Respiratory System and Mechanics of Breathing II Flashcards
PTotal =
Pelastic + Presistive = V/C + V(dot)R
Pulmonary Resistance (R) Composed of:
- frictional resistance of lung & chest wall tissue (~20%)
- airways resistance (~80%)
The movement of fluid (i.e. air) flowing through a rigid,
smooth bore tube is governed by
Poiseuille’s Law:
The total airway resistance to flow is the sum of all
the
resistances of the nose and mouth (a substantial portion
of the total) and of the 23 generations of the
tracheobronchial tree.
• Airway resistance is from the friction between
gas
molecules and between gas molecules and the walls.
• Airway resistance is important (~80%) and makes the
sliding of
lung tissue over each other (viscous tissue
resistance, ~20%) a minor issue.
Turbulent flow requires a much greater
driving pressure
• Doubling the length (l) of
the airways doubles the
airway resistance.
• But halving the radius (r)
increases the resistance by
sixteen-fold.
Poiseuille’s Law
- Gives the relationship for laminar flow in a cylindrical tube.
- It states that the rate of flow is due to the difference in pressure (DP) between the two ends:
- i.e. Flow is proportional to DP.
Intermediate sized
airways contribute
most
of the total resistance.
• Total cross-sectional
area increases towards
the periphery, whereas
total airflow is
constant.
• Flow is therefore more
laminar in the
small
airways.
Flow is:
• effort dependent at
• effort independent at
high lung volumes.
low lung volumes.
Work is proportional to ΔP x ΔV
The work of inspiration consists of three different
fractions:
(i) compliance work, or elastic work i.e. that required
to expand the lungs against elastic forces (recoil).
(ii) tissue resistance work, i.e. that required to
overcome the viscosity of the lung and chest wall
structures.
(iii) airway resistance work, i.e. that required to move
air through the airways into the lungs.
0AECD0 Insp. work done overcoming
elastic forces.
ABCEA Insp. work done overcoming
viscous (airway + tissue) resistance.
AECFA Work done on expiration to overcome
airway (+ tissue) resistance.
Emphysema
destruction of lung tissue
around alveoli makes them
collapse on expiration. creating larger air spaces instead of many small ones.
Bronchitis
Increased mucous buildup in
the airways.
Obstructive disease
e.g.
Resistive work greatly increased (ABCEA) insp
COPD (i.e. emphysema and bronchitis.)
Obstruct airways, resulting in increased work of breathing especially during
expiration.
Restrictive disease
e.g.
Elastic work increased (0AECD0)
fibrosis, pulmonary congestion.
Restrict lung expansion, resulting in a decreased lung volume, an
increased work of breathing, and inadequate ventilation and/or oxygenation.
The Work of Breathing
Rapid shallow breathing ¯
• Slow deep breathing ¯
decr elastic work but incr frictional (viscous) work.
decr frictional work but incr elastic
work.
During INCREASED ventilation to levels of ~50 L min-1:
Total cost of breathing =
total VO2 - resting VO2
Control of breathing must:
• Establish -
• Match -
the automatic rhythm for contraction of respiratory muscles (rate and volume). rhythm to metabolic demands, varying mechanical conditions, & episodic non-ventilatory behaviours (talking, eating etc).
Respiratory control is an example of a
______________ system
“negative feedback”
Control of Breathing
Reflexes from:
Lungs Airways CV system Muscles & joints Skin Arterial chemoreceptors Central chemoreceptors
• PaCO2 normally _____
controlled.
tightly
______chemoreceptors provide most of stimulus with
contribution from __________
chemoreceptors more rapid
Central
peripheral
Response magnified when PaO2 is
lowered.
With Exercise:
Increases in:
Whereas ____ remains normal until
very high exercise level.
VT, fR,VE
PaO2
Neural control of ventilation
3 resp control areas:
All located in?
- Rhythmicity Area
- Apeunistic Area
- Pneumotaxic Area
BRAINSTEM
- Rhythmicity Area
Where?
Inspiratory cells stimulate:
Expiratory cells stimulate:
The rhythmicity Area:
medulla oblongata brainstem
Inspiratory and expiratory portions.
Inspiratory- stimulate phrenic and intercostall nerves. Expiratory cells stimlate lower spinal and intercostal nerves
- Apeunistic Area
Where?
stimulates ?
pons of Brain stem
stimulates inspiratory cells of rhythmicity area and promotes insp.
- Pneumotaxic Area
Where?
stimulates ?
Upper Pons
Inhibitory effect of apneustic area and inhibts insp. During excercise promotes exp
3 Mechanisms that control of ventilation
Nervous
Voluntary
Chemical
Voluntry control of ventilation
where?
what?
cerebral cortex
limited control
can incr of decr rate and tidal vol.
singing excercise etc
Central chemoreceptors
where
how
medulla oblaongata brain stem
activated by changes in chemical composition of cerebral spinofluid
Directly stimulate rhythymicity centre
peripheral chemoreceptors
where
how
Aortic arch and carotid arteries
changes in CO2 and PH and O2 in blood
Two types of propriocepters
joint propriocepters
stretch receptors
joint propriocepters
stimulated by movement of limbs
excite resp centre to incr rate and depth of breath
stretch receptors
mechanoreceptors sense stretch/ tension in bronchi. Inhibit insp ( Hering Breur Inflation Reflex)
