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Biomedical subjects

A Miyamoto

Publications and source records attributed to A Miyamoto.

At least 91 records · Page 5Linked to original sources
PubMed1999

Proton magnetic resonance spectroscopy to study the metabolic changes in the brain of a patient with Leigh syndrome.

Localized proton magnetic resonance spectroscopy (MRS) was performed to study the metabolic changes in the brain of a patient with Leigh syndrome, who had a T-->G point mutation at nt 8993 of mitochondrial DNA. In this patient, sodium dichloroacetate therapy normalized the lactate and pyruvate levels in both blood and cerebrospinal fluid (CSF). However, his psychomotor retardation did not improve and magnetic resonance imaging showed progressive cerebral atrophy. In the patient's spectra, elevation of brain lactate was observed throughout the brain with regional variations, predominantly in the basal ganglia and brainstem with an abnormal MRI appearance. Although the lactate/creatine ratio observed on proton-MRS was related to the CSF lactate level, the ratio did not completely parallel the CSF lactate level, i.e. brain lactate was detected even when the CSF lactate level had become normalized. Furthermore, proton-MRS revealed a decrease in the N-acetylaspartate/creatine ratio and an increase in the choline/creatine ratio, representing neuronal loss and breakdown of membrane phospholipids. The clinical and MRI findings were well related to the changes in spectroscopically determined brain metabolites. These results indicate that the brain metabolites observed on proton-MRS are useful indicators of a response to therapy and prognosis in Leigh syndrome.

Brain↗
PubMed1999

Beta-2-microglobulin and ferritin in cerebrospinal fluid for evaluation of patients with meningitis of different etiologies.

To determine whether or not the beta-2-microglobulin (beta2-m) and/or ferritin levels in cerebrospinal fluid (CSF) can be used as markers for the differential diagnosis of meningitis and determination of the response to treatment, 122 subjects with etiologically well-characterized diagnoses were classified into three groups: bacterial meningitis (n = 5; mean age +/- SD. 1.0+/-1.0 year), viral meningitis (n = 39; 5.9+/-3.8 years), and a non-meningitis group (n = 78; 5.2+/-4.9 years). The levels of beta2-m and ferritin in CSF were determined by means of a latex photometric immunoassay. The statistical significance of the data was analyzed with the Mann Whitney U-test. A receiver operating characteristic curve was used to evaluate the diagnostic accuracy of each prediction marker. This study indicated that (1) the levels of beta2-m and ferritin in CSF were related with age in the non-meningitis group: subjects of up to 5 months of age exhibited higher concentrations of these proteins than ones of above 6 months of age (beta2-m, 1.89+/-1.13 vs. 0.84+/-0.65 mg/l. P < 0.01; ferritin, 2.97+/-2.04 vs. 1.81+/-1.34 microg/l, P = 0.09); (2) the beta2-m level was significantly higher in the CSF of patients with viral meningitis than in ones without meningitis (2.41+/-1.23 vs. 0.84+/-0.65 mg/l, P < 0.01): the best cut-off value was 1.2 mg/l (3) the ferritin level was significantly higher in the CSF of patients with bacterial meningitis than in ones with viral meningitis (43.24+/-39.49 vs. 6.81+/-7.41 microg/l, P < (.01): the best cut-off value was 7.5 microg/l; and (4) sequential measurement of the CSF ferritin level was of value for determination of the response to antibiotic treatment for bacterial meningitis. These results only apply to patients of greater than 6 months of age. beta2-m and ferritin in the CSF can be used as an ancillary tool for diagnostic guidance in the acute phase of meningitis and determination of the response to treatment for bacterial meningitis.

Adolescent↗
PubMed1999

Cognitive deterioration associated with focal cortical dysplasia.

