Lou's Pathophysiology Flashcards
Does ventilatory capacity limit healthy people during exercise?
No, HR does
What are the mechanical changes that occur due to pulmonary oedema?
Decrease lung compliance - fluid makes the increases the elastic work of breathing
Decrease lung volume - lungs are harder to expand
Increased airway resistance - due to fluid in the airways
Increased work of breathing (elastic and resistive)
What is the clinical presentation of abestosis?
Progressive breathlessness and cough
Crepitations (the type due to opening of alveolar during inspiration)
Clubbing
+/- Cyanosis
Why is systolic BP lower during inspiration
Negative interthoracic pressure > expands the compliance of pulmonary vasculature > blood pools there > reduces pulmonary return > SV is lower > BP is lower (the body response by increase HR).
What are some causes of increase pulmonary hydrostatic pressure?
Left ventricular failure,
mitral stenosis
fluid overload
pulmonary veno-occlusive disease
What causes pulmonary hypertension?
- Increase LA pressure - eg mitral stenosis, left heart failure
- Increased pulmonary blood flow - eg excess central volume
- Increased pulmonary vascular resistance - eg vasocontriction,
vasculature damage (emphysema), obstruction (PE)
What are 5 causes of hypoventilation?
Motor centre depression
Neuromuscular disease
Chest wall deformities
Obesity
Sleeping disordered breathing
What is MUD?
Medically undiagnosed dyspnoea
Why does obstruction occur during sleep?
- Muscles relax
- Airway is already narrowed (obesity, tonsils)
- Tongue falls back (esp if suprine)
What happens to residual volume with gas trapping?
It increases
Why is a low V/Q match bad?
Hb arrives at alveolar-capillary but isn’t filled with O2 > reduces PaO2 > hypoxaemia
What levels of PaCO2 occur during respiratory failure?
>60mmHg
How thick is the A-C membrane?
0.5 microns
When does diffusion limitation of CO2 occur?
Only if there is very severe diffusion impairment, inadequate ventilation is the primary cause
Generally, conditions that effect the alveolar membrane make the lungs …
Stiffer - increasing the elastic work of breathing
Except in Emphysema
How does metabolic acidiosis occurs due to pulmonary oedema?
Pulmonary oedema (=low gas exchange) therefore tissue hypoxia - anaerobic resp. - lactic acid - metabolic acidosis.
What physiological differences are present when breathing with an obstruction?
Active exhalation
Slower inhalation and exhalation
Reduction in maximum ventilation
Increased work of breathing/use of respiratory muscles
Increased sensation of breathing
What does anxiety do to the respiratory equilibrium?
Anxiety > hyperventilation > PaCO2 drop > pH Increases = Respiratory alkalosis
What diseases can disrupt the A-C membrane?
Infections - TB, pneumonia
Pneumonitis (inflammation of the alveoli) eg drug induced
Pulmonary fibrosis
Emphysema
Oedema
Lymphangitis
Carcinomatosis
What happens to maximum ventilation in restrictive lung disease?
It decreases
What is type I respiratory failure characterized by?
Low PaO2
What is type II respiratory failure characterised by?
PaCO2 >50mmHg and PaO2 low to normal
due to failure of ventilation
What is the normal lymphatic flow rate in the lung?
20ml/hour
What factors determine the compliance of the lungs?
Tissue composition
Surfactant
True or false, ventilation rate is higher dependent of PaO2?
False, PaO2 must drop below 60 before there is a response
What are the gas exchange changes that occur due to pulmonary oedema?
hypoxaemia due to shunt
Low V/Q units
Diffusion impairment
What makes up the alveolar-capillary membrane?
Layer of surfactant
Type I alveolar cell
Basement membrane
Endothelial cell
What is breathlessness?
Breathlessness arises when there is a recognition by the subject of an inappropriate relationship between respiratory work and total body work
What is a negative consequence of the vasocontrictory compensation of V/Q mismatch?
Increases pulmonary pressure if V/Q mismatch is wide spread
Which occurs more readily interstitial or alveolar oedema?
Interstitial as capillary endothelium is more permeable to water cf to alveolar wall (and water enters the interstitium first)
Does the pulmonary arterial pressure increase during exercise?
No, due to dilation and recruitment of extra pulmonary vessels
What is acute respiratory failure defined as?
The failure of the respiratory system to provide adequent ventilation, oxygenation or metabolic requirements of the patient
What is the problem with giving O2 to people with chronic hypercapnoea?
