Biomedical subjects
K Yajima
Publications and source records attributed to K Yajima.
Comparison of gradual and rapid onset runs in a short-arm centrifugation.
A gradual onset run (GOR) in a short-arm centrifugation was performed on ten healthy students. The centrifuge had a 1.8 m radius, and the subjects sat on a chair in a cabin. The Gz force increased to 2.2 Gz at 0.1 degree/sec2 for 32 min. and the same Gz-level was maintained for 20 min. Three out of ten subjects completed the whole protocol; the load on the others was terminated because of symptoms or increased heart rate. There were few symptoms such as vertigo, that was a common problem with a rapid onset run (ROR) in former experiments, due to the short-arm centrifugation. The changes of the flicker test after the load were much less in the GOR protocol than in the ROR protocol, even in the terminated group. GOR seemed preferable to ROR in preventing vertigo even though it took longer to reach the necessary G load.
Usefulness of daily +2Gz load as a countermeasure against physiological problems during weightlessness.
UNLABELLED: Adaptation to head-down-tilt bed rest as a simulated microgravity leads to an abnormality of reflex control of circulation, hypovolemia and reduction of exercise capacity. We hypothesized that this cardiovascular deconditioning and reduction of exercise capacity could be prevented by a daily 1 hr centrifugation at +2Gz. To test this hypothesis, twenty healthy male subjects underwent 4 day of 6 degrees head-down-tilt bed rest. Ten of them were exposed to a +2Gz load for up to 30 min twice per day (the Gz group). The remaining 10 were not exposed to a Gz load (the no-Gz group). We estimated autonomic cardiovascular control by power spectral analysis of blood pressure and R-R interval variability, and baroreflex regulation by the transfer function analysis and the sequence method, before and after bed rest. Further, we measured hematocrit as an index of changes in plasma volume and maximal oxygen consumption as an index of exercise capacity, before and after bed rest. RESULT: In the no-Gz group, heart rate increased after bed rest. The high frequency power of R-R interval variability as an index of cardiac parasympathetic nervous activity, baroreflex gains estimated by transfer function analysis and the sequence method as index of the integrated arterial-cardiac baroreflex function decreased significantly. Associated with these changes, the ratio of low to high frequency power of R-R as an indicator of cardiac sympathovagal balance tended to increase after bed rest in the no-Gz group. However, those showed no significant changes after bed rest in the Gz group. Hematocrit increased after bed rest in the no-Gz group. It also tended to increase in the Gz group, however it did not achieve statistical significance. Maximal oxygen consumption decreased significantly to similar extent in both the groups. CONCLUSION: This result suggested that 1) a daily 1hr +2Gz load produced by a centrifuge might eliminate the changes in autonomic cardiovascular control during simulated weightlessness; 2) furthermore, it might partly reverse hypovolemia induced by bed rest; 3) however, it could not prevent the decreases in exercise capacity.
Effects of repeated long duration +2Gz load on man's cardiovascular function.
Usefulness of a short-arm human centrifuge is expected when it is used in space as a countermeasure against cardiovascular deconditioning, problem of bone-calcium metabolism, etc. However, nothing is solidly established regarding the most desirable program for artificial G application. Accordingly, this study was designed to analytically evaluate the effects of repeated long duration +Gz load on human cardiovascular function. Recently heart rate spectral analysis has been recognized as a powerful tool for quantitatively evaluating parasympathetic and sympathetic activity separately in human. It is reported that power of the high frequency component (HF-p) is mediated selectively by parasympathetic activity and the power ratio of low to high frequency components(LF/HF) is indicative of cardiac sympathetic activity or cardiac sympathovagal balance. Sequence method is developed to examine spontaneous baroreceptor reflex sensitivity (BRS). We studied cardiovascular control function by using these methods in 9 healthy men before and after 7 days of daily repeated 1hour +2Gz load. When compared with the data of pre-G load period, post-G load period, decrease of HR, increases of HF-p and BRS were statistically significant. SBP, DBP and LF/HF tended to decrease, however, these changes were not statistically significant. This results indicate that repeated +2Gz load increases parasympathetic activity and arterial baroreceptor-cardiac reflex sensitivity. In recent years, many investigators suggest that space flight and head-down bedrest leads to impaired baroreceptor-cardiac reflex responses and decrease of parasympathetic activity, which may contribute to orthostatic intolerance. So our results suggest that daily repeated 1hour +2Gz load would be useful in preventing post-flight orthostatic intolerance.
Ultrastructural changes of oligodendroglia and myelin sheaths induced by ethidium bromide.
Intracisternal injection of ethidium bromide, an inhibitor of mitochondria associated RNA, DNA and protein synthesis, produced status spongiosus in the subpial surface of the CNS of rats. Ultrastructurally, numerous intra-myelinic vacuoles and prominent degenerative changes of oligodendroglia were observed. The vacuoles were formed between the myelin lamellae by splitting of the intraperiod lines, between the axolemma and the innermost myelin lamellae, and/or between the inner tongue of oligodendroglia and myelin lamellae. In the degenerating oligodendroglia, proliferation and alteration of the endoplasmic reticulum were prominent. In places, altered membranes of the endoplasmic reticulum formed concentrical scroll-like structures. These ultrastructural changes in ethidium bromide treated rats were compared with other similar previously described changes in animals treated with TET, cuprizone, hexachlorophene, hypocholesterolaemic drugs and actinomycin D.
Analysis of single neuromuscular unit (NMU) discharges as a random process.
Explore the source record for details and available documents.
The increase of CD5LOW+NK cells in patients with multiple myeloma and plasmacytoma.
CD5 antigen is present on all normal alpha beta T cells and some B cells. Human NK cells do not usually express CD5 antigen, but we found a novel subset of CD5LOW (low density of CD5) positive (CD5LOW+) natural killer cells (NK cells) in patients with multiple myeloma (MM) and plasmacytoma. To detect CD5LOW+NK cells, we examined the lymphocytes of 23 patients with MM and plasmacytoma by flow cytometry. Five out of 23 patients had CD5LOW+NK populations. These patients had many more NK cells than the other patients in the peripheral blood and bone marrow. The CD5LOW+NK cells had CD2, low density of CD8, CD16 and CD56, but no CD3, CD19, or CD20. Most of the CD5LOW+NK cells had HLA-DR, unlike the CD5-NK cells. Sorted CD5LOW+CD16+ populations were large granular lymphocytes (LGL). The CD5LOW+NK cells had some lytic activity on K562 cells in a 4-hour 51Cr release assay. Our results indicate that there is a novel subset of NK cells in some patients with MM and plasmacytoma and that CD5LOW+NK cells may be associated with NK cell activation.
Suppression of HL-60 cell proliferation by deferoxamine: changes in c-myc expression.
Deferoxamine, an iron chelating agent, inhibits growth of HL-60 cells in a dose-dependent fashion. This inhibition of proliferation was completely blocked by simultaneous addition of equal molar FeCl3, and FeCl3 added after 24 hours of deferoxamine treatment was also effective. After 48 hrs, however, the delayed addition failed to reverse growth inhibition by deferoxamine. We showed that deferoxamine-treated HL-60 cells become arrested in S phase rather than at G1/0 phase. Changes in c-myc expression were examined in these deferoxamine-treated cells. A rapid decline of c-myc RNA expression was followed by increased expression (1.6-fold over untreated controls). Similar results were obtained when the expression of c-myc protein was evaluated. These changes in c-myc expression may be involved in the growth inhibition of HL-60 cells by deferoxamine. These results are contrasted with the effects of the differentiation inducer, 1 alpha,25(OH)2D3.