Respiratory Physiology Pulmonary ventilation Diffusion of gases Transport of gases Control of respiration

Respiration Ventilation: Movement of air into and out of lungs Ventilation: Movement of air into and out of lungs External respiration: Gas exchange between air in lungs and blood External respiration: Gas exchange between air in lungs and blood Transport of oxygen and carbon dioxide in the blood Transport of oxygen and carbon dioxide in the blood Internal respiration: Gas exchange between the blood and tissues Internal respiration: Gas exchange between the blood and tissues

Respiratory System Functions Gas exchange: Oxygen enters blood and carbon dioxide leaves Gas exchange: Oxygen enters blood and carbon dioxide leaves Regulation of blood pH: Altered by changing blood carbon dioxide levels Regulation of blood pH: Altered by changing blood carbon dioxide levels Voice production: Movement of air past vocal folds makes sound and speech Voice production: Movement of air past vocal folds makes sound and speech Olfaction: Smell occurs when airborne molecules drawn into nasal cavity Olfaction: Smell occurs when airborne molecules drawn into nasal cavity Protection: Against microorganisms by preventing entry and removing them Protection: Against microorganisms by preventing entry and removing them

Respiratory System Divisions Upper tract Nose, pharynx and associated structures Lower tract Larynx, trachea, bronchi, lungs

Nasal Cavity and Pharynx

Nose and Pharynx Nose Nose External nose External nose Nasal cavity Nasal cavity Functions Functions Passageway for air Passageway for air Cleans the air Cleans the air Humidifies, warms air Humidifies, warms air Smell Smell Along with paranasal sinuses are resonating chambers for speech Along with paranasal sinuses are resonating chambers for speech Pharynx Common opening for digestive and respiratory systems Three regions Nasopharynx Oropharynx Laryngopharynx

Larynx Functions Maintain an open passageway for air movement Epiglottis and vestibular folds prevent swallowed material from moving into larynx Vocal folds are primary source of sound production

Vocal Folds

Trachea Windpipe Divides to form Primary bronchi Carina: Cough reflex

Tracheobronchial Tree Conducting zone Conducting zone Trachea to terminal bronchioles which is ciliated for removal of debris Trachea to terminal bronchioles which is ciliated for removal of debris Passageway for air movement Passageway for air movement Cartilage holds tube system open and smooth muscle controls tube diameter Cartilage holds tube system open and smooth muscle controls tube diameter Respiratory zone Respiratory zone Respiratory bronchioles to alveoli Respiratory bronchioles to alveoli Site for gas exchange Site for gas exchange

Tracheobronchial Tree

Bronchioles and Alveoli

Alveolus and Respiratory Membrane The normal adult human lung weighs about 1000g and consists of about 50% blood and 50% tissue by weight. About 10% of the total lung volume is composed of various types of conducting airways and some connective tissue. The remaining 90% is the respiratory or gas exchange portion of the lung, composed of alveoli and supporting capillaries.

Thoracic Walls Muscles of Respiration

Thoracic Volume

Pleura Pleural fluid produced by pleural membranes Acts as lubricant Helps hold parietal and visceral pleural membranes together

Ventilation Movement of air into and out of lungs Movement of air into and out of lungs Air moves from area of higher pressure to area of lower pressure Air moves from area of higher pressure to area of lower pressure Pressure is inversely related to volume Pressure is inversely related to volume

Alveolar Pressure Changes

Changing Alveolar Volume Lung recoil Lung recoil Causes alveoli to collapse resulting from Causes alveoli to collapse resulting from Elastic recoil and surface tension Elastic recoil and surface tension Surfactant: Reduces tendency of lungs to collapse Surfactant: Reduces tendency of lungs to collapse Pleural pressure Pleural pressure Negative pressure can cause alveoli to expand Negative pressure can cause alveoli to expand Pneumothorax is an opening between pleural cavity and air that causes a loss of pleural pressure Pneumothorax is an opening between pleural cavity and air that causes a loss of pleural pressure

Normal Breathing Cycle

Transpulmonary pressure [pressure difference between the alveolar pressure and the pleural pressure]. It is the measure of the elastic forces that leads to collapse of the lung and it is called the recoil pressure.

