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CHEST WALL MOVEMENTS
"I would have everie man write what he knowes and no more."—MONTAIGNE
BRITISH JOURNAL OF ANAESTHESIA VOLUME 55, No. 10
OCTOBER 1983
EDITORIAL CHEST WALL MOVEMENTS
possibly, by forcing it into a more curved shape that will generate trans-diaphragmatic pressure more effectively (Grassino et al., 1978). When the abdominal wall is tense, contraction of the diaphragm elevates and expands the ribcage rather than moving the abdomen. This is the usual pattern of movement in upright subjects. How much do muscles other than the diaphragm contribute to quiet breathing? Mead and his colleagues argued at first that the diaphragm acted to expand theribcageand abdomen in the same way as it would expand with passive lung inflation and, hence, that the movements of both ribcage and abdomen were the result of movement of the diaphragm. However, intercostal and accessory muscles have both tonic and sometimes phasic activity during quiet breathing, and it is now dear that they contribute to respiratory movements. Nondepolarizing neuromuscular blocking drugs which affect these muscles more than the diaphragm, alter the chest wall pressure-volume relationship from that found in normal subjects who have consciously tried to relax (De Troyer, Bastenier and Delhez, 1980). Halothane has a similar effect, decreasing intercostal and accessory muscle activity more than that of the diaphragm. Breathing movements during halothane anaesthesia are predominantly abdominal, and the ribcage may even move paradoxically. However, shallow breathing in normal subjects is also mainly abdominal. Another respiratory depressant, morphine, also decreases the contribution of the chest wall to tidal volume, but this contribution is appropriate for the reduced ventilation. It may help to consider the neural control of the respiratory muscles. At least two pathways in the spinal cord carry respiratory messages to the muscles, and other pathways carry messages controlling other acts such as coughing and vomiting. The intercostal muscles have two separately controlled functions, respiratory (predominantly the more cranial and parasternal muscles) and postural (the more
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 24, 2015
For the respiratory physiologist, the chest wall is all the structures outside the lungs that move when the lungs move, and so consists of not only the ribcage, but also the diaphragm and the abdomen, since the latter usually moves when the diaphragm moves. A great step in the understanding of chest wall movements was made when lung volume changes were attributed to separate movements of the ribcage and diaphragm/abdomen. Mead and his colleagues measured the antero-posterior diameter of the ribcage and abdomen as respiratory movements were made while the glottis was closed. This "isovolume manoeuvre" consists of alternately expanding the ribcage and abdomen, the type of paradoxical pattern that can be seen in anaesthetized patients with airway obstruction. Since the volume decrease of one compartment is the same as the volume increase of the other, the ribcage and abdominal movements measured indicate equal and opposite volume changes. Mead also showed that, in conscious man, these two diameters were sufficient to describe lung volume changes accurately over a wide range of lung volumes. Using oesophageal and gastric pressure to indicate pleural and abdominal pressures, the pressure-volume relationships of theribcageand abdomen were obtained (Grimby, Goldman and Mead, 1976). Different muscle groups can be responsible for the generation of these pressures. The diaphragm, as it contracts, decreases pleural pressure and increases abdominal pressure. Trans-diaphragmatic pressure, which is abdominal pressure minus pleural pressure, increases. Contraction of inspiratory intercostal and accessory muscles also decreases pleural pressure, but in the absence of diaphragmatic activity, abdominal pressure will decrease (transdiaphragmatic pressure may increase slightly if the diaphragm becomes stretched as it is drawn into the thorax). Abdominal muscles can alter diaphragmatic efficiency, both by increasing the initial tension in its fibres so that it contracts more strongly and,
926
that the pattern of action of the different postural and respiratory muscles may be changed. In anaesthetized subjects, abdominal muscles are also active, and opiates can dissociate ribcage and abdominal movement. These changes will become better understood when it becomes possible to relate the activity and the mechanical output of each group of respiratory muscles to the resultant movements of the chest wall, and these movements to overall ventilation. Gordon Drummond REFERENCES
De Troyer, A., Bastenier, J., and Delhez, L. (1980). Function of respiratory muscles during partial curarization in humans. / . Appl. Phytiol., 49,1049. Grassino, A., Goldman, M.D., Mead, J., and Sears, T.A. (1978). Mechanics of the human diaphragm during voluntary contraction: statics. / . Appl. Phytiol. 44, 829. Grimby, G., Goldman, M., and Mead, J. (1976). Respiratory muscle action inferred from ribcage and abdominal V - P partitioning. / . Appl. Phytiol., 41,739. Mead, J., and Loring, S.H. (1982). Analysis of volume displacement and length changes of the diaphragm during breathing. / . Appl. Physioi, 53, 750.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 24, 2015
caudal, lateral muscles). The abdominal oblique muscles also control posture, but, in addition, they alter the efficiency of the diaphragm and act to expand the lower ribcage. Their activity increases during halothane anaesthesia and their contribution to respiratory movements remains to be assessed. The diaphragm itself is not an homogenous muscle: its central portion and its lateral parts have different innervation and actions. Some of the diaphragm is applied to the inside of the lower ribcage and contributes to ribcage movement (Mead and Loring, 1982). Clearly, the concept of an unique pressure generator and a simple resultant volume change is not applicable to the chest wall. Some indication of changes in the relationship of driving pressure and resultant volume change have come from studies in which airway pressure was measured during occluded inspiration to give an idea of the driving pressure in the total respiratory system. In conscious subjects, the relationship of this pressure to resultant volume change can be altered by respiratory depressant drugs and by exercise, indicating
