Phox2b-expressing neurons contribute to breathing problems in Kcnq2 loss- and gain-of-function encephalopathy models

Loss- and gain-of-function variants in the gene encoding KCNQ2 channels are a common cause of developmental and epileptic encephalopathy, a condition characterized by seizures, developmental delays, breathing problems, and early mortality. To understand how KCNQ2 dysfunction impacts behavior in a mouse model, we focus on the control of breathing by neurons expressing the transcription factor Phox2b which includes respiratory neurons in the ventral parafacial region. We find Phox2b-expressing ventral parafacial neurons express Kcnq2 in the absence of other Kcnq isoforms, thus clarifying why disruption of Kcnq2 but not other channel isoforms results in breathing problems. We also find that Kcnq2 deletion or expression of a recurrent gain-of-function variant R201C in Phox2b-expressing neurons increases baseline breathing or decreases the central chemoreflex, respectively, in mice during the light/inactive state. These results uncover mechanisms underlying breathing abnormalities in KCNQ2 encephalopathy and highlight an unappreciated vulnerability of Phox2b-expressing ventral parafacial neurons to KCNQ2 pathogenic variants.

Fluoresceinated peanut agglutinin (PNA) is a marker for live O(2) sensing glomus cells in rat carotid body

Experiments using live dissociated carotid body (CB) cells for patch clamping, [Ca(++)](i) or other measurements require positive identification of the cell being recorded. At present, cell morphology is usually employed, but several cell types within the carotid body evidence similar morphologic characteristics. Therefore, we sought to develop a method utilizing a vital dye to identify glomus cells before and during experiments that require live cells, such as patch clamp studies. It was previously reported that the binding sites for peanut agglutinin (PNA) were highly expressed by all neuroendocrine-derivatives of the sympathoadrenal neural crest, including glomus cells, small, intensely fluorescent cells, PC-12 cells, and adrenal chromaffin cells in situ (katz et al. 1995). By utilizing the binding characteristics of galactose-specific lectin peanut agglutinin (PNA) on the outer cell membrane, we tested the possibility that the fluoresceinated PNA may preferentially bind to CB glomus cells. The results to date show: (1) Rhodamine tagged PNA (Rhod-PNA) binds to the live dissociated glomus cells in less than one hour incubation and can be visualized in superfused cells; (2) Rhod-PNA labeled cells are perfectly matched with tyrosine hydroxylase (TH) positive glomus cells; (3) Rhod-PNA did not interfere with Fura-2 for Ca(++) imaging; (4) Rhod-PNA bound to glomus cells in [Ca(++)](i) studies does not affect O(2) response of glomus cells. Thus fluoresceinated PNA may be a useful marker for live CB glomus studies, without adversely affecting their physiologic response.

Postnatal development of carotid body glomus cell response to hypoxia

This study examines developmental changes in CB glomus cell depolarization, intracellular calcium ([Ca(2+)](i)) and the magnitude of an O(2)-sensitive background ionic conductance that may play roles in the postnatal increase in oxygen sensitivity of glomus cells isolated from rats of 1-3 days and 11-14 days postnatal age. Using fura-2 and perforated patch whole cell recordings, we simultaneously measured [Ca(2+)](i) and membrane potential (E(m)) during normoxia and hypoxia. Resting E(m) in normoxia was similar at both ages. Hypoxia caused a larger E(m) depolarization and correspondingly larger [Ca(2+)](i) response in glomus cells from 11- to 14-day-old rats compared to 1-3-day-old rats. E(m) and [Ca(2+)](i) responses to 40mM K(+) were identical between the two age groups. Under normoxic conditions both age groups had similar background conductances. Under anoxic conditions (at resting membrane potential) background K(+) conductance decreased significantly more in cells from 11- to 14-day-old rats compared to cells from 1- to 3-day-old rats. Glomus cells from newborns therefore have less O(2)-sensitive background K(+) conductance. These results support the hypothesis that postnatal maturation of glomus cell O(2) sensitivity involves developmental regulation of the expression and/or O(2)-sensitivity of background ionic conductances.

Dopamine D2 receptor modulation of carotid body type 1 cell intracellular calcium in developing rats

