Elucidation of Schistosoma japonicum population dynamics in pigs using PCR-based identification of individuals representing distinct cohorts

The study reported here investigated the interactions of successive infections and acquired resistance of pigs to challenge infections of Schistosoma japonicum. Two morphologically indistinguishable geographical isolates from China (from Anhui and Zhejiang provinces) were used for the infections. The worms of the two isolates were distinguishable by PCR-linked restriction fragment length polymorphism analysis of the nicotinamide adenine dinucleotide phosphate dehydrogenase I gene of the mitochondrial genome. Thirty-two pigs divided into seven groups were used in the experiment. Two groups received a single infection by either the Anhui or the Zhejiang isolate. In Challenge Groups 1, 4, 6, 8 and 12, a primary infection of the Zhejiang isolate was followed by a challenge infection with the Anhui isolate at week 1, 4, 6, 8 or 12 after the primary infection. In this way it was possible to determine whether worms recovered by perfusion originated from the primary or the challenge infection. Only the challenge infection at week 1 resulted in a higher worm burden when compared with a single primary infection with the Zhejiang isolate. The results showed that challenge worms were able to establish, and that the proportion of worms originating from challenge infection increased at the later challenge infections, however without an increase in the total number of worms. In addition, mixed pairs of the two isolates were found in all challenge-infected groups. The results indicate that pigs are able to mount a partial resistance against re-infection with S. japonicum by 4 weeks after a primary infection, but that worms of the challenge infections eventually replace the primary infection. The finding of mixed pairs of the two isolates indicates that worms of S. japonicum are either polygamous or able to wait in solitude for up to 12 weeks for a partner.

Evaluation of cerebral perfusion pressure changes in laboring women: effects of epidural anesthesia

OBJECTIVE

To compare the effect of epidural anesthesia on cerebral perfusion pressure in laboring women.

STUDY DESIGN

Maternal cerebral blood flow velocity was assessed in seven laboring patients with continuous epidural anesthesia and 15 without, using transcranial Doppler. Maternal cerebral blood flow velocity was assessed during the first stage at the trough of a contraction, at the peak of a contraction and at the second stage during pushing over the course of four contractions. Calculated estimated cerebral perfusion pressure: eCPP = Vmean/(Vmean - Vdiastolic) x (mean BP - diastolic BP), where V is velocity and BP is blood pressure; modified from Aaslid and colleagues. An index of cerebrovascular resistance, the resistance area product, was calculated: RAP = mean BP/mean velocity. We calculated an index of cerebral blood flow (cerebral blood flow index): CBF index = eCPP/RAP.

RESULTS

In non-epidural patients, the eCPP fell significantly at the peak of a contraction and during pushing. Cerebrovascular resistance, RAP, rose significantly during the peak of a contraction, although cerebral blood flow did not change. In patients undergoing epidural anesthesia, the stages of labor had no significant effect on eCPP or RAP; however, these values were lower than those in patients without epidural anesthesia.

CONCLUSIONS

The epidural group had a lower eCPP and RAP and cerebral blood flow index compared to the non-epidural group. In the non-epidural group, the mean arterial pressure was higher in all stages of labor with a trend towards an increase in eCPP and cerebral blood flow index.

Plantar pressures are elevated in the neuroischemic and the neuropathic diabetic foot

OBJECTIVE

Clinical observation has noted that diabetic neuropathic ulcers occur frequently on the plantar surface, whereas neuroischemic ulcers seem to occur often on the foot margins. The reason for this difference in the site of ulceration is unknown, but it may be related to differences in pressure loading. The aim of the study was to compare vertical in-shoe foot pressures measured during walking (using the F-SCAN system) in four groups of patients whose degree of neuropathy was measured by vibration perception threshold (VPT).

RESEARCH DESIGN AND METHODS

Subjects included 14 neuroischemic diabetic patients (VPT 29.3 +/- 13.5 V) with history of ulceration on the margins of the foot, 18 patients with neuropathy alone (VPT 38.7 +/- 12.7 V) and previous history of ulceration on the plantar surface, 10 diabetic control patients (VPT 9.9 +/- 2.7 V), and 15 nondiabetic control subjects (VPT 7.0 +/- 0.5 V).

