Lecture 16 Flashcards
What is the expiratory volume equation? Why does it not tell us the amount through the lungs? How can we tell the amount through the lungs?
Total ventilation through the mouth= frequency of breaths x tidal volume.
The dead space is the space taken up by inhaled air which never reaches the alveoli so it cannot gas exchange (normally about 150 mls). To get alveolar ventilation the equation is V = frequency x (V through mouth - dead space volume).
What is hypo and hyperventilation?
Hypo ventilation is low Va
Hyper ventilation is high Va(volume into the lungs).
What occurs in relation to dead space and low/high tidal volume. What breathing rates will by hypo/hyper ventilating.
Dead space is always the same and hence shallower breaths are affected more heavily. This means fast breathing tends to be hypoventilation while deep breathing tends to be hyperventilating.
What happens to oxygen concentration as we get further in the respiratory pathway?
As we get closer to the alveoli the concentration of O2 decreases e.g due to humidification and diluting with CO2. The exchange itself occurs through the capillaries via diffusion and is not 100% effective as the concentration lowers slightly more.
What is the respiratory exchange ratio?
The ratio of volume of caron dioxide exchanged to volme of oxygen exchanges is known as the respiratory exhange ration and is typically around 0.8 on a balanced diet.
What is ficks law of diffusion? How are the lungs good for this and how does this apply to CO2 and oxygen diffusion? What is the most likely to change value.
Ficks law of diffusion is F = A/T x(D (P1 -P2) it states that more area, less thickness, larger diffusion constant (D) and higher pressure difference allows more gas exchange through the membranes, the lungs have a huge area for this (blood brain barrier) and a tiny thickness. The diffusion constant is based on the substance and is much higher for CO2 than oxygen, this means it will always diffuse out as fast as oxygen.
Pressure difference is the main factor that changes.
What do emphysema and fibrosis do to the lungs?
Emphysema increases alveolar area for diffusion and fibrosis affects the thickness of alveolar membrane.
What factors affect partial pressure of oxygen and carbon dioxide at the alveoli? What is carbon dioxides and oxygens kept at in the alveoli?
The partial pressures of oxygen and CO2 at the alveoli set the alveolar end of the partial pressure diffusion gradient, they are determined by the composition of inspired air, the alveolar ventilation, the O2 consumption or CO2 production ad the matching of alveolar ventilation to pulmonary capillary blood flow.
In the alveoli carbon dioxide’s is kept at 40 mmHg and oxygen’s is at 100mmHg.
How do we get partial pressures of carbon dioxide and oxygen in the blood (what are the normal values for the arteries and veins)? Why is the oxygen lower than in the alveoli?
Partial pressure of carbon dioxide and oxygen in the blood is gotten via measuring from an artery. This is normally 95 mmHg for oxygen(little lower than alveoli because the oxygen transfer is not complete) and 40 mmHg for carbon dioxide.
40 mmHg for oxygen in veins, 46 mmHg for CO2 in veins.
