Cardiopulmonary A & P Exam Two

dead space

areas with no gas exchange or perfusion

VDant/ Anatomic dead space

amount of air in conducting airways where no gas exchange takes place, simply provides a pathway for air

VDant equation

1 mL per pound of ideal body weight

VDA/ Alveolar dead space

volume of gas in non-perfused alveoli; abnormal

VDA equation

always 0, unless stated otherwise

VD/ physiologic deadspace

total sum of anatomic and alveolar dead space

VD equation

VD = VDant + VDA

VA/ Alveolar Ventilation

portion of breath that actually ventilates perfused alveoli

VA Equation

VE-VD (minute ventilation - physiological dead space)

VT

tidal volume

VT equation

6-8 mL per kg of IBW

VE

minute ventilation

VE equation

VE = VT x RR

VD/VT Ratio

- Dead space/ Tidal volume ratio

- determines what percentage of the airway is perfused, but not ventilated.

- figured out by the Bohr Equation!!

Normal VD/VT

- 30% at rest

- anything greater than 40% indicates dangerously excessive dead space

Bohr Equation

VD/VT = PaCO2 - PECO2/ PACO2

diffusion

movement of gas molecules from an area of high partial pressure to an area of low partial pressure, continues until equilibrium is reached

P50

- the point at which hemoglobin is 50% saturated with O2 - PO2 of 27 mmHg

FIck's Law

States that diffusion rate of a gas across a membrane is dependent upon:

1. pressure gradient

2. membrane surface area

3. membrane thickness

Graham's Law

States that gas diffusion rate is inversly proportional to its molecular weight... Lighter gases diffuse faster than heavier ones.

Henry's Law

gas dissolving in a liquid is proportional to its partial pressure

VO2

- oxygen comsumption in body's tissues

- approx. 250 ml/min

- measured by difference between O2 in the atmosphere vs in exhaled air

DO2

- oxygen delivery to body's tissues

- approx. 1000 mL (1 L)/min

- measured using cardiac output and CaO2

- technically only 1/4 of oxygen delivered is actually used, the rest is kept in a reserve for when body needs it

anemia

severe deficiency of erythrocytes, impacting the amount of O2 available for use in body's tissues at the cellular level

iron-deficiency anemia

- not enough iron to produce hemoglobin

- small, pale RBCs

vitamin B12 deficiency anemia

- insufficient B12, sometimes due to poor absorption

- large, immature RBCs

sickle cell anemia

- inhereted abnormal hemoglobin

- RBCs are sickle shaped, causing hemolysis and blood vessel blockage

aplastic anemia

- bone marrow fails to produce enough blood cells

- decreased WBCs, RBCs and platelets

hemolytic anemia

- RBCs are destroyed faster than they can be replaced

- premature RBC destruction

chronic anemia

- chronic inflammation interferes with RBC production

- normal sized RBCs but with reduced hemoglobin

HbCO/ COHb

- carboxyhemoglobin

- Hb saturated with carbon dioxide

- Effect on Hb: decreases available binding sites for O2 and has the same affect as anemia (reduction in SaO2)

COHb levels

- normal = 2% or less

- heavy cigarette smokers can have levels as high as 10-15%

- primary treatment is 100% FiO2 or hyperbaric O2 therapy

O2Hb

- oxyhemoglobin

- O2 binded to Hb inside red blood cells

- Effect on Hb: higher O2 affinity, releases H+ more readily

- normally about 97% in arterial blood, 75% in venous

SaO2

arterial oxygen saturation determined by ABG and analysis

SpO2

estimated oxygen saturation assessed via pulse oximetry (spectrometry)

PaO2

partial pressure of arterial oxygen, measured by ABG

PAO2

- alveolar partial pressure of oxygen

- calculated using the alveolar air equation

Pressure gradients

- the difference in partial pressure of gases

- larger pressure gradient = faster diffusion

- smaller pressure gradient = slower diffusion

Alveolar- capillary membrane respiration (external)

- O2: alveolus 100/ capillary 40

- CO2: alveolus 40/ capillary 45

Tissue respiration (internal)

- O2: artery 95/ tissue 40

- CO2: artery 40/ tissue 45

diffusion gradient

- the difference in concentration of chemical potential of a substance between two areas, drives net diffusion

- O2 diffuses from alveoli --> pulmonary capillaries, simulatneously CO2 diffuses from pulmonary capillaries --> alveoli

clinical conditions causing diffusion problems

- alveolar collapse (atelectasis)

- thickening of alveolar wall (alveolar fibrosis)

- alveolar consolidation (pneumonia)

- frothy secretions (pulmonary edema)

- interstitial edema

- alveolar-capillary destruction (emphysema)

inspiratory muscles of ventilation

- primary: diaphragm and external intercostals - acccessory: scalenes, pectoralis major, sternocledomastoid, and serratus anterior

expiratory muscles of ventilation

- primary: none! exhalation is passive

- accesory: rectus abdominus, internal intercostals, obliques

Haldane Effect

Hemoglobin that is bound to O2 (oxygenated) has a lower affinity for CO2 and H+.

Bohr Effect

Hb that is bound to CO2 (elevated PCO2) has a lower affinity for O2.

O2Hb DIssociation Curve

- Relationship between partial pressure of O2 (PO2) and percentage of Hb saturated with O2 (SO2). - Tells us how easily hemoglobin picks up O2 in the lungs and releases it to the tissues.

- Non-linear!

O2Hb Left curve shift

increased Hb affinity for o2

O2Hb right curve shift

decreased Hb affinity for O2

Left curve shift causes

- decreased PCO2

- increased pH

- decreased blood temperature

- decreased 2,3-DPG (diphosphyglycerate, phosphate in RBCs that affects Hb affinity)

Right curve shift causes

- increased in PCO2 (haldane effect!!)

- decrease in pH

- increased blood temperature

- increased 2,3 DPG (diphosphyglycerate, phosphate in RBCs that affects Hb affinity)

hypoxic drive

- when the body relies on low O2 levels (PaO2) to stimulate breathing rather than increased CO2 (PaCO2)

- peripheral chemoreceptors detect this

- chronically seen in COPD patients

capnography

measurement and analysis of exhaled CO2

- ETCO2: end tidal CO2

- PECO2: partial pressure of exhaled CO2

- they are the same value!!!

pulse oximetry

shines red and infared light through tissue to estimate oxygen saturation noninvasively

- SpO2: estimated arterial hemoglobin oxygen saturation

alveolar air equation

- calculates expected partial pressure of O2 in the alveoli

- PAO2 = FiO2(PB-47) - (PaCO2 x 1.25)

Alveolar absolute humidity

44 mmHg/ L

Alveolar water vapor pressure

47 torr