Surgery for an area of focal cortical dysplasia in a critical region is reported in a right-handed female manifesting intractable focal epilepsy and verbal cognitive deterioration. She developed the first seizure at 2 years of age and was treated with phenytoin and zonisamide, with good control until 10 years of age. Although seizures did not occur at 9 years of age, she manifested dyscalculia, right-left disorientation, and finger agnosia, and N-isopropyl-p-iodoamphetamine single-photon emission computed tomography (SPECT) revealed focal hypoperfusion in the left parietal lobe. At 11 years of age, she developed regular nocturnal seizures and gradually lost the ability to understand the meaning of sentences. Verbal IQ declined from 94 to 63, and the area of hypoperfusion detected by interictal N-isopropyl-p-iodoamphetamine SPECT spread over the left parietotemporal lobes. Magnetic resonance imaging revealed focal cortical dysplasia mainly in the left parietal lobe, and ictal technetium-99m-ethyl cysteinate dimer SPECT images demonstrated an area of hyperperfusion around the focal cortical dysplasia, including the left precentral gyrus. Because of the overlap between the epileptogenic and functional cortex, the authors concluded that cortical resection, including focal cortical dysplasia, was inappropriate in this patient.

Cerebral Cortex↗
PubMed1999

Cerebellar hypoperfusion and developmental dysphasia in a male.

A male with developmental dysphasia is documented with fine motor dysfunction whose improvement in expressive language was associated with increased cerebellar perfusion, as detected by serial N-isopropyl-p-[iodine-123] iodoamphetamine single photon emission computed tomography (SPECT). His expressive language has been improving since 6 years, 8 months of age, and his verbal intelligence quotient improved from less than 45 at 5 years of age to 80 at 8 years of age. Compared with the SPECT findings at 4 years of age, the ratio of the average pixel values of the cerebellum to the frontal cortices increased at 9 years of age (from 0.81 to 1.03-1.09 in the hemisphere and from 0.66 to 0.98 in the vermis). However, he was not able to understand stories presented orally even at 9 years, 4 months of age. These results suggest that developmental dysphasia, which mostly involves expressive impairment, in this patient could have been the result of delayed maturation of cerebellar function, mainly that of the vermis.

Brain↗
PubMed1999

Stimulation of bradykinin B2-receptors on endothelial cells induces relaxation and contraction in porcine basilar artery in vitro.

1. The aim of the present study was to characterize the subtypes of bradykinin (BK) receptors that evoke the relaxation and contraction induced by BK and to identify the main contracting and relaxing factors in isolated porcine basilar artery by measuring changes in isometric tension and a thromboxane (TX) metabolite. 2. Endothelial denudation completely abolished both responses. [Thi5,8, D-Phe7]-BK (a B2-receptor antagonist) inhibited the BK-induced relaxation and contraction, whereas des-Arg9, [Leu8]-BK (a B1-receptor antagonist) had no effect. 3. L-nitro-arginine (L-NA, a nitric oxide synthase inhibitor) completely inhibited BK-induced relaxation. Indomethacin (a cyclo-oxygenase inhibitor) completely and ONO-3708 (a TXA2/prostaglandin H2 receptor antagonist) partially inhibited BK-induced contraction, whereas OKY-046 (a TXA2 synthase inhibitor) and nordihydroguaiaretic acid (a lipoxygenase inhibitor) did not. 4. In the presence of L-NA, the contractile response to BK was inhibited by indomethacin or ONO-3708 and was competitively antagonized by [Thi5,8, D-Phe7]-BK (pA2=7.50). In the presence of indomethacin, the relaxant response to BK was inhibited by L-NA and was competitively antagonized by [Thi5,8, D-Phe7]-BK (pA2=7.59). 5. TXA2 release was not induced by BK-stimulation. 6. These results suggest that the endothelium-dependent relaxation and contraction to BK in the porcine basilar artery is mediated via activation of endothelial B2-receptors. The main relaxing factor may be NO and the main contracting factor may be prostaglandin H2.

Animals↗
PubMed1999

Role of the N-terminal region of ribosomal protein S7 in its interaction with 16S rRNA which binds to the concavity formed by the beta-ribbon arm and the alpha-helix.

