Physiology

Question 1

Factors affecting systolic pressure

Answer 1

Stroke volume (The main factor)
Ventricular contractility
In chronic conditions, a decrease in the compliance of the systemic arteries (age-related arteriosclerosis)

Question 2

Factors affecting diastolic pressure

Answer 2

Total peripheral resistance
Heart rate (directly related)
Stroke volume (not a major factor)

Question 3

Factors affecting Pulse Pressure

Answer 3

Increase in stroke volume

Decrease in vessel compliance (systolic increases and diastolic decreases)

Question 4

Mean Pressure Formula

Answer 4

Diastolic + 1/3 Pulse Pressure
Or
2/3 Diastolic + 1/3 Systolic

Question 5

CO Formula

Answer 5

CO = MAP/TPR

Or

MAP = CO x TPR

But if venous or RAP is severely increased, it must be taken into account when estimating TPR

TPR = (MAP - RAP)/CO

Question 6

O2 consumption (Fick Principle)

Answer 6

VO2 = CO x (CaO2 - CvO2)

Question 7

O2 Delivery

Answer 7

O2 Delivery = Q x CaO2

Question 8

Q (Flow) Formula

Answer 8

Q = Oxygen consumption/[O2]pv - [O2]pa

Question 9

What does a fall in PvO2 or SvO2 mean?

Answer 9

Indicates the patient’s O2 consumption increased and/or there was a fall in Q (flow) or CaO2 or both

Question 10

Intrinsic or auto regulation of blood flow

Answer 10

Metabolic mechanism

Tissue vasodilatory metabolite products such as Adenosine, CO2, H+ and K+

Myogenic mechanism

Increased perfusing pressure causes stretch of the arteriolar wall and the surrounding smooth muscle, causing contraction, arteriole radius decreases and Q doesn’t increase

Question 11

Alveolar ventilation Formula

Answer 11

Va = (Vt - Vd)f

Where Vt (Tidal volume)
Vd (dead space)
f (Respiration rate)

Question 12

Units of pressure (Lung mechanics)

Answer 12

1 cm H2O = 0.74 mmHg

1 mm Hg = 1.36 cm H2O

Question 13

Lung Compliance Formula

Answer 13

Compliance = Change in lung volume (tidal volume) / Change in surrounding Pressure

Examen
Vt = 0.6 L
IPP before inspiration -5 cm H2O
IPP after inspiration -8 cm H2O

Compliance = 0.6/3 = 0.200 L/cm H2O

Question 14

Partial Pressure of a Gas in ambient air

Answer 14

Pgas = Fgas x Patm

Pgas = partial Pressure of a gas 
Fgas = concentration of a gas
Patm = atmospheric pressure (760 mmHg)

Question 15

Partial Pressure of a gas in inspired air

Answer 15

PIgas = Fgas (Patm - PH2O)

PIgas = partial pressure of inspired gas
Fgas = concentration of the gas
Patm = atmospheric pressure
PH2O = partial pressure of H2O vapor (47 mmHg)

Question 16

Pulmonary capillary gases

Answer 16

PAO2 = 100 mmHg
PACO2 = 40 mmHg
PaO2 = 95 mmHg
PaCO2 = 40 mmHg
PvO2 = 40 mmHg
PvCO2 = 47 mmHg

Question 17

Factor affecting alveolar PCO2

Answer 17

Alveolar ventilation (Inverse relationship) = If VA increases, PACO2 decreases and viceversa

Metabolic rate = Direct relationship

Question 18

Factors affecting Alveolar PO2

Answer 18

Patm = An increase, increases PAO2 and a decrease (high altitude) decreases PAO2

FiO2 = an increase increases PAO2 (normally 0.21)

PACO2 = An increase, decreases PAO2 and a decrease, increases PAO2

RQ (Respiratory exchange ratio) = normally 0.8

Formula
PAO2 = (Patm - 47)FiO2 - PACO2/RQ

Question 19

Rate of Gas difusión

Answer 19

Vgas = A/T x D x (P1-P2)

A = surface area for exchange (decrease in emphysema, increase in exercise)
T = Thickness of the membranes (increase in fibrosis and restrictive diseases) 
D = Diffusion constant = Solubility
P1-P2 = gradient across the membranes (e.g gradient for O2 = 100-40 = 60 mmHg)

Question 20

Hemoglobin O2 Content

Answer 20

Each gram of Hb combine with 1.34 mL of O2
For example, if the Hb is 15 g/100 mL (15g%), then the maximal amount of O2 per 100 mL (100% saturation) in combination with Hb is

1.34(Hb) = 1.34(15) = 20 mL O2/100 mL blood = 20 vol%

Question 21

Oxygen - Hb dissociation curves

Shifting the curve to the right

Answer 21

Increased CO2
Increased hydrogen ion (Acidosis)
Increased temperature
Increased 2-3 biphosphoglycerate

Reduced affinity of the Hb molecule for oxygen
Easier for tissues to extract oxygen
Strep part of curve, O2 content decreases
P50 increased (PO2 required for 50% saturation)

Question 22

Oxygen - Hb dissociation curves

Shift the curve to the left

Answer 22

Decrease temperature
Decrease PCO2
Decrease 2-3 biphosphoglycerate
Decrease hydrogen ion (Alkalosis)

More difficult for tissues to extract oxygen
Steep part of curve, O2 content increased
P50 decreases

Question 23

Carbon monoxide and Hemoglobin

Answer 23

CO ha a greater affinity for Hb than does oxygen (240 times greater)
O2-Hb dissociation curve is shifted to the left
HbO2 content is reduced

Question 24

Carbamino compounds

Answer 24

When Carbon Dioxide reacts with terminal amine groups of proteins (hemoglobin). About 5% of the total CO2 is carried as carbamino compounds

Question 25

Causes of Hypoxemia - Hypoventilation

Answer 25

No increase in the A-a oxygen gradient Supplemental oxygen can relieve the hypoxemia End tidal air still reflects the systemic arterial compartment The problem is not within the lung itself Equal decrease in PO2 in all 3 compartments (PAO2, pulmonary end capillary PO2 and PaO2)

Question 26

Causes of hypoxemia - Diffusion impairment

Answer 26

Increase in A-a oxygen gradient Supplemental oxygen can relieve the hypoxemia End tidal air does not reflect the arterial values Decrease in DLCO PAO2 is OK Pulmonary end capillary Pressure < PAO2 PaO2< PAO2

Question 27

Causes of hypoxemia - Low VA/Q units

Answer 27

Increased A-a oxygen gradient because PAO2 is normal in areas that don’t have low VA/Q Supplemental oxygen corrects the hypoxemia because regions still have some ventilation, just much lower than normal End tidal air does not reflect the arterial values Low VA/Q creates alveolar and end pulmonary capillary blood gases that are approaching venous gases Examples (status astmaticus, cystic fibrosis, anaphylaxis, partial occlusion of an airway)

Question 28

Causes of hypoxemia - Intrapulmonary shunt (right to left)

Answer 28

Increase in A-a gradient Supplemental oxygen ineffective at returning PaO2 to normal End tidal air does not reflect the arterial values Examples (at electric lung regions in pneumothorax and ARDS, complete occlusion of an airway, right to left shunts created by heart defects)