BRITISH JOURNAL OF ANAESTHESIA
BRITISH JOURNAL OF ANAESTHESIA VOLUME 55, No. 10
OCTOBER 1983
EDITORIAL CHEST WALL MOVEMENTS
possibly, by forcing it into a more curved shape that will generate trans-diaphragmatic pressure more effectively (Grassino et al., 1978). When the abdominal wall is tense, contraction of the diaphragm elevates and expands the ribcage rather than moving the abdomen. This is the usual pattern of movement in upright subjects. How much do muscles other than the diaphragm contribute to quiet breathing? Mead and his colleagues argued at first that the diaphragm acted to expand theribcageand abdomen in the same way as it would expand with passive lung inflation and, hence, that the movements of both ribcage and abdomen were the result of movement of the diaphragm. However, intercostal and accessory muscles have both tonic and sometimes phasic activity during quiet breathing, and it is now dear that they contribute to respiratory movements. Nondepolarizing neuromuscular blocking drugs which affect these muscles more than the diaphragm, alter the chest wall pressure-volume relationship from that found in normal subjects who have consciously tried to relax (De Troyer, Bastenier and Delhez, 1980). Halothane has a similar effect, decreasing intercostal and accessory muscle activity more than that of the diaphragm. Breathing movements during halothane anaesthesia are predominantly abdominal, and the ribcage may even move paradoxically. However, shallow breathing in normal subjects is also mainly abdominal. Another respiratory depressant, morphine, also decreases the contribution of the chest wall to tidal volume, but this contribution is appropriate for the reduced ventilation. It may help to consider the neural control of the respiratory muscles. At least two pathways in the spinal cord carry respiratory messages to the muscles, and other pathways carry messages controlling other acts such as coughing and vomiting. The intercostal muscles have two separately controlled functions, respiratory (predominantly the more cranial and parasternal muscles) and postural (the more
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 24, 2015
For the respiratory physiologist, the chest wall is all the structures outside the lungs that move when the lungs move, and so consists of not only the ribcage, but also the diaphragm and the abdomen, since the latter usually moves when the diaphragm moves. A great step in the understanding of chest wall movements was made when lung volume changes were attributed to separate movements of the ribcage and diaphragm/abdomen. Mead and his colleagues measured the antero-posterior diameter of the ribcage and abdomen as respiratory movements were made while the glottis was closed. This "isovolume manoeuvre" consists of alternately expanding the ribcage and abdomen, the type of paradoxical pattern that can be seen in anaesthetized patients with airway obstruction. Since the volume decrease of one compartment is the same as the volume increase of the other, the ribcage and abdominal movements measured indicate equal and opposite volume changes. Mead also showed that, in conscious man, these two diameters were sufficient to describe lung volume changes accurately over a wide range of lung volumes. Using oesophageal and gastric pressure to indicate pleural and abdominal pressures, the pressure-volume relationships of theribcageand abdomen were obtained (Grimby, Goldman and Mead, 1976). Different muscle groups can be responsible for the generation of these pressures. The diaphragm, as it contracts, decreases pleural pressure and increases abdominal pressure. Trans-diaphragmatic pressure, which is abdominal pressure minus pleural pressure, increases. Contraction of inspiratory intercostal and accessory muscles also decreases pleural pressure, but in the absence of diaphragmatic activity, abdominal pressure will decrease (transdiaphragmatic pressure may increase slightly if the diaphragm becomes stretched as it is drawn into the thorax). Abdominal muscles can alter diaphragmatic efficiency, both by increasing the initial tension in its fibres so that it contracts more strongly and,
926
that the pattern of action of the different postural and respiratory muscles may be changed. In anaesthetized subjects, abdominal muscles are also active, and opiates can dissociate ribcage and abdominal movement. These changes will become better understood when it becomes possible to relate the activity and the mechanical output of each group of respiratory muscles to the resultant movements of the chest wall, and these movements to overall ventilation. Gordon Drummond REFERENCES
De Troyer, A., Bastenier, J., and Delhez, L. (1980). Function of respiratory muscles during partial curarization in humans. / . Appl. Phytiol., 49,1049. Grassino, A., Goldman, M.D., Mead, J., and Sears, T.A. (1978). Mechanics of the human diaphragm during voluntary contraction: statics. / . Appl. Phytiol. 44, 829. Grimby, G., Goldman, M., and Mead, J. (1976). Respiratory muscle action inferred from ribcage and abdominal V - P partitioning. / . Appl. Phytiol., 41,739. Mead, J., and Loring, S.H. (1982). Analysis of volume displacement and length changes of the diaphragm during breathing. / . Appl. Physioi, 53, 750.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 24, 2015
caudal, lateral muscles). The abdominal oblique muscles also control posture, but, in addition, they alter the efficiency of the diaphragm and act to expand the lower ribcage. Their activity increases during halothane anaesthesia and their contribution to respiratory movements remains to be assessed. The diaphragm itself is not an homogenous muscle: its central portion and its lateral parts have different innervation and actions. Some of the diaphragm is applied to the inside of the lower ribcage and contributes to ribcage movement (Mead and Loring, 1982). Clearly, the concept of an unique pressure generator and a simple resultant volume change is not applicable to the chest wall. Some indication of changes in the relationship of driving pressure and resultant volume change have come from studies in which airway pressure was measured during occluded inspiration to give an idea of the driving pressure in the total respiratory system. In conscious subjects, the relationship of this pressure to resultant volume change can be altered by respiratory depressant drugs and by exercise, indicating
BRITISH JOURNAL OF ANAESTHESIA