Dynamics-driven allosteric stimulation of diguanylate cyclase activity in a red light-regulated phytochrome.

Sensor-effector proteins integrate information from different stimuli and transform this into cellular responses. Some sensory domains, like red-light responsive bacteriophytochromes, show remarkable modularity regulating a variety of effectors. One effector domain is the GGDEF diguanylate cyclase catalyzing the formation of the bacterial second messenger cyclic-dimeric-guanosine monophosphate. While critical signal integration elements have been described for different phytochromes, a generalized understanding of signal processing and communication over large distances, roughly 100 Å in phytochrome diguanylate cyclases, is missing. Here we show that dynamics-driven allostery is key to understanding signal integration on a molecular level. We generated protein variants stabilized in their far-red-absorbing Pfr state and demonstrated by analysis of conformational dynamics using hydrogen-deuterium exchange coupled to mass spectrometry that single amino acid replacements are accompanied by altered dynamics of functional elements throughout the protein. We show that the conformational dynamics correlate with the enzymatic activity of these variants, explaining also the increased activity of a non-photochromic variant. In addition, we demonstrate the functional importance of mixed Pfr/intermediate state dimers using a fast-reverting variant that still enables wild-type-like fold-changes of enzymatic stimulation by red light. This supports the functional role of single protomer activation in phytochromes, a property that might correlate with the non-canonical mixed Pfr/intermediate-state spectra observed for many phytochrome systems. We anticipate our results to stimulate research in the direction of dynamics-driven allosteric regulation of different bacteriophytochrome-based sensor-effectors. This will eventually impact design strategies for the creation of novel sensor-effector systems for enriching the optogenetic toolbox.

Lenticels are sites of initiation of microcracking and russeting in 'Apple' mango.

The mango cultivar 'Apple' is an important fruitcrop in Kenya, but it is highly susceptible to russeting. The objective was to establish whether lenticels predispose cv. 'Apple' mango to russeting. Fruit mass and surface area increased in a sigmoidal pattern with time. The frequency of lenticels per unit surface area decreased during development. The number of lenticels per fruit was constant. Lenticels were most frequent in the apex region and least common in the cheek and nak (ventral) regions. The cheek region also had lenticels with the largest core areas, whereas the lenticel core areas in the apex region were significantly smaller. Microscopy revealed stomata became covered over with wax deposits at 33 days after full bloom (DAFB). By 78 DAFB, periderm had formed beneath the pore. At 110 and 161 DAFB, cracks had developed and the periderm had extended tangentially and radially. The presence of lenticels increased the strain released upon excision of an epidermal segment, further strain releases occurred subsequently upon isolation of the cuticle and on extraction of the cuticular waxes. The number of lenticels per unit surface area was negatively correlated with the fruit surface area (r2 = 0.62 **), but not affected by fruit size. Mango cv. 'Apple' had fewer, larger lenticels and more russet, compared with 'Ngowe', 'Kitovu' or 'Tommy Atkins' mango. In cv. 'Apple', the lowest lenticel frequency, the largest lenticels and the most russeting occurred at a growing site at the highest altitude, with the highest rainfall and the lowest temperature. Moisture exposure of the fruit surface resulted in enlarged lenticels and more microcracking of the cuticle. Our results establish that russeting in 'Apple' mango is initiated at lenticels and is exacerbated if lenticels are exposed to moisture.

Illuminating the inner workings of a natural protein switch: Blue-light sensing in LOV-activated diguanylate cyclases.

