3) Partial Pressure & Time Constants (lecture not finished)

define barometric pressure

force exerted by the atmosphere at a given point

P_b in mmHg and kPa at sea level

760mmHg, 101kPa

define Dalton’s law

total pressure = sum of individual gas pressures

PO₂ at sea level (mmHg)

159.6mmHg

PN₂ at sea level (mmHg)

592.8mmHg

PAr. at sea level (mmHg)

6.8mmHg

PCO₂ at sea level (mmHg)

0.3mmHg

when talking about gas in the lung, ________ ________ ________ must be considered

water vapor pressure

water vapor in the lung, ________ PO₂

lowers

PH₂O at sea level (mmHg)

47mmHg

formula for inspired pressure of oxygen in the lung (P_iO₂)

PiO2 = FiO2 x (Pb-PH2O)

what pressure does P_A refer to?

alveoli/lungs

what pressure does P_a refer to?

arterial/blood

alveolar gas equation

PAO2 = PiO2 - (PaCO2/RQ)

respiratory quotient (RQ) of a healthy patient

0.8

diffusion of gas into a fluid

why do climbers need O2 if there is still 21% O2 in the air at the summit of Mt. Everest?

high altitude = smaller PO2 = smaller driving force for diffusion

10,000m is approximately how many ft?

35,000ft

PO₂ at 10,000m (mmHg)

179mmHg

define Henry’s law

solubility of gas is directly linked to pressure

why are blood gases obtained?

assess oxygenation capacity of the cardiopulmonary system

arterial blood gases get sampled from…

peripheral arterial blood

venous blood gases get sampled from…

peripheral venous blood

mixed venous blood gases get sampled from…

pulmonary artery

capillary blood gases get sampled from…

scalp, finger

how does a pulmonary artery catheter (PAC) get placed?

through right atrium into right ventricle into pulmonary artery

which of the blood gas analytes are measured vs calculated?

measured: PO2, PCO2, pH, SO2 (functional, fractional), Na+, K+, Cl-, Ca++, Mg++, lactate, glucose

measured indirectly: Hb

calculated: HCO3-

lactate in the blood is an indicator of…

anaerobic metabolism

why does the oxyhemoglobin dissociation curve have a steep curve?

Hb affinity for O2 increases as more O2 binds so as PO2 increases, binding increases

why does the oxyhemoglobin dissociation curve flatten out at high PaO2?

Hb sites for O2 are already bound

what’s the units for oxygen content in the blood (C_aO₂)?

mL O2 / 100mL whole blood

formula for oxygen content in the blood (C_aO₂)

CaO2 = (0.0031 x PaO2) + (1.34 x Hb x SaO2)

in the C_aO₂ formula, 0.0031 is…

coefficient of O2 dissolved in plasma

in the C_aO₂ formula, 1.34 is…

constant (mL O2/gm Hb)

formula O2 delivery to tissues (DO₂)

DO2 = Q x CaO2

formula for O2 uptake by tissues (VO₂ = oxygen consumption, Fick equation)

VO2 = Q x (CaO2 - CvO2)

in the O2 delivery and uptake equations, what does Q represent and how can it be calculated?

blood flow, Q = SV x HR

in the Fick equation, what can decrease Q?

heart disease, lung disease, muscle disease, deconditioning

in the Fick equation, what can decrease C_(a-v)O₂?

anemia, lung disease (low SaO2)