High levels of HIV drug resistance among adults failing second-line antiretroviral therapy in Namibia

To support optimal third-line antiretroviral therapy (ART) selection in Namibia, we investigated the prevalence of HIV drug resistance (HIVDR) at time of failure of second-line ART. A cross-sectional study was conducted between August 2016 and February 2017. HIV-infected people ≥15 years of age with confirmed virological failure while receiving ritonavir-boosted protease inhibitor (PI/r)-based second-line ART were identified at 15 high-volume ART clinics representing over >70% of the total population receiving second-line ART. HIVDR genotyping of dried blood spots obtained from these individuals was performed using standard population sequencing methods. The Stanford HIVDR algorithm was used to identify sequences with predicted resistance; genotypic susceptibility scores for potential third-line regimens were calculated. Two hundred thirty-eight individuals were enrolled; 57.6% were female. The median age and duration on PI/r-based ART at time of enrolment were 37 years and 3.46 years, respectively. 97.5% received lopinavir/ritonavir-based regimens. The prevalence of nucleoside reverse transcriptase inhibitor (NRTI), non-nucleoside reverse transcriptase inhibitor (NNRTI), and PI/r resistance was 50.6%, 63.1%, and 13.1%, respectively. No significant association was observed between HIVDR prevalence and age or sex. This study demonstrates high levels of NRTI and NNRTI resistance and moderate levels of PI resistance in people receiving PI/r-based second-line ART in Namibia. Findings underscore the need for objective and inexpensive measures of adherence to identify those in need of intensive adherence counselling, routine viral load monitoring to promptly detect virological failure, and HIVDR genotyping to optimize selection of third-line drugs in Namibia.

Health students' knowledge and infectious disease exposure: findings from a cross-sectional study in Namibia

BACKGROUND

Namibia has recently introduced a number of health training programmes that expose students to infectious disease risks such as human immunodeficiency virus (HIV) and tuberculosis (TB). We explored the knowledge of students in relation to HIV and TB and whether or not there was evidence of exposure.

METHODS

We conducted two cross-sectional surveys of Namibian health students (medicine and pharmacy) in 2018.

RESULTS

There was a strong association between knowledge and exposure to HIV, but not TB (i.e. explicit exposure versus latent). Regression analysis suggested the time-related risk (age/year of study) to be predictive of knowledge in both studies. The training rotation in the respiratory unit predicted TB knowledge and post-exposure prophylaxis predicted HIV knowledge.

CONCLUSIONS

Knowledge of TB and HIV appears mostly related to the duration of study in health students. Exposure or specific experience may enhance knowledge. Future training in infection control may be better focussed on improving knowledge in earlier years.

Health workforce planning in Namibia: assessing a pilot workforce survey of pharmacists

Background

Southern Africa lacks resources necessary to combat presenting health challenges. This crisis will likely be remedied through the in-country training of healthcare professionals, for example, in Namibia. Monitoring the workforce will be essential to inform planning in health services and training. A national pilot workforce survey in Namibia using a multi-modal sampling approach aimed to test methodology for describing the pharmacy workforce and quantifying preferences towards further training.

Methods

The survey tool included questions relating to socio-demographics, professional and practice aspects. A conjoint analysis approach was utilised to quantify preferences around study programme, modality of study and cost.

Key findings

Respondents (N = 135; ~20% response) represented a diverse range of individuals in various pharmacy sectors in Namibia. The majority of respondents reported female gender, private sector working, studying outside Namibia and societal group membership. Societal membership and pharmacy ownership – indicators of professional engagement – were associated with higher age; ownership was also associated with study outside Namibia and practice in community pharmacy. Regarding further study preferences, respondents placed more importance on study programme and modality over cost with the most preferred scenario being a 2-year full-time Masters programme in pharmaceutical industry/regulation by distance learning at the highest cost bracket.

Conclusions

This national survey sampled the population of pharmacists in Namibia exploring the composition of the profession and preferences towards training. Further work will validate the findings and provide ongoing monitoring of the pharmacy workforce that can be expanded to other professional groups over a larger geographical area.

The relationship between lay and technical views of Escherichia coli O157 risk

Here, we bring together and contrast lay (accessible primarily through social science methodologies) and technical (via risk assessment and epidemiological techniques) views of the risk associated with the Escherichia coli O157 pathogen using two case study areas in the Grampian region of Scotland, and North Wales. Epidemiological risk factors of contact with farm animals, visiting farms or farm fields and having a private water supply were associated with postcode districts of higher than average disease incidence in the human population. However, this was not the case for the epidemiological risk factor of consumption of beef burgers, which was independent of disease incidence in the postcode district of residence. The proportion of the population expressing a high knowledge of E. coli O157 was greatest in high-incidence disease districts compared with low-incidence areas (17% cf. 7%). This supports the hypothesis that in high-disease-incidence areas, residents are regularly exposed to information about the disease through local cases, the media, local social networks, etc. or perhaps that individuals are more likely to be motivated to find out about it. However, no statistically significant difference was found between high- and low-incidence postcode districts in terms of the proportion of the population expressing a high likelihood of personal risk of infection (10% cf. 14%), giving a counterintuitive difference between the technical (epidemiological and quantitative microbiological risk assessment (QMRA)) and the lay assessment of E. coli O157 risk. This suggests that lay evaluations of E. coli O157 risk reflect intuitive and experience-based estimates of the risk rather than probabilistic estimates. A generally strong correspondence was found in terms of the rank order given to potential infection pathways, with environment and foodborne infection routes dominating when comparing public understanding with technical modelling results. Two general conclusions follow from the work. First, that integrative research incorporating both lay and technical views of risk is required in order that informed decisions can be made to handle or treat the risk by the groups concerned (e.g. the public, policy makers/risk managers, etc.). Second, when communicating risk, for example, through education programmes, it is important that this process is two-way with risk managers (e.g. including Food Standards Agency officials and communications team, public health infection control and environmental health officers) both sharing information with the public and stakeholder groups, as well as incorporating public knowledge, values and context (e.g. geographical location) into risk-management decisions.

Computation models simulating notochordal cell extinction during early ageing of an intervertebral disc

Lower back pain due to intervertebral disc (IVD) degeneration is a prevalent problem which drastically affects the quality of life of millions of sufferers. Healthy IVDs begin with high populations of notochordal cells in the nucleus pulposus, while by the second stage of degeneration, these cells will be replaced by chondrocyte-like cells. Because the IVD is avascular, these cells rely on passive diffusion of nutrients to survive. It is thought that this transition in cell phenotype causes the shift of the IVD's physical properties, which impede the flow of nutrients. Our computational model of the IVD illustrates its ability to simulate the evolving chemical and mechanical environments occurring during the early ageing process. We demonstrate that, due to the insufficient nutrient supply and accompanying changes in physical properties of the IVD, there was a resultant exponential decay in the number of notochordal cells over time.

