Breathing Mechanics Flashcards
What establishes the pressure gradient in eupnea?
The alveolar pressure is less than atmospheric pressure
How is the pressure gradient established in forced ventilation?
The mouth pressure is higher than alveolar pressure
What is the typical value assigned to atmospheric pressure in the context of pulmonary physiology?
0
What are the two types of work used in breathing?
Elastic work and resistance work
What is the general term for diseases that affect the resistance work done in breathing? For elastic work?
Obstructive diseases; Restrictive diseases
What happens to total cross sectional area moving down the respiratory tree?
Cross sectional area increases geometrically
What are the parts of the chest wall?
Diaphragm and rib cage
At the point between breaths following expiration, what is alveolar pressure?
0
What is the name of the pressure of the pleural cavity?
Intrapleural pressure
What kind of recoil does the lung have? The chest wall?
Inward; Outward
What is the functional residual capacity?
The balance point between lung inward recoil and chest wall’s outward recoil
What is transmural pressure?
The pressure difference across the wall of alveoli
How can alveolar pressure be calculated?
Intrapleural pressure and aleolar elastic recoil pressure
What physical changes in the chest wall occur during inspiration?
Diaphragm moves down and the ribcage moves up and out
How does chest wall expansion facilitate inspiration?
As the chest expands it yanks alveoli open since the lung is effectively stuck to the chest wall, and the increase in volume decreases pressure
What is the alveolar pressure relative to atmospheric pressure during inspiration?
Alveolar pressure is less that atmospheric for the extent of inspiration
How is air exhaled in eupnea?
BY relaxing the inspiratory muscles
What muscles are used for normal inspiration? What are the accessory muscles?
External intercostals, parasternals, and diaphragm; sternocleidomastoid and scalenes
Approximately what fraction of tidal volume is due to the diaphragm’s movement in a supine position? In an upright position?
2/3; 1/2
What muscles are involved in forced expiration?
Internal intercostals, abdominal muscles
What muscle(s) is/are necessary for effective respiration?
Diaphragm and external intercostals
What happens to intrapleural pressure during inspiration? To alveolar transmural pressure gradient?
It becomes more negative; Transmural pressure increases
What is the effect of an increased transmural pressure gradient on elastic recoil?
Increases
At functional residual capacity, what is the inward elastic recoil of the alveoli relative to the intrapleural pressure?
Equal and opposite
What is the direction of airlow at function residual capacity?
No airflow
True or false: The time spent during inspiration is equal to the time spent in expiration?
False
What is the difference between the pressure volume curves generated during inspiration and during expiration? What is the name of this difference?
Surfactant; Hysteresis
What is the formula for compliance?
Change in volume/ change in pressure
How does alveolar compliance change going from low lung volumes to high lung volumes?
More compliance at low volumes and less compliance with higher lung volumes
True or False: All alveoli are equally compliant.
False
How does compliance add in seried? In parallel?
Compliance in series adds reciprocally in series and directly in parallel
What sort of pulmonary conditions decrease lung compliance?
Fibrosis, pulmonary vasculature congestion, pneuothorax, obesity, kyphoscoliosis
What sort of pulmonary conditions increase lung compliance?
Emphysemia
How can tension be estimated using LaPlace’s Law?
Tension is proportional to pressure * radius
What reduces the alveolar surface tension below that of water?
Pulmonary surfactant
What is the name of alveolar collapse?
Atelectasis
What is the result of disturbing the mechaical interdependence of the lungs and the chest wall?
The lung will collapse
Pressure measured at the mouth is the sum of what pressures?
Inward recoil pressure and outward chest wall pressure
How does standing up facilitate inspiration?
When standing up, gravity is pulling abdominal contents and the diaphragm down
How does laying down affect the FRC
Decreases it by 1/3
In a healthy person what accounts for most resistance to airflow?
Airway resistance
What airways have more resistance?
Upper airways
Which method of inhalation has more resistance in adults?
Through the nose
What is the formula for resistance?
R= (8viscositylength)/(pi*r^4)
Flow through the majority of airway is what kind of flow?
Turbulent
In what airways does laminar flow occur?
Very small airways
What is the formula for Reynold’s number?
Re=(densityvelocitydiameter)/(viscosity)
What is the effect of increased blood flow on pulmonary vascular resistace?
Increased blood flow decreases pulmonary vascular resistance
What is the effect of parasympathetic stimulation on airways?
