Lung Physiology Flashcards
What is PaC02?
Arterial CO2
What is PACO2?
Alveolar CO2
What is PaO2?
Arterial O2
What is PAO2?
Alveolar O2
What is PiO2?
Pressure of inspired O2
What is VA?
Alveolar Ventilation
What are equations for CO2 elimination and oxygenation
PaCO2 = k v̇CO2 / v̇A
PAO2 = PiO2 – PaCO2/R (Alveolar Gas Equation)
R=Respiratory Quotient (approx 0.8)
What is the equation for carbonic acid equilibrium?
Carbonic acid equilibrium
CO2 + H2O H2CO3 H+ + HCO3-
Carbonic anhydrase
What is the Henderson-Hasselbach equation?
pH=6.1 + log10[[HCO3-]/[0.03*PCO2]]
What is FEV1?
Forced expiratory volume in one second (litres)
What is FVC?
Forced Vital Capacity (litres)
How do you plot a graph for forced expiration?
Volume/Time plot
What is TLC?
Breathe in to total lung capacity
What is RV?
Exhale as fast as possible to residual volume
What is FVC?
Volume produced is the vital capacity
How to plot a forced expiration (flow/volume) graph?
Take the exact same procedure
Re plot the data showing flow as a function of volume
PEF; peak flow
FEF25; flow at point when 25% of total volume to be exhaled has been exhaled
FVC; forced vital capacity
What is PEF?
Peak expiratory flow (rate)
Single measure of highest flow during expiration
Peak Flow Meter, spirometer
Gives reading in L/min
Very effort dependent
May be measured over time, by giving a patient a PEF meter and chart
Give ways to measure RV and TLC?
Gas dilution
Body box (total body plethysmography; shown)
What is Gas Dilution?
Measurement of all air in the lungs that communicates with the airways
Does not measure air in non-communicating bullae
Gas dilution techniques use either closed-circuit helium dilution or open-circuit nitrogen washout.
Usually, the patient is connected at the end-tidal position of the spirometer, measuring FRC
What is the nitrogen-washout technique?
In the nitrogen-washout technique, the patient breathes 100% oxygen, and all the nitrogen in the lungs is
washed out.
The exhaled volume and the nitrogen concentration in that volume are measured.
The difference in nitrogen volume at the initial concentration and at the final exhaled concentration allows a calculation of intrathoracic volume, usually FRC.
What is total body plethysmography?
Alterative method of measuring lung volume, (Boyle’s law), including gas trapped in bullae.
From the FRC, patient “pants” with an open glottis against a closed shutter to produce changes in the box pressure proportionate to the volume of air in the chest.
The volume measured (TGV) represents the lung volume at which the shutter was closed
FRC, inspiratory capacity, expiratory reserve volume, vital capacity all measured
From these volumes and capacities, the residual volume and total lung capacity can be calculated.
What is the equation for Total Lung Capacity (TLC)?
TLC = VC+RV
Explain Transfer estimates?
Carbon monoxide used to estimate DLCO, as it has high affinity for binding to haemoglobin
DLCO is an overall measure of the interaction of;
- alveolar surface area
- alveolar capillary perfusion
- physical properties of the alveolar capillary interface
- capillary volume
- haemoglobin concentration, and the reaction rate of carbon - monoxide and hemoglobin.
Single 10 second breath-holding technique
10% helium, 0.3% carbon monoxide, 21% oxygen, remainder nitrogen.
Alveolar sample obtained;
DLCO is calculated from the total volume of the lung, breath-hold time, and the initial and final alveolar concentrations of carbon monoxide.
What is the compliance lung?
Compliance of the lung
Change in volume per unit change in pressure gradient between the pleura and the alveoli; (transpulmonary pressure)
Can be measured during breath-hold;
STATIC COMPLIANCE
Can be measured during regular breathing;
DYNAMIC COMPLIANCE
What is Static Compliance?
A measure of distensibility
A lung of high compliance expands more than one of low compliance when exposed to same trans-pulmonary pressure
What is Dynamic Compliance?
Measured during tidal breathing at end of inspiration and expiration when lung is apparently stationary
Similar to static compliance in normal lungs
Reduced compared to static compliance in airway obstruction
What is the requirement of respiration?
Requirement is to
- Ensure haemoglobin is as close to full saturation with oxygen as possible
- Efficient use of energy resource
- Regulate PaCO2 carefully
- variations in CO2 and small variations in pH can alter physiological function quite widely
What is Respiration?
