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PubMed2004

Interaction between the canine diaphragm and intercostal muscles in lung expansion.

Changes in intrathoracic pressure produced by the various inspiratory intercostals are essentially additive, but the interaction between these muscles and the diaphragm remains uncertain. In the present study, this interaction was assessed by measuring the changes in airway opening (DeltaPao) or transpulmonary pressure (DeltaPtp) in vagotomized, phrenicotomized dogs during spontaneous inspiration (isolated intercostal contraction), during isolated rectangular or ramp stimulation of the peripheral ends of the transected C(5) phrenic nerve roots (isolated diaphragm contraction), and during spontaneous inspiration with superimposed phrenic nerve stimulation (combined diaphragm-intercostal contraction). With the endotracheal tube occluded at functional residual capacity, DeltaPao during combined diaphragm-intercostal contraction was nearly equal to the sum of the DeltaPao produced by the two muscle groups contracting individually. However, when the endotracheal tube was kept open, DeltaPtp during combined contraction was 123% of the sum of the individual DeltaPtp (P < 0.001). The increase in lung volume during combined contraction was also 109% of the sum of the individual volume increases (P < 0.02). Abdominal pressure during combined contraction was invariably lower than during isolated diaphragm contraction. It is concluded, therefore, that the canine diaphragm and intercostal muscles act synergistically during lung expansion and that this synergism is primarily due to the fact that the intercostal muscles reduce shortening of the diaphragm. When the lung is maintained at functional residual capacity, however, the synergism is obscured because the greater stiffness of the rib cage during diaphragm contraction enhances the DeltaPao produced by the isolated diaphragm and reduces the DeltaPao produced by the intercostal muscles.

Animals↗
PubMed1993

Ramification of the intercostal nerves in the rhesus monkey (Macaca mulatta) with special reference to the innervation of the intercostal muscles.

Detailed dissection was performed on the ventral primary rami from the first thoracic to the second lumbar nerves in order to obtain more comprehensive data of the ramification of the intercostal nerves in the rhesus monkey. The nerves to the intercostalis intimus and internus and the obliquus externus abdominis tended to arise as a common trunk from the main intercostal nerve. A comparison of the intercostal nerve ramification with that in man is included.

Animals↗
PubMed1987

Effects of transient hypoxia on internal intercostal muscle activity in vagotomized rabbits.

The effects of transient hypoxia on the responses of internal intercostal (IIC) muscle activity before and after surgical denervation of the carotid sinus nerves were studied in the bilaterally vagotomized rabbits. Bilateral vagotomy caused a complete inhibition of IIC activity in 11 of 13 animals. In the vagotomized animals with no expiratory activity in the IIC muscles, lung inflations with low O2 gas mixture (6% O2 in N2) produced an increase in IIC activity, whereas these excitatory effects were remarkably reduced after sectioning the carotid sinus nerves. In addition, the effects of lung inflation with low O2 gas mixture (6% O2 in N2) on carotid chemoreceptor activity were also studied in the vagotomized rabbits. Lung inflations with hypoxic gas caused an increase in carotid chemoreceptor activity. These results indicate that in the absence of proprioceptive input from the lungs, hypoxic stimulation of the carotid chemoreceptors is capable of activating the expiratory activity in the IIC muscles.

Animals↗
PubMed1993

Load compensatory response of external intercostal muscles during assisted ventilation in rabbits.

Phrenic and external intercostal motor responses to inspiratory load were studied in anaesthetized rabbits and after bilateral vagotomy. Animals were ventilated with a phrenic nerve driven respirator set at different gains, i.e. volume to phrenic-signal ratio. Load was imposed by occluding the trachea at the end of expiration for the period of one breath. It was found that vagally mediated low threshold facilitation may be observed in rabbits on late-inspiratory external intercostal motor units. After vagotomy, external intercostal EMG response to load depended on the given of the servorespirator set during the period of assisted ventilation.

Adaptation, Physiological↗
PubMed1982

Penetration of ceforanide and cefamandole into the right atrial appendage, pericardial fluid, sternum, and intercostal muscle of patients undergoing open heart surgery.

Doses of 30 mg of ceforanide or cefamandole per kg were administered intravenously to 26 patients just before their chests were opened for coronary artery bypass or cardiac valve replacement surgery. Samples of right atrial appendage, pericardial fluid, plasma, aortic wall, intercostal muscle, and sternum were obtained at different times after the antibiotic was injected, and these samples were assayed for cephalosporin concentration. For ceforanide the pre-bypass plasma half-life was 2.5 h, and the atrial appendage half-life was 2.1 h; for cefamandole the pre-bypass plasma half-life was 0.75 h and the atrial appendage half-life was 0.72 h. At 3 h the concentrations of ceforanide and cefamandole in atrial appendages were 28.0 and 5.0 micrograms/g, respectively. Ceforanide achieved higher and more sustained concentrations in other tissues than cefamandole. Considering the minimal inhibitory concentrations of these drugs for staphylococci, cefamandole and ceforanide should provide adequate protection against infection by these organisms for the duration of the surgical procedure.

Cardiac Surgical Procedures↗
PubMed1989

Perisynaptic satellite cells in human external intercostal muscle: a quantitative and qualitative study.