Carotid chemoreceptor type 1 cells release dopamine, which inhibits carotid chemoreceptor activity via dopamine D2 autoreceptors on type 1 cells. Postnatal changes in dopaminergic modulation may be involved in postnatal chemoreceptor development. The present study explores dopaminergic modulation of the intracellular calcium ([Ca(2+)](i)) response to hypoxia in type 1 cells from 1, 3, and 11- to 16-day-old rats. Using fura-2, we studied the effects of quinpirole, a D2 receptor agonist, on type 1 cell [Ca(2+)](i) response to 90-s hypoxia challenges (Po(2) approximately 1-2 mmHg). Cells were sequentially exposed to the following challenges: 1) hypoxia control, 2) hypoxia plus quinpirole, and 3) hypoxia plus quinpirole plus sulpiride (D2 receptor antagonist). In the 11- to 16-day-old group, type 1 cell [Ca(2+)](i) increased approximately 3 to 4-fold over resting [Ca(2+)](i) in response to hypoxia. Quinpirole (10 microM) significantly blunted the peak [Ca(2+)](i) response to hypoxia. Repeat challenge with hypoxia plus 10 microM quinpirole in the presence of 10 microM sulpiride partially restored the hypoxia [Ca(2+)](i) response. In sharp contrast to the older aged group, 10 microM quinpirole had minimal effect on hypoxia response of type 1 cells from 1-day-olds and a small but significant effect at 3 days of age. We conclude that stimulation of dopamine D2 receptors inhibits type 1 cell [Ca(2+)](i) response to hypoxia, consistent with an inhibitory autoreceptor role. These findings suggest dopamine-mediated inhibition and oxygen sensitivity increase with age on a similar time course and do not support a role for dopamine as a major mediator of carotid chemoreceptor resetting.

The role of natural killer cells in adenovirus-mediated p53 gene therapy

Adenovirus-mediated gene therapy is a promising new approach for treatment of ovarian cancer. In animal models, complete elimination of cancer cells is often achieved, although the therapeutic gene has not been delivered to all these cells. This is referred to as a bystander effect, because tumor cells near those that receive the therapeutic gene are also eliminated. Several mechanisms have been proposed for the bystander effect, including intercellular communication within the tumor via gap junctions, apoptosis, antiangiogenesis, cytokines or other soluble mediators, and immunological mechanisms. There are two well-documented antitumor effector cell populations in athymic nude mice: macrophages and natural killer (NK) cells. We hypothesize that peritoneal populations of NK cells in nude mice treated with adenoviruses are involved in the observed bystander effect in this in vivo model. We investigated the role of NK cells as immunological mediators for the bystander effect using the p53 tumor suppressor as the therapeutic anticancer gene. Most ovarian cancer cell lines tested were sensitive to lysis by NK cells, although different ovarian cancer cell lines exhibited different sensitivities to NK cell-mediated lysis. To determine the importance of NK cells in the overall efficacy and in the bystander effect of gene therapy, NK cells were depleted in mice by administration of anti-NK1.1 monoclonal antibodies. To study the efficacy of NK depletion, C57BL/6 (nu/nu) mice were given injections i.v. by a single tail vein injection or i.p. with increasing doses of anti-NK1.1 IgG. All doses of anti-NK1.1 antibody, from 100-500 micrograms, essentially eliminated cytotoxic NK activity. To assess the duration of depletion after a single dose of anti-NK1.1 IgG, a time-course experiment was performed. NK 1.1 antibody was effective in completely depleting cytotoxic NK cell activity in the mice for up to 7 days, whether given as 500 micrograms (i.p.) or 200 micrograms (i.v.). Flow cytometric analysis performed on peritoneal cell populations confirmed depletion of NK cells by approximately 80%. Finally, a survival study was performed, in which animals were depleted of NK cells. In this experiment, NK cell-depleted mice were injected with anti-NK1.1 IgG, and control mice were mice were treated with normal saline. Two days later, all mice were inoculated with a lethal i.p. dose of NIH:OVCAR-3 ovarian cancer cells. After 3 days, the mice were divided into two treatment groups; one treatment group received three consecutive daily i.p. injections of Ad-CMV-p53 (SCH58500), and the second treatment group received three consecutive daily i.p. injections of control adenovirus construct, rAd-null. All of the NK cell-depleted animals, whether treated with rAd-null or with Ad-CMV-p53 (SCH58500) were dead of disease by 116 and 138 days, respectively, after initiation of adenovirus treatment, and no statistically significant difference in survival was observed (P = 0.349). A significant survival advantage was seen in control (NK-competent) mice treated with rAd-null (P = 0.04), although all were dead of disease by day 184. Importantly, control NK-competent mice treated with Ad-CMV-p53 (SCH58500) showed no tumor growth or ascites production, and all animals survived. These results indicate that immunological mechanisms involving natural killer cells play an important role in the bystander effect involving adenovirus-p53 gene therapy for ovarian cancer.

Autoreceptor mechanism regulating carotid body dopamine release from adult and 10-day-old rabbits

