Neural regulation of respiration

The effects of slow breathing on postural muscles during standing perturbations in young adults

Maintaining standing balance is vital to completing activities in daily living. Recent findings suggest an interaction between cardiovascular and postural control systems. Volitional slow breathing can modulate the cardiovascular response and affect postural control during quiet standing. However, the effects of slow breathing during threats to standing balance have not been studied. The study examined the effect of slow breathing on the latency and amplitude of postural muscle responses to perturbations of the base of support in healthy, young adults. Twenty-seven participants completed two balance perturbation tasks in standing on an instrumented split-belt treadmill while breathing spontaneously and breathing at 6 breaths per minute. Each perturbation task consisted of 25 posteriorly directed translations of the treadmill belts every 8-12 s. Muscle latency and muscle burst amplitude were measured using surface electromyography from the right limb for the quadriceps (QUADS), medial hamstring (MH), gastrocnemii (GASTROC), soleus (SOL), and tibialis anterior (TA) muscle groups, while a respiratory belt was used to record respiratory rate. Results indicated that during the slow breathing task both muscle latency (p = 0.022) and muscle burst amplitude (p = 0.011) decreased compared to spontaneous breathing. The EMG pre-perturbation activation was not significantly different in any muscle group between conditions (p > 0.167). The study found that reducing respiratory rate to approximately 6 breaths per minute affects the neuromuscular responses in the lower limb muscles to perturbations.

Mapping the functional brain state of a world champion freediver in static dry apnea

Voluntary apnea showcases extreme human adaptability in trained individuals like professional free divers. We evaluated the psychological and physiological adaptation and the functional cerebral changes using electroencephalography (EEG) and functional Magnetic Resonance Imaging (fMRI) to 6.5 min of dry static apnea performed by a world champion free diver. Compared to resting state at baseline, breath holding was characterized by increased EEG power and functional connectivity in the alpha band, along with decreased delta band connectivity. fMRI connectivity was increased within the default mode network (DMN) and visual areas but decreased in pre- and postcentral cortices. While these changes occurred in regions overlapping with cerebral signatures of several meditation practices, they also display some unique features that suggest an altered somatosensory integration. As suggested by self-reports, these findings could reflect the ability of elite free divers to create a state of sensory dissociation when performing prolonged apnea.

Diaphragm Pacing in Patients with Spinal Cord Injury: A European Experience

BACKGROUND

Patients with high spinal cord injury (SCI) are unable to breathe on their own and require mechanical ventilation (MV). The long-term use of MV is associated with increased morbidity and mortality. In patients with intact phrenic nerve function, patients can be partially or completely removed from MV by directly stimulating the diaphragm motor points with a diaphragm pacing system (DPS).

OBJECTIVES

We describe our multicenter European experience using DPS in SCI patients who required MV.

METHODS

We conducted a retrospective study of patients who were evaluated for the implantation of DPS. Patients evaluated for DPS who met the prospectively defined criteria of being at least 1 year of age, and having cervical injury resulting in a complete or partial dependency on MV were included. Patients who received DPS implants were followed for up to 1 year for device usage and safety.

RESULTS

Across 3 centers, 47 patients with high SCI were evaluated for DPS, and 34 were implanted. Twenty-one patients had 12 months of follow-up data with a median DPS use of 15 h/day (interquartile range 4, 24). Eight patients (38.1%) achieved complete MV weaning using DPS 24 h/day. Two DPS-related complications were surgical device revision and a wire eruption. No other major complications were associated with DPS use.

CONCLUSIONS

Diaphragm pacing represents an attractive alternative stand-alone treatment or adjunctive therapy compared to MV in patients with high SCI. After a period of acclimation, the patients were able to reduce the daily use of MV, and many could be completely removed from MV.

