Human Ventilation

Tutorial

V_T	f
Minute Ventilation

Ventilation is the action of air moving in and out of a system. In this case the air is moving in and out of the lungs. The amount of air moving in and out of the lungs is measured per unit time. The unit of time used with human ventilation is called Minute Volume, or

. Minute volume is the product of Tidal Volume (V_T) times frequency (f). The dot (called a tittle) over the

indicates volume per unit time. The device to measure the air in the lungs was first used by Tissot (pronounced Tee-soe) in 1904. The Tissot Spirometer (see illustration above, right-side of page header) is a stainless steel water-sealed tank approximately four and a half feet tall. It's filled with water and within the water is another inverted tank. The patient breathes into a valve and piping system allowing his exhaled air to go into the spirometer, causing the inverted tank to rise. Attached to the top of the inverted tank is a chain and wheel system. As the inverted tank rises, the opposite end of the chain, which is attached to a pen, moves down along a rotating drum with spirometer paper wrapped around it. The paper is calibrated to a specific measurement, and the drum rotates at an equally specific rate. Because of this, a tracing is obtained yielding the person's average minute volume. The system is so constructed that for every millimeter of change in tank volume, 133.2 milliliters of air is measured. All the measurements will also yield a person's Tidal Volume. Tidal Volume is the amount of air moved with each breath, and frequency is the number of breaths per unit time. You can use the drop-down boxes to the right to test it out for yourself. For example: a Tidal Volume of 500 ml and a Frequency of 12 breaths gives us a Minute Volume of 6,000 ml. Place your curser over the arrow in the drop-down box. Just choose a Tidal Volume (V_T) and a frequency (f). The Minute Volume (V_E) is measured in milliliters per minute.
---------------

	BSA
Minute Ventilation/BSA

It's not enough to just measure the Minute Volume. The question you should ask is, is the Minute Volume acceptable for everyone? That is, a Minute Volume of 6,000 milliliters may be enough for a person who is 5 ft. tall, but is it enough for someone who is 6 ft. tall? Because of this, a person's Body Surface Area (BSA) comes into play. Body Surface Area is a function of both height AND weight. Body Surface Area is measured in square meters. To give you some idea how much a square meter is, with an average height of 5'10" tall and a weight of 185 lbs, a person's BSA will be approximately 2.00 square meters. When adjusted for BSA, the normal Minute Volume adjusted for BSA falls within a range of 3-5 liters per minute per square meter (3-5 l/min/M²). Use the drop-down boxes in the table to the left of this paragraph to see for yourself.
---------------

etCO₂	P_B	F_ECO₂	V_D/V_T
DeadSpace Ratio

Okay, so we've measured a person's Minute Volume and we've adjusted it for Body Surface Area, but that's not all we have to consider. Since actual gas exchange only takes place in the alveoli, we have to deduct the amount of air that fills the airways. The air in the airways is considered wasted ventilation. It moves back and forth but doesn't contribute to the actual gas exchange. Because of this, it's called Dead Space or anatomical Dead-Space. Dead Space is a mining term. It refers to a mine shaft that comes to a dead-end, and where there's no significant exchange of air. Physiology borrowed the term to refer to air that moves back and forth in the airways but where there's no gas exchange. Dead Space is a function of End-Tidal Carbon Dioxide (etCO₂), Barometric Pressure (P_B), Water-vapor Pressure in the lungs (P_H₂O), and the Fraction of Expired Carbon Dioxide (F_ECO₂) and is a ratio but is displayed as a decimal. Water-vapor pressure is considered to be at Body Temperature Pressure Saturated (BTPS) as are all measurements in this tutorial and is, therefore, a constant value of 47. End-Tidal CO₂ is the amount of CO₂ measured at the end of a normal breath. It's measured in millimeters of mercury (mmHg). The Fraction of Expired CO₂ is measured as a percentage of the total gases in the lungs. Barometric Pressure is also measured in millimeters of mercury (mmHg). The normal Dead-Space ratio is approximately 0.28 - 0.32. You can use the drop-down boxes at the right of this paragraph to see how it works.
---------------

