The gender gap in stone-related surgery: A comprehensive analysis from an Israeli perspective

OBJECTIVE

To investigate the gender gap in the context of stone-related surgery within an Israeli population.

METHODS

We conducted a retrospective cohort study using administrative databases from Clalit Health Services to identify adults aged 18 and above who had their initial surgical treatment for upper tract urolithiasis. We employed descriptive statistics to outline the baseline patient characteristics, and the Cochran-Armitage test for trend was utilized to analyze surgical trends.

RESULTS

Between 2003 and 2020, a total of 36,624 adult patients underwent surgical treatment for upper tract urinary stones. The mean age of patients was 55.01 years (standard deviation (SD) 16.6) for ureteroscopy (URS), 55.05 years (SD 15.1) for percutaneous nephrolithotripsy (PCNL), and 51.07 years (SD 15.1) for shockwave lithotripsy (SWL). When considering the distribution of procedures by gender, males accounted for 69.5% of URS cases, 58.3% of PCNL cases, and 70.6% of SWL cases, whereas females represented 30.5%, 41.7%, and 29.4% of URS, PCNL, and SWL cases, respectively. Across all surgical modalities, the male-to-female ratio exhibited fluctuations without a consistent trend, with both increases and decreases observed. In URS, the ratio saw a modest increase from 1.967 in 2003 to 2.173 in 2020. For PCNL, the ratio initially increased from 2.361 in 2003 to 2.549 in 2014, followed by subsequent fluctuations, but an overarching trend was not apparent. In contrast, for SWL, the ratio decreased from 2.15 in 2003 to 1.32 in 2020, with varying changes in between.

CONCLUSION

This study highlights the dynamic nature of gender gap in stone-related surgery outcomes. While the male-to-female ratio exhibited fluctuations over a 17-year period, no consistent trend emerged. The absence of a clear trend underscores the complex and multifaceted factors influencing the gender gap in urolithiasis.

Trends in Emergency Department Admissions Due to Renal Colic in the Pediatric Population: A Multicenter Study

BACKGROUND

Pediatric urolithiasis is relatively uncommon and is generally associated with predisposing anatomic or metabolic abnormalities. In the adult population, emergency department (ED) admissions have been associated with an increase in ambient temperature. The same association has not been evaluated in the pediatric population.

OBJECTIVES

To analyze trends in ED admissions due to renal colic in a pediatric population (≤ 18 years old) and to assess the possible effect of climate on ED admissions.

METHODS

We conducted a retrospective, multicenter cohort study, based on a computerized database of all ED visits due to renal colic in pediatric patients. The study cohort presented with urolithiasis on imaging during their ED admission. Exact climate data was acquired through the Israeli Meteorological Service (IMS).

RESULTS

Between January 2010 and December 2020, 609 patients, ≤ 18 years, were admitted to EDs in five medical centers with renal colic: 318 males (52%), 291 females (48%). The median age was 17 years (IQR 9-16). ED visits oscillated through the years, peaking in 2012 and 2018. A 6% downward trend in ED admissions was noted between 2010 and 2020. The number of ED admissions in the different seasons was 179 in autumn (30%), 134 in winter (22%), 152 in spring (25%), and 144 in summer (23%) (P = 0.8). Logistic regression multivariable analysis associated with ED visits did not find any correlation between climate parameters and ED admissions due to renal colic in the pediatric population.

CONCLUSIONS

ED admissions oscillated during the period investigated and had a downward trend. Unlike in the adult population, rates of renal colic ED admissions in the pediatric population were not affected by seasonal changes or rise in maximum ambient temperature.

A retrospective cohort study, analyzing trends in management of upper urinary tract stones in the adult Israeli population

OBJECTIVE

To assess trends of surgical intervention in adults with upper urinary tract stones in Israel.

METHODS

A retrospective cohort study utilizing administrative databases held at Clalit Health Services, to identify all adults (⩾18 years) who underwent their first surgical treatment for upper tract urolithiasis. Descriptive statistics were employed to summarize baseline patient demographics and surgical trends were analyzed using the Cochrane-Armitage test for trend.

RESULTS

Between 2003 and 2020, 36,624 adult patients were treated surgically for upper tract urinary stones. Mean age was 53.6 years (SD16.1). During the period investigated, the number of insured by Clalit Health Services increased by 25% and the total number of surgically treated stones increased by 98.7%. By type of procedure: Ureteroscopy (URS) increased by 351%, percutaneous nephrolithotripsy (PCNL) increased by 67%, shockwave lithotripsy (SWL) declined by 79%. The number of procedures per 100,000 population grew from to 37.5 in 2003 to 58.05 in 2022. The percentage increase in total number of surgical procedures was 103% and 90% in males and females, respectively.

CONCLUSIONS

Our findings reveal significant increases in the total number of surgically treated stones over the investigated period. Notably, this increase far outpaced the growth in the number of individuals insured by Clalit Health Services. Further research and interventions are warranted to explore the underlying factors driving these trends and to develop targeted approaches for prevention, early detection, and minimally invasive treatment of upper urinary tract stones in Israel.

A population-based retrospective cohort study of surgical trends and outcomes of pediatric urolithiasis in Ontario, Canada (2002-2019)

INTRODUCTION

The worldwide incidence of pediatric urinary stone disease (PUSD) is increasing. However, there is no commensurate data on whether this translates to an increasing need for surgical intervention for PUSD, given the role of conservative management.

OBJECTIVE

We aimed to evaluate the trends and outcomes of clinically significant PUSD, using administrative databases to identify patients surgically treated for PUSD.

STUDY DESIGN

This retrospective population-based cohort study assessed the incidence and trends of surgically treated PUSD and outcomes in Ontario, Canada in patients <18 years of age who underwent their first PUSD procedure between 2002 and 2019 utilizing administrative databases held at the Institute of Clinical Evaluative Sciences (ICES). We assessed the incidence of surgically treated PUSD, demographics, initial surgical treatment and imaging modality, and risk factors for repeat intervention within 5 years. Statistical analyses summarized demographics, surgical trends, and logistic regression was used to identify risk factors for repeat surgical intervention.