Regulatory proteins play a crucial role in adaptation to environmental cues. Especially for lifestyle transitions, such as cell proliferation or apoptosis, switch-like characteristics are desirable. While nature frequently uses regulatory circuits to amplify or dampen signals, stand-alone protein switches are interesting for applications like biosensors, diagnostic tools, or optogenetics. However, such stand-alone systems frequently feature limited dynamic and operational ranges and suffer from slow response times. Here, we characterize a LOV-activated diguanylate cyclase (LadC) that offers precise temporal and spatial control of enzymatic activity with an exceptionally high dynamic range over four orders of magnitude. To establish this pronounced activation, the enzyme exhibits a two-stage activation process in which its activity is inhibited in the dark by caging its effector domains and stimulated upon illumination by the formation of an extended coiled-coil. These switch-like characteristics of the LadC system can be used to develop new optogenetic tools with tight regulation.

Acoustic resonance effects and cavitation in SAW aerosol generation.

The interaction of surface acoustic waves (SAWs) with liquids enables the production of aerosols with adjustable droplet sizes in the micrometer range expelled from a very compact source. Understanding the nonlinear acousto-hydrodynamics of SAWs with a regulated micro-scale liquid film is essential for acousto-microfluidics platforms, particularly aerosol generators. In this study, we demonstrate the presence of micro-cavitation in a MHz-frequency SAW aerosol generation platform, which is touted as a leap in aerosol technology with versatile application fields including biomolecule inhalation therapy, micro-chromatography and spectroscopy, olfactory displays, and material deposition. Using analysis methods with high temporal and spatial resolution, we demonstrate that SAWs stabilize spatially arranged liquid micro-domes atop the generator's surface. Our experiments show that these liquid domes become acoustic resonators with highly fluctuating pressure amplitudes that can even nucleate cavitation bubbles, as supported by analytical modeling. The observed fragmentation of liquid domes indicates the participation of three droplet generation mechanisms, including cavitation and capillary-wave instabilities. During aerosol generation, the cavitation bubbles contribute to the ejection of droplets from the liquid domes and also explain observed microstructural damage patterns on the chip surface eventually caused by cavitation-based erosion.

Subject-specific tribo-contact conditions in total knee replacements: a simulation framework across scales.

Fundamental knowledge about in vivo kinematics and contact conditions at the articulating interfaces of total knee replacements are essential for predicting and optimizing their behavior and durability. However, the prevailing motions and contact stresses in total knee replacements cannot be precisely determined using conventional in vivo measurement methods. In silico modeling, in turn, allows for a prediction of the loads, velocities, deformations, stress, and lubrication conditions across the scales during gait. Within the scope of this paper, we therefore combine musculoskeletal modeling with tribo-contact modeling. In the first step, we compute contact forces and sliding velocities by means of inverse dynamics approach and force-dependent kinematic solver based upon experimental gait data, revealing contact forces during healthy/physiological gait of young subjects. In a second step, the derived data are employed as input data for an elastohydrodynamic model based upon the finite element method full-system approach taking into account elastic deformation, the synovial fluid's hydrodynamics as well as mixed lubrication to predict and discuss the subject-specific pressure and lubrication conditions.

Fully Microfabricated Surface Acoustic Wave Tweezer for Collection of Submicron Particles and Human Blood Cells.

Precise manipulation of (sub)micron particles is key for the preparation, enrichment, and quality control in many biomedical applications. Surface acoustic waves (SAW) hold tremendous promise for manipulation of (bio)particles at the micron to nanoscale ranges. In commonly used SAW tweezers, particle manipulation relies on the direct acoustic radiation effect whose superior performance fades rapidly when progressing from micron to nanoscale particles due to the increasing dominance of a second order mechanism, termed acoustic streaming. Through reproducible and high-precision realization of stiff microchannels to reliably actuate the microchannel cross-section, here we introduce an approach that allows the otherwise competing acoustic streaming to complement the acoustic radiation effect. The synergetic effect of both mechanisms markedly enhances the manipulation of nanoparticles, down to 200 nm particles, even at relatively large wavelength (300 µm). Besides spherical particles ranging from 0.1 to 3 µm, we show collections of cells mixed with different sizes and shapes inherently existing in blood including erythrocytes, leukocytes, and thrombocytes.

Calcium decreases cell wall swelling in sweet cherry fruit.

