The work of breathing

what sort of compliance should lungs have

high compliance to easily expand and accomodate air

two types of forces opposing ventilation

restrictive and obstructive

restrictive (what and causes)

reduced lung capacity due to reduced compliance

what causes surface tension and how does it affect lung compliance

water molecules bond to create surface tension which restricts expansion of the thin-walled alveoli therefore reducing lung compliance

how does surfactant affect lung compliance?

complex phospholipid surfactant molecules interrupt interactions between water molecules decreasing surface tension and therefore increasing lung compliance

obstructive (what and causes)

resistance to airflow from walls of bronchioles

restrictive conditions

pulmonary fibrosis (pneumocytes replaced with inflexible fibrotic/scar tissue), insufficient surfactant secretion

obstructive conditions

asthma, chronic bronchitis

spinometry trace volumes

tidal, inspiratory/expiratory reserve, residual, minimal

spinometry trace capacities

vital, total lung, inspiratory, functional residual

Tidal volume

volume of air moved in and out during normal quiet breath

Inspiratory reserve volume (IRV)

Extra volume of air brought in with maximal inhalation

Expiratory reserve volume (ERV)

extra volume of air pushed out with maximal effort

Residual volume

Volume remaining in lungs after maximal exhalation

minimal volume

volume remaining in lungs if they collapsed

vital capacity (definition and calculation)

Volume of air shifted in and out of lungs with maximal inhalation and exhalation
expiratory reserve + tidal volume + inspiratory reserve

total lung capacity (definition and calculation)

volume in lungs when filled to max
residual volume + vital capacity

inspiratory capacity (definition and calculation)

total volume inspired from rest with maximal inhalation
tidal + inspiratory

functional residual capacity (definition and calculation)

volume remaining in lungs after normal exhalation
residual + expiratory

advantages of spirometry

easy, non-invasive
can indicate type of condition

what does spirometry measure

FEV1 forced expiratory volume in one second/how quickly we can breathe out air

FEV1/VC ratio defintion

percentage of total vital capacity breathed out in one second

what can FEV1/VC ratio tell us about condition?

below 70%, likely to be obstructive (restricted airflow, easy accomodation)
above 70% likely to be restrictive (easy airflow, stiff accomodation)

what is emphysema and causes

reduced alveolar surface area due to damage from irritants that decreases efficiency of diffusion

3 factors determining diffusion efficiency

surface area, membrane thickness, pressure gradient 

3 factors affecting pressure gradient

atmospheric pressure, alveolar ventilation, blood oxygen levels

average partial pressure of oxygen in alveoli

100

average partial pressure of oxygen in pulmonary capillaries

enters at 40, leaves at 95

average partial pressure of carbon dioxide in alveoli

40

average partial pressure of carbon dioxide in pulmonary capillaries

enters at 45, leaves at 40

average partial pressure of oxygen in tissues

40

average partial pressure of carbon dioxide in tissues

45

how do chemoreceptors regulate breathing?

monitor oxygen and carbon dioxide concentrations in blood → send signals to brain → send afferent signals to change respiratory rate

signalling pathway when arterial BP decreases

flow reduces → sensed by baroreceptors in arteries → respiratory minute volume increases → increase BP

signalling pathway when arterial BP increases

flow increases → sensed by baroreceptors in arteries → respiratory minute volume decreases → decrease BP

protective reflexes of lung stretch receptors (2)

send signals to prevent damage to lungs from over-inhalation/exhalation
detect irritants and cause sneezing/coughing

why are carbon dioxide chemoreceptors primary?

oxygen levels fluctuate, carbon dioxide must stay constant to maintain pH of blood

why do we increase ventilation in response to low BP

to ensure same amount of gas exchanged despite reduced flow

why do we decrease ventilation in response to high BP

there will be greater gas exchange with minimal ventilation when there is higher flow