Measurements of functional residual capacity during intensive care treatment: the technical aspects and its possible clinical applications.

Direct measurement of lung volume, i.e. functional residual capacity (FRC) has been recommended for monitoring during mechanical ventilation. Mostly due to technical reasons, FRC measurements have not become a routine monitoring tool, but promising techniques have been presented. We performed a literature search of studies with the key words 'functional residual capacity' or 'end expiratory lung volume' and summarize the physiology and patho-physiology of FRC measurements in ventilated patients, describe the existing techniques for bedside measurement, and provide an overview of the clinical questions that can be addressed using an FRC assessment. The wash-in or wash-out of a tracer gas in a multiple breath maneuver seems to be best applicable at bedside, and promising techniques for nitrogen or oxygen wash-in/wash-out with reasonable accuracy and repeatability have been presented. Studies in ventilated patients demonstrate that FRC can easily be measured at bedside during various clinical settings, including positive end-expiratory pressure optimization, endotracheal suctioning, prone position, and the weaning from mechanical ventilation. Alveolar derecruitment can easily be monitored and improvements of FRC without changes of the ventilatory setting could indicate alveolar recruitment. FRC seems to be insensitive to over-inflation of already inflated alveoli. Growing evidence suggests that FRC measurements, in combination with other parameters such as arterial oxygenation and respiratory compliance, could provide important information on the pulmonary situation in critically ill patients. Further studies are needed to define the exact role of FRC in monitoring and perhaps guiding mechanical ventilation.

[Breaking new ground in teaching medical students emergency medicine. Evaluation of a multi-centre student-guided teaching concept]. / Neue Wege in der Notfallausbildung von Medizinstudierenden. Evaluation eines multizentrischen, studentisch geleiteten Kurskonzepts.

BACKGROUND: Medical students who want to apply for preliminary medical examinations in Germany have to prove that they have attended a first-aid course. However, lay courses are often not up to the standards and needs that medical students require. As a result since 1996 members of the task group "AGEHMED", all of whom are medical students, have been teaching their peers in target groups orientated first aid and emergency techniques at medical school. The task group is (currently) active with 190 students at 6 German medical schools. All students, even those without any previous knowledge, can participate in emergency medicine education of their peers following a supervised 5-step model. OBJECTIVE: The aim of this study was to examine the results of a questionnaire that was used for evaluation of peer-guided first-aid courses at medical schools over the last 7 years and to assess its validity and reliability. MATERIALS AND METHODS: From 2000 to 2007 59 first-aid courses with 4,941 medical students were evaluated. After carrying out descriptive analyses the factorial validity and reliability (Cronbach's alpha) of the questionnaire were assessed. The inter-scale correlation of the significant factors was also analysed. RESULTS: The courses were continuously well rated. The amount of variance explained by the factors"quality of the course","learning success","comparison to other university courses","overall satisfaction" and"scheduling of the course" was 68%. The mean inter-scale correlation was r=0.23 and Cronbach's alpha was between 0.62 and 0.81. CONCLUSIONS: The peer-guided courses have been continually well received by the course participants over the last 7 years. The questionnaire shows sufficient validity and reliability. Based on these results, it can be presumed that this approach can be more widely put into practice in the education of medical students.

Patient mood and neuropsychological outcome after laparoscopic and conventional colectomy.

The study was designed to compare patients after laparoscopic and conventional colectomy with regard to early postoperative mood, cognitive function, and neurocognitive variables S100beta and neuron-specific enolase (NSE). Forty-five laparoscopic and 25 open colectomies were enrolled into the prospective study. Outcome measurements were positive and negative postoperative mood (BSKE), neuropsychological tests (Trail-Making Test; word reproduction; Stroop Test), and serum biochemical parameters (S100beta; NSE). Following laparoscopic procedure, patients described significantly better positive mood (P< .05), tended to require less time in the Trail-Making Test and Stroop Test, and had lower postoperative serum concentrations of S100beta compared to conventional colectomy patients (P< .01). The current results revealed several group differences, which, in their entirety, seem to represent a more beneficial outcome after laparoscopic colonic surgery.

Respiratory protection during high-fidelity simulated resuscitation of casualties contaminated with chemical warfare agents.