The Opposing Force of Pulmonary Elastance or Compliance The Opposing Force of Pulmonary Elastance or Compliance The lung is an elastic structure with an anatomical organization that promotes its collapse to essentially zero volume, much like an inflated balloon. The lung is an elastic structure with an anatomical organization that promotes its collapse to essentially zero volume, much like an inflated balloon. The term elastic means a material deformed by a force tends to return to its initial shape or configuration when the force is removed. It oppose lung inflation. Elastance. The term elastic means a material deformed by a force tends to return to its initial shape or configuration when the force is removed. It oppose lung inflation. Elastance. Compliance (distensibility) is the reciprocal of elastance, is a measure of the ease of deformation (inflation). Compliance (distensibility) is the reciprocal of elastance, is a measure of the ease of deformation (inflation).

Compliance Measure of the ease with which lungs and thorax expand Measure of the ease with which lungs and thorax expand The greater the compliance, the easier it is for a change in pressure to cause expansion The greater the compliance, the easier it is for a change in pressure to cause expansion A lower-than-normal compliance means the lungs and thorax are harder to expand A lower-than-normal compliance means the lungs and thorax are harder to expand Conditions that decrease compliance Conditions that decrease compliance Pulmonary fibrosis Pulmonary fibrosis Pulmonary edema Pulmonary edema Respiratory distress syndrome Respiratory distress syndrome

Lung compliance: Which equals to change in volume divided by change in pressure (1 cm = 200 ml). That is, every time the transpulmonary pressure increases 1 centimeter of water, the lung volume, after 10 to 20 seconds, will expand 200 milliliters. Lung compliance: Which equals to change in volume divided by change in pressure (1 cm = 200 ml). That is, every time the transpulmonary pressure increases 1 centimeter of water, the lung volume, after 10 to 20 seconds, will expand 200 milliliters. 1/3 to overcome pleural pressure 1/3 to overcome pleural pressure 2/3 to overcome surface tension 2/3 to overcome surface tension Effect of thoracic cage: Compliance of both lung + cage = 110 ml (instead of 200ml/cm) Effect of thoracic cage: Compliance of both lung + cage = 110 ml (instead of 200ml/cm)

Surfactant: The surface active agent in water and it consists of lipids, protein and ions. Surfactant: The surface active agent in water and it consists of lipids, protein and ions. Fetal lung surfactant also is not fully functional until about the seventh month of gestation. Respiratory Distress Syndrome (RDS) is related to non-functional alveolar surfactant. Fetal lung surfactant also is not fully functional until about the seventh month of gestation. Respiratory Distress Syndrome (RDS) is related to non-functional alveolar surfactant.

Work of breathing: Work of breathing: Compliance work: against elastic forces of lung + cage Compliance work: against elastic forces of lung + cage Tissue resistance work: against viscosity of both lung and cage Tissue resistance work: against viscosity of both lung and cage Airway resistance work Airway resistance work During quite breathing, 3-5% of total energy of the body are spent for respiration, while in heavy exercise, it increases up to 50 folds During quite breathing, 3-5% of total energy of the body are spent for respiration, while in heavy exercise, it increases up to 50 folds

Pulmonary Volumes Tidal volume Tidal volume Volume of air inspired or expired during a normal inspiration or expiration Volume of air inspired or expired during a normal inspiration or expiration Inspiratory reserve volume Inspiratory reserve volume Amount of air inspired forcefully after inspiration of normal tidal volume Amount of air inspired forcefully after inspiration of normal tidal volume Expiratory reserve volume Expiratory reserve volume Amount of air forcefully expired after expiration of normal tidal volume Amount of air forcefully expired after expiration of normal tidal volume Residual volume Residual volume Volume of air remaining in respiratory passages and lungs after the most forceful expiration Volume of air remaining in respiratory passages and lungs after the most forceful expiration

Pulmonary Capacities Inspiratory capacity Inspiratory capacity Tidal volume plus inspiratory reserve volume Tidal volume plus inspiratory reserve volume Functional residual capacity Functional residual capacity Expiratory reserve volume plus the residual volume Expiratory reserve volume plus the residual volume Vital capacity Vital capacity Sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume Sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume Total lung capacity Total lung capacity Sum of inspiratory and expiratory reserve volumes plus the tidal volume and residual volume Sum of inspiratory and expiratory reserve volumes plus the tidal volume and residual volume

