Relationships between abdominal and diaphragmatic volume displacements

We investigated the relationship between the volumes displaced by the diaphragm and the abdominal wall during spontaneous breathing in supine anesthetized dogs. Diaphragmatic volume displacement (Vdi) was calculated from measurements taken from anteroposterior fluoroscopic images employing a previously described geometric model. The volume displacement of the abdominal wall (Vabd) was measured with a calibrated Respitrace. Shortening of single diaphragm muscle bundles in costal and crural regions was measured as the distance between radiopaque beads sutured to the peritoneal surface of the muscle. We found that Vdi always exceeded Vabd, but Vabd/Vdi was larger in animals in which the abdominal wall was more compliant. In this preparation, Vdi is better correlated with costal than with crural shortening. Vabd did not correlate with either costal or crural shortening. We infer that the difference between Vdi and Vabd reflects the volume displacement of the lower rib cage caused by diaphragm contraction. This volume difference was tightly correlated with costal shortening. We conclude from these data that coupling between Vdi and Vabd is influenced by the relative compliances of the chest wall and abdomen. Shortening of regions of the diaphragm may have variable relationships to the measured volume displacement, but costal shortening is intimately related to expansion of the lower rib cage.

Meibomian gland morphology and tear osmolarity: changes with Accutane therapy

We evaluated the meibomian gland function of 11 patients before and during treatment with isotretinoin (Accutane) by assessing tear osmolarity, meibomian gland morphology, tear production, rose bengal staining, and meibomian gland excreta. We found, during Accutane use, that meibomian glands appeared significantly less dense and atrophic by meibography. Excreta thickness increased from 1.7 +/- 0.9 to 3.1 +/- 1.2 (p less than 0.005), and expressible excreta volume decreased from 1.52 +/- 0.68 to 1.10 +/- 0.3 (p less than 0.05) (scale 1-4). We also found a significant increase in tear osmolarity from 304.9 +/- 11 to 316.3 +/- 10 mosmol/L (p less than 0.005). There was no significant change in the Schirmer test during treatment. We suggest that the clinical symptoms of blepharitis during Accutane therapy are related to decreased meibomian gland function and consequent increased tear evaporation and tear osmolarity.

Meibomian gland dysfunction in chronic blepharitis

We examined 57 patients with symptoms of chronic blepharitis using meibomian gland expression, meibography, tear osmolarity, and the Schirmer's test. We also performed meibography on 20 normal patients free of chronic blepharitis. We found that 42 blepharitis patients (74%) had evidence of meibomian gland loss, whereas only four of 20 normal patients (20%) had any gland dropout. We performed cluster analysis on the data from the patients with blepharitis and found that these patients tended to fall into distinct groups with clinically relevant characteristics. We also found that tear osmolarity correlated positively with gland dropout (+0.413) and negatively with excreta volume (-0.499). This study demonstrates that an objective analysis of meibomian gland function may be used to assess chronic blepharitis and define subsets of blepharitis with measurable differences. It also supports the significance of meibomian gland dysfunction on tear osmolarity and the evaporative state of the eye.

Tandem scanning confocal microscopy (TSCM) of normal and ischemic living kidneys

Tandem Scanning Confocal Microscopy (TSCM) allows one to section optically into and record real-time images of living organs and tissues in a noninvasive fashion. In this paper, we will present some initial TSCM observations of subcapsular nephrons in the living, intact kidneys of Munich-Wistar rats and evaluate the nephron's responses to temporary ischemia and to intravenous infusion of mannitol. The rats were anesthetized with Inactin and a laparotomy performed to expose the kidneys. Using a TSCM equipped with a 20 x water-immersion objective, we optically sectioned through the intact kidney capsule and recorded real-time images of living subcapsular glomeruli and uriniferous tubules. The proximal tubule brush border was highly reflective and allowed us to distinguish between the first and second segments of the proximal tubules as well as the distal tubules. Cellular elements of the blood could be seen passing rapidly through peritubular capillaries and individual glomerular capillary loops. With fluorescent filters in place, intravenously injected carboxyfluorescein was seen to pass through the glomerular capillary loops and then progressively through the different segments of the uriniferous tubules. Ligation of the renal artery resulted in rapid swelling of proximal tubule cells into the tubular lumens, loss of reflectiveness of the microvillous brush borders, and closure of the peritubular capillary spaces. Upon release of the ligature, the proximal tubule lumens again became patent, often opening up abruptly and in a zipper-like fashion down the length of the tubules. Increasing the glomerular filtration rate by intravenous infusion of mannitol resulted in increases in tubular luminal and perimeter dimensions. Mannitol also acted as an effective impermeant osmotic agent and prevented most of the cellular swelling which was otherwise seen in response to renal ischemia.

