Climate-driven variability of the Southern Ocean CO2 sink

The Southern Ocean is a major sink of atmospheric CO2, but the nature and magnitude of its variability remains uncertain and debated. Estimates based on observations suggest substantial variability that is not reproduced by process-based ocean models, with increasingly divergent estimates over the past decade. We examine potential constraints on the nature and magnitude of climate-driven variability of the Southern Ocean CO2 sink from observation-based air-sea O2 fluxes. On interannual time scales, the variability in the air-sea fluxes of CO2 and O2 estimated from observations is consistent across the two species and positively correlated with the variability simulated by ocean models. Our analysis suggests that variations in ocean ventilation related to the Southern Annular Mode are responsible for this interannual variability. On decadal time scales, the existence of significant variability in the air-sea CO2 flux estimated from observations also tends to be supported by observation-based estimates of O2 flux variability. However, the large decadal variability in air-sea CO2 flux is absent from ocean models. Our analysis suggests that issues in representing the balance between the thermal and non-thermal components of the CO2 sink and/or insufficient variability in mode water formation might contribute to the lack of decadal variability in the current generation of ocean models. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

Major Outcomes With Personalized Dialysate TEMPerature (MyTEMP): Rationale and Design of a Pragmatic, Registry-Based, Cluster Randomized Controlled Trial

BACKGROUND

Small randomized trials demonstrated that a lower compared with higher dialysate temperature reduced the average drop in intradialytic blood pressure. Some observational studies demonstrated that a lower compared with higher dialysate temperature was associated with a lower risk of all-cause mortality and cardiovascular mortality. There is now the need for a large randomized trial that compares the effect of a low vs high dialysate temperature on major cardiovascular outcomes.

OBJECTIVE

The purpose of this study is to test the effect of outpatient hemodialysis centers randomized to (1) a personalized temperature-reduced dialysate protocol or (2) a standard-temperature dialysate protocol for 4 years on cardiovascular-related death and hospitalizations.

DESIGN

The design of the study is a pragmatic, registry-based, open-label, cluster randomized controlled trial.

SETTING

Hemodialysis centers in Ontario, Canada, were randomized on February 1, 2017, for a trial start date of April 3, 2017, and end date of March 31, 2021.

PARTICIPANTS

In total, 84 hemodialysis centers will care for approximately 15 500 patients and provide over 4 million dialysis sessions over a 4-year follow-up.

INTERVENTION

Hemodialysis centers were randomized (1:1) to provide (1) a personalized temperature-reduced dialysate protocol or (2) a standard-temperature dialysate protocol of 36.5°C. For the personalized protocol, nurses set the dialysate temperature between 0.5°C and 0.9°C below the patient's predialysis body temperature for each dialysis session, to a minimum dialysate temperature of 35.5°C.

PRIMARY OUTCOME

A composite of cardiovascular-related death or major cardiovascular-related hospitalization (a hospital admission with myocardial infarction, congestive heart failure, or ischemic stroke) captured in Ontario health care administrative databases.

PLANNED PRIMARY ANALYSIS

The primary analysis will follow an intent-to-treat approach. The hazard ratio of time-to-first event will be estimated from a Cox model. Within-center correlation will be considered using a robust sandwich estimator. Observation time will be censored on the trial end date or when patients die from a noncardiovascular event.

TRIAL REGISTRATION

www.clinicaltrials.gov; identifier: NCT02628366.

Prevalence of Pre-pregnancy Obesity, 2011-2014

IMPORTANCE

Obesity before and during pregnancy increases risk among mothers for poor health outcomes, such as diabetes, high blood pressure, and cardiovascular disease.

OBJECTIVE

To describe trends in pre-pregnancy obesity rates among women in Wisconsin.

METHODS

Cross-sectional data from Wisconsin birth certificates were analyzed. Prevalence of pre-pregnancy obesity (defined as body mass index ≥ 30) among Wisconsin women who gave birth from 2011 through 2014 was compared across demographic and geographic dimensions.