Investigation of the intervertebral disc and fused joint dynamics through experimental modal analysis and the receptance coupling method

Identification of intervertebral disc (IVD) dynamics is important in understanding the spine mechanism and behavior. This paper experimentally identifies the dynamics of the bovine caudal IVD using experimental modal analysis and the inverse receptance coupling method. Experimental modal analysis was performed on free-free mounted bovine caudal vertebrae joined by an IVD and a fused IVD joint. Shear, rotational, and axial dynamics of the joints are identified by curve fitting of the frequency response functions, and identifying the damping ratio, stiffness, and modal frequency in each axis. The identified dynamics are compared with the IVD joints with and without fusion. Results provide important insight into IVD dynamics and fused IVD dynamics. This method can be extended to identify human IVD joint dynamics.

Nitrite infusion in humans and nonhuman primates: endocrine effects, pharmacokinetics, and tolerance formation

BACKGROUND

The recent discovery that nitrite is an intrinsic vasodilator and signaling molecule at near-physiological concentrations has raised the possibility that nitrite contributes to hypoxic vasodilation and to the bioactivity of nitroglycerin and mediates the cardiovascular protective effects of nitrate in the Mediterranean diet. However, important questions of potency, kinetics, mechanism of action, and possible induction of tolerance remain unanswered.

METHODS AND RESULTS

In the present study, we performed biochemical, physiological, and pharmacological studies using nitrite infusion protocols in 20 normal human volunteers and in nonhuman primates to answer these questions, and we specifically tested 3 proposed mechanisms of bioactivation: reduction to nitric oxide by xanthine oxidoreductase, nonenzymatic disproportionation, and reduction by deoxyhemoglobin. We found that (1) nitrite is a relatively potent and fast vasodilator at near-physiological concentrations; (2) nitrite functions as an endocrine reservoir of nitric oxide, producing remote vasodilation during first-pass perfusion of the opposite limb; (3) nitrite is reduced to nitric oxide by intravascular reactions with hemoglobin and with intravascular reductants (ie, ascorbate); (4) inhibition of xanthine oxidoreductase with oxypurinol does not inhibit nitrite-dependent vasodilation but potentiates it; and (5) nitrite does not induce tolerance as observed with the organic nitrates.

CONCLUSIONS

We propose that nitrite functions as a physiological regulator of vascular function and endocrine nitric oxide homeostasis and suggest that it is an active metabolite of the organic nitrates that can be used therapeutically to bypass enzymatic tolerance.

A novel method of measuring reduction of nitrite-induced methemoglobin applied to fetal and adult blood of humans and sheep

The reaction of nitrite with deoxyhemoglobin results in the production of nitric oxide and methemoglobin, a reaction recently proposed as an important oxygen-sensitive source of vasoactive nitric oxide during hypoxic and anoxic stress, with several animal studies suggesting that nitrite may have therapeutic potential. Accumulation of toxic levels of methemoglobin is suppressed by reductase enzymes present within the erythrocyte. Using a novel method of measuring methemoglobin reductase activity in intact erythrocytes, we compared fetal and adult sheep and human blood. After nitrite-induced production of 20% methemoglobin, the blood was equilibrated with carbon monoxide, which effectively stopped further production. Methemoglobin disappearance was first order in nature with specific rate constants (k x 1,000) of 12.9 +/- 1.3 min(-1) for fetal sheep, 5.88 +/- 0.26 min(-1) for adult sheep, 4.27 +/- 0.34 for adult humans, and 3.30 +/- 0.15 for newborn cord blood, all statistically different from one another. The effects of oxygen tensions, pH, hemolysis, and methylene blue are reported. Studies of temperature dependence indicated an activation energy of 8,620 +/- 1,060 calories/mol (2.06 kJ/mol), appreciably higher than would be characteristic of processes limited by passive membrane diffusion. In conclusion, the novel methodology permits absolute quantification of the reduction of nitrite-induced methemoglobin in whole blood.

Hemodynamic and functional assessment of patients with sickle cell disease and pulmonary hypertension

RATIONALE

Although pulmonary hypertension (PH) is a common complication of sickle cell disease (SCD) associated with high mortality, there exist few data characterizing hemodynamics and cardiopulmonary function in this population.

OBJECTIVES

To characterize hemodynamics and cardiopulmonary function in patients with SCD with and without PH.

METHODS

Patients with SCD with PH (n = 26) were compared with control subjects with SCD but without PH (n = 17), matched for age, hemoglobin levels, and fetal hemoglobin levels.

MEASUREMENTS AND MAIN RESULTS

Upon catheterization, 54% of the patients with PH had pulmonary arterial hypertension, and 46% had pulmonary venous hypertension. When compared with control subjects, patients with PH exhibited lower six-minute-walk distance (435 +/- 31 vs. 320 +/- 20 m, p = 0.002) and oxygen consumption (50 +/- 3% vs. 41 +/- 2% of predicted, p = 0.02), and also had mild restrictive lung disease and more perfusion abnormalities on radionuclide lung scans. The six-minute-walk distance in this population inversely correlated with tricuspid regurgitant jet velocity (r = -0.55, p < 0.001), and mean pulmonary artery pressure (r = -0.57, p < 0.001), and directly correlated with maximal oxygen consumption (r = 0.49, p = 0.004), even after adjustment for hemoglobin, supporting an independent contribution of increasing pulmonary artery pressures to loss of exercise capacity.

CONCLUSIONS

Patients with SCD-associated PH have both pulmonary arterial and venous PH associated with severe limitations in exercise capacity, likely compounded by interstitial lung fibrosis and severe anemia. These data support the use of the six-minute-walk distance as an index of PH and cardiopulmonary function in patients with SCD.

Role of prostanoids in the regulation of cerebral blood flow during normoxia and hypoxia in the fetal sheep

The fetal cardiovascular responses to hypoxia include decreased peripheral blood flow and increased cerebral, cardiac, and adrenal blood flow. Prostanoids, metabolites of cyclooxygenase enzyme activity, have potent effects on vascular tone in both the adult and the fetus. To examine the role of prostanoids in the regulation of fetal cerebral blood flow (CBF) during acute hypoxic stress, eight near term fetal sheep were studied after infusing vehicle or diclofenac, a cyclooxygenase inhibitor, followed by a 30-min period of hypoxia (arterial Po(2) 12 Torr). In the control experiments, CBF, measured continuously with laser Doppler flowmetry, increased to 148% of baseline values (p < 0.01) and cerebral vascular resistance decreased to 70% of baseline values after 30 min of hypoxic stress. During diclofenac infusion, hypoxia resulted in a CBF increase to only 129% of baseline, a significant attenuation (p < 0.05), accompanied by decreased plasma prostanoid concentrations. Increases in mean arterial blood pressure during hypoxia were also attenuated by diclofenac infusion. Flow and pressure responses were not accompanied by changes in cerebral vascular resistance. These results indicate that prostanoids indirectly modulate fetal CBF responses to hypoxia, but that their effects are mediated through modulation of systemic rather than cerebral vascular tone.

