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PubMed1982

Response of ventilatory muscles of the rat to endurance training.

The effect of endurance training on the oxidative and glycolytic potentials of the diaphragm and intercostal muscles of rats has been studied. Training consisted of treadmill running (28 m/min, 60 min/day, 5 days/wk) for periods ranging from 8-26 weeks. Exercise of similar duration and intensity produced a glycogen depletion in the diaphragm and intercostal muscles of nontrained rats. Oxidative potential was estimated from the activity of the mitochondrial marker enzyme succinate dehydrogenase (SDH). The activities of phosphorylase (PHOS), hexokinase (HK), and lactate dehydrogenase (LDH) were determined as well as the distribution of the LDH isozymes. SDH activity averaged 44 (42-51) and 17 (10-22)% (P less than 0.0l) greater in the plantaris and diaphragm muscles, respectively, after 8-12 weeks of endurance running as compared to the sedentary animals. There was no change in the SDH activity of the intercostal muscles or in the activities of the glycolytic enzymes. There was also no change in the distribution of the isozymes of LDH. Extending the duration of the training program to 26 weeks did not produce any additional alteration in the magnitude of the adaptation observed after the initial training period. Comparative studies of different types of muscles demonstrated that the diaphragm, although having a fiber composition somewhat similar to that of a fast-twitch skeletal muscle, has a metabolic profile that is intermediate between pure slow twitch skeletal muscle and cardiac muscle.

Adaptation, Physiological↗
PubMed1988

Effect of stimulation of pulmonary C-fiber receptors on canine respiratory muscles.

The effects of stimulation of pulmonary C-fiber receptors on the distribution of motor activity to upper airway, rib cage, and abdominal muscles were studied in anesthetized, tracheotomized, spontaneously breathing dogs. Stimulation of pulmonary C-fiber receptors by injection of capsaicin (3-20 micrograms/kg) into the right atrium resulted in complete cessation of electrical activity of the upper airway dilating muscles (UADM) and the inspiratory chest wall pumping muscles. The activity of abdominal muscles was also inhibited. The duration of electrical silence was longer for the diaphragm than for the UADM. Upper airway constricting muscles and expiratory intercostal muscles, including the triangularis sterni, remained tonically active during the apneic period. The responses of these muscles were qualitatively the same when the animals breathed 100% O2, 7% CO2 in O2, or 12% O2 in N2, and without or in the presence of an expiratory threshold load. Bilateral vagotomy abolished the inhibitory effects of capsaicin on UADM, chest wall, and abdominal muscle activity, suggesting that the vagus is the major afferent pathway for the reflex. The qualitative difference in the response of intercostal expiratory muscles and abdominal muscles suggests that these two groups of synergistic muscles may be independently regulated.

Animals↗
PubMed1993

Differential recruitment of inspiratory muscles in response to chemical drive.

Changes in the intensity of EMG activity in the costal diaphragm, crural diaphragm and external intercostal muscle during inspiration were assessed in intact, awake lambs following abrupt transitions in the composition of the inspired gases from air to either a hypoxic/hypoxic mixture (10% O2, 90% N2), a hyperoxic/hypercapnic mixture (40% O2, 6% CO2, 54% N2) or a hypoxic/hypercapnic mixture (10% O2, 6% CO2, 84% N2). A regression method was used to compare the dynamic responses of the three muscles over the 10-min period following each transition. The relationship between the dynamic response functions of the costal and crural diaphragm was the same in each of the three experimental conditions, indicating that these separate components of the diaphragm comprise a single functional unit during breathing. The relationship between the dynamic response functions of the external intercostal muscle and the costal diaphragm varied according to the composition of the inspired gas mixture. This result suggests that the central and peripheral chemoreceptors exert differential effects on the activation of the diaphragm and the external intercostal muscles during breathing, consistent with the hypothesis that sensory information from these receptors is processed, at least in part, in parallel pathways which project separately to the phrenic and external intercostal motoneurons.

Animals↗
PubMed1999

Characterization of the early development of specific hypaxial muscles from the ventrolateral myotome.