VolumesCapacities 1- Tidal vol. (500ml)1- Inspiratory cap. (3500ml) 2- Inspiratory reserve vol. (3000ml) 2- Functional residual cap. (2300ml) 3- Expiratory reserve vol. (1100ml) 3- Vital cap. (4600ml) 4- Residual vol. (1200ml)4- Total lung cap. (5800ml)

Spirometer and Lung Volumes/Capacities

Minute and Alveolar Ventilation Minute ventilation: Total amount of air moved into and out of respiratory system per minute Minute ventilation: Total amount of air moved into and out of respiratory system per minute Respiratory rate or frequency: Number of breaths taken per minute Respiratory rate or frequency: Number of breaths taken per minute Anatomic dead space: Part of respiratory system where gas exchange does not take place Anatomic dead space: Part of respiratory system where gas exchange does not take place Alveolar ventilation: How much air per minute enters the parts of the respiratory system in which gas exchange takes place Alveolar ventilation: How much air per minute enters the parts of the respiratory system in which gas exchange takes place

Respiratory dead space Is the space where no gas exchange occurs. It is either anatomically (150 ml) (anatomical dead space (nose, pharynx, larynx, trachea, bronchi, bronchioles); or physiological dead space whereby some alveoli are not functional because of absent or partial blood supply (normally it should be zero). Is the space where no gas exchange occurs. It is either anatomically (150 ml) (anatomical dead space (nose, pharynx, larynx, trachea, bronchi, bronchioles); or physiological dead space whereby some alveoli are not functional because of absent or partial blood supply (normally it should be zero). So the total dead space is the sum of anatomical and physiological dead spaces and so equals to 150 ml. So the alveolar ventilation per minute equals to pulmonary ventilation per minute minus dead space and equals to = 350 ml/min X 12 = 4200 ml/min. So the total dead space is the sum of anatomical and physiological dead spaces and so equals to 150 ml. So the alveolar ventilation per minute equals to pulmonary ventilation per minute minus dead space and equals to = 350 ml/min X 12 = 4200 ml/min.

Nerve stimulation (sympathetic, i.e., adrenalin dilatation; parasympathetic, i.e., Ach. constriction). Nerve stimulation (sympathetic, i.e., adrenalin dilatation; parasympathetic, i.e., Ach. constriction). Cough reflex: afferent vagus nerve medulla autonomic inspiration of 2.5 liters closure of epiglottis and vocal cords contraction of abdominal muscles sudden opening expel air at a velocity of 400 miles per hour + narrowing of trachea and bronchi. Cough reflex: afferent vagus nerve medulla autonomic inspiration of 2.5 liters closure of epiglottis and vocal cords contraction of abdominal muscles sudden opening expel air at a velocity of 400 miles per hour + narrowing of trachea and bronchi. Sneeze reflex: Similar except to nasal passages instead of lower airways. Afferent is fifth cranial medulla similar but depression of uvula so that large amounts of air pass through the nose. Sneeze reflex: Similar except to nasal passages instead of lower airways. Afferent is fifth cranial medulla similar but depression of uvula so that large amounts of air pass through the nose.

Pulmonary circulation: Pulmonary circulation: Blood supply to the lungs goes to bronchi (nutrition) and respiratory units (gaseous exchange). Blood supply to the lungs goes to bronchi (nutrition) and respiratory units (gaseous exchange). When O2 concentration drops to 70% (73mmHg), pulmonary blood vessels constricts (opposite to other capillaries) and this is important to shift the blood to more aerated areas. When O2 concentration drops to 70% (73mmHg), pulmonary blood vessels constricts (opposite to other capillaries) and this is important to shift the blood to more aerated areas. Right atrial pressure is 25 mmHg systolic and 0 mmHg diastolic. Right atrial pressure is 25 mmHg systolic and 0 mmHg diastolic. Pulmonary artery pressure is 25mmHg systolic and 8mmHg diastolic (mean arterial pressure equals 15 mmHg) Pulmonary artery pressure is 25mmHg systolic and 8mmHg diastolic (mean arterial pressure equals 15 mmHg)

Lung Zones In the normal, upright adult, the lowest point in the lungs is about 30 centimeters below the highest point. This represents a 23 mm Hg pressure difference, about 15 mm Hg of which is above the heart and 8 below. In the normal, upright adult, the lowest point in the lungs is about 30 centimeters below the highest point. This represents a 23 mm Hg pressure difference, about 15 mm Hg of which is above the heart and 8 below. For the whole lung, an ideal ventilation to perfusion ratio is between 0.8 to 1.0. For the whole lung, an ideal ventilation to perfusion ratio is between 0.8 to 1.0.