Emergency room personnel are threatened by secondary poisoning when treating victims affected by chemical warfare agents. Therefore, resuscitation skills practised with respiratory protection equipment in place require evaluation. We investigated the influence of wearing air-purifying respirators on the simulated resuscitation of chemical warfare agent casualties. We studied 22 anaesthetic trainees in a simulated resuscitation scenario requiring five set tasks, either unprotected, wearing a binocular visor respirator or a panoramic visor respirator in a randomised, crossover study. Treatment times did not differ between the three groups, with mean (SD) times to complete the tasks being 122 (8) s without a mask, 126 (7) s when wearing the panoramic visor mask and 129 (8) s when wearing the binocular respirator mask. All anaesthetists preferred the panoramic visor in terms of visual orientation but 88% of them rated the binocular mask as being more comfortable. Modern respirators have a negligible effect on simulated resuscitation scenarios for victims affected by chemical warfare agents. Panoramic visor respirators allow better visual orientation for anaesthetists during simulated resuscitation.

The Na+/H+ exchange inhibitor cariporide is washed out of the myocardium by crystalloid cardioplegia.

BACKGROUND: Inhibition of the Na (+)/H (+) exchanger (NHE) is cardioprotective, but dosage and timing of NHE-inhibitors are critical for their efficacy. We studied the effect of a new dosing regime of the NHE-inhibitor cariporide on myocardial function and damage after cardioplegic arrest (CPA) and determined its myocardial and serum concentrations. METHODS: 3 pigs received a bolus of 180 mg cariporide intravenously (i. v.) and were sacrificed shortly thereafter to allow measurement of the myocardial concentrations of cariporide. Subsequently, 10 pigs were randomized to receive either i. v. cariporide (bolus followed by an infusion of 40 mg/h) or placebo. Cardiopulmonary bypass was initiated, and the heart was arrested for 60 minutes by infusion of St. Thomas Hospital solution. Left ventricular (LV) function was studied using microsonometry. Myocardial damage was assessed by troponin T. Serum concentrations of cariporide were measured throughout the study, and myocardial concentrations were measured before the end of CPA and 180 minutes thereafter. RESULTS: Cariporide was present in all myocardial specimens (median: 1.4 ng/mg) studied previously. In the main study, LV function or myocardial damage did not differ significantly between the groups at any time point. Stable serum cariporide concentrations were achieved (3.4 +/- 0.5 microg/ml). Cariporide was detectable in only one of the myocardial biopsies obtained before the end of CPA, but 180 minutes thereafter, the myocardial cariporide concentration was 2.5 +/- 0.3 ng/mg. CONCLUSION: We observed no effect of i. v. cariporide on LV function or myocardial damage after cardioplegic arrest. Our data suggest that cariporide is washed out of the myocardium by repeated application of crystalloid cardioplegia. Thus, the mode of delivery also appears to be critical for cardioprotection with NHE-inhibitors.

Effects of candesartan and enalaprilat on the organ-specific microvascular permeability during haemorrhagic shock in rats.

BACKGROUND: To counteract the contribution of angiotensin II to shock-induced ischaemic organ damage pharmacologic blockade of the renin-angiotensin-system (RAS) is currently under investigation. To evaluate potential side-effects of RAS blockade regarding capillary leak, we studied alterations in microvascular permeability in various organs during haemorrhagic shock (HS) in rats pretreated with candesartan (AT(1)-receptor antagonism) or enalaprilat (ACE-inhibition). METHODS: Thirty-eight instrumented and anaesthetized animals received either candesartan, enalaprilat or placebo. Within each of the three groups 6-7 animals were exposed to HS and 6 animals of each group served as normovolaemic controls. After 30 min of shock, 50 mg kg(-1) Evans blue (EB) was injected i.v. followed by a distribution period of 20 min. Exsanguination was performed with saline, before harvesting organs to quantify albumin-bound EB extravasation. RESULTS: To reduce cardiac output from 37.5 (1.3) to 20.4 (1.1) ml min(-1) [mean (SEM)] in the shock groups, withdrawal of 4.0 (0.25) ml [mean (SEM)] blood was necessary. Simultaneously mean arterial pressure decreased from 77.5 (3.2) to 36.1 (2) mm Hg. Serum lactate increased significantly from 1.3 (0.1) to 3.5 (0.24) mmol litre(-1). Treatment with candesartan increased EB extravasation in the kidney in normovolaemic controls. Specific AT(1) and ACE-blockade before acute non-resuscitated HS significantly increased EB extravasation in the rat ileum by 53 and 66%, respectively. CONCLUSION: This observation of increased microvascular albumin extravasation should be borne in mind for any interventional use of candesartan or enalaprilat during circulatory stress.