We have previously found that the myotome is formed by a first wave of pioneer cells generated along the medial epithelial somite and a second wave emanating from the dorsomedial lip (DML), rostral and caudal edges of the dermomyotome (Kahane, N., Cinnamon, Y. and Kalcheim, C. (1998a) Mech. Dev. 74, 59-73; Kahane, N., Cinnamon, Y. and Kalcheim, C. (1998b) Development 125, 4259-4271). In this study, we have addressed the development and precise fate of the ventrolateral lip (VLL) in non-limb regions of the axis. To this end, fluorescent vital dyes were iontophoretically injected in the center of the VLL and the translocation of labeled cells was followed by confocal microscopy. VLL-derived cells colonized the ventrolateral portion of the myotome. This occurred following an early longitudinal cell translocation along the medial boundary until reaching the rostral or caudal dermomyotome lips from which fibers emerged into the myotome. Thus, the behavior of VLL cells parallels that of their DML counterparts which colonize the opposite, dorsomedial portion of the myotome. To precisely understand the way the myotome expands, we addressed the early generation of hypaxial intercostal muscles. We found that intercostal muscles were formed by VLL-derived fibers that intermingled with fibers emerging from the ventrolateral aspect of both rostral and caudal edges of the dermomyotome. Notably, hypaxial intercostal muscles also contained pioneer myofibers (first wave) showing for the first time that lateral myotome-derived muscles contain a fundamental component of fibers generated in the medial domain of the somite. In addition, we show that during myotome growth and evolution into muscle, second-wave myofibers progressively intercalate between the pioneer fibers, suggesting a constant mode of myotomal expansion in its dorsomedial to ventrolateral extent. This further suggests that specific hypaxial muscles develop following a consistent ventral expansion of a 'compound myotome' into the somatopleure.

Animals↗
PubMed2004

Histamine induced airway response in pre-school children assessed by a non-invasive EMG technique.

The aim of the study was to investigate the association between surface electromyographic (EMG) activity of the diaphragm and intercostal muscles, and clinical symptoms (wheeze, cough, increased respiratory rate and prolonged expiration) during bronchial challenge testing and after administration of salbutamol in asthmatic pre-school children. A histamine challenge test was performed in 20 asthmatic pre-school children. The histamine dose at the appearance of 1 or more clinical symptoms was defined as the maximum histamine provocation dose (PDcs). The clinical symptoms were recorded with a microphone over the trachea. The logarithm of the EMG-Activity-Ratio (log EMGAR; mean peak activity ratio to baseline of respiratory muscles during tidal breathing) was used as EMG parameter. In both the diaphragmatic and the intercostal log EMGAR values a linear increase was observed in the four histamine dose-steps prior to PDcs. At PDcs the mean log EMGAR of the diaphragm (di) and intercostal muscles (int) was significantly increased as compared to the baseline values. After administration of salbutamol the log EMGARdi and log EMGARint returned to baseline values and the clinical symptoms normalized in all children. At PDcs, no significant differences in the log EMGAR values could be detected at the appearance of the distinctive clinical symptoms, which suggests that wheezing is not the only indicator for the detection of airway responsiveness in young children. We found a linear association between histamine dose and the increase in surface diaphragmatic and intercostal respiratory EMG activity during a bronchial challenge test in pre-school asthmatic children, which returned to baseline values after inhalation of salbutamol. These findings support the idea that EMG measurements of the diaphragm and intercostal muscles may offer an opportunity to estimate airway response in young children in an alternative way.

Administration, Inhalation↗
PubMed1999

[Peroxide metabolism on respiratory muscles: effect of growth, maturation and aging].

BACKGROUND: Glutathione peroxidase (GSHPx) and catalase are two important cellular antioxidant enzymes involved in H2O2 and lipid-peroxide metabolism. AIM: To study the effects of growth, maturation and aging on the activity of these enzymes. MATERIAL AND METHODS: GSHPx and catalase specific activities were measured in samples of diaphragm and intercostal muscle of male Sprague-Dawley rats of different ages (21, 50, 70, 180 and 365 days), anesthetised with chloral hydrate (45 mg/100 g i.p.). RESULTS: The diaphragm and intercostal muscles did not differ in GSHPx activity at 21 days. After that, GSHPx activity increased progressively with age, but following a different pattern, in each muscle, suggesting an increase in enzyme substrates with age. In one year old animals, GSHPx activity was 5 times higher for the diaphragm and 3 times higher for the intercostal muscles, when compared with values observed at 21 days of age. Catalase activity also increased with age in the diaphragm but not in the intercostal muscles. CONCLUSIONS: GSHPx activity increases progressively with age in rat respiratory muscles, with a time course that is specific of each muscle. Catalase activity increases with age only in the diaphragm. These results support the hypothesis that antioxidants in respiratory muscles undergo specific regulatory changes with age.

Age Factors↗
PubMed1995

Chest wall responses to rebreathing in halothane-anesthetized dogs.

