Low-Intensity Exercise Expired Gas Analysis May Determine Cardiac Stability in HF
November 18, 2009 – The Journal of Cardiac Failure published results from a study showing ventilatory expired gas analysis during a short bout of low-intensity exercise may provide insight into prognosis and cardiac stability in heart failure patients.
Ventilatory efficiency and the partial pressure of end-tidal carbon dioxide, obtained during moderate to high levels of physical exertion, have been widely accepted to demonstrate prognostic value in heart failure. This study validates the method of testing at or below anaerobic threshold used with the Shape-HF Cardiopulmonary Exercise Testing System, a new noninvasive medical device that assesses heart-lung interaction and ventilation in patients with chronic heart failure and other cardiopulmonary disease’s method of testing at or below the anaerobic threshold.
“Cardiopulmonary exercise testing (CPX) has been used for many years to help doctors understand the pathophysiology of heart failure,” says Dean MacCarter, Ph.D., one of the study’s authors. “During maximal exercise testing key measurements can guide physicians in their clinical decision making. But conducting CPX tests at such levels comes with its own set of problems. The tests require a maximal physical effort by the patient, they require specialized training to conduct, and interpreting the results can be challenging. We wanted to determine the value of measuring key parameters during low-level, or submaximal, exercise. Our results show that important prognostic measures in heart failure are as good as, and in some cases superior to, similar measures obtained during peak exercise. What’s important about this research is that it shows that clinically relevant information can be obtained using a test that is more simple, less costly, and requires less staffing than standard tests. Importantly, the test is easier on the patient, and provides highly relevant clinical information related to a heart failure patient’s status and stability.”
The study involved 130 patients diagnosed with heart failure. As part of the exercise protocol, each underwent a two-minute, constant-rate, treadmill session at two miles per hour. Both the ventilatory efficiency (VE/VCO2 ratio) and the partial pressure of end-tidal carbon dioxide (PETCO2) were recorded during low level exercise and their change from rest. B-type and atrial natriuretic peptide (BNP and ANP) were also determined. Only PETCO2 and the change in PETCO2 emerged from the multivariate Cox regression. Receiver operating characteristic curve analysis revealed the prognostic classification schemes were significant with thresholds of ≥ 34 mmHg (hazard ratio: 4.2, 95 percent CI: 2.2-8) and ≥ 1 mmHg (hazard ratio: 3.5, 95 percent CI: 1.9-6.6) being optimal for PETCO2 and the change PETCO2, respectively. Patients with a PETCO2 of greater than or equal to 34 mmHg had a significantly lower BNP (214.1 ± 1854.0 pg/mL) and ANP (108.2 ± 103.6 vs. 246.2 ±200.4 pg/mL).
The Shape-HF System is the first gas exchange testing device specifically designed for cardiology. It quantifies the severity of dyspnea and fatigue on exertion and evaluates the interaction between the heart, lungs, and other organ systems involved in oxygen uptake and transport. This makes it possible for the physician to evaluate therapy options for the individual patient and track patient progress. In addition, cardiac resynchronization therapy (CRT) has become a mainstay in treating patients with advanced heart failure when alternative treatment options have been exhausted. The Shape-HF test takes 15 minutes and involves measuring ventilation parameters while the patient exercises on a treadmill at a very low intensity. As the patient exercises at a steady state heart rate, the physician adjusts the pacemaker therapy settings every two minutes, enough time for the adjustments to be reflected in breathing physiology. At the end of the test, during which four to five therapy settings are tested, the Shape-HF System uses a proprietary computer algorithm to rank the physiological response to exercise at each setting. The physician then reviews the results and chooses the therapy setting he or she believes is most appropriate for the patient.
For more information: www.onlinejcf.com
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