It is not known whether or not satellite cell nuclei are more common in the vicinity of motor endplates than in extrasynaptic regions of human muscle, as in animals. If so, perisynaptic satellite cells may have a role in preserving neuromuscular function. We compared the frequencies of satellite cell nuclei and of myonuclei in perisynaptic and extrasynaptic regions of human external intercostal muscle, and found an absolute as well as a relative increase of perisynaptic satellite cells. The mean frequency of satellite cell nuclei per sarcomere was 0.016 in perisynaptic and 0.00003 in extrasynaptic regions. The mean frequency of myonuclei per sarcomere was 0.098 in perisynaptic and 0.014 in extrasynaptic regions. We could not demonstrate any influence of aging on satellite cell distribution. Perisynaptic satellite cells had many processes, and some features suggested a more active state. These cells might add to the pool of junctional myonuclei for synthesis of acetylcholine-receptor molecules or help in the repair of the postsynaptic membrane. Alternatively, they may synthesize basal lamina substances that are specific for the endplate.

Adult↗
PubMed1996

Composition of newly forming motor units in prenatal rat intercostal muscle.

We have examined the composition of rat intercostal motor units during the period of late gestation, when most muscle fibres are formed, in order to see the pattern of the contacts initially made between single motoneurons and myotubes. At this early stage, the muscle contains two types of myotubes, primary and secondary myotubes, and a major aim was to see whether individual motoneurons preferentially made contact with a particular myotube type. The technique used to define myotubes contacted by a single motoneuron was anterograde labelling of the neuron, followed by electron microscopic detection of labelled terminals and their postsynaptic targets. We find that prenatal motor units are inhomogeneous with respect to their primary/secondary myotube composition. Most individual motoneurons show many permutations of contact with primary myotubes, secondary myotubes, and undifferentiated cells, including single nerve terminals which contact both primary and secondary myotubes. Our results are interpreted in terms of changes to the composition of both the muscle and of the motor units during the final 5 days of gestation. We demonstrate that motoneurons necessarily make their initial contacts on primary myotubes, but that these are surprisingly sparse. As secondary myotubes appear and become innervated, motor units are at first all similar and all heterogeneous. However, primary myotubes are represented more often in motor units than in the muscle as a whole. This probably reflects the relative densities of polyinnervation of primary vs. secondary myotubes. By embryonic day 20, motor units have become divergent in composition, with some dominated by primary myotubes and others by secondaries. We propose that motoneurons initially establish contacts at random on either myotube type, but then begin to express preference for one type or the other and reorganise their periphery. Refining of motor unit composition towards homogeneity in the postnatal period probably involves other elements, such as mutability of muscle fibre and/or motoneuron characteristics as a function of usage and muscle position, perhaps influenced by sensory feedback mechanisms.

Affinity Labels↗
PubMed2005

Respiratory action of the intercostal muscles.

The mechanical advantages of the external and internal intercostals depend partly on the orientation of the muscle but mostly on interspace number and the position of the muscle within each interspace. Thus the external intercostals in the dorsal portion of the rostral interspaces have a large inspiratory mechanical advantage, but this advantage decreases ventrally and caudally such that in the ventral portion of the caudal interspaces, it is reversed into an expiratory mechanical advantage. The internal interosseous intercostals in the caudal interspaces also have a large expiratory mechanical advantage, but this advantage decreases cranially and, for the upper interspaces, ventrally as well. The intercartilaginous portion of the internal intercostals (the so-called parasternal intercostals), therefore, has an inspiratory mechanical advantage, whereas the triangularis sterni has a large expiratory mechanical advantage. These rostrocaudal gradients result from the nonuniform coupling between rib displacement and lung expansion, and the dorsoventral gradients result from the three-dimensional configuration of the rib cage. Such topographic differences in mechanical advantage imply that the functions of the muscles during breathing are largely determined by the topographic distributions of neural drive. The distributions of inspiratory and expiratory activity among the muscles are strikingly similar to the distributions of inspiratory and expiratory mechanical advantages, respectively. As a result, the external intercostals and the parasternal intercostals have an inspiratory function during breathing, whereas the internal interosseous intercostals and the triangularis sterni have an expiratory function.

Animals↗
PubMed2002

Spatiotemporal distribution of heparan sulfate epitopes during myogenesis and synaptogenesis: a study in developing mouse intercostal muscle.

Formation of a basal lamina (BL) ensheathing developing skeletal muscle cells is one of the earliest events in mammalian skeletal muscle myogenesis. BL-resident heparan sulfate proteoglycans have been implicated in various processes during myogenesis, including synaptic differentiation. However, attention has focused on the proteoglycan protein core, ignoring the glycosaminoglycan moiety mainly because of a lack of appropriate tools. Recently, we selected a panel of anti-heparan sulfate antibodies applied here to study the spatiotemporal distribution of specific heparan sulfate (HS) epitopes during myogenesis. In mouse intercostal muscle at embryonic day (E14), formation of acetylcholine receptor clusters at synaptic sites coincides with HS deposition. Although some HS epitopes show a general appearance throughout the BL, one epitope preferably clusters at synaptic sites but does so only from E16 onward. During elongation and maturation of primary myotubes, a process preceding secondary myotube development, significant changes in the HS epitope constitution of both synaptic and extrasynaptic BL were observed. As a whole, the data presented here strengthen previous observations on developmental regulation by BL components, and add to the putative roles of specific HS epitopes in myogenesis and synaptogenesis.

Animals↗