Biomedical subjects

A De Troyer

Publications and source records attributed to A De Troyer.

At least 19 recordsLinked to original sources

PubMed1997

On the intercostal muscle compensation for diaphragmatic paralysis in the dog.

1. Paralysis of the diaphragm in the dog is known to cause a compensatory increase in activation of the inspiratory intercostal muscles (parasternal intercostals, external intercostals, and levator costae). The present studies were designed to assess the mechanism(s) of that compensation. 2. Complete, selective diaphragmatic paralysis was induced by injecting local anaesthetic into small silicone cuffs placed around the phrenic nerve roots in the neck. 3. Paralysis produced a decrease in tidal volume and an increase in arterial P(CO2) (P(a,CO2)). The increased hypercapnic drive was a primary determinant of the increased inspiratory intercostal activity. 4. However, paralysis also produced an increased inspiratory cranial displacement of the ribs. When this increased rib displacement was reduced to that seen before paralysis, it appeared that the increase in external intercostal and levator costae inspiratory activity was commonly greater than anticipated on the basis of the increased P(a,CO2). 5. Diaphragmatic paralysis after bilateral vagotomy also elicited disproportionate increases in inspiratory intercostal activity, thus indicating that these increases are not caused by vagal afferent inputs. 6. These observations are consistent with the idea that the intercostal muscle compensation for diaphragmatic paralysis is, in part, due to the release of an inhibition originating from the contracting diaphragm. This inhibition might arise in the diaphragmatic tendon organs.

Anesthetics, Local↗

PubMed1997

Actions of the inspiratory intercostal muscles in flail chest.

We have previously shown in dogs that the ribs in flail chest move paradoxically inward during inspiration but continue to move cranially. We have also shown that flail elicits, probably via an increased activation of the muscle spindles, a threefold to fourfold increase in external intercostal inspiratory EMG activity without inducing any changes in parasternal intercostal activity. Therefore, the present studies were undertaken to test the hypothesis that the persistent cranial motion of the fractured ribs resulted primarily from the action of the external intercostals. A flail was induced in seven supine anesthetized animals by fracturing both dorsally and ventrally ribs 3 to 6 on the right side of the chest, after which the external intercostal muscles in interspaces 1 to 7 were severed. Severing the external intercostals caused a small increase in the inspiratory inward displacement of the fractured ribs, from 2.76 +/- 0.31 to 3.25 +/- 0.38 mm (p < 0.05), but it did not affect the parasternal intercostal EMG activity or the cranial rib displacement (before, 3.61 +/- 1.03 mm; after, 3.22 +/- 1.43 mm; NS). However, when the parasternal intercostals in interspaces 1 to 7 were also denervated, the inspiratory inward displacement of the ribs increased markedly to 5.95 +/- 0.48 mm (p < 0.01), and their inspiratory cranial displacement was reversed into a 1.05 +/- 0.58 mm inspiratory caudal displacement (p < 0.01). We conclude, therefore, that in dogs with flail chest the respiratory displacements of the ribs are still primarily determined, besides pleural pressure, by the action of the parasternal intercostals. These observations also suggest that in anesthetized dogs, spindle-induced excitation of the external intercostals has little impact on the mechanical behavior of the ribs.

Animals↗

PubMed1997

Neural drive to the diaphragm in patients with severe COPD.