BACKGROUND: The pattern of respiratory muscle use during halothane-induced anesthesia differs markedly among species breathing quietly. In humans, halothane accentuates phasic activity in rib cage and abdominal expiratory muscles, whereas activity in the parasternal intercostal muscles is abolished. In contrast, halothane abolishes phasic expiratory muscle activity during quiet breathing in dogs, but parasternal muscle activity is maintained. Respiratory muscle responses to CO2 rebreathing were measured in halothane-anesthetized dogs to determine if species differences present during quiet breathing persist over a wide range of central respiratory drive. METHODS: Chronic electromyogram electrodes were implanted in three expiratory agonists (the triangularis sterni, transversus abdominis, and external oblique muscles) and three inspiratory agonists (the parasternal intercostal muscle, costal and crural diaphragm) of six mongrel dogs. After a 1-month recovery period, the dogs were anesthetized in the supine position with halothane. The rebreathing response was determined by Read's method during anesthesia with stable 1 and 2 minimum alveolar end-tidal concentrations of halothane. CO2 concentrations were measured in the rebreathing bag using an infrared analyzer. Chest wall motion was measured by fast three-dimensional computed tomographic scanning. RESULTS: Halothane concentration did not significantly affect the slope of the relationship between minute ventilation (VE) and PCO2 (0.34 +/- 0.04 [M +/- SE] and 0.28 +/- 0.05 l.min-1.mmHg-1 during 1 and 2 minimum alveolar concentration anesthesia, respectively). However, 2 minimum alveolar concentration anesthesia did significantly decrease the calculated VE at a PCO2 of 60 mmHg (from 7.4 +/- 1.2 to 4.0 +/- 0.6 l.min-1), indicating a rightward shift in the response relationship. No electromyographic activity was observed in any expiratory muscle before rebreathing. Rebreathing produced electromyographic activity in at least one expiratory muscle in only two dogs. Rebreathing significantly increased electromyographic activity in all inspiratory agonists. Rebreathing significantly increased inspiratory thoracic volume change (delta Vth), with percentage of delta Vth attributed to outward rib cage displacement increasing over the course of rebreathing during 1 minimum alveolar concentration anesthesia (from 33 +/- 6% to 48 +/- 2% of delta Vth). CONCLUSIONS: Rebreathing did not produce expiratory muscle activation in most dogs, demonstrating that the suppression of expiratory muscle activity observed at rest persists at high levels of ventilatory drive. Other features of the rebreathing response also differed significantly from previous reports in halothane-anesthetized humans, including (1) an increase in the rib cage contribution to tidal volume during the course of rebreathing, (2) recruitment of parasternal intercostal activity by rebreathing, (3) differences in the response of ventilatory timing, and (4) the lack of effect of anesthetic depth on the slope of the ventilatory response. These marked species differences are further evidence that the dog is not a suitable model to study anesthetic effects on the activation of human respiratory muscles.

Anesthetics, Inhalation↗
PubMed1989

Blood flow to the respiratory muscles during hypercapnic hyperpnoea in the newborn lamb.

The blood flow to the diaphragm, external and internal intercostal muscles, abdominal oblique muscles, and other rib-cage and abdominal muscles was measured, using radio-labelled microspheres, in 6 newborn lambs quietly breathing in air and during 3 different levels of CO2 induced hypercapnic hyperpnoea (inspired gas containing 4%, 5.5%, or 7% CO2). We also calculated the oxygen uptake of the diaphragm (VO2di). While the lambs were breathing air diaphragmatic blood flow (Qdi, 38.2 +/- 4.0 SEM ml.min-1.100 g-1) was similar to external intercostal muscle blood flow (Qei, 37.1 +/- 8.1 ml.min-1.100 g-1), and both were greater than internal intercostal muscle blood flow (Qii, 24.8 +/- 6.1 ml.min-1.100 g-1; P less than 0.05). During hyperpnoea Qdi, Qei, and Qii were augmented with Qdi equal to 200.1 +/- 12.2 ml.min-1.100 g-1 in 7% CO2 and Qei equal to 88.4 +/- 14.1 ml.min-1.100 g-1 in 7% CO2 (Qdi was greater than Qei, P less than 0.01). Qii was 40.7 +/- 5.6 ml.min-1.100 g-1 in 7% CO2 being less than Qdi (P less than 0.01) and Qei (P less than 0.05). The abdominal oblique muscles also had augmented flow in response to hyperpnoea. The level of hypercapnia that resulted in an augmentation of Qdi (5.5% inspired CO2) was lower than that which augmented Qei and Qii (7% inspired CO2). VO2di was linearly related to Qdi (r = 0.98). Our results suggest that in the newborn lamb the diaphragm is the dominant respiratory muscle in response to hypercapnia.

