Lecture 2: The respiratory cycle and mechanics of ventilation Flashcards
Define respiration:
- To extract O2 from air and with CVS transport to respiring tissues
- Remove CO2 from respiring tissues and exhaust into atmosphere
What evolutionary factors have driven the formation of lungs in mammals?
- Increased size
- Increased diffusion distances
- Increased metabolic rate i.e cold vs warm blood
- Increased oxygen demand
What sort of process is inspiration and what is the main driver?
Inspiration is an active process and the diaphragm is the main driver
What are the muscles of inspiration and exhalation?
Inspriation: Diaphragm and external intercostals
Expiration: Internal intercostals and abdominal muscles
Describe the chest movements of breathing:
Inspiration: Ribs move in and out, diaphragm flattens
Exhalation: Diaphragm moves up, ribs move in and down
What sort of breathing occurs at rest and is it active?
At rest tidal volume ~0.5L; Inspiration is an active process whilst expiration is a passive process.
What happens to the exhalation process during exercise?
Exhalation becomes active i.e internal intercostals and abdo muscles b/c you want to decrease insp and exp. time and inc RR
What happens to pulmonary pressure during the respiratory cycle?
Inspiration: Pulm. pressure become negative as air is drawn in and returns to 0mmHg at the end of insp.
Expiration: Pulm. pressure becomes positive as air is forced out and returns to 0mmHg at end of exp.
What happens to pleural pressure during the respiratory cycle?
Note pleural space is always negative relative to atmosphere; acts to adhere lungs to chest wall.
During inspiration pleural cavity space becomes MORE negative relative to atmosphere (as pleural volume increases) It is most negative at the end of inspiration.
During exhalation pleural cavity becomes less negative.
What is an extrinsic problem that impacts the pleural space?
Pneumothorax;
- Thoracic puncture wound
- Collapsed lung
- Air rushes into chest
- Loss of negative pleural pressure
What is an intrinsic problem that impacts the pleural space?
Atelectasis
- Insufficient air in the lung
- Obstruction in airway
- Surfactant deficiency (making the lung stiff)
Why is a balloon in a conical flask a poor example of lung physiology?
The glass doesnt move i.e chest wall, so poorly models a negative pressure model
What does a spirometer measure?
Lung volume
How is minute ventilation calculated?
Vt (tidal volume) x Resp. Frequency
What are some lung volumes measured in spirometry?
Tidal volume
Inspiratory reserve volume (IRV)
Inspiratory capacity = (IRV + TV)
Expiratory reserve volume
Residual volume
Functional residual capacity (ERV+RV)
Vital capacity = IRV+TV+ERV
TLC (IRV+TV+ERV+RV)
Whats a method of measuring TLC?
C1 x V1 = C2 x V2
Using helium gas you can get the subject to breath in the helium from a known C1 and V1 until equilibrium is reached and then measure the new concentration (C2) and calculate the TLC of the lungs.
i.e Measuring the new concentration in the system and using C1, V1 and C2 to deduce V2.
Then you can subtract TLC (V2) with VC
What happens to lung volumes with exercise?
Tidal volume increases reducing ERV and IRV
What happens to oxygen consumption over time with exercise?
Tidal breathing has increased, over time in a constant cardio state the oxygen consumption falls to around 1.8L per unit time. I.e as the body switches energy metabolism and enters a steady state oxygen needs change…
What is hyperventilation and hypoventilation?
Hyperventilation: >6L/min
Hypoventilation: <6L/min
What is minute ventilation also equal to?
Ve = Va + Vd
Va (Alveolar ventilation)
Vd (Dead space ventilation) (~2.2mL/kg or 150mL)
What is alveolar ventilation equal to?
Va = Vt - Vd (Dead space) x RR
What is FEV1/FVC and what does it mean?
Tests lung health
FEV1 = Forced expiratory volume over 1s FVC = Forced vital capacity (~5L), less during slow exh.
Healthy = ~80%
What factors impact respiratory rate?
Size, age, exercise, body and environmental temperature, arousal state, pregnancy, degree of filling of digestive tract, lying or standing, health
Pregnancy and digestive tract filling influence diaphragm
What is the resp-cardiac coupling?
Resp sinus arrhymia
What other coupling is there of the resp. system?
Resp-locomotive coupling.