Physiology Flashcards
What is respiratory acidosis? How is it corrected?
Accumulation of CO2 due to a disease of the lungs or a problem with the mechanics of respiration
The body tries to hold alkali by reabsorbing HCO3 from the kidneys
What is respiratory alkalosis? How is it corrected?
Relative lack of acid because of the loss of CO2 due to hyperventilation
Appropriate response is to lose HCO3 but this is too slow and rarely happens
What is metabolic acidosis? How is it corrected?
Excess of H+ due to disease e.g. lactic acidosis, DKA, renal failure, sepsis
The body tries to get rid of acid by getting rid of CO2 by hyperventialation
What is metabolic alkalosis? How is it corrected?
Net loss of acid from the body leaving an alkali surplus (typically vomiting)
To counteract the surplus the body tries to hold onto acid by hypoventilating and retaining CO2
How does respiratory acidosis appear on ABG? Give three examples
Reduced pH
Increase in CO2
Little or no change in HCO3 (increase in chronic)
Respiratory depression (opiates), asthma, COPD
How does respiratory alkalosis appear on ABG? Give three examples
Elevated pH
Hyperventilation with a low CO2
Little change in HCO3
Anxiety, pain, PE, pneumothorax
How does metabolic acidosis appear on ABG? Give three examples
Reduced pH
Tachypnoea with a reduced CO2
Reduced HCO3 as it used up by the pH
DKA, diarrhoea, renal tubular acidosis
How does metabolic alkalosis appear on ABG? Give three examples
Elevated pH
Marginal increase in CO2 (hypoventilation relatively ineffective)
Vomiting, diarrhoea, HF, cirrhosis, renal failure, diuretics
List respiratory causes of SOB
Asthma COPD Pneumonia Lung cancer Pulmonary fibrosis Pleural effusion Pneumothorax
List cardiovascular causes of SOB
Heart failure IHD Hypertension Valvular HD Cardiomyopathy Arrhythmia Pulmonary embolism
List other causes of SOB
Anaemia Acidosis Panic attack Exercise Obesity Pregnancy
State the two respiratory centres in the brainstem and give their role in respiration
Pons (modifies respiration)
Medulla (rhythm generator)
State the two main stimuli that influence respiratory centres in the brainstem
Central chemoreceptors
Peripheral chemoreceptors
Peripheral chemoreceptors sense tension of…
Oxygen
Some carbon dioxide
Hydrogen in the blood
Central chemoreceptors sense tension of…
Hydrogen in the CSF
Carbon dioxide
What is the most potent stimulant of respiration in normal people?
Arterial PCO2 acting through central chemoreceptors
Hypoxic drive of respiration is controlled by what type of chemoreceptors?
Peripheral chemoreceptors
List the major muscles of inspiration
Diaphragm
External intercostals
List the accessory muscles of inspiration
Sternocleidomastoid
Scalenus
List the muscles of active expiration
Internal intercostals
Abdominal muscles
What is the transmural pressure gradient?
Differences between intra-alveolar pressure and intrapleural pressure during the respiratory cycle
List forces keeping the alveoli open
Transmural pressure gradient
Pulmonary surfactant
Alveolar interdependance
List forces promoting alveolar collapse
Elasticity of fibres
Alveolar surface tension
Parasympathetic stimulation causes bronchoconstriction/dilatation
Bronchoconstriction
Parasympathetic stimulation causes bronchoconstriction/dilatation
Bronchodilatation
Dynamic airway compression makes active expiration to be more difficult in patients with airway obstruction. Why is this?
Rising pleural pressure during expiration compresses the alveoli (helps push air out of the lungs) and the airway (more likely to collapse)
Compliance is measure of effort that has to go into stretching or distending the lungs. What is meant by less compliance clinically?
The less compliant the lungs are, the more work is required to produce inflation
List factors influencing the rate of gas transfer across the alveolar membrane
Partial pressure gradients
Surface area of alveoli
Thickness of blood-air barrier
Diffusion coefficient (solubility of gas)
Define cardiac output
Volume of blood pumped by each ventricle per minute
CO = SV x HR
Define stroke volume
Volume of blood ejected by each ventricle per heart beat
SV = EDV - ESV
What is the Frank Starling Law?