V_T	V_D/V_T	V_D
DeadSpace Volume

Now that we've calculated the Dead Space Ratio, we can apply it to the volumes measured with the Tissot Spirometer. We'll apply it first to the Tidal Volume, then in the next table to the Minute Volume to calculate the Alveolar Ventilation. Doing so will give us the amount of Tidal Volume and Minute Volume wasted in the airways. The value we receive is called Dead-Space Volume, or V_D. For example: if we have a Tidal Volume of 500 ml and a Dead-Space Ratio of 0.20, or one-fifth, then out of a 500 ml breath 100 ml is wasted, or Dead-Space Volume. See for yourself in the table to the left. At this point you should know that in actual practice we would also consider the volume of mechanical dead-space in the mouth piece and valve system used in the Tissot, but for this tutorial that won't be necessary.
---------------

V_D	f
Alveolar Ventilation

Aveolar Ventilation is the volume of air in the alveoli and is equal to the Minute Ventilation minus the Dead-Space Volume. It's importance is that it's where perfusion of blood and gas exchange takes place. In this example we will use the Dead-Space Volume calculated in the previous table, multiply it by the Frequency (number of breaths), and subtract the product from the Minute Volume. This gives us the actual Alveolar Ventilation. For example: a Dead-Space Volume of 100 ml times a Frequency of 12 breaths gives us 1,200 ml, subtracted from a Minute Ventilation of 6,000 ml yields an Alveolar Ventilation of 4,800 ml. Try it yourself in the table to the right.
---------------

	BSA
Alveolar Ventilation/BSA

Of course, we're not content with just calculating the Alveolar Ventilation. As with Minute Volume, the Alveolar Ventilation for a 5'10" person may not be optimal for someone 6' tall, and so we have to adjust it for Body Surface Area. To do this, we divide the Alveolar Ventilation by the Body Surface Area. The normal Alveolar Ventilation adjusted for BSA is 2.4-3.0 liters per minute per square meter, or 2.4-3.0 l/min/M². For example: an Alveolar Ventilation of 4,800 ml with a BSA of 1.7 gives us an adjusted Alveolar Ventilation/BSA of 2,823 ml/min/M²...clearly enough. See for yourself in the table to the left.
---------------

	FeCO2
Carbon Dioxide Production

Body metabolism produces waste in the form of carbon. Carbon Dioxide is a by-product of metabolism and must be excreted by the lungs and is measured as the volume of CO₂ per minute. Intuitively, if a measurement of the exhaled air is made, and the fraction of the exhaled CO₂ in the air is known, then the amount of CO₂ that is produced by the body can be calculated. Example: a Minute Volume of 6,000 ml multiplied by a fraction of CO₂ of 0.04 yields us a CO₂ of 240 ml per minute. Try it yourself with the table to the right.
---------------

	BSA
Carbon Dioxide Production/BSA

Let's not forget to adjust the CO₂ Production for Body Surface Area. Again, what's appropriate for a 5'10" person isn't so for someone 6' tall. Simply divide the CO₂ by the BSA. The normal range for CO₂ adjusted for BSA is 100-110 ml per minute per square meter, or 100-110 ml/min/M². Example: a CO₂ of 240 divided by a BSA of 1.7 gives us approximately 140 ml/min/M²...a bit on the high side. Try it yourself in the table to the left.
---------------

F_ECO₂	F_EO₂	F_EN₂
Fraction of Expired Nitrogen

Before we can calculate the amount of oxygen consumed (next table) we first have to calculate the fraction of Nitrogen exhaled (F_EN₂). We can use the same intuitive process we used with CO₂ production. If we think of the total amount of gas in the air and in our lungs as equal to 1, then the gases make up a part of that total. The gases we exhale are: nitrogen, oxygen, and carbon dioxide. To obtain the nitrogen N₂, we merely have to subtract the CO₂ and O₂ from 1. Example: 1 minus a F_ECO₂ of 0.04, minus a F_EO₂ of 0.170 gives us a F_E N₂ of 0.79...just where we want it. Try it yourself in the table to the right.
---------------

	F_EN₂	F_EO₂
Oxygen Consumed

The volume of oxygen consumed is a bit more complicated than calculating the carbon dioxide produced. This is because we have to know both the nitrogen inspired AND exhaled, as well as the inspired and exhaled oxygen. But intuitively, we still start with the Minute Volume and multiply it by the difference between the inspired and exhaled oxygen, with the ratio of exhaled to inspired nitrogen thrown in to boot. The difference between the two nitrogens isn't all that great, only about 0.0017, but it's part of the equation and so we'll include it. Example: With a Minute Volume of 6,000 ml, an inspired oxygen of 0.2093, and exhaled oxygen of 0.170, and a nitrogen ratio of approximately .99, we have an Oxygen Consumption of approximately 225 ml per minute. Try it for yourself in the table to the left.
---------------