RESULTS

We identified 1149 patients (mean age 11.3 years), with 59.6% older than 12 years. There was a decrease in the number of PUSD procedures performed per year that was close to statistical significance (p = 0.059) and a trend towards increased utilization of ureteroscopy (URS) compared with Shockwave Lithotripsy (SWL). In addition, there was a significant increase in the proportion of females surgically treated with PUSD (p = 0.001). In the 706 patients followed for 5 years, 17.7% underwent a repeat procedure within 6 months, while 20.4% underwent a repeat procedure from 6-months to 5 years. Renal stone location (OR 2.79, 95% confidence interval (CI) 1.62-4.80, p = 0.0002) and index SWL (OR 1.66, 95% CI 1.20-2.31, p = 0.0025) were risk factors for repeat surgical intervention within the first 6-months. There was an increasing utilization of ultrasound (US) compared to computerized tomography (CT) (p = 0.0008).

DISCUSSION

Despite the literature reporting increasing PUSD incidence, we observed a non-significant decrease in the number of surgical PUSD procedures performed. Exclusion of those treated conservatively may explain our results. The increase in the proportion of females treated reflects the narrowing gender gap in stone disease. A trend towards increased URS utilization was observed and re-intervention rates were similar to previous studies.

CONCLUSION

The overall rate of surgically treated PUSD did not show an increasing trend in Ontario, Canada from 2002 to 2019. URS was the most common surgical treatment modality, with a corresponding decline in SWL rates. PUSD was associated with a high surgical re-intervention rate within 6 months.

Effect of gender on presentation and outcome of renal colic

OBJECTIVES

To examine gender-related differences in the presentation, management, and outcomes of patients admitted to the emergency department ED with ureteral stones.

METHODS

Retrospective analysis of all patients admitted to the ED at our institution, found to have a ureteral stone on CT. Clinical, laboratory, imaging parameters, and outcomes were collected.

RESULTS

778 patients were admitted with ureteral stones between January 2018 and December 2020. 78% (n = 609) were males and 22% (n = 169) were females. The mean ages were 49.4 (SD 14.4) and 51.6 (SD 15.7) in males and females, respectively (p = 0.08). Female patients presented with a higher body temperature (p = 0.01), pulse rate (p < 0.0001), nausea and vomiting (p < 0.0001), elevated serum C-reactive protein (CRP) (p = 0.002) compared to males. The prevalence of elevated serum creatinine was higher in males (p < 0.0001). Alpha-blockers were recommended on discharge in 54.8% (334) of males, compared to only 29.6% (50) of females (p < 0.0001). Spontaneous stone expulsion was significantly higher in males compared to females (p = 0.01).

CONCLUSIONS

Our results demonstrate that gender does effect presentation and outcome of patients presenting with renal colic. Females were found to have elevated infectious parameters, more nausea and vomiting and a higher incidence of positive urine cultures. Males admitted to the ED were found to have significantly higher serum creatinine levels. Medical expulsive therapy (MET) with alpha-blockers was prescribed significantly less in female patients, which may have resulted in a lower spontaneous stone expulsion rate.

Post-operative pain following percutaneous nephrolithotripsy- clinical correlates

OBJECTIVES

Management of postoperative pain following percutaneous nephrolithotripsy (PCNL) is a significant goal. We sought to identify risk factors and clinical correlates of postoperative pain in order to improve perioperative management and patient satisfaction.

MATERIALS AND METHODS

A single-center, retrospective analysis, from a prospectively maintained database, of all consecutive patients who underwent PCNL for renal calculi between January 2011 and August 2018. Postoperative pain was assessed using the visual analog scale (VAS) and analgesic use. We considered VAS score above 4 as meaningful. Pain management was standardized according to patirnt reported VAS scores. Multivariable logistic regression was performed to identify risk factors and clinical correlates.

RESULTS

A total of 496 patients were analyzed. Younger age was associated with VAS above 4 on the operative day and the first postoperative following PCNL (p = 0.003 and p < 0.001, respectively). Female gender was associated with VAS above 4 in the first 2 days following the operation (p < 0.001).

CONCLUSIONS

Younger age and female gender would most likely benefit from pre-emptive improved pain management protocols following PCNL.

Testis sparing management of tuberculous epididymitis – Case report

Tuberculous epididymitis is uncommonly encountered and is a very rare complication of Bacillus Calmette-Guérin (BCG) intravesical therapy for the treatment of bladder urothelial cancer. With the increased use of BCG, it is conceivable that practicing urologists will see more patients presenting with this infection. Herein, we describe an unusual presentation of tuberculous epididymitis treated successfully in a conservative fashion with anti-tuberculotic medications and describe current diagnostic, as well as medical and surgical management strategies.

Retrograde intrarenal surgery for lower pole stones utilizing stone displacement technique yields excellent results

Objective

To evaluate the long-term stone-free rate (SFR) of retrograde intra-renal surgery (RIRS) in the treatment of lower pole renal calculi using only basket relocation and identify independent predictors of stone-free status.

Methods

All consecutive patients undergoing RIRS lower pole renal calculi at a single high-volume tertiary center were analyzed retrospectively. Lower pole stones were relocated to the upper pole, where laser lithotripsy was performed. All patients were followed up in the clinic following the surgery and yearly thereafter. The stone-free status was assessed with a combination of an abdominal ultrasound and abdominal X-ray, or an abdominal non-contrast computed tomography if the stones were known to be radiolucent.

Results

A total of 480 consecutive patients who underwent RIRS for treatment of lower pole renal calculi, between January 2012 and December 2018, were analyzed from a prospectively maintained database of 3000 ureteroscopies. With a median follow-up time of 18.6 months, the mean SFR was 94.8%. The procedures were unsuccessful in 26 (5.4%) patients due to unreachable stones. The median stone size of the unreachable stones was 12 mm (range 10-30 mm). Multivariable logistic regression analysis revealed two predictors of SFR for lower pole stones: a small cumulative stone burden (odds ratio [OR]: 0.903, 95% confidence interval [CI]: 0.867-0.941, p<0.0001) and preoperative ureteral stent insertion (OR: 0.515, 95% CI: 0.318-0.835, p=0.007).

Conclusion

The long-term SFR of RIRS for the treatment of lower pole stones with basket displacement with appropriate patient selection is high.

