Cough as a neurological sign: Does it worth it?

Cough is one of the most common complaints that lead patients to see a doctor. It is not only a basic respiratory sign but also an important neurological sign. There are 3 main types of cough: reflex cough (type I), voluntary cough (type II), and evoked cough (type III). Reflex cough sensitivity may be increased in many neurological disorders, such as space-occupying lesion of the brainstem, medullary lesions secondary to type I Chiari malformations, tics disorders such as Tourette’s syndrome, somatic cough, neurodegenerative disorders of the cerebellum, and chronic vagal neuropathy due to allergic and nonallergic diseases. On the other hand, cough sensitivity decreases in the cerebral hypoxia, cerebral hemispheric stroke with a brainstem shock, dementia due to Lewy body disease, Parkinson’s disease, amyotrophic lateral sclerosis, multiple sclerosis, and peripheral neuropathy such as hereditary sensory and autonomic neuropathy type IV, diabetic neuropathy, vitamin B12, and folate deficiency. The ear-cough reflex of Arnold’s nerve, syncopal cough, cough headache, opioid associated cough and cough-anal reflex are signs that can help in the diagnosis of underlying neurological disorders. The cough reflex test is a quick, easy, and inexpensive test that can be performed during the cranial nerve exam. In this article, we have discussed cough reflex testing and various neurological disorders that increase or decrease cough sensitivity.

In Vivo Documentation of Stimulus Velocity Tuning of Mechanically Induced Reflex Cough

In order to clear airways and lungs defensive reflexes are provoked rather by the dynamic phase of mechanical stimulus. It is speculated that provocation of defensive response depends not only on stimulus duration but also on stimulus velocity. Fourteen adult rabbits were anaesthetized and tracheotomized. Mechanical stimulus was provoked by a mechanical probe introduced through the tracheotomy and rotated by a small electrical motor using a rotational velocity of 40 rpm/s and 20 rpm/s. Threshold, incidence and intensity of cough reflex (CR) were analyzed for each animal. Statistical comparisons between two velocities were performed using Friedman nonparametric test for repeated measurements. Results are median (25-75 %). The threshold of CR was significantly increased (p=0.005) from 350 ms (300-500 ms) to 550 ms (350-1150 ms) and the incidence of cough reflex was significantly reduced (p=0.002) from 50 % (19 50 %) to 0 % (0-25 %) when the rotational velocity of the mechanical probe was reduced by half. The findings of this study are of interest as they show that protective reflex cough, an important mechanism that allows clearing airways even during sleep or anesthesia, is tuned by mechanical stimulus velocity.

Voluntary upregulation of reflex cough is possible in healthy older adults and Parkinson’s disease

Cough is an airway-protective mechanism that serves to detect and forcefully eject aspirate material. Existing research has identified the ability of healthy young adults to suppress or modify cough motor output based on external cueing. However, no study has evaluated the ability of people with Parkinson’s disease (PD) and healthy older adults (HOAs) to upregulate cough motor output. The goal of this study was to evaluate the ability of people with PD and healthy age-matched controls (HOAs) to upregulate reflex and voluntary cough function volitionally with verbal instruction and visual biofeedback of airflow targets. Sixteen participants with PD and twenty-eight HOAs (56–83 yr old) were recruited for this study. Experimental procedures used spirometry to evaluate 1) baseline reflex cough (evoked with capsaicin) and voluntary sequential cough and 2) reflex and voluntary cough with upregulation biofeedback. Cough airflow was recorded and repeated-measures ANOVA was used to analyze differences in cough airflow parameters. Cough peak expiratory airflow rate and cough expired volume were significantly greater in the cueing condition for both induced reflex ( P < 0.001) and voluntary cough ( P < 0.001) compared with baseline measures. This is the first study to demonstrate the ability of people with PD and HOAs to upregulate induced reflex and voluntary cough motor output volitionally. These results support the development of studies targeting improved cough effectiveness in patients with airway-protective deficits. NEW & NOTEWORTHY Aspiration pneumonia is a leading cause of death in Parkinson’s disease (PD) and results from concurrent dysphagia and dystussia (cough dysfunction). This is the first study to demonstrate that people with PD and healthy age-matched controls can volitionally upregulate induced reflex and voluntary cough effectiveness when presented with novel cueing strategies. Thus targeting upregulation of cough effectiveness via biofeedback may be a viable way to enhance airway protection in people with PD.