	BSA
Oxygen Consumed/BSA

Oxygen Consumption is the last value we'll have to adjust for Body Surface Area. Don't forget, what's appropriate for a 5'10" person isn't the same for someone 6' tall. The normal value for Oxygen Consumed/BSA is 120-140 ml per minute per square meter, or 120-140 ml/min/M². Example: With the oxygen consumption from above of 225 ml/min, and a Body Surface Area of 1.7, this gives us an Oxygen Consumption/ BSA of 132 ml/min/M²...right in range. Try it for yourself in the table to the right.
---------------

		RER
RER

What does the Respiratory Exchange Ratio, or RER signify? Well, you can determine what fuel is being used for energy production. Is the fuel carbohydrate, protein, or fat? Oxidation of carbohydrate yields a RER = 1.0⁺; protein is 0.8-0.9, and fat yields a RER of 0.7-ish. Using the values from the tables above, a CO₂ production of 240 ml/min and an O₂ of 225 ml/min, the RER comes to just over 106. This subject is burning carbohydrates!
Try it for yourself in the table to the left.
---------------

	Height	Weight	Age	BMR
BMR: Predicted Per Day (Harris-Benedict Equation)
Males
Females

The grand finalé! The oxygen you consume is converted to heat, called a calorie. Oxygen consumption can be used to calculate the Actual Basal Metabolic Rate, or BMR. The equation for the Actual BMR is:

The constant, 4.85 is the heat (calories) from the consumption of 1 liter of O₂. The VO₂ is then multiplied by 60 and then 24 to get it for one hour and then one day, respectively.

The Actual BMR compared to the Predicted BMR is then expressed as a percent...

You can also calculate your Predicted BMR. BMR is measured while resting. If the Actual minus the Predicted BMR results in a negative value, then the subject isn't as active as he/she should be. That is, for a given activity, how many calories will you burn to perform that activity? Once you know your Actual BMR, you can multiply it by another factor to see how many calories you need for a particular activity each day (See below). BMR is affected by a person's diet, gender, height, weight (therefore BSA), environment, and age. Try out the Predicted BMR for yourself in the table to the right.
The following list gives you the factor for different life-styles:

Sedentary (Couch potato): BMR x 1.2
Light activity (Going to the fridge): BMR x 1.3
Moderate activity (Shopping): BMR x 1.4
A lot of activity (Working): BMR x 1.65
Intense activity (Marathon): BMR x 2.00

---------------

P_H₂O	F_IO₂	F_IN₂
Constants
47	0.2093	0.7907

---------------

Ventilation Formulae & Glossary

Parameter Unit/Type of Measurement

ATP = Adenosine TriPhosphate - An energy molecule

ATPS = Atmospheric Temperature Pressure Saturated floating point

BMR = Basal Metabolic Rate. The energy expenditure for a given activity kcal/L O₂

BSA = Body Surface Area Square Meters

BTPS = Body Temperature Pressure Saturated floating point

etCO₂ = End-Tidal Carbon Dioxide – measured at end of normal expiration mm Hg

f = frequency of breaths per minute

F_ECO₂ = Fraction of Expired Carbon Dioxide %, listed as floating point

F_EN₂ = Fraction of Expired Nitrogen = 1 - F_EO₂ - F_ECO₂ %, listed as floating point

F_EO₂ = Fraction of Expired Oxygen %, listed as floating point

F_IN₂ = Fraction of Inspired Nitrogen = 1 - F_IO₂ %, listed as floating point

F_IO₂ = Fraction of Inspired Oxygen %, listed as floating point

M² = Square Meters floating point

Oxidation = The interaction between oxygen molecules and everything else

P_B = Barometric Pressure mm Hg

P_H2O = Water Vapor Pressure mm Hg

RER = Respiratory Exchange Ratio = VCO₂ / VO₂ floating point

STPD = Standard Temperature Pressure Dry floating point

V_A = Volume of Alveolar Ventilation = V_E - (f * V_D) ml per minute

V_A/M² = Alveolar Ventilation, adjusted for Body Surface Area = V_A / BSA ml per minute per square meter

