Respiratory Physiology Flashcards
(34 cards)
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
