Control of Ventilation Flashcards
Respiratory Control
• Maintain homeostasis
– Oxygen
– Carbon dioxide
– Hydrogen ion concentration (pH)
- Optimize mechanical efficiency
- Complex functions
– Vocalization
– Cough
– Exercise
– Adaptation to disease
Respiratory Control
• Chemoreceptors
– Carbon dioxide
– Oxygen
– Hydrogen ion (pH)
• Mechanoreceptors
– Information from lung and chest wall
• Other
– Baroreceptors
– Temperature receptors
– Higher brain centers
Respiratory Output
• Inspiratory muscles
– Diaphragm
– External intercostals
– Accessory muscles
- Upper airway muscles
- Expiratory muscles
– Abdominal wall
– Internal intercostals
The Brainstem and Respiratory Control
- Pneumotaxic Center
- Apneustic Center
- Medullary Respiratory Center
- DRG (INSP)
- VRG (EXP)
DRG
Dorsal respiratory group: Inspiration
- Controls basic rhythm of breathing
- Oscillations in activity are due to multiple inputs +/- pacemaker cells
- Pre-Botzinger complex in ventrolateral medulla has rhythmic insp activity
- Crescendo of activity leads to inspiration and decreases in expiration
- Input from IXth and Xth nerves that terminate in nucleus tractus solitarius
- Input from pneumotaxic center in pons ends inspiration
- Output to inspiratory muscles
VRG
- Inspiration (DRG) is active, and the expiration is passive without need for VRG output to expiratory muscles
- Increases activity with
– exercise
– dyspnea (shortness of breath)
– lung disease
- Pre-Botzinger complex in ventrolateral medulla has rhythmic insp activity
- VRG has both insp and exp muscle outputs
Apneustic Center
- Lower pons
- Damage above this region isolates it from pneumotaxic center leads to prolonged inspiratory gasps
- Sends signals to inspiratory center (DRG) to prolong inspiratory ramping of diaphragmatic activity
Pneumotaxic Center
- Located in the upper pons
- Switches off inspiratory activity, thus ending inspiration
- Controls tidal volume and respiratory rate by cycling the breath into expiration
- Normal breathing can persist without this center
Central Chemoreceptors
• Change in PaCO2 alters CSF pH
– Increase PaCO2 will decrease CSF pH
– Decrease PaCO2 will increase CSF pH
- Decreased pH (Increased H+) in CSF stimulates receptors to increase ventilation
- Normal eupneic control
- Severe hypoxemia suppresses output
Peripheral Chemoreceptors
- Located in carotid bodies
- Aortic bodies have more impact on cardiovascular system
- Peripheral chemoreceptors are the only receptors that respond to hypoxia or acidemia to increase ventilation
Carotid Body Chemoreceptors
- Hypoxia, Hypercarbia, and Acidemia increase ventilation
- 20% of response to PaCO2
- Hypoxia potentiates other responses
- Need to respond to hypoxemia or metabolic acidemia effectively
Integration of Chemoreceptor Response
• Response to chemoreceptor input is integrated to protect homeostasis
– In a patient with metabolic acidosis any increase in carbon dioxide leads to a more rapid increase in ventilation
– In a patient with metabolic acidosis any hypoxemia leads to a more rapid increase in ventilation
Pulmonary Mechanoreceptors
- Pulmonary stretch receptors
- Lung irritant receptors
- J-receptors
Stretch Receptors
- Airway smooth muscle
- Slow adaptation to airway stretch
- Vagal inhibition of inspiration
- Promotion of expiration
- Hering-Breuer reflex
Irritant Receptors
- Extra-pulmonary airway epithelium
- Rapid adaptation with vagal response
- Respond to chemical or physical irritation
- Help maintain lung volume with sighs
- Cause bronchoconstriction, cough, inspiration, and rapid, shallow breathing
J-Receptors
- Alveolar walls near capillaries
- Connect via unmyelinated fibres
- Rapidly adapting.
- Stimulated by interstitial disease and inflammatory chemicals and engorgement of the capillary bed
- Cause laryngeal closure and apnea, followed by rapid shallow breathing.
Chest Wall Proprio-receptors
- Joint receptors
- Tendon receptors
- Muscle spindle receptors
Joint Receptors
- Ruffini, Pacinian, and Golgi receptors
- Located in the joints of the chest wall
- Respond to rib movement
Tendon Organs
- Intercostal and diaphragmatic muscle tendons
- Monitor the force of contraction
- Inhibit inspiration
Muscle Spindles
- Abundant in the intercostals and rare in diaphragm
- Stabilize rib cage and posture
- Spindles located on intrafusal muscle fibres aligned with extrafusal fibres that elevate the ribs
- Extrafusal = alpha motor neuron
- Intrafusal = gamma motor neuron
- Similar to limb reflexes = Intercostals are postural
Non-Respiratory Mechanoreceptors
- Proprioreceptors in the limb joints
- Thermal and cardiovascular baroreceptors
Chronic respiratory illness […] ventilatory control:
Chronic respiratory illness decreases ventilatory control:
- Increased work of breathing
- Decreased efficiency of gas exchange
- Impaired performance of the ventilatory pump
- Reduced response to chemical stimuli
Hydrogen ion is a million times […] concentrated than bicarbonate ion
Hydrogen ion is a million times less concentrated than bicarbonate ion
Chronically Increased PaCO2
- Kidney compensates for respiratory acidosis (increased PaCO2) by reabsorbing more bicarbonate (HCO3- )
- Eventually the HCO3 - enters the CSF and buffers any ph change due to increased PaCO2
Chronic CO2 Retention
- Central chemoreceptors reset their control point and lose sensitivity to changes in PaCO2
- Only drive left is peripheral hypoxic drive from carotid bodies
- High inspired oxygen (FIO2) turns off hypoxic drive and ventilation decreases
- PaCO2 rises to levels where is causes narcosis and apnea
