Safety of the CO-Rebreathing Method in Patients with Coronary Artery Disease.

Purpose: To address and study the safety concerns with the improved carbon monoxide (CO) rebreathing method for measuring total blood volume in patients with coronary artery disease to implement the use of the methodology in this patient group.

Methods: Eighteen patients with stable coronary artery disease (age 62 ± 7 yr, 24 ± 5 months since diagnosis) were investigated using the improved CO-rebreathing test. Before, during, and up to 2 h after the test, ECG, blood pressure, arterial oxygen saturation, carbon monoxide bound to hemoglobin (HbCO%), and cardiac function were measured. At 24 h, HbCO% and troponin-T were measured.

Design: Cross-over.

Results: Six minutes after the CO-rebreathing test, HbCO increased from 1.5% ± 0.4% to 6.0% ± 0.6%, with a subsequent decrease to 4.5% ± 0.4% and 1.4% ± 0.4% at 2 h and 24 h after the test, respectively. Resting heart rate, stroke volume, cardiac output, and ejection fraction were 64 ± 11 bpm, 93.9 ± 16.5 mL per beat, 5.84 ± 0.99 L, and 48.5% ± 5.7% and remained unchanged during and 10 min after the rebreathing. All patients were in sinus rhythm during the 2-h observation period, without ST- or T-wave changes, with low numbers of premature beats and normal rate variability. Systolic and diastolic blood pressure gradually decreased during the observation period. Troponin-T was below the 99th percentile for all the participants 24 h after the test.

Conclusion: Cardiovascular function and safety indices remained unchanged after exposure to approximately 6% HbCO, indicating that the method is safe to perform in patients with stable coronary artery disease.