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Peter A. Kirkwood - One of the best experts on this subject based on the ideXlab platform.
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Absence of synergy for monosynaptic Group I inputs between abdominal and Internal Intercostal motoneurons
Journal of Neurophysiology, 2014Co-Authors: T. W. Ford, C. F. Meehan, Peter A. KirkwoodAbstract:Internal Intercostal and abdominal motoneurons are strongly coactivated during expiration. We investigated whether that synergy was paralleled by synergistic Group I reflex excitation. Intracellular recordings were made from motoneurons of the Internal Intercostal nerve of T8 in anesthetized cats, and the specificity of the monosynaptic connections from afferents in each of the two main branches of this nerve was investigated. Motoneurons were shown by antidromic excitation to innervate three muscle groups: external abdominal oblique [EO; innervated by the lateral branch (Lat)], the region of the Internal Intercostal muscle proximal to the branch point (IIm), and muscles innervated from the distal remainder (Dist). Strong specificity was observed, only 2 of 54 motoneurons showing excitatory postsynaptic potentials (EPSPs) from both Lat and Dist. No EO motoneurons showed an EPSP from Dist, and no IIm motoneurons showed one from Lat. Expiratory Dist motoneurons fell into two groups. Those with Dist EPSPs and none from Lat (group A) were assumed to innervate distal Internal Intercostal muscle. Those with Lat EPSPs (group B) were assumed to innervate abdominal muscle (transversus abdominis or rectus abdominis). Inspiratory Dist motoneurons (assumed to innervate interchondral muscle) showed Dist EPSPs. Stimulation of dorsal ramus nerves gave EPSPs in 12 instances, 9 being in group B Dist motoneurons. The complete absence of heteronymous monosynaptic Group I reflex excitation between muscles that are synergistically activated in expiration leads us to conclude that such connections from muscle spindle afferents of the thoracic nerves have little role in controlling expiratory movements but, where present, support other motor acts.
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Specificity in monosynaptic and disynaptic bulbospinal connections to thoracic motoneurones in the rat.
The Journal of Physiology, 2013Co-Authors: Anoushka T. R. De Almeida, Peter A. KirkwoodAbstract:Key points • In the rat, unlike in other species, motoneurones of both the Internal Intercostal nerve and the external Intercostal nerve show a phase of excitation in expiration. • This study investigated the pathways transmitting this excitation from the medulla. • Direct (monosynaptic) excitation was found from individual expiratory neurones in the medulla to Internal Intercostal nerve motoneurones, but only indirect (disynaptic) excitation was found from the same neurones to the motoneurones of the external Intercostal nerve. • This is the first demonstration of two separate pathways from individual long descending fibres specific to two different sets of motoneurones. • This specificity could be useful in studying plasticity or regeneration in thoracic segments in investigations of mechanisms involved in spinal cord injury and repair. Abstract The respiratory activity in the Intercostal nerves of the rat is unusual, in that motoneurones of both branches of the Intercostal nerves, Internal and external, are activated during expiration. Here, the pathways involved in that activation were investigated in anaesthetised and in decerebrate rats by cross-correlation and by intracellular spike-triggered averaging from expiratory bulbospinal neurones (EBSNs), with a view to revealing specific connections that could be used in studies of experimental spinal cord injury. Decerebrate preparations, which showed the strongest expiratory activity, were found to be the most suitable for these measurements. Cross-correlations in these preparations showed monosynaptic connections from 16/19 (84%) of EBSNs, but only to Internal Intercostal nerve motoneurones (24/37, 65% of EBSN/nerve pairs), whereas disynaptic connections were seen for external Intercostal nerve motoneurones (4/19, 21% of EBSNs or 7/25, 28% of EBSN/nerve pairs). There was evidence for additional disynaptic connections to Internal Intercostal nerve motoneurones. Intracellular spike-triggered averaging revealed excitatory postsynaptic potentials, which confirmed these connections. This is believed to be the first report of single descending fibres that participate in two different pathways to two different groups of motoneurones. It is of interest compared with the cat, where only one group of motoneurones is activated during expiration and only one of the pathways has been detected. The specificity of the connections could be valuable in studies of plasticity in pathological situations, but care will be needed in studying connections in such situations, because their strength was found here to be relatively weak.