Opposite Pathways of Cholinergic Mechanisms of Hypoxic Preconditioning in the Hippocampus: Participation of Nicotinic α7 Receptors and Their Association with the Baseline Level of Startle Prepulse Inhibition

(1) Background. A one-time moderate hypobaric hypoxia (HBH) has a preconditioning effect whose neuronal mechanisms are not studied well. Previously, we found a stable correlation between the HBH efficiency and acoustic startle prepulse inhibition (PPI). This makes it possible to predict the individual efficiency of HBH in animals and to study its potential adaptive mechanisms. We revealed a bi-directional action of nicotinic α7 receptor agonist PNU-282987 and its solvent dimethyl sulfoxide on HBH efficiency with the level of PPI > or < 40%. (2) The aim of the present study was to estimate cholinergic mechanisms of HBH effects in different brain regions. (3) Methods: in rats pretested for PPI, we evaluated the activity of synaptic membrane-bound and water-soluble choline acetyltransferase (ChAT) in the sub-fractions of ‘light’ and ‘heavy’ synaptosomes of the neocortex, hippocampus and caudal brainstem in the intact brain and after HBH. We tested the dose-dependent influence of PNU-282987 on the HBH efficiency. (4) Results: PPI level and ChAT activity correlated negatively in all brain structures of the intact animals, so that the values of the latter were higher in rats with PPI < 40% compared to those with PPI > 40%. After HBH, this ChAT activity difference was leveled in the neocortex and caudal brainstem, while for membrane-bound ChAT in the ‘light’ synaptosomal fraction of hippocampus, it was reversed to the opposite. In addition, a pharmacological study revealed that PNU-282987 in all used doses and its solvent displayed corresponding opposite effects on HBH efficiency in rats with different levels of PPI. (5) Conclusion: We substantiate that in rats with low and high PPI two opposite hippocampal cholinergic mechanisms are involved in hypoxic preconditioning, and both are implemented by forebrain projections via nicotinic α7 receptors. Possible causes of association between general protective adaptation, HBH, PPI, forebrain cholinergic system and hippocampus are discussed.

Correlation of Swallowing Function With Bilateral Diaphragmatic Movement in Hemiplegic Stroke Patients

Objective

To investigate difference in bilateral diaphragm movement of patients with tracheal aspiration according to post stroke residue severity and determine correlations of Penetration-Aspiration Scale (PAS), residue scale, and bilateral diaphragm movement.

Methods

A total of 47 patients diagnosed with hemiplegic stroke were enrolled in this study. PAS, severity of valleculae, and pyriform sinus retention during videofluoroscopic swallowing study (VFSS) were assessed. Bilateral fluoroscopic diaphragm movements during spontaneous breathing and forced breathing were measured.

Results

Patients with tracheal aspiration (PAS≥6) had significantly (p=0.035) lower ipsilateral diaphragm movement during spontaneous breathing. Post-swallow residue severity showed statistically significant (p=0.028) difference in patients with ipsilateral diaphragm movement during forced breathing. In linear regression analysis, PAS showed weak correlations with ipsilateral spontaneous diaphragm movement (r=0.397, p=0.006), ipsilateral forced diaphragm movement (r=0.384, p=0.008), and contralateral forced diaphragm movement (r=0.323, p=0.027). Weak correlation was also observed between post swallow residue severity and ipsilateral diaphragm movement during spontaneous breathing (r=0.331, p=0.023) and forced breathing (r=0.343, p=0.018).

Conclusion

We confirmed the relationship between swallowing function and bilateral diaphragm movement in this study. The severity of dysphagia after hemiplegic stroke was correlated with bilateral diaphragm movement. Further longitudinal studies are needed to assess the effect of breathing exercise on post-stroke dysphagia.

Phrenic motoneurons: output elements of a highly organized intraspinal network

pontomedullary respiratory network generates the respiratory pattern and relays it to bulbar and spinal respiratory motor outputs. The phrenic motor system controlling diaphragm contraction receives and processes descending commands to produce orderly, synchronous, and cycle-to-cycle-reproducible spatiotemporal firing. Multiple investigators have studied phrenic motoneurons (PhMNs) in an attempt to shed light on local mechanisms underlying phrenic pattern formation. I and colleagues (Marchenko V, Ghali MG, Rogers RF. Am J Physiol Regul Integr Comp Physiol 308: R916–R926, 2015.) recorded PhMNs in unanesthetized, decerebrate rats and related their activity to simultaneous phrenic nerve (PhN) activity by creating a time-frequency representation of PhMN-PhN power and coherence. On the basis of their temporal firing patterns and relationship to PhN activity, we categorized PhMNs into three classes, each of which emerges as a result of intrinsic biophysical and network properties and organizes the orderly contraction of diaphragm motor fibers. For example, early inspiratory diaphragmatic activation by the early coherent burst generated by high-frequency PhMNs may be necessary to prime it to overcome its initial inertia. We have also demonstrated the existence of a prominent role for local intraspinal inhibitory mechanisms in shaping phrenic pattern formation. The objective of this review is to relate and synthesize recent findings with those of previous studies with the aim of demonstrating that the phrenic nucleus is a region of active local processing, rather than a passive relay of descending inputs.

