Immature bovine cartilage wear is due to fatigue failure from repetitive compressive forces and not reciprocating frictional forces

OBJECTIVE

Wear of articular cartilage is not well understood. We hypothesize that cartilage wears due to fatigue failure in repetitive compression instead of reciprocating friction.

DESIGN

This study compares reciprocating sliding of immature bovine articular cartilage against glass in two testing configurations: (1) a stationary contact area configuration (SCA), which results in static compression, interstitial fluid depressurization, and increasing friction coefficient during reciprocating sliding, and (2) a migrating contact area configuration (MCA), which maintains pressurization and low friction while producing repetitive compressive loading in addition to reciprocating sliding. Contact pressure, sliding duration, and sliding distance were controlled to be similar between test groups.

RESULTS

SCA tests exhibited an average friction coefficient of μ=0.084±0.032, while MCA tests exhibited a lower average friction coefficient of μ=0.020±0.008 (p<10-4). Despite the lower friction, MCA cartilage samples exhibited clear surface damage with a significantly greater average surface deviation from a fitted plane after wear testing (Rq=0.125±0.095 mm) than cartilage samples slid in a SCA configuration (Rq=0.044±0.017 mm, p=0.002), which showed minimal signs of wear. Polarized light microscopy confirmed that delamination damage occurred between the superficial and middle zones of the articular cartilage in MCA samples.

CONCLUSIONS

The greatest wear was observed in the group with lowest friction coefficient, subjected to cyclical instead of static compression, implying that friction is not the primary driver of cartilage wear. Delamination between superficial and middle zones implies the main mode of wear is fatigue failure under cyclical compression, not fatigue or abrasion due to reciprocating frictional sliding.

Peri-discharge complex interventions for reducing 30-day hospital readmissions among heart failure patients: overview of systematic reviews and network meta-analysis

AIMS

An overview of systematic reviews (SRs) and network meta-analysis (NMA) was conducted to synthesize evidence of comparative effectiveness of different peri-discharge complex interventions for reducing 30-day hospital readmissions among heart failure (HF) patients.

METHODS

We searched five databases for SRs from their inception to August 2019 and conducted additional search for randomized controlled trials (RCTs) published between 2003 and 2020. We used random-effect pairwise meta-analysis with pooled risk ratios (RRs) and 95% confidence intervals (CIs) to quantify the effect of complex interventions, and NMA to evaluate comparative effectiveness among complex interventions. Primary outcome was 30-day all-cause hospital readmissions, while secondary outcomes were 30-day HF-related hospital readmissions, 30-day mortality, and 30-day emergency department visits.

RESULTS

From 20 SRs and additional RCT search, 21 eligible RCTs (n = 5362) assessing eight different peri-discharge complex interventions were included. Pairwise meta-analysis showed no significant difference between peri-discharge complex interventions and controls on all outcomes, except that peri-discharge complex interventions were significantly more effective than controls in reducing 30-day mortality (pooled RR = 0.68, 95% CI: 0.49-0.95, 5 RCTs). NMA indicated that for reducing 30-day all-cause hospital readmissions, supportive-educative intervention had the highest probability to be the best intervention, followed by disease management; while for reducing 30-day HF-related hospital readmissions, disease management is likely to be the best intervention.

CONCLUSIONS

Our results suggest that disease management has the best potential to reduce 30-day all-cause and HF-related hospital readmissions. Benefits of the interventions may vary across health system contexts. Evidence-based complex interventions require local adaptation prior to implementation.

A hospital-wide screening programme to control an outbreak of vancomycin-resistant enterococci in a large tertiary hospital in Hong Kong

INTRODUCTION

Apart from individual small-scale outbreaks, infections with vancomycin-resistant enterococci are uncommon in Hong Kong. A major outbreak of vancomycin-resistant enterococci, however, occurred at a large tertiary hospital in 2013. We describe the successful control of this outbreak and share the lessons learned.

METHODS

In 2013, there was an abnormal increase in the incidence of vancomycin-resistant enterococci carriage compared with baseline in multiple clinical departments at Queen Elizabeth Hospital. A multipronged approach was adopted that included a 10-week hospital-wide active screening programme, which aimed to identify and isolate hidden vancomycin-resistant enterococci carriers among all in-patients. The identified carriers were completely segregated in designated wards where applicable. Other critical infection control measures included directly observed hand hygiene and environmental hygiene. A transparent and open disclosure approach was adopted throughout the outbreak.

RESULTS

The infection control measures were successfully implemented. The active screening of vancomycin-resistant enterococci was conducted between 30 September and 10 November 2013. A total of 7053 rectal swabs were collected from patients in 46 hospital wards from 11 departments. The overall carriage rate of vancomycin-resistant enterococci was 2.8% (201/7053). Pulsed-field gel electrophoresis showed a predominant outbreak clone. We curbed the outbreak and kept the colonisation of vancomycin-resistant enterococci among patients at a pre-upsurge low level.

CONCLUSIONS

We report the largest cohesive effort to control spread of vancomycin-resistant enterococci in Hong Kong. Coupled with other infection control measures, we successfully controlled vancomycin-resistant enterococci to the pre-outbreak level. We have demonstrated that the monumental tasks can be achieved with meticulous planning, and thorough communication and understanding between all stakeholders.

Animal models of cartilage repair

Cartilage repair in terms of replacement, or regeneration of damaged or diseased articular cartilage with functional tissue, is the ‘holy grail’ of joint surgery. A wide spectrum of strategies for cartilage repair currently exists and several of these techniques have been reported to be associated with successful clinical outcomes for appropriately selected indications. However, based on respective advantages, disadvantages, and limitations, no single strategy, or even combination of strategies, provides surgeons with viable options for attaining successful long-term outcomes in the majority of patients. As such, development of novel techniques and optimisation of current techniques need to be, and are, the focus of a great deal of research from the basic science level to clinical trials. Translational research that bridges scientific discoveries to clinical application involves the use of animal models in order to assess safety and efficacy for regulatory approval for human use. This review article provides an overview of animal models for cartilage repair.

Cite this article: Bone Joint Res 2014;4:89–94.