Clinical biochemical tissue monitoring during ischaemia and reperfusion in major vascular surgery.

BACKGROUND: Major vascular surgery with aortic cross-clamping is associated with temporary ischaemia of the lower limb due to lack of tissue blood flow. The present study was designed to determine if the short-term changes in cellular metabolism occurring during this situation can be detected by subcutaneous microdialysis. It was also hoped to ascertain if this new technique is useful in the continuous bedside monitoring of metabolism during aortic surgery. METHODS: In a controlled clinical study 20 patients undergoing elective aortic surgery were monitored using microdialysis probes that were inserted in the subcutaneous tissue of the left lower limb and a non-ischaemic region (shoulder). Interstitial fluid was obtained and the concentrations of glucose and lactate during lower limb ischaemia and during reperfusion were measured and compared with concentrations observed in fluid obtained from the non-ischaemic control tissue. RESULTS: Circulatory occlusion caused an immediate and significant decrease in the glucose/lactate ratio from 3.1+/-1.3 to 0.48+/-0.5 (P<0.05) that returned to preocclusion values within 2 h of commencing reperfusion. CONCLUSION: We suggest that microdialysis may be used both to assess acute changes in tissue metabolism during ischaemic periods and also to act as an additional tool for the detection of peri-operative acute variations in limb blood flow.

[Microdialysis as a procedure for evaluating intestinal hypoxia--an animal experiment approach]. / Mikrodialyse als Verfahren zur Beurteilung einer intestinalen Hypoxie--ein tierexperimenteller Ansatz.

Usual ICU monitoring of patients with abdominal pathology provides no detailed information about hepatosplanchnic haemodynamics or intestinal metabolism. In our animal experiment, the effects of systemic hypoxia on microdialysis measurements of the peritoneum in comparison with the ischiocrural muscle as reference were investigated in 7 rats. The parameter of interest was the course of glucose metabolism reflecting sympathoadrenergic activity during the experiment. Measurements were obtained at timed intervals at baseline, under hypoxia, and during reoxygenation. After induction of systemic hypoxia, the peritoneal microdialysis showed significantly higher levels of glucose in comparison with the ischiocrural muscle. The results indicate hypermetabolic activity or a hypersympathetic response of the bowel in response to hypoxic stress. In the clinical setting, the bowel has an important role in the development of multiorgan failure. Microdialysis may therefore be an interesting tool for the early detection of hypoxic metabolism during and after abdominal procedures.

Advanced glycation end products induce choroidal endothelial cell proliferation, matrix metalloproteinase-2 and VEGF upregulation in vitro.

BACKGROUND: Advanced glycation end products (AGEs) are considered to be important modulators of angiogenesis and accumulate in choroidal neovascularization (CNV). Their effects regarding cells involved in proliferation of CNV [retinal pigment epithelial (RPE) cells, Müller cells and choroidal endothelial cells (CECs)] were investigated. Furthermore, the effects of AGEs on expression of matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF) by CECs were explored. METHODS: RPE cells, CECs and Müller cells were exposed to AGEs (10 microg/ml, 50 microg/ml and 100 microg/ml) for a time course of three days in their desired medium and proliferation was estimated by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. MMP-2 expression of AGE-stimulated CECs was determined by zymography and reverse-transcription polymerase chain reaction (RT-PCR) after 36 h of exposure. Furthermore, VEGF expression of AGE-stimulated CECs (50 microg/ml and 100 microg/ml) was determined by RT-PCR after an exposure time of 36 h. RESULTS: AGEs in a concentration of 50 microg/ml and 100 microg/ml increased the proliferation of CECs (41% vs 46.1%; P<0.005). No AGE effect on RPE cell and Müller cell proliferation was seen. AGEs in all concentrations used upregulated the VEGF mRNA expression of CECs. Zymography and RT-PCR demonstrated the upregulation of MMP-2 by CECs after AGE exposure. CONCLUSION: AGEs stimulate CEC proliferation, MMP-2 secretion and VEGF upregulation and may be important promoters of CNV formation in exudative AMD in vivo.