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Patterns of expiratory and inspiratory activation for thoracic motoneurones in the anaesthetized and the decerebrate rat.
The Journal of Physiology, 2010Co-Authors: Anoushka T. R. De Almeida, Sarah Al-izki, Manuel Enríquez Denton, Peter A. KirkwoodAbstract:The nervous control of expiratory muscles is less well understood than that of the inspiratory muscles, particularly in the rat. The patterns of respiratory discharges in adult rats were therefore investigated for the muscles of the caudal Intercostal spaces, with hypercapnia and under either anaesthesia or decerebration. With neuromuscular blockade and artificial ventilation, efferent discharges were present for both inspiration and expiration in both external and Internal Intercostal nerves. This was also the case for proximal Internal Intercostal nerve branches that innervate only Internal Intercostal and subcostalis muscles. If active, this region of muscle in other species is always expiratory. Here, inspiratory bursts were almost always present. The expiratory activity appeared only gradually and intermittently, when the anaesthesia was allowed to lighten or as the pre-decerebration anaesthesia wore off. The intermittent appearance is interpreted as the coupling of a slow medullary expiratory oscillator with a faster inspiratory one. The patterns of nerve discharges, in particular the inspiratory or biphasic activation of the Internal and subcostalis layers, were confirmed by observations of equivalent patterns of EMG discharges in spontaneously breathing preparations, using denervation procedures to identify which muscles generated the signals. Some motor units were recruited in both inspiratory and expiratory bursts. These patterns of activity have not previously been described and have implications both for the functional role of multiple respiratory oscillators in the adult and for the mechanical actions of the muscles of the caudal Intercostal spaces, including subcostalis, which is a partly bisegmental muscle.
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Bulbospinal connections to Intercostal motoneurones following a chronic lateral spinal cord lesion.
Respiratory Physiology & Neurobiology, 1Co-Authors: Tim W. Ford, Peter A. KirkwoodAbstract:Abstract Previous evidence from electrophysiological experiments in anaesthetized cats with a chronic lateral lesion of the lower thoracic spinal cord indicated an expansion of the functional projections of expiratory bulbospinal neurones (EBSNs) in the segment above the lesion, measured at 16 weeks post-lesion. Here we investigate connections made by the same EBSNs to motoneurones in that segment, using cross-correlations between their discharges. The connections to the Internal Intercostal nerve motoneurones were found to be no different from controls. However, a significant increase was found in the number of connections between EBSNs and γ motoneurones of the external Intercostal nerve (8/24, compared to 1/16) with possibly additional connections to the α motoneurones of the same nerve. Increased connections to the γ motoneurones of the Internal Intercostal nerve could not be ruled out. The expanded functional projections are thus likely to include new connections to γ motoneurones. We suggest that γ motoneurones may be inherently more receptive to new inputs. If so, the previously discounted role of abnormal fusimotor discharges in motor disorders would be worth reconsideration.
Jin-shing Chen - One of the best experts on this subject based on the ideXlab platform.
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Nonintubated Thoracoscopic Pneumonectomy for Bullous Emphysema.
The Annals of Thoracic Surgery, 2016Co-Authors: Wan-ting Hung, Ya-jung Cheng, Hsien-chi Liao, Jin-shing ChenAbstract:Thoracoscopic pneumonectomy without tracheal intubation has not been reported. We describe a woman with severe bullous emphysema of the right upper lobe and hypoplasia of the remaining lung lobes who underwent thoracoscopic pneumonectomy using a nonintubated anesthetic technique of Internal Intercostal nerve block, vagal block, and targeted sedation. The successful results in this patient suggest that nonintubated thoracoscopic pneumonectomy is technically feasible and can be used in a specific group of patients.
