Ventilation Flashcards
The volume of gas inspired or expired in a single respiratory cycle
tidal volume
the maximum volume of gas that can be inspired starting at the end of normal inspiration
inspiratory reserve volume
the maximum volume of gas that can be expired starting from the end of a normal expiration
expiratory reserve volume
the volume of gas that remains in the lungs after a maximum expiration
residual volume
the total amount of gas in the lungs at the end of a maximum inspiration (the sum of all four lung volumes)
total lung capacity
the maximum volume of gas that can be expired after a maximum inspiration
vital capacity
the maximum amount of gas that can be inspired starting from FRC
inspiratory capacity
the amount of gas in the lungs at the end of a normal expiration
functional residual capacity
Three types of dead space:
anatomic dead space
alveolar dead space
physiologic dead space
within each tidal volume, there is a volume of gas that does not participate in gas exchange; it is nonfunctional air in terms of diffusion of O2 or CO2
anatomic dead space
volume of air contained within the nose, sinuses, pharynx, larynx, and conducting airways
alveolar dead space
volume of air contained within non-perfused alveoli
physiologic dead space
functional measurement bc it is the sum of anatomic dead space and alveolar dead space
Turbulant Flow
disorganized flow, requiring greater pressure v laminar flow
Transitional Flow
mixture of turbulant and laminar flow
Laminar flow
parabolic profile and smooth flow
Ohm’s Law:
Pressure = Flow * Resistance
V = P/R
Poiseullie’s Equation
solves for airflow
Poiseullie’s Equation Take Home message for increasing airflow
increase pressure
increase radius (sympathetics)
reduce viscosity
reduce length
Airway Resistance:
when total airway cross sectional area increases
airway resistance decreases
at large lung volumes…
the airways widen and the resistance to airflow decreases
at lower lung volumes…
the airways become narrow, and airflow resistance increases
at very low lung volumes,
the small airways might close completely, especially at the bottom of the lung
obstructive lung diseases
increase in airway resistance
ex: asthma, bronchitis and emphysema
Obstructive lung diseases:
emphysema
inspiration is easier due to loss of elastin/collagen
expiration is harder due to airway collapse which obstructs air flow
loss of radial traction
restrictive lung diseases
expansion of lung is restricted either bc of alterations in lung parenchyma or bc of diease of the pleura, the chest wall, or the neuromuscular apparatus
they are characterized by a reduced vital capacity and a small resting lung volume but the airway resistance is not increased
pulmonary fibrosis
thickening of interstitial spaces with a resultant increase of radial traction, making it more difficult to expand the lungs during inspiration
Forced Vital Capacity Maneuver
accomplished under maximum muscular effect to ensure maximum flow rates at all lung volumes
useful index: forced expiratory volume at one second (FEV1) which is often expressed as percentage of FVC ie FEV1/FVC
FEV1/FVC should be 80% in health person
in obstructive diseases, such as bronchial asthma, FEV1 (forced expiratory volume at one second) is…
reduced much more than FVC (forced vital capacity) , giving a low FEV1/FVC
in restrictive diseases, such as pulmonary fibrosis, both FEV1 and FVC are…
reduced and FEV1/FVC may be normal or even increased
Flow-Volume Loops:
During forced expiration
airways narrow -> increase resistance -> reduces airflow
Flow-Volume Loops:
During inspiration
airways widen -> decrease resistance -> airflow is maximal
in obstructive lung diseases, the flow rate is __ and lung volumes are ___
low; increased
in restrictive lung diseases, the flow rate and lung volumes are
reduced and a arched curve may be seen after maximum flow
Control of Airway Smooth Muscle
Tone is dependent on:
- autonomic NS activity
- circulating hormones
- inhaled particles
- paracrine signaling
Parasympathetic stimulation (ACh) on airway smooth muscle causes
bronchoconstriction
sympathetic stimulation (Epi, NE) on airway smooth muscle causes
bronchodilation
B2 adrenergic receptors
inhalers used by asthmatics contain albuterol (B2 agonist)
Control of Airway Smooth Muscle
Mast cells within the connective tissue of the lung can release
histamine and leukotrienes which induce constriction
they can also increase production of prostaglandins
Control of Airway Smooth Muscle
Physical irritants and pollutants
activate irritant receptors in the airway submucosa
these receptors induce release of ACh from efferent parasympathetic nerves which leads to bronchoconstriction