Constriction
What chemical species induce airway constriction?
ACh, Histamine, Leukotrienes, Thromboxane A2, Seotonin, and alpha-adrenergic agonists
How does PCO2 affect airway diameter?
Decreased PCO2 mediates constriction in the small airways; increased PCO2 mediates dilation in small airways
What ANS system induces bronchodilation? Through what main receptor?
Sympathetic; Beta 2
What chemical species induce bronchodilation?
Circulating beta 2 agonists, NO, increased PCO2
At what point in the tracheobronchiole tree is there no more cartilage surrounding the airways?
Terminal bronchioles
What is the relationship between lung volume and airway resistance?
Airway resistance decreases with increasing lung volume
What are the two reasons that airway resistance decreases with more lung volume?
1) Small airways are compressible/distensible- therefore greater transmural pressures will open the airways more 2) Traction pulls the airway open
During forced expiration what happens to intrapleural pressure?
Intrapleural pressure gets more and more positive
What is the relationship of lung volume and alveolar elastic recoil?
The alveolar elastic recoil pressure decreases at lower lung volumes bc the alveolus is not as distended
What is the main reason that airway resistance appears to be approaching infinity at low lung volumes?
Small airway collapse
What is dynamic compression of airways?
Increased airway resistance during a forced expiration
When dynamic compression occurs what serves as the effective pressure gradient?
Alveolar pressure minus intrapleural pressure
What is the effective driving pressure for airflow from the lung during dynamic compression?
Alveolar elastic recoil pressure
What is forced vital capacity?
The volume of air a subject is able to expire through a maximal expiratory effort following a maximal inspiration to the total lung capacity
Following expiration of the FVC, what volume remains in the lungs?
Residual volume
What is FEV1?
Forced expiratory volume in 1 second
What ratio is a good index of expiratory airways resistance?
FEV1/FVC
What is the typical value of the FEV1/FVCin young healthy persons?
~0.8
What is the forced expiratory flow rate?
The slope of a line drawn between the points on the expiratory curve at 25% and 75% of the FVC
What is the main concept underlying the FVC pulmonary function test?
Elevated airways resistance takes time to overcome
At what lung volumes is airflow entirely effort dependent? How?
High lung volumes; Alveolar elastic recoil pressure is high (increasing traction and airflow pressure gradient) and because highly positive intrapleural pressures cannot be attained
What is the equal pressure point hypothesis?
An explanation for flow limitation during forced expiration that says that at any instant during a forced expiration, there is a point along the airways where the pressure inside the airway isjust equal to the pressure outside the airway– the point at which the transmural pressure gradient is 0
As forced expiratory effort continues, what happends to the equal pressure point?
Moves down the airway from larger to smaller airways towards the alveoli
What causes effort independence in forced expiration?
Airways resistance is increasing with more effort due to greater dynamic compression. The equal pressure point moves down to small compressible airways and is fixed there. Increasing the intrapleural pressure increases the alveolar pressure by the same amount
True or false: No effort independence is seen with forceful inspiration through the mouth
True
Patients with what sort of conditions would demonstrate inspiratory effort independence?
Upper airway problems (obstructive sleep apnea or vocal cord paralysis)
What are obstructive pulmonary diseases? Restrictive?
Diseases that interfere with airflow; diseases that restrict expansion of the lung
Why is the maximal airflow rate lower in patients with restictive disease?
The total lung capacity is decreased
What is the effect of a fixed obstruction on the flow-volume loop?
Truncated inspiratory and expiratory curves
What is the effect of an variable intrathoracic obstruction on the flow-volume loop? Variable extrathoracic?
Intra- truncated expiratory loop; extra- truncated inspiratory loop
What is dynamic compliance of the lungs?
The change in the volume of the lungs divided by the change in the alveolar-distending pressure durin the course of a breath
What is the relationship between obstructive pulmonary disease and dynamic compliance? Why?
Obstructive disease decreases dynamic compliance; There is more resistance in small airways and so alveoli take longer to fill and empty and so with faster breathing they don’t contribute to changing the total lung volume and so it, and therefore dynamic compliance decrease
What is the name of the condition which can occur when putting patients with obstructive pulmonary disease on positive pressure-ventilation where more air is coming in the lungs than can leave?
Auto- PEEP or stacked breath
When does alveolar elastic recoil become negative?
Alveolar elastic recoil pressure is NEVER negative
