RS Lecture 17 - Control of Breathing Asleep Flashcards
What are the 5 stages of sleep?
Stage 1-4, then REM sleep
How long are our cycles of sleep?
90 minute cycles
What are the 3 controls of breathing?
Brainstem (reflex/automatic); motor cortex (voluntary/behavioural); limbic system (emotional)
What is the control of breathing when asleep?
Brainstem -> automatic/reflex
Where is the motor cortex for voluntary/behavioural control of breathing on the motor homonculus?
Between the shoulder and the trunk is the diaphragm, and other respiratory muscles
Where is the automatic control of breathing located?
Pre-Botzinger complex -> present in rostral ventral respiratory group -> situated on edge of medulla, close to CSF, so appropriate breathing due to PaCO2 -> not pacemaker cells, and perpetuate respiratory rhythm
How do we define emotional control of breathing?
Lack of input from other breathing controls -> like in locked-in syndrome
What happens to your minute ventilation when you go to sleep?
It reduces by 10% -> don’t breathe more; due to reduced tidal volume
What is an issue about reduced minute ventilation in patients with COPD?
Losing 10% of their minute ventilation would reduce their O2 saturation to 80%, which could be a problem, and taking blood gases in the morning is bad as they will have accumulated CO2 overnight
How does CO2 change during sleep?
PaCO2 goes up by 0.5kPa -> otherwise you won’t breathe during sleep, as you need to stimulate the chemoreceptors
What happens if PaCO2 doesn’t rise above apnoeic threshold during sleep?
Breathing will stop -> Central sleep apnoea
Why does CO2 need to increase?
The central chemoreceptors reduce sensitivity to PaCO2 during sleep -> everyone has different sensitivities which can be plotted on a CO2 sensitivity graph
What is obstructive sleep apnoea?
Reduced upper airway muscle activity during sleep, plus extra luminal pressure and negative intraluminal pressure can result in occlusion of the phalangeal airway during sleep -> mechanical problem
Which upper airway muscles reduce their activity during sleep?
Genioglossus and Levator palatini
Why do we snore?
Turbulent airflow over the vocal cords, result of airflow getting less during sleep
What is the cycle of obstructive sleep apnoea?
What is the difference between central and obstructive sleep apnoea?
Central has no thoracic/abdominal effort involved (equal and opposite in obstruction) -> central is chemosensitivity, obstructive is mechanical
How does heart failure cause central sleep apnoea?
HF can be exacerbated by sleep-related changes in breathing because 50% of patients hyperventilate (pulmonary oedema, stimulating J-receptors which causes over-breathing), so have a low PaCO2 (below apnoeic threshold)
What is the purpose of gas exchange systems?
Transport of O2 to tissues, removal of waste products (CO2)
What is the role of O2?
Required for production of energy -> combustion of glucose, lipids and proteins
What is the respiratory quotient and what is it for fat, protein and glucose?
It is the CO2:O2 ratio -> lowest for fat (0.696), next protein (0.818) and highest for glucose (1 - theoretical maximum) -> routine fuels almost entirely glucose and fat
What is the at rest O2 requirement of the average human?
3.5ml/min/kg of O2 = 1MET (metabolic equivalent)
How much MET is used in standing, walking slowly, cycling and running?
Standing=1-2, walking=2.3, cycling>4, running>7
What is the muscle’s response to exercise?
Onset of exercise - stored energy (ATP/creatine phosphate) causes muscular contraction -> inorganic phosphates, ADP, creatine drive oxidative phosphorylation -> Kreb’s cycle and glycolysis increase, O2 consumption at the muscle increases -> initially CO2 only slightly increases (buffered as HCO3-) but then rises, matching O2
What does exercise look like when plotted on a VO2/time graph?
What is the circulation’s response to exercise?
Heart rate increases over time, CO increases over time and SV increases but then decreases after a 600 seconds
What occurs to oxygen consumption and cardiac output when exercising?
CO rises 4-7 fold; O2 consumption rises 10-15 fold, with mixed venous stats 75-80% and up to 85% of O2 can be extracted
What is the lungs response to exercise?
Tidal volume increases as V.E (respiratory minute volume); increased VQ matching improves PaO2
What happens to aerobic metabolism during exercise?
O2 flow matches demand, so RQ rises towards 1 as glucose becomes predominant fuel source -> ventilation increases to match CO2 production and attempts to maintain steady state BUT anaerobic metabolism occurs during first minutes of exercise until steady state is reached
How does the body deal with metabolic acidosis from exercise?
Lactate forms excess H+, which are buffered by HCO3-, forming CO2 and H2O, which leads to increased ventilation, pH remains stable (low); H+ exceeds HCO3- and hyperventilation occurs
What occurs in the aerobic and anaerobic phase of exercise to VE, VCO2 and VO2?