Spontaneous stone expulsion in patients with history of urolithiasis

Objectives:

To examine differences in the presentation, management, and outcomes of patients admitted to the emergency department (ED) with ureteral stones, with prior history of urolithiasis compared to patients with a first stone event.

Patients and Methods:

Retrospective analysis of patients who visited the ED that were found to have a ureteral stone on CT. Patients were stratified into two groups: without history of urolithiasis (Group 1) and with history of urolithiasis (Group 2).

Results:

Between 2018 and 2020, 778 patients were admitted with ureteral stones. Patients in group 1 presented with a higher mean serum creatinine ( p = 0.02), larger mean stone size ( p < 0.0001), and a higher proportion of proximal ureteral stones ( p < 0.0001) than patients in group 2. The 30 day readmission rate was significantly higher in group 1 ( p = 0.02). Spontaneous stone expulsion was higher in group 2 ( p < 0.0001), whereas the need for endourological procedures was higher in group 1 ( p < 0.0001). On multivariable analysis serum creatinine (OR 0.264, 95% CI 0.091–0.769, p = 0.01) and stone size (OR 0.623, 95% CI 0.503–0.771, p < 0.0001) were associated with a lower spontaneous stone expulsion rate. History of prior endourological procedures (OR 0.225, OR 0.066–0.765, p = 0.01) was associated with a higher spontaneous stone expulsion rate.

Conclusions:

Our data suggests that patients who are first time stone formers present with larger and more proximal ureteral stones, with a lower likelihood of spontaneous stone expulsion and a subsequent need for surgical intervention. Previous stone surgery and not previous stone expulsion was found to be a predictor for spontaneous stone passage.

Effect of age on presentation and outcome in renal colic

Objectives:

To examine the age-related differences in the presentation, management, and outcomes of patients admitted to the emergency department (ED) with ureteral stones.

Patients and methods:

A retrospective analysis of all patients who visited the ED at a single institution that were found to have a ureteral stone on CT. Clinical, laboratory, and imaging parameters were collected, including outcomes. Patients were subdivided into age groups: 18–30, 31–50, 51–70, and >70 years.

Results:

Between January 2018 and December 2020, 778 patients were admitted to the ED with a ureteral stone. About 78% (609) were males and 22% (169) were females. The mean ages were 49.4 (SD 14.4) and 51.6 (SD 15.7) in males and females, respectively ( p = 0.08). Patients in the 36–50 age group, had significantly higher visual analogue scale (VAS) scores ( p < 0.0001). Patients older than 70 years old presented with significantly higher serum creatinine levels ( p < 0.0001), C-reactive protein (CRP) ( p < 0.001) and leukocyte levels ( p = 0.002). These patients were also found to have significantly larger stones (mean size of 6.2 mm (SD 4.8) ( p < 0.0001)) and underwent percutaneous nephrolithotripsy (PCNL) in significantly higher numbers (56.3% vs 43.8%, ( p < 0.0001)). Less than half of the patients older than 50 years were given medical expulsive therapy (MET) with alpha-blockers, compared to more than 50% in the other age groups ( p = 0.002). Spontaneous stone expulsion was noted in 70.2% of the 18–35-year group, 62.4% of the 36–50-year-old group, 51.8% of the 51–70-year-old group, and 37% of the >70-year-old group ( p < 0.0001). The ED re-admission rates at 7 and 30 days were not significantly different among all age groups.

Conclusions:

Our data suggests that older patients presented with larger stones, elevated inflammatory markers and creatinine and were more likely to require surgical intervention. The spontaneous stone expulsion rate was inversely associated with age.

Comparison of long-term results following ureteroscopic stone fragmentation with removal versus stone dusting without removal

Purpose:

To compare long-term results following ureteroscopic stone fragmentation and removal versus stone dusting.

Methods:

We conducted a retrospective analysis of patients who underwent ureteroscopy for renal calculi at two high-volume tertiary centres between 2012 and 2013, therefore allowing long-term follow-up. The surgeons differed in their technique, some performing dusting for the most part and the others fragmentation. Inclusion criteria were stone free at the first follow-up and the sole use of laser lithotripsy is either by dusting or by fragmentation. Operative and post-operative data as well as re-treatment rates were compared between the groups. Stone-free rates and long-term stone recurrence rates were analysed by a single radiologist blinded to the treatment technique.

Results:

Between 2012 and 2013, 669 ureteroscopies were performed at both centres. The study group included 100 patients, which met the inclusion criteria, equally distributed between dusting and fragmentation. The cumulative stone diameter in patients treated with dusting was significantly larger (12.7 mm versus 17 mm, p = 0.006). Operative time was shorter in patients treated with dusting (56 minutes versus 47.2 minutes, p = 0.6). The mean follow-up was 58.9 (standard deviation (SD) 17.2) and 69.4 (SD 13.8) months for the fragmentation and dusting-treated patients, respectively( p = 0.06). The long-term recurrence rate in the fragmentation group was 22% compared to 38% in the dusting group ( p = 0 .08). Most of the patients in the dusting group required a repeat ureteroscopy during their follow-up (28% versus 6%, p = 0.003). A multivariable logistic regression analysis revealed that the fragmentation was not associated with a lower stone recurrence rate when compared to dusting (OR 0.6, 95% CI 0.199-1.810, p = 0.3).

Conclusions:

The recurrence rate of renal stones was not significantly influenced by the choice of surgical techniques. However, dusting was associated with a greater need for repeat ureteroscopy than fragmentation with removal.

Level of evidence:

Not applicable

Do weather parameters affect the incidence of renal colic in a predominantly warm country? A multicenter study

Purpose:

To determine whether there is any effect of weather parameters on the incidence of renal colic patients presenting to emergency rooms (ERs) during the hottest season in Israel.

Materials and Methods:

This retrospective multicenter study involved all ER admissions related to renal colic in nine centres throughout Israel between 2010 and 2017. The collected data included the date of ER visits, the patients’ age and sex, and the weather features of ambient temperature, wind velocity, noon heat index, and barometric pressure. Multivariable logistic regression analyses identified predictors of increased ER visits for renal colic.

