Thermal Environment

1
Thermal Environment

• BME 602
• SDSMT / USD
• Spring 2007

2
Reading Assignment

• Chapter 9

3
Overview

• The body reacts thermally in a variety of ways
  with the environment. Metabolic heat is
  generated internally. Heat is dissipated
  internally and externally (skin and lungs).

4
Thermal Stress

• Thermal stress occurs at the two temperature
  extremes
• Very high and low temperatures pose hazards
• Extreme cases can be fatal
• Heat-related illness
• Cold stress

5
Thermal Homeostasis

• The body is constantly attempting to maintain a
  favorable and uniform internal temperature,
  despite fluctuations in the environment

6
Stable 1
Body Temperature (F)
60
130
Temperature of Dry Still Air (F)
7
Body Thermal Regulation is Analogous to an HVAC
System
8
Balance Equations

• Energy Balance Equation (Chapter 8)
• I M H W S
• Thermal Balance Equation (Eq. 9-8)
• H S R C K E 0
• Units watts / m2
• Where R, radiation, Eq. 9-3
• C, convection, Eq. 9-4, 9-5, 9-6
• K, conduction, Eq. 9-4
• E, evaporation, Eq. 9-7

9
Thermoreceptors

• See PCP 89
• Externally in the skin
• Free nerve endings
• Warmth
• Cold
• Internal temperature
• Hypothalamic thermostat

10
Hypothalamus and Body Temperature

• PCP 107
• Hypothalamus brain structure concerned with
  homeostasis and other internal activities
• Located above brain stem
• Essentially a thermostat with a set point (37 C)

11
Body Temperature Physiology

• PCP 140
• Set Point 37 C for core
• Skin temperature can be quite different
• Diurnal variation
• Morning 36.7 C
• Evening 37.2 C
• Heat generation oxidation of food, muscular
  activity (exercise, work, shivering), nervous and
  hormonal activity

12
Role of the Skin (PCP 140)

• Heat can be lost or gained directly
• convection and conduction
• Heat can be lost by evaporation
• Some blood capillaries near the surface to not
  exchange nutrients, but function solely for heat
  exchange
• Vasoconstriction
• During cold conditions, capillaries are closed,
  minimizing heat loss
• Vasodilation
• During hot conditions, capillaries are open,
  promoting heat loss (convection/conduction)

13
Evaporation (Perspiration/Sweating)

• Water has a high heat capacity
• 0.6 Cal/g
• Insensible perspiration
• Loss of water from the skin at lower temperatures
• Water diffuses thru skin cells and pores and
  quickly evaporates no sweat drops form
• Includes water and heat loss thru respiration
• 20 of daily basal caloric production
• Sweating when body gt 37 C
• Active secretion of water and salt by sweat glands

14
Heat Related Illnesses

• Heat Rash (prickly heat)
• Red bumps (sweat glands)
• Heat Cramps
• Heavy perspiration, loss of fluids, imbalance of
  salts/minerals, muscle cramps
• Heat Syncope (fainting)
• Standing still, usually in the sun
• Heat Exhaustion (severe case of heat cramps)
• Nausea, dizziness, headaches, tiredness,
  fainting, disoriented, sweating profusely
• Heat Stroke (most serious)
• May stop perspiring, elevated temp to above 104
  C, red face/skin, erratic behavior, confusion,
  dizziness
• This is an emergency medical situation call 911,
  move to cool area, cool aggressively

15
Monitoring the Environment

• WBGT (Wet Bulb Globe Temperature)
• WBGT(IN) 0.7 TWB 0.3 TG
• WBGT(OUT) 0.7 TWB 0.2 TG 0.1 TDB

Chapter 11 diagrams refer to Nims, Basics of
Industrial Hygiene, John Wiley, 1999
16
WBGT, not WGBT
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
Cold Stress

• Bodys inability to keep inner temperature within
  normal range
• Ultimate effect is hypothermia
• Could occur even in 30-40 F

26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
Physiology Coloring Plates

• 2nd Edition
• 89, 107, 140-141