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Non-intubated thoracoscopic surgery using Internal Intercostal nerve block, vagal block and targeted sedation.
European Journal of Cardio-Thoracic Surgery, 2014Co-Authors: Ming-hui Hung, Hsao-hsun Hsu, Kuang-cheng Chan, Ke-cheng Chen, Jr-chi Yie, Ya-jung Cheng, Jin-shing ChenAbstract:OBJECTIVES Thoracoscopic surgery using Internal Intercostal nerve block, vagal block and targeted sedation without endotracheal intubation is a promising technique for selected patients, but little is known about its feasibility and safety. METHODS We evaluated 109 patients with lung (105), mediastinal (3) or pleural (1) tumours treated using non-intubated thoracoscopic surgery. Internal, Intercostal nerve block was performed at the T3-T8 Intercostal level and vagal block was performed adjacent to the vagus nerve at the level of the lower trachea for right-sided operations and at the level of the aortopulmonary window for left-sided operations. Sedation was performed with propofol infusion to achieve a bispectral index value between 40 and 60. RESULTS Thoracoscopic lobectomy was performed in 43 patients, wedge resection in 50, segmentectomy in 12 and mediastinal or pleural tumour excision in 4. Three patients (2.8%) required conversion to intubated one-lung ventilation because of vigorous mediastinal movement and dense diaphragmatic adhesions. Anaesthetic induction and operation had a median duration of 10.0 and 127.0 min, respectively. Operative complications developed in 13 patients with air leaks for more than 3 days and 1 patient required transfusion of blood products. The median postoperative chest drainage and hospital stay were 2.0 and 4.0 days, respectively. CONCLUSIONS Non-intubated thoracoscopic surgery using Internal Intercostal nerve block, vagal block and targeted sedation is technically feasible and safe in surgical treatment of lung, mediastinal and pleural tumours in selected patients.
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Nonintubated thoracoscopic surgery using regional anesthesia and vagal block and targeted sedation.
Journal of thoracic disease, 2014Co-Authors: Ke-cheng Chen, Ming-hui Hung, Ya-jung Cheng, Yu-ding Tseng, Jin-shing ChenAbstract:Objective: Thoracoscopic surgery without endotracheal intubation is a novel technique for diagnosis and treatment of thoracic diseases. This study reported the experience of nonintubated thoracoscopic surgery in a tertiary medical center in Taiwan. Methods: From August 2009 through August 2013, 446 consecutive patients with lung or pleural diseases were treated by nonintubated thoracoscopic surgery. Regional anesthesia was achieved by thoracic epidural anesthesia or Internal Intercostal blockade. Targeted sedation was performed with propofol infusion to achieve a bispectral index value between 40 and 60. The demographic data and clinical outcomes were evaluated by retrospective chart review. Results: Thoracic epidural anesthesia was used in 290 patients (65.0%) while Internal Intercostal blockade was used in 156 patients (35.0%). The final diagnosis were primary lung cancer in 263 patients (59.0%), metastatic lung cancer in 38 (8.5%), benign lung tumor in 140 (31.4%), and pneumothorax in 5 (1.1%). The median anesthetic induction time was 30 minutes by thoracic epidural anesthesia and was 10 minutes by Internal Intercostal blockade. The operative procedures included lobectomy in 189 patients (42.4%), wedge resection in 229 (51.3%), and segmentectomy in 28 (6.3%). Sixteen patients (3.6%) required conversion to tracheal intubation because of significant mediastinal movement (seven patients), persistent hypoxemia (two patients), dense pleural adhesions (two patients), ineffective epidural anesthesia (two patients), bleeding (two patients), and tachypnea (one patient). One patient (0.4%) was converted to thoracotomy because of bleeding. No mortality was noted in our patients. Conclusions: Nonintubated thoracoscopic surgery is technically feasible and safe and can be a less invasive alternative for diagnosis and treatment of thoracic diseases.
A De Troyer - One of the best experts on this subject based on the ideXlab platform.
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Coupling between the ribs and the lung in dogs.
