Clinical evidence that V456A is a Cystic Fibrosis causing mutation in South Asians.

BACKGROUND: Cystic Fibrosis (CF) genotypes in South Asians are variable with a decreased incidence of Delta F508 and an increased incidence of novel mutations. The objective of this study is to provide clinical evidence that V456A, a novel mutation in South Asian Cystic Fibrosis patients, can cause significant lung disease. METHODS: We extracted clinical data from a retrospective chart review of 2 CF patients of South Asian descent. RESULTS: Patient 1, a 10 year and 11 month old Pakistani female at her initial clinic visit, required multiple hospitalizations for bronchiectasis and pulmonary infections. She was pancreatic sufficient but had slow weight gain. Genetic testing revealed that she is homozygous for the CFTR V456A mutation. Patient 2, an Indian female diagnosed with CF on newborn screening, is compound heterozygous for V456A/R709X. She had slow weight gain with BMI ranging from 12.9 to 13.4 kg/m(2) from 3 to 5 years of age and was 14.2 kg/m(2) at 6 years of age. At 6 years of age, pulmonary function tests revealed mild lung disease with FVC of 71%, FEV(1) of 75%, FEF(25-75) of 119%, and FEV(1)/FVC of 86% predicted. Sputum cultures were intermittently positive for Staphylococcus aureus and Haemophilus influenza. CONCLUSIONS: We provide evidence that V456A can cause significant pulmonary disease in South Asian Cystic Fibrosis patients.

Wolbachia modification of sperm does not always require residence within developing sperm.

Wolbachia are maternally inherited intracellular bacteria known to manipulate the reproduction of their arthropod hosts. Wolbachia commonly affect the sperm of infected arthropods. Wolbachia-modified sperm cannot successfully fertilize unless the female is infected with the same Wolbachia type. A study of spermatogenesis in the parasitic wasp Nasonia vitripennis reveals that Wolbachia are not required in individual spermatocytes or spermatids to modify sperm. In N. vitripennis, Wolbachia modify nearly all sperm, but are found only in approximately 28% of developing sperm, and are also found in surrounding cyst and sheath cells. In the beetle Chelymorpha alternans, Wolbachia can modify up to 90% of sperm, but were never observed within the developing sperm or within the surrounding cyst cells; they were abundant within the outer testis sheath. We conclude that the residence within a developing sperm is not a prerequisite for Wolbachia-induced sperm modification, suggesting that Wolbachia modification of sperm may occur across multiple tissue membranes or act upstream of spermiogenesis.

Genioglossal length and EMG responses to static upper airway pressures during hypercapnia in goats.

Mechanoreflexes that activate genioglossus electromyogram (EMGgg) in response to negative upper airway pressure (UAP) may help defend airway patency in obstructive sleep apnea. Hypercapnia may affect mechanoreflexes by increasing EMGgg response to actively reduce genioglossus length (Lgg, measured by sonomicrometry). We hypothesized that during normocapnia, Lgg would be reduced at positive, and increased at negative UAP but hypercapnia would increase EMGgg responses to negative pressures and cause Lgg reductions. At 0, 3.5 and 7% inhaled CO2 (balance O2), Lgg and EMGgg were measured during static negative and positive UAP applied to the isolated upper airway in four unanesthetized goats. At 3.5 and 7% CO2 EMGgg was significantly increased and Lgg decreased with negative pressure while EMGgg was also greater at 7 than 0% CO2 (P<0.05). Non-significant pressure related Lgg changes were observed during normocapnia. These results suggest that hypercapnia may stimulate greater mechanoreflex EMGgg activation and consequent Lgg reduction in response to negative UAP application.

Modulation of laryngeal and respiratory pump muscle activities with upper airway pressure and flow.

The hypothesis that upper airway (UA) pressure and flow modulate respiratory muscle activity in a respiratory phase-specific fashion was assessed in anesthetized, tracheotomized, spontaneously breathing piglets. We generated negative pressure and inspiratory flow in phase with tracheal inspiration or positive pressure and expiratory flow in phase with tracheal expiration in the isolated UA. Stimulation of UA negative pressure receptors with body temperature air resulted in a 10--15% enhancement of phasic moving-time-averaged posterior cricoarytenoid electromyographic (EMG) activity above tonic levels obtained without pressure and flow in the UA (baseline). Stimulation of UA positive pressure receptors increased phasic moving-time-averaged thyroarytenoid EMG activity above tonic levels by 45% from baseline. The same enhancement of posterior cricoarytenoid or thyroarytenoid EMG activity was observed with the addition of flow receptor stimulation with room temperature air. Tidal volume and diaphragmatic and abdominal muscle activity were unaffected by UA flow and/or pressure, whereas respiratory timing was minimally affected. We conclude that laryngeal afferents, mainly from pressure receptors, are important in modulating the respiratory activity of laryngeal muscles.

