Oxygen-evolving photosystem II structures during S1-S2-S3 transitions.

Photosystem II (PSII) catalyses the oxidation of water through a four-step cycle of Si states (i = 0-4) at the Mn4CaO5 cluster1-3, during which an extra oxygen (O6) is incorporated at the S3 state to form a possible dioxygen4-7. Structural changes of the metal cluster and its environment during the S-state transitions have been studied on the microsecond timescale. Here we use pump-probe serial femtosecond crystallography to reveal the structural dynamics of PSII from nanoseconds to milliseconds after illumination with one flash (1F) or two flashes (2F). YZ, a tyrosine residue that connects the reaction centre P680 and the Mn4CaO5 cluster, showed structural changes on a nanosecond timescale, as did its surrounding amino acid residues and water molecules, reflecting the fast transfer of electrons and protons after flash illumination. Notably, one water molecule emerged in the vicinity of Glu189 of the D1 subunit of PSII (D1-E189), and was bound to the Ca2+ ion on a sub-microsecond timescale after 2F illumination. This water molecule disappeared later with the concomitant increase of O6, suggesting that it is the origin of O6. We also observed concerted movements of water molecules in the O1, O4 and Cl-1 channels and their surrounding amino acid residues to complete the sequence of electron transfer, proton release and substrate water delivery. These results provide crucial insights into the structural dynamics of PSII during S-state transitions as well as O-O bond formation.

The structure of PSI-LHCI from Cyanidium caldarium provides evolutionary insights into conservation and diversity of red-lineage LHCs.

Light-harvesting complexes (LHCs) are diversified among photosynthetic organisms, and the structure of the photosystem I-LHC (PSI-LHCI) supercomplex has been shown to be variable depending on the species of organisms. However, the structural and evolutionary correlations of red-lineage LHCs are unknown. Here, we determined a 1.92-Å resolution cryoelectron microscopic structure of a PSI-LHCI supercomplex isolated from the red alga Cyanidium caldarium RK-1 (NIES-2137), which is an important taxon in the Cyanidiophyceae. We subsequently investigated the correlations of PSI-LHCIs from different organisms through structural comparisons and phylogenetic analysis. The PSI-LHCI structure obtained shows five LHCI subunits surrounding a PSI-monomer core. The five LHCIs are composed of two Lhcr1s, two Lhcr2s, and one Lhcr3. Phylogenetic analysis of LHCs bound to PSI in the red-lineage algae showed clear orthology of LHCs between C. caldarium and Cyanidioschyzon merolae, whereas no orthologous relationships were found between C. caldarium Lhcr1-3 and LHCs in other red-lineage PSI-LHCI structures. These findings provide evolutionary insights into conservation and diversity of red-lineage LHCs associated with PSI.

Structural insights into the action mechanisms of artificial electron acceptors in photosystem II.

Photosystem II (PSII) utilizes light energy to split water, and the electrons extracted from water are transferred to QB, a plastoquinone molecule bound to the D1 subunit of PSII. Many artificial electron acceptors (AEAs) with molecular structures similar to that of plastoquinone can accept electrons from PSII. However, the molecular mechanism by which AEAs act on PSII is unclear. Here, we solved the crystal structure of PSII treated with three different AEAs, 2,5-dibromo-1,4-benzoquinone, 2,6-dichloro-1,4-benzoquinone, and 2-phenyl-1,4-benzoquinone, at 1.95 to 2.10 Å resolution. Our results show that all AEAs substitute for QB and are bound to the QB-binding site (QB site) to receive electrons, but their binding strengths are different, resulting in differences in their efficiencies to accept electrons. The acceptor 2-phenyl-1,4-benzoquinone binds most weakly to the QB site and showed the highest oxygen-evolving activity, implying a reverse relationship between the binding strength and oxygen-evolving activity. In addition, a novel quinone-binding site, designated the QD site, was discovered, which is located in the vicinity of QB site and close to QC site, a binding site reported previously. This QD site is expected to play a role as a channel or a storage site for quinones to be transported to the QB site. These results provide the structural basis for elucidating the actions of AEAs and exchange mechanism of QB in PSII and also provide information for the design of more efficient electron acceptors.

