Inducing Hepatitis C Virus Resistance After Pig Liver Transplantation-A Proof of Concept of Liver Graft Modification Using Warm Ex Vivo Perfusion

Normothermic ex vivo liver perfusion (NEVLP) offers the potential to optimize graft function prior to liver transplantation (LT). Hepatitis C virus (HCV) is dependent on the presence of miRNA(microRNA)-122. Miravirsen, a locked-nucleic acid oligonucleotide, sequesters miR-122 and inhibits HCV replication. The aim of this study was to assess the efficacy of delivering miravirsen during NEVLP to inhibit miR-122 function in a pig LT model. Pig livers were treated with miravirsen during NEVLP or cold storage (CS). Miravirsen absorption, miR-122 sequestration, and miR-122 target gene derepression were determined before and after LT. The effect of miravirsen treatment on HCV infection of hepatoma cells was also assessed. NEVLP improved miravirsen uptake versus CS. Significant miR-122 sequestration and miR-122 target gene derepression were seen with NEVLP but not with CS. In vitro data confirmed miravirsen suppression of HCV replication after established infection and prevented HCV infection with pretreatment of cells, analogous to the pretreatment of grafts in the transplant setting. In conclusion, miravirsen delivery during NEVLP is a potential strategy to prevent HCV reinfection after LT. This is the first large-animal study to provide "proof of concept" for using NEVLP to modify and optimize liver grafts for transplantation.

Strain differences in pH-sensitive K+ channel-expressing cells in chemosensory and nonchemosensory brain stem nuclei

The ventilatory CO2 chemoreflex is inherently low in inbred Brown Norway (BN) rats compared with other strains, including inbred Dahl salt-sensitive (SS) rats. Since the brain stem expression of various pH-sensitive ion channels may be determinants of the CO2 chemoreflex, we tested the hypothesis that there would be fewer pH-sensitive K(+) channel-expressing cells in BN relative to SS rats within brain stem sites associated with respiratory chemoreception, such as the nucleus tractus solitarius (NTS), but not within the pre-Bötzinger complex region, nucleus ambiguus or the hypoglossal motor nucleus. Medullary sections (25 μm) from adult male and female BN and SS rats were stained with primary antibodies targeting TASK-1, Kv1.4, or Kir2.3 K(+) channels, and the total (Nissl-stained) and K(+) channel immunoreactive (-ir) cells counted. For both male and female rats, the numbers of K(+) channel-ir cells within the NTS were reduced in the BN compared with SS rats (P < 0.05), despite equal numbers of total NTS cells. In contrast, we found few differences in the numbers of K(+) channel-ir cells among the strains within the nucleus ambiguus, hypoglossal motor nucleus, or pre-Bötzinger complex regions in both male and female rats. However, there were no predicted functional mutations in each of the K(+) channels studied comparing genomic sequences among these strains. Thus we conclude that the relatively selective reductions in pH-sensitive K(+) channel-expressing cells in the NTS of male and female BN rats may contribute to their severely blunted ventilatory CO2 chemoreflex.

Contributions of the Kölliker-Fuse nucleus to coordination of breathing and swallowing

Herein we compare the effects of perturbations in the Kölliker-Fuse nucleus (KFN) and the lateral (LPBN) and medial (MPBN) parabrachial nuclei on the coordination of breathing and swallowing. Cannula was chronically implanted in goats through which ibotenic acid (IA) was injected while awake. Swallows in late expiration (E) always reset while swallows in early inspiration (I) never reset the respiratory rhythm. Before cannula implantation, all other E and I swallows did not reset the respiratory rhythm, and had small effects on E and I duration and tidal volume (VT). However, after cannula implantation in the MPBN and KFN, E and I swallows reset the respiratory rhythm and increased the effects on I and E duration and VT. Subsequent injection of IA into the KFN eliminated the respiratory phase resetting of swallows but exacerbated the effects on I and E duration and VT. We conclude that the KFN and to a lesser extent the MPBN contribute to coordination of breathing and swallowing.

The effects of lesions in the dorsolateral pons on the coordination of swallowing and breathing in awake goats

The purpose of this retrospective study was to gain insight into the contribution of the dorsolateral pons to the coordination of swallowing and breathing in awake goats. In 4 goats, cannulas were chronically implanted bilaterally through the lateral (LPBN) and medial (MPBN) parabrachial nuclei just dorsal to the Kölliker-Fuse nucleus (KFN). After >2weeks recovery from this surgery, the goats were studied for 5½h on a control day, and on separate days after receiving 1 and 10μl injections of ibotenic acid (IA) separated by 1week. The frequency of swallows did not change during the control and 1μl IA studies, but after injection of 10μl IA, there was a transient 65% increase in frequency of swallows (P<0.05). Under control conditions swallows occurred throughout the respiratory cycle, where late-E swallows accounted for 67.6% of swallows. The distribution of swallow occurrence throughout the respiratory cycle was unaffected by IA injections. Consistent with the concept that swallowing is dominant over breathing, we found that swallows increased inspiratory (T(I)) and expiratory (T(E)) time and decreased tidal volume (V(T)) of the breath of the swallow (n) and/or the subsequent (n+1) breath. Injections of 10μl IA attenuated the normal increases in T(I) and T(E) and further attenuated V(T) of the n breath. Additionally, E and I swallows reset respiratory rhythm, but injection of 1 or 10μl IA progressively attenuated this resetting, suggesting a decreased dominance over respiratory motor output with increasing IA injections. Post mortem histological analysis revealed about 50% fewer (P<0.05) neurons remained in the KFN, LPBN, and MPBN in lesioned compared to control goats. We conclude that dorsolateral pontine nuclei have a modulatory role in a hypothesized holarchical neural network regulating swallowing and breathing particularly contributing to the normal dominance of swallowing over breathing in both rhythm and motor pattern generation.

