Oxygen haemoglobin curve
O2 carried on haem
Binds to haemoglobin at the lungs
Detaches from haemoglobin at the tissues
CO2 + H2O ~~~~~ H2 CO3 ( carbonic acid) ——H+ + HCO3-( bicarbonate ion)
H+ is buffered by haemoglobin in erythrocytes
Ventilation perfusion matching V/Q
V = air moving in and out of the lungs Q = blood in pulmonary capillaries
Normal oxygenation needs a matching of ventilation and perfusion (V/Q)
Partial pressure of oxygen (PaO2)
Air is breathed in at 160mmHg
Air in alveoli is dropped to 100mmHg
Inspired air mixes with residual air and is also humidified
PaO2 in arterial blood is approx 100mmHg
The intrapleural pressure gradient is largest in the upper lung region
Maintaining homeostasis:
Low PaO2 causes CONSTRICTIONS of pulmonary arterioles
Lack of homeostasis:
Obstruction of airways in COPD leads to hypoxiaemia and hypercapnia
Lack of homeostasis with reduced ventilation
V/Q mismatch - reduced perfusion
Maintaining homeostasis
High PaO2 causes dilation of pulmonary arterioles
Low PaCO2 causes constriction of bronchioles
Lack of homeostasis with reduced perfusion
Lack of homeostasis occurs with pulmonary embolisms
Leading to hypoxiaemia and hypercapnia
Control of respiratory function:
SNS
Releases adrenaline and noradrenaline
Binds to B2 adrenergic receptors on bronchi which causes bronchodilation
Increased depth and rate of breathing
A sympathetic agonist enhances these effects
Sympathetic agonist
Group of medication that enhances the effects of B2 adrenergic receptors located on the bronchi …
Bronchodilation
Parasympathetic nervous system PNS
Rest and digest
Releases acetylcholine (ACh) neurotransmitter
Binds to cholinergic receptors on bronchi
bronchoconstriction
Decreases rate and depth of breathing
Parasympathetic antagonist/blocker opposes these effects
B2 agonist
Salbutamol
Increases effects of SNS
Relaxes smooth muscle of bronchi
Bronchodilation
Anti cholinergic
Iptratropium
Blocks cholinergic receptors
Relaxes smooth muscle of bronchi
Decrease the effects of PNS
Bronchodilation
Corticosteroids
Fluticasone
Anti inflammatory
Reduces swelling
Prevents bronchospasm
Respiratory control
Brain stem receives sensory input from chemoreceptors
Central chemo receptors in the
Medulla
Peripheral chemoreceptors in the
Carotid arteries and aortic arch
Chemical control of O2
Decrease in O2 ( hypoxaemia )is detected by peripheral chemoreceptors
Chemical control of CO2
Most important chemical
Increased co2 = hypercapnia
Detected by central chemoreceptors
Co2 from blood enters CSF ( cerebrospinal fluid) & forms H+
Also detects ketoacidosis in diabetes
Increased H+ detected by central chemoreceptors causes
Increased rate and depth of breathing to get rid of co2 and increase blood pH
Causes of acidosis
Hypoventilation
Diabetic ketoacidosis
Respiratory acidosis
Less than 7.35 pH
PCO2 greater than 45mmHg
Occurs with hypercapnia and hypoventilation
Any impairment of lung function
Respiratory alkalosis
PCO2 less than 35mmHg
pH greater than 7.45
Due to hypocapnia and hyperventilation
Pulmonary function test
FEV = forced exploratory volume FVC = forced vital capacity
FEV1/FVC x 100
Syncope
Loss of consciousness caused by fall in blood pressure
Haemoptysis
Coughing up of blood
Pulmonary embolism clinical features
Breathlessness or chest pain Tachycardia Tachypnoea Dyspnoea Syncope Haemoptysis
Restrictive lung disease RLD
Impaired lung expansion
Normal FEV1
RDS
Respiratory distress syndrome of the newborn
Immature lungs - premis
Alveoli collapse due to insufficient SURFACTANT
Chest wall is weak
Alveoli and blood supply underdeveloped
RDS risk factors
Premature birth
Caesarean
Maternal diabetes
Asphyxia at birth
RDS treatment
Prevent premature birth
Maternal glucocorticoids to speed up lung development
Surfactant therapy
CPAP (continuous positive air pressure )
ARDS - excessive inflammation damages the alveoli
Acute lung inflammation
Life threatening
Sepsis - blood infection
Trauma
Pneumonia
Smoke inhalation
ARDS clinical features
Develops within 24hrs following injury
Dyspnoea
Hyperventilation
Severe hypoxaemia
ARDS treatment
Oxygenation of tissues Prone position Minimise lung injury Avoid complication Pts can recover
Mixed venous blood
PO2 = 40 mm Hg
Haemoglobin is 75% saturated