Interactions between volitional and automatic breathing during respiratory apraxia

Breathing control, brain, and bodily self-consciousness: Toward immersive digiceuticals to alleviate respiratory suffering

Breathing is peculiar among autonomic functions through several characteristics. It generates a very rich afferent traffic from an array of structures belonging to the respiratory system to various areas of the brain. It is intimately associated with bodily movements. It bears particular relationships with consciousness as its efferent motor control can be automatic or voluntary. In this review within the scope of "respiratory neurophysiology" or "respiratory neuroscience", we describe the physiological organisation of breathing control. We then review findings linking breathing and bodily self-consciousness through respiratory manipulations using virtual reality (VR). After discussing the currently admitted neurophysiological model for dyspnea, as well as a new Bayesian model applied to breathing control, we propose that visuo-respiratory paradigms -as developed in cognitive neuroscience- will foster insights into some of the basic mechanisms of the human respiratory system and will also lead to the development of immersive VR-based digital health tools (i.e. digiceuticals).

Respiratory dysfunction in Parkinson's disease: a narrative review

The presence of respiratory symptoms in Parkinson's disease (PD) has been known since the first description of the disease, even though the prevalence and incidence of these disturbances are not well defined. Several causes have been reported, comprising obstructive and restrictive pulmonary disease and changes in the central ventilatory control, and different pathogenetic mechanisms have been postulated accordingly. In our review, we encompass the current knowledge about respiratory abnormalities in PD, as well as the impact of anti-Parkinsonian drugs as either risk or protective factors. A description of putative pathogenetic mechanisms is also provided, and possible treatments are discussed, focusing on the importance of recognising and treating respiratory symptoms as a key manifestation of the disease itself. A brief description of respiratory dysfunctions in atypical Parkinsonism, especially α-synucleinopathies, is also provided.

This review addresses current knowledge about respiratory dysfunctions in Parkinson's disease, from the aetiopathology to pharmacological and invasive treatments, describing the different clinical phenotypeshttps://bit.ly/2X7OLtN

Mechanisms of the breathing contribution to bodily self-consciousness in healthy humans: Lessons from machine-assisted breathing?

Previous studies investigated bodily self-consciousness (BSC) by experimentally exposing subjects to multisensory conflicts (i.e., visuo-tactile, audio-tactile, visuo-cardiac) in virtual reality (VR) that involve the participant's torso in a paradigm known as the full-body illusion (FBI). Using a modified FBI paradigm, we found that synchrony of visuo-respiratory stimulation (i.e., a flashing outline surrounding an avatar in VR; the flash intensity depending on breathing), is also able to modulate BSC by increasing self-location and breathing agency toward the virtual body. Our aim was to investigate such visuo-respiratory effects and determine whether respiratory motor commands contributes to BSC, using non-invasive mechanical ventilation (i.e., machine-delivered breathing). Seventeen healthy participants took part in a visuo-respiratory FBI paradigm and performed the FBI during two breathing conditions: (a) "active breathing" (i.e., participants actively initiate machine-delivered breaths) and (b) "passive breathing" (i.e., breaths' timing was determined by the machine). Respiration rate, tidal volume, and their variability were recorded. In line with previous results, participants experienced subjective changes in self-location, breathing agency, and self-identification toward the avatar's body, when presented with synchronous visuo-respiratory stimulation. Moreover, drift in self-location was reduced and tidal volume variability were increased by asynchronous visuo-respiratory stimulations. Such effects were not modulated by breathing control manipulations. Our results extend previous FBI findings showing that visuo-respiratory stimulation affects BSC, independently from breathing motor command initiation. Also, variability of respiratory parameters was influenced by visuo-respiratory feedback and might reduce breathing discomfort. Further exploration of such findings might inform the development of respiratory therapeutic tools using VR in patients.