Dopamine (DA) release (r) from the carotid body (CB) is thought to be modulated by feedback inhibition mediated by DA D2 autoreceptors. We tested the hypothesis that CB DAr is autoregulated in a concentration and age dependent manner. Using an in vitro CB infusion model [Bairam, A., Marchal. F., Cottet-Emard, J.M., Basson, H., Pequignot, J.M., Hascoet, J.M., Lahiri, S., 1996b. Effects of hypoxia on carotid body dopamine content and release in developing rabbits. J. Appl. Physiol. 80, 20-24.], we evaluated under unstimulated conditions the effects of 0.001, 0.01, 0.1, 1.0 and 10.0 microM of the specific DA D2 receptor antagonist domperidone on CB DAr in adult rabbits. In 10-day-old rabbit pups, concentrations of 0.01, 0.1, 1.0 microM were studied. In adult CBs, domperidone increased DAr in a concentration-dependent manner. DAr (pmol/h) was significantly greater compared to control (without domperidone) starting at a domperidone concentration of 0.1 microM (P<0.01). In 10-day-old pup CBs, 1.0 microM domperidone was required to produce a significant increase of DAr (pmol/h) compared to control (P<0.005). However, control DAr (as % of total catecholamine) was about 40%; significantly higher than 24% observed in adult CBs (P<0.001). We conclude that in rabbit CB, DAr is controlled by an autoreceptor mechanism in a concentration-dependent manner and this mechanism is less developed in pups than in adults.

Dynamic ventilatory responses in rats: normal development and effects of prenatal nicotine exposure

Infants of smoking mothers are at increased risk of SIDS, one cause of which is thought to be due to impaired ventilatory responses. We tested the hypotheses that prenatal nicotine exposure impairs the development of dynamic carotid chemoreceptor-driven ventilatory responses, and reduces the ability to lower metabolic rate in hypoxia. Osmotic minipumps were implanted into 20 pregnant rats at day 3 of gestation to deliver nicotine (6 mg/kg per day free base) or saline for 4 weeks. Minute ventilation was recorded breath by breath in rat pups at 3, 8 and 18 days (n = 6, 8 and 6) postnatal in response to 5-sec challenges of 100% O2 (Dejours test) and 5% O2 + 5% CO2. Carotid sinus nerve (CSN) responses to hypoxia and CO2 were recorded from 22 control and 17 nicotine-exposed preparations at ages between 3-20 days. Oxygen consumption (V(O)2) was measured in groups of pups at 3 days (n = 7 each for nicotine and control) and 8 days (n = 5 each for nicotine and control) in room air and 10% O2. There was no detectable effect of nicotine exposure on the development of CSN responses. Ventilatory responses to 5% O2-5% CO2 increased with age but did not differ between nicotine and control groups. Ventilatory responses to 100% O2 were unaffected by nicotine exposure at 8 and 18 days. However, the 3-day nicotine group showed no significant response to 100% O2 whereas V(E) was significantly reduced in the control group by 100% O2. There was no significant effect of nicotine exposure on the ability to reduce oxygen consumption in hypoxia at 3 or 8 days, but at 3 days, baseline (room air) variability in oxygen consumption was greater in the nicotine group. We conclude that nicotine exposure appears to result in abnormal ventilatory responses to withdrawal of baseline peripheral chemoreceptor drive during a period of early postnatal life. We speculate that a transient abnormality could contribute to a period of instability and increased vulnerability to challenges.

Chronic hypoxia abolished the postnatal increase in carotid body type I cell sensitivity to hypoxia

The O2 sensitivity of carotid chemoreceptor type I cells is low just after birth and increases with postnatal age. Chronic hypoxia during postnatal maturation blunts ventilatory and carotid chemoreceptor neural responses to hypoxia, but the mechanism remains unknown. We tested the hypothesis that chronic hypoxia from birth impairs the postnatal increase in type I cell O2 sensitivity by comparing intracellular Ca2+ concentration ([Ca2+]i) responses to graded hypoxia in type I cell clusters from rats born and reared in room air or 12% O2. [Ca2+]i levels at 0, 1, 5, and 21% O2, as well as with 40 mM K+, were measured at 3, 11, and 18 days of age with use of fura 2 in freshly isolated cells. The [Ca2+]i response to elevated CO2/low pH was measured at 11 days. Chronic hypoxia from birth abolished the normal developmental increase in the type I cell [Ca2+]i response to hypoxia. Effects of chronic hypoxia on development of [Ca2)]i responses to elevated K+ were small, and [Ca2+]i responses to CO2 remained unaffected. Impairment of type I cell maturation was partially reversible on return to normoxic conditions. These results indicate that chronic hypoxia severely impairs the postnatal development of carotid chemoreceptor O2 sensitivity at the cellular level and leaves responses to other stimuli largely intact.

Postnatal maturation of carotid body and type I cell chemoreception in the rat

The site of postnatal maturation of carotid body chemoreception is unclear. To test the hypothesis that maturation occurs synchronously in type I cells and the whole carotid body, the development of changes in the intracellular Ca2+ concentration responses to hypoxia, CO2, and combined challenges was studied with fluorescence microscopy in type I cells and compared with the development of carotid sinus nerve (CSN) responses recorded in vitro from term fetal to 3-wk animals. Type I cell responses to all challenges increased between 1 and 8 days and then remained constant, with no multiplicative O2-CO2 interaction at any age. The CSN response to hypoxia also matured by 8 days, but CSN responses to CO2 did not change significantly with age. Multiplicative O2-CO2 interaction occurred in the CSN response at 2-3 wk but not in younger groups. We conclude that type I cell maturation underlies maturation of the CSN response to hypoxia. However, because development of responses to CO2 and combined hypoxia-CO2 challenges differed between type I cells and the CSN, responses to these stimuli must mature at other, unidentified sites within the developing carotid body.