RESULTS

Overall, 27.8% of Wisconsin women who gave birth during 2011-2014 were obese. Obesity rates were highest among 40- to 44-year-old women (31.8%), women with a high school/ GED diploma (32.8 %), American Indian/Alaska Native women (43.9%), and women with 5 or more pregnancies (35.4%). Obesity rates varied by county of residence (highest in Forest County, 45.2%) and city of residence (highest in the city of Racine, 34.8%).

CONCLUSIONS

There are significant socioeconomic, racial, and geographic disparities in pre-pregnancy obesity among women who give birth in Wisconsin.

Use of withdrawal (coitus interruptus) for both pregnancy and HIV prevention among young adults in Rakai, Uganda

INTRODUCTION

Although understudied in the context of AIDS, use of withdrawal (coitus interruptus) with or in place of other prevention methods affects exposure to both pregnancy and human immunodeficiency virus (HIV).

AIM

We used mixed methods to assess use of withdrawal among 15-24-year-olds in a rural Ugandan setting with considerable HIV prevalence.

METHODS

We measured withdrawal reporting among (i) sexually active 15-24-year-olds enrolled in a quantitative community survey (n = 6,722) and (ii) in-depth qualitative interview participants systematically selected from the latest round of the community survey (N = 60). Respondents were asked about family planning and HIV prevention practices, including a direct question about withdrawal in the in-depth interviews.

MAIN OUTCOME MEASURES

The main outcome measures were reports of current use of withdrawal on the quantitative survey (general question about family planning methods) and reports of current or recent use withdrawal in qualitative interviews (specific question about withdrawal). Qualitative interviews also probed for factors associated with withdrawal use.

RESULTS

Although less than 1% of quantitative survey participants spontaneously named withdrawal as their current family planning method, 48% of qualitative interview respondents reported current or lifetime use of withdrawal. Withdrawal was often used as a pleasurable alternative to condoms, when condoms were not available, and/or as a "placeholder" method before obtaining injectable contraception. A few respondents described using withdrawal to reduce HIV risk.

CONCLUSION

Qualitative findings revealed widespread withdrawal use among young adults in Rakai, mainly as a condom alternative. Thus, withdrawal may shape exposure to both pregnancy and HIV. Future behavioral surveys should assess withdrawal practices directly--and separately from other contraceptives and HIV prevention methods. Further clinical research should further document withdrawal's association with HIV risk.

Liver-kidney transplantation in primary hyperoxaluria type-1: case report and literature review

Primary hyperoxaluria type-1 (PH1) is a rare inherited autosomal recessive disorder in which a deficiency of the hepatic enzyme alanine-glyoxylate aminotransferase leads to endogenous oxalate overproduction, renal failure, systemic oxalate deposition and death. As hemodialysis provides insufficient oxalate clearance, patients ultimately require both liver and kidney transplantation for correction of the metabolic abnormality and oxalate excretion. Herein, we describe a young adult male with end-stage renal disease and systemic oxalosis causing progressive disabling multi-organ dysfunction while awaiting transplantation. We review the literature regarding liver-kidney transplantation and suggest that for patients with PH1, a standardized assessment of organ dysfunction and functional impairment may improve identification of patients requiring urgent transplantation thereby reducing the morbidity and mortality that can occur with delayed transplantation.

Immunosuppression without calcineurin inhibition: optimization of renal function in expanded criteria donor renal transplantation

INTRODUCTION

To assess the efficacy of calcineurin inhibitor (CNI)-free immunosuppression vs. calcineurin-based immunosuppression in patients receiving expanded criteria donor (ECD) kidneys.

PATIENT AND METHODS

Thirteen recipients of ECD kidneys were enrolled in this pilot study and treated with induction therapy and maintained on sirolimus, mycophenolate mofetil (MMF) and prednisone. A contemporaneous control group was randomly selected comprised of 13 recipients of ECD kidneys who had been maintained on CNI plus MMF and prednisone.

