Evaluation of the upper airway in patients with obstructive sleep apnea

Multiple methods have been used to study the structure and physiological behavior of the upper airway (UA) in patients with obstructive sleep apnea (OSA). Valuable information may be obtained from the physiologic measurement of pressure and resistance along the UA, as well as from imaging techniques that include: direct or fiberoptic visualization, cephalometric roentgenograms, fluoroscopy, acoustic reflection, computerized tomography, and magnetic resonance imaging. This review summarizes the information that each of these methods has contributed to our understanding of the UA. The results obtained with these different methodologies have generally been complementary with structural narrowing being identified in the majority of patients with OSA. This narrowing is usually focal and located in the velopharyngeal or retropalatal segment of the UA. This is also the predominant site of initial UA collapse. Although obesity with enlargement of soft tissue structures is considered the predominant mechanism leading to UA narrowing, abnormal craniofacial development on a genetic or developmental basis plays an important contributory role.

Circumferential myocardial shortening in the normal human left ventricle. Assessment by magnetic resonance imaging using spatial modulation of magnetization

BACKGROUND

Conventional cardiac imaging methods do not depict true segmental myocardial shortening, since they cannot determine segment length between fixed points in the myocardium.

METHODS AND RESULTS

We used electrocardiographically gated magnetic resonance imaging with spatial modulation of magnetization to noninvasively "tag" the myocardium with dark stripes at uniform 7-mm intervals center to center at end diastole. We then determined end-systolic stripe separation and thereby calculated circumferential shortening. When end systole was not reached in the first image series, a second temporally overlapped series starting in late systole was used to determine late-systolic shortening. Septal, anterior, lateral, and inferior segments were assessed at endocardium, midwall, and epicardium on five midventricular short-axis sections each in 10 normal volunteers. A transmural gradient in circumferential shortening was observed, with the percentage of endocardial segment shortening consistently greater than epicardial segment shortening (epicardial, 22 +/- 5%; midwall, 30 +/- 6%; and endocardial, 44 +/- 6%; p less than 0.0001 by analysis of variance). Circumferential shortening varied from apex to base with slices closer to the base of the left ventricle showing less shortening at the midwall (28 +/- 9%) and endocardium (39 +/- 6%) than more apical slices at the midwall (34 +/- 13%) and endocardium (49 +/- 9%) (p less than 0.05 and p less than 0.01, respectively, by analysis of variance).

CONCLUSIONS

Transmural and longitudinal heterogeneity of circumferential shortening is present in the normal human left ventricle. Magnetic resonance imaging with spatial modulation of magnetization is a powerful new tool for assessment of circumferential shortening and provides information unobtainable with conventional imaging methods.

Enhanced antibody response in the presence of partial adenosine deaminase inhibition

The enzyme adenosine deaminase (ADA) catalyzes the conversion of adenosine and 2'-deoxyadenosine to inosine and 2'-deoxyinosine, respectively. In the absence of ADA activity, 2'-deoxyadenosine is phosphorylated to deoxyadenosine triphosphate. This study concerned the effects of the ADA inhibitor 2'-deoxycoformycin on the murine in vitro immune response to sheep red blood cells (Mishell-Dutton cultures). In the presence of 10(-7) M 2'-deoxycoformycin or 1 mM 2'-deoxyadenosine, there was a significant increase in the plaque-forming cell response when calculated as plaques per 10(6) viable cells recovered. Cultures containing 10(-7) M 2'-deoxycoformycin retained approximately 10% of residual ADA activity of control cultures. Partial ADA deficiency was not preferentially toxic for cells capable of suppressing plaque cell generation. However, there was a decrease of recovered viable cells in all ADA-deficient cultures. There was no change in the percentage of recovered cells which were L3T4+ or Lyt 2+. A significant decrease was observed in a population of cells expressing surface immunoglobulins. The number of plaque-forming cells/10(3) recovered B cells increased significantly. We conclude that partial ADA deficiency results in selective toxicity to a population of non-antigen-specific B cells. Further studies with antigen-specific cells are necessary to determine the possible mechanism(s) by which cellular activation may prevent susceptibility to the toxic effects of ADA deficiency.

