Gas Exchange and Transport (v/p)

What are the two main components of the respiration process?

Gas exchange at the lungs and cellular level, and transport of gases.

How does oxygen diffuse into the blood?

O2 is moved into the lungs, diffuses into the pulmonary circulation, and is transported in the blood to the tissues.

What happens to carbon dioxide in the tissues?

CO2 builds up in the tissues due to metabolism and diffuses into capillary blood before being carried to the lungs.

What is the normal inspired partial pressure of oxygen (PiO2)?

159 mm Hg.

What is the intracellular PO2 approximately?

About 5 mm Hg.

What is the diffusion gradient for CO2?

PCO2 is highest in the cells (approximately 60 mm Hg) and lowest in room air (1 mm Hg).

What factors determine alveolar carbon dioxide tension (PACO2)?

PACO2 varies directly with CO2 production and inversely with alveolar ventilation.

What is the formula for calculating PACO2?

PACO2 = (CO2 production / alveolar ventilation) * K, where K is a correction factor.

What is the normal range for PACO2?

35 to 45 mm Hg.

What happens to PACO2 during exercise or fever?

PACO2 increases if CO2 production increases while ventilation remains constant.

What determines the alveolar partial pressure of oxygen (PAO2)?

Factors include the fraction of inspired O2 (FiO2), barometric pressure, water vapor tension, and PACO2.

What is the respiratory quotient (RQ)?

Typically estimated at 0.8, it is used in calculations involving PAO2.

What is the A-a gradient (DA−aO2)?

The difference between alveolar and arterial PO2, typically small at 5-10 mm Hg.

What does an increased A-a gradient indicate?

It often indicates pulmonary parenchymal disease.

What is the P/F ratio?

The ratio of PaO2 to FiO2, used to assess oxygenation abnormality.

What is the significance of a DA−aO2 of nearly 400 mm Hg?

It indicates a large difference between alveolar and arterial PO2 values, suggesting inefficient O2 transfer.

What does a P/F ratio of 71.4 indicate?

It indicates severe hypoxemia.

What is the normal range for A-a gradient in healthy individuals?

5-10 mm Hg.

What is the primary use of the P/F ratio in ventilated patients?

To measure oxygenation abnormality.

What is the relationship between PAO2 and arterial PO2?

PAO2 is the alveolar oxygen pressure, while arterial PO2 (PaO2) is the oxygen pressure in arterial blood.

What is gaseous diffusion?

The process whereby gas molecules move from an area of high partial pressure to an area of low partial pressure.

What is DL in the context of lung diffusion?

DL is the diffusing capacity of the lungs, combining area, thickness, and diffusion properties.

What is necessary for gas exchange to occur between alveoli and pulmonary capillaries?

A difference in partial pressures (P1 − P2) must exist.

What is the average alveolar PO2 in a normal lung?

Approximately 100 mm Hg.

What is the average mean PCO2 in a normal lung?

Approximately 40 mm Hg.

What is the pressure gradient for O2 diffusion into the blood?

Approximately 60 mm Hg (100 mm Hg − 40 mm Hg).

What are the mean alveolar gas pressures for O2 and CO2?

Approximately 100 mm Hg for O2 and 40 mm Hg for CO2.

What happens to blood as it enters the venous end of the capillary?

It gives up CO2 and loads O2 until the gases are in equilibrium with alveolar pressures.

What is the pressure of oxygen at the venous end of the capillary?

40 mm Hg.

What is the pressure of carbon dioxide at the arterial end of the capillary?

40 mm Hg.

Why does CO2 diffuse from blood into the alveolus?

Because venous blood has a higher PCO2 than alveolar gas (46 mm Hg vs. 40 mm Hg), creating a pressure gradient.

What is the permeability difference between CO2 and O2 across the alveolar membrane?

Alveolar membrane permeability is approximately 20 times greater for CO2 than for O2.

What is required for blood to be adequately oxygenated in the pulmonary capillary?

Blood must spend sufficient time in contact with the alveolus to allow equilibration.

What happens to oxygen diffusion during heavy exercise?

Capillary transit time decreases, but it remains adequate for equilibration unless other factors impair diffusion.

What is an alveolar shunt?

Exchange units with V/Q values of zero where venous blood cannot pick up O2 or unload CO2.

