EVALUATION OF HYPERCAPNIA-INDUCED CHANGES IN CFV BY TTDE IN HEALTHY SUBJECTS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study is completed. Background: The effect of hypercapnia on the coronary arteries in humans is currently unknown. This pilot study assessed the feasibility of using transthoracic Doppler echocardiography (TTDE) in healthy adults to detect changes in coronary artery blood flow velocity (CFV) with varying levels of inspired CO2. Methods: Healthy adults underwent TTDE of the distal left anterior descending coronary artery (LAD) while breathing room air, oxygen supplemented to 40% of inspired air, and CO2 adjusted to +5, +7.5, and +10 mm Hg above their baseline partial end-tidal CO2 (PET CO2) levels on a background of 40% FiO2. CFV and other parameters were measured at each experimental state. Mean peak diastolic CFV values were compared at each state using one-way analysis of variance of repeated measures. Results: Among twenty adults (mean [standard deviation] age 33 [6] years, 52% female, 90% white), TTDE images could be acquired at all experimental conditions in 17 subjects. In order of room-air, 40%FiO2, and +5, +7.5, and +10 mm Hg PETCO2 conditions, mean peak (SD) CFV values were 23.1 (9.1) cm/s, 23.0 (9.0) cm/s, 25.5 (9.3) cm/s, 27.9 (11.5) cm/s, and 31.5 (13.0) cm/s. Between-treatment differences were significantly different (p0.001), with p0.05 between progressive levels of hypercapnia, adjusted for multiple comparisons. No significant CFV differences were seen between baseline conditions or between respective baseline and +5 mm Hg PETCO2 states. Conclusions: With progressive levels of hypercapnia, CFV of the LAD in healthy subjects was observed to increase, and these changes could be detected by TTDE.