Section 4 Flashcards
What is the tidal volume (VT), and what does it represent?
Tidal volume (VT) is the volume of air entering or leaving the lung during a single breath. At rest, this is typically around 500 ml.
Define inspiratory reserve volume (IRV) and provide its typical value at rest.
Inspiratory reserve volume (IRV) is the extra volume of air that can be maximally inspired above the resting tidal volume. At rest, this is typically around 3000 ml.
What is inspiratory capacity (IC), and how is it calculated?
Inspiratory capacity (IC) is the maximal volume of air that can be inhaled starting from the end of a normal expiration at rest. It is typically calculated as IC = VT + IRV, with a value of around 3500 ml.
Define expiratory reserve volume (ERV) and provide its typical value at rest.
Expiratory reserve volume (ERV) is the maximal volume of air that can be expelled starting at the end of a typical tidal volume. At rest, this is typically around 1000 ml.
What is residual volume (RV), and how is it indirectly measured?
Residual volume (RV) is the volume of air remaining in the lungs after maximal expiration. It cannot be directly measured by spirometry but is indirectly measured by the inspiration of a tracer gas such as helium, with a typical value of around 1200 ml.
Define Functional Residual Capacity (FRC) and provide its typical value.
Functional Residual Capacity (FRC) is the volume of air in the lungs at the end of normal passive expiration. It is typically around 2200 ml (FRC = ERV + RV).
What is Vital Capacity (VC), and how is it calculated?
Vital Capacity (VC) is the maximum volume of air that can be expelled during a single breath following a maximal inspiration. It is typically around 4500 ml (VC = IRV + VT + ERV).
Define Total Lung Capacity (TLC) and provide its typical value.
Total Lung Capacity (TLC) is the maximum volume of air the lungs can hold. It is typically around 5700 ml (TLC = VC + RV).
What does Forced Expiratory Volume in One Second (FEV1) represent, and how is it expressed?
Forced Expiratory Volume in One Second (FEV1) is similar to TLC but is derived from only the first second of expiratory effort. It is normally expressed as a ratio (FEV1/FVC) or converted to a percentage. At rest, this value is typically around 80%.
What are the two categories of respiratory dysfunction, and how do they differ in terms of lung volumes?
Obstructive Lung Disease: In individuals with obstructive lung disease, the FEV1 is lower, FRC and RV are greater, and VC is smaller compared to a healthy individual. This is due to difficulty exhaling as much air.
Restrictive Lung Disease: Restrictive lung disease is characterized by low lung volumes. While the absolute amount of air that can be exhaled in 1 second (FEV1) is reduced because the lungs are smaller, the proportion of the Forced Vital Capacity (FVC) that can be exhaled (FEV1/FVC) is normal since there is no obstruction to airflow.
VT - Tidal Volume:
Definition: The volume of air entering or leaving the lung during a single breath.
IC - Inspiratory Capacity:
Definition: The maximal volume of air that can be inhaled starting from the end of a normal expiration at rest.
ERV - Expiratory Reserve Volume:
Definition: The maximal volume of air that can be expelled starting at the end of a typical tidal volume.
VC - Vital Capacity:
Definition: The maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.
IRV - Inspiratory Reserve Volume:
Definition: The extra volume of air that can be maximally inspired above the resting tidal volume.
RV - Residual Volume:
Definition: The volume of air remaining in the lungs after maximal expiration.
FRC - Functional Residual Capacity:
Definition: The volume of air in the lungs at the end of normal passive expiration.
TLC - Total Lung Capacity:
Definition: The maximum volume of air the lungs can hold.
What is more commonly used during pulmonary function testing, expiratory data, or inspiratory data?
Expiratory data is more commonly used during pulmonary function testing.
In a normal person, when does the flow peak during forced expiration, and how does it decrease?
In a normal person, flow peaks around 7 L/s during forced expiration and decreases in a linear fashion.
How does a person with obstructive lung disease differ in terms of flow rates and residual volume compared to a non-diseased person?
A person with obstructive lung disease starts at a higher lung volume, cannot achieve normal peak flow rates, and ends up at a higher residual volume.
What characterizes the flow-volume curve of a person with restrictive lung disease in terms of lung volume and peak flow rates?
A person with restrictive lung disease starts off at a lower lung volume, cannot reach normal peak flow rates, and ends up at a lower residual volume.
What type of curve is seen during forced expiration, and how can flow rate be calculated from this curve?
During forced expiration, the curve seen is a flow-volume curve. Mathematically determining the slope at any given time allows the calculation of flow rate.
Why is expiratory flow more useful in assessing pulmonary function than inspiratory flow?
Expiratory flow is more useful in assessing pulmonary function because the limits on ventilation are during expiration, not inspiration. This is evident in simple experiments where exhaling from total lung capacity to residual volume takes much longer than inhaling from residual volume to total lung capacity.