Patients with severe chronic obstructive pulmonary disease (COPD) have a greater neural drive to the parasternal intercostal and scalene muscles and greater inspiratory expansion of the rib cage than do healthy individuals. However, such patients also have a reduced outward displacement or a paradoxical inward displacement of the ventral abdominal wall during inspiration. This has led to the suggestion that they may have less use of the diaphragm, possibly secondary to chronic muscle fatigue. To assess the effect of COPD on the neural drive to the diaphragm, we inserted needle electrodes into the costal part of the right hemidiaphragm in eight patients with severe disease (mean [+/- SD] FEV1: 0.82 [+/- 0.27] L) and six control subjects of similar age, and measured the discharge frequencies of single motor units during resting breathing. A total of 115 diaphragmatic motor units were recorded in the control subjects and 122 in the patients. All motor units discharged rhythmically in phase with inspiration. However, whereas 95% of the units in the control subjects had a peak discharge frequency between 7 and 14 Hz, 79% of the units in the COPD patients had a peak discharge frequency greater than 15 Hz. As a result, the discharge frequency of all units averaged 10.5 [+/- 2.4] Hz in the control subjects, but 17.9 [+/- 4.3] Hz in the patients (p < 0.001). These observations indicate that patients with severe COPD have an increased neural drive not only to the rib cage inspiratory muscles, but also to the diaphragm. Consequently, the reduced inspiratory expansion of the abdomen in severe COPD results from mechanical factors alone.

Aged↗

PubMed1997

Effect of hyperinflation on the diaphragm.

Acute hyperinflation causes the inspiratory muscles to operate at shorter than normal lengths. The ability of these muscles, in particular the diaphragm, to lower intrathoracic pressure is therefore reduced. Skeletal muscles, however, adapt to chronic shortening, and animals models of emphysema have shown that with chronic hyperinflation, the diaphragmatic muscle fibres lose sacromeres. As a result, the force-generating ability of these fibres is relatively preserved. In patients with hyperinflation due to chronic obstructive pulmonary disease, the ability of the diaphragm to generate pressure is also better than anticipated on the basis of hyperinflation alone. However, the diaphragm in these patients is also lower in the chest wall than in healthy subjects. Consequently, even though the neural drive to the muscle is greater than normal, its ability to descend during inspiration is impaired. Its rib cage expanding action is also reduced; in patients with severe hyperinflation, contraction of the diaphragm even produces deflation, rather than expansion, of the rib cage. In such patients, therefore, the ability of the diaphragm to increase lung volume is reduced, and hence the act of breathing is more dependent on the rib cage inspiratory muscles.

Animals↗

PubMed1996

Rostrocaudal gradient of mechanical advantage in the parasternal intercostal muscles of the dog.

1. Previous theoretical studies have led to the predictions that, in the dog, the parasternal intercostal muscles in the rostral interspaces shorten more during passive inflation than those in the caudal interspaces and have, therefore, a greater inspiratory mechanical advantage. The present studies were undertaken to test these predictions. 2. The effects of passive inflation on the length of the parasternal intercostals interspaces 1 to 7 were evaluated with markers implanted in the costal cartilages. Although the muscles in all interspaces shortened with passive inflation, the fractional shortening increased from the first to the second and third interspaces and then decreased continuously to the seventh interspace. 3. To understand this peculiar distribution, a geometric model of the parasternal area was then developed and a relation was obtained between muscle shortening and the angles that describe the orientation of the muscle and costal cartilage relative to the sternum. Measurement of these angles indicated that the rostrocaudal gradient of parasternal shortening resulted from the different orientations of the costal cartilages and their different rotations during passive inflation. 4. The changes in airway pressure generated by the parasternal intercostals in interspaces 3, 5 and 7 were finally measured during selective, maximal stimulation. The fall in pressure was invariably greatest during contraction of the third interspace and smallest during contraction of the seventh. 5. These observations indicate that, in the dog, the rostrocaudal gradient in rib rotation induces a rostrocaudal gradient of mechanical advantage in the parasternal intercostals, which has its climax in the second and third interspaces. These observations also support the concept that the respiratory effect of a given respiratory muscle can be computed from its behaviour during passive inflation.

Animals↗

PubMed1996

Rostrocaudal gradient of electrical activation in the parasternal intercostal muscles of the dog.

