ORCID Profile
0000-0002-3395-0059
Current Organisation
University of Adelaide
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Publisher: American Physiological Society
Date: 10-2016
DOI: 10.1152/JAPPLPHYSIOL.00435.2016
Abstract: This study presents a structure-function analysis of the mammalian left ventricle and examines the performance of the cardiac capillary network, mitochondria, and myofibrils at rest and during simulated heavy exercise. Left ventricular external mechanical work rate was calculated from cardiac output and systemic mean arterial blood pressure in resting sheep ( Ovis aries n = 4) and goats ( Capra hircus n = 4) under mild sedation, followed by perfusion-fixation of the left ventricle and quantification of the cardiac capillary-tissue geometry and cardiomyocyte ultrastructure. The investigation was then extended to heavy exercise by increasing cardiac work according to published hemodynamics of sheep and goats performing sustained treadmill exercise. Left ventricular work rate averaged 0.017 W/cm 3 of tissue at rest and was estimated to increase to ∼0.060 W/cm 3 during heavy exercise. According to an oxygen transport model we applied to the left ventricular tissue, we predicted that oxygen consumption increases from 195 nmol O 2 ·s −1 ·cm −3 of tissue at rest to ∼600 nmol O 2 ·s −1 ·cm −3 during heavy exercise, which is within 90% of the oxygen demand rate and consistent with work remaining predominantly aerobic. Mitochondria represent 21-22% of cardiomyocyte volume and consume oxygen at a rate of 1,150 nmol O 2 ·s −1 ·cm −3 of mitochondria at rest and ∼3,600 nmol O 2 ·s −1 ·cm −3 during heavy exercise, which is within 80% of maximum in vitro rates and consistent with mitochondria operating near their functional limits. Myofibrils represent 65–66% of cardiomyocyte volume, and according to a Laplacian model of the left ventricular chamber, generate peak fiber tensions in the range of 50 to 70 kPa at rest and during heavy exercise, which is less than maximum tension of isolated cardiac tissue (120–140 kPa) and is explained by an apparent reserve capacity for tension development built into the left ventricle.
Publisher: The Royal Society
Date: 13-11-2019
Abstract: Brain metabolic rate (MR) is linked mainly to the cost of synaptic activity, so may be a better correlate of cognitive ability than brain size alone. Among primates, the sizes of arterial foramina in recent and fossil skulls can be used to evaluate brain blood flow rate, which is proportional to brain MR. We use this approach to calculate flow rate in the internal carotid arteries ( Q ˙ ICA ) , which supply most of the primate cerebrum. Q ˙ ICA is up to two times higher in recent gorillas, chimpanzees and orangutans compared with 3-million-year-old australopithecine human relatives, which had equal or larger brains. The scaling relationships between Q ˙ ICA and brain volume ( V br ) show exponents of 1.03 across 44 species of living haplorhine primates and 1.41 across 12 species of fossil hominins. Thus, the evolutionary trajectory for brain perfusion is much steeper among ancestral hominins than would be predicted from living primates. Between 4.4-million-year-old Ardipithecus and Homo sapiens , V br increased 4.7-fold, but Q ˙ ICA increased 9.3-fold, indicating an approximate doubling of metabolic intensity of brain tissue. By contrast, Q ˙ ICA is proportional to V br among haplorhine primates, suggesting a constant volume-specific brain MR.
Publisher: The Royal Society
Date: 08-2016
DOI: 10.1098/RSOS.160305
Abstract: The evolution of human cognition has been inferred from anthropological discoveries and estimates of brain size from fossil skulls. A more direct measure of cognition would be cerebral metabolic rate, which is proportional to cerebral blood flow rate (perfusion). The hominin cerebrum is supplied almost exclusively by the internal carotid arteries. The sizes of the foramina that transmitted these vessels in life can be measured in hominin fossil skulls and used to calculate cerebral perfusion rate. Perfusion in 11 species of hominin ancestors, from Australopithecus to archaic Homo sapiens , increases disproportionately when scaled against brain volume (the allometric exponent is 1.41). The high exponent indicates an increase in the metabolic intensity of cerebral tissue in later Homo species, rather than remaining constant (1.0) as expected by a linear increase in neuron number, or decreasing according to Kleiber's Law (0.75). During 3 Myr of hominin evolution, cerebral tissue perfusion increased 1.7-fold, which, when multiplied by a 3.5-fold increase in brain size, indicates a 6.0-fold increase in total cerebral blood flow rate. This is probably associated with increased interneuron connectivity, synaptic activity and cognitive function, which all ultimately depend on cerebral metabolic rate.
