Please enable JavaScript.
Coggle requires JavaScript to display documents.
1.22.1.11 - Ventilation and Perfusion - Coggle Diagram
1.22.1.11 - Ventilation and Perfusion
definitions
tidal volume
volume of air flowing through airways during each inspiration & expiration is termed tidal volume
anatomic dead space
volume of the conducting airways not available for gaseous exchange
physiologic dead space
the volume of the lung that does not eliminate CO2
minute ventilation
tidal volume x frequency of breathing
volume of air expired/inspired per minute
dead space ventilation
dead space volume x frequency of breathing
proportion of the Ve that is not available for gas exchange
properties of the lung and thoracic cavity
elastic properties of the lung - net inward force
intrapleural pressure is slightly sub-atmospheric
elastic properties of the chest wall - net outward force
division of airways into two functional zones, conducting and respiratory
role of a spirometer
measures inhaled air
ventilation
total ventilation is the tidal volume x respiratory frequency
alveolar ventilation
fresh gas x respiration frequency
factors
lung compliance
alveolar surface tension
resistance to flow in the airways
distribution of resistance and compliance
synchronicity
more during exercise
healthy vs diseased
differences
different rates of filling
not all alveoli filled at the same itme
pleural pressure gradient
differs in different parts of the pleural cavity
mismatching due to posture
half the volume of the lung is dorsal to the pulmonary trunk
pulmonary systolic arterial pressure is only 20-40mmHg
in horse/ox dorsal parts are less perfused
ventilation also less in dorsal part
ventilation perfusion mismatching
alveolar dead space
hydrostatic pressure failure
low pressure of arteries entering the lung
alveolar emphysema
build up of connective tissue in wall of alveolus
pre-capillary constriction
smooth muscle in walls restricts blood flow and therefore gas exhange
pulmonary embolism
blood clot blocks blood flow to alveoli
mismatching of blood and gas
obstruction due to mucus
infection
deoxygenated blood cannot provide gases to the alveoli
COPD
partial pressures of alveolar gases
partial pressures in the alveoli are different to atmosphere
normal resting breathing the partial pressure of O2 (104 mmHg) and CO2 (40 mmHg) in alveolar gas are kept constant
These values of importance as they govern the PO2 and PCO2 of arterial blood
pulmonary perfusion
anything that affects blood flow to the lungs will affect pulmonary perfusion
hypoxic vasoconstriction
Blood flow to the alveoli allowing uptake of oxygen and removal of carbon dioxide
hypo and hypertension
hypovolaemia
right to left shunting
blood not reaching vessels
regional difference in ventilation
lower portions of the lung are ventilated more than the upper zones
Intra-pleural pressure is higher (less negative) at the bottom (base) of the lung than at the top (apex) due to the weight of the lung
The lung is easier to inflate at low
volumes than at high volumes (becomes stiffer). Resting lung volume at base small so expands well on inspiration
Regional differences in ventilation = change in volume per unit resting volume. So although the base of the lung is poorly expanded compared to the apex it is ventilated better- this also applies to the lowermost section of the lung when animals are in dorsal or lateral recumbency
Apex has a large expanding pressure, big resting volume and only a small change in volume on inspiration
ventilation in the healthy animal
Mis-match of ventilation and perfusion
The ratio at the acinar (alveoli) level determines gas exchange in each alveolus
ventilation should be evenly distributed throughout the lung and matched to the blood supply- parts of the lung doing a lot of gaseous exchange should have a high blood supply
ideal matching of gas and blood in alveoli
every alveolus should be equally ventilated
nomral volume of gas
Deoxygenated blood comes in and partial pressures of gases remains the same when it leaves
Not all the capillaries in normal alveolar walls are fully perfused at all times- reserve, exercise, capillary recruitment- increase blood flow
optimal gas exhange
V/Q less at base of lung- more blood flow than ventilation
V/Q higher at apex- more ventilation than blood flow
So ratio (V/Q) should ideally be 1
With exercise- V/Q more even throughout lungs
Optimal gas exchange in the
lungs requires appropriate ratio between ventilation and blood flow in each alveolus
ways that mismatching occur
Alveolar dead space: examples include pulmonary embolism and alveolar emphysema
Venous-to arterial shunt: hypoxemia and hypercapnia. An example would be chronic obstructive pulmonary disease