Results:

There were 85,501 renal colic-related ER visits during the study period, involving 62,935 (74%) males and 22,566 (26%) females ( p < 0.005). The mean ± standard deviation (SD) age of the males and females was 50 ± 5.8 and 48 ± 19.6 years, respectively ( p = 0.1). Most of the ER arrivals were in the 31- to 50-year-old age group (37%, 31,508) ( p = 0.02). The maximal ambient temperature (odds ratio (OR) = 2.213, 95% confidence interval (CI) = 2.148–2.279, p < 0.0001), lower heat index (i.e. low humidity; OR = 0.880, 95% CI = 0.872–0.887, p < 0.0001) and increased wind velocity (OR = 1.165, 95% CI = 1.149–1.182, p < 0.0001) had a significant linear effect on ER visits for renal colic events.

Conclusion:

Conditions that increase sweat evaporation during the hottest months, including a decreased heat index and increased wind velocity, correlated with more ER visits for renal colic events, probably due to dehydration associated with elevated sweat evaporation.

Level of evidence:

Not applicable

A population-based retrospective cohort study analyzing contemporary trends in the surgical management of urinary stone disease in adults

INTRODUCTION

We aimed to review the trends and incidence of surgical intervention for adults with upper urinary tract stones in Ontario, Canada, and to hypothesize potential causes for the observed changes.

METHODS

We carried out a retrospective, population-based cohort study using administrative databases held at the Institute of Clinical Evaluative Sciences (IC/ES) to identify all adults (≥18 years) who underwent surgical treatment for urolithiasis, defined by records using a combination of both hospital and physician billing from 2002-2019. Descriptive statistics were used to summarize baseline patient demographics, and surgical trends were analyzed using the Cochrane-Armitage test for trend.

RESULTS

From 2002-2019, 140 263 patients were treated surgically for urolithiasis. During this time period, the total number of surgically treated stone disease increased by 80.5%. By type of procedure, percutaneous nephrolithotomy (PCNL) increased by 187% and ureteroscopy (URS) increased by 158%, while the number of shockwave lithotripsy (SWL) declined by 31.4%. The adult population in Ontario in the years evaluated grew by 24.4%. The number of surgical procedures per 100 000 people over this time grew by 45.3%. For every 1% increase in the population, there was a 2.6% rise in stone-related surgical procedures.

CONCLUSIONS

The number of stone-related surgical procedures performed rose significantly and cannot be accounted for by population growth alone. This rise was proportionally larger in the female population, further supporting a narrowing of the gender gap in urinary stone disease. The reasons for the increase are likely multifactorial and may imply an increasing incidence of surgically treated stone disease. The change in the proportion of URS and SWL performed may demonstrate a continued shift in surgical preference or may be reflective of resource limitations and availability. The increase in PCNL volumes may also suggest a greater complexity of cases. These findings should be considered for future resource planning and require further study.

Simple prostatectomy using the open and robotic approaches for lower urinary tract symptoms: A retrospective, case-control series

INTRODUCTION

We aimed to assess the outcome of our series of simple prostatectomy using the open simple prostatectomy (OSP) and robotic-assisted simple prostatectomy (RASP) approaches, at our institution.

METHODS

A retrospective chart review of men who underwent OSP and RASP at Western University, in London, ON. Preoperative, intraoperative, and postoperative data were collected and analyzed.

RESULTS

From 2012-2020, 29 men underwent a simple prostatectomy at our institution. Eight patients underwent an OSP and 21 patients underwent a RASP. The median age was 69 years. Preoperative median prostate volume was 153 cm³ (range 80-432 cm³). The surgical indications were failed medical treatment, urinary retention, hydronephrosis, cystolithiasis, and recurrent hematuria. The median operative time was 137.5 minutes in OSP and 185 minutes in the robotic approach (p=0.04). Median estimated blood loss was 2300 ml (range 600-4000 ml) and 100 ml (range 50-400 ml) in the open and robotic procedures, respectively (p=0.4). The mean length of hospital stay was shorter in the RASP group, one day vs. three days (z=4.152, p<0.005). Perioperative complication rates were significantly lower in the group undergoing RASP, with no complications recorded in this group (p=0.004). Both groups demonstrated excellent functional results, with most patients reporting complete urinary continence (p=0.8).

CONCLUSIONS

We report very good perioperative outcomes, with a minimal risk profile and excellent functional results, leading to marked improvement in patients' symptoms at followup after both the OSP and RASP approaches. RASP was associated with a shorter length of hospital stay, decreased blood loss, and a lower complication rate.

Case report - Primary renal echinococcal infection

Renal echinococcal infection is an uncommonly encountered infection in North America but is endemic in many parts of the world. With increasing migration, it is conceivable that practicing Canadian physicians will see more patients presenting at various stages of infection. Herein, we describe an unusual presentation of primary renal echinococcal infection and describe current diagnostic, as well as medical and surgical management strategies.

Predicting the risk of sepsis and causative organisms following urinary stones removal using urinary versus stone and stent cultures

The association between foreign objects in the urinary system and urinary tract infections (UTI) is well established. The incidence of bacteriuria in patient with urinary catheters increases as dwelling time lengthens. The presence of ureteral stents and kidney stones is also associated with increased risk for bacteriuria and urinary tract infection. The aim of this study was to assess the bacterial characteristics of urine culture (UC) and foreign body culture (FBC), the concordance between them, and to identify risk factors for postoperative infections, in order to improve the treatment in these patients, using a prospectively collected database of patients who underwent ureteroscopy or percutaneous nephrolithotomy (PCNL) for the treatment of urinary stones between 2005 and 2016 at our institute. Preoperative UC was obtained from voided mid-stream urine for all patients. FBCs were obtained from ureteral stents removed and stones collected during the surgery. The cohort included 1011 patients. Mean age was 53 (SD 15.8), and 679 (67.2%) patients were male. Two hundred eighteen (21.6%) had a UTI in the year prior to the surgery. Among 795 patients who had sterile UC, 98 (12.3%) patients had positive FBC. Positive FBC was found in 53.7% of the patients with positive UC; however, FBC pathogens were similar to those identified in UC in 31% patients. The sensitivity of UC to detect FBC pathogens was 31.3%, and the PPV was 0.31. Urine cultures do not recognize all cases of pathogens colonizing foreign bodies in the urinary system. The colonization may be associated with an increased risk for SIRS. In more than one-quarter of the patients, the causative pathogen of sepsis is identified by FBC, but not by UC.