The ribosomal protein S7, a primary 16S rRNA-binding protein, plays an essential role in stabilizing the 3' major domain of 16S rRNA and also in feedback regulation of the str operon, as a translational repressor. We examined amino acid residues in ribosomal protein S7 from Bacillus stearothermophilus (BstS7) that are essential for 16S rRNA binding. Truncation of the N-terminal 10 residues of BstS7 abolished its binding to 16S rRNA, whereas removal of the C-terminal eight residues had no effect on the binding activity. Subsequently, we used site-directed mutagenesis to identify essential basic residues in the N-terminal region for 16S rRNA binding. Mutation of Arg3 and Lys8 significantly weakened the binding activity, and a smaller decrease in binding activity was observed with Arg2 and Arg9 mutations. These observations indicate that N-terminal basic residues, especially Arg3 and Lys8, play a crucial role as positively charged recognition groups for the negatively charged phosphate backbone of 16S rRNA. In addition, the mutagenesis study showed that Arg75, Arg78, Arg94, and Arg101, which are located in a concavity formed by the beta-ribbon arm and the alpha-helix (alpha4), individually make only a small contribution to 16S rRNA binding, but together probably form a positively charged binding site for 16S rRNA. With regard to aromatic residues, Tyr84 on the tip of the beta-ribbon arm was found to be involved in 16S rRNA binding, whereas the conserved aromatic residues Trp102 and Tyr106 in the concavity had little effect. We then probed the 16S rRNA-binding site(s) for the N-terminal region of S7 with iron tethered to the mutant of BstS7 containing a single cysteine residue at position 4. The N-terminal region of S7 is placed in close proximity to helix 43 in the 16S rRNA. Probing also revealed additional cleavages between nucleotides 1397 and 1438, near the P-site region in 16S rRNA. This finding is consistent with a three-dimensional model of 16S rRNA that shows close proximity of helix 43 to the P-site during three-dimensional folding.

Arginine↗
PubMed1999

Conformation of the primary binding loop folded through an intramolecular interaction contributes to the strong chymotrypsin inhibitory activity of the chymotrypsin inhibitor from Erythrina variegata seeds.

We previously demonstrated that amino acid residues Gln62 (P3), Phe63 (P2), Leu64 (P1), and Phe67 (P3') in the primary binding loop of Erythrina variegata chymotrypsin inhibitor (ECI), a member of the Kunitz inhibitor family, are involved in its strong inhibitory activity toward chymotrypsin [Iwanaga et al. (1998) J. Biochem. 124, 663-669]. To determine whether or not these four amino acid residues predominantly contribute to the strong inhibitory activity of ECI, they were simultaneously replaced by Ala. The results showed that a quadruple mutant, Q62A/F63A/L64A/F67A, retained considerable inhibitory activity (Ki, 5.6 x 10(-7) M), indicating that in addition to the side chains of these four amino acid residues, the backbone structure of the primary binding loop in ECI is essential for the inhibitory activity toward chymotrypsin. Two chimeric proteins, in which the primary binding loops of ECI and ETIa were exchanged: an isoinhibitor from E. variegata with lower chymotrypsin inhibitory activity, were constructed to determine whether the backbone structure of the primary binding loop of ECI was formed by the amino acid residues therein, or through an interaction between the primary binding loop and the residual structure designated as the "scaffold." A chimeric protein, ECI/ETIa, composed of the primary binding loop of ECI and the scaffold of ETIa showed weaker inhibitory activity (Ki, 1.3 x 10(-6) M) than ECI (Ki, 9.8 x 10(-8) M). In contrast, a chimera, ETIa/ECI, comprising the primary binding loop of ETIa and the scaffold of ECI inhibited chymotrypsin more strongly (Ki, 5.7 x 10(-7) M) than ETIa (Ki, 1.3 x 10(-6) M). These results indicate that the intramolecular interaction between the primary binding loop and the scaffold of ECI plays an important role in the strong inhibitory activity toward chymotrypsin. Furthermore, surface plasmon resonance analysis revealed that the side chains on the primary binding loop of ECI contribute to both an increase in the association rate constant (kon) and a decrease in the dissociation rate constant (koff) for the ECI-chymotrypsin interaction, whereas the backbone structure of the primary binding loop mainly contributes to a decrease in the dissociation rate constant.

Alanine↗
PubMed1999

Angiotensin II interacts with prostaglandin F2alpha and endothelin-1 as a local luteolytic factor in the bovine corpus luteum in vitro.