1. Because the inspiratory mechanical advantage of the canine parasternal intercostal muscles is greatest in the third interspace and decreases gradually in the caudal direction, the electromyograms of these muscles in interspaces 3, 5 and 7 have been recorded in anaesthetized, spontaneously breathing dogs. Each activity was expressed as a percentage of the activity measured during tetanic, supramaximal stimulation of the internal intercostal nerve (maximal activity). 2. Parasternal inspiratory activity during resting, room air breathing was invariably greater in the third than in the fifth interspace (62.0 +/- 6.0 vs. 41.3 +/- 4.6% of maximal activity; P < 0.001) and smallest in the seventh interspace (22.8 +/- 2.7% of maximal activity; P < 0.001). This distribution of activity persisted during hyperoxic hypercapnia and during breathing against increased inspiratory airflow resistance. 3. This rostrocaudal distribution of activity also persisted after complete paralysis of the diaphragm as well as after deafferentation of the ribcage. 4. Studies of the distribution of the muscle fibre types indicated that the parasternal intercostals in all interspaces had a higher proportion of slow-twitch oxidative (SO; type I) fibres than fast-twitch oxidative-glycolytic (FOG; type II a) fibres. 5. Thus the topographic distribution of parasternal inspiratory activity along the rostrocaudal axis of the ribcage is precisely matched with the topographic distribution of mechanical advantage. This extraordinarily effective pattern of activation probably results from the unequal distribution of central inputs throughout the parasternal motoneurone pool.

Animals↗

PubMed1996

Rib motion modulates inspiratory intercostal activity in dogs.

1. A test was performed of the hypothesis that the motion of the ribs during inspiration modulates, via changes in spindle afferent activity, the activation of the inspiratory intercostal muscles. The electrical activity of the parasternal intercostal, external intercostal, and levator costae muscles in anaesthetized spontaneously breathing dogs was thus recorded during manipulation of the inspiratory displacement of the ribs over a wide range of rib motion. 2. In agreement with the hypothesis, the external intercostal and levator costae muscles lengthened and showed increased inspiratory activities when the normal inspiratory cranial motion of the lower rib was reduced or reversed into an inspiratory caudal motion. Conversely, the inspiratory activities decreased when the inspiratory cranial motion of the rib and the inspiratory shortening of the muscles was augmented. The inspiratory activity of the parasternal intercostal remained unchanged throughout. 3. However, when the two ribs making up the interspace were linked together so that the external intercostal muscle was constant in length, the relationship of muscle activity to rib motion was maintained. 4. In addition, when the upper rather than the lower rib of the interspace was manipulated, the relationship between the change in muscle length and inspiratory activity was reversed, so that activity decreased when the muscle was lengthened and increased when the muscle was shortened. The relationship of muscle activity to lower rib motion, however, was still maintained. 5. These observations thus indicate that rib motion triggers proprioceptive reflexes which, regardless of the changes in length of the individual muscles, make the external intercostal inspiratory activity exquisitely sensitive to the direction of rib displacement.

Animals↗

PubMed1996

On the mechanism of the mediolateral gradient of parasternal activation.

Recent studies have shown that in spontaneously breathing dogs the parasternal intercostals are activated according to a mediolateral gradient. To assess the mechanism of this regionalization of activity, we assessed the pattern of activation of these muscles after section of the dorsal roots and examined the topographic distribution of the muscle fiber types from the sternum to the chondrocostal junctions. The pattern of parasternal activity after dorsal rhizotomy was similar in all respects to that previously observed in intact animals. Thus activity in the medial parasternal bundles at the onset of inspiration frequently preceded activity in the middle bundles, and no activity was recorded from the lateral bundles. The amount of medial activity, when expressed as a percentage of the activity recorded during supramaximal tetanic stimulation of the internal intercostal nerve (maximal activity), was also consistently greater than the amount of middle activity (52.6 +/- 4.6 vs. 23.1 +/- 2.6% maximal activity; P < 0.001). Furthermore, the medial, middle, and lateral parasternal bundles had a higher proportion of slow-twitch oxidative fibers than of fast-twitch oxidative-glycolytic fibers; no topographic difference in fiber type distribution was observed. We conclude, therefore, that the mediolateral gradient of parasternal activity is probably due to the unequal distribution of central inputs throughout the pool of alpha-motoneurons.

