Apnea

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Apnea

• Kylie Gray

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What is it?!?!?!

• Apnea is a technical term for the suspension of
  external breathing
• There is no movement of the muscles of
  respiration and the volume of the lungs initially
  remains unchanged
• May or may not be a flow of gas between the lungs
  and the environment
• Gas exchange within the lungs and cellular
  respiration is not affected
• It can be achieved in different ways
• 1. voluntarily ex by holding ones breath
• 2. drug induced ex opiate toxicity
• 3. mechanically induced ex strangulation
• 4. neurological disease or trauma

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Mechanism

• Under normal conditions, humans cannot store much
  oxygen in the body
• Apnea of more than one minutes duration can lead
  to severe lack of oxygen in the circulation
  system
• Permanent brain damage can occur just a little
  after 3 minutes and death will occur a few
  minutes later unless ventilation is restored.
• Untrained humans can not sustain voluntary apnea
  for more than one or two minutes
• The rate of breathing and the volume of each
  breath are tightly regulated to maintain constant
  volumes of CO2 tension and pH of the blood

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Mechanism

• In apnea, CO2 is not removed through the lungs
  and accumulates in the blood
• The consequent rise in CO2 tension and drop in pH
  result in stimulation of the respiratory center
  in the brain, which eventually cannot be overcome
  voluntarily.
• What about under water??
• When a person is immersed in water, physiological
  changes due to the mammalian diving reflex enable
  somewhat longer tolerance of apnea, even in
  untrained persons
• Tolerance can be trained Free diving requires
  breath-holding and world class free divers can
  hold their breath underwater for more than 8
  minutes.

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Mammalian Diving Reflex

• Found in all mammals humans and especially
  marine mammals
• Puts the body into oxygen saving mode to maximize
  the time spent under water
• Effect of this reflex is greater in cold water
  than in warm water and includes 3 factors
• 1. Bradycardia reduction in the heart rate (up
  to 50 in humans)
• 2. Peripheral vasoconstriction decrease in
  blood flow to the extermities, in order to
  increase the supply of blood and oxygen to the
  vital organs, especially the brain
• 3. Blood shift the shifting of the blood to
  the thoracic cavity e.g. the chest between the
  diaphragm and the neck to avoid the collapse of
  the lungs under the higher pressure during deeper
  dives

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Types of Apnea

• Classified into three types depending on whether
  inspiratory muscle activity is present (taking
  air in).
• If inspiratory muscle activity fails following an
  exhalation , it is termed Central Apnea
• If inspiratory muscle activity is present without
  air flow, it is termed Obstructive Apnea
• If both central and obstructive apnea occur
  during the same episode, this is termed Mixed
  Apnea

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Physiological Changes

• Decrease in arterial oxygen tension
• Decrease in heart rate
• Decrease in peripheral blood flow
• EEG changes suggesting CNS depression if apnea is
  severe
• Increase in venous pressure
• Decrease in muscle tone

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Apneic Oxygenation

• Because the exchange of gases between the blood
  and airspace of the lungs is independent of the
  movement of gas to and from the lungs, a
  sufficient amount of oxygen can be delivered to
  the circulation even if the person is apneic.
• With the onset of apnea, an underpressure is
  developed in the airspace of the lungs, because
  more oxygen is absorbed than CO2 is released.
• With the airways closed or obstructed, this will
  eventually lead to a collapse of the lungs (ex
  strangulation, choking),
• but if the airways are open, any gas supplied to
  the upper airways will follow the pressure
  gradient and flow into the lungs to replace the
  oxygen consumed.

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Apneic Oxygentation

• The uptake of oxygen into the blood will then
  remain at the usual level and the normal function
  of the organs will not be affected.
• However, no CO2 is removed during apnea and the
  partial pressure of CO2 in the airspace of the
  lungs will quickly equilibrate with that of the
  blood.
• As the blood is loaded with CO2 from the
  metabolism, more and more CO2 will accumulate and
  eventually displace oxygen and other gases from
  the airspace.

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Respiration measurements

• In order to diagnose apnea, the nasal and oral
  airflow must be measured
• This allows the clinician/researcher to measure
  the rate of respiration or help to diagnose apnea
  and sleep apnea
• This can be done using a thermocouple or pressure
  transducer

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Thermocouple

• Thermocouples are composed of two wires made of
  dissimilar metals, fused together at the tip.
• When the tip of the two metals is placed under a
  patients nose or in front of the mouth, the
  temperature changes associated with the patients
  breathing cause the diameter of the wires to
  expand and contract
• This increases and decreases the voltage being
  produced by the device. These changes are
  recorded by the polysomnograph.
• A multi-parametric test used in the study of
  sleep
• A comprehensive recording of the biophysiological
  changes that occur during sleep
• May measure body functions such as the brain
  (EEG), eye movements (EOG), muscle activity
  (EMG), heart rhythm (ECG), and breathing function
  during seep

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Thermocouple
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Advantages/Disadvantages

• A clear advantage of the thermocouple is that it
  is very easy to combine multiple fusion points
  in a circuit allowing for a combined oral/nasal
  signal
• The low cost of the materials used to construct a
  thermocouple, as well as the absence of an
  external power source requirement , results in a
  very inexpensive monitoring device
• A disadvantage of the thermocouple is its slow
  response to changes in temperature

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Nasal mucosal temperature during respiration

• One of the most important roles of the nose is to
  heat the air coming in
• Lindemann, Leiacker, Rettinger, Keck (2002)
• Study measured mucosal temperature during
  respiration without interruption of nasal
  breathing
• A miniaturized thermocouple was used for
  continuous detection of the mucous and the nose
  area during respiration
• The highest temperature values were found at the
  end of expiration (breathing out) and the lowest
  values were found at the beginning of inspiration
  (breathing in).
• The use of a thermocouple can detect the
  temperature changes in temperature and therefore
  can conclude if there is an exchange of air
  between the lungs and the environment

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Sleep Apnea

• Sleep disorder characterized by pauses in
  breathing during sleep
• These episodes, called apneas, each last long
  enough so one or more breaths are missed and
  occur periodically through sleep.
• Regardless of the type of apnea (Obstructive,
  Central, or Mixed), the individual affected is
  rarely aware of having difficulty breathing, even
  upon awakening.
• Sleep apnea is recognized as a problem by others
  witnessing the individual during episodes, or is
  suspected because of its effects on the body
• The definitive diagnoses of sleep apnea if made
  by polysomnography.

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Signs and Symptoms

• Signs of obstructive sleep apnea is restless
  sleep and loud snoring (with periods of silence
  followed by gasps).
• Most serious consequence is to the heart
• In severe and prolonged cases, there are
  increases in pulmonary pressures that are
  transmitted to the right side of the heart
• Can result in a severe form of congestive heart
  failure
• Other symptoms that are non-specific
• Morning headaches
• Trouble concentrating
• Irritability
• Forgetfulness
• Mood or behavioral changes
• Anxiety, depression, increased heart rate and
  urination

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Treatment

• Variety of different treatments depending on the
  individuals medical history, the severity of the
  disorder, and cause of obstruction
• Some treatments involve lifestyle changes, such
  as avoiding alcohol and medications that relax
  the CNS, losing weight and quitting smoking
• Some people are helped by special pillows or
  devices that keep them from sleeping on their
  backs, or oral appliances to keep the airway open
  during sleep. CPAP devices may need psychological
  support for use.
• There are also surgical procedures that can be
  used to remove and tighten tissue and widen the
  airway, but the success rate is not high
• Some individuals may need a combination of
  therapies to successfully treat their sleep apnea