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PubMed2004

Experimental evaluation of the optimal tidal volume for simultaneous pacing of the diaphragm and respiratory muscles.

Because of problems with pacing devices, surgical procedures, and diaphragm fatigue in pacing therapy of the phrenic nerve, we performed simultaneous pacing of the diaphragm alone and of multiple respiratory muscles in dogs and evaluated the optimal tidal volume. After intravenously anesthetizing 20 dogs with an average weight of 11 kg, their tidal volume was measured with a spirometer to obtain control values. In the first 4 dogs, electrodes were sutured to the diaphragm and the optimal voltage, pulse width, and output to maximize tidal volume were determined. In the remaining 16 dogs, we stimulated individual canine respiratory muscles, i.e., the diaphragm, the rectus thoracis, and intercostal muscles 3-5 and simultaneously stimulated the diaphragm and the rectus thoracis; the diaphragm and intercostal muscles; the rectus thoracis and the intercostal muscles; or the diaphragm, rectus thoracis, and intercostal muscles. We compared a group in which a counterelectrode was positioned in each muscle group (group A) with a group in which no counterelectrode was used (group B). The best tidal volume was obtained at 10 V, 50 Hz, and a pulse width of 1.0 ms. All the respiratory muscle pacings yielded better tidal volumes in group B than in group A. The greatest tidal volume was obtained with the rectus thoracis and intercostal muscle combination, suggesting the possibility of being able to reduce diaphragm fatigue by alternate pacing of these muscles and the diaphragm.

Animals↗

PubMed1975

Effects of mechanical loading and hypercapnia on inspiratory muscle EMG.

The electromyograms of the diaphragm and an external intercostal muscle were analyzed to see if the effects of hypercapnia on inspiratory muscle electrical activity could be distinguished from those of mechanical loading and to determine whether changes in inspiratory muscle electrical activity were a sueful measure of CO2 response during mechanical loading. Anesthetized dogs were studied: 1) during progressive hypercapnia without mechanical loading, 2) during flow-resistive and elastic loading at constant PCO2, and 3) during progressive hypercapnia and mechanical loading. Both mechanical loading and hypercapnia increased total inspiratory diaphragmatic and intercostal muscle electrical activity. However, inspiratory duration was increased by mechanical loads but reduced by hypercapnia. Because of these changes in inspiratory duration, the average rate of diaphragmatic electrical activity remained unaffected by mechanical loading before and after vagotomy but was increased by hypercapnia. In contrast, both hypercapnia and mechanical loading increased the average rate of intercostal muscle electrical activity. There was a greater increase in both total and average rate of intercostal muscle electrical activity during hypercapnia in the presence of mechanical loading than during unloaded breathing. However, the change in total and average rate of diaphragmatic electrical activity with PCO2 was unaffected by added mechanical loads. These results suggest that diaphragmatic but not intercostal muscle electrical activity can be used as an index of CO2 response even during mechanical loading.

Airway Resistance↗

PubMed1996

Mechanical ventilation increases substance P concentration in the vagus, sympathetic, and phrenic nerves.

Substance P (SP), a neurotransmitter localized to primary sensory neurons, is found in the vagus nerve, nodose ganglion, sympathetic chain, and phrenic nerve in various animal species. However, the changes in endogeneous SP concentration under various circumstances that involve the participation of cardiorespiratory afferent nerves are still unexplored. In the present study, attention was focused on the variations in SP content measured by radioimmunoassay (RIA) in respiratory afferent nerves (vagus nerve, cervical sympathetic chain, phrenic nerve) and respiratory muscles (diaphragm, intercostal muscles) during positive inspiratory pressure (PIP) breathing alone or PIP with an expiratory threshold load (ETL) in rabbits. SP was found in all sampled structures in spontaneously breathing control animals, prevailing in the nodose ganglion. Left-versus right-sided differences were noticed in nerves. As compared with that in control animals, the SP concentration was markedly higher in vagal and sympathetic nervous structures during PIP or PIP with ETL, and also in the phrenic nerve during ETL breathing. The SP content did not vary in respiratory muscles. These observations suggest that two very common circumstances of mechanical ventilation are associated with an increased SP concentration in nervous structures participating in the control of breathing.

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↗

PubMed1994

Effect of chest wall vibration on dyspnea in patients with chronic respiratory disease.

