Residential Proximity to Dioxin-emitting Facilities and Risk of Non-Hodgkin Lymphoma in the NIH-AARP Diet and Health Study

Purpose: Few studies have investigated the relationship between risk of non-Hodgkin lymphoma (NHL) and residential proximity to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) emitted from industrial combustion and manufacturing sources. Methods: We evaluated this relationship among participants of the NIH-AARP Diet and Health Study, a prospective cohort (N = 548,845) in 6 states and 2 cities in the U.S. We linked geocoded enrollment addresses (1995–1996) with a U.S. Environmental Protection Agency database of 4,478 historical PCDD/F sources, which contained toxic equivalency quotient (TEQ) emissions estimates from 1995. Exposure metrics indicated presence/absence of any facility within 3 and 5km of participant homes, overall and by type of facility (e.g., coal-fired power plants, waste incinerators), which vary in emissions levels and constituency. We also calculated exposure as a distance- and toxicity-weighted average emissions index (AEI [g TEQ]). We used Cox regression to estimate associations (hazard ratios; HR and 95% confidence intervals; CI) with NHL and major subtypes, adjusting for and by strata of sociodemographic and lifestyle characteristics. Results: With 6,747 incident cases through 2011, we found no association between living near any or specific types of PCDD/F-emitting facilities and NHL risk. However, participants with an AEI >95th percentile within 5km had increased risk of NHL compared to unexposed (HR = 1.28; CI = 1.05–1.55; p-trend = 0.01). Specifically, we observed increased risk for lymphoplasmacytic lymphoma (HR = 2.98, CI = 1.16–7.63; p-trend = 0.03) and diffuse large B-cell lymphoma (HR = 1.65, CI = 1.11–2.46; p-trend = 0.01). Non-Hispanic blacks were nearly three times as likely as whites to live <5 km of a facility, although we had limited power to evaluate heterogeneity in associations by race/ethnicity. Associations did not vary by age, smoking status, body mass index, or urbanicity of residence. Conclusions: Using an exposure metric accounting for distance and the toxicity of emissions, we found significant positive associations between residential exposure to high PCDD/F emissions and risk of NHL and two subtypes. Our results underscore the hazard for populations living near sources of these persistent organic pollutants.

Precise Control of End-tidal Carbon Dioxide Levels Using Sequential Rebreathing Circuits

Anaesthesiologists have traditionally been consulted to help design breathing circuits to attain and maintain target end-tidal carbon dioxide (PETCO2). The methodology has recently been simplified by breathing circuits that sequentially deliver fresh gas (not containing carbon dioxide (CO2)) and reserve gas (containing CO2). Our aim was to determine the roles of fresh gas flow, reserve gas PCO2 and minute ventilation in the determination of PETCO2. We first used a computer model of a non-rebreathing sequential breathing circuit to determine these relationships. We then tested our model by monitoring PETCO2 in human volunteers who increased their minute ventilation from resting to five times resting levels. The optimal settings to maintain PETCO2 independently of minute ventilation are 1) fresh gas flow equal to minute ventilation minus anatomical deadspace ventilation, and 2) reserve gas PCO2 equal to alveolar PCO2. We provide an equation to assist in identifying gas settings to attain a target PCO2. The ability to precisely attain and maintain a target PCO2 (isocapnia) using a sequential gas delivery circuit has multiple therapeutic and scientific applications.

Improved White Matter Cerebrovascular Reactivity after Revascularization in Patients with Steno-Occlusive Disease

BACKGROUND AND PURPOSE

One feature that patients with steno-occlusive cerebrovascular disease have in common is the presence of white matter (WM) lesions on MRI. The purpose of this study was to evaluate the effect of direct surgical revascularization on impaired WM cerebrovascular reactivity in patients with steno-occlusive disease.

MATERIALS AND METHODS

We recruited 35 patients with steno-occlusive disease, Moyamoya disease (n = 24), Moyamoya syndrome (n = 3), atherosclerosis (n = 6), vasculitis (n = 1), and idiopathic stenosis (n = 1), who underwent unilateral brain revascularization using a direct superficial temporal artery-to-MCA bypass (19 women; mean age, 45.8 ± 16.5 years). WM cerebrovascular reactivity was measured preoperatively and postoperatively using blood oxygen level-dependent (BOLD) MR imaging during iso-oxic hypercapnic changes in end-tidal carbon dioxide and was expressed as %Δ BOLD MR signal intensity per millimeter end-tidal partial pressure of CO₂.

RESULTS

WM cerebrovascular reactivity significantly improved after direct unilateral superficial temporal artery-to-middle cerebral artery (STA-MCA) bypass in the revascularized hemisphere in the MCA territory (mean ± SD, -0.0005 ± 0.053 to 0.053 ± 0.046 %BOLD/mm Hg; P < .0001) and in the anterior cerebral artery territory (mean, 0.0015 ± 0.059 to 0.021 ± 0.052 %BOLD/mm Hg; P = .005). There was no difference in WM cerebrovascular reactivity in the ipsilateral posterior cerebral artery territory nor in the vascular territories of the nonrevascularized hemisphere (P < .05).

CONCLUSIONS

Cerebral revascularization surgery is an effective treatment for reversing preoperative cerebrovascular reactivity deficits in WM. In addition, direct-STA-MCA bypass may prevent recurrence of preoperative symptoms.

High volatile anaesthetic conservation with a digital in-line vaporizer and a reflector

BACKGROUND

A volatile anaesthetic (VA) reflector can reduce VA consumption (VAC) at the cost of fine control of its delivery and CO₂ accumulation. A digital in-line vaporizer and a second CO₂ absorber circumvent both of these limitations. We hypothesized that the combination of a VA reflector with an in-line vaporizer would yield substantial VA conservation, independent of fresh gas flow (FGF) in a circle circuit, and provide fine control of inspired VA concentrations.

METHOD

Prospective observational study on six Yorkshire pigs. A secondary anaesthetic circuit consisting of a Y-piece with 2 one-way valves, an in-line vaporizer and a CO₂ absorber in the inspiratory limb was connected to the patient's side of the VA reflector. The other side was connected to the Y-piece of a circle anaesthetic circuit. In six pigs, an inspired concentration of sevoflurane of 2.5% was maintained by the in-line vaporizer. We measured VAC at FGF of 1, 4 and 10 l/min.

RESULTS

With the secondary circuit, VAC was 55% less than with the circle system alone at FGF 1 l/min, and independent of FGF over the range of 1-10 l/min. Insertion of a CO₂ absorber in the secondary circuit reduced P_et CO₂ by 1.3-2.0 kpa (10-15 mmHg).

CONCLUSION

A secondary circuit with reflector and in-line vaporizer provides highly efficient anaesthetic delivery, independent of FGF. A second CO₂ absorber was necessary to scavenge the CO₂ reflected by the anaesthetic reflector. This secondary circuit may turn any open circuit ventilator into an anaesthetic delivery unit.

Technology III: in-line vaporizer with reflector

As the clinical advantages of vapor anesthesia (VA) for sedation of patients in ICU become more apparent, the ergonomics, economy and safety issues need to be better addressed. Here we describe the use of a new commercial digital in-line anesthetic vaporizer that can be attached to the inspiratory limb of a ventilator. If used with a simple, and easily assembled secondary circuit and anesthetic reflector, the circuit remains remote from the patient, the VA consumption approaches a physical minimum, VA level is controlled and monitored, and the tidal volume size is not limited.