Perfusion across capillaries Capillary pressure equals 7mmHg (while it is 17 in general circulation). Capillary pressure equals 7mmHg (while it is 17 in general circulation). Plasma colloid equals 28 mmHg. Plasma colloid equals 28 mmHg. Interstitial colloid 14 mmHg (7 in general circulation) Interstitial colloid 14 mmHg (7 in general circulation) -ve interstitial pressure equals 8 mmHg -ve interstitial pressure equals 8 mmHg Total = 29, so = 1mmHg which removed by lymphatics and evaporation Total = 29, so = 1mmHg which removed by lymphatics and evaporation

Physical Principles of Gas Exchange Partial pressure Partial pressure The pressure exerted by each type of gas in a mixture The pressure exerted by each type of gas in a mixture Dalton’s law: P total = P 1 + P 2 + P P n Dalton’s law: P total = P 1 + P 2 + P P n Water vapor pressure Water vapor pressure Diffusion of gases through liquids Diffusion of gases through liquids Concentration of a gas in a liquid is determined by its partial pressure and its solubility coefficient Concentration of a gas in a liquid is determined by its partial pressure and its solubility coefficient Henry’s law: concentration of dissolved gas = pressure × SC Henry’s law: concentration of dissolved gas = pressure × SC

Gases Comprising the Earth's Atmosphere Gases Comprising the Earth's Atmosphere The earth's atmosphere is a mixture of gases consisting of about 78% molecular nitrogen (N 2 ), 20.9 % molecular oxygen (O 2 ) and 1.0 % argon (Ar). Other gases, like carbon dioxide (0.03%), are also detectable, but only in trace amounts. The earth's atmosphere is a mixture of gases consisting of about 78% molecular nitrogen (N 2 ), 20.9 % molecular oxygen (O 2 ) and 1.0 % argon (Ar). Other gases, like carbon dioxide (0.03%), are also detectable, but only in trace amounts.

Only a portion of each tidal volume is delivered to the alveoli. The total air volume of all lung alveoli before inspiration (end-expiration) is by definition the Functional Residual Capacity. For a normal adult, the FRC is about 2500 ml. So, if the volume of fresh ambient air reaching the alveoli is 300 ml, it is added to an FRC of 2500 ml. As a result, the partial pressures of alveolar gases do not fluctuate markedly with each breath since only a portion of the FRC is exchanged. Only a portion of each tidal volume is delivered to the alveoli. The total air volume of all lung alveoli before inspiration (end-expiration) is by definition the Functional Residual Capacity. For a normal adult, the FRC is about 2500 ml. So, if the volume of fresh ambient air reaching the alveoli is 300 ml, it is added to an FRC of 2500 ml. As a result, the partial pressures of alveolar gases do not fluctuate markedly with each breath since only a portion of the FRC is exchanged.

Factors affecting the diffusion of gasses in air: Factors affecting the diffusion of gasses in air: Pressure X Area X Temperature Pressure X Area X Temperature D = , distance X SQR(Molecular Weight) diff. coef. = T/SQR(MW) (constant) Solubility of O2 = Solubility of O2 = Solubility of CO2 = 0.57 (20 times of O2) Solubility of CO2 = 0.57 (20 times of O2)

Diffusion of Gases through the Respiratory Membrane The respiratory unit: respiratory bronchioles, alveolar ducts, atria, and alveoli. The respiratory unit: respiratory bronchioles, alveolar ducts, atria, and alveoli. Blood flows as a sheet. Blood flows as a sheet. Respiratory membrane is 0.2 micrometer thickness and composed of: 1) fluid (surfactant), 2) epithelium, 3) epithelial basement membrane, 4) interstitial fluid, 5) capillary basement membrane, 6) endothelial cells Respiratory membrane is 0.2 micrometer thickness and composed of: 1) fluid (surfactant), 2) epithelium, 3) epithelial basement membrane, 4) interstitial fluid, 5) capillary basement membrane, 6) endothelial cells