The Journal of physiology, 2002Co-Authors: A De Troyer, T A WilsonAbstract:In contrast to the conventional theory, the external and Internal Intercostal muscles show marked rostrocaudal gradients in their actions on the lung. We hypothesized that these gradients are the result of a non-uniform coupling between the ribs and the lung. Rib displacements (X(r)) and the changes in airway opening pressure (P(a,o)) were thus measured in anaesthetized, pancuronium-treated, supine dogs while loads were applied in the cranial direction to individual pairs of odd-numbered ribs and in the caudal direction to individual pairs of even-numbered ribs. During cranial loading, X(r) induced by a given load increased gradually with increasing rib number. The decrease in P(a,o) also increased from the third to the fifth rib pair but then decreased markedly to the eleventh pair. A similar pattern was observed during caudal loading, although X(r) and DeltaP(a,o) were smaller. These results were then combined to calculate the net X(r) and the net DeltaP(a,o) that a hypothetical Intercostal muscle lying parallel to the longitudinal body axis would produce in different interspaces. The net X(r) was cranial in all interspaces. However, whereas the net DeltaP(a,o) was negative in the cranial interspaces, it was positive in the caudal interspaces. These observations confirm that the coupling between the ribs and the lung varies from the top to the base of the ribcage. This coupling confers to both the external and the Internal Intercostal muscles an inspiratory action on the lung in the cranial interspaces and an expiratory action in the caudal interspaces.
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Coupling between the ribs and the lung in dogs
The Journal of Physiology, 2002Co-Authors: A De Troyer, T A WilsonAbstract:In contrast to the conventional theory, the external and Internal Intercostal muscles show marked rostrocaudal gradients in their actions on the lung. We hypothesized that these gradients are the result of a non-uniform coupling between the ribs and the lung. Rib displacements (Xr) and the changes in airway opening pressure (Pa,o) were thus measured in anaesthetized, pancuronium-treated, supine dogs while loads were applied in the cranial direction to individual pairs of odd-numbered ribs and in the caudal direction to individual pairs of even-numbered ribs. During cranial loading, Xr induced by a given load increased gradually with increasing rib number. The decrease in Pa,o also increased from the third to the fifth rib pair but then decreased markedly to the eleventh pair. A similar pattern was observed during caudal loading, although Xr and ΔPa,o were smaller. These results were then combined to calculate the net Xr and the net ΔPa,o that a hypothetical Intercostal muscle lying parallel to the longitudinal body axis would produce in different interspaces. The net Xr was cranial in all interspaces. However, whereas the net ΔPa,o was negative in the cranial interspaces, it was positive in the caudal interspaces. These observations confirm that the coupling between the ribs and the lung varies from the top to the base of the ribcage. This coupling confers to both the external and the Internal Intercostal muscles an inspiratory action on the lung in the cranial interspaces and an expiratory action in the caudal interspaces.
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Respiratory effects of the external and Internal Intercostal muscles in humans.
The Journal of physiology, 2001Co-Authors: T A Wilson, A Legrand, P A Gevenois, A De TroyerAbstract:The current conventional view of Intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external Intercostals have an inspiratory action on the lung and the Internal interosseous Intercostals have an expiratory action. Recent studies in dogs, however, have shown that this notion is only approximate. In the present studies, the respiratory actions of the human external and Internal Intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the orientation of the muscle fibres relative to the ribs and the masses of the muscles were first assessed in cadavers. Five healthy individuals were then placed in a computed tomographic scanner to determine the geometry of the ribs and their precise transformation during passive inflation to total lung capacity. The fractional changes in length of lines with the orientation of the muscle fibres were then computed to obtain the mechanical advantages of the muscles. These values were finally multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. The external Intercostal in the dorsal half of the second interspace was found to have a large inspiratory effect. However, this effect decreases rapidly in the caudal direction, in particular in the ventral portion of the ribcage. As a result, it is reversed into an expiratory effect in the ventral half of the sixth and eighth interspaces. The Internal Intercostals in the ventral half of the sixth and eighth interspaces have a large expiratory effect, but this effect decreases dorsally and cranially. The total pressure generated by all the external Intercostals during a maximum contraction would be -15 cmH2O, and that generated by all the Internal interosseous Intercostals would be +40 cmH2O. These pressure changes are substantially greater than those induced by the parasternal Intercostal and triangularis sterni muscles, respectively.
