Effects of vaporized perfluorocarbon on pulmonary blood flow and ventilation/perfusion distribution in a model of acute respiratory distress syndrome.

BACKGROUND: Perfluorocarbon (PFC) liquids are known to improve gas exchange and pulmonary function in various models of acute respiratory failure. Vaporization has been recently reported as a new method of delivering PFC to the lung. Our aim was to study the effect of PFC vapor on the ventilation/perfusion (VA/Q) matching and relative pulmonary blood flow (Qrel) distribution. METHODS: In nine sheep, lung injury was induced using oleic acid. Four sheep were treated with vaporized perfluorohexane (PFX) for 30 min, whereas the remaining sheep served as control animals. Vaporization was achieved using a modified isoflurane vaporizer. The animals were studied for 90 min after vaporization. VA/Q distributions were estimated using the multiple inert gas elimination technique. Change in Qrel distribution was assessed using fluorescent-labeled microspheres. RESULTS: Treatment with PFX vapor improved oxygenation significantly and led to significantly lower shunt values (P < 0.05, repeated-measures analysis of covariance). Analysis of the multiple inert gas elimination technique data showed that animals treated with PFX vapor demonstrated a higher VA/Q heterogeneity than the control animals (P < 0.05, repeated-measures analysis of covariance). Microsphere data showed a redistribution of Qrel attributable to oleic acid injury. Qrel shifted from areas that were initially high-flow to areas that were initially low-flow, with no difference in redistribution between the groups. After established injury, Qrel was redistributed to the nondependent lung areas in control animals, whereas Qrel distribution did not change in treatment animals. CONCLUSION: In oleic acid lung injury, treatment with PFX vapor improves gas exchange by increasing VA/Q heterogeneity in the whole lung without a significant change in gravitational gradient.

Determination of regional ventilation and perfusion in the lung using xenon and computed tomography.

We propose a model to measure both regional ventilation (V) and perfusion (Q) in which the regional radiodensity (RD) in the lung during xenon (Xe) washin is a function of regional V (increasing RD) and Q (decreasing RD). We studied five anesthetized, paralyzed, mechanically ventilated, supine sheep. Four 2.5-mm-thick computed tomography (CT) images were simultaneously acquired immediately cephalad to the diaphragm at end inspiration for each breath during 3 min of Xe breathing. Observed changes in RD during Xe washin were used to determine regional V and Q. For 16 mm(3), Q displayed more variance than V: the coefficient of variance of Q (CV(Q)) = 1.58 +/- 0.23, the CV of V (CV(V)) = 0.46 +/- 0.07, and the ratio of CV(Q) to CV(V) = 3.5 +/- 1.1. CV(Q) (1.21 +/- 0.37) and the ratio of CV(Q) to CV(V) (2.4 +/- 1.2) were smaller at 1,000-mm(3) scale, but CV(V) (0.53 +/- 0.09) was not. V/Q distributions also displayed scale dependence: log SD of V and log SD of Q were 0.79 +/- 0.05 and 0.85 +/- 0.10 for 16-mm(3) and 0.69 +/- 0.20 and 0.67 +/- 0.10 for 1,000-mm(3) regions of lung, respectively. V and Q measurements made with CT and Xe also demonstrate vertically oriented and isogravitational heterogeneity, which are described using other methodologies. Sequential images acquired by CT during Xe breathing can be used to determine both regional V and Q noninvasively with high spatial resolution.

Isocapnic hyperventilation increases carbon monoxide elimination and oxygen delivery.

Hyperventilation with mixtures of O2 and CO2 has long been known to enhance carbon monoxide (CO) elimination at low HbCO levels in animals and humans. The effect of this therapy on oxygen delivery (DO2) has not been studied. Isocapnic hyperventilation utilizing mechanical ventilation may decrease cardiac output and therefore decrease DO2 while increasing CO elimination. We studied the effects of isocapnic hyperventilation on five adult mechanically ventilated sheep exposed to multiple episodes of severe CO poisoning. Five ventilatory patterns were studied: baseline minute ventilation (RR. VT), twice (2. RR) and four times (4. RR) baseline respiratory rate, and twice (2. VT) and four times (4. VT) baseline tidal volume. The mean carboxyhemoglobin (HbCO) washout half-time (t1/2) was 14.3 +/- 1.6 min for RR. VT, decreasing to 9.5 +/- 0.9 min for 2. RR, 8.0 +/- 0.5 min for 2. VT, 6.2 +/- 0.5 min for 4. RR, and 5.2 +/- 0.5 min for 4. VT. DO2 was increased during hyperventilation compared with baseline ventilation for 2. VT, 4. RR, and 4. VT ventilatory patterns. Isocapnic hyperventilation, in our animal model, did not alter arterial or pulmonary blood pressures, arterial pH, or cardiac output. Isocapnic hyperventilation is a promising therapy for CO poisoning.

Validation of fluorescent-labeled microspheres for measurement of relative blood flow in severely injured lungs.

The aim of the study was to validate a nonradioactive method for relative blood flow measurements in severely injured lungs that avoids labor-intensive tissue processing. The use of fluorescent-labeled microspheres was compared with the standard radiolabeled-microsphere method. In seven sheep, lung injury was established by using oleic acid. Five pairs of radio- and fluorescent-labeled microspheres were injected before and after established lung injury. Across all animals, 175 pieces were selected randomly. The radioactivity of each piece was determined by using a scintillation counter. The fluorescent dye was extracted from each piece with a solvent without digestion or filtering. The fluorescence was determined with an automated fluorescent spectrophotometer. Perfusion was calculated for each piece from both the radioactivity and fluorescence and volume normalized. Correlations between flow determined by the two methods were in the range from 0.987 +/- 0.007 (SD) to 0.991 +/- 0.002 (SD) after 9 days of soaking. Thus the fluorescent microsphere technique is a valuable tool for investigating regional perfusion in severely injured lungs and can replace radioactivity.