Respiratory Physiology - Respiratory Volumes and Capacities Flashcards
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 Volumes (MV)
small amount of air that remains in the lungs – even if the chest is opened
Respiratory capacities
specific combinations of lung volumes
Inspiratory Capacity (IC)
TV + IRV
Functional Residual Capacity (FRC)
RV + ERV
Vital Capacity (VC)
IRV + TV + ERV
Total Lung Capacity (TLC)
sum of all lung volumes
VC
total amount of exchangeable air in the lungs
RV
total amount of non-exchangeable air
Anatomical Dead Space
air that remains in the passageways and does not contribute to gas exchange; ~150mL
Alveolar (Physiologic) Dead Space
air in non-functional alveoli
Total Dead Space
the sum of non-useful volumes – anatomical + alveolar dead space
Spirometer
Instrument used for measuring respiratory volumes and capacities
- spirometer tests help diagnose and differentiate between obstructive pulmonary diseases and restrictive disorders
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
FEV1
the amount of air exhaled during the 1st second – typically, about 80%
Minute Ventilation
the amount of air flowing in/out of the respiratory tract in 1 minute
- provides a rough estimate of respiratory efficiency
- Normal (Resting): 500mL x 12 breaths per minute = 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
- AVR (mL/min) = frequency (breaths/min) x TV – dead space (mL/breath)
- Dead space is typically constant
- Rapid, shallow breathing decreases AVR
External Respiration
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
Dalton’s Law of Partial Pressures
- Attempts to explain how gas behaves when it is part of a mixture of gases
- The total pressure exerted by a mixture of gases equals the sums of the pressures exerted by each gas individually
- The partial pressure of each gas is proportional to its percentage in the mixture
- Example: O2 makes up 21% of the atmosphere. It has a partial pressure (PO2) of 159mmHg
20.9% x 760mmHg = 159mmHg
Henry’s Law
- Attempts to explain how gases move in and out of solutions
- Each gas will dissolve into a liquid in proportion to its partial pressure
- The greater the concentration of a particular gas, the more and the faster that gas will go into solution
- The direction and amount of movement of a gas are determined by its partial pressure in the 2 phases
- Additional Factors:
– Solubility - CO2 is 20x more soluble in H2O than O2
– Temperature - as a liquid’s temperature rises, solubility decreases
high altitude
At high altitude, atmospheric pressure declines, so partial pressures also decline
- Ex: at 10,000 ft above sea level, the atmospheric pressure is 523mmHg – the partial pressure of Oxygen (Po2) is 110mmHg
523mmHg x 21% = 110mmHg
low altitude
At low altitude, atmospheric pressure increases, so partial pressures also increase
- Ex: at 99 ft below sea level, the atmospheric pressure is 3,040mmHg – the partial pressure of Oxygen (PO2) is 636 mmHg
3,040mmHg x 21% = 636mmHg
Composition of Alveolar Gas
- Atmospheric air contains mostly O2 and N2
- Alveolar air contains mostly CO2 and water vapor
- In the lungs, O2 is diffusing into the blood, and CO2 is diffusing out
- Air is humidified by the conducting passages
- With each breath, new and old alveolar gas is mixed
- The partial pressures of O2 and CO2 can be altered by increasing breathing rate and depth!
External Respiration
Exchange of O2 and CO2 across the respiratory membrane
external respiration is influenced by:
- Thickness and surface area of the respiratory membrane
- Partial pressure gradients and gas solubilities
- Ventilation-perfusion coupling
The Respiratory Membrane
- Typically, .5 to 1μm thick with 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
Diffusion
driven by the partial pressure gradients of O2 and CO2
Steep partial pressure gradient for O2 in the lungs
Venous Blood PO2 = 40mmHg
Alveolar PO2 = 104mmHg
oxygen is driven ______
into the blood
- Equilibrium is achieved in .25s - a RBC typically spends .75s in a pulmonary capillary
- Blood can flow 3x faster and still be well-oxygenated!
co2 diffusion (less steep)
CO2 diffuses down a less steep pressure gradient
Venous Blood PCO2 = 45 mmHg
Alveolar PCO2 = 40 mmHg
– CO2 and O2 diffuse across in equal amounts – CO2 is much more soluble!
Perfusion
amount of blood reaching the alveoli
Ventilation
amount of gas reaching the alveoli
– Perfusion and ventilation must be well matched for efficient gas exchange!
perfusion physiology
- Changes in PO2 control perfusion by changing arteriolar diameter
- Where alveolar O2 is high, arterioles dilate to stimulate O2 pickup
- Where alveolar O2 is low, arterioles constrict to divert blood elsewhere
- Striving for efficient O2 pickup!
Ventilation physiology
- Changes in PCO2 control ventilation by changing bronchiole diameter
- Where alveolar CO2 is high, bronchioles dilate for faster CO2 removal
- Where alveolar CO2 is low, bronchioles constrict
Striving for efficient CO2 removal!
Internal Respiration
- The exchange of O2 and CO2 between blood and body tissues
- The partial pressures and diffusion gradients are reversed!
- PO2 of tissues < PO2 of blood
O2 is driven into the tissues - PCO2 of tissues > PCO2 of blood
CO2 is driven into blood