VCO₂ = Volume of Carbon Dioxide Produced = V_E * F_ECO₂ ml per minute

VCO₂/M² = Carbon Dioxide, adjusted for Body Surface Area = VCO₂ / BSA ml per minute per square meter

V_D = Volume of Actual Dead Space = V_T * (V_D/V_T) ml

V_D/V_T = Dead Space Ratio = [etCO₂ - [(P_B - P_H20) * (F_ECO₂)]] / etCO₂ %, listed as floating point

V_E = Volume of Expired (Minute) Ventilation = V_T * f ml per minute

V_E/M² = Expired (Minute) Ventilation, adjusted for Body Surface Area= V_E / BSA ml per minute per square meter

VO₂ = Volume of Oxygen Consumed = V_E * [F_IO₂ (F_EN₂ / F_IN₂) - F_EO₂] ml per minute

VO₂/M² = Oxygen Consumed, adjusted for Body Surface Area = VO₂ / BSA ml per minute per square meter

V_T = Tidal Volume – Volume of air moving in and out of the lungs each breath ml

Go back to: eBooks You Can Read
Created by: Thomas T. Klugh - Klugh Enterprise, LLC

Note from Thomas:
I have over 30 years experience in health care, the last eleven performing the ventilation test in this tutorial. If you have any questions, you may contact me at my email address.

Parameter	Unit/Type of Measurement
ATP = Adenosine TriPhosphate - An energy molecule
ATPS = Atmospheric Temperature Pressure Saturated	floating point
BMR = Basal Metabolic Rate. The energy expenditure for a given activity	kcal/L O₂
BSA = Body Surface Area	Square Meters
BTPS = Body Temperature Pressure Saturated	floating point
etCO₂ = End-Tidal Carbon Dioxide – measured at end of normal expiration	mm Hg
f = frequency of breaths	per minute
F_ECO₂ = Fraction of Expired Carbon Dioxide	%, listed as floating point
F_EN₂ = Fraction of Expired Nitrogen = 1 - F_EO₂ - F_ECO₂	%, listed as floating point
F_EO₂ = Fraction of Expired Oxygen	%, listed as floating point
F_IN₂ = Fraction of Inspired Nitrogen = 1 - F_IO₂	%, listed as floating point
F_IO₂ = Fraction of Inspired Oxygen	%, listed as floating point
M² = Square Meters	floating point
Oxidation = The interaction between oxygen molecules and everything else
P_B = Barometric Pressure	mm Hg
P_H2O = Water Vapor Pressure	mm Hg
RER = Respiratory Exchange Ratio = VCO₂ / VO₂	floating point
STPD = Standard Temperature Pressure Dry	floating point
V_A = Volume of Alveolar Ventilation *= V_E - (f V_D)**	ml per minute
V_A/M² = Alveolar Ventilation, adjusted for Body Surface Area = V_A / BSA	ml per minute per square meter
VCO₂ = Volume of Carbon Dioxide Produced *= V_E F_ECO₂**	ml per minute
VCO₂/M² = Carbon Dioxide, adjusted for Body Surface Area = VCO₂ / BSA	ml per minute per square meter
V_D = Volume of Actual Dead Space *= V_T (V_D/V_T)**	ml
V_D/V_T = Dead Space Ratio *= [etCO₂ - [(P_B - P_H20) (F_ECO₂)]] / etCO₂**	%, listed as floating point
V_E = Volume of Expired (Minute) Ventilation *= V_T f**	ml per minute
V_E/M² = Expired (Minute) Ventilation, adjusted for Body Surface Area= V_E / BSA	ml per minute per square meter
VO₂ = Volume of Oxygen Consumed *= V_E [F_IO₂ (F_EN₂ / F_IN₂) - F_EO₂]**	ml per minute
VO₂/M² = Oxygen Consumed, adjusted for Body Surface Area = VO₂ / BSA	ml per minute per square meter
V_T = Tidal Volume – Volume of air moving in and out of the lungs each breath	ml
Go back to: eBooks You Can Read Created by: Thomas T. Klugh - Klugh Enterprise, LLC Note from Thomas: I have over 30 years experience in health care, the last eleven performing the ventilation test in this tutorial. If you have any questions, you may contact me at my email address.