Animals↗

PubMed1996

Sternomastoid muscle size and strength in patients with severe chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) imposes a major strain on the respiratory muscle pump, and it is conventionally thought that the inspiratory muscles of the neck adapt to this chronic overload by developing hypertrophy. Yet previous anthropometric studies have shown atrophy of the sternomastoid muscles. To solve this discrepancy, we have measured the cross-sectional area of these muscles by computed tomography. Ten stable patients with severe airflow obstruction (FEV1 = 0.76 +/- 0.12 L) and hyperinflation (FRC = 210 +/- 29% of predicted) and 10 control subjects matched for age, sex, and height were studied. The sternomastoid cross-sectional area in the patients averaged (mean +/- SD) 4.29 +/- 1.48 cm2, and that in the control subjects was 3.96 +/- 0.82 cm2. This small difference could be entirely accounted for by hyperinflation, and it was not statistically significant. Sternomastoid muscle torque in patients was also similar to that in the control subjects. In patients with severe COPD, therefore, the sternomastoid muscles are essentially normal. As a corollary, their frequent prominence on clinical examination is only apparent.

Aged↗

PubMed1996

Discharge frequencies of parasternal intercostal and scalene motor units during breathing in normal and COPD subjects.

To determine whether patients with chronic obstructive pulmonary disease (COPD) contract the inspiratory muscles of the rib cage more strongly than do healthy subjects, we recorded the discharge frequencies of single motor units in the scalene and second parasternal intercostal muscles of seven patients with stable COPD (FEV1 = 33 +/- 13% predicted, mean +/- SD) and seven control subjects. Recordings were made with insulated monopolar electrodes during resting breathing, and single motor-unit discharges were identified with a customized method based on "template" matching. A total of 211 motor units were recorded in the control subjects and 260 in the patients. The inspiratory discharge frequencies were greater in the COPD patients than in the control subjects for both the parasternal (13.4 versus 10.1 Hz, p < 0.05) and scalene (11.4 versus 8.5 Hz, p < 0.02) muscles. Recording sites at which no motor units were recruited were more common in the control subjects than in the patients (p < 0.001). The sternomastoid muscle was silent in both subject groups. Therefore, effective central neural drive is increased to both the scalene and parasternal intercostal muscles but not to the sternomastoid muscle in patients with COPD.

Action Potentials↗

PubMed1996

Respiratory muscle response to flail chest.

We have previously shown that flail chest in the dog causes an inspiratory inward displacement of the ribs and an increased inspiratory activity in the external intercostal muscles, and we have speculated that this increased activity is due to an increased spindle afferent activity. The present studies were designed to test this hypothesis. Twenty-nine supine anesthetized dogs were studied, and flail was produced surgically by fracturing ventrally and dorsally two to four contiguous ribs on the right side of the chest. Although flail elicited an increased inspiratory activity in the external intercostal and levator costae muscles in the disconnected segment of the rib cage, it did not alter the inspiratory activity in the diaphragm and parasternal intercostals. Expiratory activity in the triangularis sterni, internal intercostals, and transversus abdominis remained unchanged also, as did the inspiratory activity in the external intercostals on the left side of the chest. After flail, the normal inspiratory shortening of the external intercostal muscles in the disconnected segment was also reversed into an inspiratory muscle lengthening. However, when the fractured ribs were connected to the adjacent ribs so that the external intercostals were prevented from lengthening during inspiration, external intercostal and levator costae inspiratory activity was unaltered. These observations support the hypothesis that the increased external intercostal muscle activity seen in flail chest results primarily from an increased activation of the muscle spindles.

Animals↗

PubMed1995

Response of the inspiratory intercostal [correction of intercoastal] muscles to increased inertial loads.