RESULTS

When compared with the other three groups, neuroischemic patients had higher foot pressures when measured as mean peak pressures and highest peak pressures under four areas of the foot: medial and lateral forefoot, hallux, and heel. Furthermore, when measuring the maximum pressures developed at any point under the plantar surface, the neuroischemic patients also had the most elevated pressures (757.6 +/- 135.9 kPa), significantly higher than those found in the neuropathic group (482.8 +/- 68.6 kPa, P = 0.04) and in both diabetic control patients (310.2 +/- 34.7 kPa, P = 0.008) and nondiabetic controls subjects (365.1 +/- 49.8 kPa, P = 0.007).

CONCLUSIONS

Despite having increased plantar pressures and a comparable degree of neuropatny, the neuroischemic patients did not have a history of ulceration on the plantar surface. These observations may have relevance to different mechanisms of ulcer formation in the neuroischemic and neuropathic foot.

Current role of scapulectomy

Tumors of the scapula are an unusual clinical challenge. Partial or complete resection of the scapula, with its attached musculoaponeurotic tissue, is a seldom used technique for the treatment of primary bone and soft tissue tumors, as well as selected metastatic involvement of the scapula. Scapulectomy may allow wide margins of resection without amputation. The purpose of this study is to review our recent experience with scapulectomy. This study describes the recent experience with scapulectomy by the Section of Surgical Oncology and the Department of Orthopedics at Louisiana State Medical Center (New Orleans, LA). Between 1994 and 1998, 12 patients (between 16 and 79 years of age) underwent a resection of the scapula. Eleven of these patients had soft tissue tumors; one had a metastasis from a thyroid carcinoma. Six of these patients underwent a scapulectomy as a primary treatment, five for recurrence. Six patients also received postoperative radiation and/or chemotherapy. The follow-up ranged from 6 months to 4 years. There was no mortality or wound infection associated with scapulectomy. All patients had normal hand and wrist function after surgery. Three distant recurrences occurred, with no local or regional failures encountered during the follow-up period. Scapulectomy can result in excellent local tumor control. Whereas some loss of active shoulder motion may occur, hand, wrist and elbow function is preserved. Although maintenance of shoulder function should not take precedence over adequacy of resection, scapulectomy remains an excellent procedure for malignant disease that preserves hand, wrist, and elbow function.

Causative bacteria of respiratory tract infections in Kuwait by quantitative culture of sputum

To determine the bacterial etiology of lower respiratory tract infections in Kuwait, we performed quantitative culture of sputum and measured the susceptibilities of the isolated bacteria against different antibiotics. A total of 140 sputum samples were collected for a period of 14 months for the study. Single and multiple pathogens as a cause of infection were isolated from 55 and 15 samples, respectively. A total of 53.8% of Streptococcus pneumoniae were penicillin-resistant and 52% and 57% of Hemophilus influenzae and Moraxella catarrhalis were beta-lactamase positive, respectively. We concluded that the major pathogens of respiratory tract infections in Kuwait were H. influenzae, M. catarrhalis, S. pneumoniae, and Pseudomonas aeruginosa, and there was an increased resistance among the isolated bacteria against commonly used antibiotics.

Differential distribution of orexin-A and orexin-B immunoreactivity in the rat brain and spinal cord

The orexins are recently identified appetite-stimulating hypothalamic peptides. We used immunohistochemistry to map orexin-A and orexin-B immunoreactivity in rat brain, spinal cord, and some peripheral tissues. Orexin-A- and orexin-B-immunoreactive cell bodies were confined to the lateral hypothalamic area and perifornical nuclei. Orexin-A-immunoreactive fibers were densely distributed in the hypothalamus, septum, thalamus, locus coeruleus, spinal cord, and near the ventricles, but absent from peripheral sites investigated. In contrast, orexin-B-immunoreactive fibers were distributed sparsely in the hypothalamus. Orexin cells are strategically sited to contribute to feeding regulation, but their widespread projections suggest that orexins have other physiological roles.