RESULTS

For the study group vs. the control group, two-yr graft survival was 92.3% vs. 84.6% (p = NS), two-yr patient survival was 100% vs. 92.3% (p = NS) and the acute rejection rates were 23% vs. 31% (p = NS), respectively. Renal function was significantly better in the study group compared with control up to the six-month mark, after which, it remained numerically but not statistically significant. Complications were more common in the study group, but serious adverse events requiring discontinuation were rare.

CONCLUSION

This pilot study demonstrates that CNI-free regimens can be safely implemented in patients receiving ECD kidneys with excellent two-yr patient and graft survival and good renal allograft function. Longer follow-up in larger randomized controlled trials are necessary to establish these findings.

Can standardized patients replace physicians as OSCE examiners?

BACKGROUND

To reduce inter-rater variability in evaluations and the demand on physician time, standardized patients (SP) are being used as examiners in OSCEs. There is concern that SP have insufficient training to provide valid evaluation of student competence and/or provide feedback on clinical skills. It is also unknown if SP ratings predict student competence in other areas. The objectives of this study were: to examine student attitudes towards SP examiners; to compare SP and physician evaluations of competence; and to compare predictive validity of these scores, using performance on the multiple choice questions examination (MCQE) as the outcome variable.

METHODS

This was a cross-sectional study of third-year medical students undergoing an OSCE during the Internal Medicine clerkship rotation. Fifty-two students rotated through 8 stations (6 physician, 2 SP examiners). Statistical tests used were Pearson's correlation coefficient, two-sample t-test, effect size calculation, and multiple linear regression.

RESULTS

Most students reported that SP stations were less stressful, that SP were as good as physicians in giving feedback, and that SP were sufficiently trained to judge clinical skills. SP scored students higher than physicians (mean 90.4% +/- 8.9 vs. 82.2% +/- 3.7, d = 1.5, p < 0.001) and there was a weak correlation between the SP and physician scores (coefficient 0.4, p = 0.003). Physician scores were predictive of summative MCQE scores (regression coefficient = 0.88 [0.15, 1.61], P = 0.019) but there was no relationship between SP scores and summative MCQE scores (regression coefficient = -0.23, P = 0.133).

CONCLUSION

These results suggest that SP examiners are acceptable to medical students, SP rate students higher than physicians and, unlike physician scores, SP scores are not related to other measures of competence.

Loyalty or liability?

While many of your employees are likely to be an asset to your practice, some "loyal" employees aren't always what they seem. This article offers guidelines for physicians to guard against "loyalty" becoming a liability that hurts you, your staff, and your practice.

Pressor responses in rats following intravenous dynorphin A(1-13) administration are blocked by AVP-V1 receptor antagonism

Hemodynamic (blood pressure and heart rate) experiments were conducted in conscious and/or anesthetized male Sprague-Dawley (S.D.), heterozygous and homozygous Brattleboro rats given intravenous (iv) dynorphin A(1-13), arginine vasopressin (AVP), norepinephrine (HCl, (NE) or sterile saline before and 10 min after an iv bolus injection of a specific receptor antagonist. These receptor blockers (kappa receptor antagonist Mr2266, alpha adrenoceptor antagonist phentolamine HCl or the AVP-V1 receptor antagonist d(CH2)5Tyr-(Me)AVP were given in equimolar concentrations (15 nmol/kg iv). In all conscious S.D. groups, iv injection of AVP (60 pmol/kg), NE (12.5 nmol/kg) and dynorphin A(1-13) (60 nmol/kg) evoked significant increases in mean arterial pressure (MAP) associated with concomitant bradycardia. The hemodynamic responses to 'both' AVP and dynorphin A(1-13) were blocked if given subsequent to AVP-V1 administration but not following phentolamine or Mr2266 pretreatment. The pressor and bradycardic responses of conscious heterozygous and homozygous Brattleboro rats after iv AVP or dynorphin again were only blocked by the AVP-V1 receptor antagonist. Anesthetized heterozygous and homozygous Brattleboro rats again showed pressor responses following iv AVP, NE or dynorphin A(1-13) but with slight or no associated bradycardia. The rise in blood pressure with AVP 'and' dynorphin A(1-13) in these groups also was only blocked by the d(CH2)5Tyr(Me)AVP antagonist. The results indicate that the pressor responses of rats given intravenous dynorphin A(1-13) involve the interaction of AVP-V1 receptors and suggest a functional interaction of these two neuropeptides in the modulation of vascular tone.

