Regulation of blood flow in adipose tissue: involvement of the cholinergic system.

Acetylcholine (Ach) has vasodilatory actions. However, data are conflicting about the role of Ach in regulating blood flow in subcutaneous adipose tissue (ATBF). This may be related to inaccurate ATBF recording or to the responder/nonresponder (R/NR) phenomenon. We showed previously that healthy individuals are R (ATBF increases postprandially by >50% of baseline BF) or NR (ATBF increases ≤50% postprandially). Our objective was to assess the role of the cholinergic system on ATBF in R and NR subjects. ATBF was manipulated by in situ microinfusion of vasoactive agents (VA) in AT and monitored by the (133)Xenon washout technique (both recognized methods) at the VA site and at the control site. We tested incrementally increasing doses of Ach (10(-5), 10(-3), and 10(-1) mol/l; n = 15) and Ach receptor antagonists (Ra) before and after oral administration of 75-g glucose using atropine (muscarinic Ra; 10(-4) mol/l, n = 13; 10(-5) mol/l, n = 22) and mecamylamine (nicotinic Ra; 10(-3) mol/l, n = 15; 10(-4) mol/l, n = 10). Compared with baseline [2.41 (1.36-2.83) ml·100 g(-1)·min(-1)], Ach increased ATBF dose dependently [3.32 (2.80-5.09), 6.46 (4.36-9.51), and 10.31 (7.98-11.52), P < 0.0001], with no difference between R and NR. Compared with control side, atropine (both concentrations) had no effect on fasting ATBF; only atropine 10(-4) mol/l decreased post-glucose ATBF [iAUC: 1.25 (0.32-2.91) vs. 1.98 (0.64-2.94); P = 0.04]. This effect was further apparent in R. Mecamylamine had no impact on fasting and postglucose ATBF in R and NR. Our results suggest that the cholinergic system is implicated in ATBF regulation, although it has no role in the blunting of ATBF response in NR.

Intrabullous ventilation in pulmonary emphysema: assessment with dynamic xenon-133 gas SPECT.

PURPOSE: Intrabullous ventilation in patients with pulmonary emphysema (PE) was cross-sectionally evaluated using dynamic xenon-133 gas single photon emission computed tomography (SPECT). METHODS: Fifty-two patients with PE with a total of 109 bullae of more than 4 cm in maximum diameter underwent xenon-133 gas SPECT. The real xenon-133 gas half-clearance time (T1/2) at each bulla was compared with that at the surrounding lung in the same lobe. The emphysema subtype of the surrounding lung was classified into centrilobular, panlobular, and paraseptal on computed tomography (CT). RESULTS: All bullae except for one in all patients showed xenon-133 gas wash-in. Of the 108 bullae with wash-in, 95 (87.9%) bullae in 46 (88%) patients showed marked xenon-133 gas retention with a T1/2 beyond 110 s (mean: 184 s ± 91). The surrounding lungs of these bullae also showed marked retention with a T1/2 of greater than 100 s (mean: 174 s ± 82), and the majority (N=92, 96.8%) were centrilobular or panlobular on CT. The remaining 13 (12.0%) bullae in six (11%) patients showed minimal retention with a T1/2 of less than 80 s (mean: 62 s ± 11), regardless of no significant difference in size compared with the bullae with marked retention. All the surrounding lungs of these bullae except for one also showed minimal retention with a T1/2 of less than 70 s (mean: 60 s ± 18), which was significantly less compared with that of the bullae with marked retention (P<0.0001), and the majority (N=11, 84.6%) were paraseptal with or without an interstitially fibrotic change and predominantly located at the lower lung lobe on CT. The T1/2 of the 108 bullae with xenon-133 gas wash-in was significantly correlated with that of the surrounding lungs (r=0.884, P<0.0001). CONCLUSION: Intrabullous ventilation in patients with PE appears to depend on the ventilation status of the surrounding lung, and bullae with the surrounding lungs of paraseptal-type emphysema tend to show minimal air trapping. Xenon-133 gas SPECT is useful for assessment of the interaction between intrabullous and surrounding lung's ventilation, which is difficult on CT.

Effect of insulin catheter wear-time on subcutaneous adipose tissue blood flow and insulin absorption in humans.