Effects of acute controlled changes in end-tidal carbon dioxide on the diameter of the optic nerve sheath: a transorbital ultrasonographic study in healthy volunteers

Transorbital ultrasonographic measurement of the diameter of the optic nerve sheath is a non-invasive, bed-side examination for detecting raised intracranial pressure. However, the ability of the optic nerve sheath diameter to predict acute changes in intracranial pressures remains unknown. The aim of this study was to examine the dynamic changes of the optic nerve sheath diameter in response to mild fluctuations in cerebral blood volume induced by changes in end-tidal carbon dioxide. We studied 11 healthy volunteers. End-tidal carbon dioxide was controlled by a model-based prospective end-tidal targeting system (RespirAct™). The volunteers' end-tidal carbon dioxide was targeted and maintained for 10 min each at normocapnia (baseline); hypercapnia (6.5 kPa); normocapnia (baseline 1); hypocapnia (3.9 kPa) and on return to normocapnia (baseline 2). A single investigator repeatedly measured the optic nerve sheath diameter for 10 min at each level of carbon dioxide. With hypercapnia, there was a significant increase in optic nerve sheath diameter, with a mean (SD) increase from baseline 4.2 (0.7) mm to 4.8 (0.8) mm; p < 0.001. On return to normocapnia, the optic nerve sheath diameter rapidly reverted back to baseline values. This study confirms dynamic changes in the optic nerve sheath diameter with corresponding changes in carbon dioxide, and their reversibly with normocapnia.

Vascular Dysfunction in Leukoaraiosis

BACKGROUND AND PURPOSE

The pathogenesis of leukoaraiosis has long been debated. This work addresses a less well-studied mechanism, cerebrovascular reactivity, which could play a leading role in the pathogenesis of this disease. Our aim was to evaluate blood flow dysregulation and its relation to leukoaraiosis.

MATERIALS AND METHODS

Cerebrovascular reactivity, the change in the blood oxygen level-dependent 3T MR imaging signal in response to a consistently applied step change in the arterial partial pressure of carbon dioxide, was measured in white matter hyperintensities and their contralateral spatially homologous normal-appearing white matter in 75 older subjects (age range, 50-91 years; 40 men) with leukoaraiosis. Additional quantitative evaluation of regions of leukoaraiosis was performed by using diffusion (n = 75), quantitative T2 (n = 54), and DSC perfusion MRI metrics (n = 25).

RESULTS

When we compared white matter hyperintensities with contralateral normal-appearing white matter, cerebrovascular reactivity was lower by a mean of 61.2% ± 22.6%, fractional anisotropy was lower by 44.9 % ± 6.9%, and CBF was lower by 10.9% ± 11.9%. T2 was higher by 61.7% ± 13.5%, mean diffusivity was higher by 59.0% ± 11.7%, time-to-maximum was higher by 44.4% ± 30.4%, and TTP was higher by 6.8% ± 5.8% (all P < .01). Cerebral blood volume was lower in white matter hyperintensities compared with contralateral normal-appearing white matter by 10.2% ± 15.0% (P = .03).

CONCLUSIONS

Not only were resting blood flow metrics abnormal in leukoaraiosis but there is also evidence of reduced cerebrovascular reactivity in these areas. Studies have shown that reduced cerebrovascular reactivity is more sensitive than resting blood flow parameters for assessing vascular insufficiency. Future work is needed to examine the sensitivity of resting-versus-dynamic blood flow measures for investigating the pathogenesis of leukoaraiosis.

Identifying Significant Changes in Cerebrovascular Reactivity to Carbon Dioxide

BACKGROUND AND PURPOSE

Changes in cerebrovascular reactivity can be used to assess disease progression and response to therapy but require discrimination of pathology from normal test-to-test variability. Such variability is due to variations in methodology, technology, and physiology with time. With uniform test conditions, our aim was to determine the test-to-test variability of cerebrovascular reactivity in healthy subjects and in patients with known cerebrovascular disease.

MATERIALS AND METHODS

Cerebrovascular reactivity was the ratio of the blood oxygen level-dependent MR imaging response divided by the change in carbon dioxide stimulus. Two standardized cerebrovascular reactivity tests were conducted at 3T in 15 healthy men (36.7 ± 16.1 years of age) within a 4-month period and were coregistered into standard space to yield voxelwise mean cerebrovascular reactivity interval difference measures, composing a reference interval difference atlas. Cerebrovascular reactivity interval difference maps were prepared for 11 male patients. For each patient, the test-retest difference of each voxel was scored statistically as z-values of the corresponding voxel mean difference in the reference atlas and then color-coded and superimposed on the anatomic images to create cerebrovascular reactivity interval difference z-maps.

RESULTS

There were no significant test-to-test differences in cerebrovascular reactivity in either gray or white matter (mean gray matter, P = .431; mean white matter, P = .857; paired t test) in the healthy cohort. The patient cerebrovascular reactivity interval difference z-maps indicated regions where cerebrovascular reactivity increased or decreased and the probability that the changes were significant.

CONCLUSIONS

Accounting for normal test-to-test differences in cerebrovascular reactivity enables the assessment of significant changes in disease status (stability, progression, or regression) in patients with time.

Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the Southeast United States and co-benefit of SO2 emission controls

Isoprene emitted by vegetation is an important precursor of secondary organic aerosol (SOA), but the mechanism and yields are uncertain. Aerosol is prevailingly aqueous under the humid conditions typical of isoprene-emitting regions. Here we develop an aqueous-phase mechanism for isoprene SOA formation coupled to a detailed gas-phase isoprene oxidation scheme. The mechanism is based on aerosol reactive uptake coefficients (γ) for water-soluble isoprene oxidation products, including sensitivity to aerosol acidity and nucleophile concentrations. We apply this mechanism to simulation of aircraft (SEAC⁴RS) and ground-based (SOAS) observations over the Southeast US in summer 2013 using the GEOS-Chem chemical transport model. Emissions of nitrogen oxides (NO_x ≡ NO + NO₂) over the Southeast US are such that the peroxy radicals produced from isoprene oxidation (ISOPO₂) react significantly with both NO (high-NO_x pathway) and HO₂ (low-NO_x pathway), leading to different suites of isoprene SOA precursors. We find a mean SOA mass yield of 3.3 % from isoprene oxidation, consistent with the observed relationship of total fine organic aerosol (OA) and formaldehyde (a product of isoprene oxidation). Isoprene SOA production is mainly contributed by two immediate gas-phase precursors, isoprene epoxydiols (IEPOX, 58% of isoprene SOA) from the low-NO_x pathway and glyoxal (28%) from both low- and high-NO_x pathways. This speciation is consistent with observations of IEPOX SOA from SOAS and SEAC⁴RS. Observations show a strong relationship between IEPOX SOA and sulfate aerosol that we explain as due to the effect of sulfate on aerosol acidity and volume. Isoprene SOA concentrations increase as NO_x emissions decrease (favoring the low-NO_x pathway for isoprene oxidation), but decrease more strongly as SO₂ emissions decrease (due to the effect of sulfate on aerosol acidity and volume). The US EPA projects 2013-2025 decreases in anthropogenic emissions of 34% for NO_x (leading to 7% increase in isoprene SOA) and 48% for SO₂ (35% decrease in isoprene SOA). Reducing SO₂ emissions decreases sulfate and isoprene SOA by a similar magnitude, representing a factor of 2 co-benefit for PM_2.5 from SO₂ emission controls.

Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the Southeast United States and co-benefit of SO2 emission controls

Isoprene emitted by vegetation is an important precursor of secondary organic aerosol (SOA), but the mechanism and yields are uncertain. Aerosol is prevailingly aqueous under the humid conditions typical of isoprene-emitting regions. Here we develop an aqueous-phase mechanism for isoprene SOA formation coupled to a detailed gas-phase isoprene oxidation scheme. The mechanism is based on aerosol reactive uptake coefficients (γ) for water-soluble isoprene oxidation products, including sensitivity to aerosol acidity and nucleophile concentrations. We apply this mechanism to simulation of aircraft (SEAC⁴RS) and ground-based (SOAS) observations over the Southeast US in summer 2013 using the GEOS-Chem chemical transport model. Emissions of nitrogen oxides (NO_x ≡ NO + NO₂) over the Southeast US are such that the peroxy radicals produced from isoprene oxidation (ISOPO₂) react significantly with both NO (high-NO_x pathway) and HO₂ (low-NO_x pathway), leading to different suites of isoprene SOA precursors. We find a mean SOA mass yield of 3.3 % from isoprene oxidation, consistent with the observed relationship of total fine organic aerosol (OA) and formaldehyde (a product of isoprene oxidation). Isoprene SOA production is mainly contributed by two immediate gas-phase precursors, isoprene epoxydiols (IEPOX, 58% of isoprene SOA) from the low-NO_x pathway and glyoxal (28%) from both low- and high-NO_x pathways. This speciation is consistent with observations of IEPOX SOA from SOAS and SEAC⁴RS. Observations show a strong relationship between IEPOX SOA and sulfate aerosol that we explain as due to the effect of sulfate on aerosol acidity and volume. Isoprene SOA concentrations increase as NO_x emissions decrease (favoring the low-NO_x pathway for isoprene oxidation), but decrease more strongly as SO₂ emissions decrease (due to the effect of sulfate on aerosol acidity and volume). The US EPA projects 2013-2025 decreases in anthropogenic emissions of 34% for NO_x (leading to 7% increase in isoprene SOA) and 48% for SO₂ (35% decrease in isoprene SOA). Reducing SO₂ emissions decreases sulfate and isoprene SOA by a similar magnitude, representing a factor of 2 co-benefit for PM_2.5 from SO₂ emission controls.

Organic nitrate chemistry and its implications for nitrogen budgets in an isoprene- and monoterpene-rich atmosphere: constraints from aircraft (SEAC4RS) and ground-based (SOAS) observations in the Southeast US

Formation of organic nitrates (RONO₂) during oxidation of biogenic volatile organic compounds (BVOCs: isoprene, monoterpenes) is a significant loss pathway for atmospheric nitrogen oxide radicals (NO_x), but the chemistry of RONO₂ formation and degradation remains uncertain. Here we implement a new BVOC oxidation mechanism (including updated isoprene chemistry, new monoterpene chemistry, and particle uptake of RONO₂) in the GEOS-Chem global chemical transport model with ∼25 × 25 km² resolution over North America. We evaluate the model using aircraft (SEAC⁴RS) and ground-based (SOAS) observations of NO_x, BVOCs, and RONO₂ from the Southeast US in summer 2013. The updated simulation successfully reproduces the concentrations of individual gas- and particle-phase RONO₂ species measured during the campaigns. Gas-phase isoprene nitrates account for 25-50% of observed RONO₂ in surface air, and we find that another 10% is contributed by gas-phase monoterpene nitrates. Observations in the free troposphere show an important contribution from long-lived nitrates derived from anthropogenic VOCs. During both campaigns, at least 10% of observed boundary layer RONO₂ were in the particle phase. We find that aerosol uptake followed by hydrolysis to HNO₃ accounts for 60% of simulated gas-phase RONO₂ loss in the boundary layer. Other losses are 20% by photolysis to recycle NO_x and 15% by dry deposition. RONO₂ production accounts for 20% of the net regional NO_x sink in the Southeast US in summer, limited by the spatial segregation between BVOC and NO_x emissions. This segregation implies that RONO₂ production will remain a minor sink for NO_x in the Southeast US in the future even as NO_x emissions continue to decline.

Measuring cerebrovascular reactivity: what stimulus to use?

Cerebrovascular reactivity is the change in cerebral blood flow in response to a vasodilatory or vasoconstrictive stimulus. Measuring variations of cerebrovascular reactivity between different regions of the brain has the potential to not only advance understanding of how the cerebral vasculature controls the distribution of blood flow but also to detect cerebrovascular pathophysiology. While there are standardized and repeatable methods for estimating the changes in cerebral blood flow in response to a vasoactive stimulus, the same cannot be said for the stimulus itself. Indeed, the wide variety of vasoactive challenges currently employed in these studies impedes comparisons between them. This review therefore critically examines the vasoactive stimuli in current use for their ability to provide a standard repeatable challenge and for the practicality of their implementation. Such challenges include induced reductions in systemic blood pressure, and the administration of vasoactive substances such as acetazolamide and carbon dioxide. We conclude that many of the stimuli in current use do not provide a standard stimulus comparable between individuals and in the same individual over time. We suggest that carbon dioxide is the most suitable vasoactive stimulus. We describe recently developed computer-controlled MRI compatible gas delivery systems which are capable of administering reliable and repeatable vasoactive CO2 stimuli.

Respiratory, cerebrovascular and cardiovascular responses to isocapnic hypoxia

We simultaneously measured respiratory, cerebrovascular and cardiovascular responses to 10-min of isoxic hypoxia at three constant CO(2) tensions in 15 subjects. We observed four response patterns, some novel, for ventilation, middle cerebral artery blood flow velocity, heart rate and mean arterial blood pressure. The occurrence of the response patterns was correlated between some measures. Isoxic hyperoxic and hypoxic ventilatory sensitivities to CO(2) derived from these responses were equivalent to those measured with modified (Duffin) rebreathing tests, but cerebrovascular sensitivities were not. We suggest the different ventilatory response patterns reflect the time course of carotid body afferent activity; in some individuals, carotid body function changes during hypoxia in more complex ways than previously thought. We concluded that isoxic hyperoxic and hypoxic ventilatory sensitivities to CO(2) can be measured using multiple hypoxic ventilatory response tests only if care is taken choosing the isocapnic CO(2) levels used, but a similar approach to measuring the cerebrovascular response to isocapnic hyperoxia and hypoxia is unfeasible.

Increased lung clearance of isoflurane shortens emergence in obesity: a prospective randomized-controlled trial

BACKGROUND

There is a concern that obesity may play a role in prolonging emergence from fat-soluble inhalational anaesthetics. We hypothesized that increased pulmonary clearance of isoflurane will shorten immediate recovery from anaesthesia and post-anaesthesia care unit (PACU) stay in obese patients.

METHODS

After Ethics Review Board approval, 44 ASA I-III patients with BMI>30 kg/m(2) undergoing elective gynaecological or urological surgery were randomized after completion of surgery to either an isocapnic hyperpnoea (IH) or a conventional recovery (C) group. The anaesthesia protocol included propofol, fentanyl, morphine, rocuronium and isoflurane in air/O(2) . Groups were compared using unpaired t-test and ANOVA.

