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Systematic study in animals indicated, that in addition to cough there are 2 distinct airway reflexes. The aspiration reflex (AspR) characterized by rapid and strong gasp-like inspiration provoked by stimulation of nasopharynx, nasal phyltrum or auricle of ear. The expiration reflex (ExpR) manifests by prompt expiration, induced by laryngeal stimulation. Both reflexes strongly activate the brainstem inspiratory or expiratory generators, respectively, and inhibit the opposite respiratory and various functional disorders.
This paper indicates several functional disorders occurring during manipulation with airways in anaesthesiological practice, which can be influenced positively or negatively by application of these special reflexes (asphyxia, breath-holding, laryngospasm, bronchospasm, sleep apnoea episodes, arrhythmia, collapse, etc.). The AspR, ExpR and CR (cough reflex) have important clinical relevance in anaesthesia and emergency medicine applicable also in domestic therapy and in hardly accessible places particularly by application of ICT (Information & Communication Technologies) using a mobile connection of the patient with the remote hospital centre.
Studii sistematice pe animale au arătat că există două reflexe suplimentare ale căii aeriene pe lângă reflexul de tuse. Reflexul de aspiraţie (AspR) este caracterizat printr-o inspiraţie rapidă şi puternică (“gasp-like”) provocată de stimularea nazofaringelui, filtrului nazal sau a pavilionului urechii. Reflexul expirator (ExpR) se manifestă printr-o expiraţie promptă indusă de stimularea laringiană. Ambele reflexe activează puternic centrii respiratori care generează inspiraţia, respectiv expiraţia, inhibând reflexul opus precum şi alte variate tulburări funcţionale.
Această lucrare semnalează câteva tulburări funcţionale care apar pe parcursul manipulării instrumentale a căii aeriene în timpul practicii anestezice şi care pot fi influenţate pozitiv sau negativ prin aplicarea acestor reflexe particulare (asfixia, apneea voluntară, laringospasmul, bronhospasmul, episoadele de apnee de somn, aritmii, colaps etc.). AspR, ExpR şi reflexul de tuse au o importanţă particulară în practica anestezică şi în medicina de urgenţă, cu aplicabilitate şi în terapia la domiciliu, chiar şi în locuri aflate la distanţă mai mare de spital, prin utilizarea unei legături telefonice mobile cu pacientul.
Airway stimulation evokes well described reactive responses, such as cough [1–6], laryngospasm [7–11] and bronchospasm [12–15]. These reflex responses may also occur during light anesthesia. Additionally to these, two other reflexes, the expiration and aspiration reflexes have been described, though their precise mechanisms of action and implications in clinical practice have not been clearly identified. Nonetheless, both expiration reflex (ExpR) and aspiration reflex (AspR) might have important implications in various pathological processes in the anesthetized patients and in other conditions unrelated to anesthesia.
The purpose of this brief review is to familiarize the anesthesiologists with the possible implications of ExpR, AspR and cough reflex (CR) in various situations encountered in anesthesia practice.
Part of the text content relies on clinical observation and assumptions rather than being based on evidence or other published literature.
The ExpR has been described as a solitary, short-lasting activity of the abdominal muscles, indicating a prompt expiratory effort with no preceding inspiration, with reflex interruption of an occasional inspiration. It is accompanied by transient bronchoconstriction in addition to prompt activation of expiratory muscles [2, 6, 16–18].
The AspR has been described as a short-lasting, high-frequency activity in the phrenic nerve and the inspiratory muscles, indicating a rapid and strong, spasmodic sniff- and gasp-like inspiration with no subsequent active expiration. It is accompanied by a reflex interruption of any spontaneous activity of the abdominal muscles, suggesting an inhibition of active expiration [2, 18–22].
ExpR, AspR and CR are defensive reactions, which can manifest both in normal and various pathological situations. ExpR provides tracheal protection against aspiration of foreign bodies. Upon irritation by a foreign body, primarily of the vocal folds and the larynx, or less often the trachea and bronchi , a forceful expiration accompanied by transient laryngo-constriction and followed immediately by swallowing expels the foreign body away from the airways. Unlike the ExpR, the CR provides cleaning of the airways from particles that already entered them. The CR comprises a deep inspiratory phase, followed by a short lasting laryngeal closure and forceful expiration. AspR, ExpR and CR are the main airway defensive reflexes evoked by irritation of the nasopharynx, oro-pharynx, larynx and lower airways, respectively (Figure 1, ,22).
They are normal, prompt reactions to airway irritation. CR and ExpR are expulsive reflexes, designated to prevent distal dispersion of various particles in the airways and their elimination. They are accompanied by transient broncho-constriction, to further block airway penetration by irritants. Their main components are listed in Table 1 and compared with quiet Breath in Figure 1. The reflex arch, mechanism and various resuscitation potentials of these powerful airway reflexes are indicated in Figure 2 and discussed later.
