hphe 6720 - topic 9

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Topic 9:

Methods Relating to the Study of

Environmental Physiology

HPHE 6720

Dr. Cheatham

Supplemental Materials

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Outline

Introduction

Measuring temperature

Core and skin

Measuring metabolic rate

and heat production

Calculating tissue insulation

Measuring skin blood flow

Measuring sweat rate

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Introduction

Environmental and Core Temperatures

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Introduction

E-RCCMS dV

Heat Balance Equation

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What variables are we interested in

Temperature Different ways/devices to measure temperature

Measurement of core temperature Rectal, esophageal, tympanic, oral

Measurement of skin temperatures

Metabolic Rate / Heat Production Indirect Calorimetry

Tissue Insulation Combination of temperature and heat production responses

Skin Blood Flow Laser Doppler Flowmetry

Sweat Rate Whole body changes

Hygrometry

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Techniques / Devices to Measure Temperature

Thermocouples

Description: A thermocouple is a sensor for measuring temperature.

It consists of two dissimilar metals, joined together at one end.

When the junction of the two metals is heated or cooled a voltage is produced that can

be correlated back to the temperature.

The thermocouple alloys are commonly available as wire.

Type of Thermocouples: There are different types of thermocouples.

The metals/alloys are different for different types and provide different temperature

ranges.

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Thermocouples (contd)


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Thermistors

Description: A thermistor is a temperature-sensing element

composed of sintered semiconductor materialwhich exhibits a large change in resistanceproportional to a small change in temperature.

Thermistors usually have negative temperaturecoefficients which means the resistance of thethermistor decreases as the temperature increases.

A small current is applied to the thermistor and the change inresistance is related to the temperature being monitored.

Thermistors are one of the most accurate types of temperaturesensors.

Thermistors have an accuracy of 0.1C or 0.2C depending on theparticular thermistor model. However thermistors are fairly limited intheir temperature range, working only over a nominal range of 0C to100C .


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Measurement of Core Temperature

Core Temperature is the temperature inside the body

Sites of Measurement:

Rectal Temperature (TRE) Relatively comfortable, non-invasive.

Temperature probe inserted between 5 and 13 cm past than anal sphincter.

Relatively slow responding to internal temperature changes.

Esophageal Temperature (TES) Temperature probe is inserted through the nasal passage and into the throat and then

swallowed. Probe is then fed to approximately the level of the right atrium (1/4 of

subjects standing height).

Very responsive to internal temperature changes and approximates the temperature ofmixed venous blood.

Tympanic Temperature (TTY) Temperature probe is placed against the tympanic membrane.

Representative of hypothalamic temperature.

Oral Temperature (TOR)

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Measurement of Core Temperature

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Skin temperature are monitored for the following reasons:

Calculating the mean body temperature for heat storage

determinations

Calculating sensible (radiative and convective) heat

exchange and skin conductance

Integrating into an index of the skin temperature input to

the thermoregulatory controller

Usually, skin temperature is monitored at several sites and

then the different sites are weighted to get an average skin

temperature.

Temperature probes are attached to the surface of the skin

usually at sites that cover muscle areas that will influence

body temperature most greatly.

Measurement of Skin Temperatures

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Skin Temperature Equations:


Mean TSK (C) = 0.35 * TCHEST+ 0.19 * TTHIGH

+ 0.14 * TARM

+ 0.13 * TLEG+ 0.07 * T

HEAD

+ 0.07 * TFOOT+ 0.05 * THAND

Hardy, J.D. and E.F. Dubois. Journal of

Nutrition. 15: 461, 1938.

Mean TSK (C) = (0.3 * TCHEST) + (0.3 * TARM) + (0.2 * TTHIGH) + (0.2 * TLEG)

OR

Mean TSK (C) = (0.3 * (TCHEST + TARM)) + (0.2 * (TTHIGH + TLEG))

Ramanathan, N.L. A new weighting system for mean surface temperature of the human body. Journal of Applied

Physiology. 19(3): 531-533, 1964.

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Measurement of Metabolic Rate / Heat Production

Expresses the heat produced by the body during any

condition

Requires collection of respiratory gases (i.e. VO2 and

VCO2)

Metabolism can be expressed as: VO2 (ml/min or ml/kg)

Calories (kcal)

Kilojoules or Watts

Calculations: kcal = (3.9 * LO2 used) + (1.1 * LCO2 produced)

Watts = 60 * 1.163 * ((3.9 * LO2 used) + (1.1 * LCO2 produced))

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Measurement of Tissue Insulation

Terminology:

Tissue conductance The tendency to lose body heat to the environment

Tissue insulation The ability to resist loss of body heat

The reciprocal of conductance

Brief physiology of Insulation

What provides insulation? Skin, subcutaneous fat, muscle

What does shivering due to conductance and insulation?

