Relationships Among Capillary Refill Time, Peripheral Blood Flow Rate, and Fingertip Temperature: Advances in Peripheral Artery Contractility Diagnosis

Capillary refill time (CRT) is a widely used noninvasive measure of cardiovascular health. Despite its widespread diagnostic utility, it has several limitations, particularly its low sensitivity for certain conditions, because factors such as the contraction and relaxation of distal blood vessels can influence CRT readings. This study was performed to explore the relationships between CRT and distal blood flow. The right hand of each of ten healthy adult volunteers was cooled to induce blood vessel contraction. CRT, fingertip temperature, and blood flowrate were measured using a custom device, a thermometer, and a laser Doppler blood flowmeter, respectively, before and after cooling. Hand cooling significantly decreased blood flowrate and increased CRT. A robust inverse correlation was observed between blood flowrate and CRT, supporting a model where CRT is the time required for blood to flow through a cylindrical pipe. Furthermore, CRT showed a significant negative correlation with fingertip temperature. Most participants had high correlation coefficients, although two showed lower values. However, all data points exhibited a linear relationship, with the slopes of the regression lines between CRT and temperature varying among participants. These results suggested that the slope between CRT and fingertip temperature indicates individual differences in arterial contractility. These findings could improve the diagnostic utility of CRT in assessing vascular health, including arterial age and Raynaud's phenomenon, based on the contractility of peripheral arteries.