Swelling of epidermal cell walls decreases cell-to-cell adhesion and increases cracking susceptibility in sweet cherry. Ca is suggested to decrease cracking susceptibility by crosslinking of cell wall components and, possibly, by decreasing swelling. The objective is to test this hypothesis. The effect of Ca on swelling of anticlinal epidermal cell walls was quantified microscopically in vivo using excised skin sections and in vitro using extracted cell walls. After removal of turgor, cell wall thickness increased. Incubation in CaCl2 decreased cell wall thickness up to 3 mM CaCl2. At higher concentrations thickness remained constant. Decreased cell wall swelling in vivo also occurred with other salts of divalent and trivalent cations, but not with those of monovalent cations. Decreased swelling was due to the Ca cation, the anions had no effect. Ca also decreased swelling of cell walls that were already swollen. CaCl2 also decreased swelling of extracted cell walls in vitro. There was no effect on swelling pressure. The effect on swelling increased as the CaCl2 concentration increased. Chlorides of divalent and trivalent cations, but not those of monovalent cations decreased swelling in vitro. The decrease in swelling among the divalent cations was linearly related to the radius of the cation. The results indicate that Ca decreases cracking susceptibility by decreasing swelling.

The structural effect between the output module and chromophore-binding domain is a two-way street via the hairpin extension.

Signal transduction typically starts with either ligand binding or cofactor activation, eventually affecting biological activities in the cell. In red light-sensing phytochromes, isomerization of the bilin chromophore results in regulation of the activity of diverse output modules. During this process, several structural elements and chemical events influence signal propagation. In our study, we have studied the full-length bacteriophytochrome from Deinococcus radiodurans as well as a previously generated optogenetic tool where the native histidine kinase output module has been replaced with an adenylate cyclase. We show that the composition of the output module influences the stability of the hairpin extension. The hairpin, often referred as the PHY tongue, is one of the central structural elements for signal transduction. It extends from a distinct domain establishing close contacts with the chromophore binding site. If the coupling between these interactions is disrupted, the dynamic range of the enzymatic regulation is reduced. Our study highlights the complex conformational properties of the hairpin extension as a bidirectional link between the chromophore-binding site and the output module, as well as functional properties of diverse output modules.

Characterisation of sequence-structure-function space in sensor-effector integrators of phytochrome-regulated diguanylate cyclases.

Understanding the relationship between protein sequence, structure and function is one of the fundamental challenges in biochemistry. A direct correlation, however, is often not trivial since protein dynamics also play an important functional role-especially in signal transduction processes. In a subfamily of bacterial light sensors, phytochrome-activated diguanylate cyclases (PadCs), a characteristic coiled-coil linker element connects photoreceptor and output module, playing an essential role in signal integration. Combining phylogenetic analyses with biochemical characterisations, we were able to show that length and composition of this linker determine sensor-effector function and as such are under considerable evolutionary pressure. The linker length, together with the upstream PHY-specific domain, influences the dynamic range of effector activation and can even cause light-induced enzyme inhibition. We demonstrate phylogenetic clustering according to linker length, and the development of new linker lengths as well as new protein function within linker families. The biochemical characterisation of PadC homologs revealed that the functional coupling of PHY dimer interface and linker element defines signal integration and regulation of output functionality. A small subfamily of PadCs, characterised by a linker length breaking the coiled-coil pattern, shows a markedly different behaviour from other homologs. The effect of the central helical spine on PadC function highlights its essential role in signal integration as well as direct regulation of diguanylate cyclase activity. Appreciation of sensor-effector linkers as integrator elements and their coevolution with sensory modules is a further step towards the use of functionally diverse homologs as building blocks for rationally designed optogenetic tools.

Cord clamping beyond 3 minutes: Neonatal short-term outcomes and maternal postpartum hemorrhage.