Animals↗
PubMedDate not supplied

Adaptation of skeletal muscles to training.

Based on the myosin ATPase reaction, human skeletal muscles are composed of two main fibre types, named slow (ST) and fast (FT) twitch fibres, respectively. With few exceptions, ST and FT fibres are evenly represented in the muscles, however with a large interindividual variation. Endurance athletes tend to have a predominance of ST fibres while sprinters have a predominance of FT fibres. The ST fibres are surrounded by 3-4 capillaries, and they have the largest potential for terminal oxidation and the smallest for glycolysis. Of the FT fibres, two subtypes may be distinguished (a and b), of which no FTb fibres are seen in the endurance trained muscles of athletes. Training also results in an increase in the number of capillaries for all fibre types. FTa fibres have a metabolic potential which is intermediate to that of the ST and FTb fibres. With endurance training, the potential for terminal oxidation increases, resulting in a larger ability to use fat as a fuel during submaximal exercise and in a reduced production of lactate. Thus, training has a glycogen sparing effect and endurance increases. Human intercostal muscles appear to have approximately 60% ST fibres. In the external intercostal muscles, the number of capillaries and the occurrence of FTb fibres is similar to the findings in untrained muscles. In contrast, the internal intercostal muscles placed in the mid-axillary line have no FTb fibres and relatively many capillaries. Thus, these (expiratory) muscles appear to be extensively used.

Adenosine Triphosphatases↗
PubMed1978

Respiration in man affected by TVR contractions elicited in inspiratory and expiratory intercostal muslces.

Vibration-induced effects on respiration in man were studied by recording the electrical activity (EMG) from the intercostal muscles and the diaphragm. The vibration was applied in an upper thoracic region where inspiratory muscle activity prevailed or in a lower thoracic region where expiratory muscle activity prevailed. The effects were also studied by recording the movements of the thorax and the respiratory air flow. Sustained vibration in the upper region enhanced the activity of the underlying inspiratory muscles and caused an expansion of the rib cage whereas it had little or weak effects on diaphragm-activity or on expiratory intercostal muscles. Sustained vibration in the lower region enhanced the activity of the underlying expiratory muscles, often inhibited the inspiratory activity and caused a depression of the rib cage. It also tended to inhibit the diaphragm activity. It was also found that bilateral vibration, timed by the respiratory movements and alternating between upper and lower regions could aid or counteract the ventilation if it was applied respectively 'in phase' or 'out of phase' with the rhythmical contractions in the underlying muscles. The motor responses described are largely explicable in terms of tonic vibration reflexes (TVR) arising in the inspiratory and expiratory intercostal muscles underlying the vibrators.

Adult↗
PubMed1997

Patterns of inspiratory muscle shortening during hypoxia and hypercapnia in dogs.

The shortening of parasternal intercostal muscles (Para) and crural (Cru) and costal diaphragms (Cos) are not precisely understood. We therefore examined shortening patterns of these inspiratory muscles by using chronically implanted sonomicrometers in dogs. To avoid acute effects of surgery, measurements were performed 3 weeks after implanting the sonomicrometers. Patterns of length changes of Para, Cru, and Cos were measured during hypoxia and hypercapnia under two levels of anaesthesia. Respiratory length change (delta L) was assessed as a percentage change relative to the resting length at functional residual capacity (LFRC). Peak tidal shortening was defined as the maximal change from LFRC (delta L/LFRC). Under light anesthesia, the delta L/LFRC was the same among the three muscle groups at all tidal volumes (VT). Under deep anaesthesia, the delta L/LFRC both of Cru and Cos exceeded that of Para. Under light anaesthesia, the maximal shortening velocity ((delta L/LFRC)/delta t) of Cru was greater than that of Para. Under deep anaesthesia, the (delta L/LFRC)/delta t of Para was exceeded by that both of Cru and Cos. Furthermore, the (delta L/LFRC)/delta t of each inspiratory muscle was greater during hypoxia than during hypercapnia at equal volume. We conclude that: 1) the contribution of the diaphragm to ventilation increases during deep anaesthesia; 2) the muscle shortening velocity during hypoxia or hypercapnia is lower in parasternal intercostal muscles than in the diaphragm; and 3) there is no difference in the shortening pattern between crural and costal diaphragms.