Brown adipose tissue thermogenesis is activated by electrical and chemical (L-glutamate) stimulation of the ventromedial hypothalamic nucleus in cold-acclimated rats

Experiments were conducted to determine if both electrical and chemical stimulation of the ventromedial hypothalamic nucleus (VMH) could activate brown adipose tissue (BAT) thermogenesis. Age-matched, room-acclimated (21 degrees C) and cold-acclimated (4 degrees C for 3 weeks prior to testing) male Sprague-Dawley rats were given unilateral electrical or chemical stimulation to the VMH by way of a 'chemotrode apparatus'. The devised 'chemotrode' allowed both electrical stimulation (insulated piano wire stimulating electrode) and chemical stimulation (23 gauge stainless steel intracranial cannula of equal length) to be performed at the same VMH site using a common 19 gauge stainless steel outer guide tube. The first unilateral VMH electrical stimulation (0.5 ms pulse, 50 Hz and 120 microA for 30 s) caused no significant rise in interscapular brown adipose tissue temperature (TIBAT) colonic (Tc) or tail surface temperatures (Tt), compared to respective prestimulation control values in rats acclimated to 21 degrees C. In the 4 degrees C-acclimated group the first VMH electrical stimulation caused a significant rise in IBAT temperature. L-Glutamate administration to the same VMH site (60 nmol in 600 nl volume) also caused a significant increase in IBAT temperature in the 4 degrees C but not the 21 degrees C-acclimated rats. The rise in IBAT temperature following the L-glutamate injection to the 4 degrees C-acclimated group was similar to that found following the first electrical stimulation to this group. Interestingly, a second unilateral electrical stimulation of the VMH to 4 degrees C-acclimated rats could not evoke a similar increase in IBAT temperature suggesting that overall L-glutamate was acting in vivo as an excitotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Naloxone's effect on the inotropic and chronotropic responses of isolated, electrically stimulated or spontaneously beating rat atria

Experiments were conducted to determine (i) how naloxone administration alone could modify the inotropic (in electrically stimulated (ES) rat atria) and both the inotropic and chronotropic responses (in spontaneously beating (SB) rat atria) isolated from normotensive and hypotensive (hemorrhaged) rats, and (ii) how naloxone administration would modify the inotropic and chronotropic responses of isolated rat atria previously administered an opiate agonist (morphine), a muscarinic agonist (carbachol), or an alpha- and beta-adrenergic agonist (noradrenaline). Naloxone (51-340 microM) added to ES atria caused a delayed but dose-related decrease in atrial tension (AT), whereas in SB atria, naloxone caused atrial heart rate (AHR) to fall and atrial tension (AT) to increase. Naloxone (68-340 microM), given to SB atria from acutely hypotensive rats, caused a similar increase in atrial tension as seen in the "normotensive" isolated (SB) atria and a similar decrease in atrial heart rate. Morphine sulphate (MS), 37-375 microM, administered to ES atria caused a delayed fall in AT; which was further decreased when naloxone (340 microM) was also added. In the SB atria, morphine caused a dose-related decrease in atrial heart rate whereas atrial tension increased. In SB preparations, atrial heart rate fell even further when naloxone was added to morphine compared with when morphine sulphate was given alone, whereas atrial tension was increased. Noradrenaline (3 or 12 microM) caused a positive, dose-related inotropic response in the ES atria, effects not influenced by the addition of naloxone. In the SB atria, naloxone caused no change in the dose-related increases in atrial tension and heart rate when combined with the lower dose of noradrenaline but decreased AT when combined with 12 microM noradrenaline, compared with when this dose of noradrenaline was given alone. Carbachol (683 nM-1.37 microM) caused a dose-related decrease in atrial tension in ES atria, which was reversed completely by the addition of naloxone. In SB atria, carbachol decreased both atrial tension and heart rate, and with the addition of naloxone (340 microM), a further slight drop in atrial heart rate occurred, but concurrently, a marked rise in atrial tension was observed. The results indicate that naloxone can act with receptors directly within atrial tissue to cause changes in atrial tension and heart rate. The comparable delayed responses of morphine and naloxone suggest their effects are mediated by nonopiate receptors which, in time, cause decreases in calcium influx into the atria.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrathecal dynorphin A administration causes pressor responses in rats associated with an increased resistance to spinal cord blood flow

