11- Clinical Response to Hypoxemia and Hypercapnia Flashcards
Generally speakign what 3 things work togetehr to coordinator breathing in the body? How does this relate to the analogy of the thermostat?
Sensors (chemoreceptors, lungs and other receptors) **thermostat**
Central Controller (pons, medulla, and other parts of brain) **furnace**
Effectors (respiratory muscles) **piping and ducts**
What cells are the carotid body made up of?
Type I: Glomus cells
Type II:
What are the 3 kinds of sensors?
Central (pons, medulla)
Peripheral (Carotid body and aortic body)
Mechanoreceptors (lungs, GI tract, nose) Hypothalamus (anxiety, fear. pain) Voluntary control (“I want to hyperventiliate”)
What is sensed by the central and peripheral chemoreceptors? how much of the response are the central chemoreceptors vs peripher chemoreceptors responsible for?
Co2, H, O2
central: 70% of response
peripheral: 30%
WHat is ventilation?
to scatter, to dispers, a breeze/wind. to move air
What is the relationship between CO2 and H?
Everytime you have Co2 you have H!
What is the equation for pH? Are H ions good or bad? where do we find H?
pH= -logH
Hydrogen ions are bad!!
located in extracellular space
WHat is the nromal response for a person whos pCO2 increases to 60 mmHg? WHat is the relationship between CO2 and ventilation?
it should be 40mmHg
an increase in both respiratory rate and tidal volume
**As Co2 rises your ventilation rises**
What 2 forms determine the partial pressure of oxygen?
Hemoglobin bound, dissolved O2
What is the shape of the PaO2 and Hemoglobin saturation relationship? What is p50? What does it mean to right or left shift the curve?
sigmoidal due to the positive cooperativity of Hemoglobin
p50 is the PO2 required for hemoglobin to be 50% bound
right shift means hemoglobin is bound less tightly
left shift means hemoglobin is bound more tightly
What is Henrys Law?
The amount of dissolved gas is proportional to its partial pressure
Dissolved O2=PaO2 * 0.003
Ashley Matter is Anemic. She is asymptomatic ans oxygen saturation is 100% on room air. What is her expected ventilatory response?
no change in ventilatory response
Which ion is the ventilatory response most sensitive to? How does ventilation change if Co2 is constant and O2 decreases?
increases in CO2!
As O2 decreases ventilation will increase!
What is the equation for oxygen delivery? How does an anemic person (Ashley Hollo?) maintain oxygen delivery?
Delivery (DO2)= CO * CaO2
CaO2 is made up of Hb bound and dissolved
In anemia Hb is decreased
This means that viscosity is decreased, and therefore resistance is decreased. Decreased resitance leads to increased Cardiac output. SO! The body is able to compensate for decreased CaO2 by increasing cardiac output!
aka anemic person with a healthy heart can compensate and remain asymptomatic
What is the relationship between viscosity and resistance?
They are directy related! As viscosity increases so does resistance
What muscles are involved in tidal inspiration and what nerves stimulate them? What happens to the abdomen and chest during normal tidal breathing?
Diaphragm!!!!!!! C3, C5
external intercostals
chest and abdomen rise tgether during inspiration!
What muscles are involed in inspiration during respiratory distress? What nerves innervate them? What happens to the chest and abdomen during respiratory distress inhalation?
diaphragm C3-C5
scalenes: C2-C7
sternocleidomastoid: accessory nerve C2-C3
Intercostals: T1-T11
Abdominal muscles esp transversus abdominus: T7-L1
The chest rises but the abdomen falls! This is called Hoovers sign
What sensors are primarily resposible for O2? What sensors are primarily responsible for Co2?
Carotid body: O2
Central chemoreceptors: Co2
What does the body do in response to decreased O2/ increased Co2?
the central controller sends signals to the spinal cord then to the muscles to increase ventilation which will increase O2 and reduce PaCO2
what can you do to gurantee that you will win a breath holding competition?
take multiple breaths just before going under water
How do people with chronic respiratory acidosis often respond to oxygen?