Persistence of cerebral hemodynamic changes in patients with eclampsia: A report of three cases

OBJECTIVE

This study was undertaken to compare the persistence of changes in estimated cerebral perfusion pressure and the resistance area product, an index of cerebrovascular resistance, in women with preeclampsia and women with eclampsia.

STUDY DESIGN

The maternal middle cerebral artery was evaluated by transcranial Doppler ultrasonography in 6 patients with severe preeclampsia and 3 women with eclampsia, and cerebral blood flow velocities were determined. Estimated cerebral perfusion pressure was calculated according to the following equation: Estimated cerebral perfusion pressure = Mean cerebral blood flow velocity/(Mean cerebral blood flow velocity - Diastolic cerebral blood flow velocity) x (Mean blood pressure - Diastolic blood pressure). Because the diameters of the vessels could not be measured directly, an index of resistance was calculated according to the following equation: Resistance area product = Mean blood pressure/Mean cerebral blood flow velocity. We calculated an index of cerebral blood flow according to the following equation: Index = Estimated cerebral perfusion pressure/Resistance area product. Patients were reassessed at 24 and 48 hours after delivery.

RESULTS

At the initial assessment the estimated cerebral perfusion pressure was higher in women with eclampsia than in those with severe preeclampsia. In addition, cerebrovascular resistance was significantly decreased in the eclampsia group, and it remained decreased as long as 4 days in 1 patient with eclampsia.

CONCLUSIONS

Preeclampsia is associated with increases in cerebral perfusion pressure counterbalanced by increases in cerebrovascular resistance, with no change in cerebral blood flow. In eclampsia a significant increase in cerebral perfusion pressure occurs, but a significant fall in cerebrovascular resistance also occurs and a loss of autoregulation results in cerebral overperfusion similar to that of hypertensive encephalopathy. This may persist for as long as 4 days.

Hypothalamic orexin expression: modulation by blood glucose and feeding

Orexins (hypocretins), novel peptides expressed in specific neurons of the lateral hypothalamic area (LHA), stimulate feeding when injected intracerebroventricularly. We investigated their role in feeding in the rat by measuring hypothalamic prepro-orexin mRNA levels under contrasting conditions of increased hunger. Prepro-orexin mRNA levels increased significantly after 48 h of fasting (by 90-170%; P < 0.05) and after acute (6 h) hypoglycemia when food was withheld (by 90%; P < 0.02). By contrast, levels were unchanged during chronic food restriction, streptozotocin-induced diabetes, hypoglycemia when food was available, voluntary overconsumption of palatable food, or glucoprivation induced by systemic 2-deoxy-D-glucose. Orexin expression was not obviously related to changes in body weight, insulin, or leptin, but was stimulated under conditions of low plasma glucose in the absence of food. Orexins may participate in the short-term regulation of energy homeostasis by initiating feeding in response to falls in glucose and terminating it after food ingestion. The LHA is known to contain neurons that are stimulated by falls in circulating glucose but inhibited by feeding-related signals from the viscera; orexin neurons may correspond to this neuronal population.

A specific sign of pneumoperitoneum on sonography: enhancement of the peritoneal stripe

OBJECTIVE

Failure to reveal pneumoperitoneum is a recognized weakness of abdominal sonography. Our objective is to describe a reliable and reproducible sign of pneumoperitoneum that was first identified in an animal model and then confirmed in patients who had undergone laparoscopy.

SUBJECTS AND METHODS

We injected 300 ml of degassed water into the peritoneal cavity of a 15-kg anesthetized pig. Sonographic images were obtained of the anterior peritoneal area after intraperitoneal injection of a single bubble, a series of bubbles, and, subsequently, a 10-ml bolus of air. Later, abdominal sonography was performed in nine patients who had undergone laparoscopy. Close attention was paid to the anterior peritoneal area and signs of free air observed in the animal model. Ten healthy volunteers functioned as a control group.

