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Minute Ventilation and Deadspace Equations 

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Minute Ventilation and Deadspace Equations 

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Restrictive (alveolar) Lung Diseases:

Have problems with diffusion and they have low lung compliance (ball of rubber bands that doesn't inflate very well.)

Obstructive (airway) Lung Diseases:

Have problems with ventilation and they have high lung compliance (a balloon that easy inflates, but never fully empties.)

PaO2 is the partial pressure of oxygen in the artery

PAO2 is the partial pressure of oxygen in the alveoli

a/A gradient equation:

PAO2=(Barometric Pressure-PH20(it is always 47))FiO2-PaCO2. Then you take that number and divide it into the PaO2 and you will get the a/A gradient.

a/A gradient needs to be above 75%. If it is lower, it is an indication of a diffusion problem.

The normal lung compliance has a cwp of 60

Vocab and Definitions:

Physiologic Dead Space: It is the combination of anatomic and alveolar dead space.

Anatomic Dead Space: The part of the airways where air passes but no gas exchange happens (nose, trachea, etc.)

Transpulmonary Pressure Gradient: The difference in pressure between the inside of the lungs (alveoli) and the space around the lungs (pleural space).

Dysoxia: A condition where oxygen is available, but the cells can't use it properly, for example when a person suffers from carbon monoxide or cyanide poisoning.

Carboxyhemoglobin: Hemoglobin (the oxygen-carrying protein in red blood cells) bound to carbon monoxide (CO) instead of oxygen. CO has an affinity for hemoglobin roughly 200 times more than oxygen.

Methemoglobin: Hemoglobin has created the wrong type of iron (Fe3+ instead of Fe2+) and therefore it cannot carry oxygen to the tissues. This is normal in everyone, but if your body creates an excess then you have Methemoglobinemia.

Methemoglobinemia: A condition where too much methemoglobin builds up in the blood. This means that less oxygen is being carried to the tissues, which can cause cyanosis, etc.

Oxyhemoglobin: This is the name of hemoglobin that is currently carrying oxygen.

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TLC: Total Lung Capacity

IRV: Inspiratory Reserve Volume

TV: Tidal Volume

ERV: Expiratory Reserve Volume

RV: Residual Volume

IC: Inspiratory Capacity

FRC: Functional Residual Capacity

VC: Vital Capacity

RV: Residual Volume

Restrictive Lung Diseases see a decrease in VC, IC, RV, FRC, TV, TLC.

Obstructive Lung Diseases see an increase in RV, TV, FRC and a decrease in VC, IC, IRV, ERV. They will also see a decrease in all flows.

FVC: Forced Vital Capacity

FEV1: Forced Expiratory Volume in One Second

FEF 25-75%: Forced Expiratory Flow between 25-75% of Forced Vital Capacity

DLCO: Diffusing Capacity of the Lung for Carbon Monoxide

A patient with a thickened AC membrane inferes with diffusion because it forces gases to travel further across the membrane.

Patients with a new head injury need to be hyperventilated in order to cause vasoconstriction (due to a decrease in PaCO2) and it will cause the swelling (Intercranial Pressure) to decrease.

The Dorsal Respiratory Group (DRG) is a cluster of nerve cells in the brainstem (specifically, in the medulla oblongata) that helps control normal breathing.

The Ventral Respiratory Group (VRG) is a set of neurons in the medulla oblongata that helps control both breathing in and out, especially during active or forceful breathing (like during exercise or speaking).

Central Chemoreceptors are located next to the medulla oblongata. They are triggered when CO2 in the blood diffuses across the blood-brain barrier into the CSF. There they bind with hydrogen and create carbonic acid (H+). This lowers the pH and forces the brain to trigger the central chemoreceptors, so that the body will begin hyperventilating in order to lower the blood CO2 levels.