RESULTS

Minute ventilation in the IH group before extubation was 22.6 ± 2.7 vs. 6.3 ± 1.8 l/min in the C group. Compared with C, the IH group had a shorter time to extubation (5.4 ± 2.7 vs. 15.8 ± 2.7 min, P<0.01), initiation of spontaneous ventilation (2.7 ± 2.3 vs. 6.5 ± 4.5 min, P<0.01), BIS recovery >75 (3.2 ± 2.3 vs. 8.9 ± 5.8 min, P<0.01), eye opening (4.6 ± 2.9 vs. 13.6 ± 7.1 min, P<0.01) and eligibility for leaving the operating room (7.1 ± 2.9 vs. 19.9 ± 11.9 min, P<0.01). There was no difference in time for eligibility for PACU discharge.

CONCLUSION

Increasing alveolar ventilation enhances anaesthetic elimination and accelerates short-term recovery in obese patients.

Mapping white matter diffusion and cerebrovascular reactivity in carotid occlusive disease

OBJECTIVE

To characterize the relationship between cerebrovascular reactivity (CVR) and white matter (WM) diffusion in patients with internal carotid artery (ICA) occlusive disease.

METHODS

In this exploratory observational study, 41 patients with severe stenosis or occlusion of the extracranial ICA and 12 healthy control subjects underwent CVR mapping using the fMRI response to hypercapnia. Conventional anatomic and diffusion-weighted MRI sequences were used to calculate maps of the apparent diffusion coefficient (ADC) and to exclude areas of previous ischemic injury. In all subjects, ADC was compared between WM with positive and negative CVR. In 27 patients with unilateral ICA involvement, ADC and CVR were compared between ipsilateral and contralateral WM while covarying for relevant clinical risk factors.

RESULTS

In patients with bilateral disease and in the ipsilateral hemisphere of patients with unilateral disease, negative CVR was associated with increased WM ADC (p < 0.01 and p < 0.005, respectively). In patients with unilateral disease, the ipsilateral CVR deficit was correlated with the degree of hemispheric WM ADC elevation (p < 0.005). ADC elevation remained significant after correction for potential confounding risk factors.

CONCLUSIONS

CVR impairment is associated with ADC elevation in normal-appearing WM of patients with severe stenosis or occlusion of the extracranial ICA. This finding is consistent with the presence of early, low-grade ischemic injury.

Quantitative measurement of cerebrovascular reactivity by blood oxygen level-dependent MR imaging in patients with intracranial stenosis: preoperative cerebrovascular reactivity predicts the effect of extracranial-intracranial bypass surgery

BACKGROUND AND PURPOSE

CVR is a measure of cerebral hemodynamic impairment. A recently validated technique quantifies CVR by using a precise CO(2) vasodilatory stimulus and BOLD MR imaging. Our aim was to determine whether preoperative CO(2) BOLD CVR predicts the hemodynamic effect of ECIC bypass surgery in patients with intracranial steno-occlusive disease.

MATERIALS AND METHODS

Twenty-five patients undergoing ECIC bypass surgery for treatment of intracranial stenosis or occlusion were recruited. CVR was measured preoperatively and postoperatively and expressed as %ΔBOLD MR signal intensity per mm Hg ΔPetCO(2). Using normative data from healthy subjects, we stratified patients on the basis of preoperative CVR into 3 groups: normal CVR, reduced CVR, and negative (paradoxical) CVR. Wilcoxon 2-sample tests (2-sided, α = 0.05) were used to determine whether the 3 groups differed with respect to change in CVR following bypass surgery.

RESULTS

The group with normal preoperative CVR demonstrated no significant change in CVR following bypass surgery (mean, 0.22% ± 0.05% to 0.22% ± 0.01%; P = .881). The group with reduced preoperative CVR demonstrated a significant improvement following bypass surgery (mean, 0.08% ± 0.05% to 0.21 ± 0.08%; P < .001), and the group with paradoxical preoperative CVR demonstrated the greatest improvement (mean change, -0.04% ± 0.03% to 0.27% ± 0.03%; P = .028).

CONCLUSIONS

Preoperative measurement of CVR by using CO(2) BOLD MR imaging predicts the hemodynamic effect of ECIC bypass in patients with intracranial steno-occlusive disease. The technique is potentially useful for selecting patients for surgical revascularization.

Differences in the control of breathing between Himalayan and sea-level residents

We compared the control of breathing of 12 male Himalayan highlanders with that of 21 male sea-level Caucasian lowlanders using isoxic hyperoxic ( = 150 mmHg) and hypoxic ( = 50 mmHg) Duffin's rebreathing tests. Highlanders had lower mean +/- s.e.m. ventilatory sensitivities to CO(2) than lowlanders at both isoxic tensions (hyperoxic: 2.3 +/- 0.3 vs. 4.2 +/- 0.3 l min(1) mmHg(1), P = 0.021; hypoxic: 2.8 +/- 0.3 vs. 7.1 +/- 0.6 l min(1) mmHg(1), P < 0.001), and the usual increase in ventilatory sensitivity to CO(2) induced by hypoxia in lowlanders was absent in highlanders (P = 0.361). Furthermore, the ventilatory recruitment threshold (VRT) CO(2) tensions in highlanders were lower than in lowlanders (hyperoxic: 33.8 +/- 0.9 vs. 48.9 +/- 0.7 mmHg, P < 0.001; hypoxic: 31.2 +/- 1.1 vs. 44.7 +/- 0.7 mmHg, P < 0.001). Both groups had reduced ventilatory recruitment thresholds with hypoxia (P < 0.001) and there were no differences in the sub-threshold ventilations (non-chemoreflex drives to breathe) between lowlanders and highlanders at both isoxic tensions (P = 0.982), with a trend for higher basal ventilation during hypoxia (P = 0.052). We conclude that control of breathing in Himalayan highlanders is distinctly different from that of sea-level lowlanders. Specifically, Himalayan highlanders have decreased central and absent peripheral sensitivities to CO(2). Their response to hypoxia was heterogeneous, with the majority decreasing their VRT indicating either a CO(2)-independent increase in activity of peripheral chemoreceptor or hypoxia-induced increase in [H(+)] at the central chemoreceptor. In some highlanders, the decrease in VRT was accompanied by an increase in sensitivity to CO(2), while in others VRT remained unchanged and their sub-threshold ventilations increased, although these were not statistically significant.

Quantification of cerebrovascular reactivity by blood oxygen level-dependent MR imaging and correlation with conventional angiography in patients with Moyamoya disease

BACKGROUND AND PURPOSE

BOLD MR imaging combined with a technique for precision control of end-tidal pCO(2) was used to produce quantitative maps of CVR in patients with Moyamoya disease. The technique was validated against measures of disease severity by using conventional angiography; it then was used to study the relationship between CVR, vascular steal, and disease severity.

MATERIALS AND METHODS

A retrospective analysis comparing conventional angiography with BOLD MR imaging was performed on 11 patients with Moyamoya disease. Iso-oxic cycling of end-tidal pCO(2) between 2 target values was performed during BOLD MR imaging. CVR was calculated as the BOLD signal difference per Delta pCO(2). CVR was correlated with the presence of Moyamoya or pial collaterals and the degree of Moyamoya disease as graded by using a modified Suzuki score.