RESULTS

In the pig, minute amounts of intraperitoneal air showed on sonography as enhancement of the peritoneal stripe. Larger volumes of intraperitoneal air showed as enhancement of the peritoneal stripe associated with dirty shadowing or distal multiple reflection artifacts. The stripe enhanced each time it appeared in the reflection artifact. Intraluminal gas was associated with a normal thin peritoneal stripe, superficial and distinct from the underlying gas artifact. The patients who had undergone laparoscopy showed findings suggestive of small and large pockets of free air, as we saw in the pig model. The control group showed findings consistent with intraluminal gas only.

CONCLUSION

On sonography, enhancement of the peritoneal stripe alone or with reflection artifacts involving the peritoneal stripe is an accurate sign of pneumoperitoneum.

A major sporting event does not necessarily mean an increased workload for accident and emergency departments. Euro96 Group of Accident and Emergency Departments

AIM

To determine whether there were any changes in attendance at accident and emergency departments that could be related to international football matches (Euro96 tournament).

METHOD

Fourteen accident and emergency departments (seven adjacent to and seven distant from a Euro96 venue) provided their daily attendance figures for a nine week period: three weeks before, during, and after the tournament. The relation between daily attendance rates and Euro96 football matches was assessed using a generalised linear model and analysis of variance. The model took into account underlying trends in attendance rates including day of the week.

RESULTS

The 14 hospitals contributed 172 366 attendances (mean number of daily attendances 195). No association was shown between the number of attendances at accident and emergency departments and the day of the football match, whether the departments were near to or distant from stadia or the occurrence of a home nation match. The only observed independent predictors of variation were day of the week and week of the year. Attendance rates were significantly higher on Sunday and/or Monday; Monday was about 9% busier than the daily average. Increasing attendance was observed over time for 86% of the hospitals.

CONCLUSION

Large sports tournaments do not increase the number of patients attending accident and emergency departments. Special measures are not required for major sporting events over and above the capacity of an accident and emergency department to increase its throughput on other days.

A mutant HemA protein with positive charge close to the N terminus is stabilized against heme-regulated proteolysis in Salmonella typhimurium

The HemA enzyme (glutamyl-tRNA reductase) catalyzes the first committed step in heme biosynthesis in the enteric bacteria. HemA is mainly regulated by conditional protein stability; it is stable and, consequently, more abundant in heme-limited cells but unstable and less abundant in normally growing cells. Both the Lon and ClpAP energy-dependent proteases contribute to HemA turnover in vivo. Here we report that the addition of two positively charged lysine residues to the third and fourth positions at the HemA N terminus resulted in complete stabilization of the protein. By contrast, the addition of an N-terminal myc epitope tag did not affect turnover. This result confirms the importance of the N-terminal sequence for proteolysis of HemA. This region of the protein also contains a proline flanked by hydrophobic residues, a motif that has been suggested to be important for Lon-mediated proteolysis of UmuD. However, mutation of this motif did not affect the turnover of HemA protein. Cells expressing the stabilized HemA[KK] mutant protein display substantial defects in heme regulation.

Systematic review of near patient test evaluations in primary care

OBJECTIVE

To identify and qualitatively synthesise the findings from all studies that have examined the performance and effect of near patient tests in the primary care setting.

DESIGN

Systematic review of published and unpublished research 1986-99.

MAIN OUTCOME MEASURES

Test performance characteristics, measures of effect on clinical practice or patient outcome.

RESULTS

101 relevant publications were identified. The general quality of these papers was low, and consequently only 32 papers were assessed in detail. Although these papers gave some indication of the value of near patient testing in areas such as anticoagulation monitoring and group A beta haemolytic streptococcus testing, the research raised many more questions than it answered. Almost no reports were found of unbiased assessment of the effect of near patient tests in primary care on patient outcomes, organisational outcomes, or cost.

