Section 8: Respiratory Function

Acid (H30+)

A chemical that can donate a hydrogen ion (H+) in solution = proton donors (hydrogen donors) ex.) carbonic acid

Strong Acid

Low affinity for hydrogen & therefore readily dissociates in water to give up H+

Weak Acid

High affinity for hydrogen & therefore releases its hydrogen & therefore releases its hydrogen ion less readily in solution

Base (OH-)

A chemical that can accept a hydrogen ion (H+), proton acceptor, ex.) bicarbonate

Strong Base

Low affinity for hydroxyl ions & readily dissociates to give them up

Weak Base

High affinity for hydroxyl ions & holds on to them

pH

Hydrogen ion activity expressed as a negative log of the activity of the solution

pH

7.35-7.45

Buffer

Solution that protects the body by minimizing changes in pH, and is the body's first line of defense when the body's pH deviates from normal

Apnea

Absence of breathing (ventilation)

Dyspnea

Difficulty breathing

Eupnea

Normal respirations when a person is at rest

Perfusion

Process of blood delivery to a capillary bed in the tissues, and the subsequent transfer of oxygen

What is the relationship between pH & H+ ions?

- the more H+ ions, the more acidic a solution is

- the more OH- ions, the more basic a solution

What are the 4 types of buffer systems discussed in class?

1. Bicarbonate Buffer

2. Hemoglobin Buffer System

3. Phosphate Buffer System

4. Protein Buffer System

What is the most important buffer system?

Bicarbonate Buffer

Where is the bicarbonate buffer located?

Extracellular spaces

Where is the hemoglobin buffer system location?

Intracellularly in red cells

Where is the phosphate buffer system located?

Internal fluid of all cells

Where is the protein buffer system located?

Intracellularly, some in the plasma

What are the respiratory components of the bicarbonate buffer system?

Plays a role in CO2 exchange between the blood and the lungs, by controlling the respiratory rate

What are the metabolic components of the bicarbonate buffer system?

Kidneys can alter the bicarbonate concentration with the amount of substance that are reabsorbed or filtered through the renal tubules

Which organs are involved in the respiratory component of the bicarbonate buffer system?

Lungs

Which organs are involved in the metabolic component of the bicarbonate buffer system?

Kidneys

What is the ratio of bicarbonate to carbonic acid when the body pH is normal?

20:1, need more bicarbonate because the body is full of chemical reactions creating CO2, making the body acidic so it needs lots of bicarbonate to even it out

How does the H-H equation solve for an unknown parameter in order to help identify an acid-base disorder?

Important in understanding how the bicarbonate-carbonic acid buffer system regulates acid-base relationships

*if 2 parameters are known, then you can solve for the missing parameter*

H-H equation: pKa

Constant, normal avg value for pK in blood at 37 degrees Celsius = 6.103

H-H equation = a

Constant, solubility coefficient for CO2 gas in normal plasma at 37 degrees Celsius=0.0306 mole/L

H-H equation = H2CO3 concentration

PCO2, respiratory components because it is controlled by the lungs

H-H equation = HCO3-

Controlled by kidneys, metabolic components

What is the enzyme responsible for the conversion of PCO2 & water to form carbonic acid in the RBC?

Carbonic Anhydrase

Where is the enzyme responsible for the conversion of PCO2 & water to form carbonic acid in the RBC located?

Found in the RBC membrane

What is the Isohydric Shift?

H+ would alter the pH left unbound so as soon as the oxygen in the hemoglobin that was picked up in to lungs gets unloaded at the tissue site, the deoxyhemoglobin combines with H+

What is the Chloride Shift?

As the HCO3- concentration rises in the RBC, it diffuses out into the plasma, and in order to maintain electro neutrality on both sides of the RBC membranes, chloride diffuses into the cell, which is known as the chloride shift

What are the structural components of the protein that are responsible for the buffering capabilities?

The buffering capacity of proteins comes from the terminal groups/side groups of amino acids (carboxyl & amino groups)

How does the protein buffer system respond to an acidic environment?

The amino group (weak base) will bind H+ to raise the pH

How does the protein buffer system respond to a basic environment?

The carboxyl group (weak acid) will release H+ to lower the pH

What protein contributes the majority of the protein buffering capability?

