Week 7 - Respiratory System Flashcards
Describe the function of the respiratory system
The primary purpose is to maintain arterial blood-gas homeostasis
Accomplished via a 4-step process:
1. Pulmonary ventilation
2. Alveolar gas exchange
3. Gas transport
4. Systemic gas exchange
What separates the upper and lower respiratory tracts
The epiglottis
Describe the structure of the airways
23 airway generations
Main bronchi is Z1-Z16 (conducting zone)
Gas exchange occurs between Z17-Z23 (respiratory zone)
The human lung contains 300-500 million alveoli (1/3mm in diameter)
How and where does alveolar gas exchange occur
Pulmonary gas exchange takes place across pulmonary capillary
Oxygen and carbon dioxide move between air and blood by simple diffusion
There are 2 types of alveolar cells: Type I (critical for gas exchange) and Type II (release surfactant)
What factors affect the volume of gas passing through a sheet
Surface area
Thickness
Diffusion coefficient
Pressure gradient
What are the mechanics of breathing
The mechanics of breathing is concerned with the movement of air into and out of the lungs by the changes in pressure, flow, and volume
Bucket handle motion increases transverse, whilst pump handle motion increases anteroposterior diameter of thorax
What muscles assist during inspiration
Rest: diaphragm
Exercise: diaphragm, intercostal muscles, scalenes, sternocleidomastoid
There are >60 respiratory muscles
What is a technique to measure diaphragmatic fatigue
Bilateral phrenic nerve stimulation is a non-volitional measure of diaphragmatic fatigue
Define Ohm’s and Posiseuille’s law
Ohm’s law: Current = voltage/resistance applied in breathing
Airflow is dependent upon a pressure gradient and airway resistance
Poiseuille’s law: Resistance is dependent upon length and radius of a tube
What is the volume of air not participating in gas exchanged called
Dead space
What can be used to diagnose pulmonary diseases
Spirometry can be used to diagnoses diseases such as COPD
What difference is there between a normal and person with COPD during exercise
Dynamic hyperinflation in COPD
Increase end-expiratory lung volume
Increase work of breathing
Increase breathing discomfort
Describe the ventilatory response to constant load steady-state exercise
Split into 3 phases.
1. Immediate increase in Ve
2. Exponential increases in Ve
3. Plateau
Define Hyperpnoea
Hyperpnoea is defined as PaCO2 regulation due to proportional changes in alveolar ventilation and metabolic rate
Describe the ventilatory response to incremental exercise
Ventilation increases linearly with exercise intensity until the ventilatory threshold (50-75% of peak workload)
After Tvent, Ve increases exponentially, resulting in hyperventilation
What are some changes in breathing patterns during exercise
At exercise onset, changes in Ve are largely achieved by increased Vt During heavy exercise,
Vt plateaus and further increases in Ve are achieved by increased Fb
Vt does not exceed 60% of vital capacity
Arterial PO2, PCO2 and pH are well maintained during exercise
What are the 3 main groups of neurons for controlling ventilation
Ventral respiratory group (inspiratory & expiratory)
Dorsal respiratory group (inspiratory)
Pontine respiratory group (modulatory)
Describe the function of peripheral chemoreceptors
Located at the aortic arch and carotid body, it relays sensory information to medulla (decrease PaO2 concentration, increases Ve)
Temperature, adrenaline and CO2 also stimulate peripheral chemoreceptors
Describe the function of central chemoreceptors
Located in the RTN, it is sensitive to changes in PaCO2/H (increase in PaCO2 concentration, increases Ve)
Relayed to medulla
Describe the process in which these chemoreceptors provide feedback
- Chemoreceptors detect error signals
- Central and peripheral chemoreceptors increase afferent input to the brainstem in response to increasing PaCO2 or decreasing PaO2 or pH
- Premotor neurons in the dorsal respiratory group are activated
- Inspiratory muscle contract, increasing Ve
- Changes in Ve elicit changes in PaO2, PaCO2, and pH, thus restoring blood-gas balance
How does the pulmonary system limit exercise performance
- Exercise-induced arterial hypoxaemia
- Exercise-induced laryngeal obstruction
- Expiratory flow limitation
- Respiratory muscle fatigue
- Intrathoracic pressure effects on cardiac output
Do the lungs adapt to exercise training?
No they do not besides from some exceptions.
Respiratory muscles become stronger and more fatigue resistant, or be maladaptive as they become air hyper-responsiveness.
Describe Dalton’s law
The total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently
760mmHg at sea level (O2, CO2, N2)
PaO2 = 159mmHg, PaCO2 = 0.3mmHg, N2 = 600.7 mmHg
Describe the process of pulmonary circulation
- Pulmonary artery carries deoxygenated blood from right ventricle to lungs
- Gas exchange between alveoli and pulmonary capillaries occurs
- Oxygenated blood is returned to the left atrium via pulmonary vein
- Oxygenated blood is pumped around the systemic circulation to systemic cells
What are some aspects of pulmonary circulation
Low pressure, low resistance circuit
Thin walled, little smooth muscle
Accepts entire cardiac output
Does not redistribute blood flow
How is oxygen transported in the blood
O2 is carried in the blood in two forms.
1. Combined with haemoglobin
2. Dissolved
What effect does exercise have on the O2Hb dissociation curve
Exercise causes an increase in H+, CO2, and core body temperature, causing a rightward shift in the ODC known as the Bohr effect
What is myoglobin
Myoglobin is an O2 binding protein found in skeletal muscle.
1. High O2 affinity
2. Shuttles O2 from muscle cell membrane to mitochondria
3. Provides intramuscular O2 storage
How is carbon dioxide transported in the blood
CO2 is carried in 3 forms.
1. Dissolved (10%)
2. Bound to haemoglobin (20%)
3. Bicarbonate (70%)
What adaptations occur with chronic endurance training on aerobic capacity
Decreased metabolite accumulation
Decreased afferent feedback
Decreased ventilatory drive
Ventilatory control during moderate intensity exercise
No change in PaCO2 therefore primary stimulus is feedforward
Both central and peripheral neurogenic stimuli play a major role in the exercise hyperpnoea
Peripheral chemoreceptors ‘fine-tune’ breathing
Ventilatory control during heavy or severe exercise
During exercise above Tvent, metabolites accumulate, including H+ and K+ which can stimulate breathing
Additional sources of ventilatory stimulus come from increased body temperature and augmented muscle afferent input
Define Exercise-Induced Arterial Hypoxaemia
EIAH is defined as a reduction in PaO2 of > 10mmHg from rest
Occurs in highly trained males during heavy exercise and the majority of females regardless of fitness or exercise intensity
Originally theorised to occur because ventilatory demand exceeds capacity
Causes are not fully understood but generally believed to be due to:
1. Diffusion limitation
2. V/Q mismatch
3. Relative hypoventilation
Why does alveoli not collapse
Lungs are enclosed with membranes called pleura
Atmospheric pressure is greater than intrapleural pressure which prevents alveoli to collapse
What is the difference between O2 and CO2 ventilatory responses to exercise
O2 is curvilinear
CO2 is linear
Changes in CO2 has much greater effect on Ve than changes in O2
Why does V/Q increase upon exercise
Increased tidal volume
Increased pulmonary artery pressures