Mechanical and biochemical characterization of cartilage explants in serum-free culture

Allografts of articular cartilage are both used clinically for tissue-transplantation procedures and experimentally as model systems to study the physiological behavior of chondrocytes in their native extracellular matrix. Long-term maintenance of allograft tissue is challenging. Chemical mediators in poorly defined culture media can stimulate cells to quickly degrade their surrounding extracellular matrix. This is particularly true of juvenile cartilage which is generally more responsive to chemical stimuli than mature tissue. By carefully modulating the culture media, however, it may be possible to preserve allograft tissue over the long-term while maintaining its original mechanical and biochemical properties. In this study juvenile bovine cartilage explants (both chondral and osteochondral) were cultured in both chemically defined medium and serum-supplemented medium for up to 6 weeks. The mechanical properties and biochemical content of explants cultured in chemically defined medium were enhanced after 2 weeks in culture and thereafter remained stable with no loss of cell viability. In contrast, the mechanical properties of explants in serum-supplemented medium were degraded by ( approximately 70%) along with a concurrent loss of biochemical content (30-40% GAG). These results suggest that long-term maintenance of allografts can be extended significantly by the use of a chemically defined medium.

The beneficial effect of delayed compressive loading on tissue-engineered cartilage constructs cultured with TGF-beta3

OBJECTIVE

To determine whether the functional properties of tissue-engineered constructs cultured in a chemically-defined medium supplemented briefly with TGF-beta3 can be enhanced with the application of dynamic deformational loading.

METHODS

Primary immature bovine cells (2-3 months old) were encapsulated in agarose hydrogel (2%, 30 x 10(6)cells/ml) and cultured in chemically-defined medium supplemented for the first 2 weeks with transforming growth factor beta 3 (TGF-beta3) (10 microg/ml). Physiologic deformational loading (1 Hz, 3 h/day, 10% unconfined deformation initially and tapering to 2% peak-to-peak deformation by day 42) was applied either concurrent with or after the period of TGF-beta3 supplementation. Mechanical and biochemical properties were evaluated up to day 56.

RESULTS

Dynamic deformational loading applied concurrently with TGF-beta3 supplementation yielded significantly lower (-90%) overall mechanical properties when compared to free-swelling controls. In contrast, the same loading protocol applied after the discontinuation of the growth factor resulted in significantly increased (+10%) overall mechanical properties relative to free-swelling controls. Equilibrium modulus values reach 1306+/-79 kPa and glycosaminoglycan levels reach 8.7+/-1.6% w.w. during this 8-week period and are similar to host cartilage properties (994+/-280 kPa, 6.3+/-0.9% w.w.).

CONCLUSIONS

An optimal strategy for the functional tissue engineering of articular cartilage, particularly to accelerate construct development, may incorporate sequential application of different growth factors and applied deformational loading.

Amino acids supply in culture media is not a limiting factor in the matrix synthesis of engineered cartilage tissue

Increased amino acid supplementation (0.5 x, 1.0 x, and 5.0 x recommended concentrations or additional proline) was hypothesized to increase the collagen content in engineered cartilage. No significant differences were found between groups in matrix content or dynamic modulus. Control constructs possessed the highest compressive Young's modulus on day 42. On day 42, compared to controls, decreased type II collagen was found with 0.5 x, 1.0 x, and 5.0 x supplementation and significantly increased DNA content found in 1.0 x and 5.0 x. No effects were observed on these measures with added proline. These results lead us to reject our hypothesis and indicate that the low collagen synthesis in engineered cartilage is not due to a limited supply of amino acids in media but may require a further stimulatory signal. The results of this study also highlight the impact that culture environment can play on the development of engineered cartilage.

Dexmedetomidine infusion as a supplement to isoflurane anaesthesia for vitreoretinal surgery

BACKGROUND

We explored the sympatholytic property of dexmedetomidine, especially its role in intraocular pressure (IOP) reduction, haemodynamic stability, and attenuation of extubation response.

METHOD

In this double-blind, randomized, controlled trial approved by the Hospital Ethics Committee, 60 patients undergoing elective vitreoretinal surgery were allocated to two groups, receiving either placebo or dexmedetomidine. A loading dose of dexmedetomidine 2.5 microg kg(-1) h(-1) (or placebo in same volume) was infused for 10 min immediately before induction of anaesthesia with propofol, followed by a maintenance dexmedetomidine or placebo infusion at 0.4 microg kg(-1) h(-1) till 30 min before the end of the operation. Anaesthesia was maintained with isoflurane, oxygen, and air mixture. IOP was measured before the loading dose and 1 min after tracheal intubation. The mean arterial pressure (MAP) and heart rate (HR) during loading, induction, maintenance, extubation, and recovery period were measured. The degree of strain on extubation was graded from 0 to 5.

RESULTS

The use of vasopressor/labetalol/atropine and the reduction in IOP were comparable between the two groups. There was a significant variation in MAP and HR over time within group, but not between groups. The median degree of strain was significantly lower (P = 0.049), and the time to reach Aldrete score of 10 shorter (P = 0.031) in the dexmedetomidine group.

CONCLUSION

Dexmedetomidine can be used without undue haemodynamic fluctuation and can decrease the excitatory response during extubation. The reduction in IOP with dexmedetomidine was comparable with placebo.

The clinical implication of the vocal cords–carina distance in anaesthetized Chinese adults during orotracheal intubation

BACKGROUND

Previous studies have identified no strong correlation between patients' height and tracheal length in anaesthetized patients. We have attempted to compare vocal cords-carina distance (VCD) in Chinese patients with the dimensions of five commonly used tracheal tubes. In addition, we attempted to find a surface anatomy measurement that would identify patients with 'short tracheas'.

METHODS

We measured VCD in 130 anaesthetized Chinese patients with a fibreoptic bronchoscope. Also measurements were obtained of the distal ends of five commonly used tracheal tubes. We undertook various surface anatomy measurements on the patients' chest and neck region to predict those patients with short tracheas.

RESULTS

VCD averaged 12.6 (SD 1.4) cm. In seven patients (5%) this distance was particularly short (between 8.8 and 10.4 cm). Many of the commonly used tracheal tubes would be placed close to or beyond the carina when the black intubation guide mark(s) is (are) at the level of the vocal cords. The VCD of <or=11 cm (short trachea) could be predicted by patient height of <or=167.5 cm and a thyrosternal distance of <or=28.5 cm with limited reliability.

CONCLUSIONS

A significant number of patients with short VCD in our study group could be at risk of endobronchial intubation with many of the tracheal tubes. Patient height and thyrosternal distance can be useful in predicting short tracheas.