Albumin

What is the location of the phosphate buffer system?

Within the internal fluid of all cells

What is the name of the chemical buffer in the phosphate buffer system?

Dihydrogen Phosphate

Pharnyx

Oxygenated air from the atmosphere is breathed in through the nose and mouth and enters through it

Larynx

Forms the entrance to the lower respiratory system; prevents food or fluid from entering the lower respiratory system during swallowing

Tracheae

A rigid tube that is located at the opening of the bronchial tree

Alveoli

Functional unit of the respiratory system; where gas exchange takes place

What is the functional unit of the lungs?

Alveoli

Ventilation

Movement of air through the respiratory passageways into the alveoli of the lungs, followed by a reversal of air movement out of the lungs

Inspiration

Takes place when the air pressure within the lungs is less or lower than the atmospheric pressure

Expiration

Takes place when the air pressure within the lungs is greater or higher than the atmospheric pressure

For normal ventilation to occur, what events need to take place?

The rhythm of the muscles that contract must be consistent and automatic as well as be able to accommodate changing metabolic demands

Where is the location of the respiratory center of the brain?

Medulla

Phrenic Nerve

Responsible for the increase in ventilation activity to accommodate an increase in body activity

Tonic Drive

Develops from many sources, but the most important are the central & peripheral neurons/chemoreceptors that monitor O2, CO2, & pH

External Convection Systems

Exchange of oxygen for carbon dioxide between the alveoli & the pulmonary capillaries in the lungs

Internal Convection Systems

Exchange of oxygen for carbon dioxide between the blood vessels and the tissues

What are the conditions that must be present for adequate oxygenation of the tissues to occur?

- available atmospheric oxygen

- gas exchange between the lungs and arterial blood

- loading of oxygen onto hemoglobin

- adequate transport (cardiac output)

- release of oxygen (perfusion) to the tissues

In what location is the majority of oxygen found in the body?

Transported to the tissues bound to hemoglobin (oxyhemoglobin)

Oxyhemoglobin

- Contains oxygen

- makes up 95% or more of hgb in normal circumstances

- reversible

Deoxyhemoglobin

- Does not contain oxygen

- reduced form found normally in small amounts that is capable of binding O2 to become oxyhemoglobin

- reversible

Carboxyhemoglobin

- abnormal form of hgb, with a strong affinity for hgb which limits oxygen content of blood

- reversible but only separates in the presence of high levels of oxygen

Methemoglobin

- abnormal form of hgb containing oxidized Fe3+ that cannot bind to oxygen

- reversible but only separates in the presence of oxygen

Sulfhemoglobin

- abnormal form of hgb containing oxidized Fe3+ that cannot bind to oxygen

- irreversible

Explain the relationship of ferrous iron in the process of oxygen binding

Hemoglobin can only bind to oxygen in the ferrous state, binding of O2 is reversible

Explain the relationship of histidine in the process of oxygen binding

The most important amino acid involved in the binding of hemoglobin to O2

Oxygen Carrying Capacity Equation

Pt. Hemoglobin level X 1.34 = oxygen carrying capacity (mLs)

What are the 4 factors that affect perfusion rate?

1. Temperature

2. pH

3. PCO2

4. 2,3 Disphosphoglycerate

How does temperature affect the affinity for oxygen by using the hgb-oxygen dissociation curve?

- high temp shifts curve to the right

- low temp shifts curve to the left

- high temp decreases the O2 affinity of hgb and O2 is released

How does pH affect the affinity for oxygen by using the hgb-oxygen dissociation curve?

- Bohr effect

- high pH shifts curve to the left

- low pH shifts curve to the right

How does PCO2 affect the affinity for oxygen by using the hgb-oxygen dissociation curve?

- increase in CO2 levels shifts curve to the right

- decrease in CO2 levels shifts curve to the left

How does 2,3-Diphosphoglycerate affect the affinity for oxygen by using the hgb-oxygen dissociation curve?

