thermoregulation, obesity and pulmonary glossary

Body composition

quantification of different body tissue compartments (fat free (lean) vs. fat)

Body fat percentage

ratio of body tissue comprised of fat, healthy range for young adult males (10-20%) and females (20-30%)

Obesity

excess fat accumulation that poses an adverse health risk, commonly qualified as BMI>30 kg/m3

Body Mass Index (BMI)

ratio of mass in kilograms to squared height in meters, used to broadly categorize weight status

Waist Circumference

measurement around waist used to assess disease risk, proxy for visceral fat, often compared with hip

Visceral fat

intra-abdominal fat that when in excess poses an increased risk for metabolic syndrome and CVD

Computed tomography scan (CT)

medical imaging technique that details internal body structures

Dual Energy Xray Absorptiometry

a procedure used to assess body composition and bone mineral density using Xrays

Body Density (densitometry)

ratio of mass to volume, correlated to body fat % as more dense —> less fat

Hydrostatic (underwater) weighing

body composition assessment technique that uses Archimedes’ principle to determine body volume

Archimedes’ Principle

the difference in weight of an object above and below water is equal to the weight of displaced water

BOD POD

body composition assessment tool that uses air displacement to determine body volume

Skinfold Measurement

body composition assessment technique that uses skinfold thicknesses of various sites

Bioelectrical impedance analysis

body composition assessment technique that uses an electrical current speed measurement

Thermoregulation

control of core body temperature via heating and cooling mechanisms

Hemotherm

animal that maintains constant core body temperature by virtue of its own heating and cooling mechanisms

Core Body Temperature (Tc)

temperature of metabolically active/critical organs (brain/heart, etc.)

-normally 37± 0.5degC (~98.6 F)

Skin (shell) temperature

variable temperature due to the environment of which a small % of the thermoregulatory response is based

Heat Balance Equation

thermal equilibrium between heat added to and removed from a system

Metabolic Heat

heat liberated during metabolic reactions, scales with exercise intensity, reliable source of heat gain

Radiation

heat transfer of thermal energy by means of electromagnetic (infrared) waves

Conduction

heat transfer between molecules in direct contact with each other

Convection

heat transfer to or away from molecules via a fluid (liquid or gas), can be natural or forced (via fan)

Evaporation

heat loss mechanism involving conversion of a liquid to a vapor, requires ~580 kcal of heat/L of water

humidity

concentration of water vapor in air, inhibits evaporation thus threatens temperature regulation in the heat

Thermoneutral zone

ambient temperature range in which a nude individual need only use vasomotor tone to thermoregulate

Sudomotor control

regulation of sweat gland activity, involves varying sympathetic cholinergic impulses

Vasomotor control

blood vessel tone regulation, involves varying sympathetic adrenergic impulses

Sweat gland myoepithelium

specialized epithelium around sweat glands that have a contractile function and sympathetic innervation

Dehydration

excessive water loss from the body, often expressed as a % of body weight loss

Dysthermia

poor temperature regulation

Hyperthermia

elevated core body temperature

Heat Exhaustion

heat illness stage due to excessive heat, sweating, dehydration, and competition for blood (Tc= 99-102F)

Heat Stroke

most severe (life threatening) heat illness stage in which thermoregulation is impaired (Tc can be >106F)

Hypothermia

Low core body temperature (Tc below 35C/ 95F)

Central Blood Volume

Blood within major vessels of the thorax, lower in hot conditions with blood in vasodilated skin

Acclimation

process of getting accustomed to a new condition via adaptations

Ventilation

Movement of gases in and out of the lungs

Respiration

Biological process involving gas diffusion

External respiration

Diffusion of gases between alveolar air and pulmonary capillary blood

Internal respiration

Diffusion of gases between systemic capillary blood and body tissues

Cellular respiration

Metabolic (aerobic) processes in which O2 is used and CO2 is produced within mitochondria

Respiratory tree

Name given to progressively branched airways from trachea to alveoli due to tree form resemblance

Conducting zone

Airway space where gas diffusion cannot take place, airways dedicated to conducting air

Dead space

Air volume of the conducting zone

Respiratory zone

Airway space where gas diffusion takes place, primarily composed of alveoli

Alveolar cells

Primarily simple squamous cells optimized for diffusion, 3% are specialized to produce surfactant

Pulmonary surfactant

Phospholipid-protein product of specialized alveolar cells that acts to reduce alveolar surface tension

Pulmonary surface area

Total gas diffusion area, in a healthy lung equivalent to square footage of half a tennis court

Respiratory muscles

Muscles causing and/or aiding breathing (e.g. diaphragm), more aptly termed "muscles of ventilation"

Boyle's Law

The pressure of a gas, at constant temperature, varies inversely with its volume (P1V1 = P2V2 )

Atmospheric (barometric) pressure

Gas pressure exerted by air, ~745 and ~760 mmHg in Milwaukee and at sea level, respectively

Intra-alveolar pressure

Pressure within the alveolar space, is negative relative to atmospheric pressure during inspiration

Valsalva maneuver

A forced expiration against a closed glottis (think "straining")

Thorax

Thoracic cavity

Pleural membranes

Friction-reducing serous membranes that cover the lungs (visceral) and adjacent thorax surface (parietal)