The measurement of blood and plasma nitrite by chemiluminescence: pitfalls and solutions

There are a number of difficulties involved in the quantification of nitrite in biological systems. These difficulties result from oxidation of nitrite (within minutes) by heme proteins, such as hemoglobin, myoglobin, cytoglobin, and neuroglobin; its low levels in vivo; and its ubiquitous presence in laboratory buffers and glassware. The goal of this review is to present an assay suitable for the sensitive and specific measurement of intravascular nitrite in mammals using the chemiluminescence-based nitric oxide analyzer and to inform the reader on how to evade the pitfalls pertinent to nitrite determination in biological matrices.

The anion gap does not accurately screen for lactic acidosis in emergency department patients

INTRODUCTION

Lactic acidosis portends a poor prognosis in trauma, sepsis, and other shock states and is useful for triaging and resuscitating emergency department (ED) patients. The authors sought to determine whether the AG is a reliable screen for lactic acidosis when applied specifically in the ED setting.

METHODS

The authors performed a retrospective cohort study over a seven month period. Subjects were all ED patients that had a serum lactate obtained. Sensitivity analyses of the AG for detecting presence of lactic acidosis were calculated for the traditional AG normal value (AG <12) and for the lower AG normal value when using newer ion selective electrode assays (AG <6).

RESULTS

Serum lactate levels were ordered in the ED on 440 occasions. 137 samples were excluded by protocol. Using an AG cutoff of 12, the sensitivity for detecting lactic acidosis was 58.2%, specificity was 81.0%, and the negative predictive value was 89.7%. Using the AG cutoff of 6, the sensitivity was 93.2%, the specificity was 17.3%, and the negative predictive value was 91.8%.

CONCLUSIONS

The traditional definition of AG >12 was insensitive for the presence of lactic acidosis. Using the revised AG of >6 is more sensitive but non-specific for lactic acidosis. The authors conclude that employing the AG as a screen for LA may be inappropriate in ED patients. Instead, they recommend ordering a serum lactate immediately upon suspicion of a shock state. A prospective study to confirm these findings is needed.

Post-hypoxic hypoperfusion is associated with suppression of cerebral metabolism and increased tissue oxygenation in near-term fetal sheep

Secondary cerebral hypoperfusion is common following perinatal hypoxia-ischaemia. However, it remains unclear whether this represents a true failure to provide sufficient oxygen and nutrients to tissues, or whether it is simply a consequence of reduced cerebral metabolic demand. We therefore examined the hypothesis that cerebral oxygenation would be reduced during hypoperfusion after severe asphyxia, and further, that the greater neural injury associated with blockade of the adenosine A(1) receptor during the insult would be associated with greater hypoperfusion and deoxygenation. Sixteen near-term fetal sheep received either vehicle or 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) for 1 h, followed by 10 min of severe asphyxia induced by complete occlusion of the umbilical cord. Infusions were discontinued at the end of the occlusion and data were analysed for the following 8 h. A transient, secondary fall in carotid artery blood flow and laser Doppler flow was seen from approximately 1-4 h after occlusion (P < 0.001), with no significant differences between vehicle and DPCPX. Changes in laser Doppler blood flow were highly correlated with carotid blood flow (r(2)= 0.81, P < 0.001). Cortical metabolism was suppressed, reaching a nadir 1 h after occlusion and then resolving. Cortical tissue P(O(2)) was significantly increased at 1, 2 and 3 h after occlusion compared to baseline, and inversely correlated with carotid blood flow (r(2)= 0.69, P < 0.001). In conclusion, contrary to our initial hypothesis, delayed posthypoxic hypoperfusion was associated with suppression of cerebral metabolism and increased tissue P(O(2)), and was not significantly affected by preceding adenosine A1 blockade. These data suggest that posthypoxic hypoperfusion is actively mediated and reflects suppressed cerebral metabolism.

Profound hypotension and associated electrocardiographic changes during prolonged cord occlusion in the near term fetal sheep

OBJECTIVE

To determine whether the onset of fetal hypotension during profound asphyxia is reflected by alterations in the ratio between the T height, measured from the level of the PQ interval, and the QRS amplitude (T/QRS ratio) and ST waveform.

STUDY DESIGN

Chronically instrumented near-term fetal sheep received complete occlusion of the umbilical cord for either 8 (n=6) or 15-min (n=9).

RESULTS

Cord occlusion led to sustained bradycardia and severe acidosis. Mean arterial blood pressure initially rose and then fell to a nadir of 32.6 +/- 2.6 mm Hg in the 8-min group and 9.3 +/- 1.0 mm Hg in the 15-min group (P < .001). The T/QRS ratio rose initially in parallel with mean arterial blood pressure and then reduced as mean arterial blood pressure fell but remained significantly above baseline. Biphasic ST waveforms during occlusion occurred in only 2 fetuses, but biphasic and negative waveforms occurred during reperfusion in the 15-min group, with a significant rise in troponin T levels (0.58 +/- 0.46 versus 0.02 +/- 0.01 ng/mL at 6 h, P < .01).

CONCLUSION

Elevation of the T/QRS ratio does not identify fetal hypotension during severe hypoxia, but abnormal waveforms in the recovery phase may indicate developing cardiac injury.

Cerebral oxygenation during postasphyxial seizures in near-term fetal sheep

After exposure to asphyxia, infants may develop both prolonged, clinically evident seizures and shorter, clinically silent seizures; however, their effect on cerebral tissue oxygenation is unclear. We therefore examined the hypothesis that the increase in oxygen delivery during postasphyxial seizures might be insufficient to meet the needs of increased metabolism, thus causing a fall in tissue oxygenation, in unanesthetized near-term fetal sheep in utero (gestational age 125+/-1 days). Fetuses were administered an infusion of the specific adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine, followed by 10 mins of asphyxia induced by complete umbilical cord occlusion. The fetuses then recovered for 3 days. Sixty-one episodes of electrophysiologically defined seizures were identified in five fetuses. Tissue PO(2) (tPO(2)) did not change significantly during short seizures (<3.5 mins), 5.2+/-0.2 versus baseline 5.6+/-0.1 mm Hg (NS), but fell to 2.2+/-0.2 mm Hg during seizures lasting more than 3.5 mins (P<0.001). During prolonged seizures, cortical blood flow did not begin to increase until tPO(2) had begun to fall, and then rose more slowly than the increase in metabolism, with a widening of the brain to blood temperature gradient. In conclusion, in the immature brain, during prolonged, but not short seizures, there is a transient mismatch between cerebral blood flow and metabolism leading to significant cerebral deoxygenation.

