Functional significance of expiratory muscles during spontaneous breathing in anesthetized dogs

1993 ◽  
Vol 74 (1) ◽  
pp. 238-244 ◽  
Author(s):  
G. A. Farkas ◽  
M. A. Schroeder
Keyword(s):  
Tidal Volume ◽  
Spontaneous Breathing ◽  
Transversus Abdominis ◽  
Relative Role ◽  
Significant Length ◽  
Anesthetized Dogs ◽  
Length Changes ◽  
Expiratory Muscles ◽  
Prone Posture

Recent electromyographic studies in awake and anesthetized dogs have demonstrated that spontaneous breathing in prone dogs is associated with an increased activation of the expiratory muscles compared with that recorded in supine dogs. On the basis of these observations, one would infer that the mechanical role and contribution of the expiratory musculature to the act of breathing are enhanced in the prone posture. The changes in length associated with these postural increases in expiratory muscle electrical activity, however, have not been investigated and formed the basis of our investigation. We examined the active and passive changes in length of expiratory muscles during spontaneous breathing in supine and prone anesthetized dogs and assessed the relative role of the expiratory musculature in the generation of tidal volume. The experiments were performed on eight mongrel dogs anesthetized with pentobarbital sodium. In all eight animals, spontaneous breathing in the prone posture was associated with an increased activation (electromyogram) of the triangularis sterni, external oblique, and transversus abdominis muscles compared with that recorded in the supine posture. We quantitated the role of the expiratory muscles in both postures by measuring the volume difference between relaxation volume of the respiratory system and the end-expiratory lung volume. In the supine animal, 93 ml were attributed to the expiratory musculature, whereas in the prone animal, we noted that 186 ml (P < 0.01) were displaced during expiration, representing 43 and 52% (NS) of tidal volume, respectively. During spontaneous breathing in the supine or prone posture, all three expiratory muscles underwent significant length changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical role of expiratory muscle recruitment during eupnea in supine anesthetized dogs

1991 ◽  
Vol 70 (5) ◽  
pp. 2025-2031 ◽  
Author(s):  
M. A. Schroeder ◽  
H. Y. Tao ◽  
G. A. Farkas
Keyword(s):  
Tidal Volume ◽  
Spontaneous Breathing ◽  
Transversus Abdominis ◽  
Substantial Contribution ◽  
Emg Activity ◽  
Expiratory Muscle ◽  
Anesthetized Dogs ◽  
Expiratory Muscles ◽  
Phasic Activation

To assess the mechanical role of the expiratory musculature during eupnea, we recorded the electromyographic (EMG) activity of the triangularis sterni, the external oblique, and the transversus abdominis in eight supine lightly anesthetized dogs and have measured the volume generated by the phasic activation of the expiratory muscles. Activation of the expiratory muscles was invariably associated with a decrease in lung volume below the relaxed position of the respiratory system, a volume equal to 41.3 +/- 8.4 ml. This volume represented roughly 20% of tidal volume generated during spontaneous breathing. The fractional expiratory contribution to the tidal volume was unrelated to the size of the animal. Traction on the forelimbs (limb extension), however, tended to enhance the phasic expiratory activation of both the triangularis sterni and the transversus abdominis in the majority of animals. Moreover, after limb extension, the fractional contribution of tidal volume attributed to the phasic activation of the expiratory muscles increased in all but one animal. During spontaneous breathing with the forelimbs extended, roughly 25% of tidal volume was found to be due directly to phasic expiratory muscle contraction. The present observations firmly establish that in supine lightly anesthetized dogs breathing at rest the expiratory component of tidal volume represents a substantial contribution.

Mechanical role of expiratory muscles during breathing in prone anesthetized dogs

1990 ◽  
Vol 69 (6) ◽  
pp. 2137-2142 ◽  
Author(s):  
G. A. Farkas ◽  
M. A. Schroeder
Keyword(s):  
Spontaneous Breathing ◽  
Muscle Activation ◽  
Transversus Abdominis ◽  
Emg Activity ◽  
Abdominal Muscles ◽  
Cervical Vagotomy ◽  
Anesthetized Dogs ◽  
Expiratory Muscles ◽  
External Oblique

