Thermal Agents Flashcards
Whole body stimulus
Response
Goal
Reflex response
Goal is to maintain core temp
Local Stimulus
Response
Goal
Localized response
Goal is tissue prevention
Heat relies on
Temperature gradients
Heat travels down a temp gradient
Mechanisms of heat transfer - Metabolic Rate
way of generating heat
90kcal/hr at rest
>900 with max exercise
Mechanisms of heat transfer - Radiation
Infra-red emission to, or from the body
Solar and thermal (photons) radiation
Mechanisms of heat transfer - Conduction
Transfer of heat by direct contact
Minor contributor of heat exchange in air
26x greater in water
Mechanisms of heat transfer - Convection
Transfer of heat from the skin surface to a moving liquid or gas - air temp is lower than skin will lose heat due to convection
Mechanisms of heat transfer - Evaporation
Heat lost with water conversion from liquid to vapor
Skin Vasculature
Upper and lower plexus
Papillary loops have large SA - good for heat exchange
Arterioles are highly innervated with sympathetic nerves to regulate BF
Veins achieve max compliance, low blood velocity
Whole Body Response
VC = cold
VD = hot
Heat loss = heat gain
Temp Homeostasis at 37 degrees C
Thermoregulatory zone
35-41 C
Heat from muscle to core via
convection of blood going through it (liquid that is moving)
Core and periphery uses what mechanism
Convection is a big one
Power of convection
Not just moving air or water
Very little heat transfer btw tissues by conduction
Convection and Skin blood flow
Controls dry hear loss in the cold (the more skin BF, the more heat loss you will have)
Works in tandem with sweat in the heat - tendency of SKBF to warm skin is balanced by tendency of sweat evaporation to cool skin
If no inc in flow, cant lose heat (elderly)
COuntercurrent Heat exchange
Heat exchange occurs where arterial blood warms venous blood returning to the body
Advantage is that it minimizes impact on core temp
Homeotherms maintain…
a constant core temp, NOT a constant blood temp
Receptors for whole body skin response - Cold Exposure
Alpha adrenergic receptors with NE (60%) Unknown cotransmitter (40%)
Receptors for whole body skin response - Heat exposure
Muscarinic receptors with Ach (70%) Unknown cotransmitter (30%)
Acral (Glabrous) Skin
Palms, soles of feet, lips, ears Has arteriovenous anastamoses - bypass of papillary loop - deeper, less SA (less effective at heat exchange) - involved in CIVD (hunting response) - involved in Raynauds
Nonacral (nonglabrous) skin
All other areas of skin (hairy skin)
Cold Induced VD
Only present where there is AVAs
Does NOT occur in Raynauds
Why Cold Induced VD good
Good because minimze risk of cold injury and inc finger dexterity and is trainable
Why COld Induced VD Bad
Bad because dec VC and heat retention
Mechanism for Cold Induced VD
Mechanism = synaptic transmission is interrupted
What innervates skin - Motor
Autonomic - Sympathetic (dual innervation)
Adrenergic
Cholinergic (only in nonglabrous)
What innervates skin - Sensory
From small unmyelinated nerve fibers to large unmyelinated C fibers A delta A beta A alpha
C fibers
Mechanical stimulation, crude touch, slow pain, and temp warm
A delta
sharp pain, inflammation, pressure, temp cold
A beta
touch, hair
A alpha
deep touch, pressure
Normal temp and what temps lead to pain
Normal = 34 C
15 or 45 - pain
Local Responses to Hear Mediated by
Axon Reflex - flare response
NO - plateau
Vasoconstrictor nerves die away
Axon Reflex
Mediated by warm sensitive afferent nerve antidromatic release CGRP, sub P
Associated with inflammatory response
Occurs naturally with local heating
Application of heating agent - Superficial Heat
Does not affect deep tissues
Ex = whirlpool, heat pack, infrared heat lamp
Modality affects mechanism of transfer
Dilated cutaneous vessels transfer heat to core - dissipates heat faster
Deep tissues also VD
Renetention of heat in skin/fat
Application of heating agent - deep heat
Do increase deep tissue temp
Ex = ultrasound, diathermy
Local Response to cold - Mediated by
Inhibition of NO
Inc in Alpha 2c adrenergic receptors available
COld sensitive afferent (antidromatic release)
Raynauds Phenomenon
Pallor - cyanosis - rubor and swelling and paresthesia
Mechanism - excess alpha 2c adrenergic receptors, stress, caffeine, smoking
Tx - calcium channel blocker
Application of Cooling Agent - SUperfifical cold
Affects both surface and deep tissues
Surface cools faster/more than deeper tissue
Temp vs. duration - asymptomatic curve
Rewarming takes longer than cooling (more insulation and less BF)
Localised applied region
Dec intra articular temp
Tissue injury can occur from applying thermal agents how
local temp over 42-44 or less than 15 will cause burn
What to look for with tissue injury
Redness Itchiness Pain Swelling/edema Unusual coloring Blistering
What to consider when applying thermal agents
insensitivity to pain or temp Tissue thickness Raynauds Peripheral Vascular Disease Pregnancy
How long apply thermal agens
20 min (30 min nma)
Neuromuscular effects - cold
Dec conduction velocity
Dec spasticity and spasm
Dec pain
Dec muscular force production
Neuromuscular effects - heat
Inc conduction velocity
Dec spasticity and spasm
Dec pain