Presence of low-energy chlorophylls d in photosystem I trimer and monomer cores isolated from Acaryochloris sp. NBRC 102871.

Acaryochloris species belong to a special category of cyanobacteria possessing chlorophyll (Chl) d. One of the photosynthetic characteristics of Acaryochloris marina MBIC11017 is that the absorption spectra of photosystem I (PSI) showed almost no bands and shoulders of low-energy Chls d over 740 nm. In contrast, the absorption spectra of other Acaryochloris species showed a shoulder around 740 nm, suggesting that low-energy Chls d within PSI are diversified among Acaryochloris species. In this study, we purified PSI trimer and monomer cores from Acaryochloris sp. NBRC 102871 and examined their protein and pigment compositions and spectral properties. The protein bands and pigment compositions of the PSI trimer and monomer of NBRC102871 were virtually identical to those of MBIC11017. The absorption spectra of the NBRC102871 PSIs exhibited a shoulder around 740 nm, whereas the fluorescence spectra of PSI trimer and monomer displayed maximum peaks at 754 and 767 nm, respectively. These spectral properties were different from those of MBIC11017, indicating the presence of low-energy Chls d within the NBRC102871 PSIs. Moreover, we analyzed the NBRC102871 genome to identify amino acid sequences of PSI proteins and compared them with those of the A. marina MBIC11017 and MBIC10699 strains whose genomes are available. The results showed that some of the sequences in NBRC102871 were distinct from those in MBIC11017 and MBIC10699. These findings provide insights into the variety of low-energy Chls d with respect to the protein environments of PSI cores among the three Acaryochloris strains.

Predicted effect-site concentrations of remimazolam for i-gel insertion: a prospective randomized controlled study.

This study is the first to report 50% and 95% effect-site concentrations (EC50 and EC95, respectively) of the new short-acting benzodiazepine, remimazolam, for the successful insertion of i-gels with co-administration of fentanyl. Thirty patients (38 ± 5 years old, male/female = 4/26) were randomly assigned into five groups to receive one of five different remimazolam doses (0.1, 0.15, 0.2, 0.25, and 0.3 mg/kg bolus followed by infusion of 1, 1.5, 2, 2.5, and 3 mg/kg/h, respectively, for 10 min), which were designed to maintain a constant effect-site concentration of remimazolam at the time of i-gel insertion. At 6 min after the start of remimazolam infusion, all patients received 2 µg/kg fentanyl. i-gel insertion was attempted at 10 min and the success or failure of insertion were assessed by the patient response. Probit analysis was used to estimate the EC50 and EC95 values of remimazolam with 95% confidence intervals (CIs). In the five remimazolam dose groups, two, two, four, five, and six of the six patients in each group had an i-gel successfully inserted. Two patients in the lowest remimazolam dose group were conscious at the time of i-gel insertion and were counted as failures. The EC50 and EC95 values of remimazolam were 0.88 (95% CI, 0.65-1.11) and 1.57 (95% CI, 1.09-2.05) µg/ml, respectively. An effect-site concentration of ≥ 1.57 µg/ml was needed to insert an i-gel using remimazolam anesthesia, even with 2 µg/kg fentanyl. Trial registration: The study was registered in Japan Registry of Clinical Trials on 19 April 2021, Code jRCTs041210009.

The effect of assisted reproductive technology on postpartum bleeding: hormonal cycle frozen embryo transfer might increase blood loss.

