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Regional lung hematocrit in humans using positron emission tomography
Journal of Applied Physiology (Bethesda, Md. : 1985)
|April 1, 1986
Summary
Regional lung hematocrit ratio was measured in healthy individuals and patients. In healthy lungs, the ratio was 0.90, while in patients, it ranged from 0.81 to 0.86, indicating potential differences in pulmonary circulation.
Area of Science:
- Physiology
- Medical Imaging
- Cardiovascular Research
Background:
- Hematocrit, the proportion of red blood cells in blood, varies between different vascular beds.
- Accurate measurement of regional hematocrit is crucial for understanding pulmonary circulation and blood volume.
- Previous methods lacked the precision to differentiate regional hematocrit from peripheral venous values.
Purpose of the Study:
- To measure the regional lung hematocrit ratio (R) in normal subjects and patients with various conditions.
- To investigate the relationship between regional lung hematocrit and other physiological parameters like blood volume and peripheral hematocrit.
- To determine the hematocrit within the pulmonary capillary bed.
Main Methods:
- Positron emission tomography (PET) was employed to measure regional lung hematocrit ratio.
- Red blood cells were labeled with 11CO and plasma with [methyl-11C]albumin as tracers.
- Measurements were conducted in a transaxial thoracic section at midheart level with a spatial resolution of 1.7 cm.
Main Results:
- Normal regional lung hematocrit ratio was 0.90 +/- 0.014.
- Regional hematocrit ratios for the thoracic wall and heart chambers were 0.94 +/- 0.023 and 1.00 +/- 0.003, respectively.
- In patients (pneumonia, nephrotic syndrome, pancreatitis), the regional lung hematocrit ratio ranged from 0.81 to 0.86.
- No significant correlation was found between regional lung hematocrit ratio and regional blood volume, lung extravascular density, or peripheral hematocrit.
- Pulmonary capillary hematocrit was estimated to be approximately two-thirds of the peripheral venous hematocrit.
Conclusions:
- Regional lung hematocrit differs from peripheral venous hematocrit, particularly in the pulmonary capillary bed.
- The findings suggest that pulmonary capillary hematocrit is significantly lower than systemic venous hematocrit.
- Blood volume measurements using single vascular tracers should account for these regional hematocrit variations.