The effect of finite compressive strain on chondrocyte viability in statically loaded bovine articular cartilage

Recent studies have reported that certain regimes of compressive loading of articular cartilage result in increased cell death in the superficial tangential zone (STZ). The objectives of this study were (1) to test the prevalent hypothesis that preferential cell death in the STZ results from excessive compressive strain in that zone, relative to the middle and deep zones, by determining whether cell death correlates with the magnitude of compressive strain and (2) to test the corollary hypothesis that the viability response of cells is uniform through the thickness of the articular layer when exposed to the same loading environment. Live cartilage explants were statically compressed by approximately 65% of their original thickness, either normal to the articular surface (axial loading) or parallel to it (transverse loading). Cell viability after 12 h was compared to the local strain distribution measured by digital image correlation. Results showed that the strain distribution in the axially loaded samples was highest in the STZ (77%) and lowest in the deep zone (55%), whereas the strain was uniformly distributed in the transversely loaded samples (64%). In contrast, axially and transversely loaded samples exhibited very similar profiles of cell death through the depth, with a preferential distribution in the STZ. Unloaded control samples showed negligible cell death. Thus, under prolonged static loading, depth-dependent variations in chondrocyte death did not correlate with the local depth-dependent compressive strain, and the prevalent hypothesis must be rejected. An alternative hypothesis, suggested by these results, is that superficial zone chondrocytes are more vulnerable to prolonged static loading than chondrocytes in the middle and deep zones.

A theoretical analysis of water transport through chondrocytes

Because of the avascular nature of adult cartilage, nutrients and waste products are transported to and from the chondrocytes by diffusion and convection through the extracellular matrix. The convective interstitial fluid flow within and around chondrocytes is poorly understood. This theoretical study demonstrates that the incorporation of a semi-permeable membrane when modeling the chondrocyte leads to the following findings: under mechanical loading of an isolated chondrocyte the intracellular fluid pressure is on the order of tens of Pascals and the transmembrane fluid outflow, on the order of picometers per second, takes several days to subside; consequently, the chondrocyte behaves practically as an incompressible solid whenever the loading duration is on the order of minutes or hours. When embedded in its extracellular matrix (ECM), the chondrocyte response is substantially different. Mechanical loading of the tissue leads to a fluid pressure difference between intracellular and extracellular compartments on the order of tens of kilopascals and the transmembrane outflow, on the order of a nanometer per second, subsides in about 1 h. The volume of the chondrocyte decreases concomitantly with that of the ECM. The interstitial fluid flow in the extracellular matrix is directed around the cell, with peak values on the order of tens of nanometers per second. The viscous fluid shear stress acting on the cell surface is several orders of magnitude smaller than the solid matrix shear stresses resulting from the ECM deformation. These results provide new insight toward our understanding of water transport in chondrocytes.

Evaluation of the new Viewmax laryngoscope in a simulated difficult airway

BACKGROUND

In this study, we evaluated the learning curve and performance of the Viewmax laryngoscope during simulated difficult laryngoscopy in an intubation manikin (Laerdal Airway Management Trainer).

METHODS

To determine the learning curve, 25 anaesthesiologists without previous experience with the Viewmax laryngoscope performed 10 successive intubations in an intubation manikin with a normal airway. Time to intubation and failed intubation attempts were recorded. Another manikin was modified to enable comparison of the Viewmax laryngoscope with Macintosh and McCoy laryngoscopes. The time to intubation, number of failed intubation attempts, modified Cormack and Lehane (MCL) laryngeal view grading, percentage of glottic opening (POGO score), use of gum elastic bougie and subjective rating of degree of difficulty were recorded.

RESULTS

The learning curve for the Viewmax laryngoscope showed a progressive decrease in time to successful intubation and reached a plateau at the sixth attempt. In simulated difficult laryngoscopy, the Viewmax laryngoscope demonstrated significantly better laryngeal view than the Macintosh and McCoy laryngoscopes in terms of MCL grading (Macintosh, P = 0.01; McCoy, P < 0.01) and POGO score (Macintosh, P < 0.01; McCoy, P < 0.01). The time required for intubation in simulated difficult laryngoscopy for the Viewmax laryngoscope was significantly longer than that for the Macintosh (P = 0.02) and McCoy (P < 0.01) laryngoscopes. There was no significant difference in the degree of difficulty, number of failed intubations and use of gum elastic bougie.

CONCLUSION

When compared with the Macintosh and McCoy laryngoscopes in a manikin, the Viewmax laryngoscope appears to improve the view of the larynx but requires a longer time for tracheal intubation.

Clinical experience of trainee anaesthesiologists: logbook analysis

OBJECTIVE

To study the clinical experience acquired by trainee anaesthesiologists after 6 years of training in Hong Kong.

DESIGN

Retrospective observational study.

SETTING

Recognised anaesthesiology training posts in the Hong Kong Hospital Authority.

PARTICIPANTS

All anaesthesiology trainees who sat the Exit Assessment between January 2001 and June 2002 after completing more than 48 months of anaesthetic training.

MAIN OUTCOME MEASURES

Anaesthetic experience of trainees.

RESULTS

All data provided by 25 trainees were computed for analysis. Each trainee administered a mean of 2668 anaesthetics over a 6-year period, including 57 anaesthetics for thoracic surgery, 15 for cardiac surgery, 213 for caesarian section (34% under general anaesthesia), and 100 for neurosurgical operations. The paediatric anaesthesia exposure involved a mean of 12 neonates and 180 children who were younger than 4 years. Apart from cardiac and thoracic anaesthesia, there was no statistical difference in subspecialty anaesthetic experience among trainees from different parent hospitals.

CONCLUSION

The current training system provides sufficient anaesthetic experience in terms of case variety and subspecialty case numbers. There was uneven exposure to cardiac, thoracic, and paediatric anaesthesia. An accurate logbook that is reviewed regularly by a supervisor will help ensure adequate subspecialty exposure. An electronic logbook will facilitate a more comprehensive reviewing process.

Substrate modulation of osteoblast adhesion strength, focal adhesion kinase activation, and responsiveness to mechanical stimuli

Osteoblast interactions with extracellular matrix (ECM) proteins are known to influence many cell functions, which may ultimately affect osseointegration of implants with the host bone tissue. Some adhesion-mediated events include activation of focal adhesion kinase, and subsequent changes in the cytoskeleton and cell morphology, which may lead to changes in adhesion strength and cell responsiveness to mechanical stimuli. In this study we examined focal adhesion kinase activation (FAK), F-actin cytoskeleton reorganization, adhesion strength, and osteoblast responsiveness to fluid shear when adhered to type I collagen (ColI), glass, poly-L-lysine (PLL), fibronectin (FN), vitronectin (VN), and serum (FBS). In general, surfaces that bind cells through integrins (FN, VN, FBS) elicited the highest adhesion strength, FAK activation, and F-actin stress fiber formation after both 15 and 60 minutes of adhesion. In contrast, cells attached through non-integrin mediated means (PLL, glass) showed the lowest FAK activation, adhesion strength, and little F-actin stress fiber formation. When subjected to steady fluid shear using a parallel plate flow chamber, osteoblasts plated on FN released significantly more PGE2 compared to those on glass. In contrast, PGE2 release of osteoblasts attached to FN or glass was not different in the absence of fluid shear, suggesting that differences in binding alone are insufficient to alter PGE2 secretion. The increased adhesion strength as well as PGE2 secretion of osteoblasts adhered via integrins may be due to increased F-actin fiber formation, which leads to increased cell stiffness.