BACKGROUND: Among assisted reproductive technologies, frozen thawed embryo transfer (FET) is associated with increased blood loss at delivery. Anesthesiologists need to be aware of new factors that affect postpartum blood loss. This study investigated whether FET cycles with or without hormonal support affect the amount of postpartum bleeding. METHODS: We conducted a retrospective cohort study of patients admitted for delivery at a single university hospital between January 2015 and December 2018. Patients were divided into no-assisted reproductive technology (No-ART), hormonal cycle FET (HC-FET) and natural cycle FET (NC-FET) group. The primary outcome was the amount of blood loss after delivery (median [interquartile range]), which was compared among the three groups. Multiple regression analysis was performed to investigate the factors affecting blood loss. RESULTS: Between 2015 and 2018, 3187 women delivered neonates. In vaginal delivery, postpartum blood loss in the HC-FET group (1060 [830] g) was significantly greater than in the NC-FET group (650 [485] g, P = 0.001) and in the No-ART group (590 [420] g P < 0.001). Multiple linear regression analysis showed that HC-FET (P < 0.001) was one of the independent factors for the amount of bleeding. In cesarean delivery, the HC-FET group had more blood loss than the No-ART group (910 [676] g vs. 784 [524] g, P = 0.039). However, HC-FET was not an independent factor for postpartum blood loss. CONCLUSIONS: The HC-FET group had more blood loss than the No-ART group for both vaginal and cesarean deliveries. Furthermore, HC-FET was an independent factor that increased postpartum blood loss in vaginal deliveries.

Effects of volatile anesthetics on circadian rhythm in mice: a comparative study of sevoflurane, desflurane, and isoflurane.

PURPOSE: Volatile anesthetics affect the circadian rhythm of mammals, although the effects of different types of anesthetics are unclear. Here, we anesthetized mice using several volatile anesthetics at two different times during the day. Our objective was to compare the effects of these anesthetics on circadian rhythm. METHODS: Male adult C57BL/6 J mice were divided into eight groups (n = 8 each) based on the anesthetic (sevoflurane, desflurane, isoflurane, or no anesthesia) and anesthesia time (Zeitgeber time [ZT] 6-12 or ZT18-24). Mice were anesthetized for 6 h using a 0.5 minimum alveolar concentration (MAC) dose under constant dark conditions. The difference between the start of the active phase before and after anesthesia was measured as a phase shift. Clock genes were measured by polymerase chain reaction in suprachiasmatic nucleus (SCN) samples removed from mouse brain after anesthesia (n = 8-9 each). RESULTS: Phase shift after anesthesia at ZT6-12 using sevoflurane (- 0.49 h) was smaller compared with desflurane (- 1.1 h) and isoflurane (- 1.4 h) (p < 0.05). Clock mRNA (ZT6-12, p < 0.05) and Per2 mRNA (ZT18-24, p < 0.05) expression were different between the groups after anesthesia. CONCLUSION: 0.5 MAC sevoflurane anesthesia administered during the late inactive to early active phase has less impact on the phase shift of circadian rhythm than desflurane and isoflurane. This may be due to differences in the effects of volatile anesthetics on the expression of clock genes in the SCN, the master clock of the circadian rhythm.

Crystal structures of photosystem II from a cyanobacterium expressing psbA2 in comparison to psbA3 reveal differences in the D1 subunit.

Three psbA genes (psbA1, psbA2, and psbA3) encoding the D1 subunit of photosystem II (PSII) are present in the thermophilic cyanobacterium Thermosynechococcus elongatus and are expressed differently in response to changes in the growth environment. To clarify the functional differences of the D1 protein expressed from these psbA genes, PSII dimers from two strains, each expressing only one psbA gene (psbA2 or psbA3), were crystallized, and we analyzed their structures at resolutions comparable to previously studied PsbA1-PSII. Our results showed that the hydrogen bond between pheophytin/D1 (PheoD1) and D1-130 became stronger in PsbA2- and PsbA3-PSII due to change of Gln to Glu, which partially explains the increase in the redox potential of PheoD1 observed in PsbA3. In PsbA2, one hydrogen bond was lost in PheoD1 due to the change of D1-Y147F, which may explain the decrease in stability of PheoD1 in PsbA2. Two water molecules in the Cl-1 channel were lost in PsbA2 due to the change of D1-P173M, leading to the narrowing of the channel, which may explain the lower efficiency of the S-state transition beyond S2 in PsbA2-PSII. In PsbA3-PSII, a hydrogen bond between D1-Ser270 and a sulfoquinovosyl-diacylglycerol molecule near QB disappeared due to the change of D1-Ser270 in PsbA1 and PsbA2 to D1-Ala270. This may result in an easier exchange of bound QB with free plastoquinone, hence an enhancement of oxygen evolution in PsbA3-PSII due to its high QB exchange efficiency. These results provide a structural basis for further functional examination of the three PsbA variants.

