4.2 Respiration Mechanics 1
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What are the muscles for inspiration and expiration and how do they function?
- Inspiration - Diaphragm (skeletal muscle), external intercostals, and accessory muscles of inspiration
- Expiration - muscles of the abdominal wall (rectus abdominus, internal and external obliques and transverse abdominus); Internal intercostal muscles
How does the diaphragm move during inspiration and exhalation?
- On inspiration - diaphragm contracts and moves down
- On exhalation - diaphragm relaxes and moves up
How does the anatomy of the thoracic cage, ribcage respond to contraction of muscles during inspiration and expiration?
- Inhalation - scalenes elevate the first 2 ribs and sternomastoids raise the sternum
- Expiration - internal intercostal muscles pull the ribs downward and inward (opposite the external intercostal muscles) decreasing the thoracic volume and allowing air to flow outward
Why is expiration passive during "quiet" breathing?
- During inspiration it actively contracts and for expiration it just relaxes
- Active when exercising
What are the elastic properties of the lung and chest wall?
- Can automatically recoil
- Wants to collapse
What is alveolar pressure?
Pressure inside the thoracic cavity (essentially pressure inside the lungs)
What is intrapleural pressure?
- Pressure w/in the pleural sac
- Less than intra-thoracic pressure
- Pressure exerted outside the lungs w/in the thoracic cavity, usually less than atmospheric pressure at 756 mmHg
What is transpulmonary/transmural pressure?
Difference between the pressure of the respired gas at the mouth and the pleural pressure around the lung
What are the changes for intrapleural pressure, alveolar pressure, airflow, and lung volume during the breathing cycle?
What are the consequences of dynamic compression of the airways during expiration?
Won't be able to fill the lungs with air
What is compliance? And what is compliance of the lung and chest wall?
- Look at Δ in volume w/ Δ in pressure
- Represents elasticity of the lungs
- High Compliance - large increase in lung volume for small decrease in ip pressure
- Low Compliance - small increase in lung volume for large increase in ip pressure
What 2 factors does compliance depend on?
- Surface tension of the alveoli
Under what conditions is the compliance of the lung increased or decreased?
How does Emphysema/ COPD alter the lungs mechanical properties? Are they restrictive or obstructive diseases?
- Loss of elastic fibers = ↑ lung compliance = ↑ (steeper) slope of the volume-vs.-pressure curve for the lung
- At a given volume, the collapsing (elastic recoil) force on the lungs is ↓
- Breathes at higher lung volumes
- Barrel shaped chest
How does Chronic bronchitis/ COPD alter the lungs mechanical properties? Are they restrictive or obstructive diseases?
How does Asthma alter the lungs mechanical properties? Are they restrictive or obstructive diseases?
How does Pulmonary fibrosis alter the lungs mechanical properties? Are they restrictive or obstructive diseases?
What is the role of surfactant in lung mechanics?
Reduces surface tension and the collapsing pressure for a given radius
What secretes surfactant?
Type II alveolar cells
What is the difference between minute ventilation (VE) and alveolar ventilation (VA) and how are each calculated?
What is the difference between alveolar and physiological dead space?
How does rate and depth of breathing specifically alter alveolar ventilation?
What is the relationship between alveolar ventilation and alveolar levels of CO2 and O2?
What are the steps involved in respiration, gas laws, and how the lung is supported and moved?
Compare and contrast the efficiency of the apex and base of the lung in regard to ventilation, blood supply?
What is airway resistance and what factors play a role in changing it?
What is ventilation-perfusion mismatch and how does it relate to disease states?
What are the physical factors controlling gas diffusion?
Quantify the pressure gradients driving the O2/CO2 exchange in both lung and tissues
Define (Va/Q) ventilation/ perfusion ratio
Alveolar ventilation rate over pulmonary blood flow
What is ventilation?
Amount of air that reaches the lungs
What is perfusion?
Amount of blood that reaches the lungs
How does abnormal Va/Q affect pulmonary gas exchange?
AV shunting process will occur making the underventilated area also underperfused
What is PaO2 and PaCo2 and what are the normal values and the determinants?
- PaO2 -
- PaCO2 - Arterial carbon dioxide
- Normal: 40 mmHg
What is A-a gradient and what does it mean and how do you calculate it?
- A - alveolar O2
- a - arterial O2
- (Age + 10)/4
- Increasing A-a gradient = hyoxemia
What does a normal A-a gradient mean?
- No diffusion defect
- No V/Q mismatch
- No right to left shunting
What does ventilation/ perfusion vary from the apex to the base of the lung?
What Pulmonary Disorders increase the V/Q ratio?
- Pulmonary emboli
- Partial or complete obstruction in the pulmonary artery or some of the arterioles (atherosclerosis, collagen disease, Marfans)
- Extrinsic pressure on the pulmonary vessels (pneumothorax, hydrothorax, presence of tumor)
- Destruction of the pulmonary vessels (emphysema)
- Decreased CO
What Pulmonary Disorders decrease the V/Q ratio?
- Obstructive lung disorders
- Restrictive lung disorders
- Hypoventilation from any cause
What is the respiratory quotient and what is its purpose?
What is Alveolar PO2 in relation to inspired oxygen?
Alveolar PO2 is 5x the % of inspired oxygen
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