Their resp centre responds to PaO2 so if it is increased too much that can stimulate hypoventilation > further hypercapnoea
What is the normal range of A-a gradients?
15-30
What are the consequences of obstructive lung disease?
Recruitment of accessory muscles
Increase consumption of O2 by respiratory muscles
Possible fatigue of respiratory muscles
What is the A-a gradient a measure of?
Alveolar/capillary gas exchange across all A-C units
What are the mechanical effects of restrictive lung disease?
Breathlessness
Increase elastic work of breathing
Reduced lung volume
Shorter, faster breaths
Reduced maximum volume
- Increase use of inspiratory muscle and O2 comsuption by them
What are the pulmonary artery pressures during systole and diastole
25/8, mean=15mmHg
What occurs during sleep apnoea?
Fall asleep >
Muscle relaxation >
Complete Obstruction >
Fall in PaO2 and increase in PaCO2 >
Brains wakes >
Muscle contract, airway re-opens >
Fall into deep sleep again
What is lung compliance?
Change in V / Change in P
What is the consequence of chronic sleep disorders?
Physiological change occurs to facilitate sleep > Re-set the resp centre to be able to tolerate a higher PaCO2 so that sleeping can occur > chronic hypercapnoea > PaO2 becomes the driver for ventilation
What are the possible causes of high PaCO2
Predominately low ventilation
What are some symptoms of sleep apnoea?
Snoring
Arousals
Choking
Excessive daytime sleeping, lTethargy, reduced libido, mood change, poor memory
Difficult to treat hypertension and unexplain resp failure
What is gas trapping?
The obstruction of exhalation of gas due to a severe obstruction. Air is inhaled but can’t be exhaled
What is Fick’s law?
Determines the rate of diffusion of a gas
What is pulsus paradoxus?
When the difference in systolic BP between inspiration and expiration is greater.
What is the equation for A-a gradient?
PAO2 = PiO2 - PACO2/RQ
followed up PAO2 - PaO2
Where
RQ is a constant = 0.8
PiO2 (partial pressure of inspired air) for room temp and sea level = 150
PACO2 is assumed to equal PaCO2 which is measured in arterial blood gas
And PaO2 is also measured in arterial blood gases
What happens to perfusion if ventilation drops in a local area?
Compensatory drop due to divertion of blood flow in capillaries
What are some management strategies for sleep apnoea?
Nasal CPAP (continue positive airway pressure)
Manibular advancement splint
Surgery
Lie on side
What percentage of FVC (forced vital capacity) is expelled in a normal FEV1
80%
What some possible causes of MUD?
Psychologenic
Deconditioned (got fat)
New clinical disease
Maximal effort
What causes wheezing?
Airway obstruction
When does diffusion limitation of O2 occur?
In heathly people: Never
People with mild diffusion impairment: during exercise
People with a severe diffusion impairment: at rest and during exercise
What percentage of total O2 usage is required for the WOB at rest?
3%
Which has a greater impact on lung mechanic and gas exchange, fluid in the alveoli or interstitial space?
Alveoli!
What is the mechanism of asbestosis?
Chronic inflammation > progressive fibrosis > disruption and destruction to A-C membrane > Mechanical and gas exchange defect = Decrease PaO2, Increase A-a gradient, Reduced lung volume, reduced compliance, Increased work of breathing
When is breathlessnees a symptom not a sensation?
When it occurs when it shouldn’t normally, when it doesn’t usually occur for that level of exertion.
What does surfactant do?
It lower surface tension in alveoli to prevent them from collapsing, increases the compliance of the lung and keeps the alveoli dry.
The respiratory centre sends the majority of its output via which nerve?
Phrenic
What are the possible causes of low PaO2?
Low PiO2
Low Ventilation
Gas exchange abnormality - V/Q mismatch, shunt, A-C membrane problem
What type of lung disease is asbestosis?
Restrictive
What is the consequence of high V/Q mismatch?
Physiological dead space with little effect on PaO2
Where in the brain is the respiratory centre located?
The pons and medulla
How does airway obstruction increase the WOB?
It increases the resistive WOB, ie the work required to overcome the friction of airflow. (As opposed to an increase elastic work of breathing that occurs with restrictive lung disease)
What are some causes of increase pulmonary capillary permeability?
Toxins, sepsis, multiple trauma
What happens to total lung capacity with gas trapping?
It increases
