plots indicated good agreement between systems for the same gas exchange measures, independent of workload. The Shape system was sensitive to small increases in work (50 to 70 watts) and there were no differences in gas exchange measures in a subgroup of subjects (n=4) using a tight fitting mask instead of a mouthpiece (p>0.05). These data suggest that the new, simplified metabolic system developed by Shape Medical Systems, Inc. accurately quantifies key cardiopulmonary variables over a range of workloads, has a coefficient of variation similar to a well validated system and can be used with mouthpiece or mask.