Phys- Mechanics of Breathing Flashcards
Between breaths, ___ exactly opposes ___
Transmural pressure (-4) exactly opposes elastic recoil of the lung
Inspiratory muscles
Diaphragm
Accessory = external intercostals, scalenes, SCM
Expiratory muscles
Normally passive, but accessory = internal intercostals and abdominal muscles
How do the external intercostals assist in inspiration?
Move ribs up and out
How do the internal intercostals assist in inspiration?
Move ribs down and in
What occurs before transpulmonary pressure changes during breathing?
Chest wall expands/recoils, which causes the change in pressure (remember inverse relationship between volume and pressure)
What is the transpulmonary pressure mid-inhalation? Transrespiratory?
Both are negative, drawing air into lungs
more negative in case of Ptp
When is intrapleural pressure at its max?
End of inspiration = max lung capacity
What change occurs between mid-inhalation and mid-expiration?
Transpulmonary and transrespiratory pressures become less negative, drawing air out of the lungs
Describe the mechanism of pneumothorax.
Chest wall/pleura pierced
Pip becomes 0/equalizes with Patm
Chest wall then can spring out and lung can collapse
Slope of a pressure-volume curve
Compliance
Compliance =
V/P
Increased volume = ___ compliance
Increased
Decreased compliance = decreased __
Volume
Increased compliance = decreased ___
Pressure
What is hysteresis?
Difference in expiratory and inspiratory curves on pressure volume graph
What causes hysteresis?
Surfactant - When inspiration begins, alveoli must overcome surface tension to open (pressure builds but volume doesn’t increase); when expiration begins, there is no surface tension.
FRC =
ERV + RV
1.2 + 1.2 ~ 2.5L
The stiffer the lung, the (more/less) compliant
Less
The more elasticity a lung has, the (more/less) compliant
Less
(elasticity and compliance are inversely related: a thick rubber band with more elastic tissue has low compliance; a thin rubber band with less elastic tissue has high compliance)
A disease causing increased FEC1:FRC would cause (increased/decreased) compliance
Decreased
(Increased FEC1:FRC is a restrictive lung disease, meaning the lungs are stiffer = decreased compliance; fibrosis, pulm edema)
Obstructive lung diseases have (increased/decreased) FEC1:FRC and (increased/decreased) compliance
Decreased FEC1:FRC
Increased compliance
(decreased elasticity = increased compliance)
What is the consequence of increased elasticity in obstructive diseases?
Lungs are prone to collapse because pressure in the airways and alveoli is less so air can’t get out
Why is the FEV1 decreased in obstructive diseases?
Takes longer to get air out
Is lung compliance greater during inspiration or expiration?
Expiration
C=V/P, so when volume is greater at beginning of expiration, lungs are more compliant
What is the obstructive ventilatory defect in emphysema?
Decreased pressure difference
(so decreased flow, F=P/R
What is the obstructive ventilatory defect in asthma/bronchitis?
Increased resistance (so decreased flow, (F=P/R)
Describe the flow volume loop for an obstructive disease.
Inspiratory phase is normal, but expiratory flow rate is reduced while expiratory volume is normal
Describe the flow volume loop for a restrictive disease.
Volume of expiration and inhalation are reduced; inspiratory flow rate is reduced greatly; expiratory flow rate is also reduced
Describe the volume flow loop in a healthy person.
Volume of inspiration and expiration are equal. Inspiratory flow rate makes a bell curve; expiratory flow rate peaks toward the end of expiration
What two factors determine lung compliance?
Elastic forces of lung tissue
Surface forces
Describe the support of alveoli structure
Interdependence - wall of one alveolus forms part of the wall of another; if one has tendency to collapse, it’s overcome by the expanding forces of surrounding alveoli
What creates surface tension?
Nothing to counterbalance force on liquid molecules on top of solution so creates air-liquid interface
Surfactant (increases/decreases) compliance
Increases
What is the main component of surfactant?
PL (specifically DPPC)
LaPlace’s Law
P=2T/r
Small alveoli without surfactant have (increased/decreased) compliance. Why?
Decreased; C=V/P and P=2T/r; since r is decreased, P is increased and C is decreased; in other words, the strong intermolecular forces between water are strong in a small alveolus because they’re in closer contact.
Where is surfactant made? Stored?
Type II pneumocytes; Lamellar bodies in those cells
Why do we take a deep breath every few minutes?
Stretches type II pneumocytes, releasing surfactant
What is respiratory distress syndrome of the newborn/hyaline membrane disease?
Preemies born before 24 weeks gestation can’t produce surfactant; this decreases compliance and prevents lungs from expanding so it’s a restrictive disease; small alveoli are unstable and pop upon expiration, releasing hyaline into the aveoli.
Name for a collapsed airway
Atelectasis
Why not have larger alveoli rather than surfactant?
Need small alveoli to increase surface area for gas exchange
How does surfactant decrease surface tension?
Disrupts intermolecular forces between water lining alveoli via its amphipathic nature
Flow =
P/R
Resistance =
8nl/pi(r^4)
If radius is halved, resistance (increases/decreases) by ___
Increased, 16
4 factors determining airway resistance
- Anatomic factors
- Lung volume
- Bronchial smooth muscle contraction
- Density and viscosity of inhaled gas
Which has more resistance: trachea or respiratory bronchiole?
Trachea
respiratory bronchioles have greater TOTAL surface area, so trachea has smaller radius = greater resistance
What role do elastic fibers play in airway resistance?
They tend to attach to exterior of airway and pull out, thus opening the airway and increasing radius = decreasing resistance
How does lung volume contribute to airway resistance?
Greater the volume, the more airway diameter increases; increased radius = decreased resistance
How do asthmatic overcome increased resistance due to strong airway contraction?
They breathe at higher volumes = increased diameter = reduced resistance = increased flow
(Increased V also decreases P; R=FP, so R also decreases)
3 diseases for which constriction of bronchial smooth muscle plays important role
Asthma, bronchitis, emphysema
Neurotransmitter which causes dilation of BSM
Epi (via B2R)
Mediators which cause constriction of BSM
ACh and leukotrienes
How does asthma cause airway obstruction?
BSM contraction = decreased radius = increased resistance = decreased flow