Geometry and kinematics of dog ribs

Five anesthetized supine beagle dogs were scanned using a fast, multislice computed tomographic X-ray technique to determine the orientation of the ribs at total lung capacity (TLC) and functional residual capacity (FRC). A plane was fit to each rib using a coordinate system in which the z-axis was aligned approximately cephalocaudally and the x-z-plane coincided with the sagittal midplane. The orientation of each plane was described by "pump-handle" and "bucket-handle" angles. The ribs rotated downward and inward during a passive deflation of the lungs from TLC to FRC. Rib displacement was not uniform: bucket-handle motion was predominant in the upper ribs, and pump- and bucket-handle motions were equal in the lower ribs. The change in the pump-handle angles between TLC and FRC was approximately 6 degrees for ribs 3-8, and the change in the bucket-handle angles decreased with rib number from 16 degrees for rib 3 to 6 degrees for rib 8. Rib shape was described by fitting an ellipse to the data for each rib; the ribs became larger and more circular with increasing rib number.

Three-dimensional canine renovascular structure and circulation visualized in situ with the dynamic spatial reconstructor

The dynamic spatial reconstructor--a unique, high speed, volume-scanning, X-ray computed tomographic imaging system--was utilized to examine canine renovascular anatomy and renal circulation in situ. In each of the four kidneys examined in this study initial scans were done during bolus injections of angiographic contrast material into the renal artery. A subsequent scan was then performed following an injection of methyl-methacrylate-based casting compound that had been contrast enhanced with ethiodol. After the scans, each kidney was removed, and its parenchyma was digested in potassium hydroxide to expose the vascular cast. Comparison of casts with their reconstructed images and with images obtained during injection of contrast material showed that interlobar arteries and occasionally arcuate arteries could be clearly detected. Although discrete vessels less than 1 mm in diameter could not be resolved, dynamic changes in parenchymal distribution of density during passage of contrast material allowed interpretation of flow through the multiple capillary beds of the kidney. Such analysis indicated that maximal density was in the outer-middle zone of the cortex throughout the duration of the scan. Analysis of artery-to-vein transit time showed arrival of contrast material in the renal vein as soon as 3 sec, and continuation for longer than 8 sec, after the renal artery bolus. In conclusion, renal circulation in the dog can be discretely visualized with the dynamic spatial reconstructor up to the level of the arcuate arteries; however, capillary flow as a whole can be followed through the cortex, and the results suggest the presence of both rapid and slow components of peritubular circulation.

Heart-lung interaction: effect on regional lung air content and total heart volume

To study the interactions between and within the heart and lungs, end-diastolic (ED) and end-systolic (ES) volumes and intrathoracic location of the heart, and the regional air content, volume and geometry of the lungs, were measured from three-dimensional image data generated with the Dynamic Spatial Reconstructor (DSR). The DSR was used to scan the full thoracic extent of anesthetized dogs and sloths at selected transpulmonary pressures. The results show that the dependent to nondependent gradient of regional lung opacity (or conversely regional air content) in the supine animal was not present in the prone animals. While the rib cage and diaphragm of the dog deformed markedly, the shape of the sloth's rib cage and diaphragm remained essentially constant with change in body orientation. As a consequence of these findings, we deduce that the observed change in gradient of regional lung air content in both dog and sloth are in response to changes in the intrathoracic position of the heart which alter ventral lung geometry and not a response to changes in rib cage or diaphragm geometry. In a second series of studies we reconstructed the 3-D extent of the heart at ED and ES in supine anesthetized dogs and demonstrated that the total heart volume (THV) (i.e. contained by the pericardial sac) during sinus rhythm differs by less than 5% between ED and ES. The DSR image data show that this is achieved by the epicardial apex remaining essentially fixed and that the plane containing the atrio-ventricular valves moves like a plunger towards the apex in systole. When atrial fibrillation is present, the THV no longer remains constant and decreases during systole, presumably because of increased stiffness of the atrial myocardium. We conclude from the experimental results that the heart plays an important role in determining regional differences in alveolar expansion, and that by maintaining a constant THV, the heart minimizes energy expenditure which would be caused by moving the lung.

Geometry and respiratory displacement of human ribs

The three-dimensional coordinates of points in the ribs of two supine relaxed males, holding their breath at functional residual capacity (FRC) and with their glottis closed at total lung capacity (TLC), were obtained from volumetric X-ray computed tomographical images. The orientation of planes that best fit the data for each rib at each lung volume and the circular arcs that fit the points in the planes of the ribs were determined, and average values of these geometrical parameters for ribs 3-7 are reported. The planes of the ribs at TLC can be described as displaced from the planes at FRC by a rotation about an axis that passes near the spine. The pump handle and bucket handle components of rotation are 11 and 13 degrees, respectively, for rib 3 and both decrease with increasing rib number to 7 and 10 degrees at rib 7. The angles between the axes of rotation and the midplane are approximately 35 degrees for all 5 ribs. The radii of the circular arcs fit to the data at TLC are slightly larger than those at FRC, and this suggests that there is a small component of rotation normal to the plane of the rib.