Hemodynamic responses (blood pressure, as well as cardiac output (CO), peripheral and CNS blood flow changes measured via radioactive microspheres) were analyzed in anesthetized rats 2 min following intrathecal (IT) administration (10 microliters) of either 5-ion control solution or 20 nmol of dynorphin A(1-13) into the lower thoracic space (T10-T12). Mean arterial pressure (MAP) significantly increased within 2 min following IT dynorphin A(1-13) due to rise in total peripheral resistance, whereas CO significantly declined. Two minutes post-IT-dynorphin A(1-13) administration spinal cord blood flow also significantly decreased for 2 cm anterior and 1 cm posterior from the tip of the spinal catheter, which reflected a significant elevation in tissue flow resistance of spinal cord vessels in spite of the reduction of CO. As well, tissue blood flow resistance was also increased at this time in the kidneys and adrenal glands. The results indicate that within 2 min after intrathecal dynorphin A(1-13) administration an acute increase in blood flow resistance of spinal cord vessels around the tip of the spinal catheter occurs, at a time when the animal is also hypertensive. It is suggested that the associated pressor response may, in part, be caused by dynorphin A evoking localized ischemia.

Intravenous morphine infusion (IMF) to drug-naive, conscious rats evokes bradycardic, hypotensive effects, but pressor actions are elicited after IMF to rats previously given morphine

Hemodynamic (blood pressure and heart rate) responses of conscious drug-naive rats were studied following intravenous (i.v.) infusion of sterile saline, morphine sulphate, and then naloxone hydrochloride, as well as of other groups previously injected with morphine sulphate. Those groups chronically given morphine sulphate received twice daily injections of morphine sulphate (5 mg/kg, s.c. per injection) for 3 or 6 days before testing with the i.v. infusion of morphine sulphate. Drugs were infused (135 microL/min) through an indwelling femoral venous catheter via a Harvard infusion pump, and blood pressure was recorded from the abdominal aorta via a femoral arterial catheter. Other pretreatment studies were done to determine the receptor mechanisms mediating the blood pressure responses of drug-naive and chronic morphine-treated rats, whereby equimolar doses (0.32 mumol) of specific receptor antagonists were given as a bolus i.v. injection 5 min after saline but before subsequent infusion with morphine sulphate. Intravenous infusion of morphine sulphate (7.5 mg/kg total over 15 min) to drug-native rats caused a transient but precipitous fall in mean arterial pressure and mean heart rate with an associated rise in mean pulse pressure; these effects were blocked in other groups pretreated with atropine. Interestingly, however, rats chronically injected with morphine sulphate for 3 days previously evoked a transient pressor response when subsequently infused i.v. with morphine sulphate, actions that were blocked in other groups when pretreated i.v. with 0.32 mumol of phentolamine, yohimbine, prazosin, or guanethidine. A greater and persistent pressor response occurred following morphine infusion to groups of rats previously injected over 6 days with morphine sulphate, which was associated with tachycardia during the later stages of the 15-min morphine sulphate infusion period. The prolonged pressor and tachycardic responses of this 6-day chronically injected group were completely blocked in another group pretreated i.v. with both phentolamine and propranolol (0.32 mumol). The results suggest that morphine sulphate infusion to conscious, drug-naive rats evokes classical hypotensive effects due to decreases in mean heart rate caused by activation of parasympathetic vagal activity. With 3 or 6 days of chronic morphine sulphate administration beforehand, subsequent i.v. infusion of morphine sulphate evoked pressor actions felt to be caused by a progressive activation of the sympathetic nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)

