mise à jour du
24 janvier 2009
European Journal of Neurology
Amelioration of pathological yawning after tracheostomy in a patient with locked-in syndrome:
a thermo-regulatory approach
Hari Prasad
Medical Research Faculty, Microbiology,
K.S. Hegde Medical Academy, Deralakatte, Nithyanandanagar P.O., Mangalore, Karnataka, India


I have read with great interest the report by Chang et al. describing amelioration of pathological yawning after tracheostomy in a patient with locked-in syndrome [1]. It was an interesting debate but what in- trigued me most was Chang et al. spective of excessive yawning and its role in neurological practice. My purpose is to give another view of the meaning of excessive yawning observed in locked-in syndrome. Yawning is a stereotyped behaviour with an evolutionary significance, and has been described since antiquity [2].
Excessive yawning appears to be symptomatic of conditions that increase brain and/or core temperature, such as cerebral ischae- mia, traumatic brain injury and sleep deprivation. There is now a growing body of evidence suggesting that yawning may be a thermoregulatory mechanism, pro- viding compensatory brain cooling when other provisions fail to operate favourably [3].
In a recently published paper, I report the protective thermoregulatory role of yawning in patients on anti-depressant therapy [4]. Selective brain cooling appears to protect the thermally vulnerable tissue of the brain from thermal damage [5]. If so, the mechanism would be expected to be most important in locked-in syndrome, which is usually associated with, infarction of the ventral pons. In my opinion, an intense need for selective brain cooling is the major functional cause to initiate and execute yawning as an involuntary motor phenomenon, despite destruction of voluntary movements of facial and trigeminal motor functions [6].
Well-controlled animal models of nasal and tracheostomy breathing demonstrate a significantly detrimental effect of tra- cheostomy breathing on brain and body temperatures, and on clinical outcome of hyperthermia. The study by Laburn et al. (1988) indicate that selective brain cooling depends on upper respiratory tract cooling (i. e. via nasal breathing) in normo- and in hyperthermic states. Though it is true that patient tomy, I cannot agree that it is connected with termination of the pathological yawning. Conversely, the tracheostomy breathing, which bypasses the carotid rete mechanism, could cause a rise in thalamic and cortical brain temperatures [7].
One would therefore anticipate that a predis- position towards abolition of body-brain temperature difference during tracheos- tomy breathing would produce a proportional increase in brain tempera- ture thereby augmenting other selective brain cooling mechanisms and, ostensibly, placing one at increased risk for aggravation, instead of amelioration of pathological yawning. In this connection, I would again like to mention the experiments made by Laburn et al., who observed that, intermittent nasal breathing after hours of upper respiratory bypass results in a dramatic and significant brain cooling [7].
This precipitous temperature fall has been attributed to the evaporative cooling of the re-ventilated nasal mucosal surfaces which had been wetted by copious secretion, for the period of bypass breathing. On the basis of this evidence, I suggest that the cerebral cooling stimulated by intermittent nasal air passage following tracheostomy might be strong enough to inhibit mechanisms that would normally trigger yawning in patients with locked-in syndrome. Further studies are needed before conclusions can be drawn. Conflicts of interest The author has no conflicts of interest to declare.
1. Chang CC, Chang ST, Chang HY, Tsai KC. Amelioration of pathological yawning after tracheostomy in a patient with locked-in syndrome. European Journal of Neurology 2008; 15: e66&endash;e67.
2. Prasad H. Yawning... and why yawns are contagious: a theory on evolution and atavism. Medical Hypotheses 2008; 71: 307.
3. Gallup AC, Gallup GG Jr. Yawning and thermoregulation. Physiology and Behavior 2008; 95: 10&endash;16.
4. Prasad H. Drug-induced yawning: A vital protective reflex. Medical Hypotheses 2008; 71: 457.
5. Gluckman PD, Wyatt JS, Azzopardi D, et al. Selective head cooling with mild systemic hypothermia after neonatal encephalopathy: multicentre randomised trial. Lancet 2005; 365: 663&endash;670.
6. Smith E, Delargy M. Locked-in syndrome. British Medical Journal 2005; 330: 406&endash;409.
7. Laburn HP, Mitchell D, Mitchell G, et al. Effects of tracheostomy breathing on brain and body temperatures in hyperthermic sheep. Journal of Physiology 1988; 406: 331&endash; 344.
Medical implications of excessive yawning in relation to thermoregulatory dysfunction Gallup AC