Recent findings suggest that the ovarian renin-angiotensin system may regulate ovarian function through the paracrine/autocrine actions of angiotensin II (Ang II). In this study, we have examined and characterized the local effects of Ang II as a luteolytic factor and its interaction with prostaglandin F2alpha (PGF2alpha) and endothelin-1 (ET-1) in the bovine corpus luteum (CL) of the mid-luteal phase, by using an in vitro microdialysis system (MDS). Ang II was detected in the MDS perfusate (4 pg/ml), and infusion of PGF2alpha (10(-6) M) for 2 h increased the Ang II release by 50-100% during the following experimental period, in addition to its stimulation of ET-1 release. Two 2-h infusions of Ang II (10(-7)-10(-5) M) separated by a 2-h interval induced a dose- and time-dependent decrease of progesterone (P4) release by 41-66%. When the luteal explants were pre-perfused with PGF2alpha (10(-6) M) for 2 h, two consecutive perfusions of Ang II (10(-6) M) at a 2-h interval rapidly reduced the P4 release (by 50%). This reduction occurred 6 h earlier than those of infusions of PGF2alpha or Ang II alone. The simultaneous infusion of either 1) Ang II (10(-6) M) with PGF2alpha (10(-6) M), 2) ET-1 (10(-7) M) with PGF2alpha, or 3) Ang II + ET-1 with PGF2alpha (10(-6) M) for 2 h also induced a rapid and pronounced (60%) decrease in P4 release. Perfusion with the Ang II antagonist blocked the P4-suppressing activity of Ang II alone or PGF2alpha + Ang II infusion. Ang II stimulated the release of ET-1 and oxytocin during infusion but inhibited them after infusion. These results show that Ang II is released in the bovine midcycle CL in vitro, and this peptide, either alone or together with PGF2alpha, can suppress the release of P4. As PGF2alpha directly stimulated Ang II release, Ang II may influence the critical period for starting the cascade of functional luteolysis in vivo and might lead to structural luteolysis with ET-1 as a major vasoconstrictor. The overall results suggest that Ang II may have an important role at luteolysis in the bovine CL.

Abortifacient Agents, Nonsteroidal↗
PubMed1999

Tumor necrosis factor alpha receptors in microvascular endothelial cells from bovine corpus luteum.

There is sufficient evidence to prove that tumor necrosis factor alpha (TNFalpha) modulates bovine corpus luteum (CL) function. Our previous study demonstrated that functional TNFalpha receptors are present on luteal cells in bovine CL throughout the estrous cycle. The purpose of the present study was to identify the presence of functional TNFalpha receptors on the microvascular endothelial cells derived from developing bovine CL. TNFalpha receptors were analyzed by a radioreceptor assay using (125)I-labeled TNFalpha on two types of cultured endothelial cells. One has a cobblestone appearance (CS cells), and the other has a tube-like structure (TS cells). (125)I-Labeled TNFalpha binding was maximal after incubation for 30 h at 37 degrees C, and the specificity of binding was confirmed. A Scatchard analysis showed the presence of two binding sites (high- and low-affinity) for TNFalpha receptors on both CS and TS cells. The dissociation constant (K(d)) values and concentrations of the high-affinity binding sites for TNF receptors were similar for CS and TS cells. However, K(d) values and concentrations of the low-affinity binding sites in CS cells were significantly higher than those in TS cells (P < 0.05 or lower). The expression of TNF receptor type 1 (TNF-RI) mRNA was determined in both cell types. Furthermore, TNFalpha significantly stimulated prostaglandin E(2) and endothelin-1 secretion by both CS and TS cells (P < 0.05 or lower). These results indicate the presence of two types of TNF receptors and the expression of TNF-RI mRNA in the endothelial cells derived from bovine CL, and suggest that TNFalpha plays two or more roles in regulating the secretory function of the endothelial cells.

Animals↗
PubMed1999

Evidence for a local endothelin-angiotensin-atrial natriuretic peptide systemin bovine mature follicles in vitro: effects on steroid hormones and prostaglandin secretion.