Anatomic changes in multiple brainstem nuclei after incremental, near-complete neurotoxic destruction of the pre-Bötzinger Complex in adult goats

Abrupt, bilateral destruction of the pre-Bötzinger Complex (preBötC) leads to terminal apnea in unanesthetized goats and rats. In contrast, respiratory rhythm and pattern and arterial blood gases in goats during wakefulness and sleep are normal after incremental (over a month) destruction of > 90% of the preBötC. Here, we tested the hypothesis that the difference in effects between abrupt and incremental destruction of the preBötC are a result of time-dependent plasticity, which manifests as anatomic changes at sites within the respiratory network. Accordingly, we report data from histological analyses comparing the brainstems of control goats, and goats that had undergone bilateral, incremental, ibotenic acid (IA)-induced preBötC lesioning. A major focus was on the parafacial respiratory group/retrotrapezoid nucleus (pFRG/RTN) and the pontine respiratory group (PRG), which are sites thought to contribute to respiratory rhythmogenesis. We also studied the facial (FN), rostral nucleus ambiguus (NA), medullary raphé (MRN), hypoglossal (HN), and the dorsal motor vagal (DMV) nuclei. Neuronal counts, count region area (mm²), and neuronal densities were calculated using computer-assisted analyses and/or manual microscopy to compare control and preBötC-lesioned animals. We found that within the ventral and lateral medulla 2mm rostral to the caudal pole of the FN (presumed pFRG/RTN), there were 25% and 65% more (P < 0.001) neurons, respectively, in preBötC-lesioned compared to control goats. Lesioned goats also showed 14% and 13% more (P < 0.001) neurons in the HN and medial parabrachialis nucleus, but 46%, 28%, 7%, and 17% fewer (P < 0.001) neurons in the FN, NA, DMV, and Kölliker-Fuse nuclei, respectively. In the remaining sites analyzed, there were no differences between groups. We conclude that anatomic changes at multiple sites within the respiratory network may contribute to the time-dependent plasticity in breathing following incremental and near-complete destruction of the preBötC.

Differences between three inbred rat strains in number of K+ channel-immunoreactive neurons in the medullary raphé nucleus

Ventilatory sensitivity to hypercapnia is greater in Dahl salt-sensitive (SS) rats than in Fawn Hooded hypertensive (FHH) and Brown Norway (BN) inbred rats. Since pH-sensitive potassium ion (K(+)) channels are postulated to contribute to the sensing and signaling of changes in CO(2)-H(+) in chemosensitive neurons, we tested the hypothesis that there are more pH-sensitive K(+) channel-immunoreactive (ir) neurons within the medullary raphé nuclei of the highly chemosensitive SS rats than in the other two strains. Medullary tissues from male and female BN, FHH, and SS rats were stained with cresyl violet or with antibodies targeting TASK-1, K(v)1.4, and Kir2.3 channels. K(+) channel-ir neurons were quantified and compared with the total neurons in the region. The total number of neurons in the medullary raphé 1) was greater in male FHH than the other male rats, 2) did not differ among the female rats, and 3) did not differ between sexes. The average number of K(+) channel-ir neurons per section was 30-60 neurons higher in the male SS than in the other rat strains. In contrast, for the females, the number of K(+) channel-ir neurons was greatest in the BN. We also found significant differences in the number of K(+) channel-ir neurons between sexes in SS (males > females) and BN (females > males) rats, but not the FHH strain. Our findings support the hypothesis for males but not for females, suggesting that both genetic background and sex are determinants of K(+) channel immunoreactivity of medullary raphé neurons, and that the expression of pH-sensitive K(+) channels in the medullary raphé does not correlate with the ventilatory sensitivity to hypercapnia.

CO2/H+ chemoreceptors in the cerebellar fastigial nucleus do not uniformly affect breathing of awake goats

Our objective in this study was to test the hypothesis that focal acidosis (FA) in the cerebellar fastigial nucleus (CFN) of awake goats arising from global brain acidosis induced by increasing inspired CO2 will increase breathing. FA was created by reverse microdialysis of mock cerebral spinal fluid, equilibrated with 6.4, 25, 50, or 80% CO2 through chronically implanted microtubules (cannula). Dialysis with 6.4% CO2 had no significant effects on any physiological parameters. However, microdialysis at higher levels of CO2 increased pulmonary ventilation (V(I)) in one group of studies and decreased V(I) in a second group and the difference between the groups was significant (t = 9.16, P < 0.001). In one group of studies (n = 8), FA with 50 and 80% CO2 significantly increased (P < 0.05) Vi by 16 and 12%, respectively, and significantly increased (P < 0.05) heart rate by 13 and 9%, respectively. In contrast, in another group of studies (n = 6), FA with 25 and 50% CO2 significantly decreased (P < 0.05) Vi by 7 and 10%, respectively. In this group oxygen consumption was decreased during dialysis with 80% CO2. On the basis of histology, we estimate that the increased and decreased responses were associated with FA primarily in the rCFN and cCFN, respectively. We conclude that there are CO2/H+-sensitive neurons in the CFN that do not uniformly affect breathing. In addition, the significant changes in heart rate and oxygen consumption during FA indicate that the CFN can also influence non-respiratory-related control systems.

Voriconazole versus a regimen of amphotericin B followed by fluconazole for candidaemia in non-neutropenic patients: a randomised non-inferiority trial

BACKGROUND

Voriconazole has proven efficacy against invasive aspergillosis and oesophageal candidiasis. This multicentre, randomised, non-inferiority study compared voriconazole with a regimen of amphotericin B followed by fluconazole for the treatment of candidaemia in non-neutropenic patients.

METHODS

Non-neutropenic patients with a positive blood culture for a species of candida and clinical evidence of infection were enrolled. Patients were randomly assigned, in a 2:1 ratio, either voriconazole (n=283) or amphotericin B followed by fluconazole (n=139). The primary efficacy analysis was based on clinical and mycological response 12 weeks after the end of treatment, assessed by an independent data-review committee unaware of treatment assignment.

