Pulmonary Mechanics II Flashcards
Describe the changes in alveolar volume, alveolar flow, and intrapleural and alveolar pressures that occur during the respiratory cycle
Alveolar pressure: flow parallels alveolar pressure. Maximum flow corresponds to minimum Palv at mid-inspiration and maximum Palv at mid-expiration.
Intrapleural pressure is always negative during eupneic breathing and reaches a minimum at end-inspiration, corresponding to maximum inflation.
Describe laminar flow
Laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption between the layers. Flow is laminar when Re < 2000, like in the trachea
Describe turbulent flow
Flow becomes turbulent when Re > 3000 for air, just as for liquids such as blood. It produces the sounds of quiet respiration @ each bifurcation.
Describe eddy flow
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle, like a bifurcation.
Describe orifice flow
Since airways are not rigid tubes with uniform diameter, but are distensible and compressible branching tubes often with irregular bores, the ideal laminar flow equation (Poiseuille’s law) can only give a limited qualitative appreciation of the relative importance of a few of the variables that affect airway resistance.
Define the factors that determine resistance to pulmonary airflow, distinguishing between tissue and airway resistance
Frictional resistance is present only during motion. It includes components from the motion of tissues, or tissue resistance. Tissue resistance is due to the motion of the lung and chest wall tissue; this resistance will increase in fibrotic disease and will not be described by Poiseuille’s law.
Airway resistance is due to the motion of the air; this resistance is the R in Ohm’s and Poiseuille’s laws.
Both tissue and airway resistance are due to viscous flow–either of the tissue itself or of the air.
Define dynamic lung compliance, how it is measured, and how it relates to the diagnosis of alterations in airway resistance in small airway disease
Dynamic compliance represents pulmonary compliance during periods of gas flow, such as during active inspiration. Dynamic compliance is always less than or equal to static lung compliance (uses esophageal balloon to measure).
With an abnormally increased airway resistance, there will be less flow for a given pressure change, and therefore less air inhaled per breath, thus resulting in a decreased CDYN at high breathing rates. Thus a discrepancy between static and dynamic compliance could suggest an abnormal resistance (static compliance would not change in airway disease only dynamic). Small airway disease is difficult to detect by other means. In other words tidal volume is decreased @ increased respiratory rates due to increased airway resistance. Therefore, dynamic compliance is decreased since V, volume is decreased.
A complete respiratory cycle averages 4 sec with about __ of the time spent during inspiration and about __ of the time spent during expiration.
A complete respiratory cycle averages 4 sec with about 1/3 of the time spent during inspiration and about 2/3 of the time spent during expiration.
Tidal volume
Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration
The transmural pressure across the lung, or lung pressure Pl = ___ – ____ sets the lung ______.
The transmural pressure across the lung, or lung pressure PL = Palveolar - Pintarpleural sets the lung volume.
Functional residual capacity
Functional Residual Capacity (FRC) is the volume of air present in the lungs at the end of passive expiration.
Static compliance
Static compliance determines what particular volume the lung and chest wall will assume for a given transmural pressure when the elastic vessels are at mechanical equilibrium with no air moving.
After being attached to a spirometer through a breathing tube connected to a pressure gauge, the patient is instructed to inspire, then hold the breath with the glottis open, and then relax the chest muscles and diaphragm against a weighted spirometer. The respiratory muscles must be relaxed since the passive elastic recoil pressure is being measured; any muscle activity would change the pressures and interfere with the measurement of static compliance. The weight on the spirometer simply maintains lung inflation while the muscles are relaxed.
What is the equation for compliance?
C=V/P
Total compliance
Total compliance is the compliance for the lung plus chest wall; the system consists of two compliances in series.
When air gets to the lungs, its velocity _______ due to the large surface area of the lungs that promote diffusion. Furthermore, airway resistance _____ until it hits the large surface area of the lungs, where it _______. Therefore, resistance ______ as the lung volume increases during inflation.
Decreases, since Q = A • v
Increases
Decreases
falls
The main resistance is thus in the beginning of the system serving the functions of humidifying, warming, filtering and cleansing the air before it is accelerated into the lung.