Quantification of thoracic volumes by three-dimensional imaging

End-expiratory thoracic cavity volume (Vthx) was measured in eight volunteers lying supine by three-dimensional X-ray computed tomography using the Dynamic Spatial Reconstructor. Untrapped end-expiratory pulmonary gas volume at functional residual capacity (FRC) was determined by nitrogen clearance. Both measurements were done before and after induction of anesthesia-paralysis. After induction of anesthesia-paralysis, Vthx and FRC were consistently and significantly (P less than 0.01) reduced by 0.28 +/- 0.22 (SD) and 0.59 +/- 0.24 liter, respectively. The reduction of FRC was larger than the reduction of Vthx (delta Vthx) in six of the eight subjects, a finding suggesting that intrathoracic fluid (blood) plus trapped gas volume (Vtt) increased. Changes in Vthx were partitioned into volume changes from the thoracic rib cage (delta Vrc) and from shape and/or position changes of the diaphragm (delta Vdi). delta Vrc contributed significantly (0.17 +/- 0.15 liter, P less than 0.02) to delta Vthx, whereas delta Vdi contributed only in four of the eight subjects. We conclude that delta Vrc, delta Vdi, and delta Vtt contribute to the reduction of FRC after induction of anesthesia-paralysis in humans; the relative contribution of them varies among subjects.

Measurement of three-dimensional anatomy and function of pulmonary arteries with high-speed x-ray computed tomography

Pulmonary arterial geometry was quantitatively evaluated in five dogs. One was a control dog, two were subjected to monocrotaline administration, and two had a subclavian-to-pulmonary artery shunt. Measurements of pulmonary arterial anatomy were made with the dynamic spatial reconstructor (DSR), a high-temporal-resolution, volumetric, roentgenographic, computed tomographic scanner. In the control dog, pulmonary arterial cross-sectional areas and segment lengths were measured both from images generated from DSR scans obtained during injection of contrast medium and from a methylmethacrylate cast of the same vascular tree. The correlations between the DSR and cast-based measurements of cross-sectional area and segment lengths were 0.98 and 0.97, respectively. Over periods of eight and 11 months' observation, the pulmonary arterial pressure in the two dogs with surgically created left-to-right shunts increased from 29/15 to 42/17 mm Hg and 19/12 to 25/16 mm Hg, respectively. The cross-sectional areas increased progressively in the proximal portion of the main lobar arteries, remained unchanged in the midportion, and decreased in the distal portion of these arteries. Similar changes occurred in one of the two dogs treated with monocrotaline injections, while in the other the taper of the distal vessels did not change significantly. Pulmonary vascular resistance, computed from cardiac output and pulmonary artery pressure, increased proportionately to the decrease of the cross-sectional areas of distal vessel in both the monocrotaline administration dogs; the resistance decreased proportionately to the increase of the pulmonary arterial cross-sectional areas in both of the surgical dogs.

Invariant total heart volume in the intact thorax

Fast multisliced computerized tomography (Dynamic Spatial Reconstructor or DSR) was used to study the change in total heart volume (content of the pericardial sac) between end diastole (ED) and end systole (ES) with lungs held at 0 and 15 cmH2O airway inflation pressure (Paw). Nine dogs were anesthetized and scanned in the DSR. At 0 cmH2O airway pressure, mean total heart volume changed, on the average, only 2.7 +/- 0.6% (SE) of its ED volume comparing ED with ES. With lungs inflated to 15 cmH2O Paw, total heart volume decreased 12 +/- 0.5%. However, at this new heart volume, the change in total heart volume between ED and ES was only 1.7 +/- 0.5%. The data indicate that the epicardial apex of the heart remains relatively stationary while the atrioventricular groove moves toward the apex during systole and away from the apex during diastole. Thus the atria and ventricles empty and fill reciprocally even when the pericardial contents do not fully distend the pericardial sac. The invariant total heart volume observed in these species would minimize the work of the heart by maximizing the percentage of work expended to move blood and minimizing the work expended to move tissue (i.e., lung).