Decreases insulation

Increases conductance

Why? Muscle layer lost as insulative layer

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How do we measure or calculate insulation?

Need to know

Skin temps

Core temperature

Heat flow or metabolic rate

BSA and Bodyweight

Veicsteinas, A., G. Ferretti, and D.W. Rennie. Superficial shell insulation inresting and exercising men in cold water. Journal of Applied Physiology.

52: 1557-1564, 1982.


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I = ((TCO TSK) * AD) / ((0.92 * HP) + ( TCO) * 0.965 * 0.6 * Wt))

TCO = Core temp (Final (or given) time point)

TSK = Skin temp (Final (or given) time point) AD = Body Surface Area

HP = Metabolism / Heat production (W)

TCO = Change in TCO (Final (or given) Initial)

Wt = Bodyweight (kg)

Toner, M.M., M.N. Sawka, M.E. Foley, and K.B. Pandolf. Effects of body mass

and morphology on thermal responses in water. Journal of Applied

Physiology. 60(2): 521-525, 1986.

Calculation:


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Measurement of Skin Blood Flow

Why is the measurement of skin blood flow important?

The skin is the interface between the body and the environment.

So, blood flow to the skin is a major determinant of how much heat from

the body is lost to the environment.

Response in SBF due to the environment:

Heat exposure: Vasodilation. Increase heat loss to environment. Increase blood flow for

sweat response.

Cold exposure:

Vasoconstriction. Decrease heat loss to the environment.

How is it measured?

Plethysmography

Laser Doppler Flowmetry

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Laser Doppler Flowmetry Introduction:

Laser Doppler is a standard technique for the non-invasiveblood flow monitoring and measurement of blood flow in

the microcirculation. The strength of the technique is in looking at changes in

flow - either over time or differences in flow over an areaof skin or other exposed tissue.

For example you might compare flow in normal tissue withflow in a burnt area of tissue.

You might also use a provocation (stimulus) to changeflow. This could be skin heating, drug delivery byiontophoresis, pressure cuffs etc.


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Laser Doppler Flowmetry

Operating Principle:

The laser Doppler technique measures blood flow in the verysmall blood vessels of the microvasculature, such as the low-speed flows associated with nutritional blood flow incapillaries close to the skin surface and flow in the underlyingarterioles and venules involved in regulation of skintemperature.

The technique depends on the Doppler principle whereby lowpower light from a monochromatic stable laser is scattered bymoving red blood cells and as a consequence is frequencybroadened.

The frequency broadened light, together with laser lightscattered from static tissue, is photo-detected and theresulting photocurrent processed to provide a blood flowmeasurement.


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Measurement of Sweat Rate

Why is sweat rate an important variable to measure?

Clinical application: Autonomic Dysfunction

Environmental or exercise application: Sweating is one of the main mechanisms by which the body loses heat, especially

during exercise is a warm or hot environment.

Fluid losses from sweat can also affect the fluid balance of the body (dehydration,

heat stress, heat exhaustion, heat stroke).

How is sweat rate determined?

Whole-body mass changes: Any body weight change as a result of acute exercise is mostly due to fluid losses.

Therefore, measurements of body weight changes from exercise can be used to

estimate whole body fluid losses (sweat rate)

Hygrometry The release of moisture (i.e. sweat) from a site on the skin is used to measure a

localized sweat rate.

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Whole-Body Mass Changes:


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Hygrometry (Q-Sweat System)

Trans Epidermal Water Loss (TEWL) The Q-Sweat uses room air that is drawn across a desiccant to pick up any

moisture (water) that is found in the sweat emitted from the skin.

The moisture given off by the skin is captured inside a capsule, where it is

transported by airflow to temperature and humidity measuring sensors. There, an accurate measure of the amount of moisture found within the

moving air sample is made.


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Laboratory Demonstration

15 minutes Baseline (25C, 77F)

60 minutes Cold Air Exposure (5C, 41F)

Variables

Core Temperature (Rectal Temperature)

Skin Temperature (TSK) Chest, Tricep, Thigh, Calf

Mean TSK

Metabolic Rate / Heat Production

Skin Blood Flow (SBF) Finger (SBFFIN)

Forearm (SBFFA)

Expressed as a percentage change from Baseline

hphe 6720 - topic 9

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