Anesthesia↗
PubMed1975

Experience with surgical salvage in pulmonary tuberculosis: application to general thoracic surgery.

The diminishing incidence of pulmonary tuberculosis and the increasing effectiveness of drug therapy have resulted in an almost complete disappearance of surgical problems in the management of patients with this disease. However, the lessons learned from the management of such problems should not be forgotten, for they are equally applicable to the management of disabling and life-endangering problems in general thoracic surgical practice. "Salvage" situations develop when therapeutic requirements for control of disease are combined with factors affecting a patient's health so as to increase the surgical risk beyond the range usually considered acceptable. Attempts to salvage patients are indicated when treatment has failed to arrest disease, when life expectancy is threatened, or when return to normal activity is imperiled. Risk may be increased because of age, inadequate cardiopulmonary reserve, or chronic toxemia; in tuberculosis, risk may be increased because of positive sputum culture or resistance of organisms. Experience with 146 tuberculous patients has provided a basis for evaluation of the indications for resection, prophylactic and therapeutic thoracoplasty, and closure of bronchopleural fistulas in general thoracic surgical salvage. Both infection in residual spaces and bronchopleural fistulas are serious complications that can be controlled by thoracoplasty and pedicled muscle grafts. Prophylactic use of osteoplastic thoracoplasty and intercostal muscle grafts warrant more serious consideration. In established complications a "tailored" thoracoplasty can also be combined with an intercostal muscle graft.

Bronchial Fistula↗
PubMed1992

Peripheral and central delays in the cortical projections from human truncal muscles. Rapid central transmission of proprioceptive input from the hand but not the trunk.

In contrast to the cortical connections to and from the muscles of the hand, the transmission of an afferent volley from the intercostal muscles to the cerebral cortex takes approximately 10 ms longer than it takes a cortical motor volley to reach the muscle. This disparity in afferent and efferent cortical transmission times could be due to a slower peripheral conduction velocity of intercostal muscle afferents or a slower afferent conduction within the central nervous system. The present study derived peripheral and central conduction times for the truncal muscles from the onsets of the mechanically evoked intercostal and abdominal spinal reflexes and the onsets of the cortical sensory potentials. Mean latencies of the ipsilateral intercostal and abdominal reflexes (evoked and recorded in the mid-clavicular line) were 11.9 +/- 0.7 (SEM) ms and 13.7 +/- 0.9 ms, respectively; calculated peripheral conduction velocities were 69.4 +/- 4.1 m/s and 56.2 +/- 2.3 m/s (assuming equal velocities for the sensory and motor axons and an intraspinal delay of 1 ms). Central sensory conduction time (spinal cord to cortex) was calculated by subtracting the peripheral conduction times for the intercostal and abdominal afferents (5.5 +/- 0.3 ms and 6.4 +/- 0.4 ms) from the onsets of the cortical sensory potentials (19.4 +/- 0.8 ms and 25.3 +/- 12.3 ms); central sensory conduction times (14.2 +/- 1.7 ms and 18.6 +/- 2.3 ms) were 8-11 ms longer than central motor conduction times. These results demonstrate that peripheral conduction velocities of intercostal and abdominal afferents are not slow, and that, when compared with the extremities, there is a relatively long central conduction time for proprioceptive information from the trunk to the cerebral cortex.

Adult↗
PubMed1992

Expiratory activity of the inspiratory muscles during cough.

To investigate the neural mechanism of the expiratory activity of the inspiratory muscles during a cough, EMG of the respiratory muscles were recorded in anesthetized and tracheostomized dogs. A laparoscope was used to minimize injury to the abdominal muscles for implantation of the electrodes into the costal diaphragm. During the expulsive phase of a cough, the diaphragm was active in 7 of 12 dogs and the external intercostal muscle was active in 3 of 6 dogs. During a cough, the expiratory activity of the diaphragm, after the termination of its inspiratory activity, started at 52.9 +/- 24.6 ms, and that of external intercostal muscle started at 51.1 +/- 20.5 ms. The expiratory activity of the internal intercostal muscle and of the transversus abdominis started at 34.3 +/- 13.0 and 27.8 +/- 15.2 ms, respectively. The onset of expiratory activity of the inspiratory muscles is significantly later than that of expiratory muscles. Continuous activity in the expiratory muscles evoked by airway occlusion, i.e., Hering-Breuer reflex, was suppressed during the inspiratory phase of a cough, but not suppressed during the expulsive phase even when the expiratory activity of the diaphragm was observed. We concluded that the expiratory activity of inspiratory muscles is controlled independently of both expiratory activity of the expiratory muscles and inspiratory activity of the inspiratory muscles.