Resetting and postnatal maturation of oxygen chemosensitivity in rat carotid chemoreceptor cells

1. Carotid chemoreceptor sensitivity is minimal immediately after birth and increases with postnatal age. In the present study we have investigated the peri- and postnatal developmental time course of [Ca2+]i responses to hypoxia in clusters of type I cells isolated from near-term fetal rats and rats that were 1, 3, 7, 11, 14 and 21 days old, using the Ca2+-sensitive fluoroprobe fura-2. 2. In type I cells from all age groups a graded increase in [Ca2+]i occurred in response to lowering the PO2 from 150 mmHg to 70, 35, 14, 7, 2 and 0 mmHg. The graded [Ca2+]i response to hypoxia was hyperbolic at all ages. 3. Type I cells from rats near-term fetal to 1 day old exhibited small [Ca2+]i responses, mainly to the most severe levels of hypoxia. After day 1, an increase in the [Ca2+]i responses to submaximal hypoxia stimulation resulted in a rightward shift in the O2 response curve. Using the Delta[Ca2+]i between 35 and 2 mmHg PO2 as an index of O2 sensitivity, type I cell O2 sensitivity increased approximately 4- to 5-fold between near-term fetal to 1 day old and 11 to 14 days of age. 4. Exposure to elevated extracellular potassium (10, 20 and 40 mM K+) caused a dose-dependent [Ca2+]i rise in type I cells from all age groups. There were no age-related changes in [Ca2+]i responses to any level of K+ between near-term fetal and 21 days. 5. We conclude that the maximal type I cell [Ca2+]i response to anoxia, as well as the sensitivity to submaximal hypoxic stimulation, of rats aged from near-term fetal to 21 days depends on the level of postnatal maturity. The lack of an age-related increase in the [Ca2+]i response to elevated K+ during the timeframe of maximal development of O2 sensitivity suggests that resetting involves maturation of O2 sensing, rather than non-specific developmental changes in the [Ca2+]i rise resulting from depolarization.

Mechanism of suppressed neutrophil mobilization in a mouse model for binge drinking: role of glucocorticoids

The goals of this study were to determine if suppression of neutrophil accumulation and TNF-alpha production in the peritoneal cavity occurs in mice exposed to a chemical stressor [ethanol (EtOH)], to evaluate the role of EtOH-induced increases in endogenous glucocorticoids in any such suppression, and to determine if decreased tumor necrosis factor-alpha (TNF-alpha) production is responsible for decreases in neutrophil accumulation in EtOH-treated mice. An inflammatory response induced in the peritoneal cavity of mice by administration of heat-killed Propionibacterium acnes (P. acnes) was suppressed by a single dose of EtOH given 1 h before administration of the bacteria, as indicated by decreased accumulation of neutrophils in the peritoneal cavity. The concentration of TNF-alpha in the peritoneal cavity was also decreased by EtOH, but exogenous TNF-alpha did not prevent the suppression of neutrophil accumulation. The glucocorticoid antagonist RU-486 did not prevent the suppression of neutrophil accumulation in mice treated with EtOH, but RU-486 did block suppression of neutrophil accumulation caused by administration of exogenous corticosterone. The suppression of neutrophil accumulation caused by exogenous corticosterone was less than produced by EtOH. These observations suggest that the increase in endogenous corticosterone induced by EtOH may explain some of the suppression of neutrophil accumulation, but other neuroendocrine mediators (or EtOH per se) are sufficient to cause the full suppressive effect when the action of corticosterone is blocked by RU-486. The results also demonstrate that EtOH decreases TNF-alpha production, but this is not the mechanism by which neutrophil accumulation is decreased in this model.

Expression of dopamine D1-receptor mRNA in the carotid body of adult rabbits, cats and rats

Dopamine is a major neurotransmitter in the carotid body of several animal species and its functional role at the level of peripheral arterial chemoreflex pathway is attributed to the presence of the dopamine D2-receptors. We present evidence that the dopamine D1-receptor mRNA is also expressed in the carotid body of adult rabbits, cats and rats. A DNA fragment of 611 bp of this receptor was first isolated from rabbit. The nucleic acid sequence of this fragment was found to be 84.5% identical to that of rat. This specific 611 bp fragment was used as a probe to detect, either by Northern analysis or by the reverse transcription-polymerase chain reaction, the dopamine D1-receptor mRNA. The results revealed the presence of dopamine D1-receptor transcript in the carotid body as well as in the petrosal ganglion and the superior cervical ganglion from the three animal models studied here. The physiological significance of dopamine D1-receptor expression in the carotid body is discussed.