Effect of body orientation on regional lung expansion in dog and sloth

Recent studies (E.A. Hoffman, J. Appl. Physiol. 59: 468-480, 1985) using fast multisliced X-ray computed tomography have demonstrated a ventral-dorsal gradient of fractional lung air content (3.29% air/cm lung height) in supine dogs and an essentially uniform ventral-dorsal air content distribution in the prone dogs [mean = 66 +/- 0.6% (SE) air content]. Since the prone orientation is the dog's normal body posture, we sought to study an animal whose normal body posture was "opposite" to that of the dog. Four two-toed sloths were scanned in the Dynamic Spatial Reconstructor in the prone and supine postures. A supine fractional air content gradient was demonstrated with a regression equation of y = 2.09x + 74.3 (r = 0.92), where y is percent air content and x is vertical height in the lung, and ventral-dorsal air content distribution in the prone posture was uniform with a mean of 85 +/- 0.4% (SE) air content. The low functional residual capacity lung density in the sloth was attributable to unusually large alveoli. The mean heart volume-to-body weight ratio in the dogs was 16.4 +/- 0.6 (SE) ml/kg and that in the sloth was 7.3 +/- 0.4 (SE) ml/kg. Mean lung volume-to-body weight ratios for dogs and sloths were 57 +/- 7 (SE) and 89 +/- 6 ml/kg, respectively. Of particular interest was the fact that large changes in prone vs. supine rib cage and diaphragm geometry previously found in dogs did not occur in sloths, though significant alterations of ventral and dorsal lung geometry prone vs. supine were demonstrated, and lung shape changes in both dog and sloth are attributable to shifts in the intrathoracic position of mediastinal structures.

Effect of body orientation on regional lung expansion: a computed tomographic approach

The Dynamic Spatial Reconstructor (DSR) was used to study in vivo lung geometry and function. By replacing the lungs of three dogs with potato flakes and ping-pong balls of known air content and scanning these realistic phantoms in the DSR we have estimated accuracy of lung density to be within 7% and have demonstrated a high (+/- 3%) internal consistency (relative density within dogs). Change in total lung air content (y) as calculated from DSR volume imaging of anesthetized dogs matched the known inflation steps (x) to within 7% [range was 1-7% with a mean of 3 +/- 0.5% (SE)]. A gradient of decreasing percent lung air content was measured in the ventral-dorsal direction at functional residual capacity (FRC) in the supine body posture (y = 3.29% air content/cm lung height + 46.48% air content; r = 0.90). Regional lung air content change with lung inflation was greatest in the dependent lung regions. In contrast, regional lung air content at FRC was approximately uniform along the ventral-dorsal direction with the dog in the prone posture and was 66 +/- 0.6% (SE). Ventral-dorsal gradients in lung air content measured within an isogravimetric plane of the dogs in the left or right lateral body posture suggest that regional differences in lung air content cannot be explained solely on the basis of a direct gravitational effect on the lung. Evidence is presented to suggest a possible major role of the intrathoracic position of the mediastinal contents in determining these lung air content distributions.

Three-dimensional cardiac anatomy and function in heart disease in adults: initial results with the dynamic spatial reconstructor

The dynamic spatial reconstructor, or DSR, is a unique high-speed volume-imaging x-ray scanner based on computed tomographic principles. In this report, we present data obtained from the first feasibility DSR studies of adult patients with heart disease. Information from three patients--one with hypertrophic obstructive cardiomyopathy, one with calcific aortic valvular disease, and one with a left ventricular aneurysm--is described in detail. The mean DSR scanning time for each patient was 20 seconds, and the mean total irradiation to the sternum was 15.3 R. Transverse cross sections were reconstructed and then retrospectively reformatted to provide operator-selected oblique sections in space (for example, long-axis and short-axis sections of the left ventricle), to follow these sections through time (such as from end-diastole through end-systole), and to create three-dimensional displays (for instance, of the left ventricular chamber). Unique quantitative measurements of structure and function were made by using these images. For generation of most imaging data, only one injection of contrast material into the right side of the heart is necessary. Clinically useful three-dimensional dynamic imaging data can be acquired from adult patients with heart disease by using the DSR. Compared with conventional angiocardiography, DSR studies can provide information with less x-ray exposure and fewer angiographic injections.

