partial pressure

Examples of partial pressure in the following topics:

• Dalton's Law of Partial Pressure

  • Dalton's law of partial pressures states that the pressure of a mixture of gases is the sum of the pressures of the individual components.
  • Dalton's law states that the total pressure exerted by the mixture of inert (non-reactive) gases is equal to the sum of the partial pressures of individual gases in a volume of air.
  • Mathematically, the pressure of a mixture of gases can be defined as the sum of the partial pressures of each of the gasses in air.
  • Because gasses flow from areas of high pressure to areas of low pressure, atmospheric air has higher partial pressure of oxygen than alveolar air (PO2=159mmHg compared to PAO2=100 mmHg).
  • Infer from Dalton's law of partial pressure the sum of partial pressures in alveoli

• Henry's Law

  • Henry's law states that the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas.
  • In addition, the partial pressure is able to predict the tendency to dissolve simply because the gasses with higher partial pressures have more molecules and will bounce into the solution they can dissolve into more often than gasses with lower partial pressures.
  • The amount of oxygen that dissolves into the bloodstream is directly proportional to the partial pressure of oxygen in alveolar air. 
  • Recall that the difference in partial pressures between the bloodstream and alveoli (the partial pressure gradient) are much smaller for carbon dioxide compared to oxygen.
  • Oxygen has a larger partial pressure gradient to diffuse into the bloodstream, so it's lower solubility in blood doesn't hinder it during gas exchange. 

• External Respiration

  • Partial pressure gradients (differences in partial pressure) allow the loading of oxygen into the bloodstream and the unloading of carbon dioxide out of the bloodstream.
  • The partial pressure of oxygen in the oxygenated blood of the capillary after oxygen loading is about 100 mmHg.
  • The partial pressure gradient for carbon dioxide is much smaller compared to oxygen, being only 5 mmHg (45 mmHg in deoxygenated blood and 40 mmHg in alveolar air).
  • The partial pressure of carbon dioxide in the blood leaving the capillaries is 40 mmHg.
  • External respiration is a result of partial pressure gradients, alveolar surface area, and ventilation and perfusion matching.

• Pressure Changes During Pulmonary Ventilation

  • When gasses dissolve in the bloodstream during ventilation, they are generally described by the partial pressure of the gasses.
  • Partial pressure more specifically refers to the relative concentration of those gasses by the pressure they exert in a dissolved state.
  • In respiratory physiology, PAO2 and PACO2,refer to the partial pressures of oxygen and carbon dioxide in the alveoli.
  • PaO2 and PaCO2 refer to the partial pressures of oxygen and carbon dioxide within arterial blood.
  • Differences in partial pressures of gasses between the alveolar air and the blood stream are the reason that gas exchange occurs by passive diffusion.

• Adjustments at High Altitude

  • At high altitude there is lower air pressure compared to a lower altitude or sea-level altitude.
  • Due to Boyle's law, at higher altitude the partial pressure of oxygen in the air is lower, and less oxygen is breathed in with every breath.
  • The partial pressure gradients for gas exchange are also decreased, along with the percentage of oxygen saturation in hemoglobin.

• Internal Respiration

  • The factors that influence tissue gas exchange are similar to the factors of alveolar gas exchange, and include partial pressure gradients between the blood and the tissues, the blood perfusion of those tissues, and the surface areas of those tissues.
  • Regarding the partial pressure gradients in systemic capillaries, they have a PaO2 of 100mmHg and a PaCO2 of 40mmHG within the capillary and a PaO2 of 40 mmHg and PaCO2 of 45 mmHg inside issue cells, which allows gas exchange to occur.

• Hypoxia

  • ., due to anemia) but maintain high oxygen partial pressure (pO2).
  • To assist the lungs to distribute oxygenated blood throughout the body, infants at risk of hypoxia are often placed inside an incubator capable of providing continuous positive airway pressure (also known as a humidicrib).
  • The term "hypoxemic hypoxia" specifies hypoxia caused by low partial pressure of oxygen in arterial blood.
  • In the other causes of hypoxia that follow, the partial pressure of oxygen in arterial blood is normal.
  • Acclimatization, the means by which the body adapts to higher altitudes, only partially restores pO2 to standard levels.

• Scuba Diving, the Bends, and Hyperbaric Oxygenation

  • Hyperbaric medicine, also known as hyperbaric oxygen therapy, is the medical use of oxygen at a level higher than atmospheric pressure.
  • For many other conditions, the therapeutic principle of HBOT lies in its ability to drastically increase partial pressure of oxygen in the tissues of the body.
  • The oxygen partial pressures achievable using HBOT are much higher than those achievable while breathing pure oxygen at normobaric conditions (i.e. at normal atmospheric pressure).
  • After elimination of bubbles, the pressure is gradually reduced back to atmospheric levels.
  • Again, these dives last for about an hour and can be administered via a hard, high-pressure chamber or a soft, low-pressure chamber - the major difference being per-dive "dose" of oxygen.

• Plasma and Blood Volume Expanders

  • For instance, the heart pumps more blood with each beat, which increases blood pressure.
  • Blood pressure is detected by the renal system, which increases blood volume and blood pressure by excreting less water during blood filtration.
  • As a result of partial pressure gradient changes, more oxygen is released to the tissues.
  • Colloids: These solutions preserve a high-colloid osmotic pressure (protein-exerted pressure) in the blood, while this parameter is decreased by crystalloids due to hemodilution.
  • They decrease osmotic pressure by diluting the blood.

• Measuring Blood Pressure

  • Measurement of blood pressure includes systolic pressure during cardiac contraction and diastolic pressure during cardiac relaxation.
  • Blood pressure is the pressure blood exerts on the arterial walls.
  • These pressures, called segmental blood pressures, are used to evaluate blockage or arterial occlusion in a limb (for example, the ankle brachial pressure index).The difference between the systolic and diastolic pressure is called the pulse pressure.
  • A blood pressure cuff and associated monitor used for determining systolic and diastolic pressures within an artery.
  • Explain how blood pressure is measured and the ranges of blood pressure readings