Animals↗
PubMed1997

MyoD and Myf-5 differentially regulate the development of limb versus trunk skeletal muscle.

The myogenic progenitors of epaxial (paraspinal and intercostal) and hypaxial (limb and abdominal wall) musculature are believed to originate in dorsal-medial and ventral-lateral domains, respectively, of the developing somite. To investigate the hypothesis that Myf-5 and MyoD have different roles in the development of epaxial and hypaxial musculature, we further characterized myogenesis in Myf-5- and MyoD-deficient embryos by several approaches. We examined expression of a MyoD-lacZ transgene in Myf-5 and MyoD mutant embryos to characterize the temporal-spatial patterns of myogenesis in mutant embryos. In addition, we performed immunohistochemistry on sectioned Myf-5 and MyoD mutant embryos with antibodies reactive with desmin, nestin, myosin heavy chain, sarcomeric actin, Myf-5, MyoD and myogenin. While MyoD(-/-) embryos displayed normal development of paraspinal and intercostal muscles in the body proper, muscle development in limb buds and brachial arches was delayed by about 2.5 days. By contrast, Myf-5(-/-) embryos displayed normal muscle development in limb buds and brachial arches, and markedly delayed development of paraspinal and intercostal muscles. Although MyoD mutant embryos exhibited delayed development of limb musculature, normal migration of Pax-3-expressing cells into the limb buds and normal subsequent induction of Myf-5 in myogenic precursors was observed. These results suggest that Myf-5 expression in the limb is insufficient for the normal progression of myogenic development. Taken together, these observations strongly support the hypothesis that Myf-5 and MyoD play unique roles in the development of epaxial and hypaxial muscle, respectively.

Animals↗
PubMed2006

Effect of diaphragmatic contraction on the action of the canine parasternal intercostals.

The inspiratory intercostal muscles enhance the force generated by the diaphragm during lung expansion. However, whether the diaphragm also alters the force developed by the inspiratory intercostals is unknown. Two experiments were performed in dogs to answer the question. In the first experiment, external, cranially oriented forces were applied to the different rib pairs to assess the effect of diaphragmatic contraction on the coupling between the ribs and the lung. The fall in airway opening pressure (deltaPa(O)) produced by a given force on the ribs was invariably greater during phrenic nerve stimulation than with the diaphragm relaxed. The cranial rib displacement (Xr), however, was 40-50% smaller, thus indicating that the increase in deltaPa(O) was exclusively the result of the increase in diaphragmatic elastance. In the second experiment, the parasternal intercostal muscle in the fourth interspace was selectively activated, and the effects of diaphragmatic contraction on the deltaPa(O) and Xr caused by parasternal activation were compared with those observed during the application of external loads on the ribs. Stimulating the phrenic nerves increased the deltaPa(O) and reduced the Xr produced by the parasternal intercostal, and the magnitudes of the changes were identical to those observed during external rib loading. It is concluded, therefore, that the diaphragm has no significant synergistic or antagonistic effect on the force developed by the parasternal intercostals during breathing. This lack of effect is probably related to the constraint imposed on intercostal muscle length by the ribs and sternum.

Airway Resistance↗
PubMed1993

Respiratory function of the rib cage muscles.

Elevation of the ribs and expansion of the rib cage result from the co-ordinated action of the rib cage muscles. We wished to review the action and interaction of the rib cage muscles during ventilation. The parasternal intercostal muscles appear to play a predominant role during quiet breathing, both in humans and in anaesthetized dogs. In humans, the parasternal intercostals act in concert with the scalene muscles to expand the upper rib cage, and/or to prevent it from being drawn inward by the action of the diaphragm. The external intercostal muscles are considered to be active mainly during inspiration, and the internal intercostal muscles during expiration. The respiratory activity of the external intercostals is minimal during quiet breathing both in man and in dogs, but increases with increasing ventilation. Inspiratory activity in the external intercostals can be enhanced in anaesthetized animals and humans by inspiratory mechanical loading and by CO2 stimulation, suggesting that the external intercostals may constitute a reserve system, that may be recruited when the desired expansion of the rib cage is increased. The triangularis sterni is an important expiratory muscle during quiet breathing in animals, but it is not active during quiet breathing in man. However, during expiration below functional residual capacity (FRC), and during speech, laughing and coughing, the triangularis sterni is recruited and plays an increasingly important role.

Biomechanical Phenomena↗