BACKGROUND: Delaying cord clamping (CC) for 3-5 minutes reduces iron deficiency and improves neurodevelopment. Data on the effects of CC beyond 3 minutes in relation to short-term neonatal outcomes and maternal risk of postpartum hemorrhage are scarce. METHODS: This was a prospective observational study performed in two delivery departments. Pregnant women with vaginal deliveries were included. Time to CC, estimated postpartum blood loss, and perinatal data were recorded. Spearman's correlation analysis and comparisons between newborns clamped before and after 3 minutes were performed. RESULTS: In total, 904 dyads were included. The mean gestational age ± standard deviation was 40.1 ± 1.2 weeks. CC was performed at a median time of 6 minutes (range 0-23.5). Apgar scores at 5 and 10 minutes were positively correlated with time to CC (correlation coefficient .140, P < .001 and .161, < .001). There was no correlation between CC time and bilirubin level (correlation coefficient .021, P = .54). The median postpartum blood loss was 300 mL (70-2550 mL), with a negative correlation between CC time and postpartum blood loss (-0.115, P = .001). The postpartum blood loss was larger in the group clamped at ≤3 minutes (median [interquartile range] 400 mL [300-600] vs 300 mL [250-450], [P = .003]]. CONCLUSIONS: Umbilical CC times beyond 3 minutes in vaginal deliveries were not associated with negative short-term outcomes in newborns and were associated with a smaller maternal postpartum blood loss. Although CC time as long as 6 minutes could be considered as safe, further research is needed to decide the optimal timing.

Successful long-term management of spasticity in people with multiple sclerosis using a software application: Results from a randomized, controlled, multicenter study.

BACKGROUND AND PURPOSE: Successful long-term treatment of spasticity in people with multiple sclerosis (pwMS) is challenging. We investigated the effects of multidisciplinary inpatient rehabilitation (MIR) and an individualized self-training program delivered by an app on spasticity in pwMS. METHODS: First, we assessed the efficacy of 4-week MIR in ambulatory pwMS (Expanded Disability Status Scale < 7.0) with moderate to severe lower limb spasticity (defined by ≥4 points on the Numeric Rating Scale for spasticity [NRSs]) in a cohort of 115 pwMS at seven rehabilitation centers in Austria. In the case of a clinically relevant improvement in spasticity of ≥20% on the NRSs following MIR (n = 94), pwMS were randomly allocated in a 1:1 ratio to either the newly designed MS-Spasticity App or to a paper-based self-training program for 12 weeks. The primary outcome was change in NRSs (German Clinical Trials Registry DRKS00023960). RESULTS: MIR led to a significant reduction of 2.0 points on the NRSs (95% confidence interval [CI] = 2.5-2.0, p < 0.000). MIR was further associated with a statistically significant improvement in spasticity on the Modified Ashworth Scale, strength, and all mobility outcomes. Following MIR, self-training with the MS-Spasticity App was associated with a sustained positive effect on the NRSs, whereas paper-based self-training led to a worsening in spasticity (median NRSs difference = 1.0, 95% CI = 1.7-0.3, p = 0.009). The MS-Spasticity App was also associated with a significantly better adherence to self-training (95% vs. 72% completion rate, p < 0.001). CONCLUSIONS: In pwMS, MIR is able to significantly improve lower limb spasticity, strength, and mobility. Following MIR, an individually tailored antispasticity program delivered by an app leads to sustained positive long-term management.

Diameter Changes in Traumatic Aortic Injury: Implications for Stent-Graft Sizing.