Laryngeal muscle response to phasic and tonic upper airway pressure and flow.

The hypothesis that respiratory modulation due to upper airway (UA) pressure and flow is dependent on stimulus modality and respiratory phase-specific activation was assessed in anesthetized, tracheotomized, spontaneously breathing piglets. Negative pressure and flow applied to the isolated UA at room or body temperature during inspiration only enhanced posterior cricoarytenoid muscle activity from that present without UA pressure and flow (baseline) by 15--20%. Time shifting the onset of UA flow relative to tracheal flow decreased this enhancement. The same enhancement was observed with oscillatory or constant airflow. UA positive pressure and flow at room or body temperature applied during expiration only enhanced thyroarytenoid muscle activity from baseline by 50--160%. The same enhancement was observed with oscillatory or constant airflow at body temperature. Constant positive pressure and flow enhanced thyroarytenoid muscle activity more than oscillatory pressure and flow at room temperature. We conclude that the respiratory modulation of UA afferents is processed in a phase-specific fashion and is dependent on stimulus modality (tonic vs. phasic).

Force production of the genioglossus as a function of muscle length in normal humans.

Resting muscle length affects both maximum force production and force maintenance. The strength and force maintenance characteristics of the genioglossus as a function of resting muscle length have not been described. We hypothesized that genioglossus optimum length (L(o)) could be defined in vivo and that the ability of the genioglossus to sustain a given workload would decrease as resting length deviated from L(o). To test this, 11 normal men repeated maximal isometric genioglossus protrusions at different muscle lengths to determine L(o). L(o) was also obtained by using submaximal efforts while simultaneously recording electromyographic activity of the genioglossus, with L(o) defined as the length at which the force-to-genioglossus electromyographic activity ratio was maximum. Both methods provided similar results. Force maintenance was measured at four muscle lengths on separate days. Target efforts representing 60% of each subject's maximum at L(o) and lasting 5 s were performed at 12-s intervals. Time limit of endurance of the genioglossus was defined as the time from trial onset at which 90% of the target could not be maintained for three consecutive efforts. Time limit of endurance was greatest at L(o) and fell to 47.5% at L(o) + 1 cm, 53.8% at L(o) - 1 cm, and 47.4% at L(o) - 1.5 cm. We conclude that L(o) of the genioglossus can be determined in vivo and that force maintenance of the genioglossus is decreased when operating length deviates from L(o).

The use of ultrasound in the diagnosis of injuries of the ulnar collateral ligament of the thumb.

We describe the use of a specialist referral clinic and ultrasound assessment for all injuries to the ulnar collateral ligament of the metacarpophalangeal joint of the thumb presenting to an Accident and Emergency (A&E) department. Senior House Officers in the A&E department were able to correctly diagnose only 45% of the ruptures of the ulnar collateral ligament. The overall agreement between specialist clinic examination and ultrasound for injury to the ulnar collateral ligament was 85% (kappa 0.647). When compared with the operative finding ultrasound had a positive predictive value for rupture of 94%. An algorithm is presented for the assessment of injuries to the ulnar collateral ligament in A&E departments.

Dopaminergic therapy in children with restless legs/periodic limb movements in sleep and ADHD. Dopaminergic Therapy Study Group.

The long-term effects of monotherapy with levodopa or the dopamine agonist pergolide on the motor/sensory, behavioral, and cognitive variables in seven children with restless legs syndrome/periodic limb movements in sleep (RLS/PLMS) and attention-deficit-hyperactivity disorder (ADHD) were investigated. Five of the seven children had previously been treated with stimulants that had either been determined to be ineffective or to have intolerable side effects. Dopaminergic therapy improved the symptoms of RLS and reduced the number of PLMS per hour of sleep (P = 0.018) and associated arousals (P = 0.042) for the entire group. After treatment, three children no longer met the criteria for ADHD, and three reverted to normal on the Test of Variable Attention. ADHD improved in all seven as measured by the Connors parent rating scale (P<0.04) and the Child Behavior Checklist (P<0.05). A significant improvement also occurred in the visual, but not verbal, memory scores on the Wide Range Assessment of Memory and Learning (P<0.001). Five of seven children continue on dopaminergic therapy 3 years after treatment initiation, with good response. We postulate that the improvement in ADHD may be the result of the amelioration of RLS/PLMS and its associated sleep disturbance. Alternatively, ADHD and RLS/PLMS may share a common dopaminergic deficit.