Respiratory modulation of intensity ratings and psychomotor response times to acoustic startle stimuli

Respiratory interoception may play an important role in the perception of respiratory symptoms in pulmonary diseases. As the respiratory cycle affects startle eye blink responses, startle modulation may be used to assess visceral-afferent signals from the respiratory system. To ascertain the potential impact of brainstem-relayed signals on cortical processes, we investigated whether this pre-attentive respiratory modulation of startle (RMS) effect is also reflected in the modulation of higher cognitive, evaluative processing of the startle stimulus. Twenty-nine healthy volunteers received 80 acoustic startle stimuli (100 or 105 dB(A); 50 ms), which were presented at end and mid inspiration and expiration, while performing a paced breathing task (0.25 Hz). Participants first responded to the startle probes by 'as fast as possible' button pushes and then rated the perceived intensity of the stimuli. Psychomotor response time was divided into 'reaction time' (RT; from stimulus onset to home button release; represents stimulus evaluation) and 'movement time' time (MT; from home button release to target button press). Intensity judgments were higher and RTs accelerated during mid expiration. No effect of respiratory cycle phase was found on eye blink responses and MTs. We conclude that respiratory cycle phase affects higher cognitive, attentional processing of startle stimuli.

Evaluation, treatment, and analysis of a rare case of motor speech systems dyscoordination syndrome

This report describes an unusual presentation of a voice disorder arising from inability to coordinate the three components of motor speech: respiration, phonation, and articulation. These systems were individually intact, as demonstrated by laryngoscopy, motor speech examination, and treatment methods achieving success under controlled conditions. Following initial programming of his deep brain stimulation (DBS) device, a 62-year-old male, diagnosed with Parkinson's disease (PD) 14 years previously, abruptly experienced a vocal disorder characterized by pressed, very low frequency creaky voice produced on held breath. Evaluation and therapy sessions revealed intact respiration, phonation, and articulation as component systems of motor speech, while indicating a severe deficit in coordinating these systems for articulated speech. Performance varied with mode of vocal production. Vowel prolongation and singing were normal in contrast to severe impairment when respiration and phonation were integrated with articulated speech. A listening study utilizing speech samples from five spoken modes-conversation, repetition, formulaic expressions, continuously phonated material and singing, yielded higher intelligibility on sung and continuously phonated phrases, confirming clinical impressions. Acoustic measures of fundamental frequency, vowel quality (harmonic-to-noise ratios) and duration supported the intelligibility results. Repetition and conversation were similarly impaired, suggesting that the disability was not attributable to the basal ganglia. This case reveals the role of higher order management of respiration, articulation, and voice for speech and describes a successful treatment utilizing breath control.

Respiratory modulation of startle eye blink: a new approach to assess afferent signals from the respiratory system

Current approaches to assess interoception of respiratory functions cannot differentiate between the physiological basis of interoception, i.e. visceral-afferent signal processing, and the psychological process of attention focusing. Furthermore, they typically involve invasive procedures, e.g. induction of respiratory occlusions or the inhalation of CO₂-enriched air. The aim of this study was to test the capacity of startle methodology to reflect respiratory-related afferent signal processing, independent of invasive procedures. Forty-two healthy participants were tested in a spontaneous breathing and in a 0.25 Hz paced breathing condition. Acoustic startle noises of 105 dB(A) intensity (50 ms white noise) were presented with identical trial frequency at peak and on-going inspiration and expiration, based on a new pattern detection method, involving the online processing of the respiratory belt signal. The results show the highest startle magnitudes during on-going expiration compared with any other measurement points during the respiratory cycle, independent of whether breathing was spontaneous or paced. Afferent signals from slow adapting phasic pulmonary stretch receptors may be responsible for this effect. This study is the first to demonstrate startle modulation by respiration. These results offer the potential to apply startle methodology in the non-invasive testing of interoception-related aspects in respiratory psychophysiology.This article is part of the themed issue 'Interoception beyond homeostasis: affect, cognition and mental health'.

Habituation to experimentally induced electrical pain during voluntary-breathing controlled electrical stimulation (BreEStim)

Objective

Painful peripheral electrical stimulation to acupuncture points was found to cause sensitization if delivered randomly (EStim), but induced habituation if triggered by voluntary breathing (BreEStim). The objective was to systematically compare the effectiveness of BreEStim and EStim and to investigate the possible mechanisms mediating the habituation effect of BreEStim.