The effect of chest wall vibration on dyspnea at rest was investigated in 15 patients with severe chronic respiratory diseases. The magnitude of their baseline dyspnea was 17.9 +/- SE 3.3 mm on a 150-mm visual analog scale. One hundred hertz out-of-phase vibration (OPV; inspiratory intercostal muscles vibrated during expiration and expiratory intercostal muscles vibrated during inspiration) increased dyspnea an average of 21.9 +/- SE 7.8 mm (p < 0.05). One hundred hertz in-phase vibration (IPV; inspiratory intercostal muscles vibrated during inspiration and expiratory intercostal muscles vibrated during expiration) decreased dyspnea an average of 6.9 +/- SE 2.8 mm (p < 0.05). Changes in the respiratory pattern and arterial blood gas determinations elicited by 5-min IPV were investigated in eight of the 15 patients. Tidal volume was significantly increased in all eight of these patients. Respiratory frequency was decreased in seven patients and increased in one. Functional residual capacity, measured before and during the application of IPV for a period of about 10 breaths, was increased in one patient and decreased in the remaining seven. PaCO2 decreased by 1.3 +/- 1.0 mm Hg (p < 0.05), from 49.6 +/- 8.4 mm Hg; PaO2 increased by 3.4 +/- 2.3 mm Hg (p < 0.05), from 67.7 +/- 12.7 mm Hg. The results indicate that in-phase chest wall vibration decreased pathologic dyspnea in patients with chronic respiratory disease and suggest that the effects on respiratory sensation are mediated by afferent information from chest wall respiratory muscles to supraspinal centers.

Aged↗

PubMedDate not supplied

Congenital myasthenia: further evidence of disease heterogeneity.

The findings in two cases of congenital myasthenia investigated by intercostal muscle biopsy are presented. The first case, a 16-year-old boy, showed reduced miniature endplate potential amplitude and normal 125I-alpha-bungarotoxin binding to postsynaptic acetylcholine receptors. Muscle biopsy and endplate ultrastructure were normal. Tubocurarine affinity, ion channel properties, and passive membrane properties were normal. Limited data showed reduced effectiveness of applied acetylcholine in opening ion channels. The second case was an 18-year-old girl with consanguineous parents. Type 2 muscle fiber atrophy was seen in both limb and intercostal muscle. Intercostal endplates were elongated, although ultrastructure was normal. Negligible postsynaptic alpha-bungarotoxin binding suggested an abnormality of the acetylcholine receptor macromolecule.

Adenosine Triphosphatases↗

PubMed1986

Blood flow to the respiratory and limb muscles and to abdominal organs during maximal exertion in ponies.

Using radionuclide-labelled microspheres, 15 micron in diameter, we studied blood flow in the respiratory muscles (diaphragm and intercostal muscles), abdominal organs (adrenal glands, kidneys, pancreas, spleen and the small and large intestines), muscles of propulsion (gluteus medius and biceps femoris), and other working (triceps brachii and longissimus dorsi lumborum) and non-working (temporal and masseter) muscles of ponies at rest and during maximal exercise performed on a treadmill. During maximal exercise heart rate, whole body O2 consumption, cardiac output and mean aortic pressure increased 4.4-fold, 38-fold, 8-fold and 1.5-fold of their resting values, respectively. During maximal exertion arterial CO2 tension and arterial pH decreased while arterial O2 content increased by 58% due to a 59.6% rise in haemoglobin concentration. Arterial O2 tension decreased somewhat and the calculated alveolar to arterial O2 tension gradient widened during exertion. During maximal exertion blood flow in the adrenal glands increased while that in the kidneys, spleen, pancreas, small intestine and colon decreased precipitously. Thus ponies exhibited intense vasoconstriction in the renal and splanchnic vascular beds, similar to that reported in man but not in exercising dogs. During maximal exertion stride (and hence respiratory) frequency of galloping ponies was 138 +/- 3 min-1, and the blood flow and O2 delivery in the diaphragm were not different from those in other strenuously working muscles, namely gluteus medius, biceps femoris (muscles of propulsion) and triceps brachii. Blood flow in the intercostal muscles was only 54% of that in the diaphragm at rest, but with maximal exercise it registered a marked increment and the perfusion became similar to that in the longissimus dorsi lumborum, a powerful extensor of the back and loins.

Abdomen↗

PubMed1988

Respiratory pattern changes produced by intercostal muscle/rib vibration.