Erythrocytes are the major intravascular storage sites of nitrite in human blood

Plasma levels of nitrite ions have been used as an index of nitric oxide synthase (NOS) activity in vivo. Recent data suggest that nitrite is a potential intravascular repository for nitric oxide (NO), bioactivated by a nitrite reductase activity of deoxyhemoglobin. The precise levels and compartmentalization of nitrite within blood and erythrocytes have not been determined. Nitrite levels in whole blood and erythrocytes were determined using reductive chemiluminescence in conjunction with a ferricyanide-based hemoglobin oxidation assay to prevent nitrite destruction. This method yields sensitive and linear measurements of whole blood nitrite over 24 hours at room temperature. Nitrite levels measured in plasma, erythrocytes, and whole blood from 15 healthy volunteers were 121 plus or minus 9, 288 plus or minus 47, and 176 plus or minus 17 nM, indicating a surprisingly high concentration of nitrite within erythrocytes. The majority of nitrite in erythrocytes is located in the cytosol unbound to proteins. In humans, we found a significant artery-to-vein gradient of nitrite in whole blood and erythrocytes. Shear stress and acetylcholine-mediated stimulation of endothelial NOS significantly increased venous nitrite levels. These studies suggest a dynamic intravascular NO metabolism in which endothelial NOS-derived NO is stabilized as nitrite, transported by erythrocytes, and consumed during arterial-to-venous transit.

Absence of robust ischemic preconditioning by five 1-minute total umbilical cord occlusions in fetal sheep

OBJECTIVE

To determine to what extent a series of five 1-minute total umbilical cord occlusions, intended to induce ischemic preconditioning (IP), affects the physiologic responses to a 10-minute total umbilical cord occlusion (damaging insult [DI]) 1 hour later and provides cardio- and neuroprotection.

METHODS

In 14 chronically catheterized late gestation fetal sheep (127-131 days' gestation), we performed a 10-minute total umbilical cord occlusion (DI), preceded by a series of five 1-minute total cord occlusions with 2-minute intervals (5CO, n = 7) or sham occlusions (n = 7) 1 hour prior to DI.

RESULTS

The 5CO induced a reduction in the arterial partial pressure of oxygen (Po(2)) from 21 +/-1 to 14 +/-3 Torr, arterial O(2) content from 6.9 +/- 0.4 to 3.1 +/- 0.7 vol%, and increases in the partial pressure of carbon dioxide (Pco(2)) from 46 +/- 2 to 58 +/- 3 Torr, and [H(+)] from 43 +/- 1 to 54 +/- 2 nM. 5CO reduced fetal heart rate from 178 +/- 6 to 151 +/- 6 beats per minute (bpm), and increased arterial pressure from 45 +/- 1 to 57 +/- 2 mmHg, cerebral blood flow (CBF) from 100 +/- 3 to 129 +/- 10%, and cerebral heat production (H(brain)) from 25 +/- 2 to 29 +/- 1% degrees C. The responses to DI were not significantly different between the groups without and with 5CO; values for Po(2) were 5.6 +/- 1.5 and 5.8 +/- 1.9 Torr, O(2) content 0.6 +/- 0.1 and 0.8 +/- 0.1 vol%, lactate 10.7 +/- 0.7 and 10.8 +/- 0.7 mM, fetal heart rate 97 +/- 5 and 87 +/- 8 bpm, mean arterial pressure 22 +/- 3 and 21 +/- 2 mmHg, CBF 50 +/- 10 and 36 +/- 5%, and H(brain) 7.0 +/- 1.4 and 5.9 +/- 1.1% degrees C, respectively, except for Pco(2) (126 +/- 4 and 112 +/- 2 Torr) and [H(+)] (126 +/- 3 and 114 +/- 3 nM). Histologic proof of cardio- or neuroprotection by 5CO could not be obtained because five fetuses died before they were to be killed at day 3 after the experiment; two fetuses in the 5CO group demonstrated major histologic damage of myocardium and brain.

CONCLUSION

In the late gestation fetal sheep, a series of five 1-minute total umbilical cord occlusions did not result in major changes in physiologic responses to a hypoxic-ischemic DI 1 hour later. In addition, the procedure did not result in robust cardio- and neuroprotection, in contrast to IP reported in adults.

Inhaled nebulized nitrite is a hypoxia-sensitive NO-dependent selective pulmonary vasodilator

The blood anion nitrite contributes to hypoxic vasodilation through a heme-based, nitric oxide (NO)-generating reaction with deoxyhemoglobin and potentially other heme proteins. We hypothesized that this biochemical reaction could be harnessed for the treatment of neonatal pulmonary hypertension, an NO-deficient state characterized by pulmonary vasoconstriction, right-to-left shunt pathophysiology and systemic hypoxemia. To test this, we delivered inhaled sodium nitrite by aerosol to newborn lambs with hypoxic and normoxic pulmonary hypertension. Inhaled nitrite elicited a rapid and sustained reduction ( approximately 65%) in hypoxia-induced pulmonary hypertension, with a magnitude approaching that of the effects of 20 p.p.m. NO gas inhalation. This reduction was associated with the immediate appearance of NO in expiratory gas. Pulmonary vasodilation elicited by aerosolized nitrite was deoxyhemoglobin- and pH-dependent and was associated with increased blood levels of iron-nitrosyl-hemoglobin. Notably, from a therapeutic standpoint, short-term delivery of nitrite dissolved in saline through nebulization produced selective, sustained pulmonary vasodilation with no clinically significant increase in blood methemoglobin levels. These data support the concept that nitrite is a vasodilator acting through conversion to NO, a process coupled to hemoglobin deoxygenation and protonation, and evince a new, simple and inexpensive potential therapy for neonatal pulmonary hypertension.

Cerebral blood flow and oxygenation during venoarterial and venovenous extracorporeal membrane oxygenation in the newborn lamb

BACKGROUND

Concern exists that extracorporeal membrane oxygenation (ECMO) may decrease cerebral blood flow (CBF), impair cerebral autoregulation, and thereby increase the risk of neurologic injury.

OBJECTIVE

This study was undertaken in newborn lambs to compare the effects of initiation of venoarterial and venovenous ECMO on CBF and cerebral oxygen delivery as measured by laser-Doppler flowmetry. This study also evaluates the effects of carotid artery and jugular vein ligation on CBF.

DESIGN

CBF, arterial blood pressure, sagittal sinus pressure, heart rate, cardiac output, arterial blood gases, and hemoglobin saturation were measured. After anesthesia, instrumentation, and a 1-2 hr stabilization period, values were recorded during a 30-min control period, and the carotid artery or jugular vein was cannulated. The animals were then studied during venoarterial or venovenous ECMO for 1 hr.