Indicators used in livestock to assess unconsciousness after stunning: a review

Assessing unconsciousness is important to safeguard animal welfare shortly after stunning at the slaughter plant. Indicators that can be visually evaluated are most often used when assessing unconsciousness, as they can be easily applied in slaughter plants. These indicators include reflexes originating from the brain stem (e.g. eye reflexes) or from the spinal cord (e.g. pedal reflex) and behavioural indicators such as loss of posture, vocalisations and rhythmic breathing. When physically stunning an animal, for example, captive bolt, most important indicators looked at are posture, righting reflex, rhythmic breathing and the corneal or palpebral reflex that should all be absent if the animal is unconscious. Spinal reflexes are difficult as a measure of unconsciousness with this type of stunning, as they may occur more vigorous. For stunning methods that do not physically destroy the brain, for example, electrical and gas stunning, most important indicators looked at are posture, righting reflex, natural blinking response, rhythmic breathing, vocalisations and focused eye movement that should all be absent if the animal is unconscious. Brain stem reflexes such as the cornea reflex are difficult as measures of unconsciousness in electrically stunned animals, as they may reflect residual brain stem activity and not necessarily consciousness. Under commercial conditions, none of the indicators mentioned above should be used as a single indicator to determine unconsciousness after stunning. Multiple indicators should be used to determine unconsciousness and sufficient time should be left for the animal to die following exsanguination before starting invasive dressing procedures such as scalding or skinning. The recording and subsequent assessment of brain activity, as presented in an electroencephalogram (EEG), is considered the most objective way to assess unconsciousness compared with reflexes and behavioural indicators, but is only applied in experimental set-ups. Studies performed in an experimental set-up have often looked at either the EEG or reflexes and behavioural indicators and there is a scarcity of studies that correlate these different readout parameters. It is recommended to study these correlations in more detail to investigate the validity of reflexes and behavioural indicators and to accurately determine the point in time at which the animal loses consciousness.

Enhanced non-eupneic breathing following hypoxic, hypercapnic or hypoxic-hypercapnic gas challenges in conscious mice

C57BL6 mice display non-eupneic breathing and spontaneous apneas during wakefulness and sleep as well as markedly disordered breathing following cessation of a hypoxic challenge. We examined whether (1) C57BL6 mice display marked non-eupneic breathing following hypercapnic or hypoxic-hypercapnic challenges, and (2) compared the post-hypoxia changes in non-eupneic breathing of C57BL6 mice to those of B6AF1 (57BL6 dam × A/J sire) and Swiss-Webster mice, which display different ventilatory responses than C57BL6 mice. C57BL6 mice displayed marked increases in respiratory frequency and non-eupneic breathing upon return to room-air after hypoxic (10% O2, 90% N2), hypercapnic (5% CO2, 21% O2 and 74% N2) and hypoxic-hypercapnic (10% O2, 5% CO2 and 85% N2) challenges. B6AF1 mice displayed less tachypnea and reduced non-eupneic breathing post-hypoxia, whereas Swiss-Webster mice displayed robust tachypnea with minimal increases in non-eupneic breathing post-hypoxia. These studies demonstrate that non-eupneic breathing increases after physiologically-relevant hypoxic-hypercapnic challenge in C57BL6 mice and suggest that further studies with these and B6AF1 and Swiss-Webster mice will help define the genetics of non-eupneic breathing.

