Local temperature control improves the accuracy of cardiac output estimation using lung‐to‐finger circulation time after breath holding

摘要

As timely measurement of the cardiac index (CI) is one of the key elements in heart failure management, a noninvasive, simple, and inexpensive method of estimating CI is keenly needed. We attempted to develop a new device that can estimate CI from the data of lung‐to‐finger circulation time (LFCT) obtained after a brief breath hold in the awake state. First, we attempted to estimate CI from the LFCT value by utilizing the correlation between 1/LFCT and CI estimated with MRI. Although we could obtain LFCT from 45 of 53 patients with cardiovascular diseases, we could not find the anticipated relation between 1/LFCT and CI. However, we realized that when we adopted only LFCT from patients with a finger temperature of ≥31°C, we could obtain a consistent and clear correlation with CI (correlation coefficient, r?=?.81). Thus, we next measured LFCT before and after warming the forearm. We found that LFCT decreased after the local temperature increased (from 27.5?±?13.6 to 18.4?±?5.3?s, p??0.01). The correlation between the inverse of LFCT and CI improved after warming (1/LFCT vs. CI, from r?=?.69 to r?=?.82). The final Bland–Altman analysis between the measured and estimated CI values revealed that the bias and precision were ?0.05 and 0.37?L?min?1?m?2, respectively, and the percentage error was 34.3%. This study clarified that estimating CI using a simple measurement of LFCT is feasible in most patients and a low fingertip temperature strongly affects the CI‐1/LFCT relationship, causing an error that can be corrected by proper local warming.