FINDINGS

Of 422 patients randomised, 370 were included in the modified intention-to-treat population. Voriconazole was non-inferior to amphotericin B/fluconazole in the primary efficacy analysis, with successful outcomes in 41% of patients in both treatment groups (95% CI for difference -10.6% to 10.6%). At the last evaluable assessment, outcome was successful in 162 (65%) patients assigned voriconazole and 87 (71%) assigned amphotericin B/fluconazole (p=0.25). Voriconazole cleared blood cultures as quickly as amphotericin B/fluconazole (median time to negative blood culture, 2.0 days). Treatment discontinuations due to all-cause adverse events were more frequent in the voriconazole group, although most discontinuations were due to non-drug-related events and there were significantly fewer serious adverse events and cases of renal toxicity than in the amphotericin B/fluconazole group.

INTERPRETATION

Voriconazole was as effective as the regimen of amphotericin B followed by fluconazole in the treatment of candidaemia in non-neutropenic patients, and with fewer toxic effects.

RELEVANCE TO PRACTICE

There are several options for treatment of candidaemia in non-neutropenic patients, including amphotericin B, fluconazole, voriconazole, and echinocandins. Voriconazole can be given both as initial intravenous treatment and as an oral stepdown agent.

Homing in on the specific phenotype(s) of central respiratory chemoreceptors

To some it may seem that we now know less about respiratory chemoreception than we did 20 years ago. Back then, it was widely accepted that the central respiratory chemoreceptors (CRCs) were located exclusively on or near the surface of the ventrolateral medulla (VLMS). Now, instead, it is generally believed that there are widespread sites of chemoreception, and there is little agreement on when and how each of these sites is involved in respiratory control. However, those in the field know that this actually is progress, primarily because we have gone from simply identifying candidate regions, to identifying specific neuronal subtypes that may be the sensors. In this invited review, we have been asked to discuss some of the current controversies in the field. First, we define the minimal requirements for a cell to be a CRC, and what assumptions can not be made without more data. Then we review the evidence that two neuronal subtypes, serotonergic neurones of the midline raphe and glutamatergic neurones of the retrotrapezoid nucleus, are chemoreceptors. There is evidence supporting a role in respiratory chemoreception for both types of neurone, as well as the other candidates, but there is also information that is missing. Future work will need to focus on which of the candidates are indeed chemoreceptors, what percentage of the overall response each one contributes, and how this percentage varies under different conditions.

Carotid body denervation alters ventilatory responses to ibotenic acid injections or focal acidosis in the medullary raphe

Our aim was to determine the effects of carotid body denervation (CBD) on the ventilatory responses to focal acidosis and ibotenic acid (IA) injections into the medullary raphe area of awake, adult goats. Multiple microtubules were chronically implanted into the midline raphe area nuclei either before or after CBD. For up to 15 days after bilateral CBD, arterial PCO2 (PaCO2) (13.3 +/- 1.9 Torr) was increased (P < 0.001), and CO2 sensitivity (-53.0 +/- 6.4%) was decreased (P <0.001). Thereafter, resting PaCO2 and CO2 sensitivity returned (P <0.01) toward control, but PaCO2 remained elevated (4.8 +/- 1.9 Torr) and CO2 sensitivity reduced (-24.7 +/- 6.0%) > or =40 days after CBD. Focal acidosis (FA) at multiple medullary raphe area sites 23-44 days post-CBD with 50 or 80% CO(2) increased inspiratory flow (Vi), tidal volume (Vt), metabolic rate (VO2), and heart rate (HR) (P <0.05). The effects of FA with 50% CO2 after CBD did not differ from intact goats. However, CBD attenuated (P <0.05) the increase in Vi, Vt, and HR with 80% CO2, but it had no effect on the increase in VO2. Rostral but not caudal raphe area IA injections increased Vi, BP, and HR (P < 0.05), and these responses were accentuated (P <0.001) after CBD. CO2 sensitivity was attenuated (-20%; P <0.05) <7 days after IA injection, but thereafter it returned to prelesion values in CBD goats. We conclude the following: 1) the attenuated response to FA after CBD provides further evidence that the carotid bodies provide a tonic facilitory input into respiratory control centers, 2) the plasticity after CBD is not due to increased raphe chemoreceptor sensitivity, and 3) the "error-sensing" function of the carotid body blunts the effect of strong stimulation of the raphe.

Effects on breathing of focal acidosis at multiple medullary raphe sites in awake goats

To gain insight into why there are chemoreceptors at widespread sites in the brain, mircrotubules were chronically implanted at two or three sites in the medullary raphe nuclei of adult goats (n = 7). After >2 wk, microdialysis (MD) probes were inserted into the microtubules to create focal acidosis (FA) in the awake state using mock cerebral spinal fluid (mCSF) equilibrated with 6.4% (pH = 7.3), 50% (pH = 6.5), or 80% CO(2) (pH = 6.3), where MD with 50 and 80% CO(2) reduces tissue pH by 0.1 and 0.18 pH unit, respectively. There were no changes in all measured variables with MD with 6.4% at single or multiple raphe sites (P > 0.05). During FA at single raphe sites, only 80% CO(2) elicited physiological changes as inspiratory flow was 16.9% above (P < 0.05) control. However, FA with 50 and 80% CO(2) at multiple sites increased (P < 0.05) inspiratory flow by 18.4 and 30.1%, respectively, where 80% CO(2) also increased (P < 0.05) tidal volume, heart rate, CO(2) production, and O(2) consumption. FA with 80% CO(2) at multiple raphe sites also led to hyperventilation (-2 mmHg), indicating that FA had effects on breathing independent of an increased metabolic rate. We believe these findings suggest that the large ventilatory response to a global respiratory brain acidosis reflects the cumulative effect of stimulation at widespread chemoreceptor sites rather than a large stimulation at a single site. Additionally, focal acidification of raphe chemoreceptors appears to activate an established thermogenic response needed to offset the increased heat loss associated with the CO(2) hyperpnea.

