Affiliation:
1. the Cyclotron Unit, MRC Clinical Sciences Centre and Cardiovascular Research Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK.
Abstract
Background
The purpose of this study was to validate a novel method for noninvasive quantification of regional myocardial oxygen consumption (MMR
o
2
, mL·min
−1
·100 g
−1
) and oxygen extraction fraction (OEF) by use of positron emission tomography (PET) and inhalation of
15
O-labeled molecular oxygen gas (
15
O
2
).
Methods and Results
Twenty-four measurements were performed in eight closed-chest anesthetized greyhounds at baseline and during infusions of adenosine (100 to 200 μg·kg
−1
·min
−1
), isoproterenol (1 to 10 μg/min), and propranolol (5 mg bolus+0.2 to 1 mg/min) with morphine (5 mg slow infusion+0.2 to 0.5 mg/min) to obtain a wide range of oxidative metabolism. The PET imaging protocol consisted of
15
O
2
emission (OEF and MMR
o
2
), transmission, [
15
O]CO emission (blood pool), and [
15
O]CO
2
emission (myocardial blood flow: MBF
pet
, mL·min
−1
·g
−1
) scans. OEF was calculated from the PET data (OEF
pet
) by three different analytical techniques: steady-state, 5-minute, and 8-minute autoradiographic analyses. Reference measurements of MBF (MBF
ref
) and OEF (OEF
ref
) were obtained during
15
O
2
inhalation with radiolabeled microspheres and paired arterial and coronary sinus blood sampling, respectively. MMR
o
2
was calculated from the PET (MMR
o
2pet
) and the reference (MMR
o
2ref
) data as follows: MMR
o
2
=OEF×MBF×(O
2
content of arterial blood). OEF measured by the steady-state PET method was well correlated with the reference data over the range 0.16 to 0.73 (OEF
pet
=1.03 OEF
ref
−0.01,
r
=.97), as was MMR
o
2
over the range 2.4 to 27.5 mL·min
−1
·100 g
−1
(MMR
o
2pet
=0.98 MMR
o
2ref
+0.91,
r
=.94). OEF
pet
calculated by use of the 5-minute and 8-minute autoradiographic analyses were equally well correlated with the reference measurements (
r
=.95 and
r
=.97, respectively). There were no significant differences between values of MMR
o
2pet
calculated by use of the steady-state, 5-minute, and 8-minute autoradiographic analyses (
P
=NS by ANOVA). Regional values of MBF
pet
, OEF
pet
, and MMR
o
2pet
were homogeneously distributed and similar to the whole-heart values both at baseline and during the various pharmacological interventions.
Conclusions
Accurate quantification of OEF and MMR
o
2
is feasible with
15
O
2
inhalation and PET imaging using both the steady-state and autoradiographic analytical approaches. These studies suggest the applicability of this method for quantitative assessments of regional cardiac oxidative metabolism in clinical studies.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Physiology (medical),Cardiology and Cardiovascular Medicine
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