Shape and dimensions of cardiac chambers: importance of CT section thickness and orientation

Three-dimensional (3D) computed tomography (CT) scan data were used to quantitate the geometry of all heart chambers. The Dynamic Spatial Reconstructor (DSR) was used to scan dogs with in situ casts of the cardiac chambers. Chamber volumes estimated from DSR images were accurate within 5% of water displacement volume measurements of the actual casts for chambers greater than 11 ml and within 10% of water displacement volumes for chambers less than 11 ml. Anatomic features of the actual cast correlated closely with anatomy visible in computer-generated surface images of the 3D DSR image data. The important effect of reconstructed section thickness and orientation on the fidelity of 3D cardiac geometry is demonstrated.

Cardiogenic motion of right lung parenchyma in anesthetized intact dogs

Cardiogenic motion of the right lung parenchyma (CGLM) was measured in six morphine-pentobarbital-anesthetized dogs (11-16 kg) under conditions of varying paced and spontaneous sinus heart rates. Motion of 1-mm-diameter percutaneously implanted radiopaque lung parenchymal markers were measured using a computer-based biplane video-roentgenographic assembly. Correlation of the amplitudes and phases of marker motions to the R wave of the electrocardiogram (ECG) were determined utilizing a modified fast Fourier transform algorithm. Of initial importance was the observation that CGLM was significantly greater than the variability of repeated measurements. The total amplitudes of motion of the markers (where AT = square root A2X + A2Y + A2Z and AX, AY, AZ are the amplitudes of marker motion along the orthogonal X, Y, and Z body axes) in the right apical, cardiac, and diaphragmatic lobes were 0.025 +/- 0.005 (SE), 0.046 +/- 0.005, and 0.023 +/- 0.025 cm, respectively, (P less than 0.01, cardiac lobe vs. others). The total amplitude of motion observed in the cardiac lobe was equivalent to earlier observations of total amplitude (0.045 +/- 0.004 cm) of marker motion in response to high frequency airway oscillation at a pump stroke volume of 22-26 ml. An analysis of the higher harmonics of marker oscillation suggested that the second harmonic of CGLM is also larger than the variability of our measurements.

Anatomy and function of the heart and intrathoracic vessels in congenital heart disease: evaluation with the Dynamic Spatial Reconstructor

The Dynamic Spatial Reconstructor is a unique high speed volume imaging X-ray scanner based on computed tomographic principles. It has several potential advantages over conventional angiographic methods, including reduced invasion, reduced rate of false negative results and increased accuracy of measurements of structure and function. To evaluate the utility of the Dynamic Spatial Reconstructor in the investigation of congenital heart disease, scanning was performed in several pediatric patients with pulmonary valve atresia. Early results show that three-dimensional images of the cardiac chambers and intrathoracic vessels can be acquired and displayed with the system. All the information necessary for quantitative analysis of the pulmonary arteries can be obtained with a single scan involving injection of 0.6 to 2.0 cc/kg of contrast agent and radiation exposure of 0.54 to 0.95 rad/s over 5 to 8 seconds.

The effect of preclotting on surface thrombogenicity and thromboembolic complications of Dacron grafts in the canine thoracic aorta

Previous reports have advocated preclotting and autoclaving of Dacron grafts to prevent graft hemorrhage, yet no data delineate possible changes in surface thrombogenicity or thromboembolic risks. To assess these factors, preclotted and preclotted-autoclaved woven Dacron prostheses were implanted in the thoracic aorta of 31 dogs. Grafts were harvested 1 week to 1 month following implantation, and the thrombus-free surface of each graft was calculated by computerized morphometry. Values for thrombus-free surface were lowest in autoclaved grafts preclotted in nonheparinized blood (72%) or in heparinized blood (78%). Grafts preclotted in platelet-rich plasma and autoclaved had a thrombus-free surface value of 85%. Regular preclotted grafts or grafts without preclotting had the greatest thrombus-free surface value (97% and 99%). Distal embolization to the kidneys was detected in seven of 31 animals (23%). No emboli were found in animals with grafts that were not preclotted or if grafts were preclotted with platelet-rich plasma and autoclaved. Thrombus-free surface values were lower (p less than 0.01) in grafts with embolic complications (71% versus 91%). These data suggest that, if the risk of severe bleeding in fully heparinized patients precludes the use of a woven Dacron graft without preclotting, autoclaving a graft preclotted with platelet-rich plasma appears to be the method of choice.