MAIN RESULTS

Carotid ligation resulted in a transient decrease in right cortex CBF that resolved within 60 secs. Next, during a 60-min period of venoarterial ECMO (flow rate of 100 mL.min(-1).kg(-1), n = 11), cerebral resistance to flow increased, CBF decreased 25%, and cerebral oxygen delivery decreased by 30%. Native cardiac output and Paco(2) remained constant. Pulsatility in the lingual artery, representing the pulsatility of arterial flow to the brain, decreased throughout venoarterial ECMO. In contrast, in those lambs receiving ECMO in the venovenous mode (n = 7), resistance to flow, CBF, cerebral oxygen delivery, and pulsatility did not change.

CONCLUSIONS

There was no sustained decrease in CBF after ligation of either the carotid artery or jugular vein. Venoarterial but not venovenous ECMO induced decreases of CBF that could not be attributed to changes in blood gases or blood pressure but that may relate to diminished pulsatility in cerebral resistance vessels or to differences in levels of circulating vasoactive compounds.

Emerging role of nitrite in human biology

Nitric oxide (NO) plays a fundamental role in maintaining normal vascular function. NO is produced by endothelial cells and diffuses both into smooth muscle causing vasodilation and into the vessel lumen where the majority of this highly potent gas is rapidly inactivated by dioxygenation reaction with oxyhemoglobin to form nitrate. Diffusional barriers for NO around the erythrocyte and along the endothelium in laminar flowing blood reduce the inactivation reaction of NO by hemoglobin, allowing sufficient NO to escape for vasodilation and also to react in plasma and tissues to form nitrite anions (NO(2)(-)) and NO-modified peptides and proteins (RX-NO). Several recent studies have highlighted the importance of the nitrite anion in human biology. These studies have shown that measurement of plasma nitrite is a sensitive index of constitutive NO synthesis, suggesting that it may be useful as a marker of endothelial function. Additionally, recent evidence suggests that nitrite represents a circulating storage pool of NO and may selectively donate NO to hypoxic vascular beds. The conversion of nitrite to NO requires a reaction with a deoxygenated heme protein, suggesting a novel function of hemoglobin as a deoxygenation-dependent nitrite reductase. This review focuses on the role of nitrite as a circulating NO donor, its potential as an index of NO synthase (NOS) activity and endothelial function, and discusses potential diagnostic and therapeutic applications.

Polyuria and impaired renal blood flow after asphyxia in preterm fetal sheep

Renal impairment is common in preterm infants, often after exposure to hypoxia/asphyxia or other circulatory disturbances. We examined the hypothesis that this association is mediated by reduced renal blood flow (RBF), using a model of asphyxia induced by complete umbilical cord occlusion for 25 min (n = 13) or sham occlusion (n = 6) in chronically instrumented preterm fetal sheep (104 days, term is 147 days). During asphyxia there was a significant fall in RBF and urine output (UO). After asphyxia, RBF transiently recovered, followed within 30 min by a secondary period of hypoperfusion (P < 0.05). This was mediated by increased renal vascular resistance (RVR, P < 0.05); arterial blood pressure was mildly increased in the first 24 h (P < 0.05). RBF relatively normalized between 3 and 24 h, but hypoperfusion developed again from 24 to 60 h (P < 0.05, analysis of covariance). UO significantly increased to a peak of 249% of baseline between 3 and 12 h (P < 0.05), with increased fractional excretion of sodium, peak 10.5 +/- 1.4 vs. 2.6 +/- 0.6% (P < 0.001). Creatinine clearance returned to normal after 2 h; there was a transient reduction at 48 h to 0.32 +/- 0.02 ml.min(-1).g(-1) (vs. 0.45 +/- 0.04, P < 0.05) corresponding with the time of maximal depression of RBF. No renal injury was seen on histological examination at 72 h. In conclusion, severe asphyxia in the preterm fetus was associated with evolving renal tubular dysfunction, as shown by transient polyuria and natriuresis. Despite a prolonged increase in RVR, there was only a modest effect on glomerular function.

Effect of mild hypothermia and hypoxia on blood flow and oxygen consumption of the fetal sheep brain

This study was undertaken to measure the effects of mild hypothermia on cerebral blood flow and metabolism and cardiovascular responses to hypoxia in the fetal sheep. Near-term fetal sheep were chronically instrumented with laser Doppler flowmetry in the parietal cortex for measurement of relative changes in cerebral blood flow, as well as with arterial and sagittal sinus catheters for measurement of oxygen extraction by the brain and a cooling coil around the fetal thorax. Fetuses were studied during cooling alone, cooling with superimposed maternal hypoxia to achieve a fetal arterial Po2 of 1.33 to 1.60 kPa, or hypoxia alone. In response to cooling alone [1.6 degrees +/- 0.1 degrees C (mean +/- SEM) decrease in brain temperature], fetal blood pressure and heart rate both increased significantly whereas cerebral blood flow decreased 14 +/- 4%, commensurate with a 24 +/- 8% decline in cerebral metabolic rate. Administration of moderate hypoxia during cooling resulted in a significant increase in cerebral blood flow, decreased heart rate, and no further increase in blood pressure. In response to hypoxia alone, fetal blood pressure was significantly increased, heart rate was decreased, and cerebral blood flow increased by 24 +/- 8%, whereas cerebral metabolic rate decreased by 38 +/- 13%. Arteriovenous oxygen extraction was unchanged by cooling alone but increased significantly in response to hypoxia administered during cooling. We therefore conclude that oxygen delivery to the fetal sheep brain remains coupled to metabolic rate during hypothermia and that hypothermia does not impair the compensatory cardiovascular responses of the fetus to acute moderate hypoxia.

Cerebral metabolism during cord occlusion and hypoxia in the fetal sheep: a novel method of continuous measurement based on heat production

This study was undertaken to validate a new method of measuring cerebral metabolic rate in the fetal sheep based on heat production in a local region of the brain. Heat production was compared to oxygen use in 20 near-term fetuses during basal conditions, moderate hypoxia and cord occlusion. Thermocouples were placed to measure core and brain temperature and a composite probe placed in the parietal cortex to measure changes in cortical blood flow (CBF) using laser Doppler flowmetry and tissue PO2 using fluorescent decay. Catheters were inserted in a brachiocephalic artery and sagittal sinus for blood sampling. With moderate hypoxia, induced by administering 10-12 % oxygen to the ewes, fetal arterial PO2 declined from 23 +/- 1 to 11 +/- 1 Torr and brain tissue PO2 fell from 7.6+/- 0.7 to a nadir of 0.8 +/- 0.4 Torr, while CBF increased to 139 +/- 5 % of baseline. Cortical heat production, calculated as the product of CBF, the temperature gain from artery to brain tissue, and the specific heat of blood, decreased by 45 +/- 11 % in parallel to similar declines in oxygen uptake. With severe asphyxia induced by complete cord occlusion for 10 min, fetal arterial PO2 declined from 23 +/- 1 to 9 +/- 2 Torr and brain tissue PO2 fell from 7.0 +/- 0.7 to essentially 0 Torr while CBF decreased 40 +/- 5 %. Cortical heat production decreased by 78 +/- 6 % while oxygen use declined by 90 +/- 3 %. Glucose uptake increased significantly relative to oxygen use and lactate concentration increased in sagittal sinus blood. We conclude that local measurements of heat production in the brain provide a useful index of overall metabolic rate, closely reflecting oxygen use in moderate hypoxia and indicating a significant contribution from anaerobic metabolism during severe asphyxia.