Large-amplitude vibration of the intercostal muscles/ribs has an inhibitory effect on inspiratory motor output. This effect has been attributed, in part, to the stimulation of intercostal muscle tendon organs. Intercostal muscle/rib vibration can also produce a decrease or increase in respiratory frequency. Studies were conducted 1) to determine whether, in addition to intercostal tendon organs, costovertebral joint mechanoreceptors (CVJR's) contribute to the inspiratory inhibitory effect of intercostal muscle/rib vibration (IMV) and 2) to explain the different respiratory frequency responses to IMV previously reported. Phrenic (C5) activity was monitored in paralyzed thoracotomized, artificially ventilated cats. Vibration (125 Hz) at amplitudes greater than 1,200 micron of one T6 intercostal space in decerebrated vagotomized rats reduced phrenic activity. This response was still present but weaker in some animals after denervation of the T6 intercostal muscles. Subsequent denervation of the T6 CVJR's by dorsal root sections eliminated this effect. Respiratory frequency decreased during simultaneous vibration (greater than 1,200 micron) of the T5 and T7 intercostal spaces in vagotomized cats. Respiratory frequency increased during IMV of two intercostal spaces (greater than 1,300 micron) in vagal intact cats. The use of different anesthetics (pentobarbital, allobarbital) did not alter these results. We conclude that CVJR's may contribute to the inhibitory effect of IMV on medullary inspiratory activity. The presence or absence of pulmonary vagal afferents can account for the different respiratory frequency responses to IMV, and different anesthetics did not influence these results.

Animals↗

PubMed1998

The canine phrenic-to-intercostal reflex.

1. Paralysis of the diaphragm in the dog causes a non-vagal, non-chemical increase in the activity of the inspiratory intercostal muscles. In the present studies, the hypothesis was tested that phrenic afferent fibres may elicit a reflex inhibition of inspiratory intercostal activity. 2. The electrical activity of the three groups of inspiratory intercostal muscles (parasternal intercostals, external intercostals, levator costae) was recorded in twenty vagotomized, spontaneously breathing dogs, and the proximal end of one or both C5 phrenic nerve roots was stimulated during inspiration. 3. Stimulation of the ipsilateral and contralateral C5 phrenic roots caused an immediate reduction in inspiratory intercostal activity. This reduction was abolished when phrenic stimulation was repeated after section of the C5 dorsal roots. 4. The reduction in external intercostal and levator costae activity during bilateral C5 afferent stimulation appeared when the stimulus strength was 3 times the motor threshold and it increased in magnitude when stimulus intensity was increased further. In contrast, the reduction in parasternal intercostal activity occurred only when the stimulus strength was 12 times the motor threshold. 5. These observations confirm the hypothesis that diaphragmatic receptors may reflexly inhibit efferent activity to the inspiratory intercostal muscles, in particular the external intercostals and levator costae. This inhibition appears to be primarily mediated by small myelinated fibres.

Animals↗

PubMed1991

Human respiratory muscles: fibre morphology and capillary supply.

In man the diaphragm (DIA) and abdominal muscles comprise approximately 50% slow-twitch (ST) fibres, whereas a higher proportion (60%) is found in intercostal muscles and the scalenes. All respiratory muscles show an equal distribution of fast-twitch (FTa and b) fibres with the exception of the expiratory intercostal muscles which have few FTb fibres. The inspiratory muscles have a uniformly small fibre size, in contrast to the expiratory intercostal muscle fibres which are large. The fibre size of the inspiratory muscles is maintained with ageing, whereas that of the expiratory intercostal muscles appears to be reduced after the age of 50 yrs. Capillary supply is most abundant in the expiratory muscles followed by DIA and the inspiratory intercostal muscles. In patients with chronic obstructive pulmonary disease (COPD) it is unknown whether a reduction in fibre size of the thoracic respiratory muscles is caused by extreme use due to increased ventilatory work, or by disuse due to an increased involvement of the extrathoracic respiratory muscles. Histochemical characteristics suggest that, in normal humans, the load on the inspiratory muscles is relatively small during contractions, whereas the expiratory intercostal muscles are exposed to severe continuous activity with a heavy load.

Adolescent↗

PubMed1992

[Dyspnea and respiratory reflexes].

It has been suggested that afferents from intercostal muscles may play a role in the genesis of dyspnea. In this study, lower intercostal muscles were tapped or vibrated to induce a reflex, evoked potentials, and sensation. The tapping stimulus induced H reflex in the same muscle with a latency of 12 msec. Also the same stimulus induced evoked potentials in the cerebral cortex (N1: 19.8 +/- 1.2 msec). This suggests projection of the intercostal muscle spindle afferents to the cerebral cortex. 100 Hz vibration induced a later component, presumably an event-related potential, at 250 msec after the onset of both the inspiratory and expiratory phase. Thus, it may be possible that intercostal muscle spindle afferents project to the cerebral cortex and play a role in respiratory sensation. It has been suggested that dyspnea is reduced by increasing inspiratory and expiratory intercostal muscle spindle afferents during the inspiratory and expiratory phases, respectively. Thus, stretching the inspiratory and expiratory intercostal muscles during the respective muscular contraction phase may be effective in reducing dyspnea.