In an awake or a lightly anesthetized patient, breath-holding “on the endotracheal tube” occasionally called by some authors as “cough and strain afterward”  is a well known clinical problem. This “strain afterward” is best explained by an ExpR activity.
Breath holding with desaturation is also not uncommon after extubation of the trachea. A typical clinical picture is convulsive expiratory movements (“strain”) of chest and abdomen and difficulty to ventilate the patient through a facemask. Often, this is related to laryngospasm though the manifestations of ExpR and laryngospasm seem to be different. This is especially evident with partial laryngeal closure often manifested by stridor which is absent in the case of ExpR. We thus speculate that in post extubation breath holding, similarly to a “strain” on the endotracheal tube, the patient holds his breath during expiration and cannot generate inspiration effort supposedly owing to an active ExpR, whereas during laryngospasm the patient cannot drive gas into the lungs because of upper airway obstruction.
ExpR may also be activated as an exaggerated response to aggressive upper airway manipulations. In our clinical experience, this can be encountered in lightly anesthetized pediatric patients and morbidly obese patients, especially in those suffering from obstructive sleep apnea.
The AspR, another defensive airway reflex, might explain the mechanism of post-obstructive negative pressure pulmonary edema following a laryngospasm, because it manifests by strong, gasping movements that can create excessive negative pressures in the chest cavity.
The ExpR may play an important role in children suffering from “Breath-holding spells”, where breath-holding and desaturation occur at the end of expiration, instead of normally starting an inspiratory effort. Remarkably many of these children suffer from ENT (ear throat and nose) problems and improve significantly after adenoidectomy [12, 24].
The management of post-extubation breath holding seems to be similar to that of post-extubation laryngospasm. We empirically but successfully use rapid, shallow mask ventilation along with CPAP. Recently, Al-Metwalli , successfully managed post-extubation laryngospasm (or ExpR?) with gentle chest compressions. All these management tools promote air movement within the chest and thus, supposedly help brake the ExpR and/or laryngospasm.
Gasping respiration observed in infants in critical conditions before death has a strong resuscitation potential. Survival or death depends on the prevalence of either the gasps or the inhibitory effect on vital organs with morphological destruction or functional impairment of control mechanisms, such as in SIDS (Sudden Infant Death Syndrome . Contact stimulation of the nasopharynx in cats provokes strong impulses (~200 Hz) in the glossopharyngeal afferents , which activate the brainstem inspiratory generator located in the pre-Botzinger complex . This provokes a rapid and strong inspiratory effort, the gasp-like aspiration reflex [19–23]. The AspR has similar resuscitation and revitalization potential as gasping, proved mostly in animals . Stimulation and suction by a nasopharyngeal catheter, proved to interrupt supraventricular tachycardia in 4 from 12 infants , similarly as in adults observed accidentally during introduction of a naso-gastric catheter for gastric juice collection . Nasopharyngeal stimulation could also interrupt hiccough attacks . Provocation of AspR proved to interrupt hypoxic apnoea in cats . Therefore, it can speed up normalization of breathing also in artificially ventilated patients, resulting from reflex activation of the brainstem inspiratory generator .
Rapid sniff through the nose for one second with closed mouth, representing a voluntary equivalent of AspR has a broncho-protective and broncho-dilatory effect in patients with asthma, chronic obstructive pulmonary disease, smokers and healthy people [38, 39]. Strong activation of brainstem inspiratory generator during rapid sniffs may be transferred to other central structures and may dilate the airway lumen , or inhibit various pathological states such as laryngospasm, bronchospasm, Parkinson’s tremor, epileptic seizure, etc.
Sudden hypotension with imminent loss of consciousness caused by anaphylactic reaction or other reasons such as ventricular arrhythmias can be prevented by cough “on demand” . The deep inspiration of cough (“sniff and expire”) increases venous return and the successive strong expiratory effort provides prompt brain perfusion to prevent a collapse.
The persisting AspR might allow differentiation of patients in a vegetative state by the presence of activity in the pre-motor area of brain in fMRI on the instruction to move the hand, from non-reacting patient with brain death . Similar activities might also be observed by fMRI after provocation of AspR by mechanical means even in more severe disorders of consciousness without voluntary but persisting reflex signs. Since AspR persists even in the stage of pre-mortal gasping at least in cats, the procedure might allow exclusion of brain death in selected cases of moribund patients .
The persisting AspR and ExpR, representing diametrical different reactions, as binary signals allow for paraplegics to communicate using a computer and control their wheelchair, as described by Plotkin et al. .
In this review we tried to familiarize the anesthesia and intensive care medicine specialties readers with the concepts of ExpR, CR and AspR and their possible clinical relevance, including in the field of anesthesia and emergency medicine.
Conflict of interest
Nothing to declare