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Treadmill stress testing for cardiovascular disease (CVD) is typically done with ECG and blood pressure monitoring alone, with respiratory monitoring via sealed face mask and gas sampling occurring rarely in clinical settings. We sought to examine whether a simple electronic, non-invasive, chest-mounted respiratory monitoring device could successfully be used to reveal clinically useful insights during stress testing.
Methods and Results
Twenty-five adult patients referred for treadmill exercise stress testing at an outpatient cardiology clinic were equipped with a small, lightweight, electronic chest band (Airgo, MyAir Inc.) capable of measuring respiratory rate (RR) and minute ventilation (Ve) during completion of an unmodified Bruce protocol stress test. Univariate regression was used to assess patient characteristics such as age, sex, and cardiovascular comorbidities as predictor variables for Ve and RR slope (change in Ve and RR over time). Log transformations were performed for non-normally distributed variables (Ve slope, RR slope, and body mass index, BMI). The mean age of patients was 55.0 years (SD 13.4); 18 males and 7 females. Group mean results (+/- SD): stress test duration 8.6 +/- 3.5 min, peak Ve (expressed as % of baseline at rest) 489 +/- 297%, resting RR 17.0 +/- 3.8 breaths per minute, peak RR 35.5 +/- 6.9 breaths per minute, resting heart rate (HR) 78.4 +/- 15.5 bpm, peak HR 156.7 +/- 19.7 bpm, stress test positivity: 1 out of 25 patients. Presence of CVD (defined as current or previous HTN, angina, CVA, A-fib, or sleep apnea) was found to be a significant predictor of both Ve (Figure 1) and RR response over time to exercise (p=0.004, 0.002, respectively, Table 1), with patients having comorbid CVD demonstrating a mean 124% (95%CI 32.2-280%) higher Ve slope and 71.0% (95%CI 23.7-139%) higher RR slope versus patients without these comorbidities. None of age, sex, body mass index (BMI), stress test duration, or delta HR were significant predictors of Ve slope; BMI and stress test duration were found to be significantly associated with RR slope (p=0.001 and 0.007, respectively).
Non-invasive chest-mounted electronic respiratory monitoring may provide a useful supplement to current routinely gathered data during treadmill stress testing and may identify morbidity not seen with standard measures.