Highlights:- Incidence of
obstructive sleep apnea in tetraplegic (paralysis of all four limbs and
torso) patients is high (nearly 70 percent) and the reason for this is not
clear.
- Scientists
identify possible reason for this phenomenon in the current study, which
may help develop targeted therapies, that would help improve quality of life for these patients.
- Obstructive sleep
apnea refers to repetitive narrowing of the upper airway (back of nose and
throat) during sleep with potentially serious health consequences and an
increased risk of diabetes and high blood pressure (hypertension).
Possible mechanism for the high incidence of obstructive
sleep apnea in tetraplegic patients has been outlined in a recent study. The
details of the study appear in
The Journal of Physiology and
could pave the way for developing targeted treatments aimed at improving the
quality of life of these patients.
Aim
of Study
The current study aims at
finding out how throat muscles
respond in tetraplegic patients suffering from sleep apnea. The answer to
this question may explain the reason for the high incidence of OSA in these
patients and using this knowledge to develop better and more effective
treatments that could improve the quality of their life.
Details
of Study
- Volunteers
suffering from OSA (including tetraplegics as well as those without
tetraplegia for comparison) were assessed in sleep physiology studies in
Sydney (NeuRA) and Melbourne (IBAS).
- To replicate
upper airway narrowing characteristic of OSA, brief pulses of suction were
delivered to the volunteers through a breathing mask.
- Simultaneously,
electrodes were inserted into the largest muscle of the upper respiratory
tract, namely the genioglossus, to measure key reflex responses.
- The study team
thought that the throat reflex responses would be same in all patients
with OSA, irrespective of whether they were suffering from tetraplegia or
not.
- The current study
however found that in several cases of tetraplegics with sleep apnea, key
protective throat reflexes were not present, resulting in the switching
off (rather than increased activity) of the genioglossus muscle, normally
observed in OSA patients who do not have tetraplegia.
Thus, the findings of this study may help to explain why OSA is so common
in those with tetraplegia who have sleep apnea.
Activity of Genioglossus Muscle in OSA
Patients Who Don't Have Tetraplegia/Have Tetraplegia
- Normally, the
contraction of upper airway dilator muscles, such as the genioglossus is
critical in keeping the upper airway open enabling unrestricted air flow.
- Patients (without
tetraplegia) suffering from OSA demonstrated increased activity on
genioglossus electromyogram (EMG) during the wakeful state.
- This
neuromuscular compensation prevents apneic episodes during the day by
keeping the airway open.
- In tetraplegics
with OSA, genioglossus muscle activity was found to be reduced.
Optimism
and Enthusiasm of Participants Key to Success of Study
Laura Gainche, one of the study team members, praised the
optimism, endurance and willingness of all the research's participants,
especially
shown by their first participant, JV, who suffered his spinal injury at the
age of 16
"We were worried that nobody would take part in our
long, tedious protocol. However, he (JV) just brushed it off like it was
nothing", saying "A two millimeter wide catheter in the nose? What a joke compared to the feeding tubes I
had before"!
‘Reduced or absent throat reflexes in tetraplegic patients may account for the high incidence of obstructive sleep apnea in these patients.’
"The experimental day was intense to say the least; six
people wheeled his bed up a steep slope to a test room about 100m away from the
main hospital. Somehow, we made it through the lengthy protocol together, and it was mostly
thanks to him, our first rock star patient! These participants gave us
confidence that this project was feasible, and in the future the data produced
will hopefully make their lives a tiny bit easier".
What
is Obstructive Sleep Apnea (OSA)?
Apnea means absence of breathing. Sleep apnea refers to
apneic episodes occurring when a person is asleep. In
obstructive sleep apnea the
breathing stops due to obstruction to air flow in the upper airway. When the
airway is narrowed with resultant restricted air flow, the person snores
(breathes through mouth). If however, the airflow is completely blocked,
breathing stops for about 10 seconds and resumes once again.
Persons suffering from OSA have impaired sleep and suffer
from excessive daytime drowsiness, irritability and inability to concentrate.
The most effective treatment for OSA is continuous positive
airway pressure (CPAP). The
slightly high air pressure keeps the throat open while the patient is breathing
and prevents blockage of the airway.
Conclusion
Despite the fact that the study was conducted in the wakeful
state and not during sleep, the scientists are optimistic that the findings of
their study would help future sleep physiology studies, as
well as in development of safe and effective targeted therapies for tetraplegic
patients with sleep apnea.
Reference:- Noradrenergic Activation of Hypoglossal Nucleus Modulates the Central Regulation of Genioglossus
in Chronic Intermittent Hypoxic Rats -
(https://www.frontiersin.org/articles/10.3389/fneur.2017.00171/full)
Source-Medindia
Careers