Breathing is automatic
- No conscious effort for the basic rhythm
Rate and depth under additional influences
- Depends on cyclical excitation and control of many muscles
Upper airway, lower airway, diaphragm, chest wall
Near linear activity
Increase thoracic volume
Explain the basic breathing rhythm?
Pons
- Pneumotaxic and Apneustic Centres
Medulla Oblongata
- Phasic discharge of action potentials
Two main groups
- Dorsal respiratory group (DRG)
- Ventral respiratory group (VRG)
Each are bilateral, and project into the bulbo-spinal motor neuron pools and interconnect
What is DRG?
DRG; predominantly active during inspiration
What is VRG?
VRG; active in both inspiration and expiration
What is Central Pattern Generator?
Neural network (interneurons)
Located within DRG/VRG
- Precise functional locations not known
- Start, stop and resetting of an integrator of background ventilatory drive
Explain what happens in inspiration
- Progressive increase in inspiratory muscle activation
Lungs fill at a constant rate until tidal volume achieved
End of inspiration, rapid decrease in excitation of the respiratory muscles
Explain what happens in expiration
- Largely passive due to elastic recoil of thoracic wall
First part of expiration; active slowing with some inspiratory muscle activity
With increased demands, further muscle activity recruited
Expiration can be become active also; with additional abdominal wall muscle activity
What are chemoreceptors?
- Central (60% influence from PaCO2) and peripheral (40% influence from PaCO2)
- Stimulated by [H+] concentration and gas partial pressures in arterial blood
- Brainstem [primary influence is PaCO2]
- Carotids and aorta [PaCO2, PaO2 and pH]
- Significant interaction
What is the general rule of minute ventilation?
Proportional to PaCO2 and 1 / PaO2
What are central chemoreceptors?
- Central is located in brainstem
- Pontomedullary junction
- Not within the DRG/VRG complex
- Sensitive to PaCO2 of blood perfusing brain
- Blood brain barrier relatively impermeable to H+ and HCO3-
- PaCO2 preferentially diffuses into CSF
Where are peripheral chemoreceptors found?
These are located in;
- Carotid bodies
Bifurcation of the common carotid
IX cranial nerve afferents
- Aortic bodies
Ascending aorta
Vagal nerve afferents
What are peripheral chemoreceptors?
Responsible for [all] ventilatory response to hypoxia (reduced PaO2)
Generally not sensitive across normal PaO2 ranges
When exposed to hypoxia, type I cells release stored neurotransmitters that stimulate the cuplike endings of the carotid sinus nerve
Linear response to PaCO2
Interactions between responses
[Poison (e.g. cyanide) and blood pressure responsive]
What are lung receptors?
Stretch, J and irritant
Afferents; vagus (X)
Combination of slow and fast adapting receptors
Assist with lung volumes and responses to noxious inhaled agents
What is a stretch lung receptor?
Stretch
- Smooth muscle of conducting airways
- Sense lung volume, slowly adapting
What is an irritant lung receptor?
- Larger conducting airways
- Rapidly adapting [cough, gasp]
What is an J; juxtapulmonary capillary lung receptor?
- Pulmonary and bronchial C fibres
What are the different types of airway receptors?
Nose, nasopharynx and larynx
- Chemo and mechano receptors
- Some appear to sense and monitor flow
Stimulation of these receptors appears to inhibit the central controller
Pharynx
- Receptors that appear to be activated by swallowing
respiratory activity stops during swallowing protecting against the risk of aspiration of food or liquid
What are muscle proprioceptors?
Joint, tendon and muscle spindle receptors
Intercostal muscles > > diaphragm
Important roles in perception of breathing effort
What is a spirometry?
Functional test of the lungs.
The most important spirometry test is the FVC (Forced Vital Capacity).
Other tests include the CV (Vital Capacity or Slow Vital Capacity) and MVV (Maximum Voluntary Ventilation).
What is Forced Vital Capacity?
The Forced Vital Capacity consists of a forced expiration in the spirometer.
The patient either sits or stands.
He inspires fully and expires all the air out of the lungs as fast as he can.
The results of the test are compared to the predicted values that are calculated from his age, size, weight, sex and ethnic group.
Two curves are shown after the test: the flow-volume loop and volume-time curve.
How much does a healthy patient expire in the first second during the FVC manoeuvre?
Approximately 80% of all the air out of their lungs
What is a Slow Vital Capacity?
This test resembles the FVC.
The difference is that the expiration in the spirometer is done slowly.
The patient inspires fully and than slowly expires all the air in his lungs (Inspiratory Vital Capacity) or the other way around: the patient expires fully and inspires slowly to a maximum (Expiratory Vital Capacity).
How much of the lung capacity is residual volume?