Transient attenuation of CO2 sensitivity after neurotoxic lesions in the medullary raphe area of awake goats

The major objective of this study was to gain insight into whether under physiological conditions medullary raphe area neurons influence breathing through CO(2)/H(+) chemoreceptors and/or through a postulated, nonchemoreceptor modulatory influence. Microtubules were chronically implanted into the raphe of adult goats (n = 13), and breathing at rest (awake and asleep), breathing during exercise, as well as CO(2) sensitivity were assessed repeatedly before and after sequential injections of the neurotoxins saporin conjugated to substance P [SP-SAP; neurokinin-1 receptor (NK1R) specific] and ibotenic acid (IA; nonspecific glutamate receptor excitotoxin). In all goats, microtubule implantation alone resulted in altered breathing periods, manifested as central or obstructive apneas, and fractionated breathing. The frequency and characteristics of the altered breathing periods were not subsequently affected by injections of the neurotoxins (P > 0.05). Three to seven days after SP-SAP or subsequent IA injection, CO(2) sensitivity was reduced (P < 0.05) by 23.8 and 26.8%, respectively, but CO(2) sensitivity returned to preinjection control values >7 days postinjection. However, there was no hypoventilation at rest (awake, non-rapid eye movement sleep, or rapid eye movement sleep) or during exercise after these injections (P > 0.05). The neurotoxin injections resulted in neuronal death greater than three times that with microtubule implantation alone and reduced (P < 0.05) both tryptophan hydroxylase-expressing (36%) and NK1R-expressing (35%) neurons at the site of injection. We conclude that both NK1R- and glutamate receptor-expressing neurons in the medullary raphe nuclei influence CO(2) sensitivity apparently through CO(2)/H-expressing chemoreception, but the altered breathing periods appear unrelated to CO(2) chemoreception and thus are likely due to non-chemoreceptor-related neuromodulation of ventilatory control mechanisms.

Large lesions in the pre-Bötzinger complex area eliminate eupneic respiratory rhythm in awake goats

In awake goats, 29% bilateral destruction of neurokinin-1 receptor-expressing neurons in the pre-Bötzinger complex (pre-BötzC) area with saporin conjugated to substance P results in transient disruptions of the normal pattern of eupneic respiratory muscle activation (Wenninger JM, Pan LG, Klum L, Leekley T, Bastastic J, Hodges MR, Feroah T, Davis S, and Forster HV. J Appl Physiol 97: 1620-1628, 2004). Therefore, the purpose of these studies was to determine whether large or total lesioning in the pre-BötzC area of goats would eliminate phasic diaphragm activity and the eupneic breathing pattern. In awake goats that already had 29% bilateral destruction of neurokinin-1 receptor-expressing neurons in the pre-BötzC area, bilateral ibotenic acid (10 microl, 50 mM) injection into the pre-BötzC area resulted in a tachypneic hyperpnea that reached a maximum (132 +/- 10.1 breaths/min) approximately 30-90 min after bilateral injection. Thereafter, breathing frequency declined, central apneas resulted in arterial hypoxemia (arterial Po2 approximately 40 Torr) and hypercapnia (arterial Pco2 approximately 60 Torr), and, 11 +/- 3 min after the peak tachypnea, respiratory failure was followed by cardiac arrest in three airway-intact goats. However, after the peak tachypnea in four tracheostomized goats, mechanical ventilation was initiated to maintain arterial blood gases at control levels, during which there was no phasic diaphragm or abdominal muscle activity. When briefly removed from the ventilator (approximately 90 s), these goats became hypoxemic and hypercapnic. During this time, minimal, passive inspiratory flow resulted from phasic abdominal muscle activity. We estimate that 70% of the neurons within the pre-BötzC area were lesioned in these goats. We conclude that, in the awake state, the pre-BötzC is critical for generating a diaphragm, eupneic respiratory rhythm, and that, in the absence of the pre-BötzC, spontaneous breathing reflects the activity of an expiratory rhythm generator.

Small reduction of neurokinin-1 receptor-expressing neurons in the pre-Bötzinger complex area induces abnormal breathing periods in awake goats

In awake rats, >80% bilateral reduction of neurokinin-1 receptor (NK1R)-expressing neurons in the pre-Bötzinger complex (pre-BötzC) resulted in hypoventilation and an "ataxic" breathing pattern (Gray PA, Rekling JC, Bocchiaro CM, Feldman JL, Science 286: 1566-1568, 1999). Accordingly, the present study was designed to gain further insight into the role of the pre-BötzC area NK1R-expressing neurons in the control of breathing during physiological conditions. Microtubules were chronically implanted bilaterally into the medulla of adult goats. After recovery from surgery, the neurotoxin saporin conjugated to substance P, specific for NK1R-expressing neurons, was bilaterally injected (50 pM in 10 microl) into the pre-BötzC area during the awake state (n = 8). In unoperated goats, 34 +/- 0.01% of the pre-BötzC area neurons are immunoreactive for the NK1R, but, in goats after bilateral injection of SP-SAP into the pre-BötzC area, NK1R immunoreactivity was reduced to 22.5 +/- 2.5% (29% decrease, P < 0.01). Ten to fourteen days after the injection, the frequency of abnormal breathing periods was sixfold greater than before injection (107.8 +/- 21.8/h, P < 0.001). Fifty-six percent of these periods were breaths of varying duration and volume with an altered respiratory muscle activation pattern, whereas the remaining were rapid, complete breaths with coordinated inspiratory-expiratory cycles. The rate of occurrence and characteristics of abnormal breathing periods were not altered during a CO2 inhalation-induced hyperpnea. Pathological breathing patterns were eliminated during non-rapid eye movement sleep in seven of eight goats, but they frequently occurred on arousal from non-rapid eye movement sleep. We conclude that a moderate reduction in pre-BötzC NK1R-expressing neurons results in state-dependent transient changes in respiratory rhythm and/or eupneic respiratory muscle activation patterns.