RESULTS

A good correlation between mean CVR and Suzuki score was found for the MCA and ACA territories (Pearson correlation coefficient, -0.7560 and -0.6140, respectively; P < .0001). A similar correlation was found between mean CVR and the presence of pial and Moyamoya collateral vessels for combined MCA and ACA territories (Pearson correlation coefficient, -0.7466; P < .0001). On a voxel-for-voxel basis, there was a greater extent of steal within vascular territories with increasing disease severity (higher modified Suzuki score). Mean CVR was found to scale nonlinearly with the extent of vascular steal.

CONCLUSIONS

Quantitative measures of CVR show direct correlation with impaired vascular supply as measured by the modified Suzuki score and enable direct investigation of the physiology of autoregulatory reserve, including steal phenomenon, within a given vascular territory.

Isocapnic hyperpnoea accelerates recovery from isoflurane anaesthesia

BACKGROUND

Hyperventilation should speed up elimination of volatile anaesthetic agents from the body, but hyperventilation usually results in hypocapnia. We compared recovery from isoflurane anaesthesia in patients allowed to recover with assisted spontaneous ventilation (control) and those treated with isocapnic hyperpnoea.

METHODS

Fourteen patients were studied after approximately 1 h of anaesthesia with isoflurane. Control patients were allowed to recover in the routine way. Isocapnic hyperpnoea patients received 2-3 times their intraoperative ventilation using a system to maintain end tidal PCO(2) at 45-50 mm Hg. We measured time to removal of the airway and rate of change of bispectral index (BIS) during recovery.

RESULTS

With isocapnic hyperpnoea, the time to removal of the airway was markedly less (median and interquartile range values of 3.6 (2.7-3.7) vs 12.1 (6.8-17.2) min, P<0.001); mean (SD) BIS slopes during recovery were 11.8 (4.4) vs 4.3 (2.7) min(-1) (P<0.01) for isocapnic hyperpnoea and control groups, respectively. Isocapnic hyperpnoea was easily applied in the operating room.

CONCLUSIONS

Isocapnic hyperpnoea at the end of surgery results in shorter and less variable time to removal of the airway after anaesthesia with isoflurane and nitrous oxide.

A simple apparatus for accelerating recovery from inhaled volatile anesthetics

Hyperpnea increases anesthetic elimination but is difficult to implement with current anesthetic circuits without decreasing arterial PCO2. To circumvent this, we modified a standard resuscitation bag to maintain isocapnia during hyperpnea without rebreathing by passively matching inspired PCO2 to minute ventilation. We evaluated the feasibility of using this apparatus to accelerate recovery from anesthesia in a pilot study in four isoflurane-anesthetized dogs. The apparatus was easy to use, and all dogs tolerated being ventilated with it. Under our experimental conditions, isocapnic hyperpnea reduced the time to extubation by 62%, from an average of 17.5 to 6.6 min (P = 0.012), but not time from extubation to standing unaided. This apparatus may provide a practical means of applying isocapnic hyperpnea to shorten recovery time from volatile anesthetics.

IMPLICATIONS

A simple modification to a standard resuscitation bag allows one to increase ventilation without decreasing blood carbon dioxide levels. In dogs, we confirmed that this circuit can be used to accelerate the elimination of and recovery from volatile anesthetics.

Secretion of whey acidic protein and cystatin is down regulated at mid-lactation in the red kangaroo (Macropus rufus)

Milk collected from the red kangaroo (Macropus rufus) between day 100 and 260 of lactation showed major changes in milk composition at around day 200 of lactation, the time at which the pouch young begins to temporarily exit the pouch and eat herbage. The carbohydrate content of milk declined abruptly at this time and although there was only a small increase in total protein content, SDS PAGE analysis of milk revealed asynchrony in the secretory pattern of individual proteins. The levels of alpha-lactalbumin, beta-lactoglobulin, serum albumin and transferrin remain unchanged during lactation. In contrast, the protease inhibitor cystatin, and the putative protease inhibitor whey acidic protein (WAP) first appeared in milk at elevated concentrations after approximately 150 days of lactation and then ceased to be secreted at approximately 200 days. In addition, a major whey protein, late lactation protein, was first detected in milk around the time whey acidic protein and cystatin cease to be secreted and was present at least until day 260 of lactation. The co-ordinated, but asynchronous secretion of putative protease inhibitors in milk may have several roles during lactation including tissue remodelling in the mammary gland and protecting specific proteins in milk required for physiological development of the dependent young.

MRI mapping of cerebrovascular reactivity using square wave changes in end-tidal PCO2

Cerebrovascular reactivity can be quantified by correlating blood oxygen level dependent (BOLD) signal intensity with changes in end-tidal partial pressure of carbon dioxide (PCO2). Four 3-min cycles of high and low PCO2 were induced in three subjects, each cycle containing a steady PCO2 level lasting at least 60 sec. The BOLD signal closely followed the end-tidal PCO2. The mean MRI signal intensity difference between high and low PCO2 (i.e., cerebrovascular reactivity) was 4.0 +/- 3.4% for gray matter and 0.0 +/- 2.0% for white matter. This is the first demonstration of the application of a controlled reproducible physiologic stimulus, i.e., alternating steady state levels of PCO2, to the quantification of cerebrovascular reactivity.

Aluminium tolerance and lime increase wheat yield on the acidic soils of central and southern New South Wales

Acidic soils constrain wheat yield in some parts of central and southern New South Wales. This paper describes research designed to evaluate the usefulness of aluminium (Al) tolerance, manganese (Mn) tolerance and the interaction of lime use and Al tolerance in improving wheat yields. Closely related pairs of wheat lines with tolerance and sensitivity of Al and Mn were bred. Carazinho (a Brazilian wheat cultivar) was used as a source of Al tolerance in a backcrossing, recurrent selection program to introduce tolerance into an Egret background (a locally adapted Australian cultivar). Aluminium tolerance was determined using the haematoxylin root tip test and Mn tolerance was determined using a subirrigated gravel bed system. Eight pairs divergent in tolerance of Al were evaluated for their yield on 3 acidic soil types in 5 field experiments. Grain yield increased in Egret-derived lines when Al tolerance from Carazinho was introduced. Yield from the Al-sensitive genotypes (averaged over the 8 pairs) compared with the Al-tolerant genotypes was 0.43 to 0.98 t/ha and 0.88 to 1.38 t/ha respectively on an acid earthy sand in central western New South Wales (Binnaway) in 2 seasons, and 1.08 to 1.96 t/ha and 1.29 to 1.88 t/ha on an acid podsolic soil in southern New South Wales (Borambola). On a moderately acidic red earth site (pH Ca 4.8) at Wagga Wagga, no such advantage accrued to the Al-tolerant group with the average yield for the sensitive and tolerant pairs being 5.00 and 4.78 t/ha, respectively. Manganese tolerance was assessed in only 1 of these experiments (Borambola) using 6 pairs of lines tolerant of Al but with contrasting Mn tolerance. No advantage of Mn tolerance was apparent at this site. At Binnaway the tolerant and sensitive lines responded to lime application with the tolerant lines yielding on average about 0.42 t/ha of grain more than the sensitive lines even when 5 t/ha of lime was applied. At Borambola the tolerant lines yielded 0.59 t/ha of grain more than the sensitive lines when no lime was applied. With lime application this difference in performance disappeared and Al-tolerant and sensitive lines yielded equally. At the Wagga Wagga site, the addition of lime did not affect the yield of the sensitive lines, while the tolerant lines showed a yield depression of 0.32 t/ha of grain with lime application. Three different relationships between lime application and Al tolerance were observed. While 2 relationships fit with our previous understanding, grain yield depression resulting from the combined use of Al tolerance and lime at our least acidic site remains poorly understood.