What is the difference between anatomic and alveolar shunts?

Anatomic shunts involve blood bypassing ventilated areas, while alveolar shunts involve blood in areas with no perfusion.

What is the shunt equation used for?

To quantify the portion of blood included in the V/Q mismatch, expressed as a percentage of total cardiac output.

What does a significant shunting indicate under the 50/50 rule?

If FiO2 is greater than 50% and PaO2 is less than 50 mm Hg, significant shunting is present.

What does dead space refer to in the context of ventilation?

Areas with ventilation but no blood flow, leading to wasted ventilation.

What are the two components of dead space?

Anatomic dead space (upper airways) and alveolar dead space (alveoli without perfusion).

What is physiologic dead space?

The sum of alveolar and anatomic dead space.

How does increased dead space affect alveolar ventilation?

It decreases alveolar ventilation and increases PaCO2.

What causes regional differences in the V/Q ratio in the lungs?

Gravity affects blood flow and ventilation, with more perfusion at the lung bases.

What is the V/Q ratio at the lung apexes?

Approximately 3.3, with high PO2 (132 mm Hg) and low PCO2 (32 mm Hg).

What is the V/Q ratio at the bottom of the lung?

Approximately 0.66, with low PO2 (89 mm Hg) and slightly higher PCO2 (42 mm Hg).

What happens to blood flow in the lungs due to gravity?

Most blood flows to the lung bases, resulting in lower PO2 and higher PCO2.

What is the ideal V/Q ratio in healthy lungs?

The V/Q ratio is kept as close to 1 as possible.

What condition causes significant gas exchange abnormalities due to fluid accumulation in the alveoli?

Adult Respiratory Distress Syndrome (ARDS).

What is one method to improve V/Q matching in patients with ARDS?

Placing patients in a prone position.

What is the primary way blood carries oxygen?

Most O2 is bound to hemoglobin (Hb) inside red blood cells (RBCs).

How much O2 can 1 g of normal hemoglobin carry?

Approximately 1.34 mL of O2.

What is the normal range for arterial oxygen saturation (SaO2)?

95% to 100%.

What is the formula for calculating total oxygen content of the blood?

CaO2 = (0.003 × PaO2) + (1.34 × Hb × SaO2).

Venous content formula

CV02=(1.34 x Hb x SV02) + (0.003 x PV02)

Capillary content formula

CC02=(1.34 x Hb x 1.0) + (0.003 x PA02)

Pa02 formula

(pb-ph20)fi02-pac02/rq

shunt equation

Qs/Qt = (CcO2 - CaO2)/(CcO2 - CvO2)

Low hemoglobin

anemia

What does the oxyhemoglobin dissociation curve illustrate?

The relationship between hemoglobin saturation and partial pressure of oxygen (PO2).

What is the significance of the flatter upper part of the oxyhemoglobin dissociation curve?

It indicates that major changes in PaO2 have little effect on SaO2 in the normal operating range.

What happens to SaO2 when PaO2 drops below 60 mm Hg?

SaO2 drops significantly due to the steepening of the curve.

What is the 40-50-60/70-80-90 rule in relation to pulse oximetry?

Saturations of 70%, 80%, and 90% correspond to approximate PaO2 values of 40, 50, and 60 mm Hg.

What is the role of deoxygenated hemoglobin in blood?

It serves as an important blood buffer for H+ and aids in CO2 transport.

What is the relationship between dissolved oxygen and partial pressure according to Henry's law?

The amount of dissolved O2 is directly proportional to the partial pressure of O2.

What is the effect of breathing pure oxygen on PaO2?

PaO2 can increase to approximately 670 mm Hg.

What is the total oxygen content of normal arterial blood with PaO2 of 100 mm Hg, Hb of 15 g/dL, and SaO2 of 0.97?

Approximately 19.8 mL/dL.

How does hemoglobin saturation (SaO2) relate to total oxygen content?

SaO2 plays a greater role in total blood O2 content than PaO2.

What should clinicians consider when evaluating a patient's oxygenation?

Both SaO2 and PaO2 should be considered for a complete understanding of gas-exchange status.

What is the significance of the iron ion in hemoglobin?

It binds O2 molecules and determines the affinity of hemoglobin for oxygen.

What happens to hemoglobin when it is fully saturated with oxygen?

