The participants were 11 healthy males who agreed to cooperate in measuring lower extremity blood flow volume during the study (age: 28.3 ± 6.2 years, height: 170.0 ± 6.9 cm). The participants underwent either HPTT or WT in a random sequence (randomized crossover study). HPTT and WT were separated by a minimum of 1 day and a maximum of 1 month.
The study protocols for both thermal therapies are summarized in previous study 17. The participants avoided physical exercise, eating, and smoking for 3 hours before the treatment, and they avoided caffeine consumption 6 hours prior to the procedure on the day of therapy. This study was carried out in a quiet room at 28–30 ℃. The participants wore hygroscopic gowns.
Whole-body hot pack thermal therapy (HPTT)
Hot packs, which had been warmed up to 80 ℃, were used after wrapping a plastic bag and towel around them (Minatopack KPA1076 25×30 cm, hydro advertiser HC-6U, Minato Ikagaku Inc., Osaka, Japan).
The HPTT protocol involved a participant lying in the supine position on a bed for at least 10 minutes. The participant was covered with thin aluminum foil sheets (heat-retaining aluminum sheets JTH-1321 130×210 cm, IRIS OHYAMA, Sendai, Japan). Subsequently, the hot packs were applied to the participant’s back (on the third lumbar vertebra), lower abdomen (anterior superior iliac spine), and popliteal regions for 15 minutes (the warming phase). After 15 minutes, the hot packs were removed and the participants continued bed rest for 30 minutes (the heat-retention phase). During the warming and heat-retention phases, the participant remained covered with thin aluminum foil sheets and a blanket.
Waon therapy; WT
We used far-infrared dry sauna equipment for the WT (CTW-5000, Fukuda Densi, Tokyo, Japan). The WT protocol involved the patients lying in a supine position on a bed for at least 10 minutes. Subsequently, they were seated in the dry sauna for 15 minutes. During the heat-retention phase they rested supine on the bed for 30 minutes wrapped in a blanket.
The variables measured included heart rate, blood pressure (BP), bodyweight (before and after thermal therapy), tympanic temperature (taken every minute), and leg blood flow volume (before and after thermal therapy).
We continuously measured the tympanic temperature as an index of deep body temperature during both thermal therapies. Tympanic temperature, which reflects the deep body temperature, was measured in the right ear 20–22. We inserted the thermistor probe in the right ear and confirmed its position when a participant reported a “scratch noise” or “sharp pain” caused when the head of the probe touched the tympanic membrane.
Lower Extremity Blood Flow Volume
We used a venous occlusion plethysmography to measure the leg blood flow volume (EC6 Strain Gauge & Photoplethysmography System, D. E. Hokanson, Inc., Bellevue, USA). To measure the leg blood flow volume, the right lower limb was lifted and the foot rested on the cushion about 10 cm high in the supine position. the strain gauge was wrapped around the bulge of the lower leg and cuff was wrapped right thigh (Rapid Cuff Inflation System, D. E. Hokanson, Inc., Bellevue, USA).
The leg blood flow volume was measured at least two times (at rest and after 30 min of heat-retention). We measured the electrical potential from strain gauge after the cuff was momentarily pressurized with 50 mmHg. And we calculated blood flow volume from the obtained electrical potential of circumferential change.
Data are presented as mean ± standard deviation. Statistical analyses were performed with Statistics for Excel 2012 (Social Survey Research Information Co., Tokyo). Four timings (rest, at the end of warming, 15min and 30 min heat retention) for tympanic temperature, systolic, mean and diastolic BP, heart rate were extracted from the data of previous studies. Statistical analyses included 2-way analysis of variance (ANOVA) and post-hoc Bonferroni correction. Significance was defined as p < 0.05. Body weights and blood flow volume before and after the therapies were compared using paired t-test with significance defined as p < 0.05.
The study was conducted in accordance with the principles outlined in the Declaration of Helsinki and was approved by the ethical committee of Hakodate National Hospital (approval number: H28-1114006). Informed consent was obtained from all participants for their participation in the study and for the publication of this report. The authors confirm that all participants cannot be identified via the paper and that they have been fully anonymized. Furthermore, the authors affirm that all mandatory health and safety procedures were complied with in the course of conducting any experimental work reported in the paper.