Respiratory Physiology Flashcards
pulmonary ventilation
breathing
2 phases of pulmonary ventilation
- inspiration: air flowing into the lungs
- expiration: air flowing out of the lungs
respiratory pressures
Respiratory pressures are always described relative to atmospheric pressure (Patm)
- Patm: the pressure exerted by the gases/air surrounding the body
- At sea level, atmospheric pressure is 760mmHg or 1atm
negative respiratory pressure
pressure that is lower than atmospheric pressure
- ex: -4mmHg means 760mmHg-4mmHg or 756mmHg
positive respiratory pressure
pressure that is higher than atmospheric pressure
zero respiratory pressure
pressure that is equal to atmospheric pressure
intrapulmonary pressyre (Ppul)
pressure within the alveoli
- rises/falls with the phase of breathing - always equalizes with atmospheric pressure
intrapleural pressure (Pip)
the pressure in the pleural cavity
- rises/falls with the phases of breathing - always about 4 mmHg less than Ppul
- Pip is always negative relative to Ppul
Negative Intrapleural Pressure
Forces causing the lungs to collapse:
- Lungs’ natural elasticity/tendency to recoil
- Surface tension of the fluid lining the alveoli
Force causing the lungs to expand:
- Natural elasticity of the chest wall
Typically, neither force wins!
- Secondary to the presence of pleural fluid, there is a strong adhesive force between the parietal and visceral pleurae
- amount of pleural fluid is closely regulated and drained by the lymphatics
Net Result: a negative Pip!
Transpulmonary pressure
the difference between Ppul and Pip
- The pressure that keeps the air spaces of the lungs open and prevents lung collapse!
- A greater transpulmonary pressure means the lungs are larger in size
- Any condition that equalizes Pip with Ppul or atmospheric pressure will cause lung collapse
Atelectasis
- “Lung Collapse”
- Occurs when a bronchiole becomes plugged
- The associated alveoli will collapse
- Often an extension of pneumonia
Pneumothorax
- “Air Thorax”
- Presence of air in the pleural cavity
- Reversed by drawing the air out via a chest tube
- Lung will reinflate
pulmonary ventilation
- Pulmonary ventilation is the mechanical process of breathing – inspiration and expiration
- It is entirely dependent on volume changes in the thoracic cavity
- Volume changes -> pressure changes -> flow of gases to equalize pressure
Boyle’s Law
- Gives the relationship between pressure and volume of a gas
- At a constant temperature, pressure varies inversely with volume
- P1V1 = P2V2
- “gases always fill their container”
Pulmonary Ventilation: Inspiration
- Diaphragm + external intercostal muscles contract
- Height AND diameter of the thorax increase
- Volume of the thoracic cavity increases by ~500mL
- Lungs are stretched, intrapulmonary volume increases
- Ppul decreases
- Air rushes into the lungs
- Ppul equalizes to Patm
Pulmonary Ventilation: Expiration
- In healthy individuals, quiet expiration is a passive process
- It is dependent on lung elasticity
- Inspiratory muscles relax – rib cage descends, lungs recoil
- Thoracic + intrapulmonary volumes decrease
- Ppul rises
- When Ppul > Patm, air flows out
Forced Expiration
- active process
- produced through contraction of the abdominal muscles
- intra-abdominal pressure rises, and the abdominal organs press against the diaphragm
- internal intercostal muscles depress the rib cage and decrease thoracic volume
deep/forced inspiration
- utilizes accessory muscles - the scalenes, SCM, and pectoralis minor further increase thoracic volume
- spinal extension flattens the thoracic curve
- “barrel chest”
precise expiration
requires fine control and coordination of the accessory muscles
non-respiratory air movements
- coughing, sneezing, crying, laughing, hiccupping, and yawning - all alter normal respiratory rhythm
3 physical factors that influence the ease of air passage and the amount of energy required for ventilation
- airway resistance
- alveolar surface tension
- lung compliance
airway resistance (R)
friction or drag encountered in the respiratory passageways
- F = ΔP/R
- Gas flow varies inversely with resistance (R)
- R is predominantly determined by the diameters of the conducting tubes
- The highest resistance is in the medium-sized bronchi
- Resistance disappears at the terminal bronchioles, and diffusion takes over
ΔP
the difference in pressure between the external environment and the alveoli
- typically, a small ΔP can create large changes in gas flow
- the average pressure gradient during normal, quiet breathing is 2mmHg or less
bronchodilators
smooth muscle in the bronchiolar walls is extremely sensitive to neural controls and chemicals
- inhaled irritants can activate a reflex of the parasympathetic ANS - a vigorous constriction of the bronchioles
asthma attacks
histamine can cause such strong bronchoconstriction that pulmonary ventilation stops
- epinephrine is the antidote
alveolar surface tension
attracts liquid molecules to each other, resists any force that attempts to increase the liquid’s surface area
- because it is composed of highly polar molecules, water has a high surface tension
- water is always working to keep alveoli at their smallest possible size
surfactant
detergent-like complex of lipids and proteins produced by type II alveolar cells
- reduces surface tension and discourages alveolar collapse - less energy is required to expand the lungs
Infant Respiratory Distress Syndrome
Condition when surfactant levels are not adequate
- Alveoli will collapse, and it takes significant energy to reinflate them
- Treated with artificial surfactant, devices that maintain positive airway pressure, ventilators
Bronchopulmonary Dysplasia
- Potential complication of IRDS
- Often caused by prolonged ventilation and O2 therapy
Lung Compliance
measure of the change in lung volume that occurs with a given change in transpulmonary pressure
- higher compliance = lungs that are easier to expand
2 determining factors of lung compliance
- Distensibility of lung tissue
- Alveolar surface tension
reducing lung compliance
Lung compliance is reduced by: fibrosis, reduced amounts of surfactant, and decreased flexibility of the thoracic cage
Total Respiratory Compliance
Total compliance of the respiratory system is influenced by lung compliance and compliance of the thoracic wall
Compliance of the thoracic wall is reduced by:
- Thoracic deformity
- Ossification of the costal cartilage
- Paralysis of the intercostal muscles