Correlation between expression of selectins and migration of eosinophils into the bovine ovary during the periovulatory period.

Leukocytes enter specific ovarian areas at a precisely defined moment, influencing cyclically changing structures such as follicles and corpora lutea. As yet, no studies have been published on the trafficking mechanisms involving the interaction between adhesion molecules on endothelial cells (ECs) and those on leukocytes. First, antibodies against human adhesion molecules were examined by flow cytometry with the aim of identifying the same bovine antigen. Western blot analysis and immunoprecipitation revealed that the molecules had the same molecular weight as their human counterparts. Afterwards, we investigated the distribution of these antigens in various ovarian stages using immunohistology. Among the molecules, P-selectin (CD62P) and L-selectin (CD62L) showed stage-dependent expression, and were thus examined further. In the preovulatory follicle, microvascular ECs were negative for CD62P. Few of the leukocytes expressed CD62L. In a freshly ruptured follicle, CD62P expression was found in the dilated vessels of the former thecal layer. Simultaneously, a large proportion of the rapidly increased numbers of leukocytes, mainly eosinophils, located around the microvessels of the outer thecal layer expressed CD62L. In the early corpus luteum development stage, CD62L showed peak expression with 70%-80% positive cells compared to leukocytes. In the secretory stage, the septal venules showed a consistent, but now weak, staining for CD62P. Few leukocytes expressed CD62L. During regression, the total number of leukocytes, now representing macrophages, increased significantly, but the proportion of CD62L-positive cells remained constant. In summary, we found a strong correlation of CD62P expression on activated ECs and the appearance of CD62L-positive leukocytes in the early corpus luteum development stage, suggesting the participation of both selectins in the migration of eosinophils under physiological conditions.

Hypoxia: modulation of endothelial cell proliferation by soluble factors released by retinal cells.

A devastating complication of ischemic retinopathies is retinal neovascularization. We studied the impact on retinal endothelial cell proliferation of soluble factors released from cultured retinal glial (Müller) cells and from retinal explant cultures. Hypoxia strongly stimulated VEGF release by all types of cultures but endothelial cell growth was not further increased by the corresponding conditioned media if compared to supernatants obtained under normoxia. When the final concentration of the hypoxia-conditioned media was adjusted to the VEGF level of normoxia-conditioned media, they even inhibited endothelial cell proliferation. Inhibition may be exerted by TGF-beta 2 but TGF-beta 2 mRNA and protein expression in Müller cells were found to be down-regulated under hypoxia. We conclude that retinal endothelial cell proliferation is controlled by the balance of the amount and/or efficacy of several stimulatory and inhibitory factors.

Direct measurement of VEGF-induced nitric oxide production by choroidal endothelial cells.

Vascular endothelial growth factor (VEGF) and nitric oxide (NO) seem to be involved in the process of angiogenesis, but their interactions are not clearly understood. The aim of this study was to investigate the influence of VEGF on NO production of choroidal endothelial cells (CEC) and its importance in angiogenesis. Experiments were performed using cultured bovine CEC. Basal NO release of unstimulated CEC was measured and compared to NO release of VEGF-stimulated CEC (1, 10, and 100 ng/ml). Further, cells were pretreated with N(omega)-nitro-L-arginine methyl ester (L-NAME, 1 and 2 mM) and incubated with and without VEGF (10 ng/ml) to investigate the effect of blocking NO synthase. NO release into the medium was assessed by an amperometric NO sensor. To show the importance of NO in angiogenesis, proliferation and migration of CEC were measured after VEGF stimulation and in the presence or absence of L-NAME (1 and 2 mM). Unstimulated CEC continuously produced low levels of NO. Stimulation of the cells with VEGF resulted in a dose-dependent increase in NO release. The time course after stimulation with 10 ng/ml VEGF was characterized by a prompt initial rise up to 140% of unstimulated levels and a subsequent sustained increase over 120 min. Pretreatment with L-NAME attenuated the VEGF-induced response. L-NAME incubation alone led to a reduction in basal NO release. L-NAME also significantly diminished the VEGF-enhanced CEC proliferation and migration. The results demonstrate that VEGF enhances the formation of NO in cultured CEC. The blockade of NO production reduces CEC proliferation and migration, an effect which may be important for controlling angiogenesis, especially in reducing neovascularization in age-related macular degeneration in the eye.