Tracheal constrictor drive above the apneic threshold in anesthetized dogs

We have previously shown that raising arterial PCO(2) (Pa(CO(2))) by small increments in dogs ventilated below the apneic threshold (AT) results in almost complete tracheal constriction before the return of phrenic activity (Dickstein JA, Greenberg A, Kruger J, Robicsek A, Silverman J, Sommer L, Sommer D, Volgyesi G, Iscoe S, and Fisher JA. J Appl Physiol 81: 1844-1849, 1996). We hypothesized that, if increasing chemical drive above the AT mediates increasing constrictor drive to tracheal smooth muscle, then pulmonary slowly adapting receptor input should elicit more tracheal dilation below the AT than above. In six methohexital sodium-anesthetized, paralyzed, and ventilated dogs, we measured changes in tracheal diameter in response to step increases in tidal volume (VT) or respiratory frequency (f) below and above the AT at constant Pa(CO(2)) ( approximately 40 and 67 Torr, respectively). Increases in VT (400-1,200 ml) caused significantly more (P = 0.005) tracheal dilation below than above AT (7.0 +/- 2.2 vs. 2.8 +/- 1.0 mm, respectively). In contrast, increases in f (14-22 breaths/min) caused similar (P = 0.93) tracheal dilations below and above (1.0 +/- 1.3 and 1.0 +/- 0.8 mm, respectively) AT. The greater effectiveness of dilator stimuli below compared with above the AT is consistent with the hypothesis that drive to tracheal smooth muscle increases even after attainment of maximal constriction. Our results emphasize the importance of controlling PCO(2) with respect to the AT when tracheal smooth muscle tone is experimentally altered.

Determinants of the annual pattern of reproduction in mature male merino and Suffolk sheep: modification of endogenous rhythms by photoperiod

In mediterranean environments, pastures are very poor during the autumn and consequently small ruminants, such as sheep, would have been losing body mass for many months so, during mating, gamete production would be depressed in both sexes. Effectively, the nutritive requirements for a photoperiod-driven, annual reproductive cycle are out of phase with seasonal changes in food availability. The problem could be overcome through more flexible timing of reproduction, perhaps explaining variations in seasonality between breeds that originate from differing latitudes. To study these concepts and the mechanisms involved, the endogenous rhythms and responses to photoperiod were compared in rams of 'mediterranean origin' (Merino) and 'temperate origin' (Suffolk). Groups of 16 rams of each breed were given a constant food supply and subjected to 16 months of constant equinoctial photoperiod (12L : 12D) or simulated 'mediterranean' changes in daylength (from 14L : 10D to 14D : 10L). With nutritional and photoperiodic inputs held constant, Merino and Suffolk rams showed similar endogenous rhythms in reproductive activity. Under constant nutritional inputs and a mediterranean photoperiodic cycle, the endogenous rhythms were modified differently in the two breeds, with the Merinos starting and finishing their seasons about 2 months earlier than the Suffolks. These observations partially explain the patterns observed in rams kept under field conditions. It is now necessary to test whether the rhythms of reproduction in these breeds are also modified by changes in nutrition and social cues.

The gene for a novel member of the whey acidic protein family encodes three four-disulfide core domains and is asynchronously expressed during lactation

Secretion of whey acidic protein (WAP) in milk throughout lactation has previously been reported for a limited number of species, including the mouse, rat, rabbit, camel, and pig. We report here the isolation of WAP from the milk of a marsupial, the tammar wallaby (Macropus eugenii). Tammar WAP (tWAP) was isolated by reverse-phase HPLC and migrates in SDS-polyacrylamide gel electrophoresis at 29.9 kDa. tWAP is the major whey protein, but in contrast to eutherians, secretion is asynchronous and occurs only from approximately days 130 through 240 of lactation. The full-length cDNA codes for a mature protein of 191 amino acids, which is comprised of three four-disulfide core domains, contrasting with the two four-disulfide core domain arrangement in all other known WAPs. A three-dimensional model for tWAP has been constructed and suggests that the three domains have little interaction and could function independently. Analysis of the amino acid sequence suggests the protein belongs to a family of protease inhibitors; however, the predicted active site of these domains is dissimilar to the confirmed active site for known protease inhibitors. This suggests that any putative protease ligand may be unique to either the mammary gland, milk, or gut of the pouch young. Examination of the endocrine regulation of the tWAP gene showed consistently that the gene is prolactin-responsive but that the endocrine requirements for induction and maintenance of tWAP gene expression are different during lactation.

A simple "new" method to accelerate clearance of carbon monoxide

The currently recommended prehospital treatment for carbon monoxide (CO) poisoning is administration of 100% O(2). We have shown in dogs that normocapnic hyperpnea with O(2) further accelerates CO elimination. The purpose of this study was to examine the relation between minute ventilation (V E) and the rate of elimination of CO in humans. Seven healthy male volunteers were exposed to CO (400 to 1,000 ppm) in air until their carboxyhemoglobin (COHb) levels reached 10 to 12%. They then breathed either 100% O(2) at resting V E (4.3 to 9.0 L min) for 60 min or O(2) containing 4.5 to 4.8% CO(2) (to maintain normocapnia) at two to six times resting V E for 90 min. The half-time of the decrease in COHb fell from 78 +/- 24 min (mean +/- SD) during resting V E with 100% O(2) to 31 +/- 6 min (p < 0. 001) during normocapnic hyperpnea with O(2). The relation between V E and the half-time of COHb reduction approximated a rectangular hyperbola. Because both the method and circuit are simple, this approach may enhance the first-aid treatment of CO poisoning.

Isocapnic hyperpnea accelerates carbon monoxide elimination

A major impediment to the use of hyperpnea in the treatment of CO poisoning is the development of hypocapnia or discomfort of CO2 inhalation. We examined the effect of nonrebreathing isocapnic hyperpnea on the rate of decrease of carboxyhemoglobin levels (COHb) in five pentobarbital-anesthetized ventilated dogs first exposed to CO and then ventilated with room air at normocapnia (control). They were then ventilated with 100% O2 at control ventilation, and at six times control ventilation without hypocapnia ("isocapnic hyperpnea") for at least 42 min at each ventilator setting. We measured blood gases and COHb. At control ventilation, the half-time for elimination of COHb (t1/2) was 212 +/- 17 min (mean +/- SD) on room air and 42 +/- 3 min on 100% O2. The t1/2 decreased to 18 +/- 2 min (p < 0.0005) during isocapnic hyperpnea. In two similarly prepared dogs treated with hyperbaric O2, the t1/2 were 20 and 28 min. We conclude that isocapnic hyperpnea more than doubles the rate of COHb elimination induced by normal ventilation with 100% O2. Isocapnic hyperpnea could improve the efficacy of the standard treatment of CO poisoning, 100% O2 at atmospheric or increased pressures.

