Myocardial transmural pressure in ventilated patients

The validity of oesophageal pressure measurement as an indicator of intrathoracic pressure changes during IPPV and CPPV was evaluated in 14 patients after open heart surgery. Simultaneously recorded pressures from the airway, pericardium, oesophagus and left atrium all demonstrated an increase following IPPV and CPPV directly proportional to the increasing PEEP level. A significant positive correlation was found between the pressure increase in the pericardium and oesophagus. Therefore the measurement of oesophageal pressure closely reflected the changes in intrathoracic pressure, in recumbent, ventilated patients and enables the cardiac transmural pressure to be calculated. However, during CPPV the increase in oesophageal pressure did not fully reach the corresponding pressure changes in the pericardium and resulted in an over-estimation of the cardiac transmural pressures. Transmural left atrial pressure appeared to decrease as the lung was inflated during mechanical ventilation with increasing PEEP. This decrease is probably due to the direct effect of regional lung pressure on the pericardium and heart, an effect that cannot be recognized by measurement of oesophageal pressure. Such constraints limit the evaluation of myocardial performance according to the Starling relationship during mechanical ventilation with high airway pressures.With the support of the Swiss National Fund for the advancement of Scientific Research, Berne. Application no. 3.831-0.79     

Effect of dimethylsulfoxide on isolated rat heart and lacticodehydrogenase release

Isolated perfused rat hearts were submitted to different concentrations of dimethylsulfoxide (DMSO). Mechanical and cellular electrical activities, electrogram and perfusate lacticodehydrogenase (LDH) activity were recorded.     

Constraint stress, microstructural characteristics, and enhanced mechanical properties of a special fibroblast-embedded collagen construct

Cell-contracted collagen gels could provide rejection-free biomaterials for tissue engineering, but their application is limited by relatively low mechanical strength. We developed a special type I collagen construct (based on embedded fibroblasts) that was formed into a gel thread by using two anchors to constrain gel contraction in one direction. Each gel thread contained 2 mg of type I collagen and 1.0 x 10(6) fibroblasts, and had an initial volume of 3 mL. After 9 days in culture, this preparation was transformed into a thread-like construct measuring 26 x 2.3 x 0.21 mm. Investigation of the microstructure showed that the collagen fibrils longitudinally between two cells had most aligned with the direction of the constraint stress and had assumed higher density than those in the freely contracted controls. During culturing, the constraint stress first increased then decreased, with implications for the nature of the interaction between the embedded cells and collagen matrix. Under uniaxial tensile testing, the ultimate stress and material modulus increased by factors of 6 and 16, respectively, compared with controls, while the maximal strain decreased by 590%. Compared with the similar constructs in the literature, the thread gel was fabricated by means of a novel mold configuration so that it contracted to thread shape much faster, and more importantly, the constraint force was firstly reported in this article. The improved mechanical properties show that the gel thread could be an effective biomaterial for such tissue engineering applications as the fabrication of blood vessels, ligaments, and tendon grafts.     

A flow sensor suitable for use with split-flow ventilation--first preclinical data

Volutrauma caused by artificial ventilation represents a major morbidity risk for premature infants. Our working group has recently developed an innovative "split-flow ventilation" system aiming at the reduction of tidal volumes (TVs). The main problem for the practical use of this system is the fact that conventional measurements of commercially available flow sensors are distorted by the split flow. In this study, we present the first preclinical data from testing an adapted flow sensor combination recognizing the split flow. A preterm infant test lung was conventionally ventilated, modified by insertion of a split-flow line. In addition to the customary flow sensor (FS-1), a second flow sensor (FS-2) was integrated into the split-flow line, and a third (FS-3) was placed at the exit of the test lung for reference measurements. The signals of all three flow sensors were read and processed by a computer. The program was set to graphically add up flow curves 1, 2, and 3 during one ventilation loop. After 10 runs, a mean curve of FS-1+2 was calculated and compared to the mean curve of FS-3. Furthermore, the mean TV of 10 runs measured by FS-1+2 was calculated and compared with the mean TV calculated by FS-3. The summation curve FS-1+2 proved identical to the reference curve FS-3. FS-1+2 yielded a TV of 6.6 +/- 0.01 mL (inspiratory) and 6.7 +/- 0.02 mL (expiratory). The corresponding values of FS-3 were 6.5 +/- 0.20 mL and 6.6 +/- 0.09 mL, respectively. According to our results, the presented flow sensor constellation allows exact flow measurements in the experimental setting and appears suitable for usage in a split-flow ventilation circuit under clinical conditions.     

