Vertical distribution of specific ventilation in normal supine humans measured by oxygen-enhanced proton MRI

• Published in: Journal of applied physiology (1985) Vol. 109; no. 6; pp. 1950 - 1959
• Main Authors: Sá, Rui Carlos, Cronin, Matthew V., Cortney Henderson, A., Holverda, Sebastiaan, Theilmann, Rebecca J., Arai, Tatsuya J., Dubowitz, David J., Hopkins, Susan R., Buxton, Richard B., Kim Prisk, G.
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Physiological Society 01.12.2010
• Subjects: Administration, Inhalation; Adult; Biological and medical sciences; Contrast Media - administration & dosage; Female; Forced Expiratory Volume; Fractals; Fundamental and applied biological sciences. Psychology; Humans; Image Interpretation, Computer-Assisted; Lung - physiology; Lungs; Magnetic Resonance Imaging - methods; Male; Middle Aged; Models, Biological; NMR; Nuclear magnetic resonance; Oxygen; Oxygen - administration & dosage; Physiology; Protons; Pulmonary Ventilation; Reference Values; Respiratory system; Signal transduction; Supine Position; Tidal Volume; Time Factors; Ventilation; Vertical distribution; Vital Capacity; Young Adult; Human; Oxygen; oxygen-enhanced magnetic resonance imaging; Respiratory system; Nuclear magnetic resonance imaging; Vertebrata; Mammalia; Distribution; Pulmonary ventilation; Respiration; functional magnetic resonance imaging; Gravity; Functional imaging
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00220.2010

Specific ventilation (SV) is the ratio of fresh gas entering a lung region divided by its end-expiratory volume. To quantify the vertical (gravitationally dependent) gradient of SV in eight healthy supine subjects, we implemented a novel proton magnetic resonance imaging (MRI) method. Oxygen is used as a contrast agent, which in solution changes the longitudinal relaxation time (T1) in lung tissue. Thus alterations in the MR signal resulting from the regional rise in O 2 concentration following a sudden change in inspired O 2 reflect SV—lung units with higher SV reach a new equilibrium faster than those with lower SV. We acquired T1-weighted inversion recovery images of a sagittal slice of the supine right lung with a 1.5-T MRI system. Images were voluntarily respiratory gated at functional residual capacity; 20 images were acquired with the subject breathing air and 20 breathing 100% O 2 , and this cycle was repeated five times. Expired tidal volume was measured simultaneously. The SV maps presented an average spatial fractal dimension of 1.13 ± 0.03. There was a vertical gradient in SV of 0.029 ± 0.012 cm −1 , with SV being highest in the dependent lung. Dividing the lung vertically into thirds showed a statistically significant difference in SV, with SV of 0.42 ± 0.14 (mean ± SD), 0.29 ± 0.10, and 0.24 ± 0.08 in the dependent, intermediate, and nondependent regions, respectively (all differences, P < 0.05). This vertical gradient in SV is consistent with the known gravitationally induced deformation of the lung resulting in greater lung expansion in the dependent lung with inspiration. This SV imaging technique can be used to quantify regional SV in the lung with proton MRI.