Differentially induced expression of C-type lectins in activated lymphocytes.

The human NK gene complex encodes for the leucocyte C-type lectins, CD69, AICL (activation-induced C-type lectin), LLT1 (lectin-like transcript), CD161/NKR-P1A, CD94, and for NKG-2 molecules. These gene products have been implicated in the regulation of the function of natural killer (NK) cells and other lymphocytes. In this study the expression of C-type lectins during the early activation of PMA-stimulated peripheral blood lymphocytes was examined. To investigate the influence of de novo protein synthesis on activation-dependent expression of C-type lectins, cells were cultured in presence of cycloheximide (CHX) and mRNA levels were analyzed by semi-quantitative reverse transcription-polymerase chain reaction. Upregulated levels of CD69, AICL, and LLT1, but less pronounced changes of CD161/NKR-P1A and CD94 mRNA were found at early time points of cellular activation. CD69 was superinduced by CHX at the nuclear precursor transcript and the mRNA level suggesting that regulation of transcriptional activity and mRNA stability contribute to extent of CD69 mRNA accumulation. CHX treatment resulted also in an overexpression of AICL, LLT1, and CD161/NKR-P1A mRNAs. Conversely, CHX blocked CD94 mRNA expression in PMA-stimulated cells, demonstrating that this process is dependent on new protein synthesis. Expression kinetics in context with susceptibility to CHX indicate that the mechanisms responsible for upregulated CD69, AICL, and LLT1 expression are distinct from those which control CD161/NKR-P1A or CD94 expression. J. Cell. Biochem. Suppl. 36: 201-208, 2001.

Comparison of three sedation regimes for spinal anesthesia in sheep.

The authors considered three protocols for spinal anesthesia using sheep as a model. An appropriate spinal anesthesia method would obviate the need for general anesthesia in certain surgical approaches.

Influence of body water distribution on skin thickness: measurements using high-frequency ultrasound.

BACKGROUND: Although it is known that the skin acts as a water reservoir and participates in the fluid content of the whole body, no method has been established to quantify the fluid shifts in superficial tissue. OBJECTIVES: The aim of this study was to investigate changes in dermal and subcutis thickness and echodensity at the forehead and lower leg by high-frequency (20 MHz) ultrasound under various physiological conditions influencing water balance. METHODS: These parameters were measured in the skin of 20 healthy male volunteers at baseline and successively at 30 min after lying down, in a head-down position, after physical activity and after infusion of 10 mL kg-1 body weight of Ringer's solution. RESULTS: Dermal thickness at the forehead showed a significant increase from baseline to a horizontal position and a further increase in the head-down position. Physical activity did not lead to further changes, whereas after fluid infusion the dermal thickness also increased markedly. The echodensity showed inverse changes, with decreasing values. The thickness of the subcutis increased slightly from baseline to a lying position and decreased in the head-down position and after fluid infusion. At the lower leg, skin thickness decreased slightly in the head-down position with elevated legs, and increased after fluid infusion. CONCLUSIONS: Our results show that slight changes in the water distribution of the body influence the thickness and the echodensity of the dermis. Changes are more pronounced at the forehead than on the lower legs. Further, the fluid storage takes place mainly in the dermis and not in the subcutis. High-frequency ultrasound is able to quantify these effects and is a sensitive method for measuring fluid intake and balance during anaesthesia and therapy.

Blood levels of atrial natriuretic peptide, endothelin, cortisol and ACTH in patients undergoing coronary artery bypass grafting surgery with cardiopulmonary bypass.

