Ventilatory Control Flashcards
Breathing Pattern - Inspiration
Progressive increases in diaphragm activation
Lungs fill a constant rate until end of tidal volume
Activation of inspiratory muscles ceases
Breathing Pattern - Expiration
Relaxation of Inspiratory muscles (dia relaxes)
Elastic recoil allows for passive expiration
Activation of inspiratory muscles controls rate of expiration
Feedforward Control
Ventilation adjustment based on exercise (muscle contraction) or motor activity
Apparent particularly at onset of exercise
Doesnt require much, it just does it…but with exercise the feedforward sys stimulates ventilatory response proportional to amount of muscle you have contracting
Feedback Control
Allows for matching of response to some control value
Requires a sensor, and a comparator (sensor, controller, and effector)
Pre-Botzinger Complex
Rhythmic inspiration initiated by pacemakeer cells in the PBC
Located in the medulla
Stimulates ventilation and inhalation to occur
Between lateral reticular nucleus and nucleus ambiguous
Respiratory Centers
- Medullary respiratory center - the rhythm generator
2. Pntine (pneumotaxic) respiratory group: fine tuning
Medullary Respiratory Center
PBC - initiates inspiration
Dorsal Respiratory Group - Stimulates to diaphragm - activates phrenic and allows for continuous inspiration
Ventral Respiratory Group - Stimualtes the intercostal and abdominal muscles - When respiratory drive inc (exercise) VRG is recruited, contributes to inhalation and exhalation, sends powerful signal for forceful exhalation
Pontine Respiratory Group
Transmits signal to the inspiratory area to limit inspiration
Controls the switch off point of the inspiratory ramp
Causes the shut off of inspiration - so shuts down DRG
Normal Breathing Pattern Firing
PBC - initiate inhale
DRG - inhale
PRG - shut down DRG and leads to passive exhale
What are the things that we are sensing and what is the effector response
Chemoreceptors
Mechanoreceptors
Input from working muscle (spindles)
Response - phrenic and other muscles for respiration
Reflex - Pulmonary Stretch Receptors
Mechanoreceptors Located in smooth muscle airways Slowly adapting receptors - they will fire anytime there is a stretch and say when need to shut down inspiration so can stop to exhale and can have another inhale (inhibits the DRG) Increases resp rate Prolongs expiration
Reflex - Chest Wall Proprioceptors
Muscle spindle and GTOs
Reflex - Irritant Receptors
Located btw airway epithelial cells in larger airways
Rapidly adapting receptor - firing is proportional to lung volume amount and rate of change
Responds to chemical and mechanical stimuli
Cough reflex. sneezing, bronchoconstriction, rapid breathing
Reflex - Juxtacapillary Receptors (C fiber endings)
Unmyelinated and serve protective function
Give feeling of dyspnea
Two groups
1. Pulmonary C fibers - located next to alveoli and are sensitive to mechanical events (edema)
2. Bronchial C fibers - located in airways, responsive to inflammatory events
Reflex - Central Chemoreceptors
Located in medulla and are sensitive to H+ in the ISF
H+ can’t cross, so CO2 crosses, binds with water, and then is converted into H+ and HCO3-
HCO3- is buffer in CSF
Reflex - Peripheral Chemoreceptors
Located in carotid and aortic bodies
Unlike central, they are sensitive to PaO2
More sensitive driver for ventilation
CO2
If hold breath, inc response from CO2
People hyperventialte before holding breath so that CO2 gets low so that then you dont get a sens of needing to breathe for longer period of time
As you inc arterial PCO2
(normally at 40)
As inc, sensed by central chemoreceptors
PO2, as you drop ventilation…
100, as drop ventilation, not much of anything is happening until at hypoxic level of like 60 or so and this is sensed by the peripheral chemoreceptors
Kidneys vs. Lungs
Kidneys = Bicarbonate Control
Lungs = pCO2 control
Acid/base balance - kidneys and lungs play role in keeping this balance
Acid Base Chemistry - Acid
Proton Donor
H+ - molecule that can liberate H+ ions
Acid Base Chemistry - Base
Proton Acceptor
Molecule that is capable of combining with H+
Bicarbonate –> Carbonic Acid
Buffer
Minimizes pH changes but doesn’t add or remove acid from the body
Bicarbonate is Ex
pH
Measure of H+ ion concentration
The more acid = the lower the pH
Normal pH
7.4
Abnormal pH
Inhibit ATP production
Interfere with muscle contraction
Acid Base balance is maintained by
buffers
- Release H+ ions when pH is high
- Accept H+ ions when pH is low
Tolerable limits for pH
Muscle
Urine
6.9 - 7.5
Muscle with normal breathing = 7-7.1
Urine = 4.5-8
Acidosis
A lot of H+
- Resp. Acidosis (Inc pCO2)
- Metabolic Acidosis (dec HCO3-)
Alkalosis
- Resp Alkalosis (dec PCO2)
2. Metablic Alkalosis (inc. HCO3-)
Respiratory
Issue with CO2
Acidosis = high pCO2 (comp with raise bicarb)
Alkalosis = low pCO2 (comp with low bicarb)
Metabolic
Issue with Bicarbonate
Acidosis = low bicarb (comp with low pCO2)
Alkalosis = high bicarb (comp with raise pCO2)
1st line of defense against acid-base status
Intra and Extracellular buffers
Immediate
Ex = Buffers
2nd line of defense against acid base status
respiratory compensations
1 to 15 minutes
Ex: blowing out more CO2
3rd line of defense against acid base status
kidney compensations
Most powerful
hours to days
kidney can alter how much acid or base we have
Buffers
Combine with acid or base to buffer
Intracellular = bicarbonate and proteins
Extracellular = bicarbonate and phosphates
Bicarbonate Buffering System
Can go either way
Eqn to the right = to the tissues, more acid produced and buffer with bicarb
Eqn to the left = go to lungs, excrete CO2 by blowing out
Respiratory Compensations
2nd line of defense
Inc Ventilation, exhale more CO2
Stimulated by inc H+ (acidic) –> so this reduces H+ and blood pCO2
CO2 exhalation has to match CO2 production though
Need carbonic anahydrase
Renal Compensation
3rd line of defense
Urinary excretion of H+ (acid) and sometime bicarb
Kidneys dont excrete free H+ - 2/3 of it is excreted with ammonia
Most bicarb filtered in kidneys is reabsorbed back into the bloodstream
What is decreased at altitude
Decreased O2 diffusion
Decreased pO2 in the air as go to altitude
Hyperventialtion shifts the curve…
Left - pH going up
Hypoxemia –> paO2 is low –> peripheral chemo –> hyperventilate –> Inc PaO2 and dec PaCO2 –> resp alkalosis –> Inc pH
