Objectives: To determine the effect of hot bathing on blood circulation, we analyzed pressure wave using Wave Intensity (WI), which is defined as changes in blood pressure (dP)×changes in blood flow velocity (dV) during hot bathing, as the index for assessment.
Methods: Using a combined Doppler and ultrasonic echo-tracking system, we recorded changes in vascular diameter (dD) and dV of the common carotid artery simultaneously in six healthy subjects before (Pre-bathing), during (Bathing), and 10 minutes after bathing (41°C) (Post-bathing). We then measured the product of their changes at fixed intervals as WI and evaluated the positive component of the early systolic phase (FE) (representing the forward-traveling pressure wave), negative components following FE (B) (representing the reflection pressure wave), and the appearance time of (RT). RT was measured as the percentage ratio.
Results: 1) The magnitudes of FE and B tended to decrease during 10min of bathing (Bathing) and recover to the level of the pre-bathing stage after 10min of bathing. 2) The value of RT measured after 10min of bathing (Post-bathing) was significantly longer than the level before bathing (Pre-bathing).
Conclusion: The effect of the reflection pressure wave (i. e., the after load on the vascular system) decresses during hot bathing. We can thus conjecture that the time phase of appearance of the reflecting pressure wave is delayed when the arrival time of the forwardtraveling pressure wave to the periphery is delayed and the propagation of the reflection pressure wave from the periphery slows down due to the expansion of vessels during hot bathing. Hot bating can therefore be expected to reduce after loads of healthy adult subjects.

We conducted a seroepidemiological study in a northern Japanese prefecture where the incidence of identified COVID-19 cases was low. In June 2020, residual sera from 1009 outpatients were tested for antibody to SARS-CoV-2 by electrochemiluminescence immunoassay. Five specimens (0.5%) tested positive, suggesting low prevalence of SARS-CoV-2 infections in this population.