BACKGROUND: Insertion of an insulin catheter for continuous subcutaneous insulin infusion into the subcutaneous adipose tissue (SAT) causes a tissue trauma that may have consequences for insulin absorption. We evaluated the importance of insulin catheter wear-time on subcutaneous adipose tissue blood flow (ATBF) and absorption of the rapid-acting insulin analog insulin aspart over a period of 4 days. METHODS: Teflon insulin catheters (Medtronic, Minneapolis, MN) were inserted into the abdominal SAT of 10 healthy men without diabetes (mean +/- SEM age, 23.0 +/- 1.1 years; body mass index, 22.1 +/- 0.7 kg/m(2)) and connected to an insulin pump delivering a constant rate of isotonic saline for 4 days. Subjects participated in four study days (days 0, 1, 2, and 4) during which ATBF around the catheter tip was measured by (133)Xe clearance and absorption of an insulin aspart bolus (0.1 U/kg) was measured for 4 h. RESULTS: ATBF increased from day 0 to day 2 after catheter insertion (2.6 +/- 0.6 to 4.5 +/- 0.8 mL/100 g/min; P = 0.030). By day 4, ATBF had returned to day 0 level. Time to peak plasma insulin aspart concentration after bolus administration decreased with catheter wear-time from 55 +/- 3 min on day 0 to 45 +/- 4 min on day 4 (P = 0.019). Neither peak plasma concentration nor area under the curve of insulin aspart changed significantly. CONCLUSIONS: Insertion of a Teflon insulin catheter into the SAT results in increased ATBF and faster absorption of insulin aspart in a period of 4 days without any change in the total amount of insulin aspart absorbed.

Comparative analysis of different scintigraphic approaches to assess pulmonary ventilation.

A study was carried out to investigate the predictive value of 81-metastable-krypton (81mKr) distribution, high-size 99-metastable-technetium (99mTc) aerosol deposition and low-size 99mTc aerosol (Technegas) deposition on the pulmonary ventilation evaluated by 133-xenon (133Xe) lung scintigraphy, and to assess the correlation between the 81mKr distribution, the 99mTc aerosols deposition, and the respiratory parameters of patients with chronic obstructive pulmonary disease (COPD). Twenty COPD patients were included. The 81mKr, 133Xe, and 99mTc aerosol lung scintigraphies were successively carried out. The 81mKr distribution and 99mTc deposition were compared to the 133Xe distribution at equilibrium and to the 133Xe clearance. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 81mKr and Technegas lung scintigraphies to detect alterations in ventilation revealed by 133Xe were defined. The 81mKr distribution and 99mTc deposition according to respiratory parameters were described using a principal component analysis. Compared to 133Xe distribution, a significantly higher distribution of 81mKr in the upper parts of the lungs in the more severe patients (p = 0.05), a significantly higher deposition of Technegas in the lower parts of the lungs (p = 0.0008), and a significantly higher deposition in the central parts of the high-size 99mTc aerosol were observed (p = 0.0001). The PPV and the NPV were, respectively, 0.54 and 0.58 for 81mKr and 0.54 and 0.55 for Technegas. There was a significant negative correlation between 81mKr distribution and 133Xe clearance (p = 0.0001) between Technegas deposition and 133Xe clearance (p = 0.0007), and between 99mTc diethylene-triamino-penta-acetate (DTPA) deposition and 133Xe clearance (p = 0.001). Both the 81mKr peripheral distribution and Technegas peripheral deposition correlated negatively with increased obstruction, as measured by forced expiratory volume in 1 sec (FEV1). Peripheral deposition of the high-size 99mTc aerosol deposition correlated with the inspiration/expiration time ratio. In conclusion, 81mKr and 99mTc aerosols' lung scintigraphies do not reflect exactly the pulmonary ventilation as measured by 133Xe scintigraphy.

Characterization of 133Xe gas washout in pulmonary emphysema with dynamic 133Xe SPECT functional images.