Experimental replacement of the inferior vena cava: factors affecting patency

To evaluate factors influencing graft patency in the venous system, we replaced the inferior vena cava (IVC) in 50 dogs. Expanded polytetrafluoroethylene ( ePTFE ) grafts with external support were implanted into 32 animals while autogenous, spiral jugular vein grafts were used to replace the IVC in 18 dogs. 111In-labeled autologous platelets and 125I-labeled canine fibrinogen were utilized to evaluate early thrombus formation. A distal arteriovenous (AV) fistula significantly (P less than 0.05) decreased both platelet and fibrin deposition on ePTFE grafts 3 hours following implantation. Patency rate of 12 ePTFE grafts with a temporary AV fistula was higher (75%) than that of grafts without fistula (25%) at 3 months (P less than 0.05). Spiral vein grafts with fistula showed 91% patency at 3 months; without fistula patency was only 67%. Venograms confirmed patency in five grafts followed up to 6 months. Antiplatelet therapy resulted in 100% patency in ePTFE and vein grafts during its administration, and vein grafts maintained patency after discontinuation of antiplatelet treatment. Spiral vein grafts showed no decrease in cross-sectional area at 3 months, while the cross-sectional area of ePTFE grafts decreased significantly (59%). Distal AV fistula decreases platelet and fibrin deposition leading to early occlusion in ePTFE grafts and produces excellent patency in spiral vein grafts. Antiplatelet therapy appears to further improve patency.

The Dynamic Spatial Reconstructor: investigating congenital heart disease in four dimensions

The Dynamic Spatial Reconstructor (DSR) is a high-temporal resolution, three-dimensional (3-D) X-ray scanning device based on computed tomography (CT) principles. It was designed for investigation of some problems inherent in current diagnostic imaging techniques, and to allow quantitative studies of cardiovascular structure and function. One of the research protocols in which DSR is currently used involves studying selected pediatric patients with complex congenital heart disease. Initial results show that 3-D dynamic images can be obtained from these patients with minimal invasiveness and that these images may provide useful diagnostic information.

Subtraction gated computed tomography with the dynamic spatial reconstructor: simultaneous evaluation of left and right heart from single right-sided bolus contrast medium injection

Three-dimensional (3-D) dynamic computed tomography of the heart with the dynamic spatial reconstructor (DSR) is being used for studies of cardiovascular function. Formerly, continuous infusion of bilateral bolus injections of contrast medium were required to visualize both sides of the heart simultaneously. The DSR was used to circumvent many of the drawbacks of these methods. In anesthetized dogs a bolus of 1 ml/kg body weight contrast medium was injected into the superior vena cava and 60/s scans were performed during the dextro- and levophases of the resulting angiogram. The recorded scan data were used to generate successive volume (3-D) images with a scan aperture time of 0.06 s each. Each scanned cardiac cycle was thus represented by sequential volume images with either the right or left chambers opacified. Matching equal time intervals from the R wave of the electrocardiogram, the volume images of the left heart phase were digitally subtracted (voxel for voxel) from the images of the right heart phase, with all resulting negative voxel values set to zero. Only the contrast enhanced right ventricle (RV) chamber remained in the subtraction images, whose brightness was then scaled to match the brightness of the opacified left ventricle (LV). The modified RV phase images were then added to the LV phase images. The resulting volume images contain equally enhanced LV and RV chambers and can be used for retrospective analysis, including display of static and dynamic oblique planar images. Verification of the accuracy of this technique was made by estimation of LV muscle mass in five dogs. Dynamic spatial reconstructor estimates from subtracted gated images were compared with postmortem measurements. The correlation was 0.999 with a mean discrepancy of 2.3 +/- 0.4% SEM.

Mass of left ventricular myocardium estimated with dynamic spatial reconstructor

Using the Dynamic Spatial Reconstructor (DSR), a unique multiple X-ray source, high-repetition-rate CAT scanner, we estimated left ventricular (LV) myocardial volume and chamber volume of eight dogs ranging from 2.5 to 32.5 kg. Dogs were given subcutaneous morphine (3 mg/kg) and anesthetized with intravenous pentobarbital sodium (22 mg/kg). A bolus of 1 ml/kg body wt contrast medium was injected into the superior vena cava and 60/s scans repeated over 7 s were performed. Each 0.0167-s scan generated image data for 120 1.8-mm-thick transverse slices, in the dextro and levo phases of the angiograms. Retrospective reformatting of the scan data was used to generate images of thin slices perpendicular to the aortoapical axis of the LV. The LV muscle and chamber volumes were estimated from their outlines in each imaged slice using a manually operated trackball interfaced to a computer. Values of the LV muscle ranged from 18.0 to 146.8 cm3 by DSR and showed a good correlation with the postmortem values (r = 0.99, y = 0.94x + 4.1). Ratios of volume of the myocardium to chamber volume ranged from 1.19 to 3.10.