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Response of the Canine Internal Intercostal Muscles to Chest Wall Vibration
American Journal of Respiratory and Critical Care Medicine, 2001Co-Authors: Dimitri Leduc, E. Brunko, A De TroyerAbstract:Although high-frequency mechanical vibration of the rib cage reduces dyspnea, its effects on the respiratory muscles are largely unknown. We have previously shown that in anesthetized dogs, vibrating the rib cage during inspiration elicits a marked increase in the inspiratory electromyographic (EMG) activity recorded from the external Intercostal muscles but does not affect tidal volume (Vt). In the present studies, we have tested the hypothesis that the maintenance of Vt results from the concomitant contraction of the Internal interosseous (expiratory) Intercostals. When the rib cage was vibrated (40 Hz) during hyperventilation-induced apnea, a prominent activity was recorded from the external Intercostals but no activity was recorded from the Internal Intercostals, including when the muscles were lengthened by passive inflation. The Internal Intercostals remained also silent when vibration was applied during spontaneous inspiration, and the phasic expiratory EMG activity recorded from them was unaltered...
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Respiratory mechanical advantage of the canine external and Internal Intercostal muscles.
The Journal of physiology, 1999Co-Authors: A De Troyer, A Legrand, T A WilsonAbstract:1. The current conventional view of Intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external Intercostals have an inspiratory action on the lung and the Internal interosseous Intercostals have an expiratory action. This notion, however, remains unproved. 2. In the present studies, the respiratory actions of the canine external and Internal Intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. 3. The external Intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The Internal Intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. 4. These observations indicate that the canine external and Internal Intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive.
T A Wilson - One of the best experts on this subject based on the ideXlab platform.
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Coupling between the ribs and the lung in dogs.
The Journal of physiology, 2002Co-Authors: A De Troyer, T A WilsonAbstract:In contrast to the conventional theory, the external and Internal Intercostal muscles show marked rostrocaudal gradients in their actions on the lung. We hypothesized that these gradients are the result of a non-uniform coupling between the ribs and the lung. Rib displacements (X(r)) and the changes in airway opening pressure (P(a,o)) were thus measured in anaesthetized, pancuronium-treated, supine dogs while loads were applied in the cranial direction to individual pairs of odd-numbered ribs and in the caudal direction to individual pairs of even-numbered ribs. During cranial loading, X(r) induced by a given load increased gradually with increasing rib number. The decrease in P(a,o) also increased from the third to the fifth rib pair but then decreased markedly to the eleventh pair. A similar pattern was observed during caudal loading, although X(r) and DeltaP(a,o) were smaller. These results were then combined to calculate the net X(r) and the net DeltaP(a,o) that a hypothetical Intercostal muscle lying parallel to the longitudinal body axis would produce in different interspaces. The net X(r) was cranial in all interspaces. However, whereas the net DeltaP(a,o) was negative in the cranial interspaces, it was positive in the caudal interspaces. These observations confirm that the coupling between the ribs and the lung varies from the top to the base of the ribcage. This coupling confers to both the external and the Internal Intercostal muscles an inspiratory action on the lung in the cranial interspaces and an expiratory action in the caudal interspaces.