Periodic limb movement disorder and restless legs syndrome in children with attention-deficit hyperactivity disorder.

Sleep disruption can lead to symptoms of attention-deficit hyperactivity disorder (ADHD) in children. Since periodic limb movement disorder and/or restless legs syndrome can cause sleep disruption, we assessed whether these two specific sleep disorders are likely to occur in children with ADHD. We asked a series of 69 consecutive parents of children with ADHD questions about the symptoms of periodic limb movement disorder. Based on a positive response to these periodic limb movement disorder queries, 27 children underwent all-night polysomnography. Eighteen children (aged 2 to 15 years) of the 27 (26% of the 69 children with ADHD) had 5 or more periodic leg movements in sleep per hour of sleep and had complaints of sleep disruption, thus fulfilling the criteria for periodic limb movement disorder. A comparably age- and sex-matched group of children referred to a sleep laboratory for sleep complaints but without ADHD showed only a 5% prevalence (2 of 38 subjects) of periodic leg movements in sleep (P=.017). Eight of the 18 children with ADHD and periodic limb movement disorder and one of the two control patients with periodic limb movement disorder had both a personal and parental history of restless legs syndrome symptomatology. This study further documents the occurrence of periodic limb movement disorder and restless legs syndrome in children and is the first large-scale study establishing a possible comorbidity between ADHD and periodic limb movement disorder. We propose that the sleep disruption associated with periodic limb movement disorder and restless legs syndrome and the motor restlessness of restless legs syndrome while awake could contribute to the inattention and hyperactivity seen in a subgroup of ADHD-diagnosed children.

Influence of preload and afterload on genioglossus muscle length in awake goats.

The genioglossus is an upper airway dilator muscle, the length of which is directly related to patency in the oropharyngeal region. We hypothesized that genioglossal length (Lgg) is dynamically influenced by the afterload exerted by negative upper airway pressure during inspiration and by the intrinsic length-tension characteristics of the muscle (preload). Seven awake goats were chronically instrumented with electrodes for EMGgg and sonomicrometry for Lgg. We examined the Lgg-EMGgg relationship during hypercapnia and inspiratory resistive loading (18 cm H2O/L/s). The goats breathed through the upper airway (TC) or airflow was diverted through a tracheostomy (TO). We found that: (1) passive inspiratory lengthening was observed with negative upper airway pressure (UAP) but not when UAP = 0 (TO breathing), (2) Lgg shortening for a given EMGgg was significantly decreased with negative inspiratory UAP, and (3) phasic Lgg shortening per unit EMGgg was greatest when Lgg was near optimal length (Lo). We conclude that genioglossal length is substantially influenced by afterload exerted by negative UAP and that genioglossal active shortening may be limited if the muscle operates at a length significantly greater or less than the optimal length.

Activity of respiratory neurons during hypoxia in the chemodenervated cat.

Exposure of anesthetized paralyzed vagotomized peripherally chemodenervated cats to hypoxia results in initial depression and subsequent loss of the phrenic neurogram. To determine whether hypoxic respiratory depression results from the inhibition of respiratory premotor neurons by bulbospinal neurons of the Bötzinger complex (Böt-E neurons), extracellular recordings were made of dorsal and ventral respiratory group bulbospinal inspiratory neurons and Böt-E neurons during acute hypoxic hypoxia. All neurons recorded decreased firing rate during hypoxia. Böt-E neurons became silent before the loss of phasic phrenic activity during hypoxia and commenced firing before or coincident with the return of the phrenic neurogram during reoxygenation. Inspiratory neurons ceased firing coincident with phrenic silence. Dorsal respiratory group and ventral respiratory group neurons that had a late onset of firing with respect to the phrenic neurogram during normoxia fired progressively earlier in inspiration during hypoxia, an effect that was reversed during reoxygenation. These data are consistent with inhibition and/or disfacilitation as the mechanism of hypoxic respiratory depression but suggest that Böt-E neurons are not the source of this inhibition.

Abdominal muscle activation by respiratory stimuli in conscious dogs.