The purpose of the present study was to assess the mechanical role of the expiratory muscles during spontaneous breathing in prone animals. The electromyographic (EMG) activity of the triangularis sterni, the rectus abdominis, the external oblique, and the transversus abdominis was studied in 10 dogs light anesthetized with pentobarbital sodium. EMGs were recorded during spontaneous steady-state breathing in supine and prone suspended animals both before and after cervical vagotomy. We also measured the end-expiratory lung volume [functional residual capacity (FRC)] in supine and prone positions to assess the mechanical role of expiratory muscle activation in prone dogs. Spontaneous breathing in the prone posture elicited a significant recruitment of the triangularis sterni, the external oblique, and the transversus abdominis (P less than 0.05). Bilateral cervical vagotomy eliminated the postural activation of the external oblique and the transversus abdominis but not the triangularis sterni. Changes in posture during control and after cervical vagotomy were associated with an increase in FRC. However, changes in FRC, on average, were 132.3 +/- 33.8 (SE) ml larger (P less than 0.01) postvagotomy. We conclude that spontaneous breathing in prone anesthetized dogs is associated with a marked phasic expiratory recruitment of rib cage and abdominal muscles. The present data also indicate that by relaxing at end expiration the expiratory muscles of the abdominal region are directly responsible for generating roughly 40% of the tidal volume.

Mechanical role of expiratory muscles during breathing in upright dogs

1988 ◽  
Vol 64 (3) ◽  
pp. 1060-1067 ◽  
Author(s):  
G. A. Farkas ◽  
R. E. Baer ◽  
M. Estenne ◽  
A. De Troyer
Keyword(s):  
Tidal Volume ◽  
Progressive Increase ◽  
Substantial Contribution ◽  
Postural Changes ◽  
Before And After ◽  
Cervical Vagotomy ◽  
Anesthetized Dogs ◽  
Expiratory Muscles ◽  
Spontaneously Breathing

To examine the mechanical effects of the abdominal and triangularis sterni expiratory recruitment that occurs when anesthetized dogs are tilted head up, we measured both before and after cervical vagotomy the end-expiratory length of the costal and crural diaphragmatic segments and the end-expiratory lung volume (FRC) in eight spontaneously breathing animals during postural changes from supine (0 degree) to 80 degrees head up. Tilting the animals from 0 degree to 80 degrees head up in both conditions was associated with a gradual decrease in end-expiratory costal and crural diaphragmatic length and with a progressive increase in FRC. All these changes, however, were considerably larger (P less than 0.005 or less) postvagotomy when the expiratory muscles were no longer recruited with tilting. Alterations in the elastic properties of the lung could not account for the effects of vagotomy on the postural changes. We conclude therefore that 1) by contracting during expiration, the canine expiratory muscles minimize the shortening of the diaphragm and the increase in FRC that the action of gravity would otherwise introduce, and 2) the end-expiratory diaphragmatic length and FRC in upright dogs are thus actively determined. The present data also indicate that by relaxing at end expiration, the expiratory muscles make a substantial contribution to tidal volume in upright dogs; in the 80 degrees head-up posture, this contribution would amount to approximately 60% of tidal volume.

Expiratory muscle contribution to tidal volume in head-up dogs

1989 ◽  
Vol 67 (4) ◽  
pp. 1438-1442 ◽  
Author(s):  
G. A. Farkas ◽  
M. Estenne ◽  
A. De Troyer
Keyword(s):  
Tidal Volume ◽  
Lung Volume ◽  
Muscle Relaxation ◽  
Rib Cage ◽  
Expiratory Muscle ◽  
Residual Capacity ◽  
Anesthetized Dogs ◽  
Expiratory Muscles ◽  
S Period ◽  
Average Contribution

A change from the supine to the head-up posture in anesthetized dogs elicits increased phasic expiratory activation of the rib cage and abdominal expiratory muscles. However, when this postural change is produced over a 4- to 5-s period, there is an initial apnea during which all the muscles are silent. In the present studies, we have taken advantage of this initial silence to determine functional residual capacity (FRC) and measure the subsequent change in end-expiratory lung volume. Eight animals were studied, and in all of them end-expiratory lung volume in the head-up posture decreased relative to FRC [329 +/- 70 (SE) ml]. Because this decrease also represents the increase in lung volume as a result of expiratory muscle relaxation at the end of the expiratory pause, it can be used to determine the expiratory muscle contribution to tidal volume (VT). The average contribution was 62 +/- 6% VT. After denervation of the rib cage expiratory muscles, the reduction in end-expiratory lung volume still amounted to 273 +/- 84 ml (49 +/- 10% VT). Thus, in head-up dogs, about two-thirds of VT result from the action of the expiratory muscles, and most of it (83%) is due to the action of the abdominal rather than the rib cage expiratory muscles.