Dyspnea↗

PubMed1981

Analysis of oxime-induced neuromuscular recovery in guinea pig, rat and man following soman poisoning in vitro.

The bispyridinium oximes HS6 and HI6 were tested in vitro for their ability to restore neuromuscular function in soman-poisoned tissue, using diaphragm and intercostal muscle of the rat and guinea pig and intercostal muscle of man. It was found that the oxime-mediated recovery of function in both tissues of the rat and guinea pig was composed of direct oxime actions, AChE reactivation and adaptation. In the human intercostal muscle, however, only adaptation was observed. These findings might suggest that HS6 and HI6 may have only limited value in the treatment of soman poisoning in man. However, recovery of function in rodent tissues was consistently greater in the diaphragm than in the intercostal muscle and, since human diaphragm tissue was not included in this study the therapeutic efficacy of these oximes in this tissue remains unknown.

Aged↗

PubMed1994

Upper airway muscle activity during REM and non-REM sleep of patients with obstructive apnea.

We measured electromyograms (EMGs) of genioglossus muscle (GG) and inspiratory intercostal muscle (IIM) in both rapid eye movement (REM) sleep and non-REM sleep of 12 patients with obstructive sleep apnea (OSA) to examine the influence of different sleep stages on upper airway muscle activity during sleep apnea. Quantifications of both muscle activities were assessed by their individual peak amplitude of integrated inspiratory EMG. Genioglossus and IIM activities showed a qualitatively similar cyclic change with an alteration of apneic and ventilatory phases during both non-REM and REM sleep. Both muscle activities increased gradually in the late apneic phase and reached each peak at the opening of the upper airway and, subsequently, decreased gradually. There were no significant differences in both muscles activities in either the ventilatory or early apneic phase between non-REM sleep and REM sleep. On the other hand, GG and IIM activities in the late apneic phase during REM sleep were significantly lower than those during non-REM sleep. The relative activity of GG to IIM in the late apneic phase was significantly lower during REM sleep than that during non-REM sleep. These results indicate that upper airway and intercostal muscle activation in the later apneic phase during REM sleep were inhibited compared with those during non-REM sleep and that this inhibition was observed predominantly in upper airway muscles.

Adult↗

PubMed2006

Dose response effect of cement dust on respiratory muscles competence in cement mill workers.

Electromyography (EMG) of respiratory muscles is a reliable method of assessing the ventilatory muscle function, but still its use has not been fully utilized to determine the occupational and environmental hazards on respiratory muscles. Therefore, EMG of intercostal muscles was performed to determine the dose response effect of cement dust on respiratory muscles competence. Matched cross-sectional study of EMG in 50 non-smoking cement mill workers with an age range of 20 - 60 years, who worked without the benefit of cement dust control ventilation or respiratory protective devices. EMG was performed by using surface electrodes and chart recorder. Significant reduction was observed in number of peaks (p < 0.0005), maximum peak amplitude (p < 0.0005), peak-to-peak amplitude (p < 0.0005) and duration of response (p < 0.0005) in cement mill workers compared to their matched control. Cement dust impairs the intercostal muscle competence and stratification of results shows a dose-effect of years of exposure in cement mill.

Adult↗

PubMed1992

Regional intercostal activity during coughing and vomiting in decerebrate cats.

Regional variations in the discharge patterns of the internal and external intercostal muscles of the middle and caudad thorax were studied in decerebrate, spontaneously breathing cats during coughing and vomiting. Coughing, induced by electrical stimulation of the superior laryngeal nerves, consisted of increased and prolonged diaphragmatic activity followed by a burst of abdominal activity. Mid-thoracic external and internal intercostal muscles discharged synchronously with the diaphragm and abdominal muscles, respectively. Caudal external and internal intercostal muscles, however, discharged synchronously with the abdominal muscles. Vomiting, induced by stimulation of the lower thoracic vagi, consisted of a series of synchronous bursts of diaphragmatic and abdominal activity (retching) followed by a prolonged abdominal discharge after the cessation of diaphragmatic activity (expulsion). Caudal external and internal intercostals discharged in phase with diaphragmatic and abdominal activity but both mid-thoracic intercostal muscles discharged out of phase with these muscles. These results indicate major differences in the control and functional roles of intercostal muscles at different thoracic levels during these behaviours.

Abdominal Muscles↗

PubMed1989

Costal pleura: appearances at high-resolution CT.