Adenosine mediates decreased cerebral metabolic rate and increased cerebral blood flow during acute moderate hypoxia in the near-term fetal sheep

Exposure of the fetal sheep to moderate to severe hypoxic stress results in both increased cortical blood flow and decreased metabolic rate. Using intravenous infusion of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective adenosine A1 receptor antagonist that is permeable to the blood brain barrier, we examine the role of adenosine A1 receptors in mediating cortical blood flow and metabolic responses to moderate hypoxia. The effects of DPCPX blockade are compared to controls as well as animals receiving intravenous 8-(p-sulfophenyl)-theophylline) (8-SPT), a non-selective adenosine receptor antagonist which has been found to be blood brain barrier impermeable. Laser Doppler flow probes, tissue PO2, and thermocouples were implanted in the cerebral cortices of near-term fetal sheep. Catheters were placed in the brachial artery and sagittal sinus vein for collection of samples for blood gas analysis. Three to seven days later responses to a 30-min period of fetal hypoxemia (arterial PO2 10-12 mmHg) were studied with administration of 8-SPT, DPCPX, or vehicle. Cerebral metabolic rate was determined by calculation of both brain heat production and oxygen consumption. In response to hypoxia, control experiments demonstrated a 42 +/- 7 % decrease in cortical heat production and a 35 +/- 10 % reduction in oxygen consumption. In contrast, DPCPX infusion during hypoxia resulted in no significant change in brain heat production or oxygen consumption, suggesting the adenosine A1 receptor is involved in lowering metabolic rate during hypoxia. The decrease in cerebral metabolic rate was not altered by 8-SPT infusion, suggesting that the response is not mediated by adenosine receptors located outside the blood brain barrier. In response to hypoxia, control experiments demonstrated a 35 +/- 7 % increase in cortical blood flow. DPCPX infusion did not change this increase in cortical blood flow, however 8-SPT infusion attenuated increases in flow, indicating that hypoxic increases in cerebral blood flow are mediated by adenosine but not via the A1 receptor. In summary, adenosine appears to play a key role in fetal hypoxic defences, acting to increase O2 delivery via adenosine A2 receptors and to decrease metabolic rate via A1 receptors inside the blood brain barrier. These data show for the first time in the mammalian fetus that the adenosine A1 receptor is an important mediator of brain metabolic rate during moderate hypoxia.

Key neuroprotective role for endogenous adenosine A1 receptor activation during asphyxia in the fetal sheep

BACKGROUND AND PURPOSE

The fetus is well known to be able to survive prolonged exposure to asphyxia with minimal injury compared with older animals. We and others have observed a rapid suppression of EEG intensity with the onset of asphyxia, suggesting active inhibition that may be a major neuroprotective adaptation to asphyxia. Adenosine is a key regulator of cerebral metabolism in the fetus.

METHODS

We therefore tested the hypothesis that infusion of the specific adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), given before 10 minutes of profound asphyxia in near-term fetal sheep, would prevent neural inhibition and lead to increased brain damage.

RESULTS

DPCPX treatment was associated with a transient rise and delayed fall in EEG activity in response to cord occlusion (n=8) in contrast with a rapid and sustained suppression of EEG activity in controls (n=8). DPCPX was also associated with an earlier and greater increase in cortical impedance, reflecting earlier onset of primary cytotoxic edema, and a significantly smaller reduction in calculated cortical heat production after the start of cord occlusion. After reperfusion, DPCPX-treated fetuses but not controls developed delayed onset of seizures, which continued for 24 hours, and sustained greater selective hippocampal, striatal, and parasagittal neuronal loss after 72-hour recovery.

CONCLUSIONS

These data support the hypothesis that endogenous activation of the adenosine A1 receptor during severe asphyxia mediates the initial suppression of neural activity and is an important mechanism that protects the fetal brain.

The Notochordal Cell in the Nucleus Pulposus: A Review in the Context of Tissue Engineering

An understanding of developmental biology can provide useful insights into how different tissue-engineered repairs might be designed. During embryogenesis of the intervertebral disk, the cells of the notochord play a critical role in initiating tissue formation, and may be responsible for development of the nucleus pulposus. In some species, including humans, these notochordal cells may eventually be lost, either through apoptosis or terminal differentiation, and are replaced by chondrocyte-like cells. However, there is some evidence that the notochordal cells may persist in at least some humans. This review discusses some of the potential applications of notochordal cells in tissue engineering of the nucleus pulposus.

Ten-minute umbilical cord occlusion markedly reduces cerebral blood flow and heat production in fetal sheep

OBJECTIVE

The study was undertaken to determine to what extent a 10-minute total umbilical cord occlusion affects autoregulation of cerebral blood flow and cerebral heat production in the fetus.

STUDY DESIGN

In seven chronically catheterized late-gestation fetal sheep (127-131 days' gestation), we studied fetal blood gas, hemodynamic, and thermal responses to 10-minute total umbilical cord occlusion.

RESULTS

Ten-minute umbilical cord occlusion resulted in marked hypoxia/ischemia, with oxygen content decreasing from 6.5 +/- 0.4 to 0.6 +/- 0.1 vol% and lactate concentration increasing from 1.8 +/- 0.2 to 10.7 +/- 0.7 mmol/L. During this period, the fetuses showed reductions in heart rate from 163.5 +/- 3.4 to 97.1 +/- 5.4 beats/min, mean arterial pressure from 39.4 +/- 2.1 to 21.2 +/- 2.5 mm Hg, cerebral blood flow from 101.3% +/- 8.9% to 49.7% +/- 10.3%, and cerebral heat production from 95.0% +/- 6.3% to 29.6% +/- 4.8%. During cord occlusion, cerebral blood flow was pressure passive from the fourth minute onward. The reduction in cerebral heat production preceded the reduction in perfusion pressure and cerebral blood flow. Recovery of cerebral blood flow and heat production to control values was incomplete for more than 60 minutes after restoration of umbilical flow.

CONCLUSION

Ten-minute total umbilical cord occlusion results in major reductions in cerebral blood flow and heat production. Autoregulation of cerebral blood flow was lost within 4 minutes of occlusion, probably as a result of hypoxia, combined with hypotension. The fact that the reduction in cerebral heat production preceded and exceeded the reduction in blood flow may suggest active down-regulation of cerebral metabolism, the mechanism of which is unclear at present.