OBJECTIVES: The aim of this study was to compare aortic diameters from admission computed tomography angiography (CTA) scans to postoperative aortic diameters in patients with traumatic aortic injury (TAI) and evaluate the influence of substantial blood loss on aortic diameter. METHODS: The aortic databases of two tertiary university centers were retrospectively screened for patients with TAI between February 2002 and February 2019. Concomitant organ injuries, bone fractures, blood loss, and clinical outcomes were evaluated. Aortic diameters were measured in CTA upon admission and were compared with the CTA before discharge at three different aortic levels (mid-ascending, 5 cm distal to the end of the stent graft, and at the celiac trunk level). RESULTS: We identified 45 patients, aged 43 (first quartile; third quartile [26; 55]) years with a TAI treated by thoracic endovascular aortic repair. The most frequent cause of TAI was a car accident (n = 24). Concomitant injuries were seen in all but one patient. Bone and pelvic fractures were seen in 40 (89%) and 15 (33%) patients, respectively. Type III aortic injury was present in 25 patients (56%). Increase of aortic diameter after stabilization was +1.7 mm (-0.6 mm; 2.5 mm; p = 0.004) at the mid-ascending aorta, +2.1 mm (0.2 mm; 3.8 mm; p < 0.001) 5 cm distal to the stent graft, and +1.5 mm (0.5 mm; 3.2 mm; p < 0.001) at the celiac trunk level. CONCLUSION: In patients with TAI, the aortic diameter is significantly reduced as compared with the aortic diameter at discharge. The reduction of aortic diameter might be caused by hemorrhagic shock and should be kept in mind for appropriate stent-graft sizing.

Impact of concomitant replacement of the ascending aorta in patients undergoing aortic valve replacement on operative morbidity and mortality.

OBJECTIVES: The aim of this study was to evaluate the impact of concomitant ascending aortic replacement on operative morbidity and mortality in patients undergoing aortic valve replacement (AVR). METHODS: We retrospectively analysed our institutional database for all patients undergoing elective isolated AVR and AVR with concomitant replacement of the ascending aorta between January 2009 and May 2020. Patients undergoing surgery for infective endocarditis or requiring hypothermic circulatory arrest were excluded. A 3:1 propensity matching was performed for 688 patients to compare isolated AVR (120 patients) with AVR + ascending aortic replacement (40 patients). RESULTS: There were significant differences in median cardiopulmonary bypass (CPB) time [92.5 (75-114) vs 118.5 (104-131) min; P < 0.001], median aortic cross-clamp time [65.0 (51.5-78.5) vs 84.5 (77-94) min; P < 0.001] and median intensive care unit stay [1 (1-3) vs 2 (1-6) days; P < 0.01]. There was no significant difference in the use of intraoperative and postoperative blood products, re-exploration for bleeding, postoperative atrial fibrillation, acute renal failure, incidence of stroke, perioperative myocardial infarction and 30-day mortality. CONCLUSIONS: Concomitant replacement of the ascending aorta significantly prolongs CPB and aortic clamp times but does not increase operative morbidity and mortality. Therefore, replacement of a dilated ascending aorta appears to be the most durable and safest treatment option in patients undergoing AVR with an aneurysmatic ascending aorta.

Patterning and control of the nanostructure in plasma thin films with acoustic waves: mechanical vs. electrical polarization effects.

Nanostructuration and 2D patterning of thin films are common strategies to fabricate biomimetic surfaces and components for microfluidic, microelectronic or photonic applications. This work presents the fundamentals of a surface nanotechnology procedure for laterally tailoring the nanostructure and crystalline structure of thin films that are plasma deposited onto acoustically excited piezoelectric substrates. Using magnetron sputtering as plasma technique and TiO2 as case example, it is demonstrated that the deposited films depict a sub-millimetre 2D pattern that, characterized by large lateral differences in nanostructure, density (up to 50%), thickness, and physical properties between porous and dense zones, reproduces the wave features distribution of the generated acoustic waves (AW). Simulation modelling of the AW propagation and deposition experiments carried out without plasma and under alternative experimental conditions reveal that patterning is not driven by the collision of ad-species with mechanically excited lattice atoms of the substrate, but emerges from their interaction with plasma sheath ions locally accelerated by the AW-induced electrical polarization field developed at the substrate surface and growing film. The possibilities of the AW activation as a general approach for the tailored control of nanostructure, pattern size, and properties of thin films are demonstrated through the systematic variation of deposition conditions and the adjustment of AW operating parameters.