Opiate and alpha receptor antagonists block the pressor responses of conscious rats given intravenous dynorphin

Conscious, unrestrained rats were used to determine the hemodynamic (blood pressure and heart rate) responses following intravenous (IV) injection of dynorphin A(1-13) and the possible receptor mechanisms mediating those changes. Male Sprague-Dawley rats (300 g) were given IV bolus injections (via femoral venous catheter) of 6.0 to 600 nmoles/kg of dynorphin A(1-13), 8.0 nmoles/kg of norepinephrine HCl (NE), 14.3 pmoles/kg of angiotensin II or a vehicle control solution. Blood pressure (BP) and heart rate (HR) were monitored via femoral arterial catheter (into abdominal aorta) over 90 sec postpeptide or -amine administration before and 10 min after IV injection of 4.2 mumoles/kg of naloxone HCl (opiate antagonist), yohimbine HCl (alpha 2 receptor antagonist) or prazosin HCl (alpha 1 receptor antagonist). Dynorphin A(1-13) caused a transient but dose-related rise in mean arterial pressure (MAP) whereas mean pulse pressures (MPP) and mean heart rates (MHR) concomitantly fell, from preinjection control values in a dose-dependent fashion. Pretreatment with naloxone blocked the pressor response of only a subsequent injection with 20 nmoles/kg but not 60 nmoles/kg of dynorphin A or NE (8.0 nmoles/kg). Pretreatment with yohimbine suppressed the marked pressor responses of subsequent NE or Dyn A (60 nmoles/kg) administration whereas prazosin antagonized the rise in MAP of only the lower doses of dynorphin as well as NE. The suppression of the pressor responses of dynorphin by opiate or alpha receptor antagonists were not caused by tachyphylaxis for repeated injections of 6.0 or 60 nmoles/kg of dynorphin caused the same rise in MAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Pressor effects of systemic administration of methionine and leucine enkephalin in the conscious rat

Experiments were designed using conscious Sprague-Dawley rats to determine the blood pressure (BP) and heart rate (HR) responses to intravenous doses of (1) the adrenal catecholamines noradrenaline (NA) and adrenaline (A), (2) adrenal pentapeptides methionine enkephalin (ME) and leucine enkephalin (LE), (3) combination (i.v.) injections of both ME or LE with NA or A that modulate the hemodynamic responses when the adrenal catecholamines were given alone, and (4) the possible receptor mechanisms mediating the resultant BP and HR response to i.v. pentapeptide administration. NA (0.48 and 2.4 nmol) and A (0.3 and 1.5 nmol) given i.v. evoked potent, dose-related pressor responses associated with reflex bradycardia. ME and LE (1.6 - 48 nmol) elicited transient (10-20 s) increases in mean arterial pressure (MAP), which was associated either with no change in mean heart rate (MHR), such as ME, or with slight bradycardia (i.e., LE). Combining ME or LE (16 nmol) with NA (2.4 nmol) or A (0.3 or 1.5 nmol) did not change MAP and MHR from when these respective doses of NA or A were given alone. However, 16 nmol of ME or LE with a low dose of NA (0.48 nmol) increased the pressor response compared with NA (0.48 nmol) given alone. Other experiments whereby specific receptor blockers (naloxone, diprenorphine, atropine, propranolol, phentolamine or guanethidine) were given i.v. 5 min before subsequent i.v. administration of LE or ME (16 nmol) indicated that only phentolamine or guanethidine could completely suppress the pressor responses of LE and ME. Naloxone and diprenorphine pretreatment attenuated the pressor response of LE but did not affect the BP response to ME.(ABSTRACT TRUNCATED AT 250 WORDS)