8 Breathlessness and Control of Breathing in the Awake State Flashcards
Q: What are the main functions of respiratory muscles? (6) Most important?
A: -Maintenance of arterial PO2, PCO2 and pH (optimal biochemistry) -> ensure biochemcical processes (ENZYMES) work in most optimum way
- Defence of airways and lung: cough, sneeze, yawn
- Exercise: fight and flight - running
- Speech/singing/blow
- cry/laugh/emotions
- Control of intrathoracic and intra-abdominal pressures
H+ concentration
Q: What does a spirogram show? Draw one. Describe (4).
A: one typical representative breath
time (s) = X and volume = Y
single line from origin goes up then down with point
- total time of a single cycle is T (tot)= at rest= 4s
- size of upstroke= inspiration= V (t)= tidal volume
- TTOT can be split into two: Inspiratory (TI) and Expiratory (TE)
- slope= VT/VI = MEAN INSPIRATORY FLOW (neural drive)
Q: What stands for minute ventilation? How is it calculated? Av value?
A: V.E = Minute ventilation (expired volume)
volume breathed per minute= sum of all inspiratory V(t)s in a minute (or expir V(t)s as are the same)
VE = Vt x f
minute vent = tidal volume x freq
where f = 60 / T(tot) = converts to respiratory frequency per minute
VE= 5.9L/min
Q: From a spirogram, what is flow? (how is it calculated). What does it show? also called? Av value?
A: take VE = Vt x 60 / T(tot)
multiply the minute ventilation equation by TI/TI then you get:
V.E = VT/TI x TI/TTOT
Where VT/TI = MEAN INSPIRATORY FLOW
This is how powerfully the muscles contract
This is called the neural drive
VT/TI = 0.26L/s
Q: From a spirogram, what is the inspiratory duty cycle? (how is it calculated). What does it show? also called? Av value?
A: take VE = Vt x 60 / T(tot)
multiply the minute ventilation equation by TI/TI then you get:
V.E = VT/TI x TI/TTOT
TI/TTOT = INSPIRATORY DUTY CYCLE
The proportion of the cycle spent actively ventilating (i.e. inspiring)
38%
Q: If metabolic demands increase and more ventilation is required, what happens? (explain with spirogram) (4)
A: -you increase VT/TI
- and you decrease TTOT
- and hence INCREASE THE FREQUENCY
TTOT is decreased by a combination of reduction in TI and TE
Q: How does the brain control the diaphragm? changes result in? (2)
A: Brain sends certain freq of impulses via phrenic nerve to diaphragm (more freq = it will shorten more strongly and faster)
Q: Summarise inspiration control. (4) Expiration? (3)
A: -at a certain moment inspiration is switched on,
- another controller controls drive- how hard the muscles contract
- third controller- stretch receptors detect chest has expanded sufficiently for metabolic requirements
- 4th controlled stops inspiration
- expiration is mostly passive
- system returns to resting volume
- lots of braking mechanisms ensure it is controlled and doesn’t occur too fast
Q: Normal. Vt? Freq? Inspiratory duty cycle? Mean inspiratory flow? Minute ventilation?
A: tidal volume= 0.4L 15/min TI/TTOT = 38% VT/TI = 0.26L/s VE= 5.9L/min
Q: What happens when you have to breathe through a tube? What happens to VT, V.E, Frequency, VT/TI (neural drive)? Inspiratory duty cycle (TI/TOT)?
A: the tube will act as extra DEAD SPACE which has to be cleared
When artificial dead space is added, VT, V.E increases compared to the middle column
Frequency decreases to 14.8
VT/TI (neural drive) also increases when there is extra dead space compared to the use of a nose clip - this change occurs to satisfy the need for more ventilation
The inspiratory duty cycle (TI/TOT) is essentially unaltered
Q: Draw 3 overlapping spirograms for normal, chronic bronchitis and emphysema. (what are they both?)
What happens with both conditions? How does this affect:
expiration and inspiration? Residual volume? TTOT? VT/TI? TE/TTOT? TI/TTOT? VT/TI? downward slope?
A: COPD
REFER
In both chronic bronchitis and emphysema, the intrathoracic airways are narrowed and so they have difficulty ventilating the lungs more on EXPIRATION than inspiration
As they have a higher residual volume than normal people, this increases the stiffness of the chest and lungs and increases the work of breathing
Compared to controls, people with COPD breathe much shallower and faster (shorter TTOT)
Inspiratory duty cycle (TI/TTOT) increases a little bit in normals to give more time for inspiration
In people with airway obstruction, TI/TTOT decreases a bit in exercise to give more time for expiration
However, people with COPD DO NOT BREATHE ANY HARDER (VT/TI is more or less the same)
Despite having an expiratory airflow obstruction, the proportion of time used for expiration in patients with COPD has NOT been altered - the gradient of the downwards slope is the same
Q: What happens when exercising to:
VT/TI?
ventilation?
TTOT?
Frequency?
Those with COPD?
A: When exercising, there is an increase in neural drive (VT/TI) and ventilation
Exercise will also bring about a halving of TTOT and hence a doubling of frequency
same effects
Q: What is the main driver of breathing? What are the 3 controls? Where are the components? What will always override?
A: diaphragm
Involuntary or metabolic centre = MEDULLA (bulbo-pontine brain) ***
Voluntary or behavioural centre = motor area of CEREBRAL CORTEX -> Behavioural components are scattered throughout the mid and upper parts of the brain
Reflex control -> coughing, sneezing
Q: What does the involuntary control of breathing respond to? What does it determine? What can influence it? (4)
A: Responds to metabolic demands for/ production of CO2
determines, in part, “set point” for CO -> generally monitored as PaCO2
- There are other parts of the cortex that are not under voluntary control and have an influence on the metabolic centre such as emotional responses (frontal cortex)
- sensory inputs (pain, startle)
- limbic system (survival responses (suffocation, hunger, thirst))
- Sleep (absence of wakefullness) via the reticular formation (set of interconnected nuclei in the brain stem) also influences the metabolic centre
Q: What is the voluntary control of breathing responsible for?
A: controls acts such as breath holding, singing
Q: Draw a diagram representing the organisation of breathing control. Most important feedback?
A: REFER
carotid bodies
Q: What is the most important feedback involved in breathing control? Passed back to? via?
Compare H+ response.
A: Peripheral chemoreceptor:
- Well perfused carotid body
- At junction of internal and external carotid arteries in the neck
- A rapid response system for detecting changes in arterial PCO2 and PO2
passed back to metabolic controller (medulla)
-glossopharyngeal nerve
rapid system when compared to response in brain to extracellular fluid (bathing metabolic centre)
Q: Compare the coordination of central breathing in brain to heart. Diseases of central breathing?
A: The heart has a single pacemaker in the SAN which is accessible to cardiologists for treating arrhythmias but breathing has many pacemakers that are close together in the brain stem and are inaccessible
The group pacemaker activity of breathing comes from around 10 groups of neurons in the medulla near the nuclei of cranial nerves IX and X
-rare
Q: Name one group of neurons in the medulla controlling breathing. Where is it? Role? Relation to other controllers?
A: pre-Borzinger complex (ventro-cranial medulla near 4th ventricle)
essential for generating respiratory rhythm -> called the ‘gasping centre’
-> its coordination with other controllers may be needed to convert into an orderly and responsive respiratory rhythm