Effects on breathing in awake and sleeping goats of focal acidosis in the medullary raphe

Our aim was to determine the effects of focal acidification in the raphe obscurus (RO) and raphe pallidus (RP) on ventilation and other physiological variables in both the awake and sleep states in adult goats. Through chronically implanted microtubules, 1) a focal acidosis was created by microdialysis of mock cerebrospinal fluid (mCSF), equilibrated with various levels of CO2, and 2) medullary extracellular fluid (ECF) pH was measured by using a custom-made pH electrode. Focal acidosis in the RO or RP, by dialyzing either 25 or 80% CO2 (mCSF pH approximately 6.8 or 6.3), increased (P < 0.05) inspiratory flow by 8 and 12%, respectively, while the animals were awake during the day, but not at night while they were awake or in non-rapid eye movement sleep. While the animals were awake during the day, there were also increases in heart rate and blood pressure (P < 0.05) but no significant change in metabolic rate or arterial Pco2. Dialysis with mCSF equilibrated with 25 or 80% CO2 reduced ECF pH by the same amount (25%) or three times more (80%) than when inspired CO2 was increased to 7%. During CO2 inhalation, the reduction in ECF pH was only 50% of the reduction in arterial pH. Finally, dialysis in vivo only decreased ECF pH by 19.1% of the change during dialysis in an in vitro system. We conclude that 1) the physiological responses to focal acidosis in the RO and RP are consistent with the existence of chemoreceptors in these nuclei, and 2) local pH buffering mechanisms act to minimize changes in brain pH during systemic induced acidosis and microdialysis focal acidosis and that these mechanisms could be as or more important to pH regulation than the small changes in inspiratory flow during a focal acidosis.

Do genes on rat chromosomes 9, 13, 16, 18, and 20 contribute to regulation of breathing?

As part of a large scale, high through-put physiologic genomics study, we sought to determine whether genes on rat chromosomes 9, 13, 16, 18, and 20 contribute to phenotypic differences in the control of breathing between two inbred rat strains (SS/Mcw and BN/Mcw). Through a chromosomal substitution breeding strategy, we created 5 consomic rat strains (SS.BN9, SS.BN13, SS.BN16, SS.BN18, and SS.BN20), which were BN/Mcw homozygous at only one chromosome and SS/Mcw homozygous at all other chromosomes. Standard plethsmography was used to assess eupneic breathing and ventilatory responses to CO(2) (FI(CO(2))=0.07) and hypoxia (FI(CO(2))=0.12), and Pa(CO(2)) during treadmill exercises provided the index of the exercise hyperpnea. There were no robust differences in eupneic breathing between any strains. The ventilatory response to CO(2) was 150% greater (P<0.001) in the SS/Mcw rats than in the BN/Mcw rats and all consomic strains had the SS/Mcw phenotype. Hyperventilation during hypoxia did not differ between the parental and the consomic strains, but ventilation during hypoxia was greater (P<0.001) in the SS/Mcw than in the BN/Mcw, and the SS.BN9, and SS.BN18 appeared to acquire this BN/Mcw phenotype. The hyperventilation during treadmill walking was greater (P<0.006) in the BN/Mcw and the SS.BN18 rats than in the SS/Mcw rats. Finally, the duration of the apnea following an augmented breath (post sigh apnea, PSA) was greater (P<0.001) in the BN/Mcw and the SS.BN9 rats than all other strains. We conclude that the robust difference between the parental strains in ventilatory CO(2) sensitivity is not due to genotypic differences on the 5 chromosomes studied to date, but genotypic differences on chromosomes 9 and 18 contribute to differences in ventilatory responses to hypoxia, exercise, and/or to the differences in the PSA.

Relaxation of postoperative astigmatism after lens implantation through a 6.25 mm scleral wound in children

PURPOSE

To investigate the evolution of postoperative astigmatism in children having cataract extraction with intraocular lens (IOL) implantation through a 6.25 mm superior scleral tunnel wound.

SETTING

A university clinical practice.

METHODS

A retrospective chart review of all pediatric patients having cataract extraction and IOL implantation in the practice of 1 surgeon from 1995 to 2000 was performed. Statistical comparisons were performed using the Student t test for nonpaired data.

RESULTS

Ten eyes of 9 children were included. Six cataracts were due to corneal or corneoscleral lacerations, 3 were idiopathic, and 1 occurred after blunt trauma. Eight eyes could not be refracted preoperatively because of mature cataract. The mean cylindrical correction of all refractions performed 1 to 15 days after surgery (n = 6) was 6.71 diopters (D) +/- 1.63 (SD); of those performed at 16 to 30 days (n = 6), 2.71 +/- 2.09 D; and of those performed at 31 to 45 days (n = 7), 1.93 +/- 1.48 D. The mean spherical equivalent of the final (dispensed) refraction was -0.21 +/- 1.79 D; the mean cylindrical correction of this refraction was 1.13 +/- 0.79 D. The difference between the cylindrical correction of the final prescription and the corneal astigmatism in fellow eyes was not statistically significant (P =.29).

CONCLUSIONS

Relaxation of large amounts of suture-induced astigmatism occurs in children having cataract extraction. Surgeons should not hesitate to secure scleral wounds meticulously in children for fear of a permanent undesirable refractive outcome.

Herpes simplex virus dermatitis in patients using latanoprost

PURPOSE

To describe the possible association of latanoprost with herpetic dermatitis of the periocular skin.