Light-induced structural changes and the site of O=O bond formation in PSII caught by XFEL.

Photosystem II (PSII) is a huge membrane-protein complex consisting of 20 different subunits with a total molecular mass of 350 kDa for a monomer. It catalyses light-driven water oxidation at its catalytic centre, the oxygen-evolving complex (OEC). The structure of PSII has been analysed at 1.9 Å resolution by synchrotron radiation X-rays, which revealed that the OEC is a Mn4CaO5 cluster organized in an asymmetric, 'distorted-chair' form. This structure was further analysed with femtosecond X-ray free electron lasers (XFEL), providing the 'radiation damage-free' structure. The mechanism of O=O bond formation, however, remains obscure owing to the lack of intermediate-state structures. Here we describe the structural changes in PSII induced by two-flash illumination at room temperature at a resolution of 2.35 Å using time-resolved serial femtosecond crystallography with an XFEL provided by the SPring-8 ångström compact free-electron laser. An isomorphous difference Fourier map between the two-flash and dark-adapted states revealed two areas of apparent changes: around the QB/non-haem iron and the Mn4CaO5 cluster. The changes around the QB/non-haem iron region reflected the electron and proton transfers induced by the two-flash illumination. In the region around the OEC, a water molecule located 3.5 Å from the Mn4CaO5 cluster disappeared from the map upon two-flash illumination. This reduced the distance between another water molecule and the oxygen atom O4, suggesting that proton transfer also occurred. Importantly, the two-flash-minus-dark isomorphous difference Fourier map showed an apparent positive peak around O5, a unique µ4-oxo-bridge located in the quasi-centre of Mn1 and Mn4 (refs 4,5). This suggests the insertion of a new oxygen atom (O6) close to O5, providing an O=O distance of 1.5 Å between these two oxygen atoms. This provides a mechanism for the O=O bond formation consistent with that proposed previously.

Stomach, liver, kidney and skeletal muscle autoregulation evaluated by near-infrared spectroscopy in a swine model.

PURPOSE: Different organs have different autoregulatory capacities for blood pressure changes and/or circulatory volume changes. This study assessed the autoregulation of the stomach, liver, kidney and skeletal muscle, under baseline, hypovolemic, and post-fluid-resuscitation conditions using near-infrared spectroscopy (NIRS). METHODS: Ten pigs (bodyweight 24.5 ± 0.5 kg) were anesthetized with 2.5% isoflurane and administered 0.5, 1, 2 and 5 µg kg- 1 min- 1 of phenylephrine at 10-min intervals, followed by similar stepwise infusion of sodium nitroprusside (SNP) to induce a wide range of mean arterial pressures (MAPs). A 600-ml bleed was induced to create the hypovolemic condition, and only phenylephrine was re-administered. Hydroxyethyl starch (600 ml) was infused to create the post-fluid-resuscitation condition, and phenylephrine and SNP were re-administered. Average relationships between mean arterial pressure (MAP) and each tissue oxygenation index (TOI) were assessed, and the individual relationships were evaluated based on the correlation coefficients between MAP and TOI during each vasoactive drug infusion. RESULTS: Based on the evaluation using each TOI as a substitute of blood flow, the kidney autoregulation was robust, similar to muscle, but had a prominent lower limit. The stomach had weaker autoregulation than the kidney and muscle. The liver had no autoregulation. The kidney TOI showed 2-fold greater changes in response to volume condition changes than the stomach and liver TOIs. CONCLUSION: In our NIRS-based assessment of autoregulatory capacity, the liver oxygenation is highly blood pressure dependent, and the kidney is highly susceptible and the skeletal muscle is highly tolerable to low blood pressure and volume loss.

Association between remimazolam and postoperative delirium in older adults undergoing elective cardiovascular surgery: a prospective cohort study.