Biophysical and molecular mechanisms underlying the modulation of heteromeric Kir4.1-Kir5.1 channels by CO2 and pH

CO2 chemoreception may be related to modulation of inward rectifier K+ channels (Kir channels) in brainstem neurons. Kir4.1 is expressed predominantly in the brainstem and inhibited during hypercapnia. Although the homomeric Kir4.1 only responds to severe intracellular acidification, coexpression of Kir4.1 with Kir5.1 greatly enhances channel sensitivities to CO2 and pH. To understand the biophysical and molecular mechanisms underlying the modulation of these currents by CO2 and pH, heteromeric Kir4. 1-Kir5.1 were studied in inside-out patches. These Kir4.1-Kir5.1 currents showed a single channel conductance of 59 pS with open-state probability (P(open)) approximately 0.4 at pH 7.4. Channel activity reached the maximum at pH 8.5 and was completely suppressed at pH 6.5 with pKa 7.45. The effect of low pH on these currents was due to selective suppression of P(open) without evident effects on single channel conductance, leading to a decrease in the channel mean open time and an increase in the mean closed time. At pH 8.5, single-channel currents showed two sublevels of conductance at approximately 1/4 and 3/4 of the maximal openings. None of them was affected by lowering pH. The Kir4.1-Kir5.1 currents were modulated by phosphatidylinositol-4,5-bisphosphate (PIP2) that enhanced baseline P(open) and reduced channel sensitivity to intracellular protons. In the presence of 10 microM PIP2, the Kir4.1-Kir5.1 showed a pKa value of 7.22. The effect of PIP2, however, was not seen in homomeric Kir4.1 currents. The CO2/pH sensitivities were related to a lysine residue in the NH2 terminus of Kir4.1. Mutation of this residue (K67M, K67Q) completely eliminated the CO2 sensitivity of both homomeric Kir4.1 and heteromeric Kir4.1-Kir5.1. In excised patches, interestingly, the Kir4.1-Kir5.1 carrying K67M mutation remained sensitive to low pHi. Such pH sensitivity, however, disappeared in the presence of PIP2. The effect of PIP2 on shifting the titration curve of wild-type and mutant channels was totally abolished when Arg178 in Kir5.1 was mutated. Thus, these studies demonstrate a heteromeric Kir channel that can be modulated by both acidic and alkaline pH, show the modulation of pH sensitivity of Kir channels by PIP2, and provide information of the biophysical and molecular mechanisms underlying the Kir modulation by intracellular protons.

Modulation of kir4.1 and kir5.1 by hypercapnia and intracellular acidosis

CO2 chemoreception may be mediated by the modulation of certain ion channels in neurons. Kir4.1 and Kir5.1, two members of the inward rectifier K+ channel family, are expressed in several brain regions including the brainstem. To test the hypothesis that Kir4.1 and Kir5. 1 are modulated by CO2 and pH, we carried out experiments by expressing Kir4.1 and coexpressing Kir4.1 with Kir5.1 (Kir4.1-Kir5. 1) in Xenopus oocytes. K+ currents were then studied using two-electrode voltage clamp and excised patches. Exposure of the oocytes to CO2 (5, 10 and 15 %) produced a concentration-dependent inhibition of the whole-cell K+ currents. This inhibition was fast and reversible. Exposure to 15 % CO2 suppressed Kir4.1 currents by approximately 20 % and Kir4.1-Kir5.1 currents by approximately 60 %. The effect of CO2 was likely to be mediated by intracellular acidification, because selective intracellular, but not extracellular, acidification to the measured hypercapnic pH levels lowered the currents as effectively as hypercapnia. In excised inside-out patches, exposure of the cytosolic side of membranes to solutions with various pH levels brought about a dose-dependent inhibition of the macroscopic K+ currents. The pK value (-log of dissociation constant) for the inhibition was 6.03 in the Kir4.1 channels, while it was 7.45 in Kir4.1-Kir5.1 channels, an increase in pH sensitivity of 1.4 pH units. Hypercapnia without changing pH did not inhibit the Kir4.1 and Kir4.1-Kir5.1 currents, suggesting that these channels are inhibited by protons rather than molecular CO2. A lysine residue in the N terminus of Kir4.1 is critical. Mutation of this lysine at position 67 to methionine (K67M) completely eliminated the CO2 sensitivity of both the homomeric Kir4. 1 and heteromeric Kir4.1-Kir5.1. These results therefore indicate that the Kir4.1 channel is inhibited during hypercapnia by a decrease in intracellular pH, and the coexpression of Kir4.1 with Kir5.1 greatly enhances channel sensitivity to CO2/pH and may enable cells to detect both increases and decreases in PCO2 and intracellular pH at physiological levels.