A simple breathing circuit minimizing changes in alveolar ventilation during hyperpnoea

Many clinical and research situations require maintenance of isocapnia, which occurs when alveolar ventilation (V'A) is matched to CO2 production. A simple, passive circuit that minimizes changes in V'A during hyperpnoea was devised. It is comprised of a manifold, with two gas inlets, attached to the intake port of a nonrebreathing circuit or ventilator. The first inlet receives a flow of fresh gas (CO2=0%) equal to the subject's minute ventilation (V'E). During hyperpnoea, the balance of V'E is drawn (inlet 2) from a reservoir containing gas, the carbon dioxide tension (PCO2) approximates that of mixed venous blood and therefore contributes minimally to V'A. Nine normal subjects breathed through the circuit for 4 min at 15-31 times resting levels. End-tidal PCO2 (Pet,CO2) at rest, 0, 1.5 and 3.0 min were (mean+/-SE) 5.1+/-0.1 kPa (38.1+/-1.1 mmHg), 4.9+/-0.1 kPa (36.4+/-1.1 mmHg), 5.0+/-0.2 kPa (37.8+/-1.6 mmHg) and 5.0+/-0.2 kPa (37.6+/-1.4 mmHg) (p=0.53, analysis of variance (ANOVA)), respectively; without the circuit, Pet,CO2 would be expected to have decreased by at least 2.7 kPa (20 mmHg). Six anaesthetized, intubated dogs were first ventilated at control levels and then hyperventilated by stepwise increases in either respiratory frequency (fR) from 10 to 24 min(-1) or tidal volume (VT) from 400 to 1,200 mL. Increases in fR did not significantly affect arterial CO2 tension (Pa,CO2) (p=0.28, ANOVA). Only the highest VT decreased Pa,CO2 from control (-0.5 +/- 0.3 kPa (-3.4 +/- 2.3 mmHg), p<0.05). In conclusion, this circuit effectively minimizes changes in alveolar ventilation and therefore arterial carbon dioxide tension during hyperpnoea.

A randomized comparison of rescuer positions for intubation on the ground

OBJECTIVE

To examine the ease of endotracheal intubation on the ground for various rescuer positions.

METHODS

Six female and 18 male emergency medical technicians were asked to intubate a Laerdal Megacode Trainer placed on the ground. Rescuers assumed the following positions in random order: prone, sitting, kneeling at the mannequin's head, and straddling the chest. The authors measured times 1) for changing from mask ventilation to assuming intubation position and 2) from touching the laryngoscope to putting it down. Incidences of esophageal tube placement and clicks (possible tooth damage) were noted. The rescuers rated their satisfaction with each position on a six-point scale (1 = very good, 6 = insufficient). Total intubation times of the other three positions were compared with that for prone by rank order test for paired observations. Handling, esophageal positions, and clicks of the other three positions were compared with those for prone by sign test for paired observations. A Bonferroni correction (factor 12) was applied.

RESULTS

Mean total intubation times (in seconds) were 11.8 +/- 3.3 for prone, 13.9 +/- 4.7 for sitting, 11.4 +/- 4.5 for kneeling, and 16.2 +/- 5.8 for straddling. The difference between straddling and prone was statistically significant (p < 0.005). For handling, the results were for prone 3.0 +/- 1.4, for sitting 3.1 +/- 1.1, for kneeling 2.2 +/- 0.6, and for straddling 2.8 +/- 1.4. Esophageal positions occurred for prone 1, for sitting 1, for kneeling 2, and for straddling 3. Clicks were counted for prone 2, for sitting 1, for kneeling 1, and for straddling 0.

CONCLUSIONS

All tested positions provide satisfactory conditions for intubation on the ground. The straddling position requires statistically, but not clinically, significantly more time for intubation than does prone and may be an important backup position if access from behind the patient's head is impossible.

Improving childhood immunizations in a family practice office

PURPOSE

In the fall of 1993, the Family Medicine Center (FMC) of the Medical Center of Delaware instituted an office-based program designed to improve preventive care for children. This study examined whether the "Pediatric Prevention Program" (PPP) resulted in an improvement in childhood immunization rates for FMC patients.

METHODS

Using chart review, we compared the percentage of two-year-old FMC patients who had completed appropriate immunizations before and after the PPP. We examined completion rates for the primary series of each immunization, for booster immunizations and for the combined total immunization series (four DPTs, three OPVs, one MMR, four HIBs). We also determined whether immunization rates were affected by patient demographics, pattern of office visits, and physician level of experience.

RESULTS

After implementation of the program, the percentage of 2-year-old children who had completed the appropriate immunizations increased for all types of immunizations. The increase was greatest for HIBs (6 percent for the primary HIB series and 7 percent increase for the HIB booster) and for the combined total series (10 percent increase). Children who made few office visits were the least likely to have completed immunizations, but also saw the greatest benefit from the PPP.

CONCLUSIONS

This study shows the positive impact of an office-based intervention for improving childhood immunizations. However, the improvements are relatively small and not sufficient to achieve optimal immunization rates throughout the community. In order to achieve these goals, additional interventions are needed which target high risk children, especially those who change physicians or who visit their physician infrequently. Targeting such children will likely require better data systems to track immunizations both in the office and across the community. These efforts should be given a high priority in Delaware.

PCO2 affects tracheal tone during apnea in anesthetized dogs

We hypothesized that CO2, like hypoxia and withdrawal of pulmonary slowly adapting receptor input, would cause tracheal constriction during neural apnea (absence of phrenic activity). In seven anesthetized paralyzed dogs ventilated to neural apnea, we increased arterial PCO2 (PaCO2) in steps by adding CO2 to the inspirate while keeping ventilation constant. Increases in PaCO2 caused tracheal constriction during neural apnea in all dogs; 69 +/- 26 (SD)% of the change in tracheal diameter occurred during neural apnea. Average sensitivity of tracheal diameter to CO2 was 0.44 mm/Torr PaCO2. Our data suggest that central chemoreceptor inputs to brain stem neurons controlling smooth muscle of the extrathoracic airway bypass central mechanisms generating inspiration.

Evaluation of a new pulse oximeter testing device

BACKGROUND

Valid routine testing of pulse oximeters and their sensors is problematic. A suitable testing device must not only generate the pulsatile signal the pulse oximeter requires for its operation, but must possess light absorption characteristics similar to those of living tissue. A new device called Pulse Oximeter Tester (POT) has recently become available which, it is claimed, addresses these problems.

PURPOSE

To evaluate the POT as a suitable stimulus for pulse oximeters.

METHOD

We tested all the pulse oximeters and their sensors with a set of POTs simulating blood oxygen saturation of 80%, 90% and 100%. The tests were performed at simulated heart rates of 30, 75 and 110 bpm.

RESULTS

The SpO2 readings (mean +/- SD) obtained with the 80%, 90% and 100% POTs were 80.7 +/- 1.3%, 90.3 +/- 0.9% and 100 +/- 0.0% respectively. There were no significant differences in readings obtained at the different simulated heart rates. Two pulse oximeters gave readings that deviated more than 2 SD from the mean. Their sensors were subsequently found to be defective.

CONCLUSION

POTs provide suitable stimuli for testing pulse oximeters. In our study sample they were found to be highly specific, but of unknown sensitivity.

