Tuning of the ocular vestibular evoked myogenic potential to bone-conducted sound stimulation

Ocular vestibular evoked myogenic potentials (oVEMPs) are a recently described clinical measure of the vestibulo-ocular reflex. Studies demonstrating differences in frequency tuning between air-conducted and bone-conducted (BC) oVEMPs suggest a separate vestibular (otolith) origin for each stimulus modality. In this study, 10 healthy subjects were stimulated with BC stimuli using a hand-held minishaker. Frequencies were tested in the range of 50-1,000 Hz using both a constant-force and constant-acceleration method. Subjects were stimulated at the mastoid process and the forehead. For constant-force stimulation at both sites, maximum acceleration occurred around 100 Hz, in differing axes. Both forms of stimulation had low-frequency peaks of oVEMP amplitudes (constant force: mastoid, 80-150 Hz; forehead, 50-125 Hz; constant acceleration: mastoid, 100-200 Hz; forehead, 80-150 Hz), for both sites of application, despite differences in the magnitude and direction of evoked head acceleration. For mastoid stimulation, ocular responses changed from out of phase to in phase for 400 Hz and above. Our results demonstrate that BC stimuli show tuning around 100 Hz, independent of stimulus site, that is not due to skull properties. The findings are consistent with an effect on a receptor with a resonance around 100 Hz, most likely the utricle.     

Climate and the inter‐annual variability of fire in southern Africa: a meta‐analysis using long‐term field data and satellite‐derived burnt area data

Aim This study investigates inter‐annual variability in burnt area in southern Africa and the extent to which climate is responsible for this variation. We compare data from long‐term field sites across the region with remotely sensed burnt area data to test whether it is possible to develop a general model. Location Africa south of the equator. Methods Linear mixed effects models were used to determine the effect of rainfall, seasonality and fire weather in driving variation in fire extent between years, and to test whether the effect of these variables changes across the subcontinent and in areas more and less impacted by human activities. Results A simple model including rainfall and seasonality explained 40% of the variance in burnt area between years across 10 different protected areas on the subcontinent, but this model, when applied regionally, indicated that climate had less impact on year‐to‐year variation in burnt area than would be expected. It was possible to demonstrate that the relative importance of rainfall and seasonality changed as one moved from dry to wetter systems, but most noticeable was the reduction in climatically driven variability of fire outside protected areas. Inter‐annual variability is associated with the occurrence of large fires, and large fires are only found in areas with low human impact. Main conclusions This research gives the first data‐driven analysis of fire–climate interactions in southern Africa. The regional analysis shows that human impact on fire regimes is substantial and acts to limit the effect of climate in driving variation between years. This is in contrast to patterns in protected areas, where variation in accumulated rainfall and the length of the dry season influence the annual area burnt. Global models which assume strong links between fire and climate need to be re‐assessed in systems with high human impact.     

Optimal protamine dosing after cardiopulmonary bypass: The PRODOSE adaptive randomised controlled trial

BackgroundThe dose of protamine required following cardiopulmonary bypass (CPB) is often determined by the dose of heparin required pre-CPB, expressed as a fixed ratio. Dosing based on mathematical models of heparin clearance is postulated to improve protamine dosing precision and coagulation. We hypothesised that protamine dosing based on a 2-compartment model would improve thromboelastography (TEG) parameters and reduce the dose of protamine administered, relative to a fixed ratio.Methods and findingsWe undertook a 2-stage, adaptive randomised controlled trial, allocating 228 participants to receive protamine dosed according to a mathematical model of heparin clearance or a fixed ratio of 1 mg of protamine for every 100 IU of heparin required to establish anticoagulation pre-CPB. A planned, blinded interim analysis was undertaken after the recruitment of 50% of the study cohort. Following this, the randomisation ratio was adapted from 1:1 to 1:1.33 to increase recruitment to the superior arm while maintaining study power. At the conclusion of trial recruitment, we had randomised 121 patients to the intervention arm and 107 patients to the control arm. The primary endpoint was kaolin TEG r-time measured 3 minutes after protamine administration at the end of CPB. Secondary endpoints included ratio of kaolin TEG r-time pre-CPB to the same metric following protamine administration, requirement for allogeneic red cell transfusion, intercostal catheter drainage at 4 hours postoperatively, and the requirement for reoperation due to bleeding. The trial was listed on a clinical trial registry (ClinicalTrials.gov Identifier: {"type":"clinical-trial","attrs":{"text":"NCT03532594","term_id":"NCT03532594"}}NCT03532594).Participants were recruited between April 2018 and August 2019. Those in the intervention/model group had a shorter mean kaolin r-time (6.58 [SD 2.50] vs. 8.08 [SD 3.98] minutes; p = 0.0016) post-CPB. The post-protamine thromboelastogram of the model group was closer to pre-CPB parameters (median pre-CPB to post-protamine kaolin r-time ratio 0.96 [IQR 0.78–1.14] vs. 0.75 [IQR 0.57–0.99]; p < 0.001). We found no evidence of a difference in median mediastinal/pleural drainage at 4 hours postoperatively (140 [IQR 75–245] vs. 135 [IQR 94–222] mL; p = 0.85) or requirement (as a binary outcome) for packed red blood cell transfusion at 24 hours postoperatively (19 [15.8%] vs. 14 [13.1%] p = 0.69). Those in the model group had a lower median protamine dose (180 [IQR 160–210] vs. 280 [IQR 250–300] mg; p < 0.001).Important limitations of this study include an unblinded design and lack of generalisability to certain populations deliberately excluded from the study (specifically children, patients with a total body weight >120 kg, and patients requiring therapeutic hypothermia to <28°C).ConclusionsUsing a mathematical model to guide protamine dosing in patients following CPB improved TEG r-time and reduced the dose administered relative to a fixed ratio. No differences were detected in postoperative mediastinal/pleural drainage or red blood cell transfusion requirement in our cohort of low-risk patients.Trial registrationClinicalTrials.gov Unique identifier {"type":"clinical-trial","attrs":{"text":"NCT03532594","term_id":"NCT03532594"}}NCT03532594.

Lachlan Miles and co-workers report on a randomized controlled trial seeking to optimise protamine dosing after cardiopulmonary bypass.     

Age and growth of longnose trevally (Carangoides chrysophrys) in the Arabian Sea

The ages and growth of longnose trevally (Carangoides chrysophrys), caught in the northwest Arabian Sea between April 2005 and September 2006, were investigated. Age and growth of 336 fish specimens were determined using sectioned sagittae otoliths. Annual opaque growth rings were formed between December and March, with the majority being laid down in February and March, coinciding with the spawning period and high water temperatures. Marginal zone or edge analysis was used to validate the annual deposition of the opaque zone in the otoliths. This species showed large variations in length‐at‐age, suggesting large growth variations among individuals of the same cohort. The estimated von Bertalanffy growth model differed significantly between the sexes, with males having larger mean lengths at age and reaching a larger asymptotic size. The von Bertalanffy growth models were TL (cm) = 73.34[1‐exp (?0.25 (t + 1.21))] and TL(cm) = 73.26[1‐exp (?0.24 (t + 1.20))] for males and females, respectively.