Week 1 Respiratory Physiology Flashcards
Central Controller
Brainstem
Effectors
receives info from central controllers and causes ventilation to occur
Sensors
gathers info and provides feedback to the central controller to allow to adjust output (eg chemoreceptors and mechanoreceptors)
Control of breathing - Sensors
- breathing stimulated and regulated by CO2, H+, & O2 concentrations
What are Chemoreceptors?
- chemical sensors in the brain and blood vessels that identify changing levels of oxygen, carbon dioxide and H+
What do Chemoreceptors - Central (medulla) detect?
- detects change in pH (H+) caused by changes in PCO2
Note: Blood brain barrier impermeable to H+ (CO2 can diffuse through CSF combines with water to give off H+)
What do Chemoreceptors - Peripheral (carotid sinus, aortic arch) detect?
- detects changes in PO2, PCO2, pH
Normal PaCO2
38-42 mmHg
What happens when there is an increase of CO2 in blood?
- increased breathing rate and depth of respiration (Increased ventilation
What happens when there is a Decrease of CO2 in blood
- reduced ventilation (less breathing)
Normal PaO2
80-100 mmHg
Ventilation is not stimulated by falling….
PaO2 until O2 reaches about 50mmHg
Hypercapnia
excessive carbon dioxide in the blood
deficiency in the amount of oxygen reaching the tissues
Hypoxia
Factors that can affect/override central control
- voluntary: eg. hyperventilation
- Disease process: eg. brain injury, fractured ribs, thoracic injury
Muscles acting on Thorax during NORMAL INSPIRATION
- diaphragm
-parasternal intercostals
- scalenes
- quadratus lumborum
Muscles acting on thorax during NORMAL EXPIRATION
- mainly passive elastic recoil
Movement of ribs 1-6
“pump handle” - moves up and down
Movement of ribs 7-10
“bucket handle”
- caused by contraction of the diaphragm
- increase transverse (lateral diameter of the rib cage)
Movement of ribs 10-12
“caliper” movement
- non fixed ribs (11-12 floating, 8-10 - false ribs)
- outwards and backwards swing of the ribs
- also increases lateral diameter
Breathing Inspiration and expiration Process - is it active or passive?
- Inspiration - active
- Expiration - passive (muscles relax, lungs recoil, compresses air, pressure in alveoli increases and gas moves outward)
Tidal Volume (VT)
Amount of air that moves in and out of the lungs during a normal breath
Minute ventilation
aka minute volume; amount of air moved in and out of the lungs in one minute
minute ventilation (MV) = tidal volume (Vt) x respiratory rate
Dead space
- ventilation but no perfusion
What is Anatomic dead space
- gas in conducting airways
What is Alveolar dead space
- gas in respiratory zone where there is no perfusion
Physiological Dead space
anatomical dead space + alveolar dead space
Blood that enters the arterial system without going through ventilated lung is called
Shunt
Extrapulmonary shunt examples:
congenital heart defect, blood going from left side of the heart to the right side of the heart (septal defect)
Intrapulmonary shunt
blood that goes through the lungs but is not exposed to a ventilated lung
- examples: lung collapse, consolidation - leads to reduction of PaO2
what is dead space?
- ventilation but no perfusion
- High V/Q ratio >1
What is a shunt
- perfusion but no ventilation
- Low V/Q ratio <1
What is the response of the pulmonary vasculature when PaO2 alveolar gas is reduced?
- Hypoxic vasoconstriction. Vasoconstriction (opposite to other mms) - acts to divert blood flow to other alveoli with better oxygen exchange
What is hypoxic vasoconstriction?
- the response of the pulmonary vasculature when there is a reduction in PaO2.
- acts to divert the blood to alveoli with better oxygen exchange
what is Diffusion?
movement of gas molecules across the alveolar capillary membrane
What are factors that affect gas diffusion?
- surface area of the membrane
- thickness and chemical composition
- pressure gradient of gas across the membrane
- solubility of the gas
- molecular weight of the gas
- Blood volume and Hb concentration
- lung volume
3 means/forms in which CO2 is transported in the blood?
- Dissolved
- Combines with Hemoglobin (Hb)
- as Bicarbonate (HCO3-)
Does CO2 diffuse quicker than oxygen? True or False
True (CO2 is more soluble)
What is the measure of the resistance to gas flow through an airway?
Airway Resistance (Raw)
What are factors that influence airway resistance?
- Length of tube
- Radius of the tube
- Driving pressure
- Viscosity of gas
Expiratory flow
- dependent on lung volumes
- the higher the lung volume, the greater the airflow
For example: - you can cough harder if you inhale first (Try coughing without inhaling first)
How distensible or elastic the lung is? The elastic properties of the lungs?
Lung compliance
Compliance equation
Compliance = volume change per unit pressure
Reduced compliance means…
stiffer lungs
Increased compliance means…
floppy lung
Alveoli are supported by?
Surfactant and Interdependence
What is Interdependence?
- interdependence what we call the alveoli attached and are working together to support each other
- if one of the alveoli collapses - the expansion of other alveoli exerts a pull on the collapsed ones which may assist in their re-expansion
What is Collateral Ventilation?
- alveoli are interconnected in which the alveoli can be ventilated through a different passage
- alternate pathways of ventilation between adjacent alveoli
Amount of time it takes for an alveoli (or region of lung to distend? It is also related to lung stiffness (Compliance) and resistance to airflow
Time constants
For normal lungs at normal lung volume, the dependent lung receives?
- greater ventilation
-Note: Dependent lung is lower lung region
When side lying, what is the dependent lung?
- the lung at the bottom
In upright sitting - the lungs dependent is the…
“bases” (lowest parts of middle and lower lobes)
For normal lungs at low volume which is a lot easier to expand? Non-dependent or dependent
Non dependent (it is more compliant and therefore is better ventilated
Is perfusion gravity dependent in the lung (true or false)
True - Ie more at the bottom
At the top of the lungs - the capillaries may be squashed
At the Bottom - capillaries may squash alveoli
What do you call when ventilation and perfusion does not match?
V/Q mismatch
- V/Q mismatch results in a drop in PaO2
what is the perfect V/Q
1
V/Q match in the Apex of the lung
Better Ventilation (V) than Perfusion(Q) >1
V/Q match in the Middle of the lung
even ventilation (V) and Perfusion (Q) = 1
V/Q match in the Bottom of the lung
better perfusion (Q) than ventilation (V) <1