Physical Principles of Gas Exchange Diffusion of gases through the respiratory membrane Diffusion of gases through the respiratory membrane Depends on membrane’s thickness, the diffusion coefficient of gas, surface areas of membrane, partial pressure of gases in alveoli and blood Depends on membrane’s thickness, the diffusion coefficient of gas, surface areas of membrane, partial pressure of gases in alveoli and blood Relationship between ventilation and pulmonary capillary flow Relationship between ventilation and pulmonary capillary flow Increased ventilation or increased pulmonary capillary blood flow increases gas exchange Increased ventilation or increased pulmonary capillary blood flow increases gas exchange Physiologic shunt is deoxygenated blood returning from lungs Physiologic shunt is deoxygenated blood returning from lungs

Effect of ventilation perfusion ratio on alveolar gas concentration VA/Q = 0 O2 = 40, CO2 = 45mmHg VA/Q = 0 O2 = 40, CO2 = 45mmHg VA/Q = infinity O2 = 149, CO2 = 0mmHg VA/Q = infinity O2 = 149, CO2 = 0mmHg VA/Q = normal O2 = 104, CO2 = 40mmHg VA/Q = normal O2 = 104, CO2 = 40mmHg If less than normal then called physiological shunt If less than normal then called physiological shunt If more than normal then called physiological dead space If more than normal then called physiological dead space

Normally at the tip of the lung, VA/Q is (2.5) times normal (phys. dead space), while at the base, it is (0.6) times normal (phys. shunt). Normally at the tip of the lung, VA/Q is (2.5) times normal (phys. dead space), while at the base, it is (0.6) times normal (phys. shunt). Normally, there are abnormal VA/Q ratios in the upper and lower portions of the lung. In the upper both ventilation and perfusion are low but VA is more than Q, so there is physiological dead space, but in the lower VA is less than Q, so there is physiological shunt. Normally, there are abnormal VA/Q ratios in the upper and lower portions of the lung. In the upper both ventilation and perfusion are low but VA is more than Q, so there is physiological dead space, but in the lower VA is less than Q, so there is physiological shunt.

Changes in Partial Pressures

Hemoglobin and Oxygen Transport Oxygen is transported by hemoglobin (97%) and is dissolved in plasma (3%) Oxygen is transported by hemoglobin (97%) and is dissolved in plasma (3%) Oxygen-hemoglobin dissociation curve shows that hemoglobin is almost completely saturated when P0 2 is 80 mm Hg or above. At lower partial pressures, the hemoglobin releases oxygen. Oxygen-hemoglobin dissociation curve shows that hemoglobin is almost completely saturated when P0 2 is 80 mm Hg or above. At lower partial pressures, the hemoglobin releases oxygen. A shift of the curve to the left because of an increase in pH, a decrease in carbon dioxide, or a decrease in temperature results in an increase in the ability of hemoglobin to hold oxygen A shift of the curve to the left because of an increase in pH, a decrease in carbon dioxide, or a decrease in temperature results in an increase in the ability of hemoglobin to hold oxygen

Hemoglobin and Oxygen Transport A shift of the curve to the right because of a decrease in pH, an increase in carbon dioxide, or an increase in temperature results in a decrease in the ability of hemoglobin to hold oxygen A shift of the curve to the right because of a decrease in pH, an increase in carbon dioxide, or an increase in temperature results in a decrease in the ability of hemoglobin to hold oxygen The substance 2.3-bisphosphoglycerate increases the ability of hemoglobin to release oxygen The substance 2.3-bisphosphoglycerate increases the ability of hemoglobin to release oxygen Fetal hemoglobin has a higher affinity for oxygen than does maternal Fetal hemoglobin has a higher affinity for oxygen than does maternal

Oxygen-Hemoglobin Dissociation Curve at Rest

Bohr effect:

Temperature effects:

Shifting the Curve

Transport of Carbon Dioxide Carbon dioxide is transported as bicarbonate ions (70%) in combination with blood proteins (23%) and in solution with plasma (7%) Carbon dioxide is transported as bicarbonate ions (70%) in combination with blood proteins (23%) and in solution with plasma (7%) Hemoglobin that has released oxygen binds more readily to carbon dioxide than hemoglobin that has oxygen bound to it (Haldane effect) Hemoglobin that has released oxygen binds more readily to carbon dioxide than hemoglobin that has oxygen bound to it (Haldane effect) In tissue capillaries, carbon dioxide combines with water inside RBCs to form carbonic acid which dissociates to form bicarbonate ions and hydrogen ions In tissue capillaries, carbon dioxide combines with water inside RBCs to form carbonic acid which dissociates to form bicarbonate ions and hydrogen ions

