Biomedical subjects

José G Venegas

Publications and source records attributed to José G Venegas.

5 recordsLinked to original sources

PubMed2006

Regional pulmonary perfusion, inflation, and ventilation defects in bronchoconstricted patients with asthma.

RATIONALE: Bronchoconstriction in asthma leads to heterogeneous ventilation and the formation of large and contiguous ventilation defects in the lungs. However, the regional adaptations of pulmonary perfusion (Q) to such ventilation defects have not been well studied. METHODS: We used positron emission tomography to assess the intrapulmonary kinetics of intravenously infused tracer nitrogen-13 ((13)NN), and measured the regional distributions of ventilation and perfusion in 11 patients with mild asthma. For each subject, the regional washout kinetics of (13)NN before and during methacholine-induced bronchoconstriction were analyzed. Two regions of interest (ROIs) were defined: one over a spatially contiguous area of high tracer retention (TR) during bronchoconstriction and a second one covering an area of similar size, showing minimal tracer retention (NR). RESULTS: Both ROIs demonstrated heterogeneous washout kinetics, which could be described by a two-compartment model with fast and slow washout rates. We found a systematic reduction in regional Q to the TR ROI during bronchoconstriction and a variable and nonsignificant change in relative Q for NR regions. The reduction in regional Q was associated with an increase in regional gas content of the TR ROI, but its magnitude was greater than that anticipated solely by the change in regional lung inflation. CONCLUSION: During methacholine-induced bronchoconstriction, perfusion to ventilation defects are systematically reduced by a relative increase in regional pulmonary vascular resistance.

Adult↗

PubMed2005

Enhanced parameter estimation from noisy PET data: Part I--methodology.

RATIONALE AND OBJECTIVES: The reliability of positron emission tomographic (PET) images depends on the number of annihilation events that are detected. Short image durations are required to capture rapid tracer dynamics, and the resultant images are noisy. Consequently, direct parameter estimation from time-activity curves at high resolution often is unreliable. If adjacent voxels are combined into larger regions of interest the reliability of parameter estimation may be improved, but at the expense of decreased spatial resolution. In this report, a method is presented that provides an alternative to degrading image resolution. MATERIALS AND METHODS: Following the approach of Kimura et al, voxels are grouped not by spatial proximity, but by the similarity of their kinetics. Parameter estimation is performed on these groups, and derived parameters are assigned to all members of the group. Spatial information thus is preserved, but at the expense of parametric discretization. An improvement to the method of Kimura et al is described, in which data are grouped using principal components derived from artificial data. RESULTS: The application of the method is demonstrated by analysis of PET images of human lungs obtained by the nitrogen-13 infusion-washout technique. In a comparison of the accuracy of parameter estimates, the enhanced method is shown to outperform the original method at all noise levels, with the difference increasing as the amount of noise increases. The robustness of this parameter estimation method in the presence of noise is described in part II of this report in this issue of Academic Radiology. CONCLUSION: A method is described that provides demonstrably robust parameter estimates from noisy PET data, while not compromising image resolution.

Humans↗

PubMed2004

Pulmonary artery occlusion increases the ratio of diffusing capacity for nitric oxide to carbon monoxide in prone sheep.