Role of triangularis sterni during coughing and sneezing in dogs

1988 ◽  
Vol 65 (6) ◽  
pp. 2440-2445 ◽  
Author(s):  
E. van Lunteren ◽  
M. A. Haxhiu ◽  
N. S. Cherniack ◽  
J. S. Arnold
Keyword(s):  
Nasal Mucosa ◽  
Respiratory Activity ◽  
Transversus Abdominis ◽  
Mechanical Stimuli ◽  
Rib Cage ◽  
Anesthetized Dogs

Studies in mammals have found that during breathing the triangularis sterni (TS) muscle regulates expiratory airflow and the end-expiratory position of the rib cage and furthermore that the respiratory activity of this muscle is influenced by a variety of chemical and mechanical stimuli. To assess the role of the TS during coughing and sneezing, electromyograms (EMGs) recorded from the TS were compared with EMGs of the transversus abdominis (TA) in eight pentobarbital-anesthetized dogs. During coughing induced by mechanically stimulating the trachea or larynx (n = 7 dogs), peak EMGs increased from 23 +/- 2 to 74 +/- 5 U (P less than 0.00002) for the TS and from 21 +/- 6 to 66 +/- 4 U (P less than 0.0002) for the TA. During sneezing induced by mechanically stimulating the nasal mucosa (n = 3 dogs), peak EMG of the TS increased from 10 +/- 3 to 66 +/- 7 U (P less than 0.005) and peak EMG of the TA increased from 10 +/- 2 to 73 +/- 7 U (P less than 0.02). For both muscles the shape of the EMG changed to an early peaking form during coughs and sneezes. Peak expiratory airflow during coughs of different intensity correlated more closely with peak TS EMG in three dogs and with peak TA EMG in four dogs; peak expiratory airflow during sneezes of different intensity correlated more closely with peak TS than TA EMG in all three animals. These results suggest that the TS is actively recruited during coughing and sneezing and that different neuromuscular strategies may be utilized to augment expiratory airflow.

Failure of tracheal distension to inhibit breathing in anesthetized dogs

1980 ◽  
Vol 48 (5) ◽  
pp. 794-798 ◽  
Author(s):  
T. C. Lloyd ◽  
J. A. Cooper
Keyword(s):  
Tidal Volume ◽  
Lung Volume ◽  
Potential Role ◽  
Minute Volume ◽  
Abdominal Compression ◽  
Frequency Increase ◽  
Before And After ◽  
Anesthetized Dogs ◽  
Spontaneously Breathing

Using anesthetized spontaneously breathing dogs, we compared the respiratory effects of tracheal distension with the effects of changes in lung volume before and after vagotomy. We used an endotracheal tube with a long cuff to distend the trachea to pressures of 10, 20, and 40 cmH2O. Lung volume increases were imposed by expiratory threshold loading, and volume was decreased by abdominal compression, both of which caused outward rib cage displacement. During expiratory loading, the tidal volume was unchanged but respiratory frequency and minute volume fell and an active expiratory effort appeared; whereas frequency and minute volume rose, but tidal volume fell during abdominal compression. Tracheal distension evoked no discernible change in breathing. Following vagotomy, tidal volume and minute volume fell, and frequency rose slightly, during expiratory loading but abdominal compression was without effect. After vagotomy, 40 cmH2O tracheal distension caused a slight frequency increase. We concluded that the potential role of tracheal deformation in the reflex control of breathing is insignificant in comparison with the other airways.

Electrical activation of expiratory muscles increases with time in pentobarbital-anesthetized dogs

1992 ◽  
Vol 72 (6) ◽  
pp. 2285-2291 ◽  
Author(s):  
D. O. Warner ◽  
M. J. Joyner ◽  
K. Rehder
Keyword(s):  
Electrical Activity ◽  
Important Variable ◽  
Transversus Abdominis ◽  
Implanted Electrodes ◽  
Expiratory Muscle ◽  
Inspiratory Muscles ◽  
Anesthetized Dogs ◽  
Expiratory Muscles ◽  
Muscle Groups ◽  
Over Time

Although the pentobarbital-anesthetized dog is often used as a model in studies of respiratory muscle activity during spontaneous breathing, there is no information regarding the stability of the pattern of breathing of this model over time. The electromyograms of several inspiratory and expiratory muscle groups were measured in six dogs over a 4-h period by use of chronically implanted electrodes. Anesthesia was induced with pentobarbital sodium (25 mg/kg iv), with supplemental doses to maintain constant plasma pentobarbital concentrations. Phasic electrical activity increased over time in the triangularis sterni, transversus abdominis, and external oblique muscles (expiratory muscles). The electrical activity of the costal diaphragm, crural diaphragm, and parasternal intercostal muscles (inspiratory muscles) was unchanged. These changes in electrical activity occurred despite stable plasma levels of pentobarbital and arterial PCO2. They were associated with changes in chest wall motion and an increased tidal volume with unchanged breathing frequency. We conclude that expiratory muscle groups are selectively activated with time in pentobarbital-anesthetized dogs lying supine. Therefore the duration of anesthesia is an important variable in studies using this model.