Ocean sequestration of carbon dioxide: modeling the deep ocean release of a dense emulsion of liquid Co2-in-water stabilized by pulverized limestone particles

The release into the deep ocean of an emulsion of liquid carbon dioxide-in-seawater stabilized by fine particles of pulverized limestone (CaCO3) is modeled. The emulsion is denser than seawater, hence, it will sink deeper from the injection point, increasing the sequestration period. Also, the presence of CaCO3 will partially buffer the carbonic acid that results when the emulsion eventually disintegrates. The distance that the plume sinks depends on the density stratification of the ocean, the amount of the released emulsion, and the entrainment factor. When released into the open ocean, a plume containing the CO2 output of a 1000 MW(el) coal-fired power plant will typically sink hundreds of meters below the injection point. When released from a pipe into a valley on the continental shelf, the plume will sink about twice as far because of the limited entrainment of ambient seawater when the plume flows along the valley. A practical system is described involving a static mixer for the in situ creation of the CO2/seawater/pulverized limestone emulsion. The creation of the emulsion requires significant amounts of pulverized limestone, on the order of 0.5 tons per ton of liquid CO2. That increases the cost of ocean sequestration by about $13/ ton of CO2 sequestered. However, the additional cost may be compensated by the savings in transportation costs to greater depth, and because the release of an emulsion will not acidify the seawater around the release point.

Limestone-particle-stabilized macroemulsion of liquid and supercritical carbon dioxide in water for ocean sequestration

When liquid or supercritical CO2 is mixed with an aqueous slurry of finely pulverized (1-20 microm) limestone (CaCO3) in a high-pressure reactor, a macroemulsion is formed consisting of droplets of CO2 coated with a sheath of CaCO3 particles dispersed in water. The coated droplets are called globules. Depending on the globule diameter and the CaCO3 sheath thickness, the globules sink to the bottom of the water column, are neutrally buoyant, or float on top of the water. The CaCO3 particles are lodged at the CO2/ H2O interface, preventing the coalescence of the CO2 droplets, and thus stabilizing the CO2-in-water emulsion. We describe the expected behavior of a CO2/H2O/CaCO3 emulsion plume released in the deep ocean for sequestration of CO2 in the ocean to ameliorate global warming. Depending on the amount of CO2 injected, the dense plume will descend a few hundred meters while entraining ambient seawater until it acquires neutral buoyancy in the stratified ocean. After equilibration, the globules will rain out from the plume toward the ocean bottom. This mode of CO2 release will prevent acidification of the seawater around the release point, which is a major environmental drawback of ocean sequestration of liquid, unemulsified CO2.

Period doubling of calcium spike firing in a model of a Purkinje cell dendrite

Recordings from cerebellar Purkinje cell dendrites have revealed that in response to sustained current injection, the cell firing pattern can move from tonic firing of Ca(2+) spikes to doublet firing and even to quadruplet firing or more complex firing. These firing patterns are not modified substantially if Na(+) currents are blocked. We show that the experimental results can be viewed as a slow transition of the neuronal dynamics through a period-doubling bifurcation. To further support this conclusion and to understand the underlying mechanism that leads to doublet firing, we develop and study a simple, one-compartment model of Purkinje cell dendrite. The neuron can also exhibit quadruplet and chaotic firing patterns that are similar to the firing patterns that some of the Purkinje cells exhibit experimentally. The effects of parameters such as temperature, applied current, and potassium reversal potential in the model resemble their effects in experiments. The model dynamics involve three time scales. Ca(2+)- dependent K(+) currents, with intermediate time scales, are responsible for the appearance of doublet firing, whereas a very slow hyperpolarizing current transfers the neuron from tonic to doublet firing. We use the fast-slow analysis to separate the effects of the three time scales. Fast-slow analysis of the neuronal dynamics, with the activation variable of the very slow, hyperpolarizing current considered as a parameter, reveals that the transitions occurs via a cascade of period-doubling bifurcations of the fast and intermediate subsystem as this slow variable increases. We carry out another analysis, with the Ca(2+) concentration considered as a parameter, to investigate the conditions for the generation of doublet firing in systems with one effective variable with intermediate time scale, in which the rest state of the fast subsystem is terminated by a saddle-node bifurcation. We find that the scenario of period doubling in these systems can occur only if (1) the time scale of the intermediate variable (here, the decay rate of the calcium concentration) is slow enough in comparison with the interspike interval of the tonic firing at the transition but is not too slow and (2) there is a biostability of the fast subsystem of the spike-generating variables.

Bistability in pulse propagation in networks of excitatory and inhibitory populations

We study the propagation of traveling solitary pulses in one-dimensional networks of excitatory and inhibitory integrate-and-fire neurons. Slow pulses, during which inhibitory cells fire well before neighboring excitatory cells, can propagate along the network at intermediate inhibition levels. At higher levels, they destabilize via a Hopf bifurcation. There is a bistable parameter regime in which both fast and slow pulses can propagate. Lurching pulses with spatiotemporal periodicity can propagate in regimes for which continuous pulses do not exist.

Effects of delay on the type and velocity of travelling pulses in neuronal networks with spatially decaying connectivity

We study a one-dimensional model of integrate-and-fire neurons that are allowed to fire only one spike, and are coupled by excitatory synapses with delay. At small delay values, this model describes a disinhibited cortical slice. At large delay values, the model is a reduction of a model of thalamic networks composed of excitatory and inhibitory neurons, in which the excitatory neurons show the post-inhibitory rebound mechanism. The velocity and stability of propagating continuous pulses are calculated analytically. Two pulses with different velocities exist if the synaptic coupling is larger than a minimal value; the pulse with the lower velocity is always unstable. Above a certain critical value of the constant delay, continuous pulses lose stability via a Hopf bifurcation, and lurching pulses emerge. The parameter regime for which lurching occurs is strongly affected by the synaptic footprint (connectivity) shape. A bistable regime, in which both continuous and lurching pulses can propagate. may occur with square or Gaussian footprint shapes but not with an exponential footprint shape. A perturbation calculation is used in order to calculate the spatial lurching period and the velocity of lurching pulses at large delay values. For strong synaptic coupling, the velocity of the lurching pulse is governed by the tail of the synaptic footprint shape. Moreover, the velocities of continuous and lurching pulses have the same functional dependencies on the strength of the synaptic coupling strength gsyn: they increase logarithmically with gsyn for an exponential footprint shape, they scale like (In gsyn)1/2 for a Gaussian footprint shape, and they are bounded for a square footprint shape or any shape with a finite support. We find analytically how the axonal propagation velocity reduces the velocity of continuous pulses; it does not affect the critical delay. We conclude that the differences in velocity and shape between the front of thalamic spindle waves in vitro and cortical paroxysmal discharges stem from their different effective delays.