Methods

Eleven pain-free, healthy subjects (6 males, 5 females) participated in the study. Each subject received the BreEStim and EStim treatments in a random order at least three days apart. Both treatments consisted of 120 painful but tolerable stimuli to the ulnar nerve at the elbow on the dominant arm. BreEStim was triggered by voluntary breathing while EStim was delivered randomly. Electrical sensation threshold (EST) and electrical pain threshold (EPT) were measured from the thenar and hypothenar eminences on both hands at pre-intervention and 10-minutes post-intervention.

Results

There was no difference in the pre-intervention baseline measurement of EST and EPT between BreEStim and EStim. BreEStim increased EPT in all tested sites on both hands, while EStim increased EPT in the dominant hypothenar eminence distal to the stimulating site and had no effect on EPT in other sites. There was no difference in the intensity of electrical stimulation between EStim and BreEStim.

Conclusion

Our findings support the important role human voluntary breathing plays in the systemic habituation effect of BreEStim to peripheral painful electrical stimulation.

Modification of electrical pain threshold by voluntary breathing-controlled electrical stimulation (BreEStim) in healthy subjects

BACKGROUND

Pain has a distinct sensory and affective (i.e., unpleasantness) component. BreEStim, during which electrical stimulation is delivered during voluntary breathing, has been shown to selectively reduce the affective component of post-amputation phantom pain. The objective was to examine whether BreEStim increases pain threshold such that subjects could have improved tolerance of sensation of painful stimuli.

METHODS

Eleven pain-free healthy subjects (7 males, 4 females) participated in the study. All subjects received BreEStim (100 stimuli) and conventional electrical stimulation (EStim, 100 stimuli) to two acupuncture points (Neiguan and Weiguan) of the dominant hand in a random order. The two different treatments were provided at least three days apart. Painful, but tolerable electrical stimuli were delivered randomly during EStim, but were triggered by effortful inhalation during BreEStim. Measurements of tactile sensation threshold, electrical sensation and electrical pain thresholds, thermal (cold sensation, warm sensation, cold pain and heat pain) thresholds were recorded from the thenar eminence of both hands. These measurements were taken pre-intervention and 10-min post-intervention.

RESULTS

There was no difference in the pre-intervention baseline measurement of all thresholds between BreEStim and EStim. The electrical pain threshold significantly increased after BreEStim (27.5±6.7% for the dominant hand and 28.5±10.8% for the non-dominant hand, respectively). The electrical pain threshold significantly decreased after EStim (9.1±2.8% for the dominant hand and 10.2±4.6% for the non-dominant hand, respectively) (F[1, 10] = 30.992, p = .00024). There was no statistically significant change in other thresholds after BreEStim and EStim. The intensity of electrical stimuli was progressively increased, but no difference was found between BreEStim and EStim.

CONCLUSION

Voluntary breathing controlled electrical stimulation selectively increases electrical pain threshold, while conventional electrical stimulation selectively decreases electrical pain threshold. This may translate into improved pain control.

Breathing-controlled Electrical Stimulation (BreEStim) for management of neuropathic pain and spasticity

Electrical stimulation (EStim) refers to the application of electrical current to muscles or nerves in order to achieve functional and therapeutic goals. It has been extensively used in various clinical settings. Based upon recent discoveries related to the systemic effects of voluntary breathing and intrinsic physiological interactions among systems during voluntary breathing, a new EStim protocol, Breathing-controlled Electrical Stimulation (BreEStim), has been developed to augment the effects of electrical stimulation. In BreEStim, a single-pulse electrical stimulus is triggered and delivered to the target area when the airflow rate of an isolated voluntary inspiration reaches the threshold. BreEStim integrates intrinsic physiological interactions that are activated during voluntary breathing and has demonstrated excellent clinical efficacy. Two representative applications of BreEStim are reported with detailed protocols: management of post-stroke finger flexor spasticity and neuropathic pain in spinal cord injury.