Peripheral Chemoreceptors are located in the Aortic Arch. They are triggered when the PaO2 levels drop below 60 mmHg and they force the body to begin hyperventilating in order to raise the PaO2 levels in the blood. They are suppressed if the PaO2 drops below 30 mmHg.

Both chemoreceptors act as a failsafe in the body to help maintain homeostasis.

Peripheral proprioceptors are sensory receptors in muscles, tendons, and joints that tell your brain where your body parts are and how they are moving. They're also responsible for telling the brain to increase breathing rate when you start moving, so you don't suffer from a drop in oxygen.

Baroreceptors are pressure sensors in your blood vessels that help your body keep your blood pressure stable. They are mainly located in the aortic arch and carotid sinus.

Hypothalamic Controls are located in the hypothalamus and can change your breathing in response to emotions (like fear or excitement) or body temperature (panting in heat). It signals the brain to adjust breathing and blood flow.

Vocab and Definitions:

Apneustic Breathing: a breathing pattern where a person takes a long, deep breath in and holds it before breathing out briefly. It's caused by an injury to the upper pons in the brain stem.

Blood-Brain Barrier: A protective barrier between the blood and the brain that only lets certain things in (like oxygen and nutrients) and keeps harmful stuff out.

Hering-Breuer Inflation Reflex: A safety reflex that stops your lungs from over-inflating when you take a deep breath.

Pneumotaxic Center: A part of the brain (in the pons) that helps control how long you breathe in.

Extrapolated Volume: Extra air that’s breathed out before a proper breathing test really starts.

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Hemoglobin: 12-15 units

PaO2: 80-100 mmHg (60-80 for patient's with chronic conditions)

PvO2: 30-50 mmHg venous pressure

SaO2 (SpO2): 90-100%

SvO2: 65-75% venous pressure

Cardiac Output (QT): 4-8 lpm

Vocab and Definitions:

Hypoxic Hypoxia: Not enough oxygen in the air or lungs for the hemoglobin to pick up.

Anemic Hypoxia: Blood can't carry enough oxygen. Not enough hemoglobin or red blood cells.

Circulatory Hypoxia: Blood isn't reaching the tissues properly. It is caused by poor perfusion.

Histotoxic Hypoxia: The tissues receive the oxygen, but can't use it. Caused by cyanide poisoning or mitochondrial dysfunction

Fibrous Pericardium: The outer layer of the of the pericardium (sac that surrounds heart.) It is made of strong fiber-like tissue.

Serous Pericardium: Thin, double layered sac that surrounds the heart. It is comprised of the visceral layer and parietal layer.

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9 requirements of tissue oxygenation

1. Atmosphere- The air all around us

2. Patent Airway- An unobstructed path for you to get oxygen to the lungs

3. Ventilation- Gas exchange

4. Pulmonary Perfusion- When blood goes to the lungs for oxygenation

5. Diffusion- When a material moves from a higher concentration to a lower

6. Hemoglobin- Oxygen transport in the blood

7. Cardiac Output- The amount of blood exiting the heart per minute

8. Pathway (Vasculature)- Veins and arteries that supply blood to the heart

9. Cells- The foundation to all things living

Two zones of the respiratory tract:

Upper: Nasal Cavity, Pharynx, Larynx

Lower: Trachea, Primary Bronchi, Lungs

Factors that impair the mucociliary escalator:

Smoking, antihistamines, supplemental oxygen, smog, pollutants.

Importance of the cricothyroid membrane is that it is located where a tracheostomy (stoma) is performed, if needed.

Horizontal Fissure separates the upper and middle lobes of the right lung.

The mainstem bronchi is at a greater angle on the right side with the trachea than the left side. This is due to the heart being in the left side of the chest.

The mainstem bronchi, blood vessels, lymphatic vessels, and nerves all meet at a juncture called the hilum.

Vocab and Definitions:

Pneumocytes: Cells that help make up the alveolar epithelium. There are two types.

Type I: Help with breathing by allowing oxygen and carbon dioxide to pass through.

