respiratory physiology Flashcards
pulmonary ventilation
breathing
inspiration
air flowing into the lungs
expiration
air flowing out of the lungs
atmospheric pressure (Patm)
the pressure exerted by the gases/air surrounding the body
Negative respiratory pressure
pressure that is lower than atmospheric pressure
positive respiratory pressure
pressure that is higher than atmospheric pressure
zero respiratory pressure
pressure that is equal to atmospheric pressure
intrapulmonary pressure (Ppul)
the pressure within the alveoli
- rises/falls with the phases 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 4mmHg less than Ppul
- Pip is always negative relative to Ppul
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
negative intrapleural pressure
- secondary to the presence of pleural fluid, there is a strong adhesive force between the parietal and visceral pleurae
- the 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
what does a greater transpulmonary pressure mean
lungs are larger in size
what will cause lungs to collapse
any condition that equalizes Pip with Ppul or atmospheric pressure
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 (extra explanation)
- 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 with volume
- P1V1 = P2V2
inspiration (longer explanation)
- diaphragm + external intercostal muscles contract
- height + diameter of the thorax increase
- volume of the thoracic cavity increases - 500 mL
- lungs are stretched, intrapulmonary volume increases
- Ppul decreases
- air rushes into the lungs
- Ppul equalizes to Patm
expiration (longer explanation)
- quiet expiration is a passive process
- 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
- an active process
- intra abdominal pressure rises, and the abdominal organs press against the diaphragm
- internal intercostal muscles depress the rib cage and decrease thoracic volume
2 muscles used for forces expiration
transverse abdomonis and obliques
deep/forced inspiration
- utilizes accessory muscles – the scalenes, SCM, and pectoralis minor further increase thoracic volume
- spinal extension flattens the thoracic curve
precise expiration
- requires the fine control and coordination of the accessory muscles
non-respiratory air movements
- coughing, sneezing, crying, laughing, hicupping, and yawning – all after the normal respiratory rhythm
what are three factors influencing 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
which branch of the autonomic nervous system is responsible for bronchiconstriction
sympathetic nervous system
- epinephrine is the antidote
Is epinephrine a bronchodilator or a bronchoconstrictor
bronchodilator
surface tension
attracts liquid molecules to each other, resists any force that attempts to increase the liquid’s surface area
Water vs. surface tensions
- water is composed of highly polar molecules, so it 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
- surfactant reduces surface tensiona nd discourages alveolar collapse – less energy is required to expand the lungs
infant respiratory distress syndrome
- when surfactant levels aren’t adequate
- alveoli will collapse, and it takes significant energy to reinflate them
- treatwe 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 in transpulmonary pressure
higher compliance = lungs that are easier to expand
- reduced by fibrosis, reduced amounts of surfactant, and decreased flexibility of thoracic cage
2 determining factors
- distensibility of lung tissue
- alveolar surface tension
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
tidal volume (TV)
air inspired/expired with normal, quiet breathing
inspiratory reserve volume (IRV)
air inspired beyond TV
expiratory reserve volume (ERV)
air expired beyond TV
residual volume (RV)
air that remains in the lungs after ERV
minimal volume (MV)
small amount of air that remains in the lungs – even if chest is opened
inspiratory capacity (IC)
TV + IRV
functional residual capacity (FRC)
RV + ERV
vital capacity (VC)
IRV + TV + ERV
total amount of exchangeable air in the lungs
total lung capacity (TLC)
sum of all lung volumes
vital capacity (VC)
the total amount of exchangeable air in the lungs
residual volume (RV)
-total amount of non-exchangeable air
- air that remains in the lungs after ERV
anatomical dead space
air that remains in the passageways and does not contribute to gas exchange - 150mL
alveolar (physiologic) dead speace
air is non-functional alveoli
total dead space
the sum of non-useful volumes – anatomical + alveolar dead space
obstructive pulmonary diseases
diseases of increased airway resistance
- TLC, FRC, RV may increase
restrictive disorders
diseases of reduced lung capacity due to fibrosis/disease
- VC, TLC, FRC, RV may decline
forced vital capacity (FVC)
the amount of gas expelled when a subject takes a deep breath and then forcefully exhales as maximally and rapidly as possible
forced expiratory volume (FEV)
determines the amount of air expelled during specific time intervals of the FVC test
FEV 1
the amount of air exhaled during the 1st second - typically about 80%
minute venitlation
the amount of air flowing in/out of the respiratory tract in 1 minute
- provides a rough estimate of respiratory efficiency
normal (resting)
500 mL x 12 breaths per minutes = 6L/min
normal (exercising)
up to 200L/min
alveolar ventilation
amount of air flowing in/out of the alveoli per unit of time
- a more effective measurement
- dead space is typically constant
- rapid, shallow breathing decrease AVR
AVR (mL/min)
frequency (breaths/min) x TV - dead space (mL/breath)
external repsiration
exchange of gases in the lungs
- O2 diffuses into the blood
- CO2 diffuses out of the blood
internal respiration
exchange of gases in the body’s tissues
- O2 diffuses out of the blood
- CO2 diffuses into the blood
what happens at high altitude
atmospheric pressure declines, so partial pressures also decline
what happens at low altitude
atmospheric pressure increases, so partial pressures also increase
the exchange of O2 and CO2 is influenced by
- thickness and surface area of the respiratory membrane
- partial pressure gradients and gas solubilities
- ventilation perfusion coupling
the respiratory membrane
- has a large surface area for exchange
- membranes thicken with edema and gas exchange becomes inadequate
- surface area is reduced with emphysema, tumors, inflammation, and mucus
what is diffusion driven by
the partial pressure gradients of O2 and CO2
perfusion
amount of blood reaching the alveoli
ventilation
amount of gas reaching the alveoli
Henry’s Law
- how gases move in and out of solutions
- gas will dissolve into liquid in proportion to its partial pressure
greater concentration = more and faster the gas goes into the solution - direction and movement of gas is determined by its partial pressure in the 2 phases
2 additional factors for henry’s law
- soubility - CO2 is 20x more soluble in H2O than O2
- temperature - as a liquid’s temperature rises, solubility decreases
Dalton’s Law
- explains how gas behaves when it is part of a mixture of gases
- total pressure exerted by a mixture of gases equals the sums of the pressures exerted by each gas individually
- partial pressure of each gas is proportional to its percentage in the mixture
