COMPLIANCE,AIRWAY RESISTANCE AND SURFACTANT BY DR AGBARAOLRUNPO FRANCIS M DEPARTMENT OF PHYSIOLOGY COLLEGE OF MEDICINE, UNIVERSITY OF LAGOS

COMPLIANCE the ease with which the lungs and thoracic wall can expand . the measure of expansibility and distensibility of the lungs and thorax Or a measure of change in lungs/thorax volume/unit change in pulmonary pressure

When a small change in alveolar pressure produces a large increase in lung volume, compliance is high Higher compliance mean the lungs and the thoracic wall expand easily Lower compliance means that they resist expansion

Factors that improves lung compliance 1 Factors that improves lung compliance 1.Elasticity of the lungs-elastic tissues of the lung which promote the ability of the lung to stretch.[↑es compliance] 2.Surface tension-surfactant reduces surface tension of the luug [↑es compliance]

Conditions that results in decrease compliance Scar lungs eg in tuberculosis Fluid in the lungs eg.pulmonary edema Deficiency of surfactant Paralysis of intercostal muscles Condition that results in increase compliance emphysema Spirometry findings FEV1/FVC<80%

Airway resistance Airway resistance becomes important determinant of airflow rates when the airways are narrowed by disease processes F=ΔP/R where F=airflow rate ΔP=difference between atmospheric and intra-alveolar pressure(pressure gradient) R= resistance of airways, determined by their radii

The primary determinant of airway resistance is the radius of the conducting airways in a disease state However, the radius is large in healthy respiratory system that airway resistance become very low Therefore, the pressure gradient between alveoli and atmosphere is usually the primary factor determining the airflow rate. So a very small pressure gradients of 1 to 2mmHg will cause airflow in and out of the lungs with low and negligible resistance

Factors that affect airway resistance Parasympathetic stimulation-brochonconstriction (narrowing of the brochioles)-increase airway resistance=reduce airflow rate Sympathetic stimulation= bronchiodilation=decreased airway resistance

3. Narrowing s or obstruction of the airways, increases airway resistance=more pressure will be required to force air through, or collapse of airways chronic obstructive pulmonary disease(COPD) e.g bronchial asthma and emphysema, airway obstruction which increases resistance 4. Force expiration: e.g in cough, wind instrument, =intrapleural pressure may increase. This compresses the airways, resulting in increase airway resistance

Airway resistance is higher during expiration compare to inspiration Therefore, COPD patient have difficulty in moving out air during expiration, resulting in expanded chest and wheeze (whistling breathing) SPIROMETRY IN AIRWAY OBSTRUCTION[OBSTRUCTIVE AIRWAY DISEASE] FEV1 <80% FRC and RV increased

Surfactant A surface acting thin liquid that lines the surface of alveolus Secreted by Type II alveolar epithelial cells** and Clara cells (?bronchiole) Note type II alveolar cell occupy only 5% of alveolar surface responsible for lowering the surface tension on the alveolar membrane

Chemistry OF SURFACTANT A lipoprotein complex formed by phospholipid, proteins and ion (ca2+)= 1.Phospholipid (75%),*dipalmitoylphosphatidylcholine Glucocorticoid[STEROID] play important role in the formation of surfactant

SURFACTANT and Alveolar Surface Tension Alveolus is lined by two liquid with opposing forces The attractive forces[centripetal force] between the water molecules in the liquid film that lines the alveolus are responsible for surface tension

Water liquid film creates surface tension Because of this surface tension, an alveolus 1.Resist being stretched 2.Tends to be reduced in surface area or size 3.Tend to recoil after being stretched

PULMONARY SURFACTANT INTERSPERS between the water molecules in the fluid lining the alveoli it lowers the alveolar surface tension because the cohensive force between a water molecules and adjacent pulmonary surfactant molecule is very low 1. By lowering the alveolar surface tension, pulmonary surfactant provides two important benefits 2. It increases pulmonary compliance, thereby reducing the work of inflating the lungs

3. it reduces the lungs tendency to recoil and thus prevent lung from collapsing . 4. it helps stabilize the alveoli and help keep them open to participate in gas exchange

Functions of surfactant in summary 1.It reduces the surface tension in the alveoli of lungs and reduces the tendency of the lung to recoil ,preventing collapsing tendency of lungs 2.Stabilization of the alveoli 3.Offer defense against infection and inflammation through the action of SP-A and SP-D via opsonization of bacteria and viruses 4.Keep the lungs patent and inflated following delivery after the first breath It increases pulmonary compliance ,thus reducing the work of inflating the lung

Respiratory distress syndrome of newborn or hyaline membrane disease Life threatening respiratory disorder in new born preterm babies Cause: deficiency of surfactant . Higher in caesarian section delivery compare to vaginal delivery Vaginal delivery causes stress at birth –producing cortisol [stress hormone]= Cortisol enhances surfactant production in premature lungs Surface tension in the lung is high and filled with fluid= lung collapse Surfactant not available to reduce surface tension of the lung during the first cry at birth First cry at birth is necessary to inflate the lungs in those with normal surfactant Therapy- 1.Cortisol administration to pregnant mother at risk of preterm delivery 2. surfactant treatment to premature baby

Pulmonary vascular disorder Pulmonary diseases Compliance disorders Airway disorders Pulmonary vascular disorder