METHOD

Interventional case reports. A 79-year-old woman with open-angle glaucoma developed a vesicular dermatitis of the left lower eyelid 14 months after starting latanoprost therapy. An 84-year-old man with pigmentary glaucoma developed a vesicular dermatitis of the right upper lid after 2 months of treatment with latanoprost and 8 days of treatment with tobramycin/dexamethasone for presumed bacterial conjunctivitis. In both cases, the dermatitis was characteristic of a herpetic infection.

RESULTS

Latanoprost was discontinued in both cases. The woman was treated with vidarabine 3% ointment, and the man was not treated with antiviral agents. In both patients, the dermatitis healed uneventfully. The lesions of the man were cultured, and a biopsy was performed; herpes simplex virus type 1 was recovered from the culture and confirmed by immunofluorescence testing.

CONCLUSION

Latanoprost, which has been associated with reactivation of herpetic keratitis, may also cause reactivation of herpetic dermatitis of the periocular skin.

Accuracy of pulse oximetry during hypoxemia

To determine the accuracy of four pulse oximeters during mild and moderate arterial hypoxemia, we produced stepwise arterial blood desaturation in 25 healthy, nonsmoking volunteers by adjusting the inhaled oxygen concentration. At plateaus of < 80%, 85% to 90%, 90% to 95%, and 95% to 100%, pulse oximetry saturation (SpO2) was measured with the four different monitors: Dinamap Plus Model 8700, Oxyshuttle, Ohmeda 3700, and MiniOx IV. Arterial blood samples were analyzed with a co-oximeter and the arterial oxyhemoglobin saturation (SaO2) was compared with the SpO2 readings at each plateau. Significant deterioration in the accuracy of pulse oximeters was observed as SaO2 decreased. In 14 instances of hypoxemia (SaO2 < 90%), subjects exhibited SpO2 values greater than 90%. In conclusion, the accuracy of pulse oximetry deteriorates as hypoxemia worsens. Confirmation of arterial blood oxyhemoglobin saturation by co-oximetry is necessary when precise determination of arterial oxyhemoglobin level is critical.

Influence of posture on arm exercise tolerance and physiologic responses in persons with spinal cord injured paraplegia

This study compared metabolic and cardiopulmonary responses to incremental supine and upright sitting arm crank ergometry (ACE) in nine men with spinal cord injured paraplegia ranging from T1-T5. Both tests consisted of continuous graded ACE from rest to volitional fatigue on a modified electronically braked cycle ergometer with the work rate increased by 8.2 W.min-1. No significant differences (P > 0.05) existed for peak ACE power output (W), oxygen uptake, pulmonary ventilation, respiratory exchange ratio, and O2 pulse between the two tests. Heart rate and O2 pulse responses at six submaximal work rates representing 0-58% peak W were also not significantly different between postures. These data indicate that ACE tolerance in persons with high-lesion paraplegia was not enhanced when ACE was performed in the supine posture.

Oxygen supplementation during electroconvulsive therapy

The effects of ventilation with 30% and 100% oxygen were investigated on the circulatory and electrocardiographic response to electroconvulsive therapy (ECT) in 12 patients during 40 treatments. Administration of 30% oxygen resulted in a 25% decrease in seizure duration compared with 100% oxygen (P less than 0.0125). Hypoxaemia, defined as SaO2 less than 90%, occurred during five of 20 treatments with 30% oxygen and during two of 20 treatments with 100% oxygen (ns), and was associated invariably with loss of airway control. Heart rate, arterial pressure, and the incidence of cardiac arrhythmias were not affected significantly by oxygen supplementation. Inspired oxygen concentration has a significant effect on seizure activity and should be of a consistent value if a reproducible seizure is to be produced during ECT. Breathing 100% oxygen does not appear to affect adversely the cardiovascular response to ECT. However, arterial hypoxaemia may develop rapidly during or after the seizure, regardless of oxygen supplementation, if adequate control of airway and ventilation is not maintained.

Continuous monitoring of gas exchange and oxygen use with dual oximetry

The utility of integrated pulse and pulmonary artery oximetry, known as dual oximetry, was evaluated by monitoring 10 critically ill surgical patients for a total of 208 patient hours. The ventilation-perfusion index (VQI), an estimate of venous admixture, and the oxygen extraction index (O2EI), an estimate of tissue oxygen utilization coefficient, previously described, were calculated on-line from arterial and mixed venous oxyhemoglobin saturations using a computer. Effective monitoring was accomplished 85% of the total time. The dual oximetry device was nonfunctional owing to equipment failure only 15% of the time, even though no undue attention was given to instructing the staff on operation of the oximeters. Accuracy of VQI and O2EI was reconfirmed by this study. Drift in the saturations, VQI, and O2EI during the 6-h period between calibrations was negligible. The 95% range of random variability was +/- 2% for SaO2, +/- 3% for SvO2, +/- 5% for VQI, and +/- 0.04 for O2EI. Thirty-six episodes of arterial blood desaturation below 90% were detected by continuous oximetry. In contrast, 74 routine arterial blood samples revealed only four such episodes. Dual oximetry appears to be a technically reliable and accurate method of monitoring pulmonary gas exchange and tissue oxygen utilization. The equipment provided stable readings for at least six hours without recalibration. Random variability is sufficiently small to allow early detection of alterations in pulmonary and circulatory function without blood sampling.

Tort reform and medical malpractice: a risk management leader's analysis

In summary, the United States Tort System, with malpractice actions based upon the law of negligence, remains a driving force in affecting health care delivery costs. The reforms and attempted reforms under consideration by legislative branches nationwide also play a key role in this endeavor. Yet, tort reform alone is not the answer. Reducing the initial occurrence of medical injury remains the ultimate method of easing the current liability crisis. Health care providers must assure the delivery of quality care to their patients or face consequences in areas of licensure qualifications, license renewal, professional discipline, suspensions, probations and fines. An effective quality assurance program that provides measurable results should be a priority for all health care providers. Administration, medical staffs and all departments within a health provider's facility must work together to achieve quality patient care. Proven risk management programs, combined with similar cooperative efforts by health care companies, physicians, attorneys, insurance companies, state regulatory agencies and the federal government, will prove extremely effective in controlling future health care delivery costs.

