Respiration: mechanics Flashcards
What are the two meanings of respiration?
tissue respiration and breathing
tissue respiration definition
the aerobic metabolism in cells
breathing definition
gas exchange and the associated processes
respiratory mechanics definition
study of mechanical properties of the lung and chest wall and the process by which air enters and leaves the lungs
Function of the lungs
bring in oxygen rich air to fuel the body and to expel waste gas (CO2)
Function of breathing
maintain blood gas homeostasis (O2, CO2, pH)
What must the movement of air in and out of the lungs be coupled with?
cellular respiration
What are the partial pressures of O2 and CO2 at rest?
PO2 = 100+-2 mmHg
PCO2 = 40+-2 mmHg
Volume of O2 and CO2 exchanged at rest
250ml O2/min and 200ml CO2/min
Volume of O2 and CO2 exchanged when walking
800ml O2/min and 750ml CO2/min
Volume of O2 and CO2 exchanged during severe exercise
5000ml O2/min and 6000ml CO2/min (due to more anaerobic respiration)
Which structures does air flow through to reach the lungs?
nasal cavities, pharynx, larynx, trachea, bronchi, bronchioles, alveoli
Which structures are regarded as the upper airways?
nasal cavity, pharynx, larynx
Major functions of the upper airway
humidify (saturate with water), warm (to body temp) and filter the air
Which epithelium lines the upper airways to the bronchioles?
pseudostratified ciliated columnar epithelium
How is inhaled air filtered?
particles become trapped in mucus which is wafted by cilia to the pharynx to be coughed out.
Function of goblet cell
produce mucus that forms a layer over the cilia
Ventilation at rest
6-7 L/min (12-15 breaths of 500ml)
Max ventilation
160L/min (40 breaths of 4L)
Cardiac output at rest
5 L/min (70bpm, 70ml/beat)
Max cardiac output
25 L/min (200bpm, 125ml/beat)
Description of inspiration during quiet breathing
active - diaphragm contracts downwards, pushing abdominal contents outwards. External intercostal muscles pull ribs outwards and upwards
Description of expiration during quiet breathing
passive - elastic recoil
Description of inspiration during strenuous breathing
active - greater contraction of diaphragm and external intercostal muscles. Inspiratory accessory muscles are active.
Difference in diaphragm contraction in quiet and strenuous breathing
1cm in quiet breathing and 10cm in strenuous breathing
Examples of inspiratory accessory muscles active during strenuous breathing
sternocleidomastoid, alae nasi, genioglossus
Description of expiration during strenuous breathing
active - abdominal muscles active and internal intercostal muscles oppose external intercostals by pushing ribs down and inwards.
Abdominal muscles active during expiration in strenuous breathing
rectus abdominus, internal oblique, external oblique, transverse abdominus
What is the major inspiratory muscle?
Diaphragm
What type of muscle is the diaphragm?
skeletal muscle
What are the muscles of inspiration?
Sternocleidomastoid, scalenus, parasternal intercartilaginous muscles, external intercostals, diaphragm
What are the muscles of expiration?
internal intercostals, abdominal muscles - rectus abdominis, external oblique, internal oblique, transversus abdominis
What is pleural pressure (Ppl)?
the pressure between the lung and chest wall (pleural space)
What is the elastic recoil pressure (Pel)?
The pressure exerted on the lung to return to the resting state
What is the alveolar pressure (Pa)?
The pressure in the lungs
What is the transpulmonary pressure (Pl)
The difference in pressure between the lung and the pleural space
What is the alveolar pressure and the barometric pressure at the beginning of inspiration?
Pa=0, Pb=0 (so no flow)
What are the pressure and volume changes during inspiration?
inspiratory muscles contract increasing the thoracic volume so Ppl becomes more negative. Pl (transpulmonary) increases which causes lungs to expand / alveolar volume to increase. Pa becomes negative (below Pb) so air flows in down the pressure gradient.
What is the relation between Pa and Pb at the end of inspiration?
Pa=Pb (no flow - muscles stop contracting and expansion stops)
Pressure and volume changes during expiration
thoracic volume decreases. Ppl and Pl return to pre-inspiration values. Thorax and lungs recoil (Pel). Air in alveoli compressed. Pa>Pb. Air flows out of lungs.
What is the efficiency of breathing in healthy lungs?
very efficient, small muscle effort - 2% of resting energy expenditure
Why is higher intensity breathing less efficient?
gas flow is turbulent and more muscles are being used. (accessory muscles fatigue easily, limiting exercise)
What is a factor for developing respiratory failure?
respiratory muscle fatigue
What is the functional residual capacity (FRC)?
the volume of air in the lung at the end of expiration during quiet breathing (ERV + RV)
How does the elastic recoil forces of the lung impact lung volume?
Decrease lung volume
How does the outward recoil of the chest wall impact lung volume?
Increase lung volume
What is the relation of the elastic recoil forces of lung and outward recoil of chest wall at FRC?
Opposite and equal and muscles are relaxed
How is the balance between the elastic recoil forces of the lung and outward recoil of chest wall disturbed?
By the contraction of respiratory muscles at the beginning of inspiration
How can weak chest wall muscles (neuromuscular disease) affect the FRC?
FRC decreases as lung elastic recoil is greater
What is the tidal volume?
Volume of air that moves in and out of lung in one resting breath
What is the name of the volume of air that cannot be forced out of the lungs?
residual volume
What is the expiratory reserve volume (ERV)?
the volume of air that can be forced out at the end of passive exhalation
What is the total lung capacity?
The maximum volume of air that can be taken into lungs
How can lung volume be measured?
Using a vitalograph or spirometer
Why is it important to measure lung volumes?
To understand normal and diseased lung function
