Ultrasound lung comets: A clinically useful sign in acute respiratory distress syndrome/acute lung injury*:

Strong correlation between lung ultrasound and chest computerized tomography imaging for the detection of acute lung injury/acute respiratory distress syndrome in rats

BACKGROUND

Lung ultrasound (LUS) is a clinical imaging technique for diagnosing acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). In humans and several large animals, LUS demonstrates similar specificity and sensitivity to computerized tomography (CT) scanning. Current study evaluated the degree of agreement between LUS and CT imaging in characterizing ALI/ARDS in rats.

METHODS

Thirty male Sprague-Dawley rats were imaged by LUS before randomization into three groups to receive intratracheal saline, 3 or 6 mg/kg LPS respectively (n=10). LUS and CT imaging was conducted 2 hours after instillation. Cross table analyses and kappa statistics were used to determine agreement levels between LUS and CT assessments of lung condition.

RESULTS

Before instillation, rats presented with a largely A-pattern in LUS images, however, a significantly increase B-lines were observed in all groups after instillation and showed dose response to LPS or to saline. One rat treated with 6 mg/kg lipopolysaccharide (LPS) presented with lung consolidation. The agreement between the LUS and the CT in detecting the main characteristics of ALI/ARDS in rat was strong (r=0.758, P<0.01, k=0.737).

CONCLUSIONS

In conclusion, LUS detects ALI/ARDS with high agreement with micro PET/CT scanning in a rat model, suggesting that LUS represents a positive refinement in rat ALI/ARDS disease models.

Assessment of extravascular lung water by quantitative ultrasound and CT in isolated bovine lung

Lung ultrasonography (LUS) and computed tomography (CT) were compared for quantitative assessment of extravascular lung water (EVLW) in 10 isolated bovine lung lobes. LUS and CT were obtained at different inflation pressures before and after instillation with known amounts of hypotonic saline. A video-based quantitative LUS analysis was superior to both single-frame quantitative analysis and visual scoring in the assessment of EVLW. Video-based mean LUS intensity was strongly correlated with EVLW density (r(2)=0.87) but weakly correlated with mean CT attenuation (r(2)=0.49) and physical density (r(2)=0.49). Mean CT attenuation was weakly correlated with EVLW density (r(2)=0.62) but strongly correlated with physical density (r(2)=0.99). When the effect of physical density was removed by partial correlation analysis, EVLW density was significantly correlated with video-based LUS intensity (r(2)=0.75) but not mean CT attenuation (r(2)=0.007). In conclusion, these findings suggest that quantitative LUS by video gray-scale analysis can assess EVLW more reliably than LUS visual scoring or quantitative CT.

Pulmonary edema in healthy subjects in extreme conditions

There are several pieces of evidence showing occurrence of pulmonary edema (PE) in healthy subjects in extreme conditions consisting of extreme psychophysical demand in normal environment and psychophysical performances in extreme environment. A combination of different mechanisms, such as mechanical, hemodynamic, biochemical, and hypoxemic ones, may underlie PE leading to an increase in lung vascular hydrostatic pressure and lung vascular permeability and/or a downregulation of the alveolar fluid reabsorption pathways. PE can be functionally detected by closing volume measurement and lung diffusing capacity test to different gases or directly visualized by multiple imaging techniques. Among them chest ultrasonography can detect and quantify the extravascular lung water, creating “comet-tail” ultrasound artefacts (ULCs) from water-thickened pulmonary interlobular septa. In this paper the physiopathological mechanisms of PE, the functional and imaging techniques applied to detect and quantify the phenomenon, and three models of extreme conditions, that is, ironman athletes, climbers and breath-hold divers, are described.

Characterization of the normal pulmonary surface and pneumonectomy space by reflected ultrasound

Interest has been increasing in the use of transthoracic ultrasound for the study of the pleuropulmonary disease. US imaging depends mainly on the physical interactions between ultrasound waves and the tissues being examined. In the thoracic region, the prescence of the chest wall and the air-containing pulmonary tissues cause various artifacts that strongly influence the resulting images. At the interface between tissues and air, the ultrasound beam is totally reflected and produces simple reverberation, comet-tail artifacts, and ring-down artifacts.We report the findings of transthoracic ultrasound in normal healthy subjects and in those who had undergone pneumonectomy.This experience shows that, in terms of the ultrasound artifacts mentioned above, the postpneumonectomy cavity is not significantly different from the healthy lung.

