Physiology 3 Flashcards
Equation for pulmonary ventilation
Pulmonary ventilation = tidal volume x respiratory rate
pulmonary ventilation
Volume of air breathed in and out per minute
Alveolar ventilation
Volume of air exchanged between atmosphere and alveoli per minute
What factor makes alveolar ventilation lower than pulmonary ventilation?
Presence of anatomical dead space - where air remains, unavailable for gas exchange
Equation for alveolar ventilation
Alveolar ventilation = (tidal volume - dead space volume) x respiratory rate
To increased pulmonary ventilation…
Both depth (tidal volume) and rate of breathing (RR) increase
Due to dead space, it is more beneficial to increase breathing rate (true/false)
False
It is now useful to increase depth of breathing
Transfer of gases between body and atmosphere depends on…
Ventilation and perfusion
Ventilation
Rate gas passes through lungs
Perfusion
Rate blood passes through lungs
Rate of ventilation is equal to rate of perfusion (true/false)
False
Ventilation and perfusion and not perfectly matched
(Blood flow lower at top of lungs c.f. Bottom of lungs)
What is considered as alveolar dead space?
Ventilated alveoli not adequately perfumed with blood
Physiological dead space
Anatomical dead space + alveolar dead space
What structures make up the anatomical dead space?
Nose Pharynx Trachea Bronchi (Where gas exchange does not occur)
Greater perfusion than ventilation in areas causes…
CO2 increase > O2 decrease
Local airway dilation > Airflow increase
Local vessel constriction > Decreased blood flow
Greater ventilation than perfusion in areas causes…
CO2 decrease > O2 increase
Local airway constriction > increased airflow
Local blood vessel dilation > increased blood flow
Four factors affecting rate of gas exchange across alveolar membrane
(1) partial pressure gradient
(2) diffusion coefficient
(3) alveolar membrane surface area
(4) alveolar membrane thickness
What is ‘Partial pressure of gas’?
Pressure exerted by gas if it occupied entire volume of mixture
What does Dalton’s law of partial pressures state?
Total pressure exerted by gaseous mixture (sum of individual partying pressures)
The air respiratory tract is saturated with _______
Water (contributes 47 mmHg to total lung pressure)
describe Partial pressure gradient
Movement of gases from high to low pressures
Partial pressure gradient for CO2 is ______ than for O2
Smaller [x20] - as CO2 is more membrane soluble than O2 (diffusion coefficient)
Diffusion coefficient
Solubility of gas in membranes
Small gradient between alveolar PO2 (PAO2) and arterial PO2 (PaO2) is present (true/false)
True
A big gradient would indicate gas exchange problems in lungs or shunt in heart