Removal of the superficial zone of bovine articular cartilage does not increase its frictional coefficient

OBJECTIVE

To investigate the role of the superficial zone in regulating the frictional response of articular cartilage. This zone contains the superficial protein (SZP), a proteoglycan synthesized exclusively by superficial zone chondrocytes and implicated in reducing the friction coefficient of cartilage.

DESIGN

Unconfined compression creep tests with sliding of cartilage against glass in saline were carried out on fresh bovine cylindrical plugs (slashed circle Ø6 mm, n=35) obtained from 16 bovine shoulder joints (ages 1-3 months). In the first two experiments, friction tests were carried out before and after removal of the superficial zone ( approximately 100 microm), in a control and treatment group, using two different applied load magnitudes (4.4 N and 22.2 N). In the third experiment, friction tests were conducted on intact surfaces and the corresponding microtomed deep zone of the same specimen.

RESULTS

In all tests the friction coefficient exhibited a transient response, increasing from a minimum value (mu(min)) to a near-equilibrium final value (micro(eq)). No statistical change (P>0.5) was found in micro(min) before and after removal of the superficial zone in both experiments 1 and 2. However, micro(eq) was observed to decrease significantly (P<0.001) after removal of the surface zone. Results from the third experiment confirm that micro(eq) is even lower at the deep zone. Surface roughness measurements with atomic force microscopy (AFM) revealed an increase in surface roughness after microtoming. Immunohistochemical staining confirmed the presence of SZP in intact specimens and its removal in microtomed specimens.

CONCLUSIONS

The topmost ( approximately 100 microm) superficial zone of articular cartilage does not have special properties which enhances its frictional response.

Mechanical response of bovine articular cartilage under dynamic unconfined compression loading at physiological stress levels

OBJECTIVE

The objective of this study was to characterize the dynamic modulus and compressive strain magnitudes of bovine articular cartilage at physiological compressive stress levels and loading frequencies.

DESIGN

Twelve distal femoral cartilage plugs (3mm in diameter) were loaded in a custom apparatus under load control, with a load amplitude up to 40 N and loading frequencies of 0.1, 1, 10 and 40 Hz, resulting in peak Cauchy stress amplitudes of 4.8 MPa (engineering stress 5.7 MPa).

RESULTS

The equilibrium Young's modulus under a tare load of 0.4N was 0.49+/-0.10 MPa. In the limit of zero applied stress, the incremental dynamic modulus derived from the slope of the stress-strain curve increased from 14.6+/-6.9 MPa at 0.1 Hz to 28.7+/-7.8 MPa at 40 Hz. At 4 MPa of applied stress, the corresponding increase was from 48.2+/-13.5 MPa at 0.1 Hz to 64.8+/-13.0 MPa at 40 Hz. Peak compressive strain amplitudes varied from 15.8+/-3.4% at 0.1 Hz to 8.7+/-1.8% at 40 Hz. The phase angle decreased from 28.8 degrees +/-6.7 degrees at 0.1 Hz to-0.5 degrees +/-3.8 degrees at 40 Hz.

DISCUSSION

These results are representative of the functional properties of articular cartilage under physiological load magnitudes and frequencies. The viscoelasticity and nonlinearity of the tissue helps to maintain the compressive strains below 20% under the physiological compressive stresses achieved in this study. These findings have implications for our understanding of cartilage metabolism and chondrocyte viability under various loading regimes. They also help establish guidelines for cartilage functional tissue engineering studies.

The role of cell seeding density and nutrient supply for articular cartilage tissue engineering with deformational loading

OBJECTIVE

Functional tissue engineering (FTE) of articular cartilage involves the use of physiologically relevant mechanical signals to encourage the growth of engineered constructs. The goal of this study was to determine the utility of deformational loading in enhancing the mechanical properties of chondrocyte-seeded agarose hydrogels, and to investigate the role of initial cell seeding density and nutrient supply in this process.

DESIGN

Chondrocyte-seeded agarose hydrogels were cultured in free-swelling conditions or with intermittent deformational loading (10% deformation, 1 Hz, 1 h on/ 1 h off, 3 h per day, five days per week) over a two-month culture period. Disks were seeded at lower (10 million cells/ml) and higher (60 million cells/ml) seeding densities in the context of a greater medium supply than previous studies (decreasing the number of cells/ml feed medium/day) and with an increasing concentration of fetal bovine serum (10 or 20% FBS).

RESULTS

Under these more optimal nutrient conditions, at higher seeding densities and high serum concentration (20% FBS), dynamically loaded constructs show >2-fold increases in material properties relative to free-swelling controls. After two months of culture, dynamically loaded constructs achieved a Young's modulus of approximately 185 kPa and a dynamic modulus (at 1 Hz) of approximately 1.6 MPa, with a frequency dependent response similar to that of the native tissue. These values represent approximately 3/4 and approximately 1/4 the values measured for the native tissue, respectively. While significant differences were found in mechanical properties, staining and bulk measurements of both proteoglycan and collagen content of higher seeding density constructs revealed no significant differences between free-swelling and loading groups. This finding indicates that deformational loading may act to increase material properties via differences in the structural organization, the production of small linker ECM molecules, or by modulating the size of macromolecular proteoglycan aggregates.

CONCLUSIONS

Taken together, these results point to the utility of dynamic deformational loading in the mechanical preconditioning of engineered articular cartilage constructs and the necessity for increasing feed media volume and serum supplementation with increasing cell seeding densities.

Acute-on-chronic subdural haematoma: a rare complication after spinal anaesthesia

An 88-year-old woman with an undiagnosed chronic subdural haematoma underwent emergency repair of a femoral hernia under spinal anaesthesia. The patient complained of headache postoperatively, and a subsequent computed tomography brain scan showed an acute-on-chronic subdural haematoma, with midline shift and impending coning. The patient recovered completely after surgical decompression. The difficulty in diagnosing chronic subdural haematoma in the elderly patient with no history of trauma is discussed, along with the differential diagnosis of headache following spinal anaesthetic in this age-group.