PURPOSE: To characterize regional ventilation impairment of pulmonary emphysema using dynamic 133Xe single photon emission computed tomography (SPECT) functional images, compared with other forms of chronic obstructive pulmonary disease (COPD). METHODS: Dynamic 133Xe SPECT was performed in 34 patients with emphysema and 15 patients with other forms of COPD. Three-dimensional voxel-based functional images of the half-clearance time (T1/2) mainly reflecting the initial rapid washout of 133Xe gas from the large airways, and of the mean transit time (MTT) reflecting 133Xe gas washout from the entire lungs, including the small airways and alveoli, were created based on an area-over-height method. T1/2 and MTT values were compared with the regional extent of low attenuation areas (%LAA) on density-mask computed tomography images and the diffusing capacity of the lungs for carbon monoxide (DLCO). RESULTS: The MTT/T1/2 ratio in each lung in emphysema was significantly higher than that in other forms of COPD (1.60+/-0.74 vs. 1.21+/-0.26; P<0.01). In the selected unilateral lungs with similar T1/2 values, MTT values were also significantly higher in emphysema. MTT values in each lung showed a significantly closer correlation with the corresponding %LAA values compared with T1/2 values in emphysema (R=0.698, P<0.0001 vs. R=0.338, P<0.01; P<0.05); while only the T1/2 values showed a significant correlation in other forms of COPD (P<0.0001). In correlation with DLCO, MTT values showed a significantly closer correlation compared with T1/2 values in emphysema (R=0.909, P<0.0001 vs. R=0.555, P<0.001; P<0.05); while either value did not show a significant correlation in other forms of COPD. CONCLUSION: MTT values are more critically affected in emphysema compared with other forms of COPD without significant alveolar destruction, and MTT and T1/2 values appear to be differently correlated with the regional extent of LAA between these two disorders. Direct comparison of regional T1/2 and MTT values on functional images may contribute to the demarcation of lung pathology of these two disorders.

Differences in regional wash-in and wash-out time constants for xenon-CT ventilation studies.

UNLABELLED: Xenon-enhanced computed tomography (Xe-CT) has been used to measure regional ventilation by determining the wash-in (WI) and wash-out (WO) rates of stable Xe. We tested the common assumption that WI and WO rates are equal by measuring WO-WI in different anatomic lung regions of six anesthetized, supine sheep scanned using multi-detector-row computed tomography (MDCT). We further investigated the effect of tidal volume, image gating (end-expiratory EE versus end-inspiratory EI), local perfusion, and inspired Xe concentration on this phenomenon. RESULTS: WO time constant was greater than WI in all lung regions, with the greatest differences observed in dependent base regions. WO-WI time constant difference was greater during EE imaging, smaller tidal volumes, and with higher Xe concentrations. Regional perfusion did not correlate with WI-WO. We conclude that Xe-WI rate can be significantly different from the WO rate, and the data suggest that this effect may be due to a combination of anatomic and fluid mechanical factors such as Rayleigh-Taylor instabilities set up at interfaces between two gases of different densities.

Development of "super rapid dynamic SPECT," and analysis of retention process of 99mTc-ECD in ischemic lesions: comparative study with 133Xe SPECT.

To analyze the retention process of technetium-99m ethyl cysteinate dimer (99mTc-ECD) in normal and ischemic lesions, we developed a super rapid dynamic SPECT system based on the CERASPECT (DSI, Inc., Waltham, MA, USA). The system made it possible to take a SPECT series every 2 seconds. Each SPECT series contains a maximum of 16 slices (6.6 mm slice interval) in a matrix size of 32 x 32. The sensitivity of this system is 175 kcps/MBq/ml/cm slice thickness, and resolution is 12 mm FWHM at the center of a 20 cm(phi) water phantom. Using the super rapid SPECT system, the kinetic behavior of the 99mTc-ECD during retention in normal and ischemic lesions was analyzed. Twenty patients with ischemic lesions that were clearly demonstrated by 133Xe-rCBF (regional cerebral blood flow) SPECT but unclear on static 99mTc-ECD SPECT were examined. For the dynamic SPECT, 700 MBq of 99mTc-ECD was injected intravenously, and dynamic SPECT data were acquired every 2 seconds during a 90-second period. The serial dynamic SPECT and time-activity curves at some lesions with reduced rCBF and at the contralateral normal brain were analyzed. These dynamic SPECT data were compared with conventional static 99mTc-ECD SPECT and quantitative 133Xe-rCBF SPECT. All of mildly or moderately reduced rCBF lesions on the 133Xe-rCBF SPECT were recognized as low activity regions only at the early phase (during about 2-20 sec or less), with the lesions then gradually vanishing. These lesions were not recognized on the conventional static SPECT taken after the dynamic study. The time-activity curve at the reduced rCBF lesion was lower than that of contralateral normal brain at the early phase, and overtook the activity in the normal region with a gradual increase. The early phase images of 99mTc-ECD SPECT within 20 seconds by the super rapid dynamic SPECT were very useful to the same extent as the 133Xe-rCBF SPECT for detecting mild or moderate ischemic lesions. This study suggests that esterase activity, participating in the ECD retention mechanism, may be tolerable to mild or moderate ischemia. This tolerance may be the main cause of the nonlinear relationship between ECD accumulation and cerebral blood flow.