Lung elastic recoil (elastance)

Resistance to deformation, property of structural elastic fibers and intra-alveolar liquid surface tension

Surface tension

Force acting across a liquid surface as a result of intermolecular attraction that minimizes surface area

Pneumothorax

Presence of air in the pleural cavity, results in a collapsed lung as pleural membranes lose fluid bond

Pulmonary fibrosis

Condition characterized by deposition of fibrous tissue in the lung, lowers compliance, restricts volume

Spirometry

Lung function test measuring lung volumes as a function of time, can also indicate maximal flow rates

Tidal volume (VT)

Amount of air inspired in a single breathe, ~500 ml/br at rest, increases with exercise

Functional residual capacity (FRC)

Lung volume after normal expiration, balance between inward lung recoil and outward thorax recoil

Total lung capacity (TLC)

Lung volume following maximal inspiration (maximal volume of air held by lungs)

Residual volume (VR)

Volume of air remaining in lungs following a complete expiration

Vital capacity (VC)

Maximal volume of air that's expired from a full inspiration, difference between TLC and RV

Forced vital capacity (FVC)

Maximal volume of air that's expired from a full inspiration when performed with maximal speed

Forced expiratory volume in 1 s

FEV1 is the volume of air expired during the first second of an FVC maneuver

Obstructive lung disease

Condition characterized by an increase in airflow resistance, diagnosed by low FEV1 /FVC ratio, difficulty exhaling air

Restrictive lung disease

Condition characterized by a low (restricted) lung volume, diagnosed by low FVC compared to predicted, difficulty inhaling

Respiratory membrane

External respiration diffusion barrier comprised of alveolar epithelium, interstitium, capillary endothelium

Dalton’s Law

Each gas in a mixture of gases exerts a pressure proportional to its concentration in the mixture

Partial pressure

Pressure exerted by a gas in a mixture of gases, the product of total pressure and gas concentration

Atmospheric O2 partial pressure

PO2 is ~160 mmHg at sea-level (760 mmHg x 21%)

Alveolar O2 partial pressure

PAO2 is ~105 mmHg during normal sea-level breathing and hyperpnea, varies by ratio of VA/VO2

Water vapor pressure (PH2O)

Partial pressure of water when in gas form, inspiration becomes fully saturated (humid) lowering PAO2

Arterial O2 partial pressure

PaO2 is ~100 mmHg during normal sea-level breathing and hyperpnea, varies based on PAO2

Venous O2 partial pressure

PvO2 is ~40 mmHg at rest, decreases during exercise as muscle PO2 decreases

Hypoventilation

A level of ventilation rate that's less than what's appropriate for the metabolic rate

Hyperpnea

Increase in ventilation during exercise that's proportional to the increase in metabolic rate

Hyperventilation

A level of ventilation that's out of proportion to (above) the level of metabolism

Henry's Law

Gas amount dissolved in a liquid is the product of the gas partial pressure and its solubility in the liquid

Solubility constant for O2 in blood

Volume of O2 dissolved in deciliter of blood per mmHg PO2 is 0.003 ml O2 , this alone won't sustain life

Fick's law of diffusion

Describes gas diffusion rate as being related to surface area and pressure gradient over surface thickness

Emphysema

Condition resulting in loss of alveolar walls, increases compliance and lowers respiratory surface area

Pulmonary edema

Condition characterized by fluid accumulation in the alveoli, often resulting from high pulmonary BP

Pulmonary transit time

Duration an RBC spends in a pulmonary capillary, is ~0.75 sec at rest and decreases during exercise

Hemoglobin saturation

Average level of O2 binding by hemoglobin, ranges from 0 - 100%

Oxy-hemoglobin dissociation curve

Figure describing hemoglobin saturation with O2 as a function of PO2 , is affected by H+ , temp, PCO2

Pulse oximeter

Medical device that sends light beams through a finger tip to assess HR and level of Hb saturation

Hemoglobin concentration

Amount of hemoglobin per blood sample, ~15 g/dl in a healthy individual

Anemia

Condition of low O2 carrying capacity by blood as a result of a depressed hemoglobin concentration

Venous CO2 partial pressure

PvCO2 is ~45 mmHg at rest, increases during exercise as muscle PCO2 increases

Alveolar CO2 partial pressure

PACO2 is ~40 mmHg during normal sea-level breathing and hyperpnea, varies by ratio of VCO2 /VA

Arterial CO2 partial pressure

PaCO2 is ~40 mmHg during normal sea-level breathing and hyperpnea, varies based on PACO2

Total CO2 content in blood

Combined CO2 total from dissolved, protein bound, and HCO3 - forms, a function of PCO2 and Hb sat

Carbonic acid reaction

Reaction in RBC with an equilibrium of dissolved CO2 and carbonic acid (CO2 + H20 ↔ H+ + HCO3 - )

Carbonic anhydrase

RBC enzyme that catalyzes the equilibration of: CO2 + H20 ↔ H+ + HCO3 -

Arterial O2 content

CaO2 is normally ~20 ml O2 / dl, which includes both the dissolved and hemoglobin bound components

Mixed venous O2 content

CvO2 is normally ~15 ml O2 / dl at rest and decreases during exercise due to tissue extraction