The appearance of the costal pleura at high-resolution computed tomography (CT) was evaluated with a cadaver and 25 normal subjects. This was contrasted with the high-resolution CT appearance of the costal pleura in 15 patients with mild pleural thickening, 13 of whom had been exposed to asbestos. On high-resolution CT scans in the normal subjects, a 1-2-mm-thick line of soft-tissue attenuation at the point of contact between lung and chest wall represents the visceral and parietal pleura, pleural contents, endothoracic fascia, and innermost intercostal muscle. In a paravertebral location, the innermost intercostal muscle is lacking, and a thin line seen on high-resolution CT scans reflects pleura and endothoracic fascia. Transverse thoracic and subcostal muscles and extrapleural fat pads can be seen as tissue internal to a rib and may be confused with pleural thickening. In 13 of the 15 patients with mild pleural thickening, the 1-3-mm-thick pleura was separable from the underlying normal intercostal muscle by a layer of extrapleural fat. High-resolution CT was more sensitive than CT with 1-cm collimation in depicting this degree of pleural abnormality.

Aged↗

PubMed1996

Mechanical significance of respiratory muscle activity in humans during halothane anesthesia.

BACKGROUND: Prior human studies have shown that halothane attenuates activity in the parasternal intercostal muscle and enhances phasic activity in respiratory muscles with expiratory actions. This expiratory muscle activity could contribute to reductions in the functional residual capacity produced by anesthesia. Termination of this activity could contribute to the maintenance of inspiratory rib cage expansion. The purpose of this study was to estimate in humans the mechanical significance of expiratory muscle activity during halothane anesthesia and to search for the presence of scalene muscle activity during halothane anesthesia that might contribute to inspiratory rib cage expansion. METHODS: Six subjects (3 males, 3 females) were studied while awake and during 1.2 MAC halothane anesthesia, both during quiet breathing and during carbon dioxide rebreathing. Respiratory muscle activity was measured using fine-wire electromyography electrodes. Chest wall configuration was determined using images of the thorax obtained by three-dimensional, fast computed tomography and respiratory impedance plethysmography. Functional residual capacity was measured by a nitrogen dilution technique. Measurements were obtained after paralysis with 0.1 mg/kg vecuronium and mechanical ventilation. RESULTS: Phasic inspiratory activity was present in the scalene muscle of four anesthetized subjects during quiet breathing and all anesthetized subjects during rebreathing. Phasic inspiratory activity was present in the parasternal intercostal muscle during halothane anesthesia in only the three female subjects and was enhanced by rebreathing; parasternal intercostal muscle activity was never present in anesthetized males. During anesthesia with quiet breathing, phasic expiratory activity was observed in the transversus abdominis muscles of only the three male subjects. Despite these differences in the pattern of respiratory muscle use, the pattern of chest wall responses to rebreathing was similar between males and females. When expiratory muscle activity was present, paralysis increased the end-expiratory thoracic volume by expanding the rib cage, demonstrating that this activity reduced thoracic volume in these subjects. Changes in thoracic blood volume were significant determinants of the change in functional residual capacity produced by paralysis. CONCLUSIONS: In humans anesthetized with 1.2 MAC end-tidal halothane, there are marked interindividual differences in respiratory muscle use during quiet breathing that may be related to sex; phasic inspiratory scalene muscle and parasternal intercostal muscle activity may contribute to inspiratory rib cage expansion in some subjects; and when present, expiratory muscle activity significantly constricts the rib cage and contributes to reductions in functional residual capacity caused by halothane anesthesia.

Adult↗

PubMed1987

Reduction of tonic ribcage muscle activity by anesthesia with thiopental.

Surface electromyograms were recorded from the scalene, sternomastoid, and parasternal intercostal muscles in 16 supine premedicated adult patients before, during, and after the induction of anesthesia with thiopental and after the administration of succinylcholine. Muscle activity was measured as the rectified, integrated signal, and expressed as a percentage of the activity detected during a maximal inspiration. Activity was found in the scalene and sternomastoid muscles of all patients, and in the intercostal muscles of 13. This activity was more commonly tonic, and, at end-expiration, it was 7%, 6%, and 5% of the activity that could be generated by a maximal inspiration, for the scalene, sternomastoid, and intercostal muscles, respectively. In all subjects, this activity was markedly reduced or abolished by the administration of thiopental, to 0.7%, 0.6%, and 0.6%, respectively. There was no tonic activity in these muscles during spontaneous respiration after induction of anesthesia. It is suggested that the reduction of tonic inspiratory activity in these muscles may contribute to the reduction in functional residual capacity associated with anesthesia.

Anesthesia↗