Oxygen Transport – Gas Transport

00:02 In this lecture, we’re dealing with the transport of O2 and CO2.

00:07 Our learning goals will be to understand O2 transport and be able to differentiate between those modes of transport.

00:16 Also, you will be to identify the factors that affect oxygen hemoglobin dissociation.

00:23 Furthermore, after this lecture, you’ll be able to understand CO2 transport and be able to differentiate the modes of transport as well as identify factors that affect that transport.

00:35 So as we think about O2 transport, we really need to concentrate on what the partial pressure of oxygen is.

00:44 And so there are three partial pressures that we need to keep in mind.

00:48 PaO2, PAO2 and PVO2.

00:53 And the reason why I very much distinguished between capital A and small A O2, is it tells you where to locate it.

01:01 So PaO2 is the partial pressure of oxygen in the arterial circulation.

01:06 PAO2 is the partial pressure of oxygen in the alveoli.

01:11 PVO2 is the partial pressure of oxygen in the venous circulation.

01:16 And you need to remember what those are as we walk through O2 transport.

01:22 So to give you an idea of those numbers, the PAO2 is around 95.

01:27 The PAO2 is around 100, and the PVO2 is around 40 millimeters of mercury.

01:34 And so those are numbers you want to kind of keep in mind as we walk through this transport of oxygen.

01:43 Those numbers seem like they are going to be very important because these are the numbers that we measure from an arterial blood gas.

01:52 So if were to take an arterial sample and measure the amount of oxygen in it, those are the numbers that you get.

01:59 So this is a very important thing to help us distinguish between if someone has a hypoxemia, versus they have a normal O2 concentration.

02:07 Those are the partial pressures.

02:11 However, partial pressure only gives us one insight into how much O2 is being carried by the blood.

02:19 The other insight that we need to think about is how much is diffused in a gaseous form and that is really based upon the amount of O2 solubility.

02:30 Unfortunately, O2 is not very soluble.

02:33 So let’s go through a calculation to [inaudible 00:02:35.4] reedify this.

02:37 Dissolved O2 is the partial pressure of O2 times the solubility of O2 at body temperature.

02:44 If we go through this calculation, it ends up that you have less than 1 milliliter of O2 per 100 mL of blood or per 1 deciliter of blood.

02:56 So just a very small amount.

02:59 If we look on the venous side, it’s even smaller 0.124.

03:04 So these are very, very, very small concentrations of oxygen in a dissolved form.

03:14 So having this amount of oxygen only in the dissolved form is unfortunately not compatible with life.

03:22 If you did not have someway to carry the oxygen, you would not be able to transport enough blood to cells to keep them alive via aerobic metabolism.