Ch 7 Mechanics Part 3 Flashcards
What is the primary function of β1 receptors?
They occur principally in the heart.
What do β2 receptors relax?
Smooth muscle in the bronchi, blood vessels, and uterus.
What are selective β2-adrenergic agonists used for?
Treatments of asthma and chronic obstructive pulmonary disease (COPD).
What effect does parasympathetic activity have on the bronchi?
Causes bronchoconstriction.
What does a fall in Pco2 in alveolar gas do?
Causes an increase in airway resistance.
What does the injection of histamine into the pulmonary artery cause?
Constriction of smooth muscle located in the alveolar ducts.
What type of agents are used in COPD?
Anticholinergic agents.
What factors affect airway resistance?
- Density of inspired gas
- Viscosity of inspired gas
How does lung volume affect airway resistance?
Airway resistance decreases as lung volume rises.
What is the main site of airway resistance?
Medium-sized bronchi.
What happens to resistance during a deep dive?
Resistance increases due to increased gas density.
What is the relationship between flow and airway resistance in medium-sized airways?
Flow is not purely laminar.
What is dynamic compression of airways?
A phenomenon where flow becomes effort-independent during forced expiration.
What is FEV1.0?
Forced expiratory volume in the first second.
What is FVC?
Forced vital capacity.
What is the normal FEV1.0 percentage of FVC?
Approximately 80%.
In restrictive diseases, how are FEV1.0 and FVC affected?
Both are reduced, but FEV1.0/FVC% is normal or increased.
In obstructive diseases, how does FEV1.0 compare to FVC?
FEV1.0 is reduced much more than FVC, giving a low FEV1.0/FVC%.
What does FEF25%–75% measure?
Average flow rate over the middle half of expiration.
What is a key factor in the cause of uneven ventilation?
Compliance of the lung units and resistance of the airways.
What defines a lung unit with a long time constant?
The product of compliance and resistance.
What is tissue resistance?
The pressure required to overcome viscous forces within the lung and chest wall.
What percentage of total resistance is tissue resistance in young normal subjects?
About 20%.
What is the work of breathing measured as?
Pressure × volume.
What does the area under the pressure-volume curve during inspiration represent?
The work done on the lung.
What does the work done on expiration primarily overcome?
Airway and tissue resistance.
How does increased airway resistance affect intrapleural pressure during inspiration?
It makes the intrapleural pressure more negative, increasing work.
What happens to maximal flow as lung volume decreases?
Maximal flow decreases due to reduced alveolar-intrapleural pressure.
What limits airflow during forced expiration in normal subjects?
Dynamic compression of airways.
What condition can exaggerate the flow-limiting mechanism during expiration?
Increased resistance of the peripheral airways.
In patients with severe lung disease, when can flow limitation occur?
During normal breathing expirations.
What is the work required to overcome airway (+ tissue) resistance during expiration called?
AECFA
This area represents the work done during expiration in the pressure-volume curve.
What does the area 0AECD0 represent in the lung pressure-volume curve?
Elastic work
This area indicates the work done to overcome elastic forces during lung inflation.
What happens to the work dissipated as heat during expiration?
It is represented by the difference between areas AECFA and 0AECD0.
How does increased breathing rate affect the work done on the lungs?
It increases the viscous work area ABCEA.
What is the relationship between tidal volume and elastic work area?
A larger tidal volume results in a larger elastic work area 0AECD0.
What is the primary muscle of respiration?
Diaphragm.
Is inspiration active or passive?
Active.
Is expiration during rest active or passive?
Passive.
What is the efficiency percentage of the work done in breathing?
5% to 10%.
What is the O2 cost of quiet breathing compared to total resting O2 consumption?
Less than 5%.
What happens to the O2 cost of breathing during voluntary hyperventilation?
It can increase to 30%.
What happens to lung compliance in premature babies with an immature surfactant system?
Lung has low compliance and is unstable and edematous.
What does the chest wall do at functional residual capacity (FRC)?
Expands outward.
In laminar flow, how is resistance related to the radius?
Inversely proportional to the fourth power of the radius.
How does lung volume affect airway resistance?
Lung airway resistance is reduced by increasing lung volume.
What effect do β2-adrenergic agonists have on airway resistance?
They reduce resistance.
What is dynamic compression of the airways during forced expiration?
Flow that is effort independent.
What is the driving pressure during dynamic compression?
Alveolar minus intrapleural pressure.
What respiratory pattern do patients with reduced compliance tend to exhibit?
Small rapid breaths.
What respiratory pattern do patients with severe airway obstruction tend to exhibit?
Slow breathing.
What happens to the right lung during a spontaneous pneumothorax?
It contracts.
What does pulmonary surfactant help prevent?
Transudation of fluid from capillaries into alveolar spaces.
What is the expected effect of a reduced airway diameter on resistance?
Resistance increases significantly.
What is the effect of surfactant absence on lung compliance?
Increases compliance.
What happens to intrapleural pressure during expiration?
Gradually becomes more negative.
What happens to the alveolar pressure during normal expiration?
It is less than atmospheric pressure.
What happens to the diaphragm during normal expiration?
It moves up.
What is the relationship between airflow and lung resistance?
Airway resistance increases with decreasing lung volume.
What is Poiseuille’s law regarding airway radius and resistance?
Reducing the radius to one-third increases resistance 81-fold.
What is the relationship between flow rate and forced expiration in patients with obstructive lung disease?
The flow rate is limited during expiration.
What happens to the peak expiratory flow when a subject exhales with maximum effort?
It increases.
How does increased airway mucus production affect airway resistance?
It increases resistance.
What is the most important factor limiting flow rate during forced expiration?
Compression of airways.
What is the expected change in FEV1.0 in a patient with emphysema?
Decreased.
What is the expected change in FVC in a patient with emphysema?
Decreased.
What is the expected change in FEV1.0/FVC ratio in a patient with emphysema?
Decreased.