Voluntary breathing influences corticospinal excitability of nonrespiratory finger muscles

The present study aimed to investigate neurophysiologic mechanisms mediating the newly discovered phenomenon of respiratory-motor interactions and to explore its potential clinical application for motor recovery. First, young and healthy subjects were instructed to breathe normally (NORM); to exhale (OUT) or inhale (IN) as fast as possible in a self-paced manner; or to voluntarily hold breath (HOLD). In experiment 1 (n = 14), transcranial magnetic stimulation (TMS) was applied during 10% maximal voluntary contraction (MVC) finger flexion force production or at rest. The motor-evoked potentials (MEPs) were recorded from flexor digitorum superficialis (FDS), extensor digitorum communis (EDC), and abductor digiti minimi (ADM) muscles. Similarly, in experiment 2 (n = 11), electrical stimulation (ES) was applied to FDS or EDC during the described four breathing conditions while subjects maintained 10%MVC of finger flexion or extension and at rest. In the exploratory clinical experiments (experiment 3), four patients with chronic neurological disorders (three strokes, one traumatic brain injury) received a 30-min session of breathing-controlled ES to the impaired EDC. In experiment 1, the EDC MEP magnitudes increased significantly during IN and OUT at both 10%MVC and rest; the FDS MEPs were enhanced only at 10%MVC, whereas the ADM MEP increased only during OUT, compared with NORM for both at rest and 10%MVC. No difference was found between NORM and HOLD for all three muscles. In experiment 2, when FDS was stimulated, force response was enhanced during both IN and OUT, but only at 10%MVC. When EDC was stimulated, force response increased at both 10%MVC and rest, only during IN, but not OUT. The averaged response latency was 83 ms for the finger extensors and 79 ms for the finger flexors. After a 30-min intervention of ES to EDC triggered by forced inspiration in experiment 3, we observed a significant reduction in finger flexor spasticity. The spasticity reduction lasted for ≥ 4 wk in all four patients. TMS and ES data, collectively, support the phenomenon that there is an overall respiration-related enhancement on the motor system, with a strong inspiration-finger extension coupling during voluntary breathing. As such, breathing-controlled electrical stimulation (i.e., stimulation to finger extensors delivered during the voluntary inspiratory phase) could be applied for enhancing finger extension strength and finger flexor spasticity reduction in poststroke patients.

Control of breathing and volitional respiratory rhythm in humans

When breathing frequency (f) is imperceptibly increased during a volitionally paced respiratory rhythm imposed by an auditory signal, tidal volume (Vt) decreases such that minute ventilation (V̇e) rises according to f-induced dead-space ventilation changes ( 18 ). As a result, significant change in alveolar ventilation and Pco2 are prevented as f varies. The present study was performed to determine what regulatory properties are retained by the respiratory control system, wherein the spontaneous automatic rhythmic activity is replaced by a volitionally paced rhythm. Six volunteers were asked to trigger each breath cycle on hearing a brief auditory signal. The time interval between subsequent auditory signals was imperceptibly changed for 10–15 min, during 1) air breathing ( condition 1), 2) the addition of a 300 ml of instrumental dead space ( condition 2), 3) an increase in the inspired level of CO2 ( condition 3), and 4) light exercise ( condition 4). We found that as f was slowly increased the elaborated Vt decreased in accordance to the background level of CO2 and metabolic rate. Indeed, for any given breath duration, Vt was shifted upward in condition 2 vs. 1, whereas the slope of Vt changes according to the volitionally rhythm was much steeper in conditions 3 and 4 vs. 1. The resulting changes in V̇e offset any f-induced changes in dead-space ventilation in all conditions. We conclude that there is an inherent, fundamental mechanism that elaborates Vt based on f when imposed by the premotor cortex in humans. The chemoreflex and exercise drive to breath interacts with this cortically mediated rhythm maintaining alveolar rather than V̇e constant as f changes. The implications of our findings are discussed in the context of our current understanding of the central generation of breathing rhythm.