The responses of the diaphragm, external oblique, and transversus abdominis muscles to hyperoxic hypercapnia and isocapnic hypoxia were studied in four awake dogs to test the hypothesis that central and peripheral chemoreceptor inputs result in different patterns of respiratory muscle activation. The dogs were trained to lie quietly in place, and electromyographic (EMG) discharges of the diaphragm (EMGdi), external oblique (EMGeo), and transversus abdominis (EMGta) were recorded from chronically implanted electrodes. Both hypercapnia and hypoxia recruited EMGeo and EMGta activity, but at comparable levels of minute volume of ventilation the EMG activity of the abdominal muscles was greater during hypercapnia than during hypoxia. However the two chemical stimuli also resulted in different tidal volume (VT) and respiratory frequency responses at any given minute volume of ventilation. When EMG activity was reanalyzed as a function of VT, EMGeo and EMGta were the same for a given VT whether induced by hypercapnia or hypoxia, but EMGdi was consistently greater during hypoxia than during hypercapnia. When the vagus nerves were blocked by cooling exteriorized cervical vagal loops, all abdominal muscle EMG activity was abolished. The findings support the concept that stimulation of the central and peripheral chemoreceptors results in asymmetric activation of the inspiratory and expiratory respiratory muscles. The findings also indicate that afferent vagal stimuli play an important facilitatory role in activation of the abdominal expiratory muscles.

Respiratory muscle activation by chemical stimuli in awake and sleeping dogs.

The present findings in awake and sleeping dogs confirm the early observations in anesthetized cats (Bainton et al., 1978; Sears et al., 1982), and more recent studies in awake and sleeping humans (Takasaki et al., 1989), that suggest an asymmetry in pattern of respiratory motoneuron and muscle activation by central and peripheral chemoreceptor stimulation, with central chemoreceptor stimulation driving both inspiratory and expiratory mechanisms, and peripheral chemoreceptor stimulation driving inspiratory and inhibiting expiratory mechanisms. Because REM sleep inhibits the nondiaphragmatic muscles, which include the expiratory muscles, there is a reduction in CO2 response during this sleep stage. In contrast because the response to hypoxia is mediated predominantly by the diaphragm, which is not generally inhibited by REM sleep, there is less effect of REM sleep on the overall response to hypoxia. In addition to being of basic importance, these concepts may have important clinical implications.

Cardiopulmonary effects of the volume recruitment manoeuvre in infant swine.

The volume recruitment manoeuvre is a non-invasive technique used to measure respiratory mechanics in infants. Because airway pressure increases during this manoeuvre, lung volume, compliance and cardiac output may change. In order to assess possible changes in cardiopulmonary function caused by the volume recruitment manoeuvre, we applied this technique to seven intubated infant swine breathing spontaneously during anaesthesia with halothane and N2O. Tidal volume (VT), respiratory frequency, arterial blood gases, cardiac output (CO) and total respiratory compliance were measured before and after the manoeuvre. In three swine functional residual capacity (FRC) was measured by helium dilution before the manoeuvre, and in four swine diaphragmatic EMG was recorded continuously. Finally, all swine were paralysed during volume recruitment to assess the contribution of the respiratory muscles to post-manoeuvre respiratory mechanics. VT and f increased immediately after the manoeuvre but there were no significant changes in PaCO2, or alveolar to arterial oxygen gradient. There was a small but statistically significant decrease in CO. Compliance increased by 17.8 +/- 3.6 per cent and FRC increased by a mean of 41.1 ml (or 51.9 per cent increase above the baseline FRC). The increase in FRC could not be explained by active mechanisms since the diaphragmatic EMG showed no post-inspiratory activity and neuromuscular paralysis did not decrease FRC. We conclude that the volume recruitment manoeuvre increases FRC and compliance by recruiting collapsed alveoli, and this effect must be taken into consideration when applying this test to infants.

Glottic dimensions in healthy men and women.

Glottic aperture is important in modulating respiratory system resistance. Male patients with obstructive sleep apnea (OSA) have a smaller glottic cross-sectional area compared to controls. Since OSA has a strong male predominance, we reasoned that glottic dimensions may differ between healthy men and women. Therefore, we utilized the acoustic reflection to measure glottic cross-sectional area in 44 non-smoking, non-obese, healthy subjects, 25 men and 19 women. Glottic area was measured during a continuous slow expiration from total lung capacity (TLC) to residual volume (RV). We compared glottic areas in men and women at three lung volumes: TLC, 50% of vital capacity (VC), and RV. We found that in all but 2 subjects, glottic areas at TLC was greater than at 50% VC or RV. At any given lung volume, there was no significant difference in glottic area between men and women. The reduction in glottic area between TLC and RV was also similar between men and women (36 +/- 24% and 33 +/- 21%, respectively). However, this reduction in glottic area occurred mainly at low lung volumes in women, and more uniformly throughout the vital capacity range in men. We conclude that changes in glottic dimensions are dependent on lung volume, that healthy men and women have similar glottic areas, and that the glottic aperture shows similar variation with lung volume among both sexes.

A model of the maturation of respiratory control in the newborn infant.