It becomes oxyhemoglobin (HbO2) with paired electrons.

What is the impact of gravity on ventilation and perfusion in lung disease?

Gravity-dependent areas receive more perfusion but less ventilation, worsening V/Q mismatch.

What is the clinical implication of pulse oximetry readings?

They provide noninvasive estimates of Hb saturation but can be inaccurate.

What is the importance of maintaining PaO2 above 60 mm Hg?

To prevent significant drops in SaO2 and maintain oxygen-carrying capacity.

What is the effect of hypoxemic respiratory failure on oxygen transport?

It complicates oxygen transport and may require mechanical ventilation.

What is the role of hemoglobin in increasing oxygen-carrying capacity?

It increases the capacity nearly 70-fold compared to plasma alone.

How does the shape of hemoglobin affect its function?

The coiled structure of hemoglobin determines its affinity for oxygen.

What is the role of 2,3-diphosphoglycerate (2,3-DPG) in red blood cells?

2,3-DPG forms a loose bond with deoxygenated hemoglobin (Hb), stabilizing it in its deoxygenated state and reducing its affinity for O2.

How does increased concentration of 2,3-DPG affect hemoglobin's oxygen affinity?

Increased 2,3-DPG concentrations shift the HbO2 curve to the right, promoting O2 unloading.

What conditions tend to increase 2,3-DPG concentrations?

Alkalosis, chronic hypoxemia, and anemia increase 2,3-DPG concentrations, promoting O2 unloading.

What effect does acidosis have on 2,3-DPG levels?

Acidosis results in lower intracellular levels of 2,3-DPG, increasing hemoglobin's affinity for O2.

What is carboxyhemoglobin (HbCO) and its effect on oxygen transport?

HbCO is formed when hemoglobin binds with carbon monoxide (CO), which has a much higher affinity for Hb than O2, impairing O2 delivery.

How does carbon monoxide (CO) poisoning affect oxygen levels in the blood?

Patients may present with normal PaO2 values despite severe tissue hypoxia due to CO displacing O2 from hemoglobin.

What are the three forms in which carbon dioxide (CO2) is transported in the blood?

CO2 is transported dissolved in physical solution, chemically combined with proteins, and ionized as bicarbonate.

What percentage of CO2 is released at the lungs in dissolved form?

Approximately 8% of CO2 is released at the lungs in dissolved form due to its higher solubility in plasma.

What is the significance of the leftward shift of the HbO2 curve?

A leftward shift indicates an increased affinity of hemoglobin for O2, which can hinder O2 unloading.

What effect does increased CO2 or H+ ions have on hemoglobin's affinity for oxygen?

It decreases hemoglobin's affinity for oxygen, promoting oxygen release to tissues.

How is most CO2 transported in the blood?

As bicarbonate (approximately 80%)

What is the initial product of CO2 hydrolysis in plasma?

Carbonic acid

What ions are produced when carbonic acid ionizes?

H+ ions and bicarbonate ions (HCO3−)

What enzyme enhances the hydrolysis of CO2 inside erythrocytes?

Carbonic anhydrase

What phenomenon describes the inward movement of anions to maintain electrolytic equilibrium in erythrocytes?

Chloride shift (Hamburger phenomenon)

What is the relationship between blood PCO2 and CO2 content depicted in?

The CO2 dissociation curve

What effect does oxyhemoglobin saturation have on the CO2 dissociation curve?

It modifies the position of the CO2 dissociation curve (Haldane effect).

What happens to O2 delivery (DO2) when there is inadequate oxygen supply for cellular needs?

Hypoxia occurs.

What is hypoxemia?

A decrease in the partial pressure of O2 in arterial blood (PaO2).

What can cause hypoxemia?

Low ambient PO2, hypoventilation, impaired diffusion, V/Q imbalances, and shunting.

What is the physiological significance of the Bohr effect?

CO2 levels influence pH, which modifies the O2 dissociation curve.

What is the role of plasma proteins in buffering H+ ions?

They help buffer H+ ions produced during CO2 hydrolysis.

What happens to CO2 content as blood transitions from arterial to venous?

CO2 content increases due to lower O2 saturation in venous blood.

What is ARDS?

Acute Respiratory Distress Syndrome, a severe lung condition causing hypoxemia.