Effectiveness of clozapine and a social learning program for severely disabled psychiatric inpatients

OBJECTIVE

This study examined the combined effectiveness of clozapine and a comprehensive inpatient psychosocial rehabilitation program on the clinical functioning and aggressive behaviors of patients with chronic schizophrenia.

METHODS

Two groups of 11 subjects each were selected from among patients being treated in the social learning program at Fulton (Mo.) State Hospital. Group 1 subjects were placed on clozapine at various times after the introduction of the program, while group 2 subjects remained on traditional antipsychotics throughout the study period. Group 1 and group 2 subjects were matched on clinical functioning as measured by the Time-Sample Behavioral Checklist (TSBC). For each subject, scores on six TSBC subscales were examined at five time points. Data were analyzed using repeated-measures multiple analysis of variance and univariate analyses of variance. Data on frequency of aggressive behaviors were aggregated into three six-month time periods and were analyzed using Wilcoxon signed-rank tests.

RESULTS

Both groups demonstrated significant improvement on several measures. However, the addition of clozapine resulted in accelerated improvement for group 1 subjects, especially in aggressive behaviors.

CONCLUSIONS

Comprehensive psychosocial treatment programming resulted in significant improvements in clinical functioning for many inpatients. Clozapine may enhance responsiveness to such programming for some patients.

The analysis of the NSW wheat variety database. II. Variance component estimation

The efficiency of various trialling systems for wheat variety evaluation in New South Wales (NSW) is considered. This involved the estimation of the variance components due to genotype, genotype-by-year, genotype-by-location and genotype-by-year-by-location. It is shown that there is a significant reduction in the magnitude of these variance components by the inclusion of the interaction of genotype maturity, winter habit and aluminium tolerance with environment.

The analysis of the NSW wheat variety database. I. Modelling trial error variance

The retrospective analysis of a large database on wheat variety testing in New South Wales (NSW) is considered. This analysis involved three key steps. Initially error variance heterogeneity is modelled, indicating significant differences in error variance due to trial location, year of trialling, sowing date and trial mean yield. The implication of this modelling for the estimaion of variance components is discussed.

Co-chemotactic effect of Gc-globulin (vitamin D binding protein) for C5a. Transient conversion into an active co-chemotaxin by neutrophils

Gc-globulin (vitamin D binding protein) has been shown to augment significantly the leukocyte chemotactic activity of the activated C peptides C5a and C5adesArg (i.e., the co-chemotactic effect). However, the mechanism of chemotaxis enhancement is not known. To investigate the role that the neutrophil plays in this process, cells were co-incubated with Gc-globulin for up to 45 min and washed, and their subsequent chemotactic response to a suboptimal concentration of C5a alone was measured during a 30-min assay. The generation of co-chemotactic activity during the preincubation period was time dependent, showed minimal activity for the first 10 min and a steep rise from 10 to 20 min, and was maximal and stable at 30 min. The binding of radiolabeled Gc-globulin by neutrophils at 37 degrees C mirrored this time-dependent generation of C5a co-chemotactic activity, with stable cellular levels achieved between 30 and 45 min at 36 +/- 4 fmol (2 +/- 0.1 ng)/10(6) cells. The binding of radiolabeled Gc-globulin and the generation of co-chemotactic activity were dependent upon physiologic temperatures (37 degrees C) and levels of Ca2+ (1.3 mM) and Mg2+ (0.8 mM), and were inhibited by an Ab to Gc-globulin. Finally, the C5a co-chemotactic activity of Gc-globulin would decay rapidly if neutrophils were washed and then incubated a second time at 37 degrees C before chemotaxis to C5a. These results demonstrate that neutrophils bind exogenous Gc-globulin and generate C5a co-chemotactic activity in a time-, temperature-, and divalent cation-dependent manner. Moreover, this activity is transient if neutrophils lack a continuous supply of Gc-globulin.

Co-chemotactic effect of Gc-globulin (vitamin D binding protein) for C5a. Transient conversion into an active co-chemotaxin by neutrophils

Gc-globulin (vitamin D binding protein) has been shown to augment significantly the leukocyte chemotactic activity of the activated C peptides C5a and C5adesArg (i.e., the co-chemotactic effect). However, the mechanism of chemotaxis enhancement is not known. To investigate the role that the neutrophil plays in this process, cells were co-incubated with Gc-globulin for up to 45 min and washed, and their subsequent chemotactic response to a suboptimal concentration of C5a alone was measured during a 30-min assay. The generation of co-chemotactic activity during the preincubation period was time dependent, showed minimal activity for the first 10 min and a steep rise from 10 to 20 min, and was maximal and stable at 30 min. The binding of radiolabeled Gc-globulin by neutrophils at 37 degrees C mirrored this time-dependent generation of C5a co-chemotactic activity, with stable cellular levels achieved between 30 and 45 min at 36 +/- 4 fmol (2 +/- 0.1 ng)/10(6) cells. The binding of radiolabeled Gc-globulin and the generation of co-chemotactic activity were dependent upon physiologic temperatures (37 degrees C) and levels of Ca2+ (1.3 mM) and Mg2+ (0.8 mM), and were inhibited by an Ab to Gc-globulin. Finally, the C5a co-chemotactic activity of Gc-globulin would decay rapidly if neutrophils were washed and then incubated a second time at 37 degrees C before chemotaxis to C5a. These results demonstrate that neutrophils bind exogenous Gc-globulin and generate C5a co-chemotactic activity in a time-, temperature-, and divalent cation-dependent manner. Moreover, this activity is transient if neutrophils lack a continuous supply of Gc-globulin.

Appetite and eating behavior in children

The authors propose that individual differences among children in the controls of food intake can be viewed in terms of differences in balance of power in feeding. They also argue that the individual differences in styles of intake control that emerge by adolescence and adulthood, including chronic dieting, eating disorders, and out-of-control eating, begin in the early balance of control in the feeding context. Limited evidence suggests that the course of development of shared control differs for intermeal interval, food selection, and meal size.

Mediastinal obstruction of the trachea

Acute tracheal obstruction by a mediastinal mass is uncommon in otolaryngologic practice. Choosing techniques for securing the airway, induction of anaesthesia, and the surgical approach require careful deliberation. We report our experience in a patient with acute respiratory distress due to external compression of the trachea in the mediastinum by metastatic carcinoma. We used a fibre-optic bronchoscope ensheathed by an endotracheal tube to secure the airway. Standard tracheotomy tubes were too short to splint open the obstruction in the distal trachea, whereas the long Montgomery T-tube was effective.

Dynamic measurement of tracheal diameter in dogs

We describe and validate a new minimally invasive method for continuous measurement of tracheal diameter in anesthetized dogs. The method is based on measuring displacement of water into and out of a modified endotracheal tube cuff placed in the trachea. The system was calibrated to allow tracheal diameter to be calculated from known cuff volume. The resolution of the method in measuring changes in tracheal diameter is 0.1 mm over a range of approximately 10-25 mm. The apparatus was tested in five dogs by observing the response of the trachea to four stimuli previously shown to alter tracheal tone: stimulation of nasal mucosa, hyperinflation of the lungs, induction of hypocapnea, and infusion of atropine. The observed changes in tracheal diameter were generally consistent with those of previous studies. The direction and extent of changes in tracheal diameter in response to the test conditions were confirmed by fluoroscopy. We conclude that continuous measurement of volume changes in the cuff reflects corresponding changes in tracheal diameter.