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Coupling between the ribs and the lung in dogs
The Journal of Physiology, 2002Co-Authors: A De Troyer, T A WilsonAbstract:In contrast to the conventional theory, the external and Internal Intercostal muscles show marked rostrocaudal gradients in their actions on the lung. We hypothesized that these gradients are the result of a non-uniform coupling between the ribs and the lung. Rib displacements (Xr) and the changes in airway opening pressure (Pa,o) were thus measured in anaesthetized, pancuronium-treated, supine dogs while loads were applied in the cranial direction to individual pairs of odd-numbered ribs and in the caudal direction to individual pairs of even-numbered ribs. During cranial loading, Xr induced by a given load increased gradually with increasing rib number. The decrease in Pa,o also increased from the third to the fifth rib pair but then decreased markedly to the eleventh pair. A similar pattern was observed during caudal loading, although Xr and ΔPa,o were smaller. These results were then combined to calculate the net Xr and the net ΔPa,o that a hypothetical Intercostal muscle lying parallel to the longitudinal body axis would produce in different interspaces. The net Xr was cranial in all interspaces. However, whereas the net ΔPa,o was negative in the cranial interspaces, it was positive in the caudal interspaces. These observations confirm that the coupling between the ribs and the lung varies from the top to the base of the ribcage. This coupling confers to both the external and the Internal Intercostal muscles an inspiratory action on the lung in the cranial interspaces and an expiratory action in the caudal interspaces.
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Respiratory effects of the external and Internal Intercostal muscles in humans.
The Journal of physiology, 2001Co-Authors: T A Wilson, A Legrand, P A Gevenois, A De TroyerAbstract:The current conventional view of Intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external Intercostals have an inspiratory action on the lung and the Internal interosseous Intercostals have an expiratory action. Recent studies in dogs, however, have shown that this notion is only approximate. In the present studies, the respiratory actions of the human external and Internal Intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the orientation of the muscle fibres relative to the ribs and the masses of the muscles were first assessed in cadavers. Five healthy individuals were then placed in a computed tomographic scanner to determine the geometry of the ribs and their precise transformation during passive inflation to total lung capacity. The fractional changes in length of lines with the orientation of the muscle fibres were then computed to obtain the mechanical advantages of the muscles. These values were finally multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. The external Intercostal in the dorsal half of the second interspace was found to have a large inspiratory effect. However, this effect decreases rapidly in the caudal direction, in particular in the ventral portion of the ribcage. As a result, it is reversed into an expiratory effect in the ventral half of the sixth and eighth interspaces. The Internal Intercostals in the ventral half of the sixth and eighth interspaces have a large expiratory effect, but this effect decreases dorsally and cranially. The total pressure generated by all the external Intercostals during a maximum contraction would be -15 cmH2O, and that generated by all the Internal interosseous Intercostals would be +40 cmH2O. These pressure changes are substantially greater than those induced by the parasternal Intercostal and triangularis sterni muscles, respectively.
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Respiratory mechanical advantage of the canine external and Internal Intercostal muscles.
The Journal of physiology, 1999Co-Authors: A De Troyer, A Legrand, T A WilsonAbstract:1. The current conventional view of Intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external Intercostals have an inspiratory action on the lung and the Internal interosseous Intercostals have an expiratory action. This notion, however, remains unproved. 2. In the present studies, the respiratory actions of the canine external and Internal Intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. 3. The external Intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The Internal Intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. 4. These observations indicate that the canine external and Internal Intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive.