Acute pain services in Hong Kong: facilities, volume, and quality

Acute pain services in public hospitals in Hong Kong were studied. Audit data on the volume and quality of acute pain services were collected prospectively from 1997 to 1999, and data on related facilities were collected in 2000. About 20% of patients undergoing a major operation received an acute pain service; of these, 78.6% were satisfied with the treatment provided. In 2000, 86% (18/21) of hospitals providing anaesthetic services were running an acute pain service. Staffing was better in hospitals providing a high volume of acute pain services, ranging from a full-time specialist anaesthesiologist assisted by a half-time trainee to a half-time specialist assisted by a full- or half-time trainee. However, only four hospitals were staffed with pain nurses. In total, 57% of patients received intravenous patient-controlled analgesia and 32% epidural analgesia. The mean duration of acute pain service treatment was 3.1 days. Currently anaesthesiologist-based acute pain services take care of a limited number of patients. To expand the coverage, there should be a move towards an anaesthesiologist-led, pain nurse-based, acute pain service. The present shortage of pain nurses should be addressed.

Haemorrhage of a thyroid cyst as an unusual complication of intubation

A case is presented of haemorrhage into a thyroid cyst after endotracheal intubation for an elective nasal operation in a healthy young man. The haemorrhagic cyst compressed the trachea and the patient was taken to the intensive care unit with the endotracheal tube left in situ. Hemithyroidectomy was performed uneventfully two days later. Causes of haemorrhage into thyroid cysts are reviewed.

Herbal medicine and anaesthesia

Herbal medicines are increasingly used in both western and Chinese societies. This is partly attributed to the alleged limitations of scientific medicine in the cure and control of chronic diseases. Many patients do not disclose that they have used herbs before surgery and hence their physicians remain unaware of the potential herb-drug interactions. With respect to anaesthesia, herbs can cause coagulation disorders, cardiovascular side-effects, water and electrolyte disturbances, endocrine effects, hepatotoxicity, and prolongation of the effects of anaesthetic agents. Anaesthesiologists should obtain a history of herbal medicine use from patients and work out the adverse perioperative herb-drug interactions in advance of the actual operation. If in doubt, the herbal medicine should be stopped for 2 weeks prior to anaesthesia and surgery.

Safety and comfort during sedation for diagnostic or therapeutic procedures

Sedation during diagnostic or therapeutic procedures must be safe and comfortable for patients. To achieve this, additional suitably qualified staff must be available throughout the procedure to administer sedation and monitor the patient. Anaesthesiologists possess the necessary knowledge and skills to perform sedation safely but are often unavailable. Non-anaesthesiologists performing sedation should be fully trained in the physiology of sedation, the pharmacology of sedatives and analgesics, the monitoring of patients, and in airway support, ventilatory care, and cardiopulmonary resuscitation. The presence of an anaesthesiologist is desirable when dealing with patients at high-risk of complications. Good sedation practice involves presedation assessment and optimal selection of patients, careful monitoring and support from dedicated staff, and adherence to recovery and discharge criteria.

Comparison of two new rapid serology tests for diagnosis of Helicobacter pylori infection in Chinese patients

BACKGROUND

Rapid serology test is a simple and convenient way for diagnosing Helicobacter pylori infection. However performances of these tests are usually less satisfactory than expected, particularly in developing countries.

AIM

To evaluate the performances of two newly developed rapid serology tests for Helicobacter pylori infection.

PATIENTS

Consecutive Chinese dyspeptic patients undergoing upper gastrointestinal endoscopy.

METHODS

Gastric biopsies were obtained from antrum and corpus for rapid urease test and histological examination. Diagnosis of Helicobacter pylori infection was based on two or more positive results in rapid urease test, histology and [13C] urea breath test. Patients' sera were tested against two rapid serology tests: ASSURE Hp Rapid Test (Genelabs Diagnostics, Singapore) and SureStep (Applied Biotech, San Diego, CA, USA).

RESULTS

A total of 148 patients were evaluated and Helicobacter pylori infection was diagnosed in 78 (53%) patients by gold standard. The sensitivities of ASSURE Hp and SureStep were, respectively, 94% and 71% (p=0.0003). Specificities of the two test kits were both 90%. The overall accuracy of ASSURE Hp was significantly higher than SureStep (92% versus 80%, p=0.004).

CONCLUSION

Both rapid serology tests appear to be specific in diagnosing Helicobacter pylori infection in the Chinese populations. However the ASSURE Hp test is more sensitive and accurate than the SureStep test.

Time-dependent aggrecan gene expression of articular chondrocytes in response to hyperosmotic loading

OBJECTIVE

To investigate the effects of increasing extracellular osmolality on aggrecan gene expression and cell size in cultured chondrocytes.

DESIGN

Aggrecan promoter activity and mRNA levels were measured in bovine monolayer chondrocytes subjected to hyperosmotic loading for different time periods, using transient transfection assays or RT-PCR. Cell size changes were also determined using an epifluorescence microscopy system.

RESULTS

Hyperosmotic loading for 24 h suppressed aggrecan promoter activity and mRNA levels approximately two-fold. However no suppression of promoter activity was observed when exon 1 was deleted from the human aggrecan promoter construct. Osmotic regulation of aggrecan gene expression was time-dependent and found to correlate with cell shrinking and swelling. No suppression in promoter activity was observed when the hyperosmotic stimulus was applied in a cyclic manner, or when serum was present in the culture medium.

CONCLUSION

Hyperosmotic loading regulates aggrecan gene expression and cell size in isolated chondrocytes. Osmotic regulation of gene expression is also affected by the time-varying nature of loading and the presence of serum.

Effect of age on recovery from remifentanil anaesthesia

In a prospective, randomized study, the effect of age on recovery from remifentanil anaesthesia was evaluated. Twenty consecutive patients classified as ASA 1 and 2 and having elective laparotomy were recruited to one of two groups based on age (Group 1 age <60 y and Group 2 age >60 y). Remifentanil boluses and infusion were used for induction and maintenance of anaesthesia. Dosage was titrated against clinical response to perioperative stimulation and the infusion was terminated at the end of the operation. Time intervals between termination of remifentanil infusion and 1) spontaneous respiration, 2) adequate respiration, 3) eye opening, 4) limb movement, 5) extubation, 6) Aldrete score >9, 7) discharge to recovery room and 8) discharge to the ward were recorded. Patient controlled analgesia with morphine was used for postoperative pain control. Student's t test was used to compare the differences in these time intervals between Groups 1 and 2. A P value <0.05 was taken as significant. We found that the younger age group regained spontaneous respiration (0.8+/-0.7 min vs 3.2+/-3.6 min), adequate respiration (3.4+/-3.7 min vs 7.6+/-5.8 min), opened their eyes (0.9+/-1.0 min vs 3.6+/-4.4 min), had their endotracheal tubes removed (5.0+/-4.6 min vs 9.0+/-6.5 min) and were discharged to recovery room (8.8+/-4.3 min vs 14.5+/-7.1 min) earlier than their older counterparts. In conclusion, age was a co-variate for recovery from remifentanil anaesthesia.

