The effects of probe placement on measured flow velocity in transcranial Doppler ultrasound imaging in-vitro and in-vivo experiments

The measurement of the blood flow in the middle cerebral artery (MCA) using transcranial Doppler ultrasound (US) imaging is clinically relevant for the study of cerebral autoregulation. Especially in the aging population, impairement of the autoregulation may coincide or relate to loss of perfusion and consequently loss of brain function. The cerebral autoregulation can be assessed by relating the blood pressure to the blood flow in the brain. Doppler US is a widely used, non-invasive method to measure the blood flow in the MCA. However, Doppler flow imaging is known to produce results that are dependent of the operator. The angle of the probe insonation with respect to the centerline of the blood vessel is a well known factor for output variability. In patients also the skull must be traversed and the MCA must be detected, influencing the US signal intensity. In this contribution we report two studies. We describe first an in-vitro setup to study the Doppler flow in a situation where the ground truth is known. Secondly, we report on a study with healthy volunteers where the effects of small probe displacements on the flow velocity signals are investigated. For the latter purpose, a special probe holder was designed to control the experiment

Transfer function analysis for the assessment of cerebral autoregulation using spontaneous oscillations in blood pressure and cerebral blood flow

Cerebral autoregulation (CA) is a key mechanism to protect the brain against excessive fluctuations in blood pressure (BP) and maintain cerebral blood flow. Analyzing the relationship between spontaneous BP and cerebral blood flow velocity (CBFV) using transfer function analysis is a widely used technique to quantify CA in a non-invasive way. The objective of this review was to provide an overview of transfer function techniques used in the assessment of CA.\ud \ud 113 publications were included. This literature showed that there is no gold standard for the execution and implementation of the transfer function. There is a high diversity in settings and criteria used for transfer function analysis. Notable is also the high number of studies which report little on the settings.\ud \ud This disparity makes it difficult to replicate or compare the results of the different studies and further hinders the opportunity to make a distinction between intact and impaired CA in different patient groups.\ud \ud More research on the effects of different implementation techniques on CA results and optimization of the transfer function analysis is urgently needed. Furthermore, international guidelines should be created to inform the minimal description of the applied technique and the interpretation of transfer function outcomes in scientific research

Transfer function analysis of dynamic cerebral autoregulation: A white paper from the International Cerebral Autoregulation Research Network

Cerebral autoregulation is the intrinsic ability of the brain to maintain adequate cerebral perfusion in the presence of blood pressure changes. A large number of methods to assess the quality of cerebral autoregulation have been proposed over the last 30 years. However, no single method has been universally accepted as a gold standard. Therefore, the choice of which method to employ to quantify cerebral autoregulation remains a matter of personal choice. Nevertheless, given the concept that cerebral autoregulation represents the dynamic relationship between blood pressure (stimulus or input) and cerebral blood flow (response or output), transfer function analysis became the most popular approach adopted in studies based on spontaneous fluctuations of blood pressure. Despite its sound theoretical background, the literature shows considerable variation in implementation of transfer function analysis in practice, which has limited comparisons between studies and hindered progress towards clinical application. Therefore, the purpose of the present white paper is to improve standardisation of parameters and settings adopted for application of transfer function analysis in studies of dynamic cerebral autoregulation. The development of these recommendations was initiated by (but not confined to) the Cerebral Autoregulation Research Network (CARNet - www.car-net.org)

Cardicola beveridgei n. sp. (Digenea: Aporocotylidae) from the mangrove jack, Lutjanus argentimaculatus (Perciformes: Lutjanidae), and C. bullardi n. sp. from the Australian spotted mackerel, Scomberomorus munroi (Perciformes: Scombridae), from the northern Great Barrier Reef

Cardicola Short, 1953 is a genus of the Aporocotylidae Odhner, 1912 (Digenea), with 25 currently recognised species described from 32 species of Perciformes and Mugiliformes fishes around the world, including eight species from the Great Barrier Reef. Here, we describe two new species from this region, namely Cardicola beveridgei n. sp. from the ventricle and atrium of the mangrove jack, Lutjanus argentimaculatus (Forsskål) (Perciformes: Lutjanidae), and Cardicola bullardi n. sp. from the ventricle of the Australian spotted mackerel, Scomberomorus munroi Collette & Russo (Perciformes: Scombridae), from off Lizard Island, Queensland, Australia. These two new species are most easily distinguished from the 25 current members of Cardicola in having the combination of i) a spinous oral sucker, ii) an anteriorly intercaecal ovary, iii) a uterus that extends anteriorly from the oötype, iv) the number of spines per ventrolateral transverse row, and in v) body size and the length/width ratio, vi) the oesophagus and caecal length(s) relative to body total length, vii) the length of the posterior caeca relative to the anterior pair, viii) the testis length/width ratio and its total size relative to that of the body, ix) the postovarian field as a percentage of body length, and x) egg size. In addition, C. beveridgei n. sp. is further differentiated by possessing a female genital pore that opens anterodextral to the male pore while C. bullardi n. sp. differs further in possessing a testis that is almost entirely intercaecal and does not extend anteriorly to the level of the intestinal bifurcation. Employing genetic analysis of ITS2 rDNA sequence data, representing these species and a further 13 recognised and three putative species of Cardicola, we were able to unequivocally confirm these specimens as distinct (9–22% different over 420 nucleotide positions). Distance analysis of ITS2 showed that i) species of Cardicola from the Siganidae formed a monophyletic clade, to the exclusion of other Cardicola species reported from the Scombridae, Sparidae, Lutjanidae and Chaetodontidae, ii) a general phylogenetic isolation exists between the species of Cardicola reported from scombrid fishes, and iii) C. beveridgei n. sp. and Cardicola milleri Nolan & Cribb, 2006 from lutjanids and Cardicola chaetodontis Yamaguti, 1970 from chaetodontids are phylogenetically close, despite the evolutionary remoteness between the host groups and their highly disparate biology. Given the likelihood of many additional species being attributed to Cardicola, we predict that continued molecular analyses will indicate that this genus will prove to incorporate a series of radiations in association with particular fish taxa as well as evidence of host-switching. (Nucleotide sequences reported in this paper are available in the GenBank database under accession no. KF752497)