Role of nitric oxide in hypoxic cerebral vasodilatation in the ovine fetus

To investigate the role of nitric oxide (NO) in fetal cerebral circulatory responses to acute hypoxia, near-term fetal sheep were instrumented with laser Doppler probes placed in the parasagittal parietal cortices and vascular catheters in the sagittal sinus and brachiocephalic artery. After a 3 day recovery period, responses of cortical blood flow (CBF) to hypoxia were compared with and without inhibition of nitric oxide synthase (NOS). After an initial 30 min baseline period, fetuses were given a bolus followed by a continuous infusion of Nomega-nitro-L-arginine methyl ester (L-NAME), or saline vehicle as control. After administration of L-NAME, CBF decreased by 14 +/- 6 % (P < 0.01) despite increases in arterial blood pressure of 15 mmHg, resulting in an ~60 % increase in cerebrovascular resistance. Thirty minutes following initiation of L-NAME or vehicle infusion, fetal systemic hypoxia was induced by allowing the ewes to breathe 10-11 % oxygen. In control fetuses CBF increased progressively to 145 +/- 9 % of baseline (P < 0.01) after 30 min, while cortical release of cyclic guanylate cyclase (cGMP), an index of NOS activity, increased 26 +/- 8 % (P < 0.05). In contrast, CBF in L-NAME-treated fetuses increased to only 115 % of the reduced CBF baseline, whereas cortical release of cGMP did not change significantly. In summary, basal levels of NO lower resting cortical vascular resistance by ~15 % in the fetal sheep. Inhibition of NO synthesis attenuates hypoxic cerebral relaxation but does not completely prevent the characteristic increases in CBF. Hypoxic increases in NO directly increase cortical production of cGMP and inhibition of NO synthesis ablates these changes in cGMP.

Fetal lamb cerebral blood flow (CBF) and oxygen tensions during hypoxia: a comparison of laser Doppler and microsphere measurements of CBF

This study was undertaken to compare microsphere and laser Doppler flowmetry techniques for the measurement of cerebral blood flow, to assess the effect of probe implantation at the tip of the sensing probe and to measure brain tissue P(O2) (tP(O2)) in response to acute hypoxia. Fetal sheep of ~131 days gestation (n = 8) were chronically instrumented with bilateral laser Doppler probes in the parietal cortices and catheters for injection of fluorescent microspheres. Five days after surgery fetuses were subjected to 1 h periods of baseline control breathing, hypoxia and recovery. Microspheres were injected 10 min prior to and 10, 30, 50 and 120 min after initiation of hypoxia. Microspheres were counted in four 12 mm(3) tissue samples from each hemisphere, the tip of the laser Doppler probe being positioned in the centre of one of the cubes. The cube containing the probe tip was also subdivided into 4 mm(3) pieces of tissue. In response to hypoxia, fetal arterial P(O2) declined from 21 +/- 2 to 12 +/- 1 Torr and brain tissue P(O2) fell from 10 +/- 1 to a nadir of 1 +/- 1 Torr. Each method detected a significant increase in CBF that reached a maximum after 30-45 min, although the increase of flow measured by laser Doppler flowmetry was less than that measured by spheres after 10 and 30 min (P < 0.05). Microspheres did not detect altered flow at the probe tip or heterogeneity of flow in surrounding volumes of cortical tissue. In summary, laser Doppler flowmetry is a useful measure of continuous relative changes of CBF in the chronically instrumented fetal sheep. Flow compensations in acute hypoxia are not adequate to sustain O(2) delivery, and other compensations, including reduced metabolic rate, are possible.

The role of adenosine in regulation of cerebral blood flow during hypoxia in the near-term fetal sheep

The aim of this study was to determine in the near-term ovine fetus the role of adenosine in the basal regulation of cerebral blood flow and in the increases in cerebral blood flow in response to acute hypoxic insult. We measured cerebral blood flow in chronically instrumented fetal sheep (127-135 days gestation, term approximately 145 days) using laser Doppler flowmetry probes implanted in the parietal cortices. Hypoxia was administered for 30 min by lowering the ewe's inspired oxygen to 10-12 % during an infusion of either saline or theophylline, a non-specific adenosine receptor antagonist. The theophylline infusion was begun 30 min prior to and ended 30 min after the completion of the hypoxic insult. The administration of theophylline had no significant effect on cerebral blood flow during the baseline period. During control hypoxic periods, cerebral blood flow increased by approximately 45 %. During theophylline experiments, however, there was no significant increase in cerebral blood flow during hypoxia. In the control experiments, cerebral blood flow returned to baseline levels during the recovery period, while in the theophylline experiments cerebral blood flow fell below baseline levels. We conclude that, in the near-term ovine fetus, adenosine plays a minimal role in the regulation of basal cerebral blood flow. However, these data are strong evidence for the involvement of adenosine in increased fetal cerebral blood flow during an acute hypoxic insult. Finally, adenosine may also play an important role in the maintenance of fetal cerebral blood flow immediately following hypoxic insult.

In vitro characterization of radiolabeled monoclonal antibodies specific for the extracellular domain of prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA) is a well-characterized cell surface antigen expressed by virtually all prostate cancers (PCas). PSMA has been successfully targeted in vivo with (111)In-labeled 7E11 monoclonal antibody (mAb; ProstaScint; Cytogen, Princeton, NJ), which binds to an intracellular epitope of PSMA. This work reports the in vitro characterization of three recently developed mAbs that bind the extracellular domain of PSMA (PSMAext). Murine mAbs J415, J533, J591, and 7E11 were radiolabeled with 131I and evaluated in competitive and saturation binding studies with substrates derived from LNCaP cells. J415 and J591 were conjugated to 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid labeled with (111)In. The uptake and cellular processing of these antibodies were evaluated in viable LNCaP cells. All four mAbs could be labeled with 131I up to a specific activity of 350 MBq/mg with no or little apparent loss of immunoreactivity. Competition assays revealed that J415 and J591 compete for binding to PSMAext antigen. J533 bound to a region close to the J591 binding epitope, but J533 did not interfere with J415 binding to PSMA. mAb 7E11 did not inhibit the binding of J415, J533, or J591 (or vice versa), consistent with earlier work that these latter mAbs bind PSMAext whereas 7E11 binds the intracellular domain of PSMA. Saturation binding studies demonstrated that J415 and J591 bound with a similar affinity (Kds 1.76 and 1.83 nM), whereas J533 had a lower affinity (Kd, 18 nM). In parallel studies, all four mAbs bound to a similar number of PSMA sites expressed by permeabilized cells (1,000,000-1,300,000 sites/cell). In parallel studies performed with viable LNCaP cells, J415, J533, and J591 bound to a similar number of PSMA sites (i.e., 600,000-800,000 sites/cell), whereas 7E11 bound only to a subpopulation of the available PSMA sites (95,000 sites/cell). This apparent binding of 7E11 to viable cells can be accounted for by a 5-7% subpopulation of permeabilized cells produced when the cells were trypsinized and suspended. Up to five DOTA chelates could be bound to either J415 or J591 without compromising immunoreactivity. A comparison of the cellular uptake and metabolic processing of the 131I- and (111)In-labeled antibodies showed a rapid elimination of 131I from the cell and a high retention of (111)In. All four mAbs recognized and bound to similar numbers of PSMAs expressed by ruptured LNCaP cells (i.e., the exposed intracellular and extracellular domains of PSMA). By comparison to J415 and J591, J533 had a lower binding affinity. Both J415 and J591 recognized and bound to the same high number of PSMAs expressed by intact LNCaP. By contrast, 7E11 bound to fewer sites expressed by intact LNCaP cells (i.e., the exposed extracellular domain of PSMA). Both J415 and J591 are promising mAbs for the targeting of viable PSMA-expressing tissue with diagnostic and therapeutic metallic radionuclides.