PURPOSE: Postoperative delirium is one of the most common complications after cardiovascular surgery in older adults. Benzodiazepines are a reported risk factor for delirium; however, there are no studies investigating remimazolam, a novel anesthetic agent. Therefore, we prospectively investigated the effect of remimazolam on postoperative delirium. METHODS: We included elective cardiovascular surgery patients aged ≥ 65 years at Hamamatsu University Hospital between August 2020 and February 2022. Patients who received general anesthesia with remimazolam were compared with those who received other anesthetics (control group). The primary outcome was delirium within 5 days after surgery. Secondary outcomes were delirium during intensive care unit stay and hospitalization, total duration of delirium, subsyndromal delirium, and differences in the Mini-Mental State Examination scores from preoperative to postoperative days 2 and 5. To adjust for differences in the groups' baseline covariates, we used stabilized inverse probability weighting as the primary analysis and propensity score matching as the sensitivity analysis. RESULTS: We enrolled 200 patients; 78 in the remimazolam group and 122 in the control group. After stabilized inverse probability weighting, 30.3% of the remimazolam group patients and 26.6% of the control group patients developed delirium within 5 days (risk difference, 3.8%; 95% confidence interval -11.5% to 19.1%; p = 0.63). The secondary outcomes did not differ significantly between the groups, and the sensitivity analysis results were similar to those for the primary analysis. CONCLUSION: Remimazolam was not significantly associated with postoperative delirium when compared with other anesthetic agents.

Obstetric admission to intensive care units in Japan: a cohort study using the Japanese Intensive care PAtient Database.

PURPOSE: This study aimed to describe the epidemiology and annual trends of obstetric patients using a multicenter intensive care database. METHODS: This multicenter, retrospective cohort study used the Japanese Intensive care PAtient Database (JIPAD). We included obstetric patients registered in the JIPAD between 2015 and 2020. We investigated the proportion of obstetric patients among all patients in the intensive care unit (ICU). We also described the characteristics, procedures, and outcomes of obstetric patients. In addition, the annual trends were examined by nonparametric tests for trends. RESULTS: Of the 184,705 patients enrolled in the JIPAD, 750 (0.41%) were obstetric patients from 61 facilities. The median age was 34 years, the number of post-emergency surgeries was 450 (60.0%), and the median APACHE III score was 36. Mechanical ventilation was the most common procedure performed in 247 (32.9%) patients. There were five (0.7%) in-hospital deaths. The proportion of obstetric patients in the ICU did not change between 2015 and 2020 (P for trend = 0.32). However, there was a trend for a significant decrease in the severity of illness and length of hospital stay on an annual basis between 2015 and 2020. Most patients were admitted to the ICU because of a pregnancy-related disorder postoperatively. CONCLUSION: The proportion of obstetric patients was 0.41% of all ICU admissions. The proportion of obstetric patients admitted to the ICU did not change from 2015 to 2020, but the patients' severity of illness and length of hospital stay significantly decreased over time.

Influence of hemorrhage and subsequent fluid resuscitation on transcranial motor-evoked potentials under desflurane anesthesia in a swine model.

PURPOSE: Hemorrhage increases the effect of propofol and could contribute to false-positive transcranial motor-evoked potential (TcMEP) responses under total intravenous anesthesia (TIVA). We investigated the influence of hemorrhage and subsequent fluid resuscitation on TcMEPs under desflurane anesthesia. METHODS: Sixteen swine (25.4 ± 0.4 kg) were anesthetized with a 4% end-tidal desflurane concentration (EtDes), which was incrementally increased to 6%, 8%, and 10% and then returned to 4% every 15 min. This procedure was repeated twice (baseline). After baseline measurements, animals were allocated to either the hemorrhage (n = 12) or control (n = 4) group. In the hemorrhage group, 600 ml of blood was removed and the EtDes protocol described above was applied. Hypovolemia was resuscitated using 600 ml of hydroxyethyl starch and the EtDes protocol was applied again. TcMEPs were measured at each EtDes. In the control group, measurements were performed without hemorrhage or fluid infusion. RESULTS: TcMEP responses were observed in all conditions in all limbs with 4% EtDes (0.4 MAC). TcMEP amplitudes decreased according to the EtDes to a greater degree in the lower limbs compared with the upper limbs. Hemorrhage enhanced the effect of desflurane on TcMEP amplitudes, and decreased TcMEP by 41 ± 12% in upper limbs and 63 ± 17% in lower limbs compared with baseline. Subsequent fluid resuscitation did not reverse TcMEP amplitudes. CONCLUSIONS: TcMEP amplitudes decrease during hemorrhage under desflurane anesthesia. This phenomenon might result from an enhanced effect of desflurane on the spinal motor pathway without increasing the desflurane concentration.