Recent evidence suggests the presence of a functional endothelin-angiotensin-atrial natriuretic peptide system at the ovarian level. This study aimed to investigate 1) the local interrelationships among angiotensin II (Ang II), endothelin-1 (ET-1), and atrial natriuretic peptide (ANP); 2) the possible effect of each vasoactive peptide on the secretion of steroid hormones and prostaglandins (PGs) in isolated bovine mature follicles; and 3) the expression of mRNAs for Ang II, ET-1, and ANP receptors in the theca layer of follicles at different developmental stages. Each preovulatory follicle obtained before the LH surge (based on the concentrations of steroids and PGs) received implants of 4 capillary dialysis membranes into the theca layer. The follicles were then incubated in organ culture chambers and perfused with Ringer's solution for 12 h. Stimulation by infusion of the different substances into the microdialysis system was carried out between 4 and 8 h. The infusion of ET-1 (10(-7) M) stimulated the release of ANP and estradiol but inhibited the release of androstenedione and progesterone. The infusion of ANP (10(-7) M) stimulated the release of Ang II, progesterone, and androstenedione. Moreover, the infusion of Ang II (10(-5) M) inhibited the release of ANP but stimulated the release of ET-1, progesterone, and estradiol. All three peptides examined increased PGE(2) and PGF(2) release. In the reverse transcription-polymerase chain reaction analysis, expression of the mRNAs for ET type A and type B, and Ang II type 1 receptors did not change with the follicular size and the intrafollicular estradiol concentrations. Expression of the mRNA for the Ang II type 2 receptor dropped in follicles when the estradiol concentration ranged from 20 to 180 ng/ml and increased again when the estradiol concentration was > 180 ng/ml. The levels of expression of ANP type C receptor mRNA were slightly greater in follicles with estradiol concentrations > 20 ng/ml than in follicles with estradiol concentrations < 20 ng/ml. These results demonstrate a complex interaction among Ang II, ET-1, and ANP that may contribute to increasing the follicular production of PGs and modulate steroidogenesis in the bovine mature follicle, thus providing evidence for a local functional endothelin-angiotensin-ANP system.

Androstenedione↗
PubMed1999

Propofol-induced depression of cultured rat ventricular myocytes is related to the M2-acetylcholine receptor-NO-cGMP signaling pathway.

BACKGROUND: It is well-known that propofol sometimes causes bradycardia or asystole during anesthesia; however, the direct effect of propofol on the myocardium remains unclear. Previous reports showed the contribution of muscarinic acetylcholine receptors to propofol-induced bradycardia. Conversely, it was suggested recently that nitric oxide (NO) plays an important role in mediating the effect of vagal stimulation in the autonomic regulation of the heart. Therefore, the authors investigated the effects of propofol on spontaneous contraction and NO production in cultured rat ventricular myocytes. METHODS: The authors measured chronotropic responses of cultured rat ventricular myocytes induced by propofol stimulation with a sensor, a fiber-optic displacement measurement instrument. The authors also quantitatively analyzed NO metabolite production in cultured myocytes by measuring the levels of nitrite and nitrate in a high-performance liquid chromatography reaction system. The influence of propofol on muscarinic acetylcholine receptors of myocyte membranes was also measured with a competitive binding assay using [3H]quinuclidinyl benzilate ([3H]QNB). RESULTS: Propofol caused negative chronotropy in a dose-dependent manner. Propofol (IC50) also caused the enhancement of nitrite production in cultured myocytes. Eighty percent of the enhancement of nitrite production induced by propofol (IC50) stimulation was abolished by pretreatment with atropine, methoctramine, or N(G)-monomethyl-L-arginine acetate (L-NMMA). The negative chronotropy induced by propofol (IC50) stimulation was reduced to 40-50% by pretreatment with atropine, methoctramine, L-NMMA, or 1H[1,2,4]oxadiazolo[4,3-alpha]quanoxalin-1-one, a selective inhibitor of guanylyl cyclase. Propofol displaced [3H]QNB binding to the cell membrane of myocytes in a concentration-dependent manner. CONCLUSION: These results suggest that the negative chronotropy induced by propofol is mediated in part by M2-acetylcholine receptor activation, which involves the enhancement of NO production in cultured rat ventricular myocytes.

Anesthetics, Intravenous↗
PubMed1999

Notch signaling imposes two distinct blocks in the differentiation of C2C12 myoblasts.