Failure of enflurane in altering renal responses to acute intracranial pressure increases

The effects of acute increases of intracranial pressure (ICP) on renal function before and during enflurane and enflurane-N2O anesthesia were determined in 12 mongrel dogs. Prior to anesthesia, acute elevations of 10 and 20 torr in ICP significantly increased urine osmolarity (Uosm), mean arterial blood pressure (MAP), and renal vascular resistance (RVR); significantly decreased urine volume (U vol), para-aminohippurate clearance (Cpah), and free water clearance (C/20); and had no effect on inuline clearance (Cin) or plasma levels of antidiuretic hormone (ADH). Thirty minutes of enflurane (2.2 percent end-tidal concentration) in 70 percent nitrogen and O2 in the presence of normal ICP caused significant increases in Uosm while MAP, CPAH, UVOL CH20, CIN, and osmolar clearance (CosM) were significantly decreased and ADH was unchanged. Substituting 70 percent N2O for nitrogen had no significant effect on any variable measured. Increasing ICP 10 torr during enflurane-N-2O anesthesia caused significant increases (compared to enflurane-N2O values in the presence of normal ICP) in UosM, RVR, and CosM, as well as significant decreases in UVOL, CH2O, AND CPAH, but had no effect on ADH, CIN, or MAP. Enflurane and N2O anesthesia moderates the elevation MAP in response to an acute increase in ICP but fails to alter the renal response to increased ICP.

Correlation of oxygen uptake and cardiovascular dynamics during N2O-fentanyl and N2O-thiopental anesthesia in the dog

The relationship between changes in wholebody O2 consumption (VO2) and cardiovascular dynamics during changing levels of N2O-fentanyl and N2O-thiopental anesthesia was determined in 24 dogs. Dose-dependent reductions in VO2, mean blood pressure, and cardiac output occurred with infusion of fentanyl and thiopental. Painful stimuli increased VO2 during light anesthesia but not during deeper levels of anesthesia. Deep levels of N2O-fentanyl and N2O-thiopental anesthesia may protect the patient with limited cardiac reserve by reducing VO2 and preventing increases in VO2 caused by painful stimuli.

Pulmonary shunt and cardiovascular responses to CPAP during nitroprusside-induced hypotension

The effects of continuous positive airway pressure (CPAP) on cardiovascular dynamics and pulmonary shunt (QS/QT) were investigated in 12 dogs before and during sodium nitroprusside infusion that decreased mean arterial blood pressure 40-50 per cent. Before nitroprusside infusion, 5 cm H2O CPAP significantly, P less than .05, decreased arterial blood pressure, but did not significantly alter heart rate, cardiac output, systemic vascular resistance, or QS/QT. Ten cm H2O CPAP before nitroprusside infusion produced a further decrease in arterial blood pressure and significantly increased heart rate and decreased cardiac output and QS/QT. Nitroprusside caused significant decreases in arterial blood pressure and systemic vascular resistance and increases in heart rate, but did not change cardiac output or QS/QT. Five cm H2O CPAP during nitroprusside did not further alter any of the above-mentioned variables. However, 10 cm H2O CPAP decreased arterial blood pressure, cardiac output, and QS/QT. These data indicate that nitroprusside infusion rates that decrease mean arterial blood pressure by 40-50 per cent do not change cardiac output or QS/QT. During nitroprusside infusion low levels of CPAP do not markedly alter cardiovascular dynamics, but high levels of CPAP (10 cm H2O), while decreasing QS/QT, produce marked decreases in arterial blood pressure and cardiac output.

Acute intravenous administration of potassium chloride to furosemide pretreated dogs

Twelve male mongrel dogs were used for this study; six were untreated (control) and six were given intravenous furosemide (1 mg/kg) daily for seven consecutive days before each study. Each animal received intravenous KCl 0.8, 1.6 or 3.2 mMol/kg/hr for one hour, but only one dose for each study and at least seven days were allowed between studies. The animals were given thiopentone for tracheal intubation and mechanically ventilated, maintaining a PaCO2 of 4.0 to 4.5 kPa (30-35 torr) and anaesthetized with nitrous oxide-oxygen and halothane. Daily administration of furosemide reduced serum potassium from 4.48 to 4.09 mMol/1 with no significant change in serum sodium. A greater number of furosemide-pretreated animals (6 vs 3) developed cardiac dysrhythmias during non-lethal intravenous KCl at 0.8, 1.6 mMol/kg/hr. The furosemide-pretreated group tended to succumb at a lower serum potassium concentration (12.2 vs 13.8 mMol/I, P less than 0.05) and developed earlier onset (44 vs 54 min, P less than 0.05) of cardiac standstill or ventricular fibrillation following intravenous KCl at 3.2 mMol/kg/hr. Cardiac output, heart rate and mean arterial pressure were significantly elevated during serum concentrations of 6.9-9.1 mMol/1, while no statistically significant changes were observed for stroke volume and peripheral resistance. There were no significant differences of urinary potassium excretion between the untreated and treated groups when like doses of KCl were infused. These data suggest that acute infusion of KCl in furosemide-pretreated dogs may not be an effective means of treating hypokalaemia and could be hazardous.