133Xe clearance estimates the effect of vasopressin on peritoneal blood flow in rats.

BACKGROUND/AIMS: When assessing the peritoneal microcirculation with invasive methods, interference with the mechanisms of vaso-regulation may occur. The 133Xe clearance technique renders the possibility, by minimal invasiveness, to estimate the influence of a vasoactive agent on the peritoneal microcirculation. METHODOLOGY: Ten to 15MBq of 133Xe were injected in the abdominal cavity in thirty-eight Wistar-FU (W-FU) rats and 35 Lister-Hooded (LH) rats. A NaI (Tl)-scintillation detector registered activity before and during vasopressin infusion. Gamma camera imaging confirmed the washout from the abdominal cavity. The laser Doppler flowmetry technique was used as a comparison. RESULTS: Vasopressin at 0.07 IU/kg/min IV significantly reduced 133Xe-clearance by 37% (p = 0.029) and 52% (p=0.036) and laser Doppler flowmetry by 69% (p=0.0019) and 44% (p=0.0039) in W-FU and LH rats, respectively. A linear correlation between dose of vasopressin and relative decrease in 133Xe clearance was demonstrated in the W-FU rat model (r2=0.98, p=0.023). The 133Xe clearance from the abdominal cavity in rat using a single-compartment model or the slow compartment in a double-compartment model gave reproducible information. CONCLUSIONS: The usefulness of this mini-invasive technique for sequential measurements before and during intervention will render the 133Xe clearance suitable for assessment of blood flow changes in the abdominal cavity.

Blood flow in liver tumors--effects of vasoactive drugs estimated with xenon (133Xe) clearance.

BACKGROUND/AIMS: The aim of the present study was to identify in a standardized experimental rat liver tumor system the drugs which are most appropriate in influencing the relationship between liver tumor and normal liver parenchyma blood flow as estimated with 133Xe washout clearance method, and thereby positively influencing the kinetics of chemotherapeutic drugs. A battery of vasoactive drugs, which according to a literature review were considered to be active, were tested. METHODOLOGY: Twelve drugs were administered intravenously on 113 Wistar-Fu rats with an experimental adenocarcinoma in the liver (weight 0.62 g). 133Xe was applied in the tumor and in normal parenchyma with and without administration of a vasoactive drug. The pulses were registered with a NaI (Tl)-scintillation detector connected to a multichannel analyzer. The disappearance rate of the isotope was calculated according to a single compartment model. Four recordings were performed in each rat randomly in tumor and liver parenchyma with and without a drug (series A) and one series twice in tumor and twice in parenchyma with a drug (series B). RESULTS: In unaffected animals the tumor to liver quotient was 0.57+/-0.35. This quotient was higher in tumors less than 0.53 g. Angiotensin-II 8 mg i.v. increased the quotient to 0.95+/-0.20. No other drug significantly influenced the quotient. CONCLUSIONS: In an experimental adenocarcinoma in the liver this study has investigated the possibility of increasing the tumor to normal liver parenchyma blood flow quotient by a variety of vasoactive substances for the beneficial modification of tumor blood flow. Angiotensin II 8 mg i.v. was the only drug, which increased the quotient. None of the other tested drugs were supporting previous presented results on influencing tumor blood flow.