The number of synaptic inputs and the synchrony of large, sparse neuronal networks

The prevalence of coherent oscillations in various frequency ranges in the central nervous system raises the question of the mechanisms that synchronize large populations of neurons. We study synchronization in models of large networks of spiking neurons with random sparse connectivity. Synchrony occurs only when the average number of synapses, M, that a cell receives is larger than a critical value, Mc. Below Mc, the system is in an asynchronous state. In the limit of weak coupling, assuming identical neurons, we reduce the model to a system of phase oscillators that are coupled via an effective interaction, gamma. In this framework, we develop an approximate theory for sparse networks of identical neurons to estimate Mc analytically from the Fourier coefficients of gamma. Our approach relies on the assumption that the dynamics of a neuron depend mainly on the number of cells that are presynaptic to it. We apply this theory to compute Mc for a model of inhibitory networks of integrate-and-fire (I&F) neurons as a function of the intrinsic neuronal properties (e.g., the refractory period Tr), the synaptic time constants, and the strength of the external stimulus, Iext. The number Mc is found to be nonmonotonous with the strength of Iext. For Tr = 0, we estimate the minimum value of Mc over all the parameters of the model to be 363.8. Above Mc, the neurons tend to fire in smeared one-cluster states at high firing rates and smeared two-or-more-cluster states at low firing rates. Refractoriness decreases Mc at intermediate and high firing rates. These results are compared to numerical simulations. We show numerically that systems with different sizes, N, behave in the same way provided the connectivity, M, is such that 1/Meff = 1/M - 1/N remains constant when N varies. This allows extrapolating the large N behavior of a network from numerical simulations of networks of relatively small sizes (N = 800 in our case). We find that our theory predicts with remarkable accuracy the value of Mc and the patterns of synchrony above Mc, provided the synaptic coupling is not too large. We also study the strong coupling regime of inhibitory sparse networks. All of our simulations demonstrate that increasing the coupling strength reduces the level of synchrony of the neuronal activity. Above a critical coupling strength, the network activity is asynchronous. We point out a fundamental limitation for the mechanisms of synchrony relying on inhibition alone, if heterogeneities in the intrinsic properties of the neurons and spatial fluctuations in the external input are also taken into account.

Continuous and lurching traveling pulses in neuronal networks with delay and spatially decaying connectivity

Propagation of discharges in cortical and thalamic systems, which is used as a probe for examining network circuitry, is studied by constructing a one-dimensional model of integrate-and-fire neurons that are coupled by excitatory synapses with delay. Each neuron fires only one spike. The velocity and stability of propagating continuous pulses are calculated analytically. Above a certain critical value of the constant delay, these pulses lose stability. Instead, lurching pulses propagate with discontinuous and periodic spatio-temporal characteristics. The parameter regime for which lurching occurs is strongly affected by the footprint (connectivity) shape; bistability may occur with a square footprint shape but not with an exponential footprint shape. For strong synaptic coupling, the velocity of both continuous and lurching pulses increases logarithmically with the synaptic coupling strength g(syn) for an exponential footprint shape, and it is bounded for a step footprint shape. We conclude that the differences in velocity and shape between the front of thalamic spindle waves in vitro and cortical paroxysmal discharges stem from their different effective delay; in thalamic networks, large effective delay between inhibitory neurons arises from their effective interaction via the excitatory cells which display postinhibitory rebound.

Models of neuronal transient synchrony during propagation of activity through neocortical circuitry

Stereotypic paroxysmal discharges that propagate in neocortical tissues after electrical stimulations are used as a probe for studying cortical circuitry. I use modeling to investigate the effects of sparse connectivity, heterogeneity of intrinsic neuronal properties, and synaptic noise on synchronization of evoked propagating neuronal discharges in a network of excitatory, regular spiking neurons with spatially decaying connectivity. The global coherence of the traveling discharge is characterized by the correlation function between spike trains of neurons, averaged over all the pairs of neurons in the system at the same distance. Local coherence of two neurons is characterized by their correlation function averaged over many trials or, for persistent activity, over a long time interval. Spike synchronization between neurons emerges as a result of the transient activity; if activity is persistent, there is no synchrony, and cross-correlation functions are flat. During discharge propagation, system-average cross-correlation between neurons does not depend on their mutual distance except for a time shift. Spike synchronization occurs only when the average number of synapses M a cell receives is large enough. As M increases, there is a cross-over from an asynchronized to a synchronized discharge. Synaptic depression appears to help synchrony; it reduces the M value at the cross-over. The strengths of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) conductances affect synchrony only weakly. Spike synchronization is robust even with large levels of heterogeneity. Synaptic noise reduces synchrony, but strong synchrony is observed at a noise level that cannot evoke spontaneous discharges. System-average spike synchronization is determined by the levels of sparseness, heterogeneity, and noise, whereas trial-average spike synchronization is determined only by the noise level. Therefore, I predict that experiments will reveal local, two-cell spike synchrony, but not global synchrony.

