L2 Mechanisms of Breathing Flashcards
What is breathing?
The bodily function that leads to ventilation of the lungs.
What is ventilation?
The process of moving gases in (inspiration) and out (expiration) of the lungs.
What are obstructive lung conditions?
It is generally characterised by inflamed and easily collapsible airways,obstructionto airflow, problems exhaling. An example of such conditions include COPD, Lung cancer and Asthma.
What are restrictive lung conditions?
Restrictive lung diseaserefers to a group oflung diseasesthat prevent the lungs from fully expanding with air. This restriction makesbreathingdifficult. Many forms ofrestrictive lung diseaseare progressive, getting worse over time. However, some causes ofrestrictive lung diseasecan be reversed.
○ Intrinsic, e.g., pulmonary fibrosis
○ Extrinsic – pneumothorax, disorders of the thoracic skeleton
What is required for inhalation?
A pressure difference. cWhen we breath in, atmospheric pressure (barometric pressure) must be greater than alveolar pressure. Under normal circumstances, atmospheric pressure is constant. Any pressure differentials must be generated by changes in alveolar pressure.
What muscles are required in quiet breathing?
Inhalation: Diaphragm and external intercostal muscle. The diaphragm moves principally downwards, compressing the abdominal contents unless the abdominal muscles relax. The diaphragm expands and squeezes the abdominal content, moving out the rib cage.
Expiration: Normally, this does not require much effort as the lungs have a tendency to recoil.
What muscles are required in forced breathing?
Inhalation: The muscles used are the diaphragm, external intercostals lift & expand rib cage, accessory muscles, neck muscles and shoulder girdle muscles. With more active breathing, when they contract, they cause the chest to move upwards and the ribcage to expand. When breathing and we use accessory muscles, principally in the neck moving the whole ribcage up. This depends on the abdominal muscles to stabilise the lower part of the ribcage.
Expiration: With increasing effort we use active contraction of the internal intercostal muscles. With even greater effort we use abdominal muscles to squeeze on the abdomen and pull up the diaphragm.
Where is the external and internal intercostal muscles located? How are the intercostal muscles innervated?
The external intercostal muscle is inserted into the rib above the relevant intercostal space. The internal intercostal muscle is inserted into the rib below the relevant intercostal space. Innervated by the respective nerves from the Segmental thoracic nerves. The first intercostal muscle is innervated by the nerve coming from the first thoracic segment of the spinal cord and the second from the second thoracic segment of the spinal cord etc.
Why are you able to survive if the spinal cord in injured at the level of the thoracic spinal cord?
If the damage to the cervical cord is below the origins of the phrenic nerve, it is a survivable injury as the diaphragm is not paralysed. However the intercostal muscles will not work as the thoracic nerves will not work as there connection with the brain is severed.
What is atmospheric pressure?
0 cm of H20 (1 atm)
How does the intrapleural pressure and alveolar pressure change during a normal breath?
The intrapleural pressure change always precedes the alveolar pressure change - it is usually lower than the alveolar pressure.
At end of inspiration, if the individual takes a pause, the system is at equilibrium. There is no movement of gas. There is equilibrium between the atmospheric pressure and the alveolar pressure. At ending expiration the alveolar pressure is equal to 0. The intrapleural pressure will be below 0 cm of H20. When you inhale, the intrapleural pressure decreases and becomes negative, the alveolar pressure decreases. When the alveolar pressure begins to drop a pressure gradient is established and air starts to move into the lungs. Air continues as the intrapleural pressure stabilises. As air rushes in, the alveolar pressure will start to go up again after it initially drops as the pressure equilibrates. As you breath out and relax your muscles, the volume will go down, the intrapleural pressure rises, increasing the alveolar pressure and so reversing the pressure gradient. Air rushes out of the lungs until the pressure equilibrates with atmospheric, again moving alveolar pressure back to 0.
What is a pneumothorax?
When there is a disruption of the pleura, you can get a pneumothorax. Here air enters the chest cavity between the layers of the pleura. The lung, since it is an elastic structure, collapses. If tension builds up, a tension pneumothorax can squash the heart and compromise it. This is treated by putting a needle between the second and third rib to release the air.
Fluid can get between the layers of the pleura. The lung will again not expand well.
What is tidal volume? What is normal tidal volume?
Tidal volume: the volume of air moved in or out of the lungs during normal breathing. A typical value for tidal volume of an adult male is 500ml. At rest this is 6-7 ml/kg. During exercise this is 15 ml/kg.
What is inspiratory reserve volume? What is the normal value?
Inspiratory reserve volume: Volume above the tidal volume that you can inspire. Typically is 3L for a 70kg man.
What is the expiratory reserve volume? What is a normal value?
Expiratory reserve volume: Your expiratory reserve volume is the amount of extra air — above anormal breath — exhaled during a forceful breath out. Around 1.5L typical for a 70kg male
