Influence of indoor and outdoor temperatures on the fingertip blood flow rate

A total of 58 healthy subjects participated to elucidate the influence of indoor and outdoor temperatures on blood flow. After walking outdoors for 20 min, the blood flow rate of a subject was measured. The subject then entered a classroom and studied for 120 min, and afterwards, the blood flow rate was measured again. The subjects were exposed to outdoor temperature ranging from −2.5 to 33.7 °C. During the summer, the average blood flow rate after walking outdoors was 45.95 ± 25.790 TPU (tissue perfusion units); after the class, this decreased to 36.14 ± 21.837 TPU (p < 0.05). During the autumn, the blood flow rate decreased from 27.69 ± 12.334 TPU to 12.47 ± 12.255 TPU (p < 0.001). When the outside air temperature was below 3 °C, the blood flow rate indoors increased significantly from 6.74 ± 3.540 TPU to 13.95 ± 11.522 TPU (p < 0.05). In a comfortable and healthy environment, the blood flow rate was not constant but fluctuated between 15 TPU and 40 TPU.