Determination of adipose tissue blood flow with local 133Xe clearance. Evaluation of a new labelling technique.

Adipose tissue blood flow was measured in six healthy, non-obese subjects with the xenon wash-out technique after labelling of the tissue by either injection of 133Xe dissolved in isotonic sodium chloride (water depot) or injection of 133Xe in gas form (gas depot). The wash-out rates were registered from four depots simultaneously. Two depots were placed above the umbilicus, and two depots were placed below the umbilicus in the abdominal, subcutaneous adipose tissue. A water depot and a gas depot were placed in the two positions, respectively. It was not possible to demonstrate any difference between the wash-out rates registered from the two depot types, and it was also not possible to demonstrate any difference between the changes in wash-out rates induced by an oral glucose load. Similarly, the tissue distribution of the water and the gas depots appeared to be similar as registered by a gamma camera. It is concluded that that the two tissue labelling modes give identical results. However, there are significant regional differences in the wash-out rates of xenon from subcutaneous, abdominal adipose tissue, the wash-out rates from infraumbilical depots being about 20% lower than from the supraumbilical depots.

Assessment of cerebral blood flow by means of blood-flow-volume measurement in the internal carotid artery: comparative study with a 133xenon clearance technique.

BACKGROUND AND PURPOSE: We sought to evaluate a new, angle-independent ultrasonic device for assessment of blood flow volume (BFV) in the internal carotid artery (ICA). METHODS: Nineteen patients and 4 healthy volunteers were enrolled in a comparative study conducted in the Care Unit of the Division of Neurosurgery at UCLA Medical Center. All patients had been admitted because of severe brain injury: 15 patients with severe head trauma (Glasgow Coma Scale score< or =8) and 4 patients with subarachnoid hemorrhage due to aneurysm rupture. In all patients and subjects, cerebral blood flow (CBF) values obtained with the 133xenon-clearance technique were compared with BFV measurements in the ipsilateral ICA. RESULTS: Hemispheric CBF values showed a close and linear correlation with BFV measurements (r=0.76, P<0.0001). Global CBF values showed a higher correlation with the total BFV value obtained from both ICAs (r=0.84, P<0.0001). With 37 mL x min(-1) x 100 g(-1) as a cutoff value for the ischemic range, a BFV value of 220 mL/min would yield a positive predictive value of 91.7% and a negative predictive value of 82.6% (sensitivity 73.3%, specificity 95%). Conversely, BFV sensitivity and specificity were 60% and 96%, respectively, for the hyperemic range defined by a CBF value >55 mL x min(-1) x 100 g(-1) (positive predictive value of 85.7% and negative prediction value of 85.7%). CONCLUSIONS: BFV measurements with this new technology proved to accurately correlate with CBF values evaluated by the 133xenon-clearance technique. These results support the implementation of this technique for bedside assessment of cerebral hemodynamics in critically ill neurosurgical patients.

A comparison study of ultrasound and Xenon-133 hepatic retention ratio in fatty liver.

BACKGROUND/AIMS: We compared ultrasound and Xenon-133 hepatic retention ratio to evaluate the accuracy of ultrasound in diagnosing fatty liver. METHODOLOGY: One hundred and forty-six patients with suspected fatty liver were included. All patients underwent an ultrasound study followed by a determination of the Xenon-133 hepatic retention. RESULTS: Using the Xenon-133 hepatic retention ratio as the diagnostic standard, the overall accuracy of ultrasound in detecting fatty liver was 57.5%, with 100% sensitivity and 6.0% specificity. CONCLUSIONS: Ultrasound can be used as a first-line screening imaging modality for fatty liver. If the result of ultrasound is equivocal, then Xenon-133 hepatic retention determination should be performed for the diagnosis and management of fatty liver.

No apparent suppression by insulin of in vivo skeletal muscle lipolysis in nonobese women.