Cerebellar role in the load-compensating response of expiratory muscle

1994 ◽  
Vol 77 (3) ◽  
pp. 1232-1238 ◽  
Author(s):  
F. Xu ◽  
D. T. Frazier
Keyword(s):  
Spinal Column ◽  
Transversus Abdominis ◽  
Vagal Afferents ◽  
Electromyographic Activity ◽  
Tracheal Occlusion ◽  
Expiratory Muscle ◽  
Expiratory Muscles ◽  
Lung Airways ◽  
Dorsal Spinal

The hypothesis that the cerebellum is involved in the load-compensating response of expiratory muscles to expiratory tracheal occlusion was tested in anesthetized cats. A continuous expiratory threshold load (ETL; 5 cmH2O) was applied to elicit consistent phasic baseline electromyographic activity in the transversus abdominis muscle (EMGab). Tracheal occlusion for single expirations (TOE) were applied, and the evoked responses were compared in the intact and decerebellate preparation. Cold blockade of the dorsal spinal column (C5-7) and bilateral vagal inactivation (cold blockade or transection) were employed to determine the role of afferents from the lung, airways, chest wall, and diaphragm in shaping the cerebellar involvement in the motor response. The results showed that 1) decerebellation increased the baseline amplitude of the integrated EMGab (fEMGab) activity (P < 0.05) with little change in expiratory duration, 2) TOE applied after decerebellation markedly increased the expiratory duration compared with the intact values (P < 0.05), with little effect on the peak fEMGab, 3) cooling the dorsal spinal columns (C5-7) did not significantly affect EMGab responses in the intact or decerebellate preparations, and 4) vagal inactivation in the intact or decerebellate preparation significantly eliminated the fEMGab responses to ETL and TOE. We conclude that the cerebellum is involved in the modulation of transversus abdominis activity during ETL and TOE. Vagal afferents provide the major sensory input for the cerebellar modulation of the expiratory loading response.

Respiratory changes in parasternal intercostal length

1984 ◽  
Vol 57 (4) ◽  
pp. 1254-1260 ◽  
Author(s):  
M. Decramer ◽  
A. De Troyer
Keyword(s):  
Tidal Volume ◽  
Lung Volume ◽  
Body Position ◽  
Quiet Breathing ◽  
Rib Cage ◽  
Relative Contribution ◽  
Inspiratory Muscles ◽  
Anesthetized Dogs ◽  
The Relationship

In an attempt to understand the role of the parasternal intercostals in respiration, we measured the changes in length of these muscles during a variety of static and dynamic respiratory maneuvers. Studies were performed on 39 intercostal spaces from 10 anesthetized dogs, and changes in parasternal intercostal length were assessed with pairs of piezoelectric crystals (sonomicrometry). During static maneuvers (passive inflation-deflation, isovolume maneuvers, changes in body position), the parasternal intercostals shortened whenever the rib cage inflated, and they lengthened whenever the rib cage contracted. The changes in parasternal intercostal length, however, were much smaller than the changes in diaphragmatic length, averaging 9.2% of the resting length during inflation from residual volume to total lung capacity and 1.3% during tilting from supine to upright. During quiet breathing the parasternal intercostals always shortened during inspiration and lengthened during expiration. In the intact animals the inspiratory parasternal shortening was close to that seen for the same increase in lung volume during passive inflation and averaged 3.5%. After bilateral phrenicotomy, however, the parasternal intercostal shortening during inspiration markedly increased, whereas tidal volume diminished. These results indicate that 1) the parasternal intercostals in the dog are real agonists (as opposed to fixators) and actively contribute to expand the rib cage and the lung during quiet inspiration, 2) the relationship between lung volume and parasternal length is not unique but depends on the relative contribution of the various inspiratory muscles to tidal volume, and 3) the physiological range of operating length of the parasternal intercostals is considerably smaller than that of the diaphragm.(ABSTRACT TRUNCATED AT 250 WORDS)

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