Recall of extubation after remimazolam anesthesia with flumazenil antagonism during emergence: a retrospective clinical study.

PURPOSE: This study was performed to examine and compare the incidence of extubation recall in surgical patients who underwent remimazolam anesthesia with flumazenil antagonism during emergence and in those who underwent propofol anesthesia. METHODS: One hundred sixty-three patients who underwent surgery using general endotracheal or supraglottic airway anesthesia with propofol (n = 97) or remimazolam (n = 66) were retrospectively analyzed. Remimazolam was antagonized by flumazenil after discontinuation of remimazolam at the end of surgery. The endotracheal tube or supraglottic airway was removed after surgery was complete, and consciousness and adequate spontaneous breathing were confirmed. The incidence of extubation recall was compared between the remimazolam and propofol anesthesia groups using propensity score matching. RESULTS: Extubation recall was observed in 28 patients (17%). After propensity score matching, the incidence of extubation recall did not significantly differ between the remimazolam and propofol anesthesia groups (15.6% vs. 18.8%; p = 1.000). CONCLUSION: The incidence of extubation recall after remimazolam anesthesia with flumazenil antagonism during emergence did not significantly differ from that after propofol anesthesia.

Native structure of photosystem II at 1.95 Å resolution viewed by femtosecond X-ray pulses.

Photosynthesis converts light energy into biologically useful chemical energy vital to life on Earth. The initial reaction of photosynthesis takes place in photosystem II (PSII), a 700-kilodalton homodimeric membrane protein complex that catalyses photo-oxidation of water into dioxygen through an S-state cycle of the oxygen evolving complex (OEC). The structure of PSII has been solved by X-ray diffraction (XRD) at 1.9 ångström resolution, which revealed that the OEC is a Mn4CaO5-cluster coordinated by a well defined protein environment. However, extended X-ray absorption fine structure (EXAFS) studies showed that the manganese cations in the OEC are easily reduced by X-ray irradiation, and slight differences were found in the Mn-Mn distances determined by XRD, EXAFS and theoretical studies. Here we report a 'radiation-damage-free' structure of PSII from Thermosynechococcus vulcanus in the S1 state at a resolution of 1.95 ångströms using femtosecond X-ray pulses of the SPring-8 ångström compact free-electron laser (SACLA) and hundreds of large, highly isomorphous PSII crystals. Compared with the structure from XRD, the OEC in the X-ray free electron laser structure has Mn-Mn distances that are shorter by 0.1-0.2 ångströms. The valences of each manganese atom were tentatively assigned as Mn1D(III), Mn2C(IV), Mn3B(IV) and Mn4A(III), based on the average Mn-ligand distances and analysis of the Jahn-Teller axis on Mn(III). One of the oxo-bridged oxygens, O5, has significantly longer distances to Mn than do the other oxo-oxygen atoms, suggesting that O5 is a hydroxide ion instead of a normal oxygen dianion and therefore may serve as one of the substrate oxygen atoms. These findings provide a structural basis for the mechanism of oxygen evolution, and we expect that this structure will provide a blueprint for the design of artificial catalysts for water oxidation.

Epidural space "ballooning" during local anaesthetic injection in infants and children: An ultrasound observational study.