Transport of Carbon Dioxide In lung capillaries, bicarbonate ions and hydrogen ions move into RBCs and chloride ions move out. Bicarbonate ions combine with hydrogen ions to form carbonic acid. The carbonic acid is converted to carbon dioxide and water. The carbon dioxide diffuses out of the RBCs. In lung capillaries, bicarbonate ions and hydrogen ions move into RBCs and chloride ions move out. Bicarbonate ions combine with hydrogen ions to form carbonic acid. The carbonic acid is converted to carbon dioxide and water. The carbon dioxide diffuses out of the RBCs. Increased plasma carbon dioxide lowers blood pH. The respiratory system regulates blood pH by regulating plasma carbon dioxide levels Increased plasma carbon dioxide lowers blood pH. The respiratory system regulates blood pH by regulating plasma carbon dioxide levels

Haldane effect It was pointed out that an increase in carbon dioxide in the blood causes oxygen to be displaced from the hemoglobin (the Bohr effect), which is an important factor in increasing oxygen transport. It was pointed out that an increase in carbon dioxide in the blood causes oxygen to be displaced from the hemoglobin (the Bohr effect), which is an important factor in increasing oxygen transport. The reverse is also true: binding of oxygen with hemoglobin tends to displace carbon dioxide from the blood. The reverse is also true: binding of oxygen with hemoglobin tends to displace carbon dioxide from the blood. The Haldane effect results from the simple fact that the combination of oxygen with hemoglobin in the lungs causes the hemoglobin to become a stronger acid. The Haldane effect results from the simple fact that the combination of oxygen with hemoglobin in the lungs causes the hemoglobin to become a stronger acid.

This displaces carbon dioxide from the blood and into the alveoli in two ways: This displaces carbon dioxide from the blood and into the alveoli in two ways: (1) The more highly acidic hemoglobin has less tendency to combine with carbon dioxide to form carbaminohemoglobin, thus displacing much of the carbon dioxide that is present in the carbamino form from the blood. (1) The more highly acidic hemoglobin has less tendency to combine with carbon dioxide to form carbaminohemoglobin, thus displacing much of the carbon dioxide that is present in the carbamino form from the blood. (2) The increased acidity of the hemoglobin also causes it to release an excess of hydrogen ions, and these bind with bicarbonate ions to form carbonic acid; this then dissociates into water and carbon dioxide, and the carbon dioxide is released from the blood into the alveoli and, finally, into the air. (2) The increased acidity of the hemoglobin also causes it to release an excess of hydrogen ions, and these bind with bicarbonate ions to form carbonic acid; this then dissociates into water and carbon dioxide, and the carbon dioxide is released from the blood into the alveoli and, finally, into the air.

CO 2 Transport and Cl - Movement

Ventilation-perfusion coupling:

Respiratory Areas in Brainstem Medullary respiratory center Medullary respiratory center Dorsal groups stimulate the diaphragm Dorsal groups stimulate the diaphragm Ventral groups stimulate the intercostal and abdominal muscles Ventral groups stimulate the intercostal and abdominal muscles Pontine (pneumotaxic) respiratory group Pontine (pneumotaxic) respiratory group Involved with switching between inspiration and expiration (respiratory ramp). Involved with switching between inspiration and expiration (respiratory ramp). Pontine (apneuostic center) prevents the switch off of the respiratory ramp. Pontine (apneuostic center) prevents the switch off of the respiratory ramp.

Respiratory Structures in Brainstem

Rhythmic Ventilation Starting inspiration Starting inspiration Medullary respiratory center neurons are continuously active Medullary respiratory center neurons are continuously active Center receives stimulation from receptors and simulation from parts of brain concerned with voluntary respiratory movements and emotion Center receives stimulation from receptors and simulation from parts of brain concerned with voluntary respiratory movements and emotion Combined input from all sources causes action potentials to stimulate respiratory muscles Combined input from all sources causes action potentials to stimulate respiratory muscles Increasing inspiration Increasing inspiration More and more neurons are activated More and more neurons are activated Stopping inspiration Stopping inspiration Neurons stimulating also responsible for stopping inspiration and receive input from pontine group and stretch receptors in lungs. Inhibitory neurons activated and relaxation of respiratory muscles results in expiration. Neurons stimulating also responsible for stopping inspiration and receive input from pontine group and stretch receptors in lungs. Inhibitory neurons activated and relaxation of respiratory muscles results in expiration.