OBJECTIVE: To test the hypothesis that the ratio of diffusing capacity of the lung for nitric oxide (DLno) to diffusing capacity of the lung for carbon monoxide (DLco) would be affected by occlusion of a fraction of the pulmonary vascular bed. DESIGN: Interventional physiologic study. SETTING: Animal laboratory of a university hospital. SUBJECTS: Thirteen sheep. INTERVENTIONS: We simultaneously measured single-breath DLno and DLco in anesthetized and mechanically ventilated sheep (fraction of inspired oxygen [Fio(2)] of 1.0) before and after pulmonary artery occlusion by inflation of a balloon (n = 6), and by autologous clot embolism (n = 4). To see if the effect also occurred on Fio(2) of 0.21, four animals were studied during ventilation with room air, one of which was also in the Fio(2) of 1.0 group (14 total experiments with 13 sheep). RESULTS: On Fio(2) of 1.0, the mean DLno/Dlco ratio rose by 35% from 4.76 +/- 0.41 in control to 6.42 +/- 0.82 after balloon occlusion (p = 0.002), and by 54% from 7.55 +/- 2.09 to 11.6 +/- 2.61 (p = 0.005) after autologous clot embolism (+/- SD). An equivalent relative increase of 27% took place during ventilation with room air, but the DLno/DLco ratio was lower (3.14 +/- 0.22 in control and 3.98 +/- 0.38 after balloon occlusion). Independent of the method of obstruction or Fio(2), the increase in DLno/DLco ratio was mostly due to a drop in DLco. The DLno/Dlco ratio reduced much of the intersubject variability of either DLno or DLco alone. CONCLUSION: The DLno/DLco ratio increased after pulmonary artery occlusion regardless of the method of occlusion or Fio(2). This increase may be a result of a greater sensitivity of DLco than DLno to a regional reduction in capillary blood flow.

Animals↗

PubMed2002

Regional VA, Q, and VA/Q during PLV: effects of nitroprusside and inhaled nitric oxide.

Partial liquid ventilation (PLV) with high-specific-weight perfluorocarbon liquids has been shown to improve oxygenation in acute lung injury, possibly by redistributing perfusion from dependent, injured regions to nondependent, less injured regions of the lung. Our hypothesis was that during PLV in normal lungs, a shift in perfusion away from dependent lung zones might, in part, be due to vasoconstriction that could be reversed by infusing sodium nitroprusside (NTP). In addition, delivering inhaled NO during PLV should improve gas exchange by further redistributing blood flow to well-ventilated lung regions. To examine this, we used a single transverse-slice positron emission tomography camera to image regional ventilation and perfusion at the level of the heart apex in six supine mechanically ventilated sheep during five conditions: control, PLV, PLV + NTP, and PLV + NO at 10 and 80 ppm. We found that PLV shifted perfusion from dependent to middle regions, and the dependent region demonstrated marked hypoventilation. The vertical distribution of perfusion changed little when high-dose intravenous NTP was added during PLV, and inhaled NO tended to shift perfusion toward better ventilated middle regions. We conclude that PLV shifts perfusion to the middle regions of the lung because of the high specific weight of perflubron rather than vasoconstriction.

Administration, Inhalation↗

PubMed2002

Tracer kinetic model of regional pulmonary function using positron emission tomography.

To determine the spatial distributions of pulmonary perfusion, shunt, and ventilation, we developed a compartmental model of regional (13)N-labeled molecular nitrogen ((13)NN) kinetics measured from positron emission tomography (PET) images. The model features a compartment for right heart and pulmonary vasculature and two compartments for each region of interest: 1) aerated alveolar units and 2) alveolar units with no gas content (shunting). The model was tested on PET data from normal animals (dogs and sheep) and from animals with experimentally injured lungs simulating acute respiratory distress syndrome. The analysis yielded estimates of regional perfusion, shunt fraction, and specific ventilation with excellent goodness-of-fit to the data (R(2) > 0.99). Model parameters were estimated to within 10% accuracy in the presence of exaggerated levels of experimental noise by using a Monte Carlo sensitivity analysis. Main advantages of the present model are that 1) it separates intraregional blood flow to aerated alveolar units from that shunting across nonaerated units and 2) it accounts and corrects for intraregional tracer removal by shunting blood when estimating ventilation from subsequent washout of tracer. The model was thus found to provide estimates of regional parameters of pulmonary function in sizes of lung regions that could potentially approach the intrinsic resolution for PET images of (13)NN in lung (approximately 7.0 mm for a multiring PET camera).

Acute Disease↗