CONCLUSIONS

Available research provides little evidence to guide the expansion of use of near patient testing in primary care. Further research is needed in areas of clinical practice where near patient tests might be most beneficial.

Human urotensin-II is a potent vasoconstrictor and agonist for the orphan receptor GPR14

Urotensin-II (U-II) is a vasoactive 'somatostatin-like' cyclic peptide which was originally isolated from fish spinal cords, and which has recently been cloned from man. Here we describe the identification of an orphan human G-protein-coupled receptor homologous to rat GPR14 and expressed predominantly in cardiovascular tissue, which functions as a U-II receptor. Goby and human U-II bind to recombinant human GPR14 with high affinity, and the binding is functionally coupled to calcium mobilization. Human U-II is found within both vascular and cardiac tissue (including coronary atheroma) and effectively constricts isolated arteries from non-human primates. The potency of vasoconstriction of U-II is an order of magnitude greater than that of endothelin-1, making human U-II the most potent mammalian vasoconstrictor identified so far. In vivo, human U-II markedly increases total peripheral resistance in anaesthetized non-human primates, a response associated with profound cardiac contractile dysfunction. Furthermore, as U-II immunoreactivity is also found within central nervous system and endocrine tissues, it may have additional activities.

The effects of idazoxan on reaction times, eye movements and the mood of healthy volunteers and patients with upper respiratory tract illnesses

An experiment was carried out to determine whether idazoxan, a drug which increases the turnover of central noradrenaline, removes the malaise (reduced alertness, slower psychomotor performance) associated with upper respiratory tract illness (URTI). Eighty-one volunteers were tested when healthy and 17 returned to the laboratory when they developed URTIs. Those who remained healthy were then recalled as a control group. Volunteers were tested before and after receiving either idazoxan (40mg) or a lactose placebo. Idazoxan removed the URTI-induced slowing in a simple reaction time task and this group performed at a comparable level to the healthy group. No significant stimulant effect of idazoxan was found in the healthy subjects. The results suggest that at least part of the malaise induced by URTIs may reflect reductions in central noradrenaline and that this can be reversed by compounds such as idazoxan.

Behavior management techniques among pediatric dentists practicing in the southeastern United States

PURPOSE

This study identifies those techniques most often utilized by pediatric dentists practicing in the Southeastern United States. It also assesses how the utilization pattern may have changed within the last five years, and identifies those factors that may have influenced the changes as perceived by the practicing dentists.

METHODS

A questionnaire was mailed to 528 pediatric dentists who were members of the American Academy of Pediatric Dentistry, or The Southeastern Society of Pediatric Dentistry, or both.

RESULTS

The response rate after one mailing and one reminder was 64%. The majority of dentists utilized less aversive behavior management techniques (e.g., parents in the operatory and nitrous oxide oxygen) and had decreased or discontinued use of such controversial techniques as Hand-Over-Mouth-Exercise (HOME) and Hand-Over-Mouth-With-Airway Restriction (HOMAR). The majority of dentists reported that their reasons for changes in the utilization pattern for most techniques were parental influences and legal and ethical concerns.

CONCLUSIONS

Chi square analysis indicated significant differences (P < 0.05) in the frequency of use of behavior management techniques and age of practitioner, American Board of Pediatric Dentistry status, type of specialty training, and type of practice.

Identification, molecular cloning, expression, and characterization of a cysteinyl leukotriene receptor