Arousal and ventilatory responses during sleep in children with obstructive sleep apnea

Abnormal central regulation of upper airway muscles may contribute to the pathophysiology of the childhood obstructive sleep apnea syndrome (OSAS). We hypothesized that this was secondary to global abnormalities of ventilatory control during sleep. We therefore compared the response to chemical stimuli during sleep between prepubertal children with OSAS and controls. Patients with OSAS aroused at a higher PCO2 (58 +/- 2 vs. 60 +/- 5 Torr, P < 0.05); those with the highest apnea index had the highest arousal threshold (r = 0.52, P < 0.05). The hypercapnic arousal threshold decreased after treatment. For all subjects, hypoxia was a poor stimulus to arousal, whereas hypercapnia and, particularly, hypoxic hypercapnia were potent stimuli to arousal. Hypercapnia resulted in decreased airway obstruction in OSAS. Ventilatory responses were similar between patients with OSAS and controls; however, the sample size was small. We conclude that children with OSAS have slightly blunted arousal responses to hypercapnia. However, the overall ventilatory and arousal responses are normal in children with OSAS, indicating that a global deficit in respiratory drive is not a major factor in the etiology of childhood OSAS. Nevertheless, subtle abnormalities in ventilatory control may exist.

Sleep-disordered breathing in children with achondroplasia

OBJECTIVE

Our objective was to characterize sleep-disordered breathing in 88 children with achondroplasia aged 1 month to 12.6 years.

RESULTS

At the time of their initial polysomnography, five children had previously undergone tracheostomy, and seven children required supplemental oxygen. Initial polysomnography demonstrated a median obstructive apnea index of 0 (range, 0 to 19.2 apneas/hr). The median number of central apneas with desaturation per study was 0.5 (0 to 49), the median oxygen saturation nadir was 91% (50% to 99%), and the median peak end-tidal pCO2 was 47 mm Hg (36 to 87 mm Hg). Forty-two children (47.7%) had abnormal initial study results, usually caused by hypoxemia. Two children with severe obstructive sleep apnea eventually required continuous positive airway pressure therapy, and three additional children required tracheostomies.

CONCLUSIONS

(1) Children with achondroplasia often have sleep-related respiratory disturbances, primarily hypoxemia. (2) The majority do not have significant obstructive or central apnea; however, a substantial minority are severely affected. (3) Tonsillectomy and adenoidectomy decreases the degree of upper airway obstruction in most but not all children with achondroplasia and obstructive sleep apnea. (4) Restrictive lung disease can present at a young age in children with achondroplasia.

Blood pressure in children with obstructive sleep apnea

Hypertension is a common complication of obstructive sleep apnea in adults. However, hypertension has not been studied systematically in children with the obstructive sleep apnea syndrome (OSAS). We therefore measured blood pressure (BP) during polysomnography in 41 children with OSAS, compared to 26 children with primary snoring (PS). Systolic and diastolic BP were measured every 15 min via an appropriately sized arm cuff, using an automated system. This was tolerated by the children without inducing arousals from sleep. Children with OSAS had a significantly higher diastolic BP than those with PS (p < 0.001 for sleep and p < 0.005 for wakefulness). There was no significant difference in systolic BP between the two groups. Multiple linear regression showed that blood pressure could be predicted by apnea index, body mass index, and age. Blood pressure during sleep was lower than during wakefulness (p < 0.001 for diastole and p < 0.01 for systole), but did not differ significantly between rapid eye movement (REM) and non-REM sleep. We conclude that childhood OSAS is associated with systemic diastolic hypertension.

SIDS: counseling parents to reduce the risk

Although the cause or causes of sudden infant death syndrome (SIDS) remain unknown, the incidence of SIDS is on the decline in the United States and other countries. This decline has been accomplished largely through public education campaigns informing parents about several important factors associated with an increased risk of SIDS. These factors are prone and side infant sleeping positions, exposure of infants to cigarette smoke and potentially hazardous sleeping environments. Risk-reduction measures such as placing healthy infants to sleep in the supine position, avoiding passive smoke exposure both before and after birth and optimizing crib safety are beginning to lower the SIDS rate in this country. Through patient education, family physicians can further reduce the incidence of the number one cause of death in infants one week to one year old.

Consequences of sleep-disordered breathing in childhood

Obstructive sleep-disordered breathing (SDB) is a common problem in children that may lead to growth failure, neurocognitive and behavioral abnormalities, cor pulmonale, and death. Primary snoring, upper airway resistance syndrome, and obstructive sleep apnea syndrome represent a spectrum of clinical manifestations accompanying increasing degrees of upper airway obstruction. Clearly, children with severe SDB need to be identified and treated promptly. Appropriate management strategies for milder forms of SDB are less clear. Some snoring children, for example, may have an increased frequency of obstructive apnea during sleep, with or without mild hypoxemia, but have essentially no daytime symptoms or apparent clinical consequences. Should these children be treated? If untreated, will these children eventually develop more severe obstructive SDB? Development of management strategies is hampered by the lack of data on the natural history of childhood SDB and on the correlation of specific polysomnographic abnormalities to symptoms and complications. In this review, we highlight recent information about the consequences of obstructive SDB in children, with particular emphasis on areas in which more data are needed.

