Respiration Flashcards
Factors affecting expansion of lungs
Factors promoting expansion of lungs
1) Action of inspiratory muscles like contraction of diaphragm and external intercostal muscles results in upper ribs increasing AP diameter which is pump handle movement & lower ribs increase transverse diameter which is bucket handle movement.
2) Intrapleural pressure which is negative during inspiration.
3) Surfactant which is mixture of dipalmitoyl lecithin, apoprotein and calcium ions.
4) Outward recoil of chest wall during end of expiration.
Factors opposing expansion of lungs.
1) Surface tension of fluid lining alveoli opposes expansion of lungs.
2) Lung parenchyma which opposes expansion of lungs by presence of elastic fibres.
3) Viscous properties of lungs like frictional resistance and inertia of lungs also opposes expansion of lungs.
4) Resistance offered by airways to flow of air like diameter of bronchi and bronchioles.
Expansion of lungs is measured in terms of lung compliance.
Applied anatomy -
1) Expansion is affected by paralysis of inspiratory muscles in diseases like myasthenia gravis and polio
2) Loss of Intrapleural negativity like in pneumothorax and pleural effusion.
3) Reduced surfactant secretion in condition like RDS.
4) Increased stiffness of lungs like in fibrosis and congestion.
Neural regulation of respiration
Neural regulation of respiration is through regulation of various functions and reflexes of neural system which regulates rate and rhythm of respration.
Neural regulation of respiration is through respiratory centre present in reticular formation of brain stem which is through DRG , VRG , PNEUMOTAXIC CENTRE AND apneustic centre.
DRG
situated around nucleus of tractus solitarius.
Receives afferents from glossopharyngeal and vagus nerves
Sends efferents to muscles of respiration like diaphragm.
Action is - normal respiration and rhythm of respration.
Discharge of DRG to inspiratory muscles is RAMP SIGNAL which is weak in beginning and becomes stronger further and stops after 2 seconds.
VRG
Present in medulla in nucleus ambiguus and nucleus retroambiguus
Receives afferent from DRG neurons.
Send efferents to inspiratory and expiratory muscles.
When DRG neurons are strongly stimulated they activate VRG neurons which increases pulmonary ventilation.
Pneumotaxic centre
Situated in upper pons in nucleus parabrachialis
Receive afferent from DRG and apneustic centre.
Function is it sends impulses to DRG neurons and causes early switch off of ramp signal. It limits phase of inspiration and increase rate of respiration.
Apneustic centre
Situated in lower pons.
It prevents switch off of ramp signal and prolongs inspiration(apneusis)
It is inhibited by DRG and vagal efferents.
Normal respiration is regulated by DRG neurons whereas VRG are responsible for Increased pulmonary ventilation.
Reflexes regulating are herring breuer reflex.
Applied physiology - Ondines curse.
Ondines curse
It is a rare and serious form of CNS failure in which there is failure of autonomic control of breathing.
Signs and symptoms
1) Respiratory arrest during sleeping.
2) Neuroblastoma meaning tumors of sympathetic ganglion.
3) Hirschsprung disease meaning partial agenesis of enteric nervous system.
4) Dysphagia and anomalies of pupilla.
5) Increased sensitivity to sedatives and narcotics.
6) Darkening of skin
Complications
Hypoxia induced pulmonary vasoconstriction and pulmonary hypertension causing cor pulmonale
It is congenital and can be acquired through injury to brain or spinal cord.
Cyanosis
Cyanosis is bluish discoloration of skin and mucus membrane.
It occurs when there is increased concentration of deoxygenated Hb about more than 5gm%.
Common sites of discoloration are lips, tongue, tip of nose , nail bed and ear lobule.
Cyanosis occurs commonly in polycythaemia than anemia.
It is of central and peripheral type.
Common causes are
1) Hypoxic hypoxia like high altitude and paralysis of respiratory muscles like in polio and mysthenia gravis, airway obstruction, lung disease like tuberculosis or emphysema,etc
2) Stagnant hypoxia due to congestive cardiac failure and venous obstruction.
Asphyxia
It is an acute condition in which there is simultaneous rise in arterial pCO2.
Causes are
1) Paralysis of diaphragm
2) Compression of chest
3) Pneumothorax
4) Strangulation
5) Hanging
6) Foreign body in trachea
7) Anaphylactic shock.
Asphyxia is divided into 3 stages:
1) Stage of Hyperpnoea
2) Stage of central excitation
3) Stage of central depression
Maximum voluntary volume or maximum breathing capacity.
It is maximum volume that can be breathed in and out of lungs in 1 minute. It is 100L in males and 80L in females.
It is measured using spirometer.
Significance of MVV
1) It is a pulmonary function test and helps to understand strength of respiratory muscles, compliance of lung and airway resistance.
2) Useful in calculation of dysphonic index.
Applied concepts-
MVV is decreased in condition like weakness of respiratory muscles, fibrosis of lungs, bronchial asthama, pulmonary congestion and pulmonary edema.
Lung compliance
Lung compliance is defined as change in lung volume per unit change in transpulmonary pressure.
200ml per cm of H2O
It is measured using spirometer
1) Static lung compliance which is recorded with breathing stopped
2) Dynamic lung compliance which is recorded while breathing.
Lung compliance denotes stretchability or elasticity of lungs.
It increases with exercise due to increased stretchability of lungs, elastic recoil of lungs and amount of surfactant.
Lung compliance is decreased in pulmonary congestion, pulmonary edema and pulmonary fibrosis
It is increased in condition like emphysema due to destruction of elastic fibres.
Respiratory dead space
It is the volume of air present in Respiratory tract which cannot be utilised for gaseous exchange.
Anatomical dead space is the volume of air present in Respiratory tract where exchange of gases is not possible due to anatomical reason. Like trachea ,bronchi and bronchioles which is not lined by respiratory membrane. If tidal volume is 500ml then it is 150ml.
Physiological dead space or total dead space includes anatomical dead space and volume of air in alveoli which is not available for gaseous exchange.
It is also called as alveolar dead space.
Alveolar and physiological dead space increases in conditions where V/P ratio is more than normal like pulmonary congestion or hyperventilation like emphysema.
Functional residual Capacity.
It is the volume of air present in lungs at the end of tidal expiration.
It’s value is 2000-2100ml .
It is sum of expiratory reserve volume and residual volume.
1) Measured by helium dilution method and 2) N2 washout method.
Applied physiology - FRC is decreased in conditions like pulmonary fibrosis and collapse of lungs.
Dyspnoea
It is conscious unpleasant sensation of difficulty in breathing.
Factors:
1) Factors that causes strong stimulation of respiratory centre.
2) Factor that causes increase in work done by respiratory muscles.
3) Psychogenic factor that makes a person fear that he will not get sufficient air in crowded place.
4) Stimulation of Lungs irritation receptors.
5) Decrease in Vital capacity.
Pathological conditions causing dyspnoea:
1) Cardiac dyspnoea seen in mitral stenosis of left atrium and left ventricular failure.
2) Respiratory conditions like asthama and pulmonary fibrosis.
3) Diabetes mellitus in which there is metabolic acidosis.
Periodic breathing.