Previous studies demonstrated a biphasic time course with post-operative dissociation of blood levels of cortisol and ACTH in patients undergoing major surgery and critically ill patients. A possible role of endothelin and atrial natriuretic peptide (ANP) in the dissociation of concentrations of cortisol and ACTH in critically ill patients has been suggested. In the present study, we investigated the perioperative course of blood levels of endothelin, ANP, ACTH, and cortisol in 13 male patients undergoing cardiac surgery with cardiopulmonary bypass (CPB): group 1 consisted of 7 patients with an uneventful perioperative period and group 2 consisted of 6 patients with perioperative complications. Blood samples were taken pre-[T1], intra-[T2], post-operatively (on the day of surgery) [T3], as well as on the first [T4] and second [T5] post-operative days. Blood samples of endothelin, ANP, cortisol, and ACTH were measured using commercially available immunoassays. Perioperatively, a biphasic time course with post-operative dissociation of ACTH and cortisol concentrations was observed in all patients studied. Intraoperatively, during CPB, the highest levels of endothelin were found. Perioperatively, ANP and endothelin levels were elevated compared to pre-operative values up to the second post-operative day. On the second post-operative day, ANP concentrations were significantly higher in patients with complications in the perioperative period compared to those with an uneventful perioperative period. Our results suggest that: 1) plasma levels of ANP increased in patients with perioperative complications; 2) plasma levels of ANP may have prognostic value for patients undergoing cardiac surgery; and 3) the dissociation of ACTH and cortisol cannot solely be explained by the increase in endothelin-1 and ANP concentrations observed in patients undergoing major surgery.

VEGF release by retinal glia depends on both oxygen and glucose supply.

Isolated retinae or isolated Müller cells were cultured in vitro, and vascular endothelial growth factor (VEGF) was assayed as protein (by ELISA) and as mRNA (by semi-quantitative RT-PCR). In both types of cultures, hypoxia (5% O2) resulted in an upregulated VEGF release. While the unstimulated VEGF secretion was virtually independent of glucose (0.125 - 25 mM), elevated glucose concentrations (10 - 25 mM) blocked most of the stimulatory effect of hypoxia on VEGF mRNA synthesis (determined in Müller cell cultures) as well as on VEGF release (in both retina and Müller cell cultures). It is concluded that in retinal glial (Müller) cells, being responsible for retinal VEGF synthesis (and, thus, for undesirable neovascularization), the metabolic effects of hypoxia can be compensated by a surplus of glucose.

CD97 isoform expression in leukocytes.

Different adhesive capacity in interactions with CD55 has been ascribed to the isoforms of the leukocyte CD97 antigen, CD97 (EGF 1,2,5), CD97 (EGF 1,2,3,5), and CD97 (EGF 1,2,3,4,5). In the study, coexpression of the three CD97 isoforms and predominance of CD97 (EGF 1,2,5) transcripts in leukocytes are demonstrated. The contribution of CD97 (EGF 1,2,3,5) and CD97 (EGF 1,2,3,4,5) to total CD97 levels varied among most cell types only slightly, although relatively higher mRNA levels of both isoforms were detected in U 937 cells and monocytes. In peripheral blood lymphocytes, CD97 isoforms did not show clear variation after PMA stimulation and were down-regulated equally after CD97 cross-linking. Moreover, the CD97 isoform pattern was not altered in monocytes after interferon-gamma stimulation and in synovial T cells from patients with rheumatoid arthritis. CD97 mRNA levels did not necessarily correspond to CD97 surface density. The findings suggest that adhesive activity of CD97 toward CD55 is unlikely to be regulated by differential CD97 isoform expression.

Changes of interstitial fluid volume in superficial tissues detected by a miniature ultrasound device.

We evaluated the changes of tissue layer thickness in circumscribed superficial tissue areas with a 10-MHz A-mode and a 20-MHz B-mode ultrasound device under alterations in body posture and plasma volume to detect fluid shifts between the different compartments. In 20 male volunteers, we measured tissue thickness by A mode and corium and subcutis thickness by B mode at the forehead before and 30 min after three procedures: change from upright to supine position (P1); change from upright to 30 degrees head-down-tilt position (P2); infusion of 10 ml/kg body wt of Ringer solution (P3). We found a significant correlation between baseline tissue thickness and the sum of corium and subcutis thicknesses (r = 0.75, P < 0.01). The changes of body posture and plasma volume resulted in significant increases of tissue thickness (P1, 2.9%; P2, 11.6%; P3, 5.8%) and corium thickness (P1, 4.7%; P2, 8.1%; P3, 9.1%) but not of the sum of chorium and subcutis thicknesses. We conclude that fluid shifts from the intravascular to the extravascular compartment are detectable by evaluating corium thickness with a B-mode, or more easily tissue thickness with an A-mode, ultrasound device.