Propagating neuronal discharges in neocortical slices: computational and experimental study

We studied the propagation of paroxysmal discharges in disinhibited neocortical slices by developing and analyzing a model of excitatory regular-spiking neocortical cells with spatially decaying synaptic efficacies and by field potential recording in rat slices. Evoked discharges may propagate both in the model and in the experiment. The model discharge propagates as a traveling pulse with constant velocity and shape. The discharge shape is determined by an interplay between the synaptic driving force and the neuron's intrinsic currents, in particular the slow potassium current. In the model, N-methyl-D-aspartate (NMDA) conductance contributes much less to the discharge velocity than amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) conductance. Blocking NMDA receptors experimentally with 2-amino-5-phosphonovaleric acid (APV) has no significant effect on the discharge velocity. In both model and experiments, propagation occurs for AMPA synaptic coupling gAMPA above a certain threshold, at which the velocity is finite (non-zero). The discharge velocity grows linearly with the gAMPA for gAMPA much above the threshold. In the experiments, blocking AMPA receptors gradually by increasing concentrations of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in the perfusing solution results in a gradual reduction of the discharge velocity until propagation stops altogether, thus confirming the model prediction. When discharges are terminated in the model by the slow potassium current, a network with the same parameter set may display discharges with several forms, which have different velocities and numbers of spikes; initial conditions select the exhibited pattern. When the discharge is also terminated by strong synaptic depression, there is only one discharge form for a particular parameter set; the velocity grows continuously with increased synaptic conductances. No indication for more than one discharge velocity was observed experimentally. If the AMPA decay rate increases while the maximal excitatory postsynaptic conductance (EPSC) a cell receives is kept fixed, the velocity increases by approximately 20% until it reaches a saturated value. Therefore the discharge velocity is determined mainly by the cells' integration time of input EPSCs. We conclude, on the basis of both the experiments and the model, that the total amount of excitatory conductance a typical cell receives in a control slice exhibiting paroxysmal discharges is only approximately 5 times larger than the excitatory conductance needed for raising the potential of a resting cell above its action potential threshold.

How well can we estimate the information carried in neuronal responses from limited samples?

It is difficult to extract the information carried by neuronal responses about a set of stimuli because limited data samples result in biased estimates. Recently two improved procedures have been developed to calculate information from experimental results: a binning-and-correcting procedure and a neural network procedure. We have used data produced from a model of the spatiotemporal receptive fields of parvocellular and magnocellular lateral geniculate neurons to study the performance of these methods as a function of the number of trials used. Both procedures yield accurate results for one-dimensional neuronal codes. They can also be used to produce a reasonable estimate of the extra information in a three-dimensional code, in this instance, within 0.05-0.1 bit of the asymptotically calculated value--about 10% of the total transmitted information. We believe that this performance is much more accurate than previous procedures.

Propagation of spindle waves in a thalamic slice model

1. We study the propagation and dynamics of spindle waves in thalamic slices by developing and analyzing a model of reciprocally coupled populations of excitatory thalamocortical (TC) neurons and inhibitory thalamic reticular (RE) neurons. 2. Each TC neuron has three intrinsic ionic currents: a low-threshold T-type Ca+2 current (ICa-T), a hyperpolarization-activated cation ("sag") current (Ih) and a leak current. Each RE cell also has three currents: ICa-T, a leak current, and a calcium-activated potassium current (IAHP). Isolated TC cells are at rest, can burst when released or depolarized from a hyperpolarized level, and burst rhythmically under moderate constant hyperpolarizing current. Isolated RE cells are at a hyperpolarized resting membrane potential and can burst when depolarized. 3. TC cells excite RE cells with fast alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) synapses, and RE cells inhibit TC cells with fast gamma-aminobutyric acid-A (GABAA) and slow GABAB synapses and inhibit each other with GABAA synapses only. GABAB postsynaptic conductances operate far from saturation, and the slow inhibitory postsynaptic potentials (IPSPs) increase with the width of the presynaptic burst. The model network is a one-dimensional cellular array with localized coupling. The synaptic coupling strength decays with the distance between the pre- and postsynaptic cells, either exponentially or as a step function. 4. The "intact" network can oscillate with partial synchrony and a population frequency of approximately 10 Hz. RE cells emit bursts almost at every oscillation cycle, whereas TC cells do so almost at every other cycle. Block of GABAB receptors hardly changes the network behavior. Block of GABAA receptors leads the network to a slowed oscillatory state, where the population frequency is approximately 4 Hz and both RE and TC cells fire unusually long bursts at every cycle and in full synchrony. These results are consistent with the experimental observations of von Krosigk, Bal, and McCormick. We obtain such consistency only when the above assumptions regarding the synaptic dynamics, particularly nonsaturating GABAB synapses, are fulfilled. 5. The slice model has a stable rest state with no neural activity. By initially depolarizing a few neurons at one end of the slice while all the other cells are at rest, a recruitment process may be initiated, and a wavefront of oscillatory activity propagates across the slice. Ahead of the wavefront, neurons are quiescent; neurons behind it oscillate. We find that the wave progresses forward in a lurching manner. TC cells that have just become inhibited must be hyperpolarized for a long enough time before they can fire rebound bursts and recruit RE cells. This step limits the wavefront velocity and may involve a substantial part of the cycle when no cells at the front are depolarized. 6. The wavefront velocity increases linearly with the characteristic spatial length of the connectivity (the footprint length). It increases only gradually with the synaptic strength, logarithmically in the case of an exponential connection function and only slightly for a step connection function. It also decreases gradually with a potassium leak conductance that hyperpolarizes RE cells. 7. To reproduce the experimentally measured wavefront velocity of approximately 1 mm/s, together with other in vitro observations, both the RE-to-TC and the TC-to-RE projections in the model should be spatially localized. The sum of the RE-to-TC and the TC-to-RE synaptic footprint lengths should be on the order of 100 microns. (ABSTRACT TRUNCATED AT 250 WORDS)

Emergent spindle oscillations and intermittent burst firing in a thalamic model: specific neuronal mechanisms

The rhythmogenesis of 10-Hz sleep spindles is studied in a large-scale thalamic network model with two cell populations: the excitatory thalamocortical (TC) relay neurons and the inhibitory nucleus reticularis thalami (RE) neurons. Spindle-like bursting oscillations emerge naturally from reciprocal interactions between TC and RE neurons. We find that the network oscillations can be synchronized coherently, even though the RE-TC connections are random and sparse, and even though individual neurons fire rebound bursts intermittently in time. When the fast gamma-aminobutyrate type A synaptic inhibition is blocked, synchronous slow oscillations resembling absence seizures are observed. Near-maximal network synchrony is established with even modest convergence in the RE-to-TC projection (as few as 5-10 RE inputs per TC cell suffice). The hyperpolarization-activated cation current (Ih) is found to provide a cellular basis for the intermittency of rebound bursting that is commonly observed in TC neurons during spindles. Such synchronous oscillations with intermittency can be maintained only with a significant degree of convergence for the TC-to-RE projection.

