Die nervöse Steuerung der Atmung

Treatment of apneustic respiratory disturbance with a serotonin-receptor agonist

Apneusis is a disturbance of respiratory rhythm characterized by severely prolonged inspiratory effort. It may occur after damage to the respiratory network within the lower brain stem and pons from an overdose of central nervous system depressants, blockade of glutamate receptors, asphyxia, hypoxia, or ischemia. Experimental studies conducted on laboratory mammals, such as anesthetized cats and rats, suggest that apneusis results mostly from depression of glutamatergic synaptic processes that are necessary for activation of inhibitory mechanisms that terminate inspiration. The impairment of synaptic transmission leads to prolonged inspiratory efforts and apneustic discharges of brainstem respiratory neurons. Apneustic patterns can be consistently converted to normal by administration of serotonin type 1A (5-HT1A) receptor agonists. This observation encouraged a treatment of severe apneusis with buspirone, an agonist for 5-HT1A receptors, in a child after neurosurgery for an astrocytoma in the pons and medulla oblongata. Oral administration of buspirone produced a prompt and highly effective remission of apneusis without side effects. Treatment with 5-HT1A agonists, therefore, might offer a novel and effective pharmacotherapy against apneustic disturbances of breathing.

Firing patterns of bulbar respiratory neurones during sniffing in the conscious, non-paralyzed rabbit

On the basis of their firing patterns, 143 of 189 cells recorded in the respiratory centres of conscious, non-paralyzed rabbits could be identified as respiratory related units (RRUs). The activities of 45 RRUs were analyzed during sniffing in response to an odour stimulus. During sniffing as well as during normal breathing neuronal activity and respiratory movements were synchronized. Synchrony was lost, however, at the start of sniffing, indicating an action of the olfactory system on the respiratory generating mechanisms.

The bulbar respiratory centre in the rabbit. I. Changes of respiratory parameters caused by intermittent electrical bulbar stimulation during inspiration or expiration

In anesthetized rabbits, spirogram and diaphragmatic activity were examined during electrical stimulation of regions of the medulla oblongata. The stimulating volleys were triggered by the phase transitions of the animal's own respiration. 1. Each early inspiratory volley of 120 ms duration at 100 pulses per second caused an immediate and transient inhibition of the diaphragmatic activity. Respiration was slowed down due to prolongation of inspiration. The tidal volume increased above control. Stimuli delivered after 30-40% of a control inspiration had elapsed cut short this phase and entailed a shortening of the following expiration, too. Respiration was thus accelerated. 2. Each early expiratory volley caused an inspiratory twitch after a short latency. The respiratory rate was slightly increased due to shortening of expiration. The spirogram exhibited a distinct inspiratory effect (elevation of the end-inspiratory and end-expiratory levels). Stimuli delivered after 60--70% of a control expiration had elapsed slowed down respiration due to prolongation of inspiration but did not alter the end-expiratory level. The expiration remained almost unaltered. The effects were still observed while an artificial state of lung distension or collapse was maintained. 3. Volleys of increasing duration were delivered, starting with onset of expiration. The initial respiratory acceleration (shortening of both phases) and elevation of the end-expiratory level, observed when short volleys were applied, changed into slowing down of respiration (prolongation of both phases) and a shift of the end-expiratory level towards active expirations when the duration of the volley was somewhat longer than a normal expiration. The end-inspiratory level remained slightly elevated. Results suggest that during inspiration a progressively increasing inhibitory state is built up. During expiration, both an increasing inspiratory and an expiratory tendency are present as revealed by mixed inexpiratory stimulation effects.

The bulbar respiratory centre in the rabbit. II. Responses of respiratory neurons to intermittent electrical bulbar stimulation during in- or expiration

In anesthetized rabbits, spirogram and diaphragmatic activity were examined during electrical stimulation of the bulbar lateral reticular formation. The activity of bulbar respiratory neurons was recorded contra- or ipsilaterally to the stimulation site. One volley of repetitive stimuli per breath was delivered during either inspiration of expiration. 1. Each volley of about 120 ms duration at 100 pulses per second, delivered early in inspiration, caused an immediate and transient inhibition of the diaphragmatic activity. An inspiratory rebound comprising lengthening of inspiration and increase in tidal volume occurred. a) "Inspiratory" and "expiratory-inspiratory" phase-spanning neurons exhibited inhibition during the volley. The burst discharge was lengthened and the spike density increased after stimulus. The same was true of some "inspiratory-expiratory" phase-spanning units. b) The discharge of most of the "inspiratory-expiratory neurons was not inhibited. "Expiratory" units were excited. In both types of cells activation occurred which outlasted the volley. 2. When applied during expiration, the volley caused a short inspiratory twitch. a) "Inspiratory" and "expiratory-inspiratory" neurons exhibited a short post-stimulus firing and the spike density was increased. In some units of the latter type, however, the burst discharge was shortened. b) Most of the "expiratory" and "inspiratory-expiratory" neurons were not inhibited by the volley. Cells of the former type often produced post-stimulus after-discharge; the burst discharge of units belonging to the latter type was shortened. The effects of expiratory stimuli upon neuronal activity, however, were less consistent than those elicited by inspiratory volleys. 3. During spontaneous irregularities of single inspirations (short interruptions), EI and I neurons exhibited comparable burst pattern changes. The changes in pattern of IE and E units were also comparable and differed distinctly from the behaviour of the EI and I cells. No major differences in behaviour were observed between neurons which were inhibited during lung inflation (alpha units) and those which were activated during inflation (beta cells). The findings are in accord with the effects observed during electrical bulbar stimulation, suggesting that EI and I units are inspiratory-activating cells, whereas IE and E neurons may have an inspiratory-inhibitory function. 4. The conclusion is drawn that the effects of bulbar stimulation on the respiratory movements are the result of manipulation on intrinsic rhythmogenesis.

The Hering-Breuer reflexes in the bronchial asthma attack

The correlation between pulmonary stretch receptor activity and inspiration-expiration duration quotient as well as respiratory frequency (Hering-Breuer reflexes) has been established before and during an asthma attack in the guinea-pig. The Hering-Breuer reflexes subserving the self-regulation of breathing during uninfluenced spontaneous breathing no longer prevail after induction of a bronchial asthma attack. Increased stretch receptor activity following increased lung volume does not lead to inhibition of inspiratory activity (lung inflation reflex), but to an enhancement of the asthmatic tachypnoea. The latter is assumed to result from the expiratory self-compression of the lungs (lung deflation reflex). The enhancement of the deflation reflex by increasing lung volume during the asthma attack is discussed with regard to the uneven ventilation and the conditions in lung mechanics underlying the excitation of the lung deflation or collapse endings.