week 3 Flashcards
Anatomy of the Lower Airway
Function
Exchange oxygen and carbon dioxide
Location
Externally, it extends from the fourth cervical vertebra to the xiphoid process.
Internally, it spans the glottis to the pulmonary capillary membrane.
Anatomy of the Lower Airway trachea
Serves as a conduit for air entry into the lungs
Tubular structure, approximately 10 to 12 cm in length and consists of a series of C-shaped cartilaginous rings
Begins immediately below the cricoid cartilage
Descends anteriorly down the midline of the neck and chest to the level of the fifth or sixth thoracic vertebra
Divides into the right and left main stem bronchi at the level of the carina
Anatomy of the Lower Airway hilum
Point of entry for blood vessels and the bronchi on each lung
Lungs consist of the entire mass of tissue that includes the smaller bronchi, bronchioles, and alveoli.
Anatomy of the Lower Airway lungs
Right lung has three lobes.
Left lung has two lobes.
Visceral pleura- lines the lungs
Parietal pleura- lines the thoracic cavity
Small amount of fluid is found between the pleurae.
Anatomy of the Lower Airway bronchus
Divides into increasingly smaller bronchi once it enters the lungs
Further divide into smaller bronchioles
Smaller bronchioles branch into alveolar ducts that end at the alveolar sacs.
Anatomy of the Lower Airway alveoli
Balloon-like clusters of single-layer air sacs
Functional site for the exchange of oxygen and carbon dioxide with the pulmonary capillaries
Surfactant decreases surface tension to keep alveoli open
Atelectasis-when alveoli collapse
Total Lung Capacity
Average adult man
6 litres
Only a fraction of this capacity is used during normal breathing.
Most of the gas exchange occurs in the alveoli.
Tidal Volume (VT)
Measure of the depth of breathing
Volume of air that is inhaled or exhaled during a single respiratory cycle
Normal tidal volume 5 to 7 ml/kg (approx 500ml)
In children 6 to 8 ml/kg
Inspiratory reserve volume- amount of air that can be inhaled in addition to normal Vt (typically around 3000ml)
Dead Space (Vd)
Anatomical
Includes trachea and larger bronchi. Air lingers but does not take place in gas exchange (typically 150 ml or 30% of normal Vt)
Physiological
Created by intrapulmonary obstructions or atelectasis (alveolar collapse)
Alveolar Volume
Volume of air that reaches the alveoli and participates in gas exchange
Equal to tidal volume(Vt) minus dead space volume (Vd)
Approx 350 ml in average adult man
Minute Volume (Vm)
Amount of air that moves into and out of the respiratory tract per minute
Multiply the tidal volume by the respiratory rate (Vt x RR)
Will increase if either the tidal volume or the respiratory rate increases
Will decrease if either the tidal volume or the respiratory rate decreases
Minute Alveolar Volume (Va)
Amount of air that actually reaches the alveoli per minute and participates in gas exchange
Multiply the tidal volume (minus dead space volume) by the respiratory rate (Vt– Vd x RR)
Will increase if either the tidal volume or the respiratory rate increases
Will decrease if either the tidal volume or the respiratory rate decreases
Functional Residual Capacity
Volume of gas remaining in lungs at the end of normal tidal volume exhalation.
PEEP limits exhalation, Ie. Increases FRC and keeps alveoli from collapsing
Expiratory reserve volume
The amount of air that can be exhaled following a normal (relaxed) exhalation, approx 1200ml
Residual volume
Cannot completely empty your lungs
Amount of air that remains in the lungs after maximal expiration, also approx 1200ml
VENTILATION VOLUMES AND CAPACITIES
Tidal Volume - The amount of air inhaled and exhaled during a normal breath.
+
Inspiratory Reserve Volume - The amount of air that can be inspired with maximum inspiration.
Expiratory Reserve Volume - The amount of air that can be expired with maximum expiration.
Vital Capacity - The sum of the tidal volume, inspiratory reserve volume and the expiratory reserve volume.
Fraction of Inspired Oxygen (FIO2)
Percentage of oxygen in inhaled air
Increases when supplemental oxygen is given to a patient
May decrease at altitude, in confined spaces, chemical vat
Expressed as decimal
Ie. breathing room air, 21% O2 (Fio2 0.21%)
Ventilation
Process of moving air into and out of the lungs
Two phases
Inspiration (inhalation): process of moving air into the lungs
oxygenation- bringing in O2
Expiration (expiration): process of moving air out of the lungs
removal of CO2- byproduct of cellular metabolism
Ventilation cycles
Cycle
One inspiration and one expiration
Inspiration: one third of the ventilation cycle
Expiration: two thirds of the ventilation cycle
Regulation of Ventilation
Body’s need for oxygen is dynamic and constantly changing
Respiratory system must be able to accommodate those changes by altering the rate and depth of ventilation.
