Lec 6 Control of breathing Flashcards
The most important stimulus for ventilatory drive is:
A) Oxygen saturation
B) Pa O2
C) Pa CO2
C) PaCO2
At maximal levels of exercise:
A) arterial blood gases show elevated PaCO2
B) arterial blood gases show reduced PaO2
C) arterial blood gases show normal PaCO2 and PaO2
C) arterial blood gases show normal PaCO2 and PaO2
Assuming a reasonable number of hours of sleep, the most common reason to be sleepy during the day is A) Obstructive Sleep Apnea B) Central Sleep Apnea C) Depression D) Narcolepsy
A) Obstructive Sleep Apnea
Normal PaO2?
90-100
Normal PaCO2?
40
Normal pH?
7.4
paCO2 if you
- hold your breath?
- fall asleep?
- exercise?
- hyperventilate?
hold breath: 55
fall asleep: 45
exercise: 40
hyperventilate: 20
What generally happens in respiration?
- brain signals phrenic nerve to send signals to inspiratory [mostly diaphragm] muscles –> causes diaphragm to contract and pull down leading to inspiration
- expiration is passive
Where are the centers that initiate breathing located?
in medulla beneath floor of 4th ventricle
Where is the dorsal respiratory group located? action?
- in nucleus tractus solitarius
- mostly inspiratory neurons
- receive afferents from CN9 and CN10
- main site for driving phrenic nerve
What is the ventral respiratory group? action?
- contains inspiratory and expiratory neurons
- main respiratory pacemaker
What is the apneustic center?
in the pons = site of neurons which normally turn off inspiration
What sets normal respiratory rhythm?
step1
pre-botzinger complex in the VRG [ventral respiratory group] of medulla
What is the pneumotaxic center?
in pons; modulates apneustic center
What are main afferents to central respiratory center?
step1
CN 9 (glossopharyngeal) and CN 10 (vagus)
Where are central chemoreceptors? action?
step1
- near surface of medulla
- on brain side of blood brain barrier
- stimulated by change in pCO2 [directly measures pCO2/pH of blood interstitial fluid which is influence by arterial CO2]
- quicker response to respiratory acidosis than metabolic acidosis b/c CO2 can diffuse across BBB and H+ cant
Where are the peripheral chemoreceptors? what stimulates them?
step1
- carotid and aortic bodies = between external/internal carotid branch and on top of aortic arch
- mostly respond to pO2 < 60
also respond to - high PCO2
- low pH
What are steps of baroreceptor reflex in hypotension?
step1
hypotension –> decrease arterial P –> decrease stretch –> decrease afferent baroreceptor firing –> increase efferent sympathetic and decrease efferent parasympathetic –> vasoconstriction, increase HR, increase contractility, increase BP
Does baroreceptor fire more with hypotension or hypertension?
step1
fires more with hypotension
Does signal to increase ventilation in response to chemoreceptors cause greater increase in rate or tidal volume?
greater increase in tidal volume
What is the slope of hypercapnic ventilation drive?
2 L/min/torr
What happens minute ventilation in person if PCO2 increase from normal 40 to 43?
hypercapnic drive = 2 L/min/torr
so if we increase by 3 torr –> increase ventilation rate by 6 L/min
normal = 6 L /min so we can more than double minute ventilation
IF someone who looks comfortable has a PCO2 of 45 what should you think?
they must have a chronic pulmonary problem
What is normal minute ventilation?
5-6
What happens to hypercapnic drive in response to hypoxemia?
in hypoxia hypercapnic drive increases = we are more sensitive to PCO2 when we don’t have enough O2
What happens to ventilation drive with hypoxia?
very little change in ventilation with decreased PO2 until you reach ~ 60 torr then exponential increase with further hypoxia
At what PO2 do you lose consciousness?
35 torr
What happens if you plot O2 sat vs ventilation rate [rather than PO2 vs ventilation]?
relationship is linear
–> increase ventilation wen decrease O2 sat
Do peripheral chemoreceptors respond to O2 sat or PO2?
PO2
What symptoms if you are hypoxic?
may be asymptomatic; not uncommon to be hypoxic with little or no dyspnea
What are the types of lung receptors?