About 20-25% of lung capacity
What is Maximum Voluntary Ventilation?
For this test the patient inspires and expires in the spirometer over and over again as fast as he can, during at least 12 seconds.
This is no longer a very common test as it can be dangerous for some people.
Sometimes the MVV is still done in athletes.
What is respiratory failure?
Failure of gas exchange
Inability to maintain normal blood gases
Low PaO2
With or without a rise in PaCO2
Respiratory failure can occur with normal or abnormal lungs
What are the different types of respiratory failure?
Acute, rapidly
- For example; opiate overdose, trauma, pulmonary embolism
Chronic, over a period of time
- For example; COPD, fibrosing lung disease
What is a respiratory quotient?
Ratio of the volume of carbon dioxide (CO2) produced to the volume of oxygen (O2) used
What is Type 1 Respiratory Failure?
- Most pulmonary and cardiac causes produce type I failure
- Hypoxia
Mismatching of ventilation and perfusion
Shunt
Diffusion impairment
Alveolar hypoventilation
Similar effects on tissues seen with
Anaemia
CO poisoning
methaemoglobinaemia
What are cases of Type 1 Respiratory Failure?
- Infection
Pneumonia
Bronchiectasis - Congenital
Cyanotic congenital heart disease - Neoplasm
Lymphangitis carcinomatosis - Airway
COPD
Asthma - Vasculature
Pulmonary embolism
Fat embolism - Parenchyma
Pulmonary fibrosis
Pulmonary oedema
Pneumoconiosis
Sarcoidosis
What are mechanisms of Type 2 Respiratory Failure?
Mechanisms
(i) Lack of respiratory drive
(ii) Excess workload
(iii) Bellows failure
What are the causes of Type 2 Respiratory Failure?
- Airway
COPD
Asthma
Laryngeal oedema
Sleep apnoea syndrome - Drugs
Suxamethonium - Metabolic
Poisoning
Overdose - Neurological
Central
Primary hypoventilation
Head and Cervical spine injury - Muscle
Myasthenia
Polyneuropathy
Poliomyelitis
Primary muscle disorders
Clinical Features of Hypoxia
- Central Cyanosis
Oral cavity
May not be obvious in anaemic patients - Irritability
- Reduced intellectual function
- Reduced consciousness
- Convulsions
- Coma
- Death
Clinical Features of Hypercapnia
- Variable patient to patient
- Irritability
- Headache
- Papilloedema
- Warm skin
- Bounding pulse
- Confusion
- Somnolence
- Coma
What is treatment for Type 2 respiratory failure?
Assisted ventilation
Invasive
Non invasive
Inadequate PaO2 despite increasing FiO2
Increasing PaCO2
Patient tiring
What are oxygen treatments?
Treatment for serious illnesses needing high levels of O2
5-10 litres/min face mask or 2-6 litres/min nasal cannulae
Aim for SpO2 of 94-98%
If saturation <85% and not at risk of hypercapnic respiratory failure
10-15 litres/ min reservoir mask
Patients with COPD and other risk factors for hypercapnia;
Aim for SpO2 of 88-92% pending blood gases
Adjust to SpO2 of 94-98% if CO2 normal unless previous history of high CO2 or ventilation
What is the requirement of the respiratory pump?
Requirement to move 5 litres / minute of inspired gas [cardiac output 5 litres / min]
What is the respiratory pump?*
Generation of negative intra-alveolar pressure
Inspiration active requirement to generate flow
Bones, muscles, pleura, peripheral nerves, airways all involved.
Bony structures support respiratory muscles and protect lungs.
Rib movements; pump handle and water handle
What are the muscles used in respiration?
Muscles of respiration
- Inspiration
Largely quiet and due to diaphragm (C3/4/5) contraction
External intercostals (nerve roots at each level)
- Expiration
Passive during quiet breathing
What is the pleura?
Pleura
- 2 layers, visceral and parietal
- Potential space only between these, few millilitres of fluid
What nerves are used in the respiratory pump?
Nerves
- Sensory;
Sensory receptors assessing flow, stretch etc..
C fibres
Afferent via vagus nerve (10th cranial nerve)
- Autonomic sympathetic, parasympathetic balance
What is meant by static lungs?
Both chest wall and lungs have elastic properties, and a resting (unstressed) volume
Changing this volume requires force
Release of this force leads to a return to the resting volume.
Pleural plays an important role linking chest wall and lungs.
What is Ventilation?
VENTILATION; Bulk flow in the airways allows;
O2 and CO2 movement
Large surface area required, with minimal distance for gases to move across. Total combined surface area for gas exchange 50-100 m2
300,000,000 alveoli per lung
What is perfusion?