The cardiorespiratory response to anoxia: normal development and the effect of nicotine

Maternal smoking increases the risk of the sudden infant death syndrome (SIDS) 2-4-fold. The mechanism is unknown but may be related to hypoxia responses. Recovery from hypoxic apnea by young mammals depends on gasping and bradycardia. We asked whether prenatal nicotine exposure, reported to reduce hypoxic survival in 2 day old rat pups, acted by impairing gasping or bradycardia. Pregnant rats were infused throughout gestation and 1 week postnatally with nicotine tartrate (NIC) 12 mg/kg per day or saline (CON). Maternal plasma nicotine was 134.4 +/- 42 ng/ml, significantly reducing pup body weight. Pups at 3-28 days were exposed to anoxia (97% N2/3% CO2) until gasping ceased, while breathing and heart rate were recorded. NIC and CON groups were not significantly different at any age, in baseline heart rate, respiratory rate, the time course for bradycardia, time to gasp onset, duration of gasping, or number of gasps, although most of these variables declined significantly with age. We conclude that responses to anoxia are not affected by prenatal high-dose nicotine.

High prevalence of allergic sensitization in children with habitual snoring and obstructive sleep apnea

STUDY OBJECTIVE

To determine whether allergic sensitization occurs frequently in children with habitual snoring and whether allergy predicts the occurrence of obstructive sleep apnea syndrome (OSAS) in snoring children.

DESIGN

Prospective study of 39 children with habitual snoring who were referred for polysomnography.

SETTING

Pediatric pulmonary sleep disorders clinic in a tertiary referral center.

MEASUREMENTS

Subjects underwent a complete history and physical examination. To assess for the presence of allergic sensitization, a multiantigen radioallergosorbent test (RAST) was performed on serum samples. Subjects then underwent nocturnal polysomnography to determine the presence and severity of OSAS.

RESULTS

Fourteen subjects (36%) demonstrated sensitivity to allergens; this is higher than expected for the general pediatric population. The frequency of OSAS was increased in subjects with positive RAST results compared to those with negative RAST results (57% vs 40%; chi 2 = 9.11; p < 0.01).

CONCLUSION

Allergy is frequently present in pediatric patients with habitual snoring. Furthermore, the presence of allergy is associated with an increased risk of OSAS in this population.

Effect of nicotine exposure on postnatal ventilatory responses to hypoxia and hypercapnia

The risk of SIDS is increased up to fourfold by maternal smoking, by an unknown mechanism. We tested the hypothesis that prenatal nicotine exposure can cause abnormal postnatal development of breathing control. Osmotic minipumps were implanted into pregnant rats to deliver either nicotine bitartrate (6 mg kg-1 day-1) (NIC) or saline (CON) throughout gestation and for 1 week postnatal. NIC and CON rat pups from 4 age groups (means 3, 8, 18 and 34 days) were studied. Ventilation was recorded at 30 degrees C in air and after 10 min at FIO2 = 0.1 and 0.15, and at FICO2 = 0.05. Ventilatory responses to FIO2 = 0.1 and FICO2 = 0.05 showed significant changes with age but were unaffected by NIC at all ages. The weak respiratory responses to FIO2 = 0.15 were unaffected by NIC or age. Oxygen consumption in normoxia and hypoxia, and hypoxic depression of oxygen consumption, declined with age but were not affected by NIC. We conclude that NIC exposure alone has no detectable effect on the postnatal development of respiratory responses to moderate levels of hypoxia or hypercapnia for short periods. However, effects of NIC on the responses to more severe or prolonged stimuli cannot be ruled out.

Ventral medullary neuronal responses to peripheral chemoreceptor stimulation

Recent findings suggest that carotid chemoreceptor input into the ventral medullary surface intermediate area during hypoxia is inhibitory (Gozal et al., (1994) Neurosci. Lett. 178, 73-76. However, systemic hypoxia is a complex stimulus, and effects of carotid chemoreceptor stimulation per se on intermediate ventral medullary surface neuronal activity are difficult to isolate. Therefore, we studied neural activation of the intermediate ventral medullary surface during peripheral chemoreceptor stimulation by intravenous sodium cyanide using optical procedures in seven pentobarbital-anesthetized cats. Control recordings were also acquired in the suprasylvian cortex of three cats. Images of reflected 660 nm light were collected at l/s with a charge-coupled device camera, triggered by the cardiac R wave, after 0.0, 0.5, 2, 5, 10, 20 and 40 micrograms/kg i.v. sodium cyanide administration before and following carotid sinus denervation. Sodium cyanide doses > 5 micrograms/kg significantly increased ventilation, an effect which was eliminated following carotid sinus denervation. A pronounced, dose-dependent activity decrease within the intermediate ventral medullary surface occurred within seconds of sodium cyanide administration, with subsequent return to baseline. Carotid sinus denervation eliminated rapid-onset neural responses to all sodium cyanide doses. However, at the 40 micrograms/kg dose, a smaller, slower onset (25 s), activity decrease occurred both pre- and postdenervation. In the neocortex, the sodium cyanide-induced fast responses were absent. Intravenous cyanide, acting via a carotid sinus nerve pathway, results in a dose-dependent decrease in neural activity within the intermediate ventral medullary surface of cats. High-dose sodium cyanide also appears to decrease intermediate ventral medullary surface neural activity directly.

