Physiology Flashcards
Tidal volume
The volume of gas inhaled or exhaled during a normal breath
Residual volume
Volume of gas remaining after a maximal forced expiration
Inspiratory Reserve Volume
Volume of gas that can be further inhaled at the end of a normal tidal inhalation
Expiratory Reserve Volume
Volume of gas that can be further exhaled at the end of a normal tidal exhalation
Vital capacity
Volume of gas inhaled when maximal expiration is followed by maximal inhalation
Sum of ERV, TV and IRV
Functional Residual Capacity
Volume of gas that remains after a normal tidal expiration
Sum of ERV and RV
3000ml
Closing Volume
Volume of gas over and above residual volume that remains in the lungs when small airways begin to close
Closing Capacity
Lung capacity at which small airways begin to close
Sum of RV and CV
Equation for Pulmonary Vascular Resistance
PVR = (MPAP - LAP)/CO X 80
Dyne.s-1/cm-5
Factors Increasing PVR
PaCO2
Acidosis
Hypoxia
Adrenaline/Noradrenaline
Thromboxane A2
Angiotensin II
5-HT3
Histamine
High or low lung volume
Factors Decreasing PVR
Alkalosis
Isoprenaline
Acetylcholine
Prostaglandins
Nitric Oxide
Increased peak airway pressures/pulmonary venous pressure
Volatile agents
Dead Space
The volume of the airways in which no gas exchange occurs
Anatomical Dead Space
Volume of the conducting airways that does not contain any respiratory epithelium
Nasal cavity to generation 16 terminal bronchioles
Measured by Fowler’s method - 2mls.kg
Alveolar Dead Space
The volume of those alveoli that are ventilated but not perfused
Physiological Dead Space
The sum of anatomical and alveolar dead space
Calculated using the Bohr equation
Fowler’s Method
Measures anatomical dead space
Vital capacity breath of oxygen and then exhales through a nitrogen analyser
Bohr Equation
Calculates physiological dead space ratio to TV
Normally around 30% / ratio 0.3
VD/VT = (PaCO2-PeCO2)/PaCO2
The Pasteur Point
The oxygen concentration below which oxidative phosphorylation cannot occur in the mitochondria.
1mmHg (0.13kPa)
Oxygen Extraction Ratio
The fraction of delivered oxygen that is taken up by the tissues
O2ER = VO2/DO2. Normally 0.2-0.3
Differs between organs, the heart having an OER of 0.6
Doubles in exercise.
P50
Partial pressure of O2 in the blood at which haemoglobin is 50% saturated.
Factors causing Left Shift - increased affinity
Decreased PaCO2
Alkalosis
Decreased temperature
Decreased DPG
Fetal haemoglobin
Carbon monoxide
Methaemoglobin
Factors causing Right Shift - increased offloading
Increased PaCO2
Acidosis
Increased temperature
Increased DPG
Pregnancy
Altitude
Haemoglobin
Bohr Effect
The affinity of haemoglobin for oxygen is reduced by a reduction in pH and increased by an increase in pH
Haldane Effect
Deoxygenated haemoglobin is able to carry more CO2 than oxygenated haemoglobin
-deoxyHb forms carb amino complexes with CO2
-deoxyHb is a better buffer of H+ forming more HCO3
In tissues - Hb gives up O2, affinity for CO2 increases
In lungs - Hb binds O2, affinity for CO2 decreases