Physiology Flashcards
Which systems can be involved in shortness of breath?
Respiratory
Cardiovascular
Haem (anaemia)
Endocrine (DKA)
Psychiatric (anxiety)
many more causes
Shortness of breath may be ___ or ___.
acute or chronic
What are some respiratory causes of shortness of breath?
Asthma
COPD
Pneumonia
Lung cancer
Pulmonary embolism
Pulmonary fibrosis
Interstitial lung disease
…
What are some cardiovascular causes of shortness of breath?
Ischaemic heart disease (angina > MI spectrum)
Hypertension
Valvular disease
Cardiomyopathy
Arrhythmias
Where generally are the body’s respiratory centres found?
Brainstem
Neurons in which parts of the brainstem control the
a) rhythm of respiration
b) inspiration / expiration modifications?
a) Medulla
b) Pons
Which group of receptors detects the H+ concentration of the CSF?
Central chemoreceptors
Which group of receptors detect the oxygen, CO2 and H+ concentrations of the blood?
Where are they found?
Peripheral chemoreceptors
Common carotid arteries and Arch of the aorta
What is an increase in CO2 concentration called?
Hypercapnia
How does CO2 reach the central chemoreceptors?
Via blood brain barrier
In what form do the central chemoreceptors detect CO2 in the CSF?
H+
Which chemoreceptors detect the oxygen concentration of the blood?
Peripheral chemoreceptors
Which receptors detect
a) hypercapnia via an increased H+ conc. in the CSF
b) hypoxia via a decreased O2 conc. in the blood?
a) Central chemoreceptors
b) Peripheral chemoreceptors
What is the main driver of respiration?
Effect of increased [CO2] on central chemoreceptors
The central chemoreceptors are the main drivers of respiration.
What are two peripheral chemoreceptor drivers of respiration?
Hypoxic drive
H+ drive
At which partial pressure of oxygen do the peripheral chemoreceptors trigger an increased rate of respiration - hypoxic drive?
< 60 mm Hg
Which muscles control the inflation and deflation of the lungs?
Respiratory muscles
How do signals reach the respiratory muscles from the chemoreceptors?
Peripheral nerves to intercostal muscles
Phrenic nerve (C3,4,5) to diaphragm
Contraction of which muscle increases the vertical dimensions of the thorax?
Diaphragm
C3,4,5
Contraction of which muscles increases the horizontal diameter of the thorax?
External intercostal muscles
What are the major muscles of respiration?
Diaphragm
External, internal and innermost intercostal muscles
What are some accessory muscles of respiration?
SCM
Scalenus anterior
Pectoralis major
Pectoralis minor
Latissimus dorsi
___ pressure is usually greater than ___ pressure.
(intra-pleural , intra-alveolar)
Intra-alveolar pressure > Intrapleural pressure
i.e the pressure WITHIN the airways is > the pressure in the pleural cavity
What is the difference between intra-alveolar and intrapleural pressure called?
Transmural pressure gradient
Why is maintaining the transmural pressure gradient important?
What can cause it to be abolished?
Allows lungs to stick to pleura during thorax expansion and collapse
Pneumothorax
What is a pneumothorax?
Air within the pleural space
Abolishes the transmural pressure gradient
Which substance is produced by Type II pneumocytes and opposes alveolar surface tension?
Pulmonary surfactant
What is the main factor contributing to airway resistance?
Airway radius
Airway ___ is the main determinant of resistance to air flow.
Airway radius
What causes bronchoconstriction?
Parasympathetic impulses
What causes bronchodilation?
Sympathetic impulses
During inspiration, the diaphragm moves (up / down).
down
to increase vertical dimensions of the thorax
reducing intra-alveolar pressure
encouraging air to move into the lungs from the greater atmospheric pressure, down the pressure gradient
During expiration, the diaphragm moves (up / down).
up
to decrease vertical dimensions of the thorax
increasing intra-alveolar pressure
encouraging air to move out of the lungs to the atmosphere, down the pressure gradient
What is the normal force which is applied to the airways by increasing intra-pleural pressure during expiration?
Dynamic airway compression
Dynamic airway compression is the normal force applied to the airways by increasing intrapleural pressure during expiration.
In which patients does this pose a problem?
Patients with obstructed airways / reduced lung elasticity
i.e those with COPD, fibrosis
What is pulmonary compliance?
Effort required to inflate the lungs
Which disease reduces pulmonary compliance?
Pulmonary fibrosis
What are
a) Type I pneumocytes
b) Type II pneumocytes?
a) Alveoli
b) Cells which produce pulmonary surfactant
Which structures accept oxygen from and transfer carbon dioxide to the alveoli?
Pulmonary capillaries
What is found between the alveoli and pulmonary capillaries?
Interstitial space
Affected in interstitial lung disease, which impairs compliance and gas exchange
Pulmonary capillaries branch from the pulmonary (arteries / veins).
pulmonary arteries
The ___ ___ of CO2 is 20x that of oxygen.
diffusion coefficient
i.e how readily it passes across membanes
What is the equation for cardiac output?
CO = HR x SV
How is stroke volume calculated?
SV = EDV - ESV
The stroke volume depends on the ___ given to the heart’s muscle fibres by the venous return.
preload
Up to an optimal length, ___ ___ is directly proportional to preload.
stroke volume is directly proportional to preload
Frank-Starling Law of the heart
Which cardiovascular disease shifts the Frank-Starling curve to the right?
Heart failure
___-___ heart failure is a common cause of shortness of breath.
Left-sided heart failure
or Cor pulmonale
Which disease results in an impaired ability for the blood to transport oxygen?
Anaemia
reduced number of circulating red blood cells, which contain haemoglobin, which binds oxygen
What are some core investigations for shortness of breath?
FBC, ABG
ECG, Troponin T
CXR
What is a tidal volume?
Volume of air entering/leaving the lungs during a single breath
What is inspiratory reserve volume?
Volume of air which can be inspired on top of a normal tidal volume
What is inspiratory capacity?
Inspiratory capacity = Tidal volume + Inspiratory reserve volume
What is expiratory reserve volume?
Volume of air which can be expired after a normal tidal volume
What is residual volume?
Volume of air left in the lungs after a full expiration
What is vital capacity?
Max volume of air which can be expired after a maximal inspiration
What is FEV1?
What is FVC?
FVC - a forcefully expired vital capacity
FEV1 - volume of FEV1 which can be expired in the first second
A normal FEV1/FVC ratio is > ___%.
> 75%
