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Articles by K. Iwasaki
Total Records ( 2 ) for K. Iwasaki
  J Kato , Y Ogawa , W Kojima , K Aoki , S Ogawa and K. Iwasaki

The low and moderate doses of dexmedetomidine reduce arterial pressure and heart rate (HR), suggesting attenuation of sympathetic activity and dominance of cardiac-vagal activity. These autonomic responses under dexmedetomidine sedation may attenuate cardiovascular reflex responses to temporal reduction in arterial pressure, inducing a severe hypotension. We therefore investigated the effects of dexmedetomidine on cardiovascular reflex responses to temporal reduction in arterial pressure induced by the thigh cuff method.


Twelve healthy men received placebo, low-dose (loading 3 µg kg–1 h–1 for 10 min; maintenance 0.2 µg kg–1 h–1 for 60 min), and moderate-dose (loading 6 µg kg–1 h–1 for 10 min; maintenance 0.4 µg kg–1 h–1 for 60 min) dexmedetomidine infusions in a randomized, double-blind, crossover study. After 70 min of drug infusion, systolic arterial pressure (SAP) and HR responses after thigh cuff deflation were evaluated as indices of cardiovascular reflex.


Reduction in SAP (SAP) [placebo 8 (4), low 12 (4), moderate 19 (5) mm Hg] after thigh cuff deflation was significantly greater in dexmedetomidine than placebo infusions, in a dose-dependent manner. The change in HR (HR), HR/SAP, and the percentage restoration of SAP were lower with dexmedetomidine compared with placebo.


The present results indicated that dexmedetomidine weakens arterial pressure preservation and HR responses after thigh cuff deflation, suggesting attenuated cardiovascular reflexes. Therefore, it must be cautioned that dexmedetomidine can lead to further and sustained reduction in arterial pressure during transient hypotension induced by postural changes, haemorrhage, and/or other stresses.

  A Kishimoto Okada , S Murakami , Y Ito , N Horii , H Furukawa , J Takagi and K. Iwasaki

Cryo-electron microscopy of vitreous sections (CEMOVIS) and cryo-electron tomography (cryo-ET) of vitrified specimens are gradually gaining popularity. However, similar to the conventional methods, these techniques tend to produce different images of the same sample. In CEMOVIS, the mechanical stress caused by sectioning may cause inaccuracies smaller than those caused by crevasses. Therefore, we examined Escherichia coli cells by using CEMOVIS and cryo-ET to determine the differences in the computed sizes of the envelope layers, which are smaller than crevasses. We found that the width of the periplasmic space in vitreous sections and tomograms was 12 and 14 nm, respectively; furthermore, while the distance between the outer membrane (OM) and the peptidoglycan (PG) layer was almost equal (11 nm) in the two techniques, that between the plasma membrane (PM) and PG was clearly different. Thus, the observed size difference can be mainly attributed to the PM–PG distance. Since our data were obtained from images acquired using the same microscope in the same conditions, the size differences cannot be attributed to microscope-related factors. One possible factor is the angle of the cutting plane against the long axis of the cell body in CEMOVIS. However, the same PG–OM distance in both methods may exclude the variations caused by this factor. Furthermore, the mechanical stress caused by vitreous sectioning or high-pressure freezing may result in shrinkage. If this shrinkage is responsible for the nanometre-scale deformation in CEMOVIS, this factor will have to be considered in determining the molecular resolution obtained by CEMOVIS.

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