To investigate the antilipolytic effect of insulin in skeletal muscle and adipose tissue in vivo, the rates of glycerol release from the two tissues were compared in 10 nonobese women during a two-step euglycemic hyperinsulinemic clamp. Tissue interstitial glycerol levels were determined by microdialysis, and tissue blood flow was assessed with the (133)Xe clearance technique. Absolute rates of glycerol release were estimated according to Fick's principle. In both adipose tissue and muscle, glycerol levels decreased significantly already during the low insulin infusion rate. The fractional release of glycerol (difference between interstitial glycerol and arterialized venous plasma glycerol) was reduced by more than one-half in adipose tissue (P < 0.0001) in response to insulin, whereas it remained unaltered in skeletal muscle. Muscle blood flow rates increased by 60% (P < 0.02) during insulin infusion; in adipose tissue, blood flow rates did not change significantly in response to insulin. The basal rate of glycerol release from skeletal muscle amounted to approximately 15% of that from adipose tissue. After insulin infusion, the rate of adipose tissue glycerol release was markedly suppressed, whereas in skeletal muscle the rate of glycerol mobilization did not change significantly in response to insulin. It is concluded that insulin does not inhibit the rate of lipolysis in skeletal muscle of nonobese women.

Quantification of [(123)I]PE2I binding to dopamine transporters with SPET.

The iodinated cocaine derivative [(123)I]PE2I is a new selective ligand for in vivo studies of the dopamine transporter (DAT) with single-photon emission tomography (SPET). The aim of the present study was to describe a method for accurate quantification of binding data following a bolus injection of [(123)I]PE2I. Six healthy subjects (age 51+/-24 years) underwent xenon-133 SPET for quantification of regional CBF and [(123)I]PE2I SPET for quantification of DAT binding. rCBFs were within normal limits in all subjects. Fitting data to a two-tissue compartment model resulted in striatal K(1) values of 0.39+/-0.08 ml ml(-1) min(-1), equal to a first-pass extraction fraction of 0.72+/-0.13. Distribution volumes (DVs) were calculated using compartment analysis, area under the curve analysis and Logan analysis. Logan analysis is preferred since stable DV values were already obtained 120 min after [(123)I]PE2I injection. Mean striatal DV was 37.9+/-9.6 ml ml(-1) and mean occipital cortex DV was 5.5+/-0.7 ml ml(-1). In the absence of local pathology in a reference tissue, Logan analysis without blood sampling is an attractive method for accurate quantification of striatal [(123)I]PE2I binding. The distribution volume ratio (DVR) (6.6+/-1.4) was in good agreement with the DVR calculated with blood (6.7+/-1.4).

Factors influencing 133-xenon washout in a nose-sinus model.

The 133-xenon washout technique is a non-invasive method for the evaluation of ventilation of the paranasal sinuses. The half-time of 133-xenon washout (T(1/2)) is considered to reflect sinus ostial function and sinus ventilation. However, it is not known how morphological and physiological factors affect the washout from the paranasal sinuses. The aim of the present study was to evaluate how sinus volume, ostial diameter and nasal ventilation influence 133-xenon washout in a nose-sinus model. This is important for the interpretation of measurements of 133-xenon washout from paranasal sinuses in healthy subjects and in subjects with sinus disease. The 133-xenon washout was measured with a scintillation camera. The statistical analysis of the results showed that the logarithm (to the base 10) of the half-time of 133-xenon washout is linearly related to the ostial diameter, the sinus volume and the nasal ventilation in the model. In a multiple linear regression model, the most important factor contributing to 133-xenon washout was found to be the ostial diameter, which explained 76% of the variation in log T(1/2). In the same statistical model the sinus volume explained 7.5% and the ventilation 5.3% of the variation in log T(1/2). Calculations of the functional ostial diameter in healthy subjects were made, based on the results of the model study. The mean functional ostial diameter was found to be 3.5 mm (range 0.5-7.5 mm). The results obtained with the present model experiments may be of importance for the correct interpretation of the results of measurements of 133-xenon washout in healthy subjects and patients.

Clinical significance of ventilation/perfusion scans in collagen disease patients.