Polysomnography in the evaluation of readiness for decannulation in children

OBJECTIVE

To determine whether polysomnography is useful in the evaluation of readiness for decannulation in children with long-term tracheotomy.

DESIGN

Descriptive, retrospective case series.

SETTING

Tertiary care pediatric center, pediatric sleep disorders laboratory, and pediatric otolaryngology referral center.

PATIENTS

Children (younger than 18 years) with tracheotomy undergoing polysomnography to assess their dependence on tracheotomy.

INTERVENTION

Polysomnography in all patients; endoscopy and decannulation in those judged clinically ready.

MAIN OUTCOME MEASURES

Success of decannulation.

RESULTS

Thirteen of 16 patients with favorable polysomnographic data were successfully decannulated.

CONCLUSION

Polysomnography is a useful supplement to airway endoscopy in the evaluation of readiness for decannulation in children with long-term tracheotomy and dynamic airway issues.

Mechanisms of carotid chemoreceptor resetting after birth. In vitro studies

The results of these studies are consistent with the hypothesis that carotid chemoreceptor type-I cell resetting occurs, at least in part, at the level of the type-I cell. Furthermore, we have developed an in vitro model of newborn type-I cell resetting, in which freshly isolated glomus cells from newborns exhibit small, immature [Ca2+]i response to anoxia, but-after 72 hours in culture-[Ca2+]i responses convert to adult magnitude and profile. Finally, work so far suggests that glomus cell resetting in this model is modulated by oxygen tension. The mechanisms of glomus cell resetting remain unknown. Resetting of O2 sensitivity could result from withdrawal of tonic inhibitory influences present in vivo, changes in the oxygen sensor itself, changes in ion channel expression, modulation, and function, or other mechanisms occurring around the time of birth. Additional work is needed to determine the mechanisms of glomus cell resetting at the cellular level, and the role of O2 tension and other potential modulators of resetting.

Supplemental oxygen during sleep in children with sleep-disordered breathing

Supplemental O2 is sometimes used to treat children with the obstructive sleep apnea syndrome (OSAS). However, its effects have not been studied. We therefore evaluated the use of supplemental O2 during sleep in children with OSAS. Oxygen and room air were delivered via nasal cannula at 1 L/min for 4 h each in a randomized, double-blind fashion. Twenty-three children were studied (mean age, 5 +/- 3 [SD] yr). Patients had a higher mean SaO2 and higher SaO2 nadir when breathing O2. There was no difference in the number (10.9 +/- 20.6/h on O2 versus 13.5 +/- 19.3 on room air) or duration of obstructive apneas. Although there was no overall change in end-tidal PCO2 when patients breathed O2, two children showed a significant increase. We conclude that breathing supplemental O2 during sleep in children with OSAS results in improved oxygenation and in most cases does not exacerbate sleep-disordered breathing. However, end-tidal PCO2 should be monitored in children with OSAS receiving O2 therapy. We speculate that supplemental O2 does not depress the ventilatory drive during sleep in most children with OSAS.

Inability of clinical history to distinguish primary snoring from obstructive sleep apnea syndrome in children

STUDY OBJECTIVE

To determine whether primary snoring (PS) could be distinguished from childhood obstructive sleep apnea syndrome (OSAS) by clinical history.

DESIGN

Retrospective study of clinical history of 83 children with snoring and/or sleep disordered breathing who were referred for polysomnography.

SETTING

Tertiary referral center; pediatric pulmonary sleep apnea clinic.

MEASUREMENTS

We evaluated the ability of a clinical obstructive sleep apnea (OSA) score and other questions about sleep, breathing, and daytime symptoms to distinguish PS from OSAS in children. Parents were asked about the child's snoring, difficulty breathing, observed apnea, cyanosis, struggling to breathe, shaking the child to "make him or her breathe," watching the child sleep, afraid of apnea, the frequency and loudness of snoring, and daytime symptoms such as excessive daytime sleepiness (EDS).