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Respiratory mechanical advantage of the canine external and Internal Intercostal muscles
The Journal of Physiology, 1999Co-Authors: A De Troyer, A Legrand, T A WilsonAbstract:The current conventional view of Intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external Intercostals have an inspiratory action on the lung and the Internal interosseous Intercostals have an expiratory action. This notion, however, remains unproved. In the present studies, the respiratory actions of the canine external and Internal Intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3·0 kg cm−2) to evaluate the potential effects of the muscles on the lung. The external Intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The Internal Intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. These observations indicate that the canine external and Internal Intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive. Although it is now well established that the interchondral portion of the Internal Intercostal muscles (the so-called parasternal Intercostals) elevates the ribs and inflates the lung when it contracts (De Troyer & Kelly, 1982; De Troyer et al. 1996), the actions of the external Intercostals and the interosseous portion of the Internal Intercostals remain uncertain. The current conventional view is based on the theory proposed 250 years ago by Hamberger (1749). According to this theory, the fibres of the external Intercostals slope obliquely caudad and ventrally from the rib above to the rib below, and so their lower insertion is further from the centre of rotation of the ribs (i.e. the costo-vertebral articulations) than their upper insertion. Consequently, when this muscle contracts with its force equal and opposite at both insertions, the torque acting on the lower rib, which tends to raise it, is greater than that acting on the upper rib, which tends to lower it. The net effect of the muscle, therefore, would be to raise the ribs and to inflate the lung. In contrast, the fibres of the Internal interosseous Intercostals slope obliquely caudad and dorsally from the rib above to the one below so that their lower insertion is closer to the centre of rotation of the ribs than the upper one. As a result, the net effect of their contraction would be to lower the ribs and to deflate the lung. This theory, however, has not been verified, and computations based on the orientation of the muscle fibres and on descriptions of rib displacement in dogs (Margulies et al. 1989) have recently suggested that the actions of the external and Internal Intercostal muscles on the lung might vary between the dorsal and the ventral aspects of the rib cage as well as between the rostral and caudal interspaces (Wilson & De Troyer, 1993). In the present studies, we have examined the effects of the canine external and Internal interosseous Intercostals on the lung by using a standard theorem of mechanics, the Maxwell reciprocity theorem. When applied to the respiratory system (Wilson & De Troyer, 1992, 1993), this theorem predicts that the respiratory effect of a particular muscle (that is, the potential change in airway pressure - ΔPao - produced by the muscle contracting alone against a closed airway) is related to the mass (m) of the muscle, the maximal active muscle tension per unit cross-sectional area (σ), and the fractional change in muscle length (ΔL/L) per unit volume increase of the relaxed chest wall (ΔVL)Rel, such that: (1) For a machine, such as a lever, mechanical advantage is defined as the ratio of the force delivered at the load to the force applied at the handle. By analogy, the mechanical advantage of a respiratory muscle may therefore be defined as ΔPao/mσ and, according to eqn (1), could be evaluated by measuring (ΔL/(L ΔVL))Rel. In other words, a muscle that shortens during passive inflation would have an inspiratory mechanical advantage and would cause a fall in Pao when it contracts. Conversely, a muscle that lengthens during passive inflation would have an expiratory mechanical advantage and would cause a rise in Pao during contraction.
A. H. Pullen - One of the best experts on this subject based on the ideXlab platform.
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Neurofilament reorganisation and neurofilament antigen redistribution in spinal motoneurones following retrograde axonal transport of diphtheria toxin
Acta Neuropathologica, 1994Co-Authors: A. H. PullenAbstract:Single unilateral injections of diphtheria toxin (DTX) into the external anal sphincter muscle or Internal Intercostal nerve of cat induced characteristic ultrastructural lesions in corresponding ipsilateral spinal motoneurones 6–8 days later. The chief neuronal lesion was a progressive disruption of Nissl body composition and organisation, which between days 8–19 post injection was accompanied by a progressive accumulation of neurofilaments in motoneuronal perikarya and dendrites. Some axons in the ipsilateral ventral horn became hypertrophied due to neurofilamentous accumulation. Related immunocytochemical investigations 6–35 days after injection of DTX revealed abnormal immunoreactivity intoxicated motoneurones for 200-kDa and 160-kDa phosphorylated neurofilament proteins, but not in contralateral motoneurones. By day 35 abnormal neurofilament immunostaining also occurred in ipsilateral and some contralateral interneurones but not contralateral motoneurones. Abnormalities of Nissl body endoplasmic reticulum, neurofilament organisation, and neurofilament protein immunostaining were identical after either intraneural and intramuscular injections of DTX, indicating abnormalities were attributable to toxicity and not injection-related axonal damage. Since DTX acts specifically in the soma to inhibit protein synthesis, neurofilament abnormalities are secondary to cytotoxicity and probably result from deficits in transference of existing partially phosphorylated neurofilaments to the axonal transport system, or axonal transport per se.