Pathophysiologies Of The Lung Flashcards
Why does Type 1 respiratory failure happen?
Due to V/Q mismatching
- lung / vascular disease
- fall in oxygen, normal / low carbon dioxide
Why does Type 2 respiratory failure happen?
- dependent on only ventilation
- depends on tidal volume of air
- respiratory rate
- resistance of airways
- compliance of lungs
- fall in oxygen, high levels of carbon dioxide
- decreased ventilation
Summary of Type 1 respiratory failure:
- partial pressure of oxygen < 60mmHg
- hypoxaemia, normal / low carbon dioxide
V/Q mismatch:
Underventilated alveoli = pulmonary oedema, pneumonia
Venous blood bypasses the ventilated alveoli = right to left cardiac shunts
- hyperventilation increases carbon dioxide removal
- does not increase oxygenation
- as blood leaving the unaffected alveoli is fully saturated
Causes of type 1 respiratory failure:
- pneumonia
- pulmonary oedema
- pulmonary fibrosis
- asthma
- pneumothorax
- pulmonary embolism
- pulmonary hypertension
- bronchiectasis
- ards
- obesity
- copd
Summary of type 2 respiratory failure:
- partial pressure of carbon dioxide > 50mmHg
- not enough ventilation in alveoli
- too much carbon dioxide in the blood = hypercapnia
- hypoxemia & hypercapnia
Causes of type 2 respiratory failure:
- copd
- reduced ventilation = sedative overdose
- reduced neuromuscular power = myopathy
- resetting of chemoreceptors that drive ventilation in chronic lung disease = copd
Clinical investigations for type 1/2 respiratory failure:
- good history
Clinical examinations:
- breathlessness
- wheeze
- cough
- sputum
- chest pain
- if haemoptysis = further investigation = cancer, bronchitis, tuberculosis
- then a chest x-ray happens
What do pulmonary function tests do?
- central to diagnosis
- allow quantification and severity to be diagnosed, monitoring of disease
Total volume contained in the lung - the subdivisions, they do not:
- overlap
- cannot be fully divided
- when they are added together, they equal the total lung capacity
Tidal volume
The volume of air moved during normal quiet breathing
Inspiratory reserve volume
The volume of air that can be forcefully inspired following a normal quiet inspiration
Expiratory reserve volume
The volume of air that can be forcefully expired after a normal / resting expiration
Residual volume
The volume of air remaining in the lungs after a forceful expiration
Vital capacity
Volume of air that can be forcibly blown out after full inspiration
Inspiratory capacity
The amount of air that the lungs will hold after a normal expiration
= inspiratory reserve + tidal volume
Functional residual capacity
The amount of air remaining in the lungs after a normal quiet expiration
= expiratory reserve volume + residual volume
What is FEV1?
The volume exhaled during the first second of a forced expiratory manouvere, starting from the level of total lung capacity
What is FVC?
- forced vital capacity
- starts with full inspiration
- the patient blows out very fast & hard until the lungs are completely empty
What are FEV1 & FVC used for?
- assessing airway obstruction / restriction
- standard index for assessing and quantifying airflow limitation
%FEV1 / FVC =
80% normally
Decrease = obstruction
What is an obstructive disease? (Summary)
- increase in resistance
- normal breathing = pressure and volume is like a normal lung
- rapid breathing = greater pressure is needed to overcome the resistance to flow, as the volume of each breath is smaller
- at the end of a full exhalation = abnormally high amount of air lingers in the lungs, which is air trapping
- as they have to increase their effort to breath, this over-distends the lungs
What are some obstructive diseases?
- asthma
- copd
- bronchitis
- emphysema
- cystic fibrosis
Relationship with lung data & obstructive disease:
- FEV1 = reduced = increased airway resistance to expiratory flow
- FVC = reduced, but not as much
- lower FEV1/FVC ratio = <80%
Summary of restrictive disease:
- lung compliance is reduced = increases stiffness of the lung & limits expansion
- greater pressure than normal is required to give the same increase in volume of the lungs
Examples of restrictive disease / causes:
- pulmonary fibrosis
- pneumonia
- pulmonary oedema
- sarcoidosis
Relationship of lung function data and restrictive disease:
- FEV1 & FVC are reduced proportionally
- normal / increased FEV1/FC ratio
What is the difference between obstructive and restrictive lung disease?
Obstructive:
- makes it harder to breathe during exercise
- as the rate of breathing increases, there is less time to breathe the air out before the next inhalation
Restrictive:
- cannot fully fill the lungs with air
- lungs are restricted from fully expanding
Asthma - what is it?
- airway inflammation
- increased airway unresponsiveness
- results in airway obstruction
Symptoms of asthma:
- wheeze
- cough
- shortness of breath
- variable & reversible
Well controlled asthmatics are:
- asymptomatic
- normal lung function
What happens during an asthma attack?
- bronchospasm
- mucus plugging
- oedema in peripheral airways
- increased airway resistance & obstruction
- lung hyperventilation
- V/Q mismatch
- increased in ventilation due to hypoxemia
Why does respiratory alkalosis occur?
- hyperventilation
- obstructed lungs being less numerous than unobstructed
- carbon dioxide removal via the fast compartment
- as the attack progresses, there is an increase in obstruction
- decrease ability for carbon dioxide removal
- raised levels of carbon dioxide
Life threatening asthma attack summary:
- doesn’t respond to the use of bronchodilators
- associated with symptoms of potential respiratory failure = status asthmaticus
Symptoms of asthma attack - life threatening:
- persistent shortness of breath
- inability to speak full sentences
- increased respiration and pulse rate
- normal or raised partial pressure of carbon dioxide
- severe hypoxia
- oxygen saturation under 92%
- low blood pH
Emphysema:
- heart has to pump more blood
- strains the heart
- causes heart failure
What can sedentary lifestyle lead to?
- obesity
- type 2 diabetes
COPD summary:
- breathing problems get worse over time as the surface area for gas exchange in the lungs decreases
1. Increased resistance to airflow caused by airway narrowing
2. Airway inflammation, thickening of airway wall
3. Accumulation of mucous secretions obstructs the airway lumen
4. Destruction of alveoli = loss of elastic recoil, no outwards traction, they collapse when expiration occurs
Symptoms & progression of COPD:
- at first, only symptom = smokers cough
Progresses to = cough with sputum, wheeze, breathlessness, more chest infections, infections increase in severity & duration - until a cough is constantly present
- increased breathlessness on exertion
- affects daily aspects of life
- end stage = bed bound, oxygen for several hours a day
Classification of severity of COPD:
- post-bronchodilator spirometery
- mild
- moderate
- severe
- very severe
Mild
> 80%
Moderate
50-79%
Severe
30-49%
Very severe
<30% of predicted FEV1 percentage of mean predicted value
What is elevated in COPD?
- total lung capacity
- residual volume
= hyperinflation & air trapping
Pulmonary embolism summary:
- blood clot forms in the femoral vein, breaks free, travels to heart
- embolus travels through the heart and blocks a blood vessel in the lung
- loss of capillary flow = shuts down all alveoli
- limits the ability of lungs to give oxygen to the blood
- results in = large V/Q ratio due to dead space
Signs and symptoms of pulmonary embolism:
- chest pain & breathlessness
- reduced PAO2 & PACO2 = hypoxia = respiratory alkalosis
- pleural bloody effusion
- hypoperfusion on a chest x-ray
- positive pulmonary angiogram = gold standard
- tachycardia = only way to tell