To test the hypothesis that the external intercostals and levator costae constitute an inspiratory reserve system, we have examined the response of these muscles to increased inertial loads. Weights were t hus attached sequentially to the ribs in ten lightly anesthetized, spontaneously breathing dogs. As weights were attached, the ribs were progressively displaced caudally at end-expiration, so that the external intercostal muscles were lengthened. In addition, the cranial motion of the ribs during inspiration was gradually reduced, the inspiratory shortening of external intercostal disappeared, and the external intercostal and levator costae inspiratory EMG activities increased. The parasternal intercostal inspiratory activity, however, remained unchanged. Studies also showed that: (1) the increases in external intercostal activity appeared with the first loaded breath and disappeared as soon as the load was removed; (2) these increases were related to the suppression of the inspiratory muscle shortening, rather than to the increase in precontraction muscle length or to vagal inputs; and (3) denervation of the external intercostal caused inspiratory muscle lengthening but had little effect on the inspiratory motion of the ribs. These observations thus indicate that increased inertial loads on the ribs trigger reflexes, possibly spindle reflexes, which cause selective increases in external intercostal and levator costae inspiratory EMG activities. In that sense, the present findings are consistent with the idea that these two muscles constitute an inspiratory reserve system. However, it appears that the major effect of these increased activities is simply to prevent the muscles from lengthening during inspiration.

Animals↗

PubMed1995

Inhomogeneous activation of the parasternal intercostals during breathing.

Recent computations of the mechanical advantage of the canine intercostal muscles have suggested that the inspiratory advantage of the parasternal intercostals is not uniform. In the present studies, we have initially tested this hypothesis. Using a caliper and markers implanted in the costal cartilages, we have thus measured, in four supine paralyzed dogs, the length of the medial, middle, and lateral parasternal fibers at functional residual capacity and after a 1-liter mechanical inflation. With inflation, the medial fibers always shortened more than did the middle fibers (-9.8 +/- 0.8 vs. -6.0 +/- 0.8%; P < 0.001), whereas the lateral fibers remained virtually constant in length (-0.2 +/- 0.8%). This gradient of mechanical advantage agreed well with the gradient of orientation of the muscle fibers. Therefore, we have also recorded the electromyograms of the medial, middle, and lateral parasternal bundles during spontaneous breathing in nine anesthetized animals (20 interspaces); each activity was expressed as a percentage of the activity recorded during tetanic, supramaximal stimulation of the internal intercostal nerve (maximal activity). The medial bundle was invariably more active than was the middle bundle during resting breathing (57.3 +/- 3.3 vs. 25.5 +/- 3.4% of maximum; P < 0.001), and in 10 interspaces, medial activity consistently preceded middle activity at the onset of inspiration. These differences persisted during hypercapnia, during inspiratory resistive loading, as well as after phrenicotomy. Activity was never recorded from the lateral bundle.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗

PubMed1995

Rib cage distortion in a canine model of flail chest.

Although blunt chest injuries frequently lead to respiratory failure, the effects of flail chest on the mechanics of breathing have not been evaluated. In the present studies, we have measured the respiratory displacements of the ribs and sternum and the electromyograms (EMG) of the parasternal and external intercostal muscles in eight supine, anesthetized, spontaneously breathing dogs before and after the third to sixth ribs on the right side of the chest were fractured both dorsally and ventrally. After flail, the fractured ribs moved inward, rather than outward, during inspiration, but their inspiratory cranial displacement remained unchanged. The inspiratory outward and caudal displacement of the sternum, the inspiratory EMG activity of the parasternal intercostals, the pattern of breathing, and the arterial blood gases were also unaltered. However, the inspiratory EMG activity recorded from the external intercostals increased consistently to 327 +/- 101% of control (p < 0.05). These observations indicate that with flail chest, the disconnected segment of the rib cage shows paradoxical motion exclusively along the lateral axis; the increased external intercostal activation may account, at least in part, for the persistent inspiratory cranial motion of the ribs. These observations also suggest that the harmful effects of blunt chest injuries are related to pulmonary contusion and pain, rather than to flail chest per se.

Animals↗

PubMed1995

[Role of expiratory muscles in chronic obstructive respiratory insufficiency].