Frequent subclinical high-altitude pulmonary edema detected by chest sonography as ultrasound lung comets in recreational climbers

OBJECTIVE

The ultrasound lung comets detected by chest sonography are a simple, noninvasive, semiquantitative sign of increased extravascular lung water. The aim of this study was to evaluate, by chest sonography, the incidence of interstitial pulmonary edema in recreational high-altitude climbers.

DESIGN

Observational study.

SUBJECTS

Eighteen healthy subjects (mean age 45 +/- 10 yrs, ten males) participating in a high-altitude trek in Nepal.

INTERVENTIONS

Chest and cardiac sonography at sea level and at different altitudes during ascent. Ultrasound lung comets were evaluated on anterior chest at 28 predefined scanning sites.

MEASUREMENTS AND MAIN RESULTS

At individual patient analysis, ultrasound lung comets during ascent appeared in 15 of 18 subjects (83%) at 3440 m above sea level and in 18 of 18 subjects (100%) at 4790 m above sea level in the presence of normal left and right ventricular function and pulmonary artery systolic pressure rise (sea level = 24 +/- 5 mm Hg vs. peak ascent = 42 +/- 11 mm Hg, p < .001). Ultrasound lung comets were absent at baseline (day 2, altitude 1350 m, 1.06 +/- 1.3), increased progressively during the ascent (day 14, altitude 5130 m: 16.5 +/- 8; p < .001 vs. previous steps), and decreased at descent (day 20, altitude 1355 m: 2.9 +/- 1.7; p = nonsignificant vs. baseline). An ultrasound lung comet score showed a negative correlation with O(2) saturation (R = -.7; p < .0001).

CONCLUSIONS

In recreational climbers, chest sonography revealed a high prevalence of clinically silent interstitial pulmonary edema mirrored by decreased O(2) saturation, whereas no statistically significant relationship with pulmonary artery systolic pressure was observed during ascent.

Chest sonography detects lung water accumulation in healthy elite apnea divers

BACKGROUND

Ultrasound lung comets (ULCs) detected by chest sonography are a simple, noninvasive, semiquantitative sign of increased extravascular lung water. Pulmonary edema may occur in elite apnea divers, possibly triggered by centralization of blood flow from the periphery to pulmonary vessels. We assessed the prevalence of ULCs in top-level breath-hold divers after immersion.

METHODS

We evaluated 31 consecutive healthy, top-level, breath-hold divers (10 female, 21 male; age 31 +/- 5 years) participating in a yearly international apnea diving contest in Sharm-el-Sheik, Egypt, November 1 to 3, 2007. We performed chest and cardiac sonography with a transthoracic probe (2.5-3.5 MHz, Esaote Mylab) in all divers, both on the day before and 10 +/- 9 minutes after immersion. In a subset of 4 divers, chest scan was also repeated at 24 hours after immersion. ULCs were evaluated on the anterior and posterior chest at 61 predefined scanning sites. An independent sonographer, blind to both patient identity and status (pre- or post-diving), scored ULCs.

RESULTS

Diving depth ranged from 31 to 112 m. Duration of immersion ranged from 120 to 225 seconds. The ULC score was 0.5 +/- 1.5 at baseline and 13 +/- 21 after diving (P = .012). At individual patient analysis, ULCs appeared in 14 athletes (45%) after diving. Of these 14 athletes, 4 were asymptomatic, 6 showed aspecific symptoms with transient loss of motor control ("Samba"), 2 had palpitations with frequent premature ventricular contractions, and 2 had persistent cough with hemoptysis and pulmonary crackles. In a subset of 4 athletes with post-diving ULCs in whom late follow-up study also was available, chest sonography findings fully normalized at 24 hours of follow-up.

CONCLUSION

In top-level breath-hold divers, chest sonography frequently reveals an increased number of ULCs after immersion, indicating a relatively high prevalence of (often subclinical) reversible extravascular lung water accumulation.