The cysteinyl leukotrienes (CysLTs) have been implicated in the pathophysiology of inflammatory disorders, in particular asthma, for which the CysLT receptor antagonists pranlukast, zafirlukast, and montelukast, have been introduced recently as novel therapeutics. Here we report on the molecular cloning, expression, localization, and pharmacological characterization of a CysLT receptor (CysLTR), which was identified by ligand fishing of orphan seven-transmembrane-spanning, G protein-coupled receptors. This receptor, expressed in human embryonic kidney (HEK)-293 cells responded selectively to the individual CysLTs, LTC(4), LTD(4), or LTE(4), with a calcium mobilization response; the rank order potency was LTD(4) (EC(50) = 2.5 nM) > LTC(4) (EC(50) = 24 nM) > LTE(4) (EC(50) = 240 nM). Evidence was provided that LTE(4) is a partial agonist at this receptor. [(3)H]LTD(4) binding and LTD(4)-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor were potently inhibited by the structurally distinct CysLTR antagonists pranlukast, montelukast, zafirlukast, and pobilukast; the rank order potency was pranlukast = zafirlukast > montelukast > pobilukast. LTD(4)-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor was not affected by pertussis toxin, and the signal appears to be the result of the release from intracellular stores. Localization studies indicate the expression of this receptor in several tissues, including human lung, human bronchus, and human peripheral blood leukocytes. The discovery of this receptor, which has characteristics of the purported CysLT(1) receptor subtype, should assist in the elucidation of the pathophysiological roles of the CysLTs and in the identification of additional receptor subtypes.

Opinions of practitioners and program directors concerning accreditation standards for postdoctoral pediatric dentistry training programs

PURPOSE

This study was performed to assess opinions of program directors and practitioners about the importance and necessary numbers of experiences required by current accreditation standards for training of pediatric dentists.

METHODS

A 32-item questionnaire was sent to all program directors of ADA-accredited postdoctoral pediatric dentistry training programs and to a random sample of 10% of the fellow/active membership of the American Academy of Pediatric Dentistry.

RESULTS

An overall response rate of 56% was obtained from the single mailing. Practitioners and program directors differed significantly (P < or = 0.05) only in their opinions about the number of submucosal and intravenous sedation cases required for proficiency of eight experiences surveyed. The two groups differed significantly in 3 of 12 areas in terms of importance attributed for practice of contemporary pediatric dentistry: initiating and completing a research paper, biostatistics/epidemiology, and practice management. Program directors had little difficulty obtaining required experiences, and program dependence on Medicaid did not negatively affect quality of education.

CONCLUSION

Practitioners and program directors agreed on the importance of most experiences and activities required by current accreditation standards.

Assessment of GABA(A)benzodiazepine receptor (GBzR) sensitivity in patients on benzodiazepines

OBJECTIVES

To measure GABA(A) benzodiazepine receptor sensitivity in patients taking benzodiazepines and compare with matched controls.

METHODS

Seven patients who were on prescribed benzodiazepines for an anxiety disorder or insomnia were recruited from general practice and an adult mental health service outpatient clinic. They were matched with seven volunteers. All subjects received an intravenous injection of midazolam 50 microgram/kg in 10 ml normal saline over 10 min. Objective responses to midazolam were assessed using saccadic eye movement velocity slowing and subjective assessments using visual analogue scales. Measurements were recorded for 120 min and plasma midazolam concentrations obtained at 15-min intervals post-infusion to 120 min. Ratios of pharmacodynamic/pharmacokinetic effects were obtained for each individual to estimate GABA(A) benzodiazepine receptor sensitivity.

RESULTS

Patients had an attenuated response to midazolam on both subjective and objective measures. GABA(A) benzodiazepine receptor sensitivity was significantly reduced in the patient group.

CONCLUSIONS

Chronic treatment with benzodiazepines was associated with reduced effects of midazolam. Saccadic eye movement velocity was especially sensitive as a measure of attenuated response.

Visualization of agonist-induced association and trafficking of green fluorescent protein-tagged forms of both beta-arrestin-1 and the thyrotropin-releasing hormone receptor-1