The PHY Domain Dimer Interface of Bacteriophytochromes Mediates Cross-talk between Photosensory Modules and Output Domains.

Protein dynamics play a major role for the catalytic function of enzymes, the interaction of protein complexes or signal integration in regulatory proteins. In the context of multi-domain proteins involved in light-regulation of enzymatic effectors, the central role of conformational dynamics is well established. Light activation of sensory modules is followed by long-range signal transduction to different effectors; rather than domino-style structural rearrangements, a complex interplay of functional elements is required to maintain functionality. One family of such sensor-effector systems are red-light-regulated phytochromes that control diguanylate cyclases involved in cyclic-dimeric-GMP formation. Based on structural and functional studies of one prototypic family member, the central role of the coiled-coil sensor-effector linker was established. Interestingly, subfamilies with different linker lengths feature strongly varying biochemical characteristics. The dynamic interplay of the domains involved, however, is presently not understood. Here we show that the PHY domain dimer interface plays an essential role in signal integration, and that a functional coupling with the coiled-coil linker element is crucial. Chimaeras of two biochemically different family members highlight the phytochrome-spanning helical spine as an essential structural element involved in light-dependent upregulation of enzymatic turnover. However, isolated structural elements can frequently not be assigned to individual characteristics, which further emphasises the importance of global conformational dynamics. Our results provide insights into the intricate processes at play during light signal integration and transduction in these photosensory systems and thus provide additional guidelines for a more directed design of novel sensor-effector combinations with potential applications as optogenetic tools.

The scope of flavin-dependent reactions and processes in the model plant Arabidopsis thaliana.

Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are utilized as coenzymes in many biochemical reduction-oxidation reactions owing to the ability of the tricyclic isoalloxazine ring system to employ the oxidized, radical and reduced state. We have analyzed the genome of Arabidopsis thaliana to establish an inventory of genes encoding flavin-dependent enzymes (flavoenzymes) as a basis to explore the range of flavin-dependent biochemical reactions that occur in this model plant. Expectedly, flavoenzymes catalyze many pivotal reactions in primary catabolism, which are connected to the degradation of basic metabolites, such as fatty and amino acids as well as carbohydrates and purines. On the other hand, flavoenzymes play diverse roles in anabolic reactions most notably the biosynthesis of amino acids as well as the biosynthesis of pyrimidines and sterols. Importantly, the role of flavoenzymes goes much beyond these basic reactions and extends into pathways that are equally crucial for plant life, for example the production of natural products. In this context, we outline the participation of flavoenzymes in the biosynthesis and maintenance of cofactors, coenzymes and accessory plant pigments (e. g. carotenoids) as well as phytohormones. Moreover, several multigene families have emerged as important components of plant immunity, for example the family of berberine bridge enzyme-like enzymes, flavin-dependent monooxygenases and NADPH oxidases. Furthermore, the versatility of flavoenzymes is highlighted by their role in reactions leading to tRNA-modifications, chromatin regulation and cellular redox homeostasis. The favorable photochemical properties of the flavin chromophore are exploited by photoreceptors to govern crucial processes of plant adaptation and development. Finally, a sequence- and structure-based approach was undertaken to gain insight into the catalytic role of uncharacterized flavoenzymes indicating their involvement in unknown biochemical reactions and pathways in A. thaliana.

Xylem, phloem and transpiration flows in developing European plums.

