About the Mechanism of Hiccup

Abstract

Every new empiric observation made over two millenia fueled the dispute as to whether hiccup (Hc) is a digestive or a respiratory reflex. A review of the literature, focusing attention on the probable mechanism of Hc, shows Hc as a neurogenic dysfunction of the ‘valve function’ between the inspiratory complex and the glottis closure complex.

A phylogenetic hypothesis for the origin of hiccough

“…The central link of this arc would be located within the spinal cord, the brainstem and the hypothalamus, and the cerebellum and cerebral hemispheres would possibly be involved. (3,4) Hiccough could also represent a form of epilepsy, although most patients with chronic hiccough do not have any cerebral dysfunction and although diazepam, a major anticonvulsant drug, can trigger or worsen hiccough (see the review in Ref. 1).…”

“…(5) Another hypothesis is that hiccough could result from a dysfunction of the reciprocal inhibition of an ''inspiratory complex'' related to breathing and a ''glottis closure complex'' related to swallowing. (3) Some authors believe that hiccough represents the persistence of a fetal digestive reflex preventing amniotic fluid aspiration. (6) For others, fetal hiccough may prepare respiratory muscles for their postnatal breathing function after birth.…”

Successful treatment of intractable hiccups with serotonin (5-HT)1A receptor agonist

“…Several researchers have hypothesized that the activation of a reflex arc, the afferent limb of which comprises the phrenic nerves, vagus nerves and sympathetic fibers, is a causative factor of hiccups ( Fig. 1) [1,2,5,9]. They propose that damage to the central link of this arc (such as damage to the cervical cord, brainstem, hypothalamus and supratentorial areas) precipitates the hiccups by stimulating this reflex arc or decreasing the normal inhibitions of hiccup neurons.…”

“…The main efferent limb causing spasms of the diaphragm is mediated by motor fibers of the phrenic nerve. The central link of this arc is thought to be located either in the brainstem close to the inspiratory centers or in the cervical cord, with the possible involvement of the hypothalamus and supratentorial areas [1,2] the 5-HT1A receptors located in the medulla, and this inhibition shortens inspiratory discharges [7,10]. Much clinical evidence suggests that 5-HT1A agonists have a beneficial effect on respiratory dysfunctions such as apneusis, which is caused by prolonged inspiratory discharges [7,10].…”

Nocturnal Vocalization

“…4 Hiccups were thought to be secondary to dysfunction of the respiratory system (i.e., diaphragmatic spasms, phrenic nerve excitation) versus disorders of the gastrointestinal system (gastric distension or reflux) or due to neurological (seizures, post-anoxic syndrome) or psychosomatic causes. 2 Interestingly, in our patient, the hiccups ANSWER: B. Nocturnal hiccups and catathrenia subsided after she was placed on omeprazole for gastroesophageal reflux disease (GERD). Current hypothesis suggests that hiccups occur due to a dysfunction in the brainstem neural trigger mechanism leading to paradoxical activation of the "glottic closure complex" soon after the activation of the "inspiratory complex" leading to closure of the glottis during inhalation causing a tonic-phasic inspiratory obstruction sound known as the hiccup.…”