Oxygen transport and acid-base balance during exercise in the tammar wallaby

Assessment of the hemorheological profile of koala and echidna

Koala, a marsupial, and echidna, a monotreme, are mammals native to Australia. Blood viscosity (62.5-1250s(-1)), red blood cell (RBC) deformability, RBC aggregation, aggregability and surface charge, and hematological parameters were measured in blood samples from six koalas and six echidnas and compared to adult human blood. Koala had the largest RBC mean cell volume (107.7+/-2.6fl) compared to echidna (81.3+/-2.6fl) and humans (88.4+/-1.2fl). Echidna blood exhibited the highest viscosity over the entire range of shear rates. Echidna RBC were significantly less deformable than koala RBC but more deformable than human RBC. Echidna RBC had significantly lower aggregability (i.e., aggregation in standardized dextran medium) than koala or human RBC, while aggregation in autologous plasma was similar for the three species. Erythrocyte surface charge as indexed by RBC electrophoretic mobility was similar for human and echidna cells but was 40% lower for koala RBC. Data obtained during this preliminary study indicate that koala and echidna have distinct hemorheological characteristics; investigation of these properties may reveal patterns relevant to specific behavioral and physiological features of these animals.

Oxygen uptake (VO2) kinetics in different species: a brief review

When a human begins to move or locomote, the energetic demands of its skeletal muscles increase abruptly and the oxygen (O2) transport system responds to deliver increased amounts of O2to the respiring mitochondria. It is intuitively reasonable that the rapidity with which O2transport can be increased to and utilized by (VO2) the contracting muscles would be greater in those species with a higher maximal VO2capacity (i.e., VO2max). This review explores the relationship between VO2maxand VO2dynamics or kinetics at across a range of species selected, in part, for their disparate VO2maxcapacities. In healthy humans there is compelling evidence that the speed of the VO2kinetics at the onset of exercise is limited by an oxidative enzyme inertia within the exercising muscles rather than by VO2delivery to those muscles. This appears true also for the horse and dog but possibly not for a certain species of frog. Whereas there is a significant correlation between VO2maxand the speed of VO2kinetics among different species, it is possible to identify species or individuals within a species that exhibit widely disparate mass-specific VO2maxcapacities but similar VO2kinetics (i.e., superlative human athlete and horse).

Partitioning locomotor energy use among and within muscles Muscle blood flow as a measure of muscle oxygen consumption

Linking the mechanics and energetics of locomotion in vertebrates has been hampered by a lack of information regarding the energy use of individual skeletal muscles in vivo. Here, we present a review of the available data concerning the relationship between the rates of skeletal muscle blood flow and oxygen consumption(V̇O2). In active muscle, during aerobically supported exercise, there is a linear relationship between these variables, irrespective of the muscle fiber type and intensity of exercise through most of the aerobic exercise range. We conclude that the rate of blood flow is the best available indicator of aerobic metabolic rate in multiple individual muscles or regions of muscles during locomotion. The practical considerations of using the injectable microsphere technique to measure muscle blood flow in this context are discussed.

Blood flow in guinea fowl Numida meleagris as an indicator of energy expenditure by individual muscles during walking and running

Running and walking are mechanically complex activities. Leg muscles must exert forces to support weight and provide stability, do work to accelerate the limbs and body centre of mass, and absorb work to act as brakes. Current understanding of energy use during legged locomotion has been limited by the lack of measurements of energy use by individual muscles. Our study is based on the correlation between blood flow and aerobic energy expenditure in active skeletal muscle during locomotion. This correlation is strongly supported by the available evidence concerning control of blood flow to active muscle, and the relationship between blood flow and the rate of muscle oxygen consumption. We used injectable microspheres to measure the blood flow to the hind-limb muscles, and other body tissues, in guinea fowl (Numida meleagris) at rest, and across a range of walking and running speeds. Combined with data concerning the various mechanical functions of the leg muscles, this approach has enabled the first direct estimates of the energetic costs of some of these functions. Cardiac output increased from 350 ml min(-1) at rest, to 1700 ml min(-1) at a running speed ( approximately 2.6 m s(-1)) eliciting a of 90% of . The increase in cardiac output was achieved via approximately equal factorial increases in heart rate and stroke volume. Approximately 90% of the increased cardiac output was directed to the active muscles of the hind limbs, without redistribution of blood flow from the viscera. Values of mass-specific blood flow to the ventricles, approximately 15 ml min(-1) g(-1), and one of the hind-limb muscles, approximately 9 ml min(-1) g(-1), were the highest yet recorded for blood flow to active muscle. The patterns of increasing blood flow with increasing speed varied greatly among different muscles. The increases in flow correlated with the likely fibre type distribution of the muscles. Muscles expected to have many high-oxidative fibres preferentially increased flow at low exercise intensities. We estimated substantial energetic costs associated with swinging the limbs, co-contraction to stabilize the knee and work production by the hind-limb muscles. Our data provide a basis for evaluating hypotheses relating the mechanics and energetics of legged locomotion.