Publisher: Springer Science and Business Media LLC
Date: 19-09-2018
DOI: 10.1007/S00360-018-1184-Z
Abstract: Chemical immobilization is necessary for the physiological study of large wild animals. However, the immobilizing drugs can adversely affect the cardiovascular and respiratory systems, yielding data that do not accurately represent the normal, resting state. We hypothesize that these adverse effects can be ameliorated by reversing the immobilizing agent while holding the animal under general anaesthesia. We used habituated sheep Ovis aries (N = 5, 46.9 ± 5.3 kg body mass, mean ± SEM) and goats Capra hircus (N = 4, 27.7 ± 2.8 kg) as ungulate models for large wild animals, and measured their cardiorespiratory function under three conditions: (1) mild sedation (midazolam), as a proxy for the normal resting state, (2) immobilization (etorphine and azaperone), and (3) general anaesthesia (propofol) followed by etorphine antagonism (naltrexone). Cardiac output for both sheep and goats remained unchanged across the three conditions (overall means of 6.2 ± 0.9 and 3.3 ± 0.3 L min
Publisher: Elsevier BV
Date: 03-2019
Publisher: The Company of Biologists
Date: 2019
DOI: 10.1242/JEB.199554
Abstract: This meta-study investigates the relationships between blood flow rate (Q̇ cm3 s−1), wall shear stress (τ dyne cm−2) and lumen radius (ri cm) in 20 named systemic arteries of nine species of mammals, weighing from 23 g mice to 652 kg cows, at rest. In the dataset, derived from 50 studies, lumen radius varies between 3.7 µm in a cremaster artery of a rat to 11.2 mm in the aorta of a human. The 92 logged data points of Q̇ and ri are described by a single second-order polynomial curve with the equation, log Q̇=−0.20 log ri2 +1.91 log ri+1.82. The slope of the curve increases from approximately 2 in the largest arteries to approximately 3 in the smallest ones. Thus, da Vinci's Rule (Q̇ ∝ ri2) applies to the main arteries and Murray's Law (Q̇ ∝ ri3) applies to the microcirculation. A subset of the data, comprising only cephalic arteries in which Q̇ is fairly constant, yielded the allometric power equation, Q̇=155 ri2.49. These empirical equations allow calculation of resting perfusion rates from arterial lumen size alone, without reliance on theoretical models or assumptions on the scaling of wall shear stress in relation to body mass. As expected, Q̇ of in idual named arteries is strongly affected by body mass, however, Q̇ of the common carotid artery from six species (mouse to horse) is also sensitive to differences in whole-body basal metabolic rate, independent of the effect of body mass.
Publisher: The Company of Biologists
Date: 12-2017
DOI: 10.1242/JEB.168187
Abstract: Flying insects have the highest mass-specific metabolic rate of all animals. Oxygen is supplied to the flight muscles by a combination of diffusion and convection along the internal air-filled tubes of the tracheal system. This study measured maximum flight metabolic rate (FMR) during tethered flight in the migratory locust
Publisher: The Royal Society
Date: 09-02-2022
Abstract: This meta-study uses phylogenetic scaling models across more than 30 species, spanning five orders of magnitude in body mass, to show that cardiac capillary numerical density and mitochondrial volume density decrease with body mass raised to the –0.07 ± 0.03 and –0.04 ± 0.01 exponents, respectively. Thus, while an average 10 g mammal has a cardiac capillary density of approximately 4150 mm −2 and a mitochondrial density of 33%, a 1 t mammal has considerably lower corresponding values of 1850 mm −2 and 21%. These similar scaling trajectories suggest quantitative matching for the primary oxygen supply and oxygen consuming structures of the heart, supporting economic design at the cellular level of the oxygen cascade in this aerobic organ. These scaling trajectories are nonetheless somewhat shallower than the exponent of –0.11 calculated for the maximum external mechanical power of the cardiac tissue, under conditions of heavy exercise, when oxygen flow between capillaries and mitochondria is probably fully exploited. This mismatch, if substantiated, implies a declining external mechanical efficiency of the heart with increasing body mass, whereby larger in iduals put more energy in but get less energy out, a scenario with implications for cardiovascular design, aerobic capacity and limits of body size.