PERFUSION; Adequate pulmonary blood supply also needed
What is alveolar ventilation?
Dead space
Volume of air not contributing to ventilation
Anatomic; Approx 150mls
Alveolar; Approx 25mls
Physiological
(Anatomic+Alveolar) = 175mls
What is bronchial circulation? *
Blood supply to the lung; branches of the bronchial arteries
Paired branches arising laterally to supply bronchial and peri-bronchial tissue and visceral pleura
Systemic pressures (i.e. LV/aortic pressures)
Venous drainage; bronchial veins draining ultimately into the superior vena cava
What is pulmonary circulation?
Left and right pulmonary arteries run from right ventricle
Low(er) pressure system (i.e. RV / pulmonary artery pressures)
17 orders of branching
Elastic (>1mm ) and non elastic
Muscular (<1mm )
Arterioles (<0.1mm )
Capillaries
What is the broncho-vascular bundle?
Pulmonary artery and bronchus run in parallel
What is the normal pulmonary artery pressure?
24mm/10mm
How many capillaries are there per alveolus?
1000
What is alveolar perfusion?
Each erythrocyte may come into contact with multiple alveoli
Erythrocyte thickness an important component of the distance across which gas has to be moved
At rest, 25% the way through capillary, haemoglobin is fully saturated
What does perfusion of the capillaries depend on?
Pulmonary artery pressure
Pulmonary venous pressure
Alveolar pressure
What is hypoxic pulmonary vasoconstriction?
A homeostatic mechanism that is intrinsic to the pulmonary vasculature
Intrapulmonary arteries constrict in response to alveolar hypoxia, diverting blood to better oxygenated lung segments, thereby optimizing ventilation/perfusion matching and systemic oxygen delivery
What is meant by perfusion?
Blood Supply
What is meant by little a in nomenclature?
Arterial
What is meant by big A in nomenclature?
Alveolar
Why is it important for the body to maintain pH?
Body maintains close control of pH to ensure optimal function (e.g. enzymatic cellular reactions)
Dissolved CO2/carbonic acid/respiratory system interface crucial to the maintenance of this control
What is normal pH level in the body?
7.40
What is normal H+ body concentration?
40nmol/l [34-44 nmol/l]
Explain the sigmoid shape in the O2Hb dissociation curve?
As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (cooperative binding)
What are the varying influences of O2/Hb dissociation curve?
2,3 diphosphoglyceric acid
H+
Temperature
CO2
What buffer is particular important?
Carbonic acid / bicarbonate buffer
What is HCO3- under predominant control of?
Renal Control (less rapid)
What is CO2 under predominant control of?
Respiratory Control (rapid)
What are the 4 main acid-base disorders?
Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis
What is respiratory acidosis?
Increased PaCO2
Decreased pH
Mild increased HCO3-
What is respiratory alkalosis?
Decreased PaCO2
Increased pH
Mild decreased HCO3-
What is metabolic acidosis?
Reduced bicarbonate
Decreased pH
What is metabolic alkalosis?
Increased bicarbonate
Increased pH
What do expiratory procedures measure?
Only measure VC not RV
Where are central chemoreceptors located?
Brainstem
- Pontomedullary junction
- Not within the DRG/VRG complex
What are central chemoreceptors sensitive to?
- Sensitive to PaCO2 of blood perfusing brain
- Blood brain barrier relatively impermeable to H+ and HCO3-
- PaCO2 preferentially diffuses into CSF
Where are peripheral chemoreceptors located?
- Carotid bodies
Bifurcation of the common carotid
(IX) cranial nerve afferents - Aortic bodies
Ascending aorta
Vagal (X) nerve afferents
What are peripheral chemoreceptors?
Responsible for [all] ventilatory response to hypoxia (reduced PaO2)
Generally not sensitive across normal PaO2 ranges
When exposed to hypoxia, type I cells release stored neurotransmitters that stimulate the cuplike endings of the carotid sinus nerve
What type of response do peripheral chemoreceptors have to PaCO2?
Linear Response
Interactions between responses
[Poison (e.g. cyanide) and blood pressure responsive]
What is respiratory failure?
Inability to maintain normal blood gases
What is Hypoxemia?
Below normal level of O2 in blood
PaO2 less than 8kPa
What is Hypercapnia?
Too much CO2 in the blood
More than 6.5kPa
What is Type 1 respiratory failure?
Hypoxia
Low/Normal CO2
What is Type 2 respiratory failure?
Hypoxia
Hypercapnia
What are treatments for Type 1 resp failure?
Airway Patency
Oxygen Delivery