Construction of functional soft tissues from premodulated smooth muscle cells using a bioreactor system

Artificial smooth muscle tissues should be constructed with well-differentiated and aligned smooth muscle cells (SMCs) for proper functioning. In a previous study, we produced cell/scaffold hybrids composed of consistently aligned SMCs in a contractile state using cyclic mechanical strain. In this study, the preconditioned hybrids were organized as functional smooth muscle constructs, which had a high cellular density, using a bioreactor system. We determined that the alignment and contractile phenotype of the initially generated SMCs would be retained after a 7-day culture period in a bioreactor. Mechanical properties of the smooth muscle constructs were measured and compared with those of native smooth muscle tissues and acellular scaffolds. The constructs had a denser cell concentration than the preconditioned hybrids, although they were not fully filled with cells. The premodulated cell alignment and contractile phenotype were retained after culture in a bioreactor. The 7-day-cultured constructs had similar allowed stress levels to native tissues while their stiffness was much lower, suggesting that they had malleable and durable characteristics. These results suggest that functional smooth muscle tissues with mechanical stability can be produced using premodulated SMCs and a bioreactor system.     

Age-Related Three-Dimensional Microarchitectural Adaptations of Subchondral Bone Tissues in Guinea Pig Primary Osteoarthrosis

We explored potential mechanisms of the microarchitectural adaptations of subchondral bone tissues in a guinea pig primary osteoarthrosis (OA) model. We harvested proximal tibiae of male Dunkin-Hartley (Charles River strain) guinea pigs at 3, 6, 9, 12, and 24 months of age (10 in each group). These proximal tibiae were scanned by micro-computed tomography to quantify the three-dimensional microarchitecture of the subchondral plate, cancellous bone, and cortical bone. Subsequently, the bones were compression-tested to determine their mechanical properties. Furthermore, bone collagen, bone mineral, and bone density were determined. Mankin’s score corresponded to OA grading from absent or minimal cartilage degeneration in 3-month-old to severe degeneration in 24-month-old guinea pigs. In young guinea pigs, the volume fraction and thickness of the subchondral plate markedly increased from 3 to 6 months, whereas the volume fraction of the subchondral cancellous bone displayed an initial decline followed by an increase. With age, the trabeculae increased in thickness, changed from rod-like to plate-like, and became more axially oriented. An increasing ratio of bone collagen to mineral in subchondral bone indicated undermineralized bone tissues. In subchondral cancellous bone, Young’s modulus was maximal at 6 months of age, whereas ultimate stress and failure energy showed a gradual increase with age. The findings show pronounced alterations of the microarchitecture and bone matrix composition of the subchondral bone. These alterations did not appear to follow the same pattern as in normal aging and may have different influences on the resulting mechanical properties.     

Catheter-direct thrombolysis versus pharmacomechanical thrombectomy for treatment of symptomatic lower extremity deep venous thrombosis