Publisher: The Company of Biologists
Date: 2018
DOI: 10.1242/JEB.184713
Abstract: The hearts of smaller mammals tend to operate at higher mass-specific mechanical work rates than those of larger mammals. The ultrastructural characteristics of the heart that allow for such variation in work rate are still largely unknown. We have used perfusion-fixation, transmission electron microscopy and stereology to assess the morphology and anatomical aerobic power density of the heart as a function of body mass across six species of wild African antelope differing by approximately 20-fold in body mass. The survival of wild antelope, as prey animals, depends on competent cardiovascular performance. We found that relative heart mass (g kg
Publisher: The Royal Society
Date: 08-2017
DOI: 10.1098/RSOS.170846
Publisher: Wiley
Date: 17-04-2019
DOI: 10.1111/JOA.12990
Publisher: The Company of Biologists
Date: 2017
DOI: 10.1242/JEB.168625
Abstract: The nutrient artery passes through the nutrient foramen on the shaft of the femur and supplies more than one-half of total blood flow to the bone. Assuming that the size of the nutrient foramen correlates with the size of the nutrient artery, an index of blood flow rate (Qi) can be calculated from nutrient foramen dimensions. Interspecific Qi is proportional to locomotor activity levels in adult mammals, birds and reptiles. However, no studies have yet estimated intraspecific Qi to test for the effects of growth and locomotor development on bone blood flow requirements. This study uses micro-CT and medical CT scanning to measure femoral dimensions and foramen radius to calculate femoral Qi across in-pouch and post-pouch life stages of western grey kangaroos Macropus fuliginosus weighing 5.7 g to 70.5 kg and representing a 12,350-fold range in body mass. A biphasic scaling relationship for Qi on body mass is evident (breakpoint at ca. 1–5 kg body mass right before permanent pouch exit), with a steep exponent of 0.96±0.09 (95% CI) across the in-pouch life stage and an exponent of –0.59±0.90 across the post-pouch life stage. In-pouch joeys show Qi values 50 to 100-times higher than adult diprotodont marsupials of the same body mass, but gradually converge with them as post-pouch adults. Bone modelling during growth appears to be the main determinant for femoral bone blood flow during in-pouch development, whereas bone remodeling for micro-fracture repair due to locomotion gradually becomes the main determinant when kangaroos leave the pouch and become more active.
Publisher: Wiley
Date: 27-11-2018
DOI: 10.1111/PCE.13097
Abstract: The respiration rate of the thermogenic inflorescences of Japanese skunk cabbage Symplocarpus renifolius can reach 300 nmol s
Publisher: Cambridge University Press (CUP)
Date: 13-09-2023
DOI: 10.1017/PAB.2023.24
Publisher: Cambridge University Press (CUP)
Date: 02-05-2023
DOI: 10.1017/PAB.2023.14
Abstract: Foramina of bones are beginning to yield more information about metabolic rates and activity levels of living and extinct species. This study investigates the relationship between estimated blood flow rate to the femur and body mass among cursorial birds extending back to the Late Cretaceous. Data from fossil foramina are compared with those of extant species, revealing similar scaling relationships for all cursorial birds and supporting crown bird–like terrestrial locomotor activity. Because the perfusion rate in long bones of birds is related to the metabolic cost of microfracture repair due to stresses applied during locomotion, as it is in mammals, this study estimates absolute blood flow rates from sizes of nutrient foramina located on the femur shafts. After differences in body mass and locomotor behaviors are accounted for, femoral bone blood flow rates in extinct species are similar to those of extant cursorial birds. Femoral robustness is generally greater in aquatic flightless birds than in terrestrial flightless and ground-dwelling flighted birds, suggesting that the morphology is shaped by life-history demands. Femoral robustness also increases in larger cursorial bird taxa, probably associated with their weight redistribution following evolutionary loss of the tail, which purportedly constrains femur length, aligns it more horizontally, and necessitates increased robustness in larger species.