A fusion protein (beta-arrestin-1-green fluorescent protein (GFP)) was constructed between beta-arrestin-1 and a modified form of the green fluorescent protein from Aequorea victoria. Expression in HEK293 cells allowed immunological detection of an 82-kDa cytosolic polypeptide with antisera to both beta-arrestin-1 and GFP. Transient expression of this construct in HEK293 cells stably transfected to express the rat thyrotropin-releasing hormone receptor-1 (TRHR-1) followed by confocal microscopy allowed its visualization evenly distributed throughout the cytoplasm. Addition of thyrotropin-releasing hormone (TRH) caused a profound and rapid redistribution of beta-arrestin-1-GFP to the plasma membrane followed by internalization of beta-arrestin-1-GFP into distinct, punctate, intracellular vesicles. TRH did not alter the cellular distribution of GFP transiently transfected into these cells nor the distribution of beta-arrestin-1-GFP following expression in HEK293 cells lacking the receptor. To detect potential co-localization of the receptor and beta-arrestin-1 in response to agonist treatment, beta-arrestin-1-GFP was expressed stably in HEK293 cells. A vesicular stomatitis virus (VSV)-tagged TRHR-1 was then introduced transiently. Initially, the two proteins were fully resolved. Short term exposure to TRH resulted in their plasma membrane co-localization, and sustained exposure to TRH resulted in their co-localization in punctate, intracellular vesicles. In contrast, beta-arrestin-1-GFP did not relocate or adopt a punctate appearance in cells that did not express VSV-TRHR-1. Reciprocal experiments were performed, with equivalent results, following transient expression of beta-arrestin-1 into cells stably expressing VSVTRHR-1-GFP. These results demonstrate the capacity of beta-arrestin-1-GFP to interact with the rat TRHR-1 and directly visualizes their recruitment from cytoplasm and plasma membrane respectively into overlapping, intracellular vesicles in an agonist-dependent manner.

Effect of nitric oxide, perfluorocarbon, and heliox on minute volume measurement and ventilator volumes delivered

OBJECTIVE

To determine the effect of heliox, nitric oxide (NO), and perfluorocarbon on differential pressure pneumotachometer characteristics and to determine the effect of heliox on volumes delivered by the Siemens S900C (S900C), and Servo Ventilator 300 (SV300) ventilators.

DESIGN

Prospective, laboratory study.

SETTING

Pulmonary laboratory of a tertiary care, nonprofit children's hospital.

APPARATUS

SV300, S900C ventilator, differential pressure pneumotachometer.

INTERVENTIONS

Dual pneumotachometers were connected in series to a 0.5-L calibration syringe and a 1-L anesthesia bag creating a closed system. Calibration of the pneumotachometers was done in room air at ambient temperature with 100 strokes. Accepted accuracy of measured volumes is within 0.5%. Flow-conductance curves were constructed using 100 strokes each for heliox (70:30 mixture), NO, and perfluorocarbon. Expired gases of room air and a 70:30 mixture of heliox from the above ventilators were collected into a nondiffusing gas collection bag, and the volume was measured in a chain-compensated gasometer. Ten sets of 500-mL breaths (20 breaths each set) and 100-mL breaths (40 breaths each set) were collected. The paired Student's t-test was used to detect significant differences in measured volumes, with significance defined as p < .01.

MEASUREMENTS AND MAIN RESULTS

Volumes measured with the pneumotachometer using 25 ppm of NO, 50 ppm of NO, and perfluorocarbon were within +0.25%, -0.7%, and +0.4%, respectively (p = .155, p = .001, p = .06). Heliox decreased the conductance of the pneumotachometer, thereby increasing the measured volume by 15% (p < .001). However, heliox did not affect its linearity. Heliox had no affect on volumes delivered by the S900C. However, the SV300 delivered 7.9% less volume of heliox at a set tidal volume of 500 mL and 10.8% less at a set tidal volume of 100 mL.

CONCLUSIONS

A 70:30 mixture of heliox caused a significantly overestimated gas volume measured and, therefore, an underestimated gas volume delivered by SV300. NO at 25 ppm and perfluorocarbon did not interfere with the accuracy of a differential pressure pneumotachometer. However, at 50 ppm, NO caused a difference in measured gas volume that was statistically, but not clinically, significant. Application of pneumotachometers in critically ill children receiving heliox requires recalibration. Heliox did not affect volumes delivered with the S900C ventilator. Although volumes delivered with the SV300 were significantly reduced by heliox, the difference can be corrected easily by increasing minute ventilation until expired tidal volume equals desired tidal volume.