Notch signal transduction regulates expression of downstream genes through the activation of the DNA-binding protein Su(H)/CBF1. In Drosophila most of Notch signaling requires Su(H); however, some Notch-dependent processes occur in the absence of Su(H) suggesting that Notch signaling does not always involve activation of this factor. Using constitutively active forms of Notch lacking CBF1-interacting sequences we identified a Notch signaling pathway that inhibits myogenic differentiation of C2C12 myoblasts in the absence of CBF1 activation. Here we show that ligand-induced Notch signaling suppresses myogenesis in C2C12 myoblasts that express a dominant negative form of CBF1, providing additional evidence for CBF1-independent Notch signal transduction. Surprisingly mutant forms of Notch deficient in CBF1 activation are unable to antagonize MyoD activity, despite the fact that they inhibit myogenesis. Moreover, Notch-induced antagonism of MyoD requires CBF1 suggesting that the CBF1-dependent pathway mediates a cell-type-specific block in the myogenic program. However, Notch signaling in the absence of CBF1 activation blocks both myogenesis and osteogenesis, indicative of a general block in cellular differentiation. Taken together our data provide evidence for two distinct Notch signaling pathways that function to block differentiation at separate steps during the process of myogenesis in C2C12 myoblasts.

3T3 Cells↗
PubMed1999

[A successful treatment with intravenous lidocaine followed by oral mexiletine in a patient with Lennox-Gastaut syndrome].

Clusters of atypical absence, myoclonic seizures and tonic seizures developed in a thirteen-year-old boy with Lennox-Gastaut syndrome. As conventional antiepileptic drugs failed to eliminate the seizures, we treated the patient with continuous intravenous lidocaine (4 mg/kg/hr). The treatment reduced the duration of paroxysmal discharges (spike-wave complexes and rapid rhythm) from 3 sec/min to 0.7 sec/min, monitored by EEG. Oral mexiletine (5.4 mg/kg/day) following the lidocaine treatment has maintained good seizure control for two years with no adverse effects, and improved his behavioral problem. The treatment with lidocaine followed by mexiletine was useful for controlling clusters of intractable seizures.

Administration, Oral↗
PubMed1999

[A case report of hepatocellular carcinoma with hepatic and portal venous tumor thrombus and multiple intrahepatic metastasis who survived over 1 year after the operation with combined locoregional chemotherapy].

Hepatocellular carcinoma (HCC) with vascular invasion and/or intrahepatic metastasis (IM) has a poor prognosis, so advanced HCC may be considered as a contraindication for hepatectomy. We experienced a case of HCC with hepatic venous and portal venous tumor thrombus and multiple IM who survived over 1 year after the operation with combined locoregional chemotherapy. (Case): A 67-year-old male patient was diagnosed with HCC with extracapsular invasion after transarterial embolization (TAE). CT scan revealed the HCC had a right portal venous tumor thrombus and multiple IM. Posterior lobectomy and thrombectomy of hepatic venous and portal venous tumor thrombus and placement of portal venous catheter ware performed. From the first day after operation the patient received continuous intravenous and intraportal 5-FU for 3 weeks. At the first month after operation, TAE and PEIT were given against residual IM. After discharge the patient received hepatic arterial infusion chemotherapy (MTX/CDDP/5-FU/Leucovorin). Fourteen months after operation, the patient is surviving in good physical condition.

Aged↗
PubMed1999

Increased expression of COX-2 in nontumor liver tissue is associated with shorter disease-free survival in patients with hepatocellular carcinoma.

Recent studies have shown increased levels of cyclooxygenase-2 (COX-2) in a variety of human malignancies including hepatocellular carcinoma (HCC), but little is known about the prognostic value of COX-2 in HCC or its associated nontumor liver tissue. We examined the expression of COX-2 protein by immunohistochemistry in 53 patients with HCCs whose corresponding nontumor tissues were hepatitis C virus-related chronic hepatitis (n = 21) and cirrhosis (n = 32). Samples of nine histologically normal livers and eight precancerous dysplasias were also analyzed. The level of COX-2 increased from normal liver to chronic hepatitis to cirrhosis. The majority of cirrhotic livers (81%) displayed marked COX-2 expression. In dysplasias, COX-2 expression was mainly moderate or strong (88%). In HCC, 17% of samples displayed a high COX-2 expression, and 37% of samples expressed COX-2 at a moderate level. Concordant results were obtained with reverse transcription-PCR and Western blot analyses. Clinicopathological survey indicated a significant correlation between COX-2 expression and differentiated carcinoma (P = 0.019). Although there was no correlation between COX-2 expression in HCC and prognosis, a striking difference was found between COX-2 expression in nontumor tissue and shorter disease-free survival (P = 0.0132). Moreover, high COX-2 expression in nontumor tissue was significantly correlated with the presence of active inflammation (P < 0.0001). The present findings suggest that COX-2 expression in nontumor tissue may play a positive role in relapse of HCC after surgery.