RESULTS

Based on polysomnography results, 48 patients were classified as PS and 35 as OSAS. Peak endtidal CO2 (49 +/- 3.2 vs 55 +/- 8.2 [SD] mm Hg); lowest arterial oxygen saturation measured by pulse oximetry (95 +/- 1.9 vs 82 +/- 14%); and apnea/hypopnea index (0.27 +/- .3 vs 8.4 +/- 6 events/h) indicated that the diagnostic criteria for PS versus OSA were reasonable. There were no differences between PS and OSA patients with respect to age, sex, race, failure to thrive, obesity, history of EDS, snoring history, history of cyanosis during sleep, or daytime symptoms except for mouth breathing. There were no significant differences in sleep variables between PS patients and those with any severity of OSAS. The OSA score misclassified about one of four patients. Comparing PS and OSA patients, significant findings were daytime mouth breathing (61 vs 85%; p = 0.024); observed apnea (46 vs 74%; p = 0.013); shaking the child (31 vs. 60%; p = 0.01); struggling to breathe (58 vs 89%; p = 0.003); and afraid of apnea (71 vs 91%; p = 0.028). However, none of these were sufficiently discriminatory to predict OSAS.

CONCLUSION

We conclude that PS in children cannot be reliably distinguished from OSAS by clinical history alone.

Ventral medullary surface responses to hypoxic and hyperoxic transient ventilatory challenges in the cat

Carotid body afferent contributions to activity of the intermediate area of the ventral medullary surface (IVMS) following transient hypoxia and hyperoxia were examined in 6 spontaneously breathing, pentobarbital-anesthetized cats. Two tidal breaths of 100% N2, 100% O2, or room air, were randomly administered before and after carotid sinus denervation (CSD). Images of scattered light from the IVMS showed that activity increased with hypoxia (10.1 +/- 2.4%), and decreased with hyperoxia (4.8 +/- 1.8%). CSD significantly increased the magnitude and delayed the onset of the hypoxic response, but reversed the initial component of the hyperoxic response. We conclude that carotid body afferents modulate the magnitude and timing of IVMS responses to transient respiratory challenges.

Alcohol use and risky sex among college students

Undergraduates, 55 men and 151 women, completed a 13-item survey about drinking behavior and sexual activity. In general, men and women were similar in their behaviors. Despite recent efforts to promote AIDS awareness, it appears that both genders may be engaging in risky behavior. The results are discussed in terms of educational efforts aimed at AIDS prevention.

Developmental changes in intracellular Ca2+ response of carotid chemoreceptor cells to hypoxia

The carotid chemoreceptor response to hypoxia is weak just after birth and increases during postnatal development. The mechanisms underlying chemoreceptor maturation are unknown. We tested the hypothesis that carotid chemoreceptor maturation occurs at the glomus cell level by measuring intracellular calcium ([Ca2+]i) mobilization in response to hypoxia, anoxia, and NaCN in freshly dissociated cells from newborn vs. adult rabbit carotid bodies. Cells were loaded with fura 2 and superfused at 37 degrees C with balanced salt solution equilibrated with 5% CO2. [Ca2+]i mobilization in response to 3-min challenges of hypoxia (PO2 approximately 15 mmHg), anoxia (PO2 approximately 0 mmHg), and NaCN (1 mM) was measured using a digital imaging microscope. The fluorescence intensity ratio was used to calculate [Ca2+]i. Peak [Ca2+]i responses to all three challenges were three- to fivefold greater in glomus cells from adult compared with newborn carotid chemoreceptors. In addition, the average normoxic [Ca2+]i baseline was approximately threefold higher in the adult glomus cells. These results suggest that carotid chemoreceptor glomus cell sensitivity to natural stimuli, as reflected by the [Ca2+]i response, depends on the level of postnatal maturity.

Pressor-induced responses of the cat ventral medullary surface

We examined ventral medullary surface activity using light reflectance procedures after blood pressure alterations induced by phenylephrine or sodium nitroprusside in 23 pentobarbital sodium-anesthetized cats. Images of reflected 660-nm light were collected and digitized at 1- to 3-s intervals after baseline and intravenous saline, 5-40 micrograms/kg phenylephrine, or sodium nitroprusside infusion. Carotid sinus nerve denervation (CSD) and bilateral vagotomy were performed in five and three animals, respectively, and challenges were repeated. Phenylephrine elicited a dose-dependent transient blood pressure elevation and reflectance increase (interpreted as activity decline) over the entire ventral medullary surface examined. The increase consisted of an initial rapid transient component, peaking at 45 s, and a 3- to 5-min recovery. CSD enhanced, and vagotomy substantially reduced, the initial transient response to phenylephrine. Sodium nitroprusside-induced lowering of blood pressure was associated with decreased reflectance in rostral sites and increased reflectance in caudal regions. CSD abolished a late component and diminished amplitude of an initial rapidly rising component of changes induced by nitroprusside, a decline further accentuated by addition of vagotomy.

Determinants of growth in children with the obstructive sleep apnea syndrome

Failure to thrive is a common complication of childhood obstructive sleep apnea syndrome (OSAS). To further evaluate its cause, we obtained 3-day dietary records, anthropometric measurements, polysomnography, and measurements of energy expenditure during sleep (SEE) in children with OSAS before and after tonsillectomy and adenoidectomy. Fourteen children were studied (mean age, 4 +/- 1 (SD) years). During initial polysomnography