- stretch receptors = increase firing with inflation of lung
- J receptors = next to capillaries; respond to inflammation or fluid in interstitium by increasing rate
- nociceptors = respond to chemicals/smoke/dust to stimulate ventilation by increasing resp frequency
- chest wall receptors = in muscle of chest wall; feedback to respiratory centers about work of breathing
What is the definition of hypoventilation?
elevated PCO2
What is can’t do vs won’t do hypoventilation?
can’t do = decreased pulmonary function from bad lungs or muscle
won’t do = decreased ventilatory drive from drugs/meds, sleep related, or ondine’s curse
What are the 3 stages of non-rem sleep?
stage 1 = light sleep, easily arousable
stage 2 = deeper sleep, about 50% of the time
stage 3 = slow wave or delta sleep = most refreshing
What kind of sleep decreases most with age?
stage 3 sleep
What is cheyne-stokes respiration?
specific pattern of periodic breathing seen mostly in sleep
respiration waxes/wanes with period of apnea betwen cycles
seen with neurologic disease or CHF
its a feedback control problem related to circulation time = like delayed thermostat
What is REM sleep?
- brain is active, muscles nearly paralyzed including respiratory muscles
- most cardiac and respiratory instability
What happens to PCO2 in sleep?
rises 2-6 torr
What is breathing like in stage 3 [slow wave] sleep?
- very regular breathing and HR
body on autopilot
What happens to breathing in REM sleep
- decrease in ventilatory drive
- greater dependence on diaphragmatic function
- decreased muscle tone
–> if you are dependent on muscle tone you will get problems here; if you die in your sleep most likely REM
What is obstructive sleep apnea?
- sleep apnea cause by diminished diameter of airway
- decreased muscular activity + supine posture creates obstruction
you keep trying to breath but you cant
have really loud snoring
What is sleep apnea?
repeated cessation of breathing for > 10 seconds during sleep 5 or more times / hr
Who most commonly gets obstructive sleep apnea?
- obese
- those with family hisotry
Is obstructive or central sleep apnea more common?
obstructive
What causes central sleep apnea?
obesity or ondines curse
What is ondine’s curse?
- congenital central hypoventilation syndrome
- due to defect in PHOX2b gene
- causes central sleep apnea
What is mild vs moderate vs severe sleep apnea?
mild = 5-15 times /hr sleep stop breathing moderate = 15-30 times / hr severe = > 30 times / hr
Sleep apnea puts you at risk for what diseases?
step1
- coronary artery disease
- stroke
- CHF
- systemic/pulp HTN
- arrhythmias [AFib/flutter]
- sudden death
What are signs/symptoms of sleep apnea?
- snoring
- daytime sleepiness
How does exercise change ox cunsumption?
- increases ox consumption
- increases minute ventilation
- arterial blood gases unchanges
What is respiratory system response to exercise?
step1
- increase CO2 production
- increase O2 consumption
- increase ventilation to meat O2 demand
- increase pulm blood flow to increase CO
- decrease pH during strenuous exercise
- no change PaO2 and PaCO2 but increase in venous CO2 and decrease venous O2
What happens to O2/CO2 in arteries in exercise? what about in veins?
step1
- no change PaO2 and PaCO2
- increase in venous CO2 and decrease venous O2
What is fick principle equation?
Qt [CO] = VO2 / (CaO2 - CvO2)
= ox consumption / (arterial O2 - venous O2)
What is the equation for CaO2 oxygen content?
step1
CaO2 = 1.34 * Hb * SaO2 + 0.003 * PaO2
SaO2 = usually closet to 1 PaO2 = usually 100
How does minute ventilation change in exercise?
Ve = Vt * frequency
- increase tidal volume and frequency
What is the anaerobic threshold?
threshold of exercise [oxygen uptake] after which you start building up lactate = function of how good your heart is [not your lungs]
usually about 40% of your max oxygen uptake
How do you increase muscle oxygen extraction in exercise?
- shunt blood from other organs [at rest muscles = 20% of CO; in max exercise 80%]
- increase CO
What is limiting factor on exercise?
mostly limited by CO not by lungs
What happens to O2 hemoglobin dissociation curve in exercise?
shifts to the right –> hemoglobin decrease affinity; increase P50
What are the risk factors for obstructive sleep apnea?
- obesity
- crowded upper airway
- male
- advanced age
- family history
- drugs and meds
- HTN and AFib
What is obesity hypoventilation syndrome?
- morbid obesity (BMI > 30) –> hypoventilation –> decrease PaO2 and increase PaCO2 during waking hours
hypoventilation during sleep without much apnea; particularly occurs in REM sleep
What is treatment for sleep apnea?
CPAP, surgery, weight loss
