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41. The Mechanics of Respiration
Goodnight
32
Biology
Graduate
10/05/2011

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Term
Spinal cord segments that innervate diaphragm
Definition
C3,4,5
Term
Muscles of inspiration
Definition
Diaphragm contraction
External intercostal muscles (In strenuous activity)
Term
Mechanism of inspiration
Definition
1. The diaphragm lengthens and flattens through contraction.
2. This increases the volume in the thoracic cage while reducing pressure, creates negative pressure in relation to atmospheric pressure.
3. Glottis opens in inspiration and air rushes into the negative space.
Term
Mechanism of expiration
Definition
1. Diaphragm relaxes, causing in decrease in volume and an increase in pressure in the thoracic cavity.
2. The pressure inside the thoracic cavity is now higher than the outside air (positive to the outside air) and air rushes out.
Term
Muscles used in COPD
Definition
COPD creates labored breathing, patient must use accessory muscles to move air. Also alters the position of the diaphragm.
Term
Factors affecting air conductivity
Definition
1. Compliance of the lung
2. Resistance of airways
Term
Compliance
Definition
(Change in volume in L)/ (change in pressure in cm)
Normal=.2L/cm
Term
Elastance
Definition
Measures the rebound of lung after being stretched, inverse of compliance.
Term
Emphysema effects on lung compliance
Definition
Changes the structure of the parenchyma of the lung so that it is more compliant, stretches more. Therefore, it is hard to expel air out during expiration due to low elastance of the lung tissue. Creates a steeper PV curve (indicative of increased compliance). Also creates increased FRC.
Term
Pulmonary fibrosis effects on compliance
Definition
Causes lung to be very stiff, hard to open alveoli. Compliance is lower, creates a flatter PV curve, indicative of decreased compliance. Also decreases the FRC.
Term
Age effects on chest wall compliance
Definition
Chest wall compliance increases with age.
Term
Factors determining compliance of the lung
Definition
1. Elastic recoil: Force that causes lung to recoil inwards. Created by collagen and elastin in the parenchyma.
2. Surface forces in the alveoli determined by surfactant (major).
Term
Transpulmonary Pressure (PTP)
Definition
PTP= PA (Alveolar)– PIP (Intrapleural)
Term
Hysteresis
Definition
Gap between expiration and inspiration curves. Surface tension in alveoli makes it so that lots of pressure is required to open alveoli initially, and less pressure is needed to open alveoli further once process has been initiated.
Expiratory phase is just relaxation, doesn't have to deal with these surface interactions.
Term
Combined lung and chest pressure at FRC
Definition
2 pull in equal and opposite ways to create 0 sum pressure at the FRC. Air is not moving in or out.
Term
PV Curve below FRC
Definition
Force of chest wall expansion is greater than force of lung collapse. Pressure is negative and air rushes in.
Term
PV Curve above FRC
Definition
Lung collapsing force is greater than chest expansion force, creates a positive thoracic pressure, air rushes out.
Term
PV Curve at high lung volumes
Definition
Both lung and chest favor collapse to create positive pressure, pushes air out.
Term
Causes of increased compliance
Definition
1. Emphysema
2. Aging
Term
Causes of decreased compliance
Definition
1. Pulmonary fibrosis
2. Pulmonary edema (alveoli are filled with fluid=harder to inflate)
3. Increased pulmonary venous pressure
4. Acute Respiratory Disease Syndrome (ARDS, creates inflammation)
Term
Surface tension
Definition
Surface tension is the attractive forces of adjacent molecules, with the forces between liquid molecules greater than between liquid and gas at the alveolar interface: tries to get as small as possible, forms a sphere.
Term
Laplace's Law
Definition
P= 2 x surface tension/ radius
Term
Atelectasis
Definition
Alveolar collapse due to surface tension.
Term
Surfactant properties
Definition
Produced by Type II pneumocyte.
Mixture of lipids: DPPC (Dipalmityl Lecithin) is main component, mixed with proteins
Final assembly takes place in the lamellar bodies.
Term
Effect of surfactant
Definition
Increases lung compliance through its amphipathic nature, breaks up attracting forces in liquid air interface of alveoli. Keeps alveoli dry.
Term
Effects of loss of surfactant
Definition
Loss of surfactant results in stiff lungs (loss of compliance), areas of atelectasis (collapse due to loss of stability), and “wet” (alveoli filled with fluid)…..collapsed lung does not participate in gas exchange (SHUNT)
Term
Infant Respiratory Distress Syndrome
Definition
Premature babies lack surfactant in the lungs. Inward pull of the alveoli draws interstitial fluid into the lungs and inhibits gas exchange.
Term
Factors governing airflow
Definition
Flow=Pressure gradient/resistance

Affected by
1. Airway radius and branching
2. Smooth muscle tone
3. Lung volume
4. Viscosity of gas
Term
Relationship of lung volume and air flow
Definition
Lung is tethered to the airway, amount of tethering is proportional to size of lung. Larger lung is more tethered and pulls open airway, which reduces air flow resistance.
Term
Poiseuille’s Law
Definition
Takes into account the viscosity(ɲ) of the gas, the “length of the tube” (l), and the radius (r)
R= 8ɲl/ π r 4
Term
Factors in smooth muscle tone
Definition
1.  Sympathetic nervous system-beta 2 receptors
2.   Parasympathetic/cholinergic nervous system
3. Nonadrenergic, noncholinergic nervous system (NANC)
Term
Forced Expiration: COPD
Definition
With loss of elastic tissue, with forced expiration, airways may collapse
Airway and alveolar P are lower due to loss of elastic tissue
Alveolar P > IP pressure, Tm pressure is +, so alveoli open
Airway P < IP pressure, so Tm – and airway collapses
Clinical correlation: COPD
Expire slowly with pursed lips
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