Lithium carbonate and neuromuscular blocking agents

The effects of lithium carbonate on the responses to five neuromuscular blocking agents were evaluated in dogs anesthetized with halothane (1 per cent) and N2O (60 per cent) in O2. Latency (time from first twitch-height depression to maximal blockade), maximal twitch-height depression, and times to return to 50 per cent and 100 per cent control twitch tension were measured before and after intravenous infusion of lithium carbonate (1 mg/kg/min for one hour) during neuromuscular blockades produced by succinylcholine, decamethonium, gallamine, d-tubocurarine, or pancuronium. Lithium prolonged the latencies of neuromuscular blockades produced by 0.1 mg/kg succinylcholine and 0.1 mg/kg decamethonium by 248.1 per cent and 49.0 per cent, respectively, but had no effect on latency produced by 0.02 mg/kg pancuronium. The times for return to 50 per cent of control twitch height were prolonged by 69.5, 40.0, and 120.1 per cent, respectively. Lithium had no effect on latency or duration of blockades produced by 0.15 mg/kg d-tubocurarine and 0.6 mg/kg gallamine, but enhanced maximal twitch-height depressions produced by 0.9 mg/kg gallamine and 0.02 mg/kg pancuronium by 22.9 and 9.9 per cent, respectively. Twitch tensions decreased 5-10 per cent over three hours in three dogs receiving lithium infusion without relaxants. Twitch tension was depressed 0-2 per cent in three dogs after five hours of anesthesia in the absence of lithium or relaxants. Lithium prolonged the time required for neostigmine to reverse neuromuscular blockade produced by pancuronium in two of three dogs from a mean of 60 seconds to 135 seconds.

Ventilatory pattern, intrapleural pressure, and cardiac output

Continuous positive-pressure ventilation may decrease cardiac output. However, a few reports have separated the effects of positive and end-expiratory pressure (PEEP) from those of mechanical ventilation. Ten surgical patients requiring mechanical ventilatory support had catheters inserted for measurement of right atrial pressure (RAP), pulmonary artery occlusion pressure (PAOP), intrapleural, radial artery, airway, and atrial filling pressures, and cardiac output. All patients breathed spontaneously between mechanical breaths delivered every 30 seconds by intermittent mandatory ventilation (IMV). Measurements were made with 0, 5, and 10 cm H2O PEEP, and during intermittent positive-pressure ventilation (IPPV) with 12 breaths/min without PEEP. Airway pressure (Paw), intrapleural pressure, RAP, and PAOP were increased by PEEP and IPPV. Intrapleural pressure increased most during IPPV (p less than 0.001). Atrial filling pressures and cardiac output were unaffected by PEEP but decreased during IPPV (p less than 0.001). Patients receiving IMV maintained negative intrapleural pressure, atrial filling pressure, cardiac output and, therefore, O2 delivery, regardless of PEEP level. The authors conclude that patients requiring mechanical respiratory support, with or without PEEP, may maintain better cardiopulmonary function when allowed some spontaneous ventilatory activity.

Acute respiratory failure and intravascular coagulation

The possible association between acute respiratory failure and disseminated intravascular coagulation was examined in eight patients with severe acute respiratory failure--a condition characterized by tachypnea, right to left intrapulmonary shunting of blood greater than 30 per cent of cardiac output, increased pulmonary artery pressure with low or normal pulmonary artery wedge pressure and roentgenologic interstitial pulmonary edema. Treatment consisted of mechanical ventilation with positive end expiratory pressure sufficient to minimize intrapulmonary shunting. There was no abnormality in platelet concentration fibrin split product concentration, fibrinogen concentration, prothrombin time or activated partial thromboplastin time during the period of most severe respiratory failure in any patient. However, mean platelet concentration fell to 90,000+/-9,000 per cubic millimeter, less than 0.001, and mean fibrin split product levels rose to 60+/-10 micrograms per milliliter, p less than 0.05, the fourth day after the onset of acute respiratory failure. No significant change occurred in other coagulation parameters. Disseminated intravascular coagulation developed in none of the patients nor was there any correlation between coagulation abnormalities and severity of acute respiratory failure that would suggest a cause and effect relationship.

Change in pulmonary venous admixture with varying inspired oxygen

Pulmonary venous admixture (Qsp/Qt) was analyzed as a function of fractional concentration of inspired O2 (FIO2) in 30 patients who required postoperative mechanical ventilation. Pulmonary and radial artery blood-gas tensions and pH were measured and Qsp/Qt was calculated with FIO2 ranging from 0.21 to 1. In all patients, Qsp/Qt decreased when FIO2 was increased from 0.21 to 0.4 and then stabilized to an FIO2 of approximately 0.6. As the FIO2 was increased to 1, Qsp/Qt increased. Since the inhalation of gas mixture with FIO2 greater than or equal to 0.6 increased right-to-left intrapulmonary shunting of blood, we recommend respiratory function be evaluated during inhalation of a clinically useful concentration of O2 rather than at an FIO2 of 1.

Hypoxemia and hypocarbia following intermittent positive-pressure breathing

The authors determined the effects of short-term, vigorous intermittent positive-pressure breathing (IPPB) on arterial blood O2 tension (Pao2) in 10 unmedicated preoperative adult patients (ASA class I). Arterial blood was analyzed before and 0.5, 5, 15, and 40 minutes after 12 minutes of IPPB with nebulized 0.9% HaCl and room air. Pao2 increased from 89.1 +/- 11 torr (mean +/- SD) to 102.1 +/- 13.9 torr, and arterial CO2 tension decreased from 29.5 +/- 4 torr to 18.4 +/- 3 torr, causing significant respiratory alkalosis (pHa 7.62 +/- 0.05). Five minutes after IPPB, Pao2 decreased to 69.2 +/- 8 torr; alveolar-arterial Po2 difference, breathing 21% O2, increased significantly; and serum K+ concentration decreased significantly. All these values returned to baseline levels within 40 minutes. The authors, acknowledging the value of IPPB when specifically indicated, counsel caution in patients with borderline pulmonary reserve and arterial oxygenation.