Type II: Make surfactant and can replace damaged lung cells.

Valsalva Maneuver: To push air out of the body with your nose and mouth closed.

Pores of Kohn: Tiny holes between air sacs in the lungs that let air move from one sac to another. This helps keep airflow going if one path is blocked.

Turbinate: Curved bones inside your nose that help clean, warm, and moisten the air you breathe in.

Costophrenic Angle: The corner where your lungs and diaphragm meet. It is visible on a chest X-ray.

Angle of Louis: Known as the sternal angle, it is angle formed between the manubrium and the body of the sternum.

Clara Cells: Special cells in the small airways of the lungs. They help protect the lungs, clean up harmful substances, and repair damage.

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ABG Normal Blood Levels

pH: 7.35-7.45

PaCO2: 35-45

PaO2: 80-100

Bicarb: 22-26

Examples:

Acute Respiratory Acidosis:

pH: 7.25

PaCO2: 65

PaO2: 58

Bicarb: 26

Acute Metabolic Acidosis:

pH: 7.34

PaCO2: 44

PaO2: 78

Bicarb: 20

Acute Respiratory Alkalosis:

pH: 7.49

PaCO2: 29

PaO2: 65

Bicarb: 24

Acute Metabolic Alkalosis:

pH: 7.55

PaCO2: 41

PaO2: 82

Bicarb: 34

Partially Compensated Respiratory Acidosis:

pH: 7.15

PaCO2: 77

PaO2: 55

Bicarb: 33

Partially Compensated Metabolic Acidosis:

pH: 7.20

PaCO2: 30

PaO2: 88

Bicarb: 12

Partially Compensated Respiratory Alkalosis:

pH: 7.55

PaCO2: 77

PaO2: 61

Bicarb: 17

Partially Compensated Metabolic Alkalosis:

pH: 7.51

PaCO2: 31

PaO2: 90

Bicarb: 34

Compensated Respiratory Acidosis:

pH: 7.37

PaCO2: 51

PaO2: 48

Bicarb: 31

Compensated Metabolic Acidosis:

pH: 7.39

PaCO2: 30

PaO2: 86

Bicarb: 15

Compensated Respiratory Alkalosis:

pH: 7.43

PaCO2: 21

PaO2: 56

Bicarb: 16

Compensated Metabolic Alkalosis:

pH: 7.44

PaCO2: 50

PaO2: 92

Bicarb: 31

When an ABG is compensated, the neutral pH level becomes 7.40. pH values 7.35-7.39 are acidotic and pH values 7.41-7.45 are alkalotic.

ABG's can be a mixed alkalosis/acidosis when the pH are relational to the PaCO2 and Bicarb levels. See Example:

pH:7.25

PaCO2: 75

PaO2: 63

Bicarb: 18

Alveolar (Restrictive) anatomical alterations are generally alkalotic in nature, while Airway (Obstructive) anatomical alterations are generally acidotic in nature.

40 50 60 70 80 90 Rule:

This means that a PaO2 of 40 translates to a SaO2 of 70, 50 is 80, and 60 is 90. This serves as a rough estimate when you only have one or the other value.

Vocab and Definitions:

Buffer Base: Buffer base is the total amount of all the buffer substances (bicarbonate, etc.) in the blood that can accept hydrogen ions (H⁺) to resist changes in pH. Buffer Base ranges from 48 to 52 mEq/L.

Closed Buffer System: A closed buffer system is a buffer system where all components stay in the system—no part can leave the body (or solution). These include nonbicarbonate buffers such as plasma proteins, hemoglobin, and phosphate.

Isohydric Buffering: Isohydric buffering is when multiple buffer systems work together and all respond to changes in pH at the same time, helping the body quickly neutralize acids or bases.

Open Buffer System: An open buffer system can remove one of its components from the body, usually as a gas or fluid. Main component that is removed is H2CO3 (broken down to H2O and CO2).