Modification of Ventilation Cerebral and limbic system Cerebral and limbic system Respiration can be voluntarily controlled and modified by emotions Respiration can be voluntarily controlled and modified by emotions Chemical control Carbon dioxide is major regulator Increase or decrease in pH can stimulate chemo- sensitive area, causing a greater rate and depth of respiration Oxygen levels in blood affect respiration when a 50% or greater decrease from normal levels exists

Modifying Respiration

Regulation of Blood pH and Gases

Herring-Breuer Reflex Limits the degree of inspiration and prevents overinflation of the lungs Limits the degree of inspiration and prevents overinflation of the lungs Infants Infants Reflex plays a role in regulating basic rhythm of breathing and preventing overinflation of lungs Reflex plays a role in regulating basic rhythm of breathing and preventing overinflation of lungs Adults Adults Reflex important only when tidal volume large as in exercise Reflex important only when tidal volume large as in exercise

Ventilation in Exercise Ventilation increases abruptly Ventilation increases abruptly At onset of exercise At onset of exercise Movement of limbs has strong influence Movement of limbs has strong influence Learned component Learned component Ventilation increases gradually Ventilation increases gradually After immediate increase, gradual increase occurs (4-6 minutes) After immediate increase, gradual increase occurs (4-6 minutes) Anaerobic threshold is highest level of exercise without causing significant change in blood pH Anaerobic threshold is highest level of exercise without causing significant change in blood pH If exceeded, lactic acid produced by skeletal muscles If exceeded, lactic acid produced by skeletal muscles

Effects of Aging Vital capacity and maximum minute ventilation decrease Vital capacity and maximum minute ventilation decrease Residual volume and dead space increase Residual volume and dead space increase Ability to remove mucus from respiratory passageways decreases Ability to remove mucus from respiratory passageways decreases Gas exchange across respiratory membrane is reduced Gas exchange across respiratory membrane is reduced

Other types of respiratory control as: Other types of respiratory control as: Voluntary control Voluntary control Irritant receptors of airways. Irritant receptors of airways. Lung “J” receptors Lung “J” receptors Brain edema Brain edema Anesthesia Anesthesia Periodic breathing (normally damped). Periodic breathing (normally damped). Slow blood flow to the brain (heart failure) Slow blood flow to the brain (heart failure) Increased negative feedback gain (brain damage) Increased negative feedback gain (brain damage)

Sleep apnea Loss of spontaneous breathing Loss of spontaneous breathing May last for > 10 seconds May last for > 10 seconds May recur per night sleep May recur per night sleep May be due to obstruction of pharynx May be due to obstruction of pharynx May be due to impaired CNS respiratory drive May be due to impaired CNS respiratory drive

Respiratory investigations Blood pH Blood pH Blood gas determination Blood gas determination Respiratory function tests Respiratory function tests Maximum expiratory flow Maximum expiratory flow FCV FCV FEV1 FEV1 FVC/FEV1 ratio FVC/FEV1 ratio

Types of respiratory abnormalities Obstructive Obstructive Restrictive Restrictive

Pulmonary emphysema Pulmonary emphysema Infection, obstruction, alveolar damage, decrease diffusing capacity, and may lead to pulmonary hypertension. Infection, obstruction, alveolar damage, decrease diffusing capacity, and may lead to pulmonary hypertension. Pneumonia Pneumonia Infection, filling of areas with fluid and consolidation leading to hypoxia and hypercapnia. Infection, filling of areas with fluid and consolidation leading to hypoxia and hypercapnia. Atelectasis Atelectasis Lung collapse Lung collapse Asthma: Spastic contraction to bronchioles leading to hypoxia. Asthma: Spastic contraction to bronchioles leading to hypoxia.

Hypoxia Circulatory hypoxia: Circulatory hypoxia: Histotoxic hypoxia Histotoxic hypoxia Anemic hypoxia Anemic hypoxia Hypoxic hypoxia Hypoxic hypoxia