Congenital central alveolar hypoventilation syndrome (Ondine's Curse): effectiveness of early home ventilation for normal development

An 8 month old Caucasian girl, with congenital central alveolar hypoventilation syndrome (Ondine's Curse), was discharged with her home ventilation managed by her parents. Her subsequent neurophysical development assessed at 22 months of age was satisfactory.

Decrementing expiratory neurons of the Bötzinger complex. I. Response to lung inflation and axonal projection

In Nembutal-anesthetized, immobilized, and artificially ventilated cats with intact vagus nerves, extracellularly recorded activities of expiratory (E) neurons whose firing patterns were of decrementing, or the early expiration type (E-DEC neurons) were recorded in the vicinity of the Bötzinger complex (BOT). A total of 32 E-DEC neurons which were not vagal motoneurons was studied by determining 1) where they were distributed, 2) how their firing was modulated by lung inflation, and 3) if they projected their axons to the respiratory area of the brain stem. E-DEC neurons were located ventromedially to the retrofacial nucleus and were intermingled with E neurons of the augmenting type (E-AUG neurons), which were abundant and representative of neurons in the BOT. Firing of 25 E-DEC neurons was facilitated by lung inflation, indicating the existence of excitatory input from stretch receptors of the lungs, although the firing of 7 other neurons was not affected. On the other hand, firing of surrounding E-AUG neurons was suppressed by lung inflation. The E-DEC neurons fired in the E phase during a brief stop of the ventilator, indicating that they received central respiratory rhythm. However, they almost never fired during the inspiratory (I) phase even when the lungs were strongly inflated, indicating the existence of strong central inhibition during the I phase. Eight E-DEC neurons were tested for antidromic activation from the contralateral brain stem and the spinal cord by microstimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory rhythm generation in the in vitro brain stem-spinal cord preparation of the neonatal rat

An in vitro preparation was described for studying electrical activity of mammalian brain stem and spinal cord. The brain stem and the spinal cord were isolated from 0-4-day-old rats, placed in a bath and perfused with modified Krebs solution. Various reflex responses could be recorded from cranial nerves by stimulation of other cranial nerves. The preparation was viable for more than 7 h. Spontaneous periodic neural activity could be recorded from phrenic, hypoglossal and other spinal nerves. The periodic discharges of phrenic nerves are synchronized with those of ventral roots C4 and the upward movements of the thorax which was isolated together with the spinal cord. The rhythm of periodic activity seems to be generated in the brain stem. The periodic activity was enhanced by perfusion with low pH solution and depressed by high pH solution. It was markedly depressed by opioid compounds such as enkephalin. It is suggested that this periodic activity corresponds to the respiratory rhythm generated in the brain stem of intact animals. The present preparation may be valuable for elucidating cellular mechanisms of generation and control of respiratory rhythm in the mammalian central nervous system.

Difference between actions of high PCO2 and low [HCO-3] on neurons in the rat medullary chemosensitive areas in vitro

To evaluate the contribution of extracellular fluid (ECF) pH in stimulating the ventral medullary chemosensors, effects on neuronal activities of changing ECF PCO2 and/or [HCO-3] were studied in tissue slices taken from the medulla oblongata of the rat. In many cases changes in neuronal discharges produced by a high PCO2-normal [HCO-3] solution differed from those produced by a low [HCO-3] normal PCO2 solution although the ECF pH was reduced to the same degree (from 7.40 to about 7.15). Only 9 of a total of 76 neurons showed an increase in discharge in response to both acid solutions. Neuronal activation due to high PCO2 was augmented when the ECF pH was returned to a normal value (7.40) by simultaneous increase in [HCO-3]. High PCO2-high [HCO-3] solution (pH 7.40) increased the activity of many neurons which were either inhibited or uninfluenced by high PCO2-normal [HCO-3] (pH 7.15). Neuronal activation due to low [HCO-3] was partially suppressed by compensating for the pH reduction with a concomitant decrease in PCO2. The results suggest that CO2 and HCO-3 independently influence the activity of neurons. Possible roles of ECF H+, CO2 and HCO-3 in activating the ventral medullary chemosensitive structures are discussed.