A model of automatic neonatal respiratory control has been constructed as an aid in the investigation of a possible maturation in respiratory control loops during the newborn period. The primary objective was to provide a framework for investigating this hypothesis without the need for external stimuli or invasive measurements. Spontaneous sighs provide a physiological disturbance to the respiratory system by transiently altering the levels of the blood gases. The dynamic ventilatory response following such a disturbance was modeled. A change from a highly damped to less damped pattern was found when model parameter values were varied to mimic maturation in the neonatal period. A perturbation model analysis demonstrated the dynamic ventilatory response is most sensitive to factors affecting the gain of the peripheral chemoreflex loop. It is concluded that the model provides valuable insight into the hypothesis that the peripheral chemoreflex matures during the neonatal period and provides a viable method for testing this in the human infant.

Expiratory muscle activity in anesthetized children: effect on the single breath technique.

Phasic expiratory activity of the abdominal muscles occurs in adults during halothane anesthesia, but has not been demonstrated in children. If present, abdominal muscle activity would preclude the use of recently developed tests of respiratory mechanics in children during anesthesia. We therefore measured abdominal muscle activity throughout induction of anesthesia with halothane in 10 patients between 1.5 and 9.5 years of age, seven with normal respiratory function and three with chronic airway obstruction. During induction of anesthesia with halothane in N2O and oxygen, the abdominal wall electromyograph (a-EMG) was continuously recorded from surface electrodes. At the same time, the expiratory time constant (tau a) was measured using the single breath test (SBT). The patients were then paralyzed with succinyl choline, and the a-EMG signal and expiratory time constant during paralysis (tau p) were recorded. The raw a-EMG signal and its moving time average were compared with the phase of respiration and with the end-tidal fraction of halothane (Fehalo), and the effect of abdominal muscle activity on tau a was noted. Of the 10 patients, 2 had no abdominal muscle activity at any time during induction. Of the remaining 8 patients, 3 had continuous abdominal muscle activity throughout induction, including one patient with asthma. In the remaining five patients, abdominal muscle activity was present during light halothane anesthesia and disappeared at increased Fehalo. When abdominal muscle activity was present, tau a was significantly less than tau p. It is concluded that abdominal muscle activity in expiration is undetectable during deep halothane anesthesia in most children.(ABSTRACT TRUNCATED AT 250 WORDS)

Expiratory airflow patterns and gas exchange in the newborn infant: results of model simulations.

A mathematical model simulating the newborn human infant's respiratory system was used to study the effects on gas exchange of varying expiratory airflow pattern and end expiratory lung volume (FRC). Inspiratory flow was modelled as a square wave and was constant for all simulations as were inspiratory and expiratory times. Expiratory airflow was also modelled as a square wave and was varied between 21 and 75 ml/sec with FRC held constant at either 30.2 or 21.2 ml/kg for each simulation. At a given FRC, expiratory airflow pattern had only a trivial effect on blood gases in the steady state. Comparing the extreme cases, fast expiration (75 ml/sec) at low FRC (21.1 ml/kg) with slow expiration (21 ml/sec) at high FRC (30.2 ml/kg), arterial PO2 was 3.8 mm Hg higher and arterial PCO2 1.0 mm Hg lower under the latter conditions. However, when short apneas were imposed, blood gases deteriorated less precipitously following the slow expiration at high FRC. We conclude that expiratory airflow retardation and the resultant elevation in end expiratory lung volume do not greatly enhance gas exchange in the healthy full term infant. However, mechanisms which slow expiratory airflow do provide a buffer for gas exchange during the short apneas often observed in infants.

Importance of vagal afferents in determining ventilation in newborn rats.

We studied the effect of acute bilateral vagotomy on ventilation and ventilatory pattern in rats. In 1- to 6-day-old unanesthetized rats, vagotomy resulted in a substantial decrease (38%) in ventilation during air breathing. After vagotomy there was a threefold increase in tidal volume (VT), inspiratory time (TI) doubled, and expiratory time (TE) was six times longer. When studied under isoflurane anesthesia, newborn rats showed decreases in ventilation similar to that observed without anesthesia, whereas anesthetized adult rats had no consistent changes in ventilation. Adult and newborn rats had nearly identical proportionate increases in VT and TI after vagotomy, but TE lengthened to a greater extent in the newborns. Additionally, we demonstrated a significant decrease in ventilation when 100% O2 rather than air was supplied to nonvagotomized unanesthetized newborn rats. Ventilation decreased by 19% after vagotomy under hyperoxic conditions. We conclude that vagal afferent input, probably of pulmonary mechanoreceptor origin, provides positive feedback to respiration in newborn rats and that newborn rats greater than 24 h old also have a degree of peripheral chemoreceptor drive during air breathing.