With acute acidosis!
With chronic acidosis the body resets so that oxygen is the main driver of ventilation (instead of CO2 like in healthy people)
so when oxygen increases there is no drive to breath. These people then hypoventilate and that is how they develop acute respiratory acidosis
What happens to the airway and FRC during COPD?
- Airway
- loss of elastin
- airway secretions
- Lungs/FRC
- loss of elastin
- consequence: air trapping so increase in PaCO2
(no elastic you cant exhale well)
What are 3 reasons that it is bad to give someone with COPD oxygen?
- Taken away drive to breath
- altered ventilation perfusion mismatch (VQ mismatch) (hypoxic vasoconstriction)
- Haldane effect
How does blood flow in the lungs respond to chronic respiratory acidosis? What happens if you give them oxygen?
hypoxic vasocontriction (blood flow is diverted away from poorly ventilated areas)
too much oxygen vasodilates! Now, blood flow is re-establish to that part of the lung which is still poorly ventilating. PaCo2 INCREASES!
WHat is the haldane effect
When you give a person with chronic acidosis oxygen there is more drive for O2 to bind to hemoglobin so there are less binding sites available for CO2 to bind to. Therefore they have more free Co2 floating around and are acidotic.
What would happen if you knock out both phrenic nerves?
shallow, fast breathing only using the accessory muscle and not the abdomen. this is a probelm with the effector!
*
What does Maximum expiratory pressure <60cm h20 predict?
what does maximum inspiratory pressure <30% predict?
What does vital capacity <55% predict?
MEP<60 predicts weak cough
MIP<30% predicts respiraoty failure
VC<55% predicts respiratory failure
What are the 4 possile effector problems?
- Polyneuropathies, HMSN (CMT)
- Spinal Muscular atrophy, poliomyelitis
- Myastenia gravis
- Muscle dystrophy, myositis myotnoia
What is the function of the pontine group?
located in pons
limits inspiration
acts as a “shut off”
WHat is the job of the cetral pattern generator for the dorsal respiratory group? How about for the ventral respiratory group?
- Dorsal respiratory group (inspiration)
- located in medulla
- pattern generator
- quiet breathing
- processing center
- Ventral respiratory group (expiration and inspiration)
- located in medulla
- not so quiet breathing
- inspiration and expiration
A stroke to the pontine respiratory center will lead to____
A stroke in the central pattern generator (medulla) will lead to_____
opioid use will lead to ____
potine-apneustic breathing (pontine inhibits excessive inhalation)
medulla-ataxic breathing (controls rhythm and rate)
opioids: slowed breathing
What happens to oxygen levels and minute ventilation during ascent of Mt Everest?
partial pressure of oxygen decreases and minute ventilation increases
WHat happens to the fraction of inspired air as you climb Mt Everest?
No change! The air you are breathing is still 22% oxyge, there just is less air in general
(think like preserved ejection fraction heart failure preserved the ejection fraction but had less volume in general to pump)
What is the alveolar gas equation?
What is PAO2 at seas level? How does it relate to PaO2
Which value changes in the equation as you ascend Mt Everest?
PAO2=((Patm-Ph20) * FiO2) - PaCo2/RQ
As you ascend Mt Everst the Patm will decrease, but all other values stay constant. As you climb up the Alveolar gas significantly decreases
sea level: PAO2= 101mmHg. Also PAO2=PaO2
Summary!
What are the sensors?
Chemoreceptors: PaO2, PaCO2
Mechanoreceptors: nose and lungs
Voluntary: cerebral cortex
What are the central controllers?
Pontine group: Pons
Central Pattern Generator: Medulla
Summary:
What are the effectors?
Spinal cord: signal from central controller
Diaphragm: quiet breathing
Accessory muscles: used with increase in ventilation
