Does corticosteroid treatment affect the respiratory muscles?
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Adrenal Cortex Hormones↗
Biomedical subjects
G Gayan-Ramirez
Publications and source records attributed to G Gayan-Ramirez.
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↗
Quantitative EEG changes under various conditions of hyperventilation in the sensorimotor cortex of the anaesthetized cat.
The effects on the EEG rhythms recorded from the sensorimotor cortex (post-sigmoid gyrus) of anaesthetized cats were studied under 4 conditions of artificial mechanical hyperventilation (HV) before and after cervical bilateral vagotomy. In animals with intact vagus nerves, using visual examination, EEG changes were only observed within the 2nd min during HV produced by increased stroke volume (delta V) with associated hypocapnia. Quantitative EEG (qEEG) showed that, for the same increase in minute ventilation and the same degree of hypocapnia, delta V induced a greater and earlier relative decrease (2nd min) in the power density of delta, theta and alpha bands, than increased pump frequency (delta F). The delta F tests produced a fall only in the theta band and within the 3rd min. With constant paCO2, transient modifications occurred only with delta V and were limited to the first 30 sec. In bivagotomized cats, moderate EEG responses to delta V plus associated hypocapnia persisted partly in the alpha band. Finally, no changes appeared with delta V or delta F when the vagus nerves were cut and paCO2 was maintained constant. The present data suggest strongly that, in anaesthetized cats, peripheral vagal afferents from the respiratory system play a major role in the EEG changes caused by artificial hyperventilation.
Animals↗
Pulmonary vagal sensory afferents and spontaneous EEG rhythms in the cat sensorimotor cortex.
Interactions between vagal afferent fibres and spontaneous electroencephalographic (EEG) activity, recorded on the sensorimotor cortex of the cat, were studied during the mechanical activation of pulmonary afferents. The interactions were compared to the cortical effects of the electrical stimulation of all vagal fibers or to the chemical activation of unmyelinated vagal afferents (C-fibers) by phenyldiguanide. The present study was performed on anesthetized cats, artificially ventilated with open chest. Over 60 locations were explored on the posterior sigmoid gyrus. Repetitive electrical stimulation (30 Hz, 0.8 ms shock duration) of the contralateral cervical vagus nerve or of both nerves induced within less than 5 s changes in the pattern and periodicity of EEG spindles, associated with depressed background rhythms or rhythmic EEG activities. Cortical responses were also observed after i.v. injection of phenyldiguanide. Changes in activity of pulmonary stretch receptors by lung hyperinflation or suppression of phasic lung inflations ('stop pump') had no effect on the EEG rhythms. On the other hand, expiratory threshold loading or passive hyperdeflation of the lungs elicited EEG changes similar to those obtained by electrical stimulation of all vagal fibers. After bilateral vagotomy, all these responses disappeared or were delayed. The present observations strongly suggest that sensory information carried by thin vagal fibers greatly influences cortical rhythms in the cat sensorimotor cortex.
Animals↗