Plaque pH Heterogeneity in Physiological Media

Tania KhanMorteza Naghavi, MD

Overview• Eagle’s Medium - pH 7.2 - 7.5; essential amino acids, glucose (5.6

mM), sodium bicarb (26.2 mM) equilabrated with 75% O2 / 5% CO2 gas mixture (balance N2) warmed to ~37ºC and placed in incubator; media pCO2 20-35 pO2 300-440 mmHg

• Sensor wire ~3 cm long sensing elements in the middle ~1-2 cm from tip; sensor values validated with media values before placing in plaque tissue; typically takes 30 min to equilibrate with tissue

• Distance between pH, pCO2, and pO2 sensors (in that order from tip) may allow the pH reading to be in thinner tissue and pO2 in thicker tissue

• Tissue pH and pCO2 stable for ~ 4 hours in the media• Conclusion: perform readings in thicker (>0.7 mm) tissue areas first

9/7 plaque• Plaque thickness 0.35 - 0.8 mm; ~3

cm x 2 cm area• plaque in media for one hour

before sensor put in • 4.5 hrs in media; tissue values

– pH : 7.03 - 7.06– pCO2 : 60 - 95 mmHg– pO2 : 170 - 290 mmHg– Correlations: pCO2 & T

strongest,R2=0.74; pH-pCO2 R2=0.38

• 2 hrs in humidified 37ºC air– pH sl. increase as pCO2, pO2

temperature dropped

tip

Sensor wire

oxygenated liquid media

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Tem

p

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pH

Temp pH

sensor in plaque out of media

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pCO

2 (m

mH

g)

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pH

pCO2 m pCO2 pH m pH

sensor in

plaque out of media

m = media values from blood-gas machine

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pO2

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Hg)

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pH

p02 m p02 pH m pH

sensor in

plaque out of media

m = media values from blood-gas machine

9/12 plaque

• Plaque thickness 0.7 - 1.6 mm; ICA thickly stenosed; whitish; branch lumen preserved

• ~4.5 hrs in media; tissue values– pH : 6.89 - 7.06 (after 30 min

stabilization)– pCO2 : 65 - 90 mmHg

– pO2 : 20 - 225 mmHg

• Correlations: pH-pCO2 strongest, R2=0.96; pH-temp R2=0.69

Post-experiment picture

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Tem

p

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pH

Temp pH

sensor in plaque

sensor out

9-12-01

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pCO

2 (m

mHg

)

6.80

6.90

7.00

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7.20

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7.40

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7.70

7.80

pH

pCO2 m pCO2 pH m pH

sensor in

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pO2

(mm

Hg)

6.80

6.90

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7.10

7.20

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pH

pO2 m pO2 pH m pH

sensor in

sensor out

9/13 plaque

• Plaque thickness 1 - 2.2 mm; heavily calcified

• ~3.5 hrs in media; tissue values– pH : 6.93 - 7.08 (after 30 min

stabilization)– pCO2 : 60 - 87 mmHg

– pO2 : 0 - 30 mmHg

• Correlations: pH-pCO2 strongest, R2=0.75; pCO2-pO2 R2=0.66

• pO2 sensor element in thickest calcified part of plaque

Post-experiment picture

Sensor tip

9-13-01

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Tem

p

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pH

Temp pH

sensor in

moved sensor

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pCO

2 (m

mH

g)

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6.90

7.00

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7.70

7.80

pH

pCO2 m pCO2 pH m pH

sensor in

attempt to move sensor into thinner part

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pO2

(mm

Hg)

6.80

6.90

7.00

7.10

7.20

7.30

7.40

7.50

7.60

7.70

7.80

pH

p02 m pO2 pH m pH

sensor in

moved sensor

Purpose

• To demonstrate hypothesized pH heterogeneity in a plaque is not equilibrating with oxygenated media

• To assess living state of plaque in physiologic conditions over expected time course

Methods• Sensor A:

– placed about half way into plaque thickness– in semi-calcified/necrotic spot thickness along sensor ~1-2.6 mm

(pO2 near thinner end)

• Sensor B:– placed closer to exterior portion of vessel wall ~0.75 mm in wall– in/under thrombus 1.2-1.6 mm thickness (pO2 near thinner piece,

closest to media)

• After 1.5 hrs, tank w/ 75% O2, 5% CO2 was empty; switched to 21% O2, 5% CO2 to keep same pH-pCO2 buffering capacity

• Monitored for additional 2.5 hrs at 21% Oxygen

Sensor A tip

Sensor B tip

m = media values

ResultsSensor A R2 = 0.9027

01020304050607080

6.90 7.00 7.10 7.20 7.30 7.40pH

pCO

2

• Strong pH-pCO2 correlation suggest sensors are firmly placed in tissue• Sensor A in thicker tissue exhibited lower pH than Sensor B over the 4 hr. time course• Physiologic pH, CO2 readings and trend with different levels of oxygenation suggest plaque is in living state closest to in vivo situation

Sensor B R2 = 0.9464

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pCO

2