Neck shrivel is a quality disorder of European plum (Prunus × domestica L.). It has been suggested that backflow in the xylem (from fruit to tree) could contribute to the incidence of neck shrivel in plum. The objective was to quantify rates of xylem, phloem and of transpiration flow in developing plum fruit. Using linear variable displacement transducers, changes in fruit volume were recorded 1) in un-treated control fruit, 2) in fruit that had their pedicels steam-girdled (phloem interrupted, xylem still functional) and 3) in detached fruit, left in the canopy (xylem and phloem interrupted). Xylem flow rates were occasionally negative in the early hours after sunrise, indicating xylem sap backflow from fruit to tree. Later in the day, xylem flows were positive and generally higher in daytime and lower at night. Significant phloem flow occurred in daytime, but ceased after sunset. During stage II (but not during stage III), the rates of xylem flow and transpiration were variable and closely related to atmospheric vapor pressure deficit. The relative contribution of xylem inflow to total sap inflow averaged 79% during stage II, decreasing to 25% during stage III. In contrast, phloem sap inflow averaged 21% of total sap inflow during stage II, increasing to 75% in stage III. Our results indicate that xylem backflow occurs early in the day. However, xylem backflow rates are considered too low to significantly contribute to the incidence of neck shrivel.

Penetration of sweet cherry skin by 45Ca-salts: pathways and factors.

Calcium is beneficial to sweet cherry physiology. The objective was to investigate factors affecting uptake of Ca into mature sweet cherry fruit through their skins. Penetration of 45Ca-salts was monitored using whole fruit or excised fruit skins mounted in diffusion cells. Penetration of 45CaCl2 into intact fruit and through excised skins increased with time. Sealing the pedicel/fruit junction decreased penetration, but sealing the stylar scar had no effect. There was little difference in permeances of the fruit skin to 45CaCl2, 45Ca(NO3)2, 45Ca-formate, 45Ca-acetate, 45Ca-lactate or 45Ca-propionate. Only 45Ca-heptagluconate penetrated at a slower rate. Increasing temperature markedly increased Ca-penetration. Penetration was most rapid at 35 °C, intermediate at 22 °C and slowest at 12 °C. Increasing relative humidity (RH) from 0, 28, 75 to 100% increased penetration of 45CaCl2, but penetration of 45Ca-formate was restricted to 100% RH. Increasing the RH from 50 to 100% at 96 h after droplet application had no effect on penetration of 45CaCl2, but increased penetration of 45Ca-formate. The results reveal that: (1) the fruit/pedicel junction is a site of preferential Ca-uptake and (2) Ca-penetration is limited by the mobility of the Ca ion in the dried-down droplet residue when the point of deliquescence of the applied salt exceeds the ambient RH.

Lower hemisternotomy: infrequently used but versatile.

BACKGROUND: A lower hemisternotomy is an infrequently used approach in cardiac surgery. This single center report evaluates applicability and clinical outcomes of procedures performed through a lower hemisternotomy. METHODS: The institutional database was reviewed. From 2014 to 2019, 55 consecutive patients had undergone minimally invasive procedures through a lower hemisternotomy (median follow-up 34 months). Demographic as well as outcome data were retrieved from our prospectively maintained institutional database. RESULTS: Performed procedures included mitral and tricuspid repairs, aortic valve replacement as well as coronary artery bypass grafting. The median patient age was 72 years. Out of the 55 patients, 55% were male. Predominantly mitral valve procedures (11 isolated, 30 combined) had been performed. Mitral valve procedures (N.=41) consisted of 36 repairs and 5 replacements. Repair rate for degenerative mitral insufficiency was 97.6%. Median EuroScore II was 3.4% (2.1-6.0). Median cross-clamp time was 67 (44-99) min. Median procedural length was 169 (138-201) min. Reoperation rate for bleeding was 1.8%. Major vascular complications occurred in two patients. Freedom from valve related reoperation was 96.1% during follow-up. Thirty-day mortality and overall mortality during follow-up was 3.6% and 10.9%. CONCLUSIONS: In properly selected cases the lower hemisternotomy allows for a variety of cardiac procedures. It permits central aortic cannulation and a direct vision of intracardiac structures and therefore should be kept in mind as an alternative minimally invasive approach.