Adaptation of laser-Doppler flowmetry to measure cerebral blood flow in the fetal sheep

The purpose of this study was to devise a means to use laser-Doppler flowmetry to measure cerebral perfusion before birth. The method has not been used previously, largely because of intrauterine movement artifacts. To minimize movement artifacts, a probe holder was molded from epoxy putty to the contour of the fetal skull. A curved 18-gauge needle was embedded in the holder. At surgery, the holder, probe, and skull were fixed together with tissue glue. Residual signals were recorded after fetal death and after maternal death 1 h later. These averaged <5% of baseline flow signals, indicating minimal movement artifact. To test the usefulness of the method, cerebral flow responses were measured during moderate fetal hypoxia induced by giving the ewes approximately 10% oxygen in nitrogen to breathe. As fetal arterial PO(2) decreased from 21.1 +/- 0.5 to 10.7 +/- 0.4 Torr during a 30-min period, cerebral perfusion increased progressively to 56 +/- 8% above baseline. Perfusion then returned to baseline levels during a 30-min recovery period. These responses are quantitatively similar to those spot observations that have been recorded earlier using labeled microspheres. We conclude that cerebral perfusion can be successfully measured by using laser-Doppler flowmetry with the unanesthetized, chronically prepared fetal sheep as an experimental model. With this method, relative changes of perfusion from a small volume of the ovine fetal brain can be measured on a continuous basis, and movement artifacts can be reduced to 5% of measured flow values.

Gas exchange and heart rate in the harbour porpoise, Phocoena phocoena

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28 kg) were measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory (12 +/- 0.3 s, mean +/- SEM) were shorter than field observations, although a few breath-holds of over 40 s were recorded. The mean percentage time spent submerged was 89 +/- 0.4%. Relative to similarly-sized terrestrial mammals, the respiratory frequency was low (4.9 +/- 0.19 breaths.min-1) but with high tidal volumes (1.1 +/- 0.011), enabling a comparatively high minute rate of gas exchange. Oxygen consumption under these experimental conditions (247 +/- 13.8 ml O2.min-1) was 1.9-fold higher than predicted by standard scaling relations. These data together with an estimate of the total oxygen stores predicted an aerobic dive limit of 5.4 min. The peak end-tidal O2 values were related to the length of the previous breath-hold, demonstrating the increased oxygen uptake from the lung for the longer dives. Blood oxygen capacity was 23.5 +/- 1.0 ml.100 ml-1, and the oxygen affinity was high, enabling rapid oxygen loading during ventilation.

Application of laser Doppler flowmetry to measure cerebral microvascular perfusion in the fetal sheep

Laser Doppler flowmetry (LDF) has been used to measure flow in various organs of the adult, but has not been applied to the mammalian fetus. The purpose of this study was to apply LDF to measure cerebral blood flow of the fetal sheep and to assess the possible errors and artifacts of the method caused by myometrial, fetal, and maternal movements. By three days after probe placement, the flow signal had decreased 55% from initial post surgical readings and thereafter it became stable. During fetal hypoxia, the signal increased 48% and during hypercarbia it increased 59%. After fetal death, the signal decreased to 48% of control level. After maternal death, it decreased to 9% and electrical zero could not be reached. LDF is useful to measure changes of fetal cerebral microvascular perfusion because it can provide continuous signals but care is required in data handling and probe fixation when used for the mammalian fetus.

The safety and success rate of sputum induction using a low output ultrasonic nebuliser

Induced sputum differential cell counts have been advocated as a method of non-invasively assessing airway inflammation in asthma and other airway diseases. Since sputum induction usually involves delivering hypertonic saline via a high output ultrasonic nebulizer there have been concerns about its safety in asthma. There are relatively little data on the effects of sputum induction in large numbers of patients. We have examined the success rate and effect of sputum induction on forced expiratory volume in 1 sec (FEV1) in 100 inductions performed on 79 patients using a low output nebulizer. Thirty-seven patients had asthma, 29 had miscellaneous conditions (mainly chronic cough) and 13 were subjects without respiratory symptoms. Sputum was induced 10 min after 200 micrograms of inhaled salbutamol by sequential 5-min inhalations of 3, 4 and 5% saline delivered via a Fisoneb ultrasonic nebulizer and FEV1 was measured after each inhalation. Sputum induction resulted in a sample suitable for analysis in 92% of asthmatics, 90% of those with miscellaneous conditions and 100% of normal subjects. The mean (SEM) maximum per cent fall in FEV1 was 5.4% (0.1), 4.3%, (1.0) and 2.6% (1.1) in subjects with asthma, miscellaneous conditions and in asymptomatic subjects respectively. Only 13 inductions resulted in a > 10% fall in FEV1, and only three of these resulted in a > 20% fall. The maximum per cent fall in FEV1 did not correlate with baseline FEV1 % predicted (r = -0.17), the log sputum eosinophil count (r = -0.12), or the methacholine PC20 (r = -0.14). We conclude that sputum induction using a relatively low output ultrasonic nebulizer with premedication with salbutamol is successful and safe in the majority of patients with asthma and other airway conditions.

Anti-Jk3 with no clinical evidence of HDN

A sample was submitted to a reference lab from a 27-year-old Asian female, gravida 4 para 1, for antibody identification. Anti-Jk3 with an IgM component was identified. Subsequently, the antibody was eluted from the infant's cord and venous red blood cells. Normal bilirubin and hematocrit levels ruled out hemolytic disease of the newborn (HDN). Anti-Jk3 has been implicated in two cases of mild HDN. In this case, this noncomplement-binding antibody caused a positive direct Coombs test without clinical signs of HDN.