- increase in 2,3-Diphosphoglycerate shifts curve to the right

-decrease in 2,3-Diphosphoglycerate shifts curve to the left

Bohr Effect

*effect of pH on hgb-oxygen affinity*

-Decreased: increase in H+, presence of H+ in the blood, observed in respiratory acidosis

-Increased: decrease in H+

Haldane Effect

Removal of oxygen from hemoglobin increases hemoglobin's affinity for carbon dioxide

What are the 3 main transporters of CO2 in the body?

1. Bicarbonate (70%)

2. Dissolved Carbon Dioxide (5-7%)

3. Carbamino Compounds (15-25%)

What transporter of CO2 accounts for the greatest carrying capacity?

Bicarbonate, most important

For blood gas analysis, what is the recommended site of collection?

Arterial from radial artery

For blood gas analysis, what is the recommended type of specimen?

Arterial blood

For blood gas analysis, what is the recommended anticoagulant that should be used?

- Heparin

- Heparin blood collection tube or heparinized syringe

*others affect pH & blood gas results*

Venous blood

- no pulse

- dark red

Arterial blood

- have a pulse

- bright red

- harder to collect on old people because of extra skin

- greater pain because they are deeper and have more nerve endings surrounding them

- prolonged pain or loss of feeling

- prolonged bleeding

- prone to hematoma formation

What is the pH in venous blood?

- low pH

- acidic

What is the pH in arterial blood?

- high pH

- alkaline

What is the pO2 in venous blood?

- low O2

What is the pO2 in arterial blood?

- high O2

What is the pCO2 in venous blood?

- high CO2

What is the pCO2 in arterial blood?

- low CO2

How do bubbles affect the accurate measurement of blood gas parameters?

- causes a lot of errors

- must remove them prior to analysis right after collection

- pH can be falsely increased

- CO2 would be falsely decreased

- O2 would be falsely increased

How does air exposure affect the accurate measurement of blood gas parameters?

- atmospheric oxygen can reach the specimen and CO2 will escape the specimen

- falsely increased O2

- falsely decreased CO2

- falsely elevated pH

How does not using an anticoagulant or using an incorrect anticoagulant affect the accurate measurement of blood gas parameters?

- not using = blood will clot

- using incorrect = increase pH, affects blood gas levels

How does dilution affect the accurate measurement of blood gas parameters?

- infused with an IV, first pull is discarded because it is full of whatever was being infused

- discarded syringe MUST be collected first

How does improper mixing affect the accurate measurement of blood gas parameters?

- can introduce air bubbles into the samples

How does improper storage & transport affect the accurate measurement of blood gas parameters?

- no tube transport system because the shaking can introduce more air bubble into specimen

- samples are required to be hand delivered

How does time affect the measurement of blood gas parameters?

- if O2/SO2 is ordered = room temp & run within 15 minutes

- if O2/SO2 not ordered = room temp & run within 30 minutes

- if testing will be delayed for more than 30 minutes = place syringe in ice water stable for 1 hour

How does temperature affect the measurement of blood gas parameters?

- cool temp = increases permeability

What are some analytical problems associated with blood gas measurement?

- improper lack of maintenance

- inadequate reagents

- poor or lack of calibration

- failure to perform QC or recognize QC problems

What are some postanalytical problems associated with blood gas measurement?

- poor turn-around times

- transcription mistakes

- reporting results without age-adjusted reference ranges, correct units, or rounding of data

- reporting results on wrong patient

- failure to interpret instrument flags or warning that something may be wrong (could also be an analytical problem)

What components are most commonly measured by blood gas analyzers?

- electrodes are used to measure pH, PCO2, & PO2

- ISEs are used to measure electrolytes

- total hemoglobin concentration is measured with a spechtrophotometer

What components are most commonly calculated by blood gas analyzers?

- bicarbonate

- total carbon dioxide

- total oxygen content

- oxygen saturation

- base excess

What membranes make up the pO2 measurement electrode?

Polarographic Clarke electrode with a polypropylene selective semi-permeable membrane

What membranes make up the pCO2 measurement electrode?

Modified pH electrode

What membranes make up the pH measurement electrode?

Indicator electrode that selects for H+ with a specific glass membrane

What are some interferences associated with electrode measurement of blood gases?

- carryover between specimens

- the pH electrode, as well as some other gases need to be maintained at 37 degrees Celsius

- excess protein buildup on the pH electrode or membranes will decrease sensitivity