BACKGROUND: Infants and children require a larger dose of a local anaesthetic (LA) to establish epidural analgesia than adults, but the reason for this remains unclear. We hypothesised that prominent ventro-dorsal expansion of the epidural space limits cranio-caudal spread of LA in infants. Accordingly, we studied the dimensions of the epidural space with real-time ultrasound (US) before and after epidural injection. METHODS: Ninety-six infants and children aged 0-12 years who underwent abdominal surgery under combined epidural and general anaesthesia were examined in this prospective observational study. Using a micro-convex probe, US recordings of the posterior epidural space were performed while a LA (0.5 ml kg-1 ) was infused at 0.54 ml s-1 . The width in the ventro-dorsal dimension (VDD) of the posterior epidural space before and after injection was recorded; the change in VDD was defined as "ballooning". Correlations between "ballooning" and patient age, body mass index, and volume and rate of LA administration were analysed. RESULTS: "Ballooning" correlated positively but weakly with age (R2  = 0.25; p < .001) and the infused LA volume (R2  = 0.32; p < .001). The "magnitude of ballooning" ("ballooning" per ml of injected LA) correlated negatively but weakly with age (R2  = 0.27; p < .001). CONCLUSIONS: "Magnitude of ballooning" of the epidural space become inconspicuous with growing during epidural injection. This effect may slow the cranio-caudal spread of LA and explain partially why larger volumes of LA are required to effect a block in children.

Assessment of the benefits of head-up preoxygenation using near-infrared spectroscopy with pulse oximetry in a swine model.

Compared with supine positioning, head-up positioning improves preoxygenation and prolongs the time to oxygen desaturation. We reevaluated benefits of head-up positioning using near-infrared spectroscopy (NIRS) with pulse oximetry in a pig model. Six pigs (mean ± SD weight: 25.3 ± 0.6 kg) were anesthetized with isoflurane and evaluated in four positions-supine, head-up, head-down, head-up to supine-just before apnea (positions' order after "supine" was randomized). In each position, after 5 min of preoxygenation with 100% oxygen, apnea was induced and the time to SpO2 < 70% measured. Hemodynamic and blood-gas variables and the cerebral tissue oxygenation index (TOI) were evaluated using NIRS and recorded. Hypovolemia was induced by collecting 600 mL blood. Apnea experiment was performed again in each position. The times (seconds) ± SD to SpO2 < 70% were 108 ± 13 (supine), 138 ± 15 (head-up; P < 0.0001 vs all other positions); 101 ± 12 (head-down) and 106 ± 15 (head-up to supine) during normovolemia, and 110 ± 29, 120 ± 7 (not significant vs all other positions), 101 ± 16, and 106 ± 11, respectively, during hypovolemia. Although the TOI was not associated with the positions during normovolemia, the head-up position during hypovolemia decreased TOI from 62% ± 6% (supine) to 50% ± 9% (head-up; P = 0.0019) before preoxygenation, and it remained low during apnea. The head-up position improves preoxygenation, but repositioning to supine negates the benefits. Head-up positioning during evident hypovolemia should be avoided because the cerebral oxygenation could decrease.

1.2% Hydrogen gas inhalation protects the endothelial glycocalyx during hemorrhagic shock: a prospective laboratory study in rats.

PURPOSE: Hydrogen gas (H2) inhalation improved the survival rate of hemorrhagic shock. However, its mechanisms are unknown. We hypothesized that H2 protected the endothelial glycocalyx during hemorrhagic shock and prolonged survival time. METHODS: 83 Sprague-Dawley rats were anesthetized with isoflurane. The animals were randomly assigned to 5 groups: room air with no shock, 1.2% H2 with no shock, room air with shock (Control-S), 1.2% H2 with shock (H21.2%-S), and 3.0% H2 with shock (H23.0%-S). Shock groups were bled to a mean arterial pressure of 30-35 mmHg and held for 60 min, then resuscitated with normal saline at fourfold the amount of the shed blood volume. RESULTS: The syndecan-1 level was significantly lower in the H21.2%-S [8.3 ± 6.6 ng/ml; P = 0.01; 95% confidence interval (CI), 3.2-35.8] than in the Control-S (27.9 ± 17.0 ng/ml). The endothelial glycocalyx was significantly thicker in the H21.2%-S (0.15 ± 0.02 µm; P = 0.007; 95% CI, 0.02-0.2) than in the Control-S (0.06 ± 0.02 µm). The survival time was longer in the H21.2%-S (327 ± 67 min, P = 0.0160) than in the Control-S (246 ± 69 min). The hemoglobin level was significantly lower in the H21.2%-S (9.4 ± 0.5 g/dl; P = 0.0034; 95% CI, 0.6-2.9) than in the Control-S (11.1 ± 0.8 g/dl). However, the H23.0%-S was not significant. CONCLUSIONS: Inhalation of 1.2% H2 gas protected the endothelial glycocalyx and prolonged survival time during hemorrhagic shock. Therapeutic efficacy might vary depending on the concentration.

