Download P215 Discussion 13

P215 Discussion 13
Problem 1: Asthma
Jan has had a mild form of asthma for most of her life.
When asthma strikes, she has a problem with air flow in the respiratory system as airways become inflamed,
obstructed and narrowed.
This is a problem because air flow is a lot like blood flow:
i) it flow is from higher pressure to lower pressure
ii) flowing air encounters resistance from the walls of the air ways along which it passes
iii) resistance to air flow depends on airway diameter; constriction and dilation affect air flow
iv) air flowing through airways can be partly or completely blocked by substances in the airway
An important part of asthma is the immune system. Some of the changes in airways are caused or worsened by
exposure to allergens such as pollen, dander, dust and bug feces. It’s a dirty world.
The immune system response in airways involves chronic (long-term) inflammation, including swelling and fluid
secretion.
small airway cross-section
(normal)
open airway;
smooth muscle in walls
small airway cross-section
(asthma)
fluid and mucus in open airway;
contracted smooth muscle in walls;
some swelling of airway tissue
? The difficulty posed by fluid and mucus in the airways is obvious. But, how does a decrease in bronchiole
diameter during an asthmatic episode affect resistance to air flow?
decrease in diameter increases resistance to air flow
And how might such a change in resistance to airflow during an asthmatic episode affect actual air flow?
decrease in air entering and leaving lungs
? Is asthma considered to be a restrictive or obstructive repsiratory disorder
obstructive
One common way to treat asthma is to administer corticosteroid drugs.
? Why would such drugs be prescribed to treat asthma? (Think back a few weeks for the answer.)
limit activity of the immune system
Like many asthma sufferers, Jan treats the chief symptom (difficult ventilation) with an inhaled medication
called Albuterol she can spray into her mouth when needed. The drug soon reaches her airways. Albuterol
is a short-acting beta 2 adrenergic agonist. Albuterol works because it binds to receptors for substances
naturally present in the body and brings about a strong response in airways.
? How does an adrenergic agonist make it easier to breathe in just a few moments?
(If the answer isn’t clear, you should be able to figure this in the seven steps found below.)
the drugs mimic a sympathetic autonomic response - relax smooth muscle in airways - widen airways
- reduce resistance to air flow - improved air flow
? Step #1 Does the word “agonist” mean the drug does the same as the natural substance when it binds to its
agonist = same
receptorsor does it means the drug does the opposite of the natural substance ?
The identity of the natural substances are indicated by the word “adrenergic.”
? Step #2 Does “adrenergic” refer to the parasympathetic or sympathetic division of the autonomic motor system?
sympathetic AMS
? Step #3 What are the two similar natural substances (a neurotransmitter, an endocrine hormone) that bind to
norepinephrine and epinephrine
receptors at adrenergic synapses?
There are several types of adrenergic receptors, including the beta 2 receptors. The beta 2 receptors are present
on smooth muscle cells in the walls of our bronchioles.
? Step #4 Does the use of a drug that mimics these natural substances that bind to beta 2 adrenergic receptors increase
or reduce contraction of smooth muscle in bronchioles? reduce contraction
? Step #5 Does this response of bronchiole smooth muscle constrict or dilate airway diameter? dilate
? Step #6 Does this change in airway diameter increase or decrease resistance to air flow? decrease resistance
? Step #7 How does this change in resistance help someone through an asthmatic episode?
- reduced resistance to air flow - improved air flow
Problem 2: Three Learned Gentleman Discuss Ventilation
? First, some background. Define the following four terms.
i) tidal volume = amount of air moved in and out of the lungs and airways during one normal breath
ii) anatomical dead space = amount of space within the conducting zone of the airways, equal to 150 ml.
iii) minute ventilation = (breaths per minute) x (tidal volume)
iv) alveolar ventilation = (breaths per minute) x (tidal volume - dead space)
Three learned physicians (Dr. Howard, Dr. Fine and Dr. Howard) are debating the best way to deliver the most
fresh air to the alveoli.
Moe (Dr. Howard) says just breathe pretty much normally. Larry (Dr. Fine) says breathe many times a minute,
but quite shallowly. Curly (the other Dr. Howard) says breathe only a few times a minute but very deeply.
(Shemp says nothing because he isn’t in this episode.)
Moe’s Suggestion
14 breaths per minute
500 ml tidal volume
Larry’s Suggestion
20 breaths per minute
350 tidal volume
Curly’s Suggestion
8 breaths per minute
875 ml tidal volume
? What is the minute ventilation for each of the suggestions? (breaths per minute) x (tidal volume)
Moe’s Suggestion
Larry’s Suggestion
7000 ml/minute
7000 ml/minute
Curly’s Suggestion
7000 ml/minute
? What is the alveolar ventilation for each of the suggestions? (breaths per minute) x (tidal volume - dead space)
(Assume dead space is 150 ml.)
Moe’s Suggestion
4900 ml/minute
Larry’s Suggestion
4000 ml/minute
Curly’s Suggestion
5800 ml/minute
where a tidal volume of 500 ml ends up
? Why is alveolar ventilation less than minute ventilation?
(The drawing at the right may help.)
minute ventilation depends on the entire tidal volume;
alveolar ventilation depends on part of the tidal volume,
the part that fills the respiratory zone
conducting zone
of air ways
respiratory zone
of airways
no gas exchange
150 ml
350 ml
gas exchange
? What’s the best tactic to deliver the most fresh air to the alveoli- Moe’s, Larry’s or Curly’s?