Publisher: Wiley
Date: 11-11-2020
DOI: 10.1111/JOA.13119
Publisher: The Royal Society
Date: 04-09-2019
DOI: 10.1098/RSOS.191099
Abstract: Novel phenotypes are often linked to major ecological transitions during evolution. Here, we describe for the first time an unusual network of large blood vessels in the head of the sea snake Hydrophis cyanocinctus . MicroCT imaging and histology reveal an intricate modified cephalic vascular network (MCVN) that underlies a broad area of skin between the snout and the roof of the head. It is mostly composed of large veins and sinuses and converges posterodorsally into a large vein (sometimes paired) that penetrates the skull through the parietal bone. Endocranially, this blood vessel leads into the dorsal cerebral sinus, and from there, a pair of large veins depart ventrally to enter the brain. We compare the condition observed in H. cyanocinctus with that of other elapids and discuss the possible functions of this unusual vascular network. Sea snakes have low oxygen partial pressure in their arterial blood that facilitates cutaneous respiration, potentially limiting the availability of oxygen to the brain. We conclude that this novel vascular structure draining directly to the brain is a further elaboration of the sea snakes' cutaneous respiratory anatomy, the most likely function of which is to provide the brain with an additional supply of oxygen.
Publisher: The Company of Biologists
Date: 15-08-2021
DOI: 10.1242/JEB.242597
Abstract: The metabolic rate of vertebrate bone tissue is related to bone growth, repair and homeostasis, which are all dependent on life stage. Bone metabolic rate is difficult to measure directly, but absolute blood flow rate () should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate () by measuring nutrient foramen sizes of long bones. is assumed to be proportional to however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific cardiac output was 338±38 ml min−1 kg−1, and the two femora received 0.63±0.10% of this. Laying hens had higher wet bone mass-specific to femora (0.23±0.09 ml min−1 g−1) than the non-laying hens (0.12±0.06 ml min−1 g−1) and roosters (0.14±0.04 ml min−1 g−1), presumably associated with higher bone calcium mobilization during eggshell production. Estimated metabolic rate of femoral bone was 0.019 ml O2 min−1 g−1. Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius (r), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min−1 mm−1. Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing.
Publisher: Wiley
Date: 12-11-2020
DOI: 10.1111/JOA.13106
Publisher: Wiley
Date: 10-12-2021
DOI: 10.1111/BRV.12822
Abstract: The whole‐body (tachymetabolic) endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. That assumption is consistent with current acceptance that the non‐shivering thermogenesis (NST) component of regulatory body heat originates differently in each group: from skeletal muscle in birds and from brown adipose tissue (BAT) in mammals. However, BAT is absent in monotremes, marsupials, and many eutherians, all whole‐body endotherms. Indeed, recent research implies that BAT‐driven NST originated more recently and that the biochemical processes driving muscle NST in birds, many modern mammals and the ancestors of both may be similar, deriving from controlled ‘slippage’ of Ca 2+ from the sarcoplasmic reticulum Ca 2+ ‐ATPase (SERCA) in skeletal muscle, similar to a process seen in some fishes. This similarity prompted our realisation that the capacity for whole‐body endothermy could even have pre‐dated the ergence of Amniota into Synapsida and Sauropsida, leading us to hypothesise the homology of whole‐body endothermy in birds and mammals, in contrast to the current assumption of their independent (convergent) evolution. To explore the extent of similarity between muscle NST in mammals and birds we undertook a detailed review of these processes and their control in each group. We found considerable but not complete similarity between them: in extant mammals the ‘slippage’ is controlled by the protein sarcolipin (SLN), in birds the SLN is slightly different structurally and its role in NST is not yet proved. However, considering the multi‐millions of years since the separation of synapsids and diapsids, we consider that the similarity between NST production in birds and mammals is