Studies of voluntary and involuntary control of human breathing


Within the central nervous system, we have identified three sites that can potentially cause respiratory issues; (1) the sensorimotor cortex, (2) the medullary respiratory centres, and (3) spinal reflex circuits. We are currently using a multi-faceted approach to investigate each of these three potential sites of failure of respiratory neural control, thus determining the central mechanisms of respiratory motor impairment.

Our team is uniquely qualified to apply a suite of specialised neurophysiological methods, many pioneered in our lab, to better understand voluntary activation of the diaphragm, cortical activation during breathing, and measure single motor unit activity.

A motor unit is made up of a motor neuron and the muscle it activates. We are the only group internationally who make motor unit recordings from human respiratory pump muscles. This is the only direct measure of neural drive.

Our current experiments are looking at voluntary and involuntary drive to the breathing muscles to try to answer this fundamental question about the neural control of breathing. In addition, we are looking at the potential cortical contributions to resting breathing in respiratory disorders.

Chronic Obstructive Pulmonary Disease

Respiratory impairment is a common and debilitating medical condition for older adults and people with chronic obstructive pulmonary disease (COPD). This condition is the third-highest ranking disease burden in Australia and New Zealand.

Respiratory illness limits daily activities and reduces health-related quality of life. These consequences and frequent hospitalisations are a public health burden that cost over $1 billion per year.

Spinal cord injury
After cervical spinal cord injury (SCI), the respiratory muscles are partly or completely paralysed. There are two major clinical consequences of this: the ability to get air into the lungs is diminished as is the ability to cough to remove secretions. This results in a lifetime of recurrent respiratory tract infections (2/year/person) that often proceed to pneumonia and frequent hospitalisations.

People with cervical SCI are 150 times more likely to die from respiratory complications than the general population. A recent longitudinal study of 283 people with cervical SCI showed that respiratory muscle weakness is linked to incidental pneumonia. There is an urgent need to identify a simple and effective treatment for weak respiratory muscles and the prevention of respiratory complications after SCI.

Obstructive Sleep Apnoea
OSA is a sleep disorder that affects more than 4 percent of the population and can lead to symptoms from daytime drowsiness to high blood pressure. People with sleep apnoea are often not breathing normally during sleep and may experience periods where the airway closes and they are unable to breathe. In severe sleep apnoea this can occur 50-60 times each hour. That is once each minute.

The closure of the upper airway is thought to be due to a number of factors, one of which is that the neural drive to the airway muscles is insufficient in people with sleep apnoea. In our lab, we have made the first extensive recordings from the major muscle of the upper airway, genioglossus.

We have shown that the neural drive to this muscle is very complex, more so than any limb muscle. At NeuRA, we have also pioneered new methods to image this muscle using fMRI and ultrasound. We are now planning to look at how changes in muscle architecture and mechanics relate to the neural drive to the muscle and whether that relationship is maintained in people with sleep apnoea.

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Abdominal muscle stimulation to improve bowel function in spinal cord injury

Bowel complications, resulting from impaired bowel function, are common for people living with a spinal cord injury (SCI). As a result, people with a SCI have high rates of bowel related illness, even compared with those with other neurological disorders. This includes high rates of abdominal pain, constipation, faecal incontinence and bloating. These problems lower the quality of life of people with a SCI and place a financial burden on the health system. A treatment that improves bowel function for people with a SCI should reduce illness, improve quality of life and lead to a large cost saving for health care providers. Bowel problems have traditionally been managed with manual and pharmacological interventions, such as digital rectal stimulation, enemas, and suppositories. These solutions are usually only partially effective, highlighting the need for improved interventions. The abdominal muscles are one of the major muscle groups used during defecation. Training the abdominal muscles should improve bowel function by increasing abdominal pressure. During our previous Abdominal FES research with people with a SCI, we observed that Abdominal FES appeared to lead to more consistent and effective bowel motion. However, this evidence remains anecdotal. As such, we are going to undertake a large randomised controlled trial to investigate the effectiveness of Abdominal FES to improve the bowel function of people with a SCI. This study will make use of a novel measurement system (SmartPill, Medtronic) that can be swallowed to measure whole gut and colonic transit time. We will also assess whether Abdominal FES can change constipation-related quality of life and the use of laxatives and manual procedures, as well as the frequency of defecation and the time taken. A positive outcome from this study is likely to lead to the rapid clinical translation of this technology for people living with a SCI.