Curly’s. Coytenly!
? In this debate, which factor - faster breathing rate or greater depth of breathing - is the most
effective at delivering more fresh air to the alveoli?
greater depth of breathing
Ventilation (breathing) and gas exchange are two prime functions of the respirator system.
? Why is alveolar ventilation more important than minute ventilation for gas exchange?
gas exchange occurs in the respiratory bronchioles and alveoli;
only air in the respiratory zone is involved in gas exchange;
alveolar ventilation (not minute ventilation) measures fresh air in the conducting zone
In the real world, the situation isn’t a simple choice between the good doctors’ tactics.
For example, breathing rate and tidal volume both increase to raise alveolar ventilation during exercise.
Initially, increasing the depth of breathing contributes most to raising alveolar ventilation. However,
after depth of breathing has increased several times its resting volume, the lungs are expanding about
as much as they can, and increasing the breathing rate starts to makes a bigger contribution to raising
alveolar ventilation.
Problem 3: Breathing and Surfactant
Breathing is work. Moving air out of the airways and lungs - normal expiration - isn’t so hard. It only requires
muscle to relax. To move air into the lungs - inspiration - that’s a job that requires skeletal muscles to contract.
One of the factors the muscle must work against is the attraction of water molecules for each other within the
respiratory system. A watery film coats walls of small airways. During inspiration, the air spaces increase in
volume as the lung expands. The attraction of water molecules for each other must be counteracted.
expansion of respiratory zone
respiratory zone
alveolar duct
alveolar duct
film
film
air space
air space
between breaths
during inspiration
close up view of watery film
lining parts of airways
close up view of watery film
lining parts of airways
expansion of airways is resisted
by interactions of water molecules
water molecules interact with each other
? What characteristic of water molecules enables them to interact
more positive
H
H
with one another?
O
more negative
they’re polar molecules
positvely charged regions in water molecules are attracted to negatively charged regions in other water
molecules
The interaction among water molecules resists expansion of the respiratory zone.
Surfactant helps makes the job of inspiration easier. It can mix with water molecules in the fluid film
along the walls of the respiratory zone.
? What is surfactant?
a complex of lipid and proteins
? What cells produce surfactant?
type II alveolar cells
non-polar part
polar part
surfactant molecule
? What part (polar or non-polar) of surfactant interacts with water molecules?
polar part
Surfactant reduces the interactions of water molecules in the film lining the respiratory zone.
Surface tension of the film declines. Water doesn’t “pull together” as strongly to resist expansion of air spaces.
On the next page are two instances in which surfactant plays a vital role.
Baby T.H. is a premature newborn with respiratory distress syndrome.
? Why is it such a struggle for immature infants like T.H. to breathe?
her immature lungs cannot produce adeuate amount of surfactant
must work against attraction of water molecules
? Before the struggle for breath exhausts them, infants with respiratory distress can be helped by supplemental
oxygen and breathing assistance. They can also inhale a surfactant preparation. How would giving surfactant
help them? reduce interaction of water molecules in respiratory zone
have benefits of surfactant until lungs mature and produce it
? Adults can also suffer from insufficient production of surfactant. For example, pain following the abdominal
or thoracic surgery often makes people take shallow breaths. These patients are regularly visited by respiratory
therapists who help them make a series of deep breaths despite the discomfort. The question is why?
(Think about what kind of alveolar cells produce surfactant and when they tend to do it.)
deeper breathing leads to more surfactant release by type II alveolar cells
Problem 4: A Pleural Sac Perforation
Jimmy G. got in the way of the sharp end of a knife. The
blade passed through his chest wall and entered the pleural
sac surrounding his right lung and the lung itself. Shortly
thereafter, most of his right lung collapsed. As a result,
Jimmy experienced difficulty in breathing. Medical care
was not long in coming and Jimmy survived. Given the
proper treatment, his right lung eventually expanded.
trachea
chest wall
chest wall
lung
lung
pleural sac
Questions
? What’s the name for the surface of the pleural sac that lines the inner surface of the chest wall? parietal pleura
? What’s the name for the surface of the pleural sac that lines the outer surface of the lung? visceral pleura
? Let’s assume the atmospheric pressure is 760 mm Hg. If the airways are open and no air is moving
into or out of the lungs, what is the air pressure in the alveoli? same
760 mm Hg
? How does intrapleural pressure compare to intrapulmonary pressure? lower than intrapulmonary pressure
? How does this difference in pressure (the transpulmonary pressure) affect the shape of the lungs?
helps keep them inflated --- lower pressure outside lungs than inside
? How does intrapleural pressure compare to atmospheric pressure?
it’s lower than atmospheric pressure
? How does this difference in pressure affect the shape of the chest wall?
helps keep chest wall in normal position --- higher pressure outside chest than inside
When the pleural sac and right lung were punctured by the knife wound, atmospheric pressure, intrapulmonary
pressure and intrapleural pressure can become equal.
? How did the position of Jimmy’s chest wall change when the pleural sac was opened to the atmospheric
pressure?moved outward from normal position
? Why did the right lung collapse?
elastic recoil of lung when no difference in air pressure between inside and outside
What
would
happen
to someone who had a lung disease (such as severe infection or tumor) that perforated
?
the surface of the pleural sac on the outer surface of the lung? same thing
? What is the medical term for Jimmy’s condition? pneumothorax