Thylakoid membrane lipid sulfoquinovosyl-diacylglycerol (SQDG) is required for full functioning of photosystem II in Thermosynechococcus elongatus.

Sulfoquinovosyl-diacylglycerol (SQDG) is one of the four lipids present in the thylakoid membranes. Depletion of SQDG causes different degrees of effects on photosynthetic growth and activities in different organisms. Four SQDG molecules bind to each monomer of photosystem II (PSII), but their role in PSII function has not been characterized in detail, and no PSII structure without SQDG has been reported. We analyzed the activities of PSII from an SQDG-deficient mutant of the cyanobacterium Thermosynechococcus elongatus by various spectroscopic methods, which showed that depletion of SQDG partially impaired the PSII activity by impairing secondary quinone (QB) exchange at the acceptor site. We further solved the crystal structure of the PSII dimer from the SQDG deletion mutant at 2.1 Å resolution and found that all of the four SQDG-binding sites were occupied by other lipids, most likely PG molecules. Replacement of SQDG at a site near the head of QB provides a possible explanation for the QB impairment. The replacement of two SQDGs located at the monomer-monomer interface by other lipids decreased the stability of the PSII dimer, resulting in an increase in the amount of PSII monomer in the mutant. The present results thus suggest that although SQDG binding in all of the PSII-binding sites is necessary to fully maintain the activity and stability of PSII, replacement of SQDG by other lipids can partially compensate for their functions.

Effective Dose of Landiolol, an Ultra-Short-Acting ß-Blocker, to Decrease Heart Rate During On-Pump, Beating Coronary Artery Bypass Grafting.

OBJECTIVE: Decreasing the heart rate (HR) using landiolol, an ultra-short-acting ß-blocker, is helpful for completing a meticulous distal anastomosis during on-pump or off-pump, beating coronary artery bypass grafting (CABG) surgery. We determine the effectiveness of landiolol to decrease the HR because the most effective dose has not been established. DESIGN: Observational open-label pharmacodynamics cohort study. SETTING: Single center, Hamamatsu University Hospital. PARTICIPANTS: 28 patients undergoing on-pump, beating CABG. INTERVENTIONS: Landiolol 5 µg/kg/min was started (time 0) and then increased to 15, 25, and 35 µg/kg/min at 10-min intervals during left internal thoracic artery (LITA) to left anterior descending artery (LAD) anastomosis. MEASUREMENTS AND MAIN RESULTS: Pharmacodynamics were characterized using a sigmoidal inhibitory maximum effect model to determine the percent decrease in HR according to the landiolol dose. Baseline (mean  ±â€¯ SD) HR (85 ±â€¯10 beats/min) decreased to 81 ±â€¯9, 71 ±â€¯10, 67 ±â€¯9, and 67 ±â€¯9 beats/min, respectively, at the four landiolol infusion points evaluated. Estimated maximum percent decrease in HR from the baseline effective dose value (ED0) was -21.5 (-25.3 to -17.8) [mean (95% confidence interval)]%. ED50, ED90, and ED95 were 9.5 (9.0-10.1), 25.0 (22.5-27.6), and 35.2 (30.3-40.1) µg/kg/min, respectively. CONCLUSIONS: Landiolol maximally decreased HR just over 20% of the baseline HR. Hence, landiolol 25 µg/kg/min is likely a sufficient dose during LITA-LAD anastomosis during on-pump, beating CABG.