Ventilation is primarily regulated by the pH of the Cerebral Spinal Fluid – directly related to the amount of CO2 dissolved in the blood (PaCO2)
Regulation of ventilation involves a series of receptors and feedback loops to sense concentrations of CO2, pH and O2 in the blood and plasma.
These receptors send signals to the respiratory centre of the brain to alter ventilations accordingly
Control of Ventilation
Neural control of ventilation
Involuntary control of breathing originates in the brain stem, in the pons and medulla
Impulses descend through the spinal cord and can be overridden by voluntary control, ie. Breath holding
Two motor nerves affect breathing
Phrenic nerve- innervates the diaphragm
Intercostal nerve- innervate the external intercostal muscles between the ribs
Respiratory Center
Respiratory center in medulla is divided into 3 regions:
Respiratory rhythmicity center
Apneustic center
Pneumotaxic center
Respiratory rhythmicity center
Sets the respiratory rate
During normal, quiet breathing, it increases its stimulation for inhalation for approximately 2 seconds, then relaxes for 3 seconds, allowing passive exhalation
Cycle then repeats, this results in a resting respiratory rate
Apneustic Center
Receives signals from the chest wall (from mechanical stretch receptors) and bronchioles via the vagus nerve to inhibit inhalation and thus expiration occurs.
This feedback loop which combines neural and mechanical control, is called Hering-Breuer reflex. Serves to prevent overexpansion
Influences respiratory rate by increasing number of inspirations per minute
Pneumotaxic Center
Working opposite the apneustic center, it inhibits inspiration.
In times of increased demand, pneumotaxic center decreases its influence, thereby increasing respiratory rate
Chemical control of ventilation
The respiratory system helps to keep the concentration of O2 & CO2 in blood, a component of acid-base balance, within a very narrow range
Carbon dioxide is the most powerful stimulant to affect the respiratory center.
Small increases, as little as 1% can increase minute volume, whereas small change in PO2 has almost no effect
Primary stimulus to breathe is termed HYPERCARBIC DRIVE
Chemoreceptors
monitor levels of CO2, O2 and the pH of the CSF and provide feedback to the respiratory center to modify rate and depth of respiration based on the body’s current needs
Hydrogen ions
regulation of ventillation
The pH of blood also has a powerful effect on respiratory center
CO2 and pH levels inversely rise and fall together causing a combined effect in the control of respirations
CO2 + H20 = H2CO3 = H + HCO3
Central chemoreceptors
regulation of ventillation
Are located adjacent to the respiratory center in the medulla
Monitor and sense minute changes in the pH of the CSF (Hydrogen ions)
An increase in hydrogen ion concentration results in a decrease in pH, causing an excitatory response in the central chemoreceptors to increase the rate and depth of breathing
Help maintain acid-base balance
Peripheral chemoreceptors
regulation of ventillation
Located in the carotid bodies and aortic arch
Monitor and sense reduction in levels of O2 and to a lesser degree, CO2 and pH, in arterial blood
Aortic arch detect levels of O2 and CO2 but not pH. Carotid bodies detect all 3
Control of ventilation by other factors
Body temperature-fever = increased metabolism
Medications
Hypoxia (increased respirations=more O2)
Acidosis (increased respiratory rate and volume to blow off more C02)
Metabolic rate
The Mechanics of Ventilation
Accomplished
Pressure changes brought about by contraction and relaxation of the intercostal muscles and diaphragm
Inhalation
Active process
Initiated by contraction of the respiratory muscles
Net effect is to increase the volume of the chest.
Lungs undergo a comparable increase in volume.
Negative-pressure ventilation-air flows into the expanded lungs because pressure inside less than outside
Exhalation
Passive process
At the end of inhalation, the respiratory muscles relax.
Natural elasticity of the lungs passively exhalesthe air.
MECHANICS OF VENTILATION relaxation inspiration expiration
RELAXATION:No movement of the muscles of ventilation
INSPIRATION:The chest expands and the diaphragm contracts.
EXPIRATION:The chest contracts and the diaphragm relaxes.