UNLABELLED: The purpose of this study was to detect disturbances in pulmonary circulation in collagen disease patients by means of a non-invasive technique. METHODS: Ventilation/perfusion scans with 133Xe gas and 99mTc-macroaggregated albumin (MAA) were performed in 109 patients with various collagen diseases. Functional images of V, Vol, Q and V/Q ratio were obtained at total lung capacity. Wash-out time was calculated from the wash-out curve. Whole body scans were performed in 65 patients to evaluate intra-pulmonary shunts. RESULTS: Increased V/Q areas were observed in 74 patients (67.9%), suggesting some impairment of pulmonary perfusion. Decreased perfusion, probably due to vasculitis or intravascular microcoagulation, was observed often, even in patients without pulmonary fibrosis. Shunt ratios over 10% were observed in 8 of the 65 patients (12.3%), indicating formation of PA-PV shunts secondary to peripheral vascular impairment. Wash-out time was prolonged in 37 patients (33.9%), shortened in 18 (16.5%), and within the normal range in 54 (49.6%). The prolonged and normal wash-out times in the patients with pulmonary fibrosis may represent obstructive changes in the small airways superimposed on the fibrosis. CONCLUSION: Ventilation/perfusion scans are a very useful tool for evaluating collagen lung diseases, and they might contribute to treatment decisions for the patients.

Xenon spill distribution and room clearance.

The purpose of these studies was to investigate actual xenon gas clearance times under different exhaust conditions, to compare them with the calculated clearance times, to observe the distribution of the xenon gas while it was being exhausted from the room, and to determine the cause of a stationary xenon cloud that appeared on some clinical images. Clearance times with and without a flexible exhaust hose placed next to a simulated 133Xe gas spill were compared with clearance times measured in a room with all exhaust closed off. Two gamma cameras were used to observe the transport and exhaust of xenon following a simulated spill. Clearance times with the flexible exhaust hose were less than one minute because the xenon gas was removed before it had a chance to disperse into the room. Conventional room clearance calculations based on uniform mixing and measured exhaust rates yielded a clearance time of 22 min. The source of an artifactual stationary cloud image was discovered to be a small amount of xenon trapped between the collimator and camera face. A negative pressure and dedicated exhaust can be even more effective in exhausting spilled xenon from a room than air transfer calculations predict. The authors believe the flexible hose should always be used.

Regional deposition and retention of particles in shallow, inhaled boluses: effect of lung volume.

The regional deposition of particles in boluses delivered to shallow lung depths and their subsequent retention in the airways may depend on the lung volume at which the boluses are delivered. To evaluate the effect of end-inspiratory lung volume on aerosol bolus delivery, we had healthy subjects inhale radiolabeled, monodisperse aerosol (99mTc-iron oxide, 3.5-microm mass median aerodynamic diameter) boluses (40 ml) to a volumetric front depth of 70 ml into the lung at lung volumes of 50, 70, and 85% of total lung capacity (TLC) end inhalation. By gamma camera analysis, we found significantly greater deposition in the left (L) vs. right (R) lungs at the 70 and 85% TLC end inhalation; ratio of deposition in L to R lung, normalized to L-to-R ratio of lung volume (mean L/R), was 1.60 +/- 0.45 (SD) and 1. 96 +/- 0.72, respectively (P < 0.001 for comparison to 1.0) for posterior images. However, at 50% TLC, L/R was 1.23 +/- 0.37, not significantly different from 1.0. These data suggest that the L and R lungs may be expanding nonuniformly at higher lung volumes. On the other hand, subsequent retention of deposited particles at 2 and 24 h postdeposition was independent of L/R at the various lung volumes. Thus asymmetric bolus ventilation for these very shallow boluses does not lead to significant increases in peripheral alveolar deposition. These data may prove useful for 1) designing aerosol delivery techniques to target bronchial airways and 2) understanding airway retention of inhaled particles.

Respiratory failure and pulmonary hypertension associated with Klippel-Feil syndrome.

A 28-year-old woman with a deformed thorax and kyphoscoliosis associated with Klippel-Feil syndrome developed respiratory failure with pulmonary hypertension. Pulmonary 133Xe ventilation and 99mTc-MAA perfusion scintigraphies showed maldistributions of lung ventilation and perfusion, and noticeably delayed 133Xe washout from the lungs. Dynamic breathing MR imaging showed poor and/or asynchronous respiratory movements of the chest wall and diaphragm. These findings indicate that the perfusion-ventilation imbalance, the decreased ventilatory turnover, and expiratory flow from the alveolar space partly derived from the impaired respiratory mechanics may be responsible for the respiratory complications in this patient.