The more blood that returns to the ventricle during diastole (EDV), the greater the volume of ejected bloods during systolic contraction (SV)
What is the primary factor that determines percent saturation of haemoglobin with O2?
Partial pressure of oxygen (PO2)
When is haemoglobin considered fully saturated?
All haemoglobin present is carrying its maximum oxygen load
List investigations for SOB
CXR ECG Full blood count Arterial blood gases Troponin T
What is the tidal volume?
Volume of air entering or leaving lungs during a single breath (500ml)
What is the inspiratory reserve volume?
Extra volume of air that can be maximally inspired over and above the typical resting tidal volume (3000ml)
What is the inspiratory capacity?
Maximum volume of air that can be inspired at the end of a normal quiet expiration (3500ml)
IRV + TV
What is the expiratory reserve volume?
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume (1000ml)
What is the residual volume?
Minimum volume of air remaining in the lungs even after a maximal expiration (1200ml)
What is functional residual capacity?
Volume of air in lungs at end of normal passive expiration (2200ml)
FRC = ERV + RV
What is vital capacity?
Maximum volume of air that can be moved out during a single breath following a maximal inspiration (4500ml)
VC = IRV + TV + ERV
What is total lung capacity?
Maximum volume of air that the lungs can hold (5700ml)
TLC = VC + RV
What is FEV1?
Volume of air that can be expired during the first second of expiration in an FVC (Forced Vital Capacity) determination
Normal > 70%
State the spirometry results of a patient with airway obstruction
FEV1: low
FVC: normal
PEF: low (<70%)
State the spirometry results of a patient with lung restriction
FEV1: low
FVC: low
PEF: normal (>70%)
What is the mechanism behind SOB in asthma and COPD?
Increased airway resistance
What pathological condition abolishes the transmural pressure gradient?
Pneumothorax
What is the mechanism behind SOB in emphysema and lung collapse?
Reduced surface area of the alveolar membrane
Destruction of alveoli leading to reduced surface area of the alveolar membrane, need to breathe harder to push air out
What is the mechanism behind SOB in pulmonary fibrosis
and pulmonary oedema (HF)?
Increased thickness of the air-blood barrier across the alveolar membrane
Reduced pulmonary compliance (have to work harder to open the lungs) and impaired gas diffusion
Pulmonary fibrosis impairs gas diffusion. How are PO2 and PCO2 affected?
% saturations are reduced
PCO2 is normal
PO2 is reduced
This is because CO2 diffuses more readily across the membrane
What is the mechanism behind SOB in pulmonary embolism?
Increased thickness of the air-blood barrier across the alveolar membrane Reduced perfusion (VQ mismatch)
What pathological process impairs the oxygen carrying capacity of the blood?
Anaemia
In anaemia, the arterial PO2 is normal. True/ False?
True
Arterial PO2 is normal therefore oxygen saturations are normal (less haemoglobin but still fully saturated)
What is the mechanism behind SOB in panic attacks?
Increased central and autonomic arousal
What moves the oxygen haemoglobin dissociation curve to the right?
Reduced affinity of haemoglobin-oxygen
Increased temperature
Increased 2,3-DPG
Increased H+
A low PO2 causes pulmonary vasoconstriction. True/ False? Why?
True
Blood doesn’t want to travel to areas where there is low oxygen, and is diverted away from the lungs by vasoconstriction
Why is there hypotension in tension pneumothorax?
Increased intra-thoracic pressure may decrease venous return, thus leading to reduced diastolic filling, reduced EDV, and lower SV
What medications are given to treat nitrates acutely?
IV furosemide
Nitrate infusion
Cause venodilatation, reduce preoload
What is the most common mediation used to control anxiety in a palliative patient?
Lorazepam
In emphysema you get an increased/decreased lung capacity
Increased lung capacity
‘Barrel-shaped chest’
