Optimal pressing strength and time for capillary refilling time
Substantial investigations on the microcirculation have highlighted the importance of the capillary refilling time (CRT), which is widely used in clinical settings [1, 2, 3]. However, CRT measurement conditions, including pressing strength and time, are inconsistent (e.g., pressing strength: light, moderate, or firm; pressing time: 3 s, 5 s, or until the capillary bed visually blanches) [2, 3, 4, 5]. CRT is conventionally measured visually after manual compression, which limits the accuracy of measurement and precludes the precise determination of how long and strong the nail bed should be pressed. Therefore, we developed a novel device which can be adjusted for pressing strength and time to precisely measure CRT using an electric actuator and strength and color sensors.
CRT was measured in age- and sex-matched healthy adults (n = 31) using the developed device under conditions of pressing strength of 1, 3, 5, and 7 N, and a pressing time 1, 2, 3, 4, 5, and 6 s (Additional file 1: Methods and supplemental data).
In the study aimed at identifying the standard pressing strength and CRT, pressing the nail bed with 3–7 N for 2 s appears to be optimal. Further development of portable CRT measurement devices fulfilling these conditions may contribute to achieving precise CRT measurements to monitor the microcirculation in clinical settings.
We thank Mr. Yutaka Furukawa, Mr. Minami Nagano, Ms. Eriko Miyazaki, Ms. Shino Tateishi, and Ms. Ayako Teratani for helping with data collection.
This work was supported by AMED (#JPhe1502001). The funder had no role in the study design, experiments, collection, analyses, interpretation of data, writing of the manuscript, or decision to submit the manuscript for publication.
Availability of data and materials
The datasets used and/or analyzed during our study are available from the corresponding author upon reasonable request.
RK and TN: These authors contributed to the study conceptualization and design, acquisition of data, analysis and interpretation of data, statistical analysis, and drafting and critical revision of the manuscript for important intellectual content. MS and TN: These authors contributed to developing the device, interpretation of data, and drafting and critical revision of the manuscript for important intellectual content. TO, HH, and SO: These authors contributed to the study conceptualization and critical revision of the manuscript for important intellectual content. All authors have read and approved the final manuscript.
Ethics approval and consent to participate
The study participants were informed of the experiment and agreements were obtained via consent form before the measurements. All procedures in this study were approved by the Ethical Review Board of the Chiba University Graduate School of Medicine.
Consent for publication
Written informed consent for the publication was obtained.
The authors declare that they have no competing interests. Chiba University has filed a provisional patent application covering aspects of this manuscript. TN, TN, HH, and SO are listed as inventors.