Bipolar disorder as maladaptive arousal: a behavioral model and evidence

Bipolar disorder can be understood as a disorder of behavioral regulation. Manic and depressed individuals are impaired in the titration of appetitive arousal, possibly at the level of neuronal plasticity. An experiment in which fixed 5% CO2 stimulates respiration and blocks satiety tests the regulation of appetitive arousal. In preliminary analysis of data from 35 individuals (24 with bipolar disorder) individuals with bipolar disorder were more likely to fail to find a stable state of respiratory adjustment to CO2. If confirmed, the unstable respiratory response to CO2 may prove useful as a bipolar-disorder endophenotype.

Control of breathing during cortical substitution of the spontaneous automatic respiratory rhythm

This study addresses the following question: does the ventilatory control system adjust total ventilation in accord with the regulatory demands of the physiological dead space ventilation (VD) when the breathing frequency changes, and if so, how? A simple proportionality between the amplitude of the respiratory motor output (VT) and the respiratory period (TTOT) during such changes will not provide for regulation of arterial (PaCO2); the relationship requires a positive intercept of magnitude VD, i.e. VT=VATTOT+VD. We therefore determined the relationship between VT and TTOT when breathing frequency was changed in a ramp-like manner (from 6 to 20 cycles/min), in an imperceptible manner, during a paced-breathing protocol in which the subjects voluntarily triggered the breath onset, thereby imposing a rhythm different from the one spontaneously generated by the automatic central pattern generators (CPGs). While the resulting breath magnitude was strongly correlated to the breath duration (slope: 6.50+/-2.91 l/min) there was, in all cases, a statistically significant positive intercept on the VT axis (238+/-112 ml) leading to a relationship of the form: VT=VATTOT+VD. Consequently, the ventilatory output changed as a function of the breathing frequency-induced dead space ventilation changes, maintaining end-tidal PCO2 (PETCO2) constant. These results are consistent with a centrally set program for generating regulatory combinations of respiratory cycle durations and magnitudes that "take into account" the f-induced variation of dead space ventilation. This appears not to be dependent on the structures producing the respiratory rhythm (cortex versus central pattern generators). It is suggested that, during volitional control of breathing rhythm, the signal used for adjusting the magnitude to the timing of the ventilatory output is derived from information contained in the duration of preceding expiration.

Respiratory apraxia in amyotrophic lateral sclerosis

Respiratory dysfunction is a critical problem in amyotrophic lateral sclerosis (ALS). We report a patient with ALS who had respiratory apraxia. A 74-year-old female presented with progressive dysarthria and dysphagia. Clinical signs and evidence of widespread denervation on electromyography (EMG) confirmed the diagnosis of ALS. She had no signs of dementia. Irregular volitional inspiratory movements on verbal command were noticed, in contrast with rhythmic automatic inspiration - respiratory apraxia. Limb and buco-facial movements showed no signs of apraxia. EMG of respiratory muscles was normal, apart from irregular phasic activity of the diaphragm on volitional inspiration; this was confirmed by recording respiratory movements with a percutaneous sensor transducer. Sleep study was normal. She deteriorated rapidly; nonetheless, no clinical sign of dementia or other apraxic findings were observed. ALS, particularly when of bulbar onset, can cause respiratory apraxia and EMG of the respiratory muscles can be useful to detect this condition.

Respiratory control at exercise onset: an integrated systems perspective

The near-immediate increase in breathing that accompanies the onset of constant load, dynamic exercise has remained a topic of interest to respiratory physiologists for the better part of a century. During this time, several theories have been proposed and tested in an attempt to explain what has been called the phase I response of exercise hyperpnoea, or the fast neural drive to breathe, and much controversy still remains as to what mediates this response. 'Central motor command' and 'afferent feedback' mechanisms, as described in animal models, have been centre stage in the debate, with much supportive evidence for their involvement. This review presents three relatively recent and controversial mechanisms and examines the increasing evidence for their involvement in the initial phase of exercise hyperpnoea: (1) the vascular distension hypothesis, (2) the vestibular feedback hypothesis and (3) the behavioral state hypothesis. Some outstanding fundamental questions and directions for future research are presented throughout, always with a focus on mechanistic efficacy in the integrated system response.