BACKGROUND: Rheolytic mechanical thrombectomy using the AngioJet catheter (Possis Medical, Minneapolis, MN) has been shown to be effective in the treatment of deep venous thrombosis (DVT). Additional infusion of thrombolytic agents via the device creates a novel treatment strategy of pharmacomechanical thrombectomy (PMT), which further enhances thrombectomy efficacy. The purpose of the current study was to compare the treatment outcome in patients with symptomatic DVT who underwent either catheter-directed thrombolysis (CDT) or PMT intervention. METHODS: During a recent 8-year period, clinical records of all patients with symptomatic lower leg DVT undergoing catheter-directed interventions were evaluated. Patients were divided into 2 treatment groups: CDT or PMT. Comparisons were made with regards to the treatment outcome between the 2 groups. RESULTS: A total of 93 patients who underwent 98 catheter-directed interventions for DVT were included in the study. Among them, CDT or PMT was performed in 46 (47%) and 52 (53%) procedures, respectively. In the CDT group, complete or partial thrombus removal was accomplished in 32 (70%) and 14 (30%) cases, respectively. In the PMT cohort, complete or partial thrombus removal was accomplished in 39 (75%) and 13 (25%) cases, respectively. Venous balloon angioplasty and/or stenting in the CDT or PMT groups was necessary in 36 (78%) and 43 (82%), respectively (difference not significant [NS]). Patients in the CDT groups underwent a mean of 2.5 venograms during the hospital course, in contrast to 0.4 venograms per patient in PMT cohorts (P < .001). Immediate (<24 hours) improvement in clinical symptoms in CDT and PMT groups was achieved in 33 (72%) and 42 (81%) cases, respectively (NS). Significant reductions in the intensive care unit (ICU) and hospital lengths of stay was noted in the PMT group (0.6 and 4.6 days) when compared to the CDT group (2.4 and 8.4 days). During follow-up visits, the primary patency rates at 1 year of CDT and PMT groups were 64% and 68%, respectively (NS). Hospital cost analysis showed significant cost reduction in the PMT group compared to the CDT group (P < .01). CONCLUSIONS: PMT with adjunctive thrombolytic therapy is an effective treatment modality in patients with significant DVT. When compared to CDT, this treatment provides similar treatment success with reduced ICU, total hospital length of stay, and hospital costs.     

Replacement of K+ with Rb+ or Cs+, and its effects on the mechanical responses to norepinephrine and methacholine in the rat vas deferens

The rat vas deferens was stored overnight in cold, K⁺-free Krebs solution to deplete intracellular K⁺ then incubated in K⁺-, Rb⁺- or Cs⁺-containing Krebs solution at 37°C to load these ions inside the cells. After 4 h, the contents of K⁺ or Rb⁺ reached the level of K⁺ in the fresh vas deferens; the content of Cs⁺ was less than half that of the fresh vas deferens. Dose-response curves to norepinephrine and methacholine were determined under these conditions, and the curves in Rb⁺ or Cs⁺ solution were compared with those in K⁺ solution. The cold storage per se had little effect on the dose-response curves in K⁺ solution except that it slightly decreased the maximal response to norepinephrine. The dose-response curves in Rb⁺ solution were to the left of those in K⁺ solution. The maximal response to methacholine was greatly increased. On the other hand, the dose-response curves in Cs⁺ solution were to the right of those in K⁺ solution. The maximal responses were greatly decreased with both drugs. The results suggest that Rb⁺ but not Cs⁺ can fully substitute for K⁺ in the rat vas deferens response to norepinephrine and methacholine.     

An application of the Ambu E2 valve: Its use as a patient-demand valve during mechanical ventilation

This paper describes an adaptation of the Ambu E2 valve which permits a patient to breathe spontaneously during mechanical ventilation. It also critically refers to some present concepts in this type of therapy.     

Prolonged severe hypercapnia complicating near fatal asthma in a 35-year-old woman

Objective: We describe a patient with a prolonged and severe hypercapnia occurring during an episode of status asthmaticus induced by ophthalmic instillation of carteolol. Setting: Prehospital Emergency Medical Service and Pulmonary Intensive Care Unit in a university hospital. Patient: A 35-year-old female developed an acute asthma attack while at home, which required advanced life support. Intervention: On hospital admission, arterial blood gases revealed a PaCO₂ of 208 mmHg. Hypercapnia persisted with a PaCO₂ of more than 190 mmHg for 10 h, with pH always less than 7.00. The patient was finally discharged after 26 days without sequelae. Conclusion: This case illustrates the cerebral and cardiovascular tolerance of severe and prolonged hypercapnia associated with major acidosis. Received: 20 April 1998 Accepted: 29 July 1998