Some considerations on the central regulation of respiration and its disturbances

The effect of increased intracranial pressure on the respiration pattern was studied in cats. It appeared that the different patterns described by Plum and Brown blend into each other under certain conditions.

Primary sleep apnoea syndrome

Polygraphic study in 18 men with the sleep apnoea syndrome showed central, upper airway obstructive, and mixed apnoeas. Fifty per cent of the total apnoea time was central, 33% was obstructive, and 17% was mixed. Apnoeic episodes were accompanied by oxygen desaturation, relative bradycardia and hypotonia of orofacial muscles innervated by ponto-medullary neurons. During regular breathing these muscles revealed tonic and phasic inspiratory EMG activities. The data suggest that the primary sleep apnoea syndrome results from a dysfunction of the central control of breathing.

Characteristics and surgical management of respiratory complications accompanying pathologic lesions of the brain stem

Three life-threatening respiratory complications are regularly encountered in patients who survive the initial insult from a diffuse brain stem lesion--central alveolar hypoventilation, upper airway obstruction, and aspiration pneumonitis. From treating 13 patients who did survive, a surgical plan for managing the respiratory sequelae of such injuries has evolved and consists of: 1)Diaphragm pacing to correct hypoventilation; 2) tracheostomy for bypass of the upper airway obstruction; 3) gastrostomy for bypass of the impaired structures of swallowing; 4) surgical closure of the larynx to prevent aspiration. All 13 patients manifested central apnea, which was controlled in five by bilateral phrenic nerve stimulation and in eight by unilateral stimulation. All patients required tracheostomy to provide an airway for artificial ventilation and for secretion removal. In ten patients aspiration necessitated gastrostomy. The spontaneous recovery of the ability to swallow allowed closure of the gastrostoma in three but in others aspiration remained a serious complication. One patient died of massive aspiration after discharge from the hospital. Three patients had surgical closure of the larynx to prevent aspiration. Seven patients are alive; six of them are leading productive lives, though several have severe disability due to paresis or ataxia. Six died after discharge from the hospital. Three deaths were not related to the basic problem but the three others may have been.

The carotid chemoreceptor input to the respiratory neurones of the nucleus of tractus solitarus

1. An investigation has been made into the connexions between the carotid body chemoreceptors and the dorsal respiratory neurones of the cat's medulla.2. In confirmation of previous work these neurones were found to be all inspiratory in firing pattern and to fall into two categories, Ralpha (forty-four units) which fire only with the central inspiratory rhythm and Rbeta (thirty-two neurones) that are also excited by lung inflation. Both categories were shown to be excited by stimuli delivered to the carotid bodies during inspiration but, with a single exception, not during expiration.3. When Rbeta neurones were made to fire tonically in expiration by maintained lung inflation, chemoreceptor activation inhibited this discharge in 7/11 cases, the remainder being unaffected.4. Iontophoretically applied DL-homocysteic acid or glutamate made both Ralpha and Rbeta neurones fire tonically in expiration. Chemoreceptor stimulation during expiration inhibited this activity in all neurones tested (nine Ralpha and three Rbeta cells).5. Using the measurement of the antidromic latency to spinal stimulation as an index of membrane potential, evidence was obtained that any subthreshold influence of the chemoreceptors on dorsal respiratory neurones during expiration was inhibitory (9/18 cases).6. It is concluded that chemoreceptors do not even subliminally excite dorsal inspiratory neurones during expiration; such influence as they have then is inhibitory. Possible reasons for this difference in chemoreceptor influence during inspiration and expiration are discussed. It is suggested that chemoreceptor excitation reaches them only as part of an enhanced central inspiratory drive from an as yet unknown source.