Role of Selected Muscles of Respiration as Influenced by Posture and Tidal Volume

doi:10.1378/chest.70.5.636

Chest

Volume 70, Issue 5, November 1976, Pages 636-640

https://doi.org/10.1378/chest.70.5.636 Get rights and content

Studies of the activity of accessory respiratory muscles were conducted in 30 normal subjects (15 male and 15 female subjects, age 5 to 62 years). Electromyograms were recorded over the right serratus anterior muscle and the adjacent sixth intercostal space, and the results were correlated with tidal volume. Phasic respiratory activity in the serratus anterior muscle was detected in every subject but was markedly affected by the prevailing posture and level of ventilation (appearing at mean tidal volumes equivalent to 60.5 percent of vital capacity when subjects were standing relaxed, and equivalent to 35.2 percent of vital capacity when subjects were seated, leaning forward with elbows supported). The activity was predominantly inspiratory in timing but in some subjects extended into early expiration. No significant differences were noted in subjects of different ages, sex, height, or weight Similar results were recorded from the inspiratory intercostal muscle. on the basis of these findings, we conclude that, contrary to reports, the serratus anterior muscle should be classified as an accessory muscle of respiration, at least at increased levels of ventilation, and that its activity is most pronounced in postures that place the muscles’ origin in an advantageous position for moving the ribs.

Section snippets

Materials and Methods

Thirty normal subjects with no histories of allergy or chest disease were tested. The group consisted of 15 male subjects with a mean age of 27 years (range, 5 to 62 years) and 15 female subjects with a mean age of 29 years (range, 18 to 55 years). Electromyographic activity was recorded simultaneously by surface electrodes from the intercostal muscles of the sixth interspace and the digitation of the serratus anterior muscle attaching to the sixth rib on the right side (to minimize cardiac

Results

The mean, standard deviation (SD), and standard error (SE) of the mean was calculated for each recorded variable, namely, age, height, weight, and commencement of respiratory activity in the various testing positions. In addition, Pearson correlation coefficients and histograms of the raw scores were computed.

Although there was the usual clumping around the mean for all data, there were abnormalities of distribution at the extremes of range. This was probably due to the small number of subjects

Discussion

The results clearly show that the serratus anterior muscle is an accessory muscle of respiration in normal subjects, at least at high values for TV. It is generally known that the resting position of the chest wall is equivalent to approximately 55 percent of the VC.¹⁵ Below this volume the chest wall has a natural tendency to expand, while above this volume, it tends to recoil inward toward the resting position. With the subject in the relaxed standing position, the activity in the serratus

ACKNOWLEDGMENT

We gratefully acknowledge the advice and assistance of Dr. Michael Grace, who performed the statistical analysis.

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There are more references available in the full text version of this article.

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Effect of chest mobilization on intercostal muscle stiffness
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Citation Excerpt :
The external abdominal oblique muscles are accessory respiratory muscles during effort expiration (Ninane et al., 1988) and are thought to have little effect on the IC muscle EMG during inspiration. However, it has been shown that the muscular activity of the SA muscle is present at about 60% of maximal inspiration (Reid et al., 1976), and it is possible that the SA muscle activity affected IC muscle activity during maximal inspiration. Future prospects include, first, studies on different participant groups.
This study examined the effect of chest mobilization on intercostal (IC) muscle stiffness using the IC muscle shear modulus. Sixteen healthy young men participated on two days with a minimum of 24 h between the stretching and control conditions (SC and CC). The tasks were resting breathing and deep breathing. The IC muscle shear modulus and muscle activity and rib cage circumference were measured before and after each condition. In the SC, IC stretching was performed for 1 min x 5 sets. In the CC, resting breathing, in a sitting position, was performed for 5 min. In the SC, the IC muscle shear modulus decreased significantly (p < 0.05) at maximum inspiration in the deep breathing task, but there was no significant difference in the CC pre- and post-intervention. The results suggest that IC muscle stretching decreases IC muscle stiffness and improves muscle flexibility and that the IC muscle shear modulus may measure the effectiveness of chest mobilization.
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The potential respiratory action of the pectoral muscles is unclear. We studied the effect of electrically stimulated contraction of the deep pectoral muscles on intrathoracic pressuer (P_es) and lung volume in 15 supine anesthetized dogs. Changes in P_es and lung volume were also compared with the forelimbs held at the animal's side and elevated 45° to the horizontal plane to alter the mechaninal advantage of the deep pectoral muscles. In all animals, bilateral supramaximal stimulation of the deep pectorals produced negative changes in P_es (−5.9 ± 0.6 cmH₂O) and inspiratory changes in lung volume (324 ± 44 ml) with the forelimbs elevated. Conversely, in all animals, stimulation of the deep pectorals with the forelimbs at the side produced positive changes in P_es (+2.6 k± 0.2 cmH₂P, Plt;0.001) and expiratory changes in lung volume (−113 ± 16ml, Plt;0.001) Furthermore, forelimb elevation increased deep pectoral muscle fiber length (mean change 39.9 ± 7,5% of resting length, Plt;0.001) and reoriented fiber alignment with the rib cage more rostrally. These data indicate that the pectoral muscles exert a respiratory action on the rib cage. Moreover, forelimb posture affects the direction (i.e., inspiratory vs. expiratory) and magnitude of pectoral muscle mechanical action by altering muscle fiber alignment and precontraction length.
Effect of posture on inter-regional distribution of pulmonary ventilation in man
1984, Respiration Physiology
Regional ventilation per unit alveolar volume (V̇/Va) and regional lung expansion (FRC_R/TLC_R) were measured in twelve normal male human subjects in seated, supine, lateral decubitus and prone postures using a gamma camera and inhalation of the radioactive gases ⁸¹Kr^m (half-life 13 sec) and ⁸⁵Kr^m (half-life 4.4 h). FRC_R/TLC_R decreased from superior to inferior in all postures except prone where it was uniform;V̇Va increased from superior to inferior except in the prone position where it was uniform. In the horizontal axis FRC_R/TLC_R and V̇Va were uniformly distributed except for cranial to caudal gradients (with lower values caudally) in supine and lateral decubitus postures. In the prone posture V̇Va tended to be higher in caudal lung zones.
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First Prize, 1973 Alfred A. Richman Essay Contest, American College of Chest Physicians.

Dr. Reid was supported by a Dr. Henry R. Viets Medical Student Research Fellowship awarded by the Myasthenia Gravis Foundation, Inc.

Manuscript received January 28; revision accepted May 18.

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Chest

Clinical InvestigationsRole of Selected Muscles of Respiration as Influenced by Posture and Tidal Volume

Section snippets

Materials and Methods

Results

Discussion

ACKNOWLEDGMENT

Physiology of Motion (1867). EB Kaplan (translator)

Descriptive and Applied

Accessory muscles

Electromyographic study of the action of the serratus anterior muscle in respiration

J Anat

The Muscular Control of Breathing in Man (PhD thesis)

Muscles Alive: Their Functions Revealed by Electromyography

Electromyographic studies of respiration: A review of current concepts

J Chart Soc Physio

Anatomy of the Human Body

Anatomy: Regional and Applied

Clinical Investigations
Role of Selected Muscles of Respiration as Influenced by Posture and Tidal Volume