Regional pleural surface expansile forces in intact dogs by wick catheters

Hoffman and co-workers (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 55: 935-948, 1983) using a technique based on distances between percutaneously inserted X-ray opaque apical and basal lung-parenchymal markers (LPM) calibrated to known transpulmonary pressures in dogs studied without thoracotomy found that apical values measured in the head-up position were more negative than values measured simultaneously by liquid-filled catheters. This finding prompted comparison of pleural pressures (Ppl) measured simultaneously by apical and basal pairs of identical percutaneously inserted liquid-filled catheters, one open ended (OE) and the other wick tipped (WT). Simultaneously OE and WT values were always closely similar in dependent regions of the thorax and usually also in nondependent regions independent of body position and the orientation of the external segment of the wick relative to the catheter tip. However, in some instances in head-up dogs when the wick was extended distal to the catheter tip, apical WT values were 10-15 cm more negative than simultaneous OE measurements. The latter observations agree with the more negative values obtained previously by the LPM technique and support the possibility that apical expansile forces in head-up dogs may be greater than indicated by Ppl measured by liquid-filled catheters and considerably greater than indicated by usually accepted balloon techniques.

Estimation of regional pleural surface expansile forces in intact dogs

Distances between percutaneously inserted apical and basal lung markers determined by biplane X-ray, computer-based videometry (J. Appl. Physiol. 34: 544, 1973) were calibrated against dependent percutaneously recorded pleural liquid pressures (J. Appl. Physiol. 31: 277, 1971) in five 10-12 kg mongrel dogs under morphine-pentobarbital anesthesia studied without thoracotomy. At the same apical pleural-liquid pressure values, the apical intermarker distances were uniformly greater when in the head-up rather than head-down position. This finding suggests that the expansile forces acting on the apical regions of the lung, in the head-up position, are greater (-30 +/- 2 cmH2O) than would be predicted from "pleural liquid" pressures (-15 +/- 1 cmH2O) measured at this nondependent site in the thorax, and much greater than the "pleural surface" pressures measured by the generally accepted balloon and counter-pressure techniques. In contrast, in the head-down body position, expansile forces acting on the nondependent basal regions of the lung estimated by the intermarker distance technique were variable to either side of the pressures measured by open-ended liquid-filled catheters, and thus were not significantly different. Mean values measured by the catheters and predicted by the markers were -14 +/- 1 and -10 +/- 3 cmH2O, respectively.

Noninvasive quantitative imaging of shape and volume of lungs

The Dynamic Spatial Reconstructor (DSR) can be used to determine detailed structure-to-function relationships or organ systems in vivo. A basic index of lung structure (shape and dimensions) is total lung volume. We checked the accuracy with which in vivo lung volumes can be measured by comparing lung volume (air plus tissue) determined by DSR scanning with that determined by excision and water displacement. Six dogs (2.5-26 kg) under morphine-pentobarbital anesthesia were scanned supine or prone at functional residual capacity and/or total lung capacity. With the trachea clamped at the lung volume scanned, a lethal dose of pentobarbital was administered, the lung excised, and its volume determined by water displacement. In vivo scan data were used to reconstruct adjacent 0.9-mm-thick transverse sections over the entire axial extent of the thorax. A three-dimensional surface-detection algorithm was used to generate shaded surface displays of the in situ lungs. The number of voxels (volume picture elements) of known dimensions contained within the three-dimensional image of the lung was summed to estimate total lung volume. Lung volumes calculated from the in vivo images ranged from -3.4 to +2.3% of the lung volume determined in vitro. The mean difference was 1.38 +/- 0.07% (SE). Regression analysis yielded an r value (correlation) of 1.00, a slope of 0.99, and an intercept of -4.35 ml. Multiple lung inflation steps scanned and analyzed in one dog showed similar accuracy. This technique is applicable to subjects with thorax dimensions up to 42 cm in cephalocaudal height and 39 cm in ventrodorsal and transverse diameters.