Blotting, Western↗
PubMed1999

Sensitivity analyses of heart rate variability variables by an incremental, passive head-up tilt.

We analyzed the sensitivity of heart rate variability (HRV) variables as an index of autonomic nervous activity by an incremental, passive head-up tilt (HUT). Twelve healthy male volunteers, mean age 20.5 years +/- 2.1 SD, were subjected, after a horizontal (0 degrees) supine posture period, to an incremental, passive HUT of 14.5, 30, 48.6, 61 and 90 degrees. The tested HRV variables were: heart rate (HR), standard deviation of the RR interval (SD(RR)), coefficient of variance of the RR interval (CV(RR)), low-frequency band [0.04-0.15 Hz] power spectrum (P(LF)), high-frequency band [0.15-0.4 Hz] power spectrum (P(HF)), the ratio of P(LF) to P(HF) (P(LF)/P(HF)), coefficients of low-frequency and high-frequency component variance (C-CV(LF), C-CV(HF)), percentages of P(LF) and P(HF) in total power spectrum (%LF, %HF), and normalized units of low frequency and high frequency band power spectra (NU(LF), NU(HF)). The SD(RR), CV(RR), P(LF) and C-CV(LF) were not sensitive to the sine of the tilt angles, i.e., the body-axis component of gravity (+Gz), in the incremental HUT. Therefore, these variables may be less suitable as indices of autonomic nervous activity. The P(LF)/P(HF), NU(LF), and NU(HF) appear to be useful as indices of sympathovagal balance. Both the NU(LF) and NU(HF) (both are equivalent and inversely related) are suitable for the comparison of sympathovagal balance between subjects of different ages and levels of physical fitness because they are not significantly influenced by age and physical fitness. The HR and HRV variables represent quite different characteristics of autonomic nervous activity, according to the Rosenblueth Simeone model. Therefore, the HR appears to be effective for combined assessment of sympathovagal balance. These results provide information useful in the selection of HRV variables while estimating autonomic nervous activity from short-term HRV.

Adolescent↗
PubMed1999

Effects of daily 2-Gz load on human cardiovascular function during weightlessness simulation using 4-day head-down bed rest.

An onboard short arm human centrifuge has been proposed as a countermeasure against physiological problems during long exposure to weightlessness in space and during extra planetary exploration. However, there are few studies on the effects of intermittent application of a Gz load via centrifuge during weightlessness. The present study evaluated the effects of a daily 2-Gz load on cardiovascular function during simulated weightlessness using a 4-day head-down bed rest (HDBR) period. Twelve young male subjects were exposed a HDBR period. Eight of them were exposed to a Gz load for up to 30 min twice per day (the Gz group). The remaining 4 were not exposed to a Gz load; they served as controls (the no-Gz group). Compared with the pre-HDBR period, the no-Gz group showed percent changes in the RR interval, the standard deviation (SD) of the RR interval, parasympathetic nervous activity, and baroreflex sensitivity (BRS) that progressively decreased and reached significance at the end of the HDBR period (-5.96 +/- 2.60%, -33.82 +/- 9.60%, -46.3 +/- 12.7% and -30.9 +/- 7.2%, respectively). In the Gz group, however, the percent changes in the RR interval, the SD of the RR interval, parasympathetic nervous activity, and BRS showed no significant changes throughout the HDBR period. At the end of the HDBR period, these indexes were 2.22 +/- 2.21%, -2.31 +/- 12.28%, 5.08 +/- 14.82% and 10.6 +/- 12.5%, respectively, and significantly greater than those of the no-Gz group. Sympathovagal balance indicators showed no significant change in the Gz and no-Gz groups (5.17 +/- 12.85% and 18.5 +/- 10.7%, respectively). These results indicate that a daily load of 2-Gz eliminates reduction of the RR interval, the SD of the RR interval, parasympathetic nervous activity, and BRS, and that it can maintain autonomic cardiovascular function in short-term weightlessness.

Adult↗