In vivo, real-time confocal imaging

We have adapted a tandem scanning confocal microscope for real-time, non-invasive imaging of cells under in vivo conditions. This form of in vivo confocal imaging relies on the optical sectioning abilities of the confocal microscope to obtain en face, sequential, reflected light images of cells at various depths, up to 1 mm, within opaque organs in living animals. Of major consideration in the design of an in vivo confocal microscope is maximizing the real-time detection of signals reflected from low contrast structures which can be affected by the microscope design, objective, and image detector systems. Using an in vivo confocal microscope design with a 20 x BioOptics surface contact objective we have obtained live cellular images from selected tissues including cornea, kidney, liver, adrenal, thyroid, epididymis, and muscle and connective tissue of rabbits and rats. Images were captured, digitized, and processed using a DAGE Mti low light level SIT camera coupled to a Gould IP9527 image processor. In vivo images were also compared with conventional bright field light and scanning electron microscopic images of "dead," fixed tissues. Overall, in vivo confocal imaging can provide remarkable detail of living cells comparable to that of conventional microscopic images of "dead," fixed, and stained tissue. A more unique feature of in vivo confocal imaging is the ability to study cellular structure and function sequentially over time in the same organ or tissue and represents a fundamentally new paradigm in microscopy. With continued refinements in the microscope, objective and detection system designs and their consequent improvements in lateral and axial resolution, in vivo confocal microscopy will enable us as observers to see what no one has been able to see before.

A model approach to assess diaphragmatic volume displacement

Diaphragmatic volume displacement (Vdi) is calculated from two models using measurements obtained from anteroposterior fluoroscopic images of supine anesthetized dogs. In model 1, diaphragmatic descent was treated as if it were a "piston in a cylinder." In contrast, model 2 incorporated thoracic configuration as well as inspiratory changes in rib cage diameter and diaphragm shape. In one dog, a computerized tomography reconstruction of Vdi was compared with Vdi calculated using the models. Vdi calculated from model 2 lay within 11% of the computerized tomographic value, whereas Vdi based on model 1 was 30% larger. In seven animals, radiopaque markers were sewn to the right costal diaphragm. Digitized fluoroscopic images were used to measure intermarker distance, an index of muscle shortening. For four tidal breaths per dog, in model 2 Vdi averaged 49 +/- 18% of tidal volume and was weakly correlated with costal diaphragm muscle shortening (R = 0.74). It is concluded that Vdi can be estimated from linear dimensions in the coronal plane, provided that inspiratory changes in rib cage diameter and diaphragmatic shape change are taken into account.

Videofluoroscopic assessment of muscle fiber shortening in the in situ canine diaphragm

We tested the hypothesis that dynamic shortening of the costal diaphragm can be accurately estimated from measurements of the radiographic width of the zone of apposition (WZapp) by studying seven supine anesthetized dogs. Both muscle fiber length, represented by the distance between implanted radiopaque markers, and WZapp were measured from digitized recordings of fluoroscopic images utilizing interactive computer software. The WZapp was highly correlated with the length of costal fibers during active respiration in all animals (mean R2 = 0.94). The accuracy in the prediction of fiber length and shortening during breathing is enhanced by inclusion of additional variables describing the displacement of the abdominal wall and the resting geometric orientation of the fibers. We conclude that dynamic fluoroscopic measurement of WZapp is a valuable technique for estimating dynamic diaphragm fiber length and shortening. Depending on the experimental circumstances, WZapp may be a more easily acquired indicator of diaphragm shortening than other variables that have been previously utilized. As such, it may provide a suitable approach to assess active shortening of the diaphragm in humans.

Effect of lower rib cage expansion and diaphragm shortening on the zone of apposition

The relationship among diaphragm length (LD), the width of the zone of apposition (WZapp), and transverse chest diameter (Drc) was developed from model equations and statistical analysis. We present a theoretical model of diaphragm motion that predicts that the decrease in WZapp during inspiration is the result not only of shortening of the diaphragm muscle but also of expansion of the lower rib cage. To test our model, static lengths of costal LD, WZapp, and Drc were measured in 15 normal volunteers using posteroanterior chest X-ray films taken at four or five lung volumes spanning the vital capacity. We found a strong correlation between WZapp and LD: WZapp = 0.95 LD - 15.2 (R2 = 0.81). Expressing WZapp as a combined function of LD and Drc significantly reduced the unexplained variance in WZapp: WZapp = 0.96 LD - 0.47 Drc - 2.18 (R2 = 0.95). The coefficients for LD and Drc derived statistically are close to those predicted from our theoretical model. Repeating the analysis with LD as the dependent variable, we obtained similar results: LD = 0.85 WZapp + 17.1 (R2 = 0.81) and LD = 0.98 WZapp + 0.46 Drc + 3.48 (R2 = 0.94). We conclude that shortening of WZapp is dependent on both diaphragm shortening and rib cage expansion and that roentgenographic measurements of Drc and WZapp can be used to predict diaphragm length and length change.