On temporal codes and the spatiotemporal response of neurons in the lateral geniculate nucleus

1. The present work relates recent experimental studies of the temporal coding of visual stimuli (McClurkin, Optican, Richmond, and Gawne, Science 253: 675, 1991) to the measurements of the spatiotemporal receptive fields of neurons within the lateral geniculate of primate. 2. We analyze both new and previously described magnocellular and parvocellular single units. The spatiotemporal impulse response function of the unit, defined as the time-resolved average firing rate in response to a weak stimulus flashed at a given location and time, is characterized by the singular value decomposition. This analysis allows one to represent the impulse response by a small number, two to three, of spatial and temporal modes. Both magnocellular and parvocellular units are weakly nonseparable, with major and minor modes that account, respectively, for approximately 78 and 22% of the response. The major temporal mode for both types is essentially identical for the first 100 ms. At later times the response of magnocellular units changes sign and decays slowly, whereas the response of parvocellular units decays relatively rapidly. 3. The spatiotemporal impulse response function completely determines the response of a unit to an arbitrary stimulus when linear response theory is valid. Using the measured impulse response, combined with a rectifying neuronal input-output relation, we calculate the responses to a complete set of spatial luminance patterns constructed of "Walsh" functions. Our predicted temporal responses are in qualitative agreement with those reported for parvocellular units (McClurkin, Optican, Richmond, and Gawne, J. Neurophysiol. 66: 794, 1991). Under the additional assumptions of Poisson statistics for the probability of spiking and a plausible background firing rate, we predict the performance of a unit in the Walsh pattern discrimination task as quantified by mutual information. Our prediction is again consistent with the reported results. 4. Last, we consider the issue of temporal coding within linear response. For stimuli presented for fixed time intervals, the singular value decomposition provides a natural relation between the temporal modes of the neuronal response and the spatial pattern of the stimulus. Although it is tempting to interpret each temporal mode as an independent channel that encodes orthogonal features of the stimulus, successively higher order modes are increasingly unreliable and do not significantly increase the discrimination capabilities of the unit.

Synchronization properties of spindle oscillations in a thalamic reticular nucleus model

Pages 1109–1126: D. Golomb, X.-J. Wang, and J. Rinzel. “Synchronization properties of spindle oscillations in a thalamic reticular nucleus model.” The following errors were inadvertently introduced when this article was printed. Page 1125, in the list of references, all the journal titles written as Physiol. Rev. should be Phys. Rev., and all the journal titles written as Physiol. Rev. Lett. should be Phys. Rev. Lett.

Synchronization properties of spindle oscillations in a thalamic reticular nucleus model

1. We address the hypothesis of Steriade and colleagues that the thalamic reticular nucleus (RE) is a pacemaker for thalamocortical spindle oscillations by developing and analyzing a model of a large population of all-to-all coupled inhibitory RE neurons. 2. Each RE neuron has three ionic currents: a low-threshold T-type Ca2+ current (ICa-T), a calcium-activated potassium current (IAHP) and a leakage current (IL). ICa-T underlies a cell's postinhibitory rebound properties, whereas IAHP hyperpolarizes the neuron after a burst. Each neuron, which is a conditional oscillator, is coupled to all other RE neurons via fast gamma-aminobutyric acid-A (GABAA) and slow GABAB synapses. 3. For generating network oscillations IAHP may not be necessary. Synaptic inhibition can provide the hyperpolarization for deinactivating ICa-T that causes bursting if the reversal potentials for GABAA and GABAB synapses are sufficiently negative. 4. If model neurons display sufficiently powerful rebound excitability, an isolated RE network of such neurons oscillates with partial but typically not full synchrony. The neurons spontaneously segregate themselves into several macroscopic clusters. The neurons within a cluster follow the same time course, but the clusters oscillate differently from one another. In addition to activity patterns in which clusters burst sequentially (e.g., 2 or 3 clusters bursting alternately), a two-cluster state may occur with one cluster active and one quiescent. Because the neurons are all-to-all coupled, the cluster states do not have any spatial structure. 5. We have explored the sensitivity of such partially synchronized patterns to heterogeneity in cells' intrinsic properties and to simulated neuroelectric noise. Although either precludes precise clustering, modest levels of heterogeneity or noise lead to approximate clustering of active cells. The population-averaged voltage may oscillate almost regularly but individual cells burst at nearly every second cycle or less frequently. The active-quiescent state is not robust at all to heterogeneity or noise. Total asynchrony is observed when heterogeneity or noise is too large, e.g., even at 25% heterogeneity for our reference set of parameter values. 6. The fast GABAA inhibition (with a reversal potential more negative than, say, -65 mV) favors the cluster states and prevents full synchrony. Our simulation results suggest two mechanisms that can fully synchronize the isolated RE network model. With GABAA removed or almost totally blocked, GABAB inhibition (because it is slow) can lead to full synchrony, which is partially robust to heterogeneity and noise.(ABSTRACT TRUNCATED AT 400 WORDS)

Corrigenda for Synchronization properties of spindle oscillations in a thalamic reticular nucleus model

Pages 1109–1126: D. Golomb, X.-J. Wang, and J. Rinzel, “Synchronization properties of spindle oscillations in a thalamic reticular nucleus model.” The following errors were inadvertently introduced when this article was printed. Page 1125, in the list of references, all the journal titles written as Physiol. Rev. should be Phys. Rev., and all the journal titles written as Physiol. Rev. Lett. should be Phys. Rev. Lett.

Radial head and neck fractures in children

This report is a review of long-term results of 42 consecutive fractures of the neck of the radius in children. More than half the patients were followed for greater than 4 years. The results were assessed clinically and radiologically at 6 months and at review. Twenty-seven children (64%) had a good result, 2 (5%) had a fair result, and 13 (31%) had a poor result. Primary angulation was the most important factor affecting the results. Periarticular ossification, avascular necrosis, enlargement of the radial head and of the proximal end of the radius were the most important causes of poor results. Unlike other fractures with unpredictable results, more accurate reduction is mandatory to improve the final outcome.