consistent with their whole‐body endothermy being homologous. If so, we should expect to find evidence for it much earlier and more widespread among extinct amniotes than is currently recognised. Accordingly, we conducted an extensive survey of the palaeontological literature using established proxies. Fossil bone histology reveals evidence of sustained rapid growth rates indicating tachymetabolism. Large body size and erect stature indicate high systemic arterial blood pressures and four‐chambered hearts, characteristic of tachymetabolism. Large nutrient foramina in long bones are indicative of high bone perfusion for rapid somatic growth and for repair of microfractures caused by intense locomotion. Obligate bipedality appeared early and only in whole‐body endotherms. Isotopic profiles of fossil material indicate endothermic levels of body temperature. These proxies led us to compelling evidence for the widespread occurrence of whole‐body endothermy among numerous extinct synapsids and sauropsids, and very early in each clade's family tree. These results are consistent with and support our hypothesis that tachymetabolic endothermy is plesiomorphic in Amniota. A hypothetical structure for the heart of the earliest endothermic amniotes is proposed. We conclude that there is strong evidence for whole‐body endothermy being ancient and widespread among amniotes and that the similarity of biochemical processes driving muscle NST in extant birds and mammals strengthens the case for its plesiomorphy.
Publisher: The Company of Biologists
Date: 07-2016
DOI: 10.1242/JEB.140988
Publisher: Wiley
Date: 17-08-2022
DOI: 10.1111/JOA.13535
Abstract: If arteries penetrate bones through foramina, regional artery blood flow rates can be estimated from the foramen sizes. Femoral bone blood flow rates estimated from nutrient foramen sizes were previously not absolute, but only a relative blood flow index ( Q i ), because the size relationship between the foramen and the occupying artery was unknown. The current study used vascular contrast and micro‐computerized tomographic scanning to investigate femoral nutrient foramen and nutrient artery sizes in three groups of sub‐adult chickens (non‐laying hens, laying hens, and roosters) of similar ages. The results indicate that the cross‐sectional area of the nutrient artery lumen occupies approximately 20.2 ± 4.1% of the foramen for femora with only one foramen. Artery lumen size is significantly correlated with foramen size. Vascular contrast imaging is capable of estimating blood flow rates through nutrient arteries, as blood flow rates estimated from artery lumen casts are similar to blood flow rates measured by infusion of fluorescent‐labeled microspheres. Laying hens tend to have higher nutrient artery perfusion rates than non‐laying hens, probably due to extra oxygen and calcium requirements for eggshell production, although the calculated blood flow difference was not statistically significant. Histological embedding and sectioning along with vascular contrast imaging reveal variable nutrient foramen morphology and nutrient artery location among femora with more than one nutrient foramen.
Publisher: Springer Science and Business Media LLC
Date: 24-04-2021
DOI: 10.1007/S00360-021-01372-Y
Abstract: Respiratory gas exchange in avian embryos progresses through three stages inside the egg. During the first 3-5 days of incubation, the chicken embryo has no specialised respiratory organs and is not reliant on blood circulation. At this stage, it obtains oxygen mainly by diffusion through the eggshell, albumen, amniotic fluid and embryonic tissues. In the second stage, gas exchange relies on diffusion through the shell in the gas phase and convection by blood circulation through the chorioallantoic membrane and body. Day 19 starts the third stage, the transition from chorioallantoic to pulmonary gas exchange, which is complete when the chick hatches on day 20. Metabolism is thought to be aerobic throughout incubation, although the early embryo is covered by fluids (albumen and amniotic fluid) which would greatly resist oxygen diffusion. This study uses fibre-optic sensors to measure oxygen partial pressure (PO
Publisher: Wiley
Date: 16-10-2017
DOI: 10.1111/JOA.12715
Location: United States of America
No related grants have been discovered for Roger Seymour.