We have studied the pattern of abdominal muscle (transversus abdominis, external oblique and rectus abdominis) contraction and its mechanical correlates in patients with CAO. When breathing at rest, many stable patients with severe CAO contract the abdominal muscles during expiration and this expiratory contraction is usually confined to the transversus muscle. Moreover, this contraction most often makes expiration a mechanically active process and is an important determinant of intrinsic positive end-expiratory pressure (PEEPi) in such patients. The pathophysiologic implications of these findings are discussed.

Abdominal Muscles↗

PubMed1994

Intercostal muscle compensation for parasternal paralysis in the dog: central and proprioceptive mechanisms.

1. Denervation of the parasternal intercostal muscles in the dog is known to cause a substantial reduction in the inspiratory cranial displacement of the ribs and a compensatory increase in the activation of the other inspiratory intercostal muscles, namely the external intercostals and the levator costae. The present studies were designed to assess the mechanism(s) of that compensation. 2. Denervating the parasternal intercostals bilaterally caused a reduction in tidal volume and an increase in arterial PCO2 (Pa, CO2). Severing the parasternal intercostals selectively produced similar changes. The concomitant increases in external intercostal and levator costae activity, however, were much greater than predicted on the basis of the increased Pa, CO2. 3. Denervating the parasternal intercostals on one side of the chest produced large increases in ipsilateral, but not contralateral external intercostal activity. 4. Manipulating the ribs after the parasternal intercostals were inactivated so as to reproduce the normal inspiratory cranial displacement of the ribs elicited immediate, clear-cut reductions in external intercostal and levator costae activities. 5. The increases in external intercostal and levator costae activities that occur after inactivation of the parasternal intercostals thus result partly from the increased hypercapnic drive but mostly from proprioceptive reflexes, presumably muscle spindle reflexes.

Animals↗

PubMed1994

Contribution of the rib cage inspiratory muscles to breathing in baboons.

We have measured the electromyograms of the rib cage inspiratory muscles, including the neck muscles, in five lightly anesthetized baboons breathing at rest in the supine and head-up postures. When supine, the animals did not have any activity in the scalene (three heads) or sternomastoid muscles. In contrast, a phasic inspiratory electrical activity was invariably recorded from the parasternal intercostals, external intercostals, and levator costae. Measurements of the changes in length of the parasternal intercostals indicated that these muscles also shortened during inspiration, and they further showed that this inspiratory shortening was eliminated after selective muscle denervation. Similar observations were made in the head-up posture, although the inspiratory shortening of the parasternal intercostals was smaller in this posture. These observations thus indicate that: (1) the inspiratory expansion of the rib cage in baboons results entirely from the actions of the inspiratory intercostal muscles and mostly from the action of the parasternal intercostals; and (2) the load imposed on these muscles is greater in the head-up posture, presumably because of the action of gravity on the chest wall.

Animals↗

PubMed1994

Do canine scalene and sternomastoid muscles play a role in breathing?

To assess the respiratory function of the scalene and sternomastoid muscles in the dog, we studied the effect of graded increases in inspiratory airflow resistance and single-breath airway occlusion on the electrical activity of these muscles in 18 supine anesthetized spontaneously breathing animals. The sternomastoids never showed any activity, and the scalenes showed some inspiratory activity during occlusion in only two animals. The adoption of the prone position and bilateral cervical vagotomy did not affect this pattern. Hypercapnia also did not elicit any sternomastoid activity and induced scalene inspiratory activity during occlusion in only four of nine animals. On microscopic examination, however, both muscles were found to contain large numbers of spindles, suggesting that they have the capacity to respond to stretch. In addition, with increases in inspiratory resistance, both the sternum and ribs were displaced in the caudal direction. As a result, the scalenes demonstrated a gradual inspiratory lengthening and the normal inspiratory lengthening of the sternomastoids was accentuated. Additional studies in three unanesthetized animals showed consistent activity in the scalene and sternomastoid muscles during movements of the trunk and neck but no activity during breathing, including occluded breathing. These observations thus indicate that the alpha-motoneurons of the scalene and sternomastoid muscles in the dog have very small central respiratory drive potentials with respect to their critical firing threshold. In this animal, these muscles do not have a significant respiratory function.

Action Potentials↗