Satoshi Iwase

We investigated the effect of change in intrathoracic pressure by total body negative pressure (TBNP) or positive pressure (TBPP) on thermoregulatory responses during -6 degree head-down bed rest (HDBR). Eight healthy male subjects participated to three of the following interventions in a randomised sequence: 1) HDBR, 2) HDBR with TBNP of -15 cmH2O, 3) HDBR with TBPP of +15 cmH2O. A rapid decrease of cutaneous blood flow occurred after the start of TBNP. In contrast, cutaneous blood flow increased slightly at TBPP. Sweat rate decreased immediately after the start of TBNP. Immediately after the TBPP was started, tympanic temperature greatly decreased. It is concluded that combination of HDBR and intrathoracic pressure changes thermoregulatory responses through the cardiopulmonary baroreceptor to reduce the wall stretch.

We evaluated a method for direct measurement of conduction velocity (CV) in sympathetic nerves in humans using a double-recording method of skin sympathetic nerve activity (SSNA) by microneurography. SSNA in the tibial nerve was recorded simultaneously at proximal and distal sites in the popliteal fossa (short-distance study) or at the popliteal fossa and ankle (long-distance study). In both studies, CVs were determined by dividing the interelectrode distance on the skin by the difference in conduction time between the rising-phases (rising-phase analysis) or peaks of the integrated bursts (peak-to-peak analysis). The measurement using long distance and peak-to-peak analysis had the highest accuracy; it is an orthodromic conduction measurement, is unrelated to eliciting stimulus, has high temporal resolution, and is not affected by the effector organ conditions. The average CV of resting SSNA was 0.93 ± 0.09 m/s. Muscle Nerve 29: 128–133, 2004

An artificial gravity and ergometric exercise loading device for human use was manufactured. It has the capacity of a max 2 G-load at the heart level, and a max 150 W of work-load. Eight subjects (six completed) were subjected to four repeated trials with or without 20 W ergometric exercise. Anti-G score, defined as the G-load x running time to the endpoint, was significantly higher in the exercise trials than standing trials. Heart rate (HR), mean arterial pressure (MAP), thoracic fluid index (TFI) were significantly superior during the exercise trials. Artificial gravity by centrifuge at 1.2 or 1.4 G with 40 or 60 W of ergometric workload may be an excellent countermeasure against cardiovascular deconditioning after long exposure to microgravity.