Anaesthetic clinical indicators in public hospitals providing anaesthetic care in Hong Kong: prospective study

OBJECTIVES

To assess the quality of anaesthetic services as defined in the six anaesthetic clinical indicators against preset standards and to identify risk factors for adverse events in the recovery room.

DESIGN

Prospective study.

SETTING

All public hospitals providing anaesthetic care in Hong Kong.

PATIENTS

Eighteen thousand, seven hundred and fifty-nine patients receiving elective or emergency anaesthesia administered by anaesthetists from June 1998 to July 1998.

MAIN OUTCOME MEASURES

Patient demographics, American Society of Anesthesiologists status, category and nature of operation, presence of preoperative anaesthetic visit in ward, type of anaesthesia, reasons for a recovery room stay of more than a 2-hour duration, intubation to relieve respiratory distress in the recovery room, presence of hypothermia in the recovery room for operations lasting more than 2 hours, and dental or ocular injuries attributable to anaesthesia.

RESULTS

There are two major findings from this study. Firstly, a high incidence of hypothermia in the recovery room was reported. Secondly, a greater risk of prolonged stay in the recovery room was identified for patients older than 65 years, major operations, and anaesthetic techniques using combined general and regional anaesthesia.

CONCLUSION

The six anaesthetic clinical indicators reflected the provision of anaesthetic care in public hospitals in Hong Kong. Good compliance to the preset standard of the anaesthetic clinical indicators was achieved during the study period.

An analysis of the effects of depth-dependent aggregate modulus on articular cartilage stress-relaxation behavior in compression

An accurate description of the mechanical environment around chondrocytes embedded within their dense extracellular matrix (ECM) is essential for the study of mechano-signal transduction mechanism(s) in explant experiments. New methods have been developed to determine the inhomogeneous strain distribution throughout the depth of the ECM during compression (Schinagl et al., 1996, Annals of Biomedical Engineering 24, 500-512; Schinagl et al 1997. Journal of Orthopaedics Research 15, 499-506) and the corresponding depth-dependent aggregate modulus distribution (Wang and Mow, 1998. Transactions of the Orthopaedics Research Society 23, 484; Chen and Sah, 1999. Transactions of the Orthopaedics Research Society 24, 635). These results provide the motivation for the current investigation to assess the influence of tissue inhomogeneity on the chondrocyte milieu in situ, e.g. stress, strain, fluid velocity and pressure fields within articular cartilage. To describe this inhomogeneity, we adopted the finite deformation biphasic constitutive law developed by Holmes and Mow (1990 Journal of Biomechanics 23, 1145-1156). Our calculations show that the mechanical environment inside an inhomogeneous tissue differs significantly from that inside a homogeneous tissue. Furthermore, our results indicate that the need to incorporate an inhomogeneous aggregate modulus. or an anisotropy, into the biphasic theory to describe articular cartilage depends largely on the motivation for the study.

Serum modulates the intracellular calcium response of primary cultured bone cells to shear flow

We investigated the effect of newborn bovine serum on the intracellular calcium [Ca(2+)](i) response of primary cultured bone cells stimulated by fluid flow. As it has been previously established that these cells exhibit [Ca(2+)](i) responses to fluid flow shear stress in saline media without growth factors or other chemically stimulatory factors, we hypothesized that the addition of serum to the flow medium would enhance the mechanosensitivity of the cells. We examined the effect of a short-term (10-15min) exposure of the cells to 2 and 10% serum prior to flow stimulation (pretreated) compared to not exposing the cells prior to flow stimulation (unpretreated). The cells were subjected to a well-defined, 90-s flow stimulus with shear stress levels ranging from 0.02 to 3.5Pa in a laminar flow chamber using a saline medium supplemented with 2 or 10% serum. For pretreatment, the serum concentration was the same from pre-flow to flow exposure. We observed a differential effect in the magnitude of the peak [Ca(2+)](i) response modulated by the concentration of serum in the pre-flow medium. Additionally, ATP-supplemented flow was examined as a comparison to the serum-supplemented flow and exhibited a similar trend in the peak [Ca(2+)](i) flow response that was dependent on ATP concentration and pre-flow exposure conditions. These findings demonstrate that under the conditions of this study, chemical agonist exposure can modulate the [Ca(2+)](i) response in bone cells subjected to fluid flow-induced shear stress.

Chondrocyte translocation response to direct current electric fields

Using a custom galvanotaxis chamber and time-lapse digital video microscopy, we report the novel observation that cultured chondrocytes exhibit cathodal migration when subjected to applied direct current (DC) electric fields as low as 0.8 V/cm. The response was dose-dependent for field strengths greater than 4 V/cm. Cell migration appeared to be an active process with extension of cytoplasmic processes in the direction of movement. In some cells, field application for greater than an hour induced elongation of initially round cells accompanied by perpendicular alignment of the long axis with respect to the applied field. Antagonists of the inositol phospholipid pathway, U-73122 and neomycin, were able to inhibit cathodal migration. Cell migration toward the cathode did not require the presence of serum during field application. However, the directed velocity was nearly threefold greater in studies performed with serum. Studies performed at physiologic temperatures (approximately 37 degrees C) revealed a twofold enhancement in migration speed compared to similar studies at room temperature (approximately 25 degrees C). Findings from the present study may help to elucidate basic mechanisms that mediate chondrocyte migration and substrate attachment. Since chondrocyte migration has been implicated in cartilage healing, the ability to direct chondrocyte movement has the potential to impact strategies for addressing cartilage healing/repair and for development of cartilage substitutes.

Functional tissue engineering of articular cartilage through dynamic loading of chondrocyte-seeded agarose gels

Due to its avascular nature, articular cartilage exhibits a very limited capacity to regenerate and to repair. Although much of the tissue-engineered cartilage in existence has been successful in mimicking the morphological and biochemical appearance of hyaline cartilage, it is generally mechanically inferior to the natural tissue. In this study, we tested the hypothesis that the application of dynamic deformational loading at physiological strain levels enhances chondrocyte matrix elaboration in cell-seeded agarose scaffolds to produce a more functional engineered tissue construct than in free swelling controls. A custom-designed bioreactor was used to load cell-seeded agarose disks dynamically in unconfined compression with a peak-to-peak compressive strain amplitude of 10 percent, at a frequency of 1 Hz, 3 x (1 hour on, 1 hour off)/day, 5 days/week for 4 weeks. Results demonstrated that dynamically loaded disks yielded a sixfold increase in the equilibrium aggregate modulus over free swelling controls after 28 days of loading (100 +/- 16 kPa versus 15 +/- 8 kPa, p < 0.0001). This represented a 21-fold increase over the equilibrium modulus of day 0 (4.8 +/- 2.3 kPa). Sulfated glycosaminoglycan content and hydroxyproline content was also found to be greater in dynamically loaded disks compared to free swelling controls at day 21 (p < 0.0001 and p = 0.002, respectively).

Mitogen-activated protein kinase signaling in bovine articular chondrocytes in response to fluid flow does not require calcium mobilization

In the present study, the role of mitogen-activated protein kinases (MAPKs) in chondrocyte mechanotransduction was investigated. We hypothesized that MAPKs participate in fluid flow-induced chondrocyte mechanotransduction. To test our hypothesis, we studied cultured chondrocytes subjected to a well-defined mechanical stimulus generated with a laminar flow chamber. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) were activated 1.6-3-fold after 5-15 min of fluid flow exposure corresponding to a chamber wall shear stress of 1.6 Pa. Activation of ERK1/2 was observed in the presence of both 10% FBS and 0.1% BSA, suggesting that the flow effects do not require serum agonists. Treatment with thapsigargin or EGTA had no significant effect on the ERK1/2 activation response to flow, suggesting that Ca2+ mobilization is not required for this response. To assess downstream effects of the activated MAPKs on transcription, flow studies were performed using chondrocytes transfected with a chimeric luciferase construct containing 2.4 kb of the promoter region along with exon 1 of the human aggrecan gene. Two-hour exposure of transfected chondrocytes to fluid flow significantly decreased aggrecan promoter activity by 40%. This response was blocked by treatment of chondrocytes with the MEK-1 inhibitor PD98059. These findings demonstrate that, under the conditions of the present study, fluid flow-induced signals activate the MEK-1/ERK signaling pathway in articular chondrocytes, leading to down-regulation of expression of the aggrecan gene.

Evaluation of the use of a platelet-counting tool in plateletpheresis

OBJECTIVE

For years, blood transfusion centers in Taiwan have used the Quantitative Buffy Coat (QBC(R)) Hematology System for platelet counts on capillary blood samples in the laboratory screening of apheresis donors. The system has not been evaluated for the prediction of yields in plateletpheresis. Methods : The QBC instrument was evaluated for reproducibility of platelet counts and compared with five electronic cell counters. We also collected both capillary and venous blood from voluntary donors before donation and counted platelets, comparing the QBC system and an electronic blood cell counter (Sysmex K1000). The correlation between donors' predonation platelet counts and plateletpheresis yields was analyzed.

RESULTS

The R values for platelet counts between the QBC Hematology System and other electronic counters are lower (0.759-0. 890) than among the electronic counters (0.929-0.973). The mean capillary platelet count and the mean venous platelet count were 241. 9+/-50.3x10(3)/microl and 233.2 +/-47.9x10(3)/microl by the QBC system, and 244.9+/-54.1x10(3)/microl and 218.9+/-46.5x10(3)/microl by the Sysmex K1000, respectively. Linear regression analysis showed that platelet yields correlated well with donors' predonation platelet counts using the Sysmex K1000 counter (R = 0.777- 0.890, p<0.001), but not with the QBC system (R = 0.326 approximately 0.755, p<0.05).

CONCLUSION

The QBC Hematology System is not accurate enough to determine predonation platelet counts that are to be used for calculating the number of processing cycles for plateletpheresis.

Radial nerve injury after intravenous cannulation at the wrist--a case report

Peripheral venous cannulation is one of the commonest procedures performed in hospitals. The dorso-lateral aspect of the wrist is one of the favourite sites. Radial nerve injury, though extremely rare, can be a serious complication and has been reported twice. One patient was left with a permanent work disability due to a painful neuroma. Another patient required surgical intervention to remove a neuroma six months after the initial venous cannulation resulting in almost complete recovery. We report the first case of injury to the radial nerve at the wrist as a complication of venous cannulation where complete recovery occurred spontaneously. In our case, immediate removal of the cannula may be responsible for the improved outcome.

Prevalence and prediction of difficult intubation in Chinese women

We conducted a prospective, blind observational study to investigate the prevalence and prediction of difficult intubation in Chinese women. Two groups of Chinese women were studied (151 pregnant and 260 non-pregnant). The prevalence of difficult intubation was 1.99% in the pregnant and 1.54% in the non-pregnant group. The difference was not statistically significant. Predictive variables for difficult intubation, including modified Mallampati class, thyromental distance and atlanto-occipital extension, had high sensitivity but low positive predictive value when used alone. A shorter thyromental distance had to be used as the criterion for prediction in Chinese women. Combination of predictive variables could improve the positive predictive value.

The extracellular matrix, interstitial fluid and ions as a mechanical signal transducer in articular cartilage

OBJECTIVE

(1) Provide an overview of the biomechanical factors that are required to analyze and interpret biological data from explant experiments; (2) Present a description of some of the mechano-electrochemical events which occur in cartilage explants during loading.

DESIGN

A thorough and provocative discussion on the effects of loading on articular cartilage will be presented. Five simplest loading cases are considered: hydrostatic pressure, osmotic pressure, permeation (pressure loading), confined compression and unconfined compression. Details of how such surface loadings are converted or transduced by the extracellular matrix (ECM) to pressure, fluid, solute and ion flows, deformation and electrical fields are discussed.

RESULTS

Similarities and differences in these quantities for the five types of loading are specifically noted. For example, it is noted that there is no practical mechanical loading condition that can be achieved in the laboratory to produce effects that are equal to the effects of osmotic pressure loading within the ECM. Some counter-intuitive effects from these loadings are also described. Further, the significance of flow-induced compression of the ECM is emphasized, since this frictional drag effect is likely to be one of the major effects of fluid flow through the porous-permeable ECM. Streaming potentials arising from the flow of ions past the fixed charges of the ECM are discussed in relation to the flow-induced compaction effect as well.

CONCLUSION

Understanding the differences among these explant loading cases is important; it will help to provide greater insights to the mechano-electrochemical events which mediate metabolic responses of chondrocytes in explant loading experiments.

Intracellular calcium response of ACL and MCL ligament fibroblasts to fluid-induced shear stress

This study examines the real-time intracellular calcium concentration, [Ca2+]i, response of canine medial collateral ligament (MCL) and anterior cruciate ligament (ACL) fibroblasts subjected to a fluid-induced shear stress of 25 dynes/cm2. In experiments using a modified Hanks' Balanced Salt Solution (HBSS) perfusate, both cell types demonstrated a significant increase in peak [Ca2+]i compared to respective no-flow controls, the response of MCL fibroblasts being nearly 2-fold greater than that of ACL fibroblasts. In studies where the cells were bathed in a medium of HBSS supplemented with 2% newborn bovine serum (NBS) and then introduced to flow with the same medium, ACL fibroblasts responded nearly 3-fold greater than MCL fibroblasts. Neomycin (10 mM), thapsigarigin (1 microM) and Ca(2+)-free media supplemented with EGTA (1 mM) were able to inhibit significantly the [Ca2+]i response to flow with HBSS in both fibroblasts. Thapsigargin also blocked the NBS flow response in both cell types, while neomycin and Ca(2+)-free media significantly inhibited the ACL response. Our findings demonstrate that ACL and MCL cells are not the same. These differences may be related to the disparate healing capacity of the ACL and MCL observed clinically.

The effectiveness of systematic stroke care

A coordinated, multidisciplinary approach had been applied to enhance the effectiveness of stroke care with varying enthusiasm; however, the effectiveness of this kind of stroke treatment model was noted in many studies. This study was designed to measure the effectiveness of systematic stroke management on the physical-functional outcome in terms of Activities of Daily Living (ADLs) scores. The higher the ADLs score, the higher the degree of physical disability, i.e., the higher the degree of dependence. Eighty-six stroke patients from the Department of Neurology in a medical center, and 88 stroke patients from the Department of Medicine in a local hospital were followed from the admission day to the discharged date. The effectiveness of stroke care in each hospital was measured by the comparisons between ADLs scores at discharge and ADLs scores at admission. Two-sample tests show that demographic characteristics, length of stay, average time elapsed since the occurrent stroke, number of families in caregiving, and ADLs scores at admission and at discharge did not differ much between these two groups. The improved ADLs scores for stroke patients treated in the Department of Neurology of the medical center were changed from the 14.1 +/- 4.9 at admission to 12.1 +/- 5.2 at discharge, and the changes of ADLs scores for patients treated in the Department of Medicine of the regional hospital was from 12.8 +/- 5.1 to 12.3 +/- 5.5 according to the degree of improvement. The significant finding was that the degree of improvement of ADLs scores for CVA patients from the medical center was significant (Wilcoxon Matched-Pairs Signed-Ranks Test, Z = -2.8, p < 0.01). Moreover, the degree of improvement of ADLs scores strongly differed between these two groups (Repeated measures of two-way ANOVA, F = 6.0, p < 0.05). The information presented here informs us that degree of physical-functional status of stroke patients should be improved because of the systematic stroke management.

Extracellular ATP modulates [Ca2+]i in retinoic acid-treated embryonic chondrocytes

When treated with low doses of retinoic acid (RA), cephalic chondrocytes of the chick embryonic sternum mature and express phenotypic characteristics of postmitotic hypertrophic cells. In concert with these maturation-dependent changes, cells release adenine nucleotides into the culture medium. To ascertain if these compounds modulate chondrocyte function, we challenged chondrocytes with nucleotides and measured one determinant of the signal transduction pathway, intracellular Ca2+ concentration ([Ca2+]i). In the presence of micromolar concentrations of ATP, there was a dose-dependent elevation in chondrocyte [Ca2+]i; ADP caused a small but significant rise in the peak [Ca2+]i response. We found that the change in the [Ca2+]i response is linked to retinoid-dependent maturation of chondrocytes. Thus the [Ca2+]i rise was dependent on the RA concentration and treatment time. Immature caudal chondrocytes, cells that were not affected by RA, were used as control cells for this study. When treated with ATP, these cells did not exhibit a [Ca2+]i response. Although the purinergic subtype receptor was not characterized, the observation that cells responded to ATP and ADP but were refractory to AMP and adenosine suggested that P2 purinoceptors were expressed by chondrocytes. Because, during the same culture period, chondrocytes exhibited many of the unique characteristics of the terminally differentiated cell, the acquisition of purinergic receptors represents a new feature associated with expression of the mature phenotype. Finally, to ascertain if the ATP-dependent response was due to release of Ca2+ from intracellular stores, cells were treated with thapsigargin. Since this compound significantly reduced the [Ca2+]i signal, we concluded that the ATP response is mediated by release of cation, from the endoplasmic reticulum.

Intracellular Ca2+ stores and extracellular Ca2+ are required in the real-time Ca2+ response of bone cells experiencing fluid flow

In this study, we sought to determine if there is a requirement for calcium entry from the extracellular space as well as calcium from intracellular stores to produce real-time intracellular calcium responses in cultured bone cells subjected to fluid flow. Understanding calcium cell signaling may help to elucidate the biophysical transduction mechanism(s) mediating the conversion of fluid flow to a cellular signal. An experimental design which utilized a scheme of pharmacological blockers was employed to distinguish between the biochemical pathways involved in this cell signaling. A parallel-plate flow chamber served as the cell stimulating apparatus and a fluorescence microscopy system using the calcium-sensitive dye fura-2 measured the intracellular calcium changes. In the present study, evidence for a role by the inositol-phospholipid biochemical pathway, specifically inositol trisphosphate (IP3) was obtained using neomycin which completely inhibited the calcium response to flow. Additionally, a concomitant role of extracellular calcium was demonstrated through experiments performed in calcium-free medium which also eliminated the flow response. Experiments conducted with gadolinium, a stretch-activated channel blocker, partially inhibited (approximately 30%) the flow response while verapamil, a type-L voltage sensitive channel blocker, had no effect on the flow response. These results suggest a requirement of extracellular calcium (or calcium influx) as well as IP3-induced calcium release from intracellular stores for generating the intracellular calcium response to flow in bone cells.

What is the role of the convective current density in the real-time calcium response of cultured bone cells to fluid flow?

Cultured cells subjected to fluid flow are exposed to mechanical forces and electrokinetic forces. The convective current establishes an electrokinetic force created by the flow-dependent transport of mobile ions in the media over the charged cell surfaces. This current can be expressed as a current density, the current normalized by the cross-sectional area in which it exists. In this study, we hypothesized that the convective current density has no role in the bone cell real-time intracellular calcium response to fluid flow. Our hypothesis was tested by incorporating electrokinetic measurements and classical electrokinetic double-layer theory to estimate the value of convective current density in a parallel-plate flow chamber and then to apply an external current during the presence of fluid flow that would alter convective current density. There was no difference between the mean peak calcium response of cells exposed to flow with an altered (canceled or doubled) convective current density versus flow with an unmodified convective current density, as was measured with fura-2 fluorescence microscopy. These results suggest that mechanical forces, such as fluid-induced shear stress, rather than concomitant electrokinetic forces are the primary stimuli in eliciting the observed calcium response of bone cells to fluid flow.