Case Study 22

The total O2 content of blood includes dissolved O2 and O2 bound to hemoglobin (O2-hemoglobin). What is the total O2 content of the blood in this case? What fraction of the total O2 content is O2-hemoglobin?

1. O2 content = dissolved O2 + O2-hemoglobin = 0.3 Ml/100 blood + 19.7 mL O2/100 mL blood = 20mL /100 mL blood 2. O2-hemoglobin = O2-binding capacity x % saturation = 20.1mL/100 mL blood x 98 = 19.7 *note = hemoglobin has 4 subunits that o2 attaches too. 100% saturation mean there is 4 O2 attached to 1 hemoglobin

If alveolar Po2 is reduced from 100 to 50 mm Hg, how would this reduction alter pulmonary capillary Po2?

50mmHg

What is the concentration of dissolved O2 in that blood? (part of a prev. question)

According to Henry's law, the concentration of dissolved O2 depends on the partial pressure of O2 in liquid phase: CX= PX x solubility where: Cx = concentration of dissolved gas Px = partial pressure of the gas solubility = solubility of gas in blood = 100 mmhg x 0.003/100 ml blood = 3.0 x 10-3

How does this equilibration occur? (part of a prev. question)

Alveolar gas has a much higher Po2 which creates a large partial pressure gradient for diffusion of O2 from alveolar gas into the pulmonary capillary. Once the equilibrium occurs, there is no more longer a dirving force for further diffusion of O2. This equilibrated blood leaves the pulmonary capillaries, enters the left side of the heart and becomes systemic arterial blood

How would it alter the concentration of dissolved O2 in pulmonary capillary blood?

Dissolved O2 = 50 x 0.003 ml/100 - 0.15/100ml

The value for alveolar Po2 (PaO2) is given as 100 mm Hg. Assuming complete equilibration of O2 across the alveolar-pulmonary capillary barrier, what is the value for Po2 in pulmonary capillary blood?

Is PO2 has a value of 100 mmhg, pulmonary capillary blood will also have 100 mmhg. The driving force for this diffusion is the partial pressure difference for O2, b/n alveolar gas and pulmonary capillary blod

When inspired air enters the trachea, it is saturated with water vapor (humidified). What is the Po2 of humidified tracheal air at sea level?

PX = (PB - PH20) X F where: Px = partial pressure of gas Pb= barometric pressure F = fractional concentration of gas PH2O = water vapor pressure = (760-47) x 0.21 = 149.7 mm Hg

What is the partial pressure of O2 (Po2) in dry air at sea level?

PX = PB X F where: Px = partial pressure of gas Pb= barometric pressure F = fractional concentration of gas = 760 x 0.21 = 159.6

How would it alter the amount of dissolved O2? (change in hemoglobin concentration)

Simply need to calculate how such a change will alter the o2-binding capacity. O2-binding capacity = 9/15 (new concentration over old conc.) x 20.1/100 mL = 12.1/100 O2-hemoglobin = O2-binding x % saturation = 12.1/100 x 98% = 11.9 mL/100 mL

If the hemoglobin concentration is reduced from 15 to 9 g/dL, how would this reduction alter the amount of O2-hemoglobin?

This will lower the amount of O2-hemoglobin because there is less hemoglobin available.

How would it alter the total O2 content of blood? (change in Hb concentration)

Total o2 content = O2-hemoglobin + dissolved O2 = 11.9/100 mL +0.3 mL/100 = 12.2 ml/100

How would it alter the total O2 content?

o2-Hb =20.1/100mL x 85% = 17.1 Total o2 content = 0.15/100 +17.1 = 17.3/100 *the saturation lowers to ~85% because PO2 is no longer 100mmhg *when Po2 halfs, the saturation goes down by 25%