Biomedical subjects

D R Carrier

Publications and source records attributed to D R Carrier.

22 records · Page 2Linked to original sources

PubMed1992

Wing bone stresses in free flying bats and the evolution of skeletal design for flight.

The primary mechanical functions of limb bones are to resist deformation, and hence provide stiff levers against which muscles can act, and to be sufficiently strong to prevent breaking under static or dynamic loads which arise from normal and accidental activities. If bones perform these functions with a minimum amount of material, the energetic costs associated with building, maintaining and transporting the skeleton will be minimized. Appropriate skeletal architecture for minimizing mass while maximizing strength depends on forces imposed on structural elements. In the evolutionary acquisition of flight in the bat lineage, the forelimb skeleton must have come to experience locomotor-forces that differed from those engendered by the terrestrial locomotion of non-flying bat relatives. Here we successfully measure in vivo strain on the wing bones of flying mammals. Our data demonstrate that torsion and shear are unique and crucial features of skeletal biomechanics during flight, and suggest that the evolution of skeletal design in bats and other flying vertebrates may be driven by the need to resist these loads.

Animals↗

PubMed1989

Ventilatory action of the hypaxial muscles of the lizard Iguana iguana: a function of slow muscle.

Patterns of muscle activity during lung ventilation, patterns of innervation and some contractile properties were measured in the hypaxial muscles of green iguanas. Electromyography shows that only four hypaxial muscles are involved in breathing. Expiration is produced by two deep hypaxial muscles, the transversalis and the retrahentes costarum. Inspiration is produced by the external and internal intercostal muscles. Although the two intercostal muscles are the main agonists of inspiration, neither is involved in expiration. This conflicts with the widely held notion that the different fibre orientations of the two intercostal muscles determine their ventilatory action. Several observations indicate that ventilation is produced by slow (i.e. nontwitch) fibres of these four muscles. First, electromyographic (EMG) activity recorded from these muscles during ventilation has an unusually low range of frequencies (less than 100 Hz). Such low-frequency signals have been suggested to be characteristic of muscle fibres that do not propagate action potentials (i.e. slow fibres). Second, during inspiration, EMG activity is restricted to he medical sides of the two intercostal muscles. Muscle fibres from this region have multiple motor endplates and exhibit tonic contraction when immersed in saline solutions of high potassium content. Like the intercostals, the transversalis and retrahentes costarum muscles also contain fibres with multiple motor endplates. Thus, although breathing is a phasic activity, it is produced by tonic (i.e. slow) muscle fibres. The intercostal muscles are also involved in postural and locomotor movements of the trunk. However, such movements employ twitch as well as slow fibres of the intercostal muscles.

Animals↗

PubMed1987

Lung ventilation during walking and running in four species of lizards.

The relationship between locomotion and aspiration breathing was investigated in the lizards Iguana iguana, Ctenosaura similis, Varanus exanthematicus and Varanus salvator, and the quail Coturnix coturnix. Respiratory air-flow during walking and running on a 7.3 m track or on a treadmill was measured with a bidirectional flow meter attached to one nostril. In all four species of lizards, lung ventilation drops markedly during locomotion. Tidal volume decreases as speed increases, often by more than an order of magnitude at intermediate and high speeds, and the rate of decline is most pronounced at the lowest speeds. Minute ventilation peaks at or before the reported maximum aerobic speed and decreases at higher speeds. In contrast, quail increase their minute ventilation during running. Several observations support the hypothesis that the aspiration of lizards is mechanically constrained by locomotion which employs lateral vertebral bending and sprawling posture. 1. Minute ventilation decreases as running speed increases. 2. Disruption of ventilation is temporally coincident with the locomotor movements. 3. During running the largest breaths correspond to the strides of longest duration or to brief pauses in the locomotor movements.

Aerobiosis↗

PubMed1983

Running and breathing in mammals.

Mechanical constraints appear to require that locomotion and breathing be synchronized in running mammals. Phase locking of limb and respiratory frequency has now been recorded during treadmill running in jackrabbits and during locomotion on solid ground in dogs, horses, and humans. Quadrupedal species normally synchronize the locomotor and respiratory cycles at a constant ratio of 1:1 (strides per breath) in both the trot and gallop. Human runners differ from quadrupeds in that while running they employ several phase-locked patterns (4:1, 3:1, 2:1, 1:1, 5:2, and 3:2), although a 2:1 coupling ratio appears to be favored. Even though the evolution of bipedal gait has reduced the mechanical constraints on respiration in man, thereby permitting greater flexibility in breathing pattern, it has seemingly not eliminated the need for the synchronization of respiration and body motion during sustained running. Flying birds have independently achieved phase-locked locomotor and respiratory cycles. This hints that strict locomotor-respiratory coupling may be a vital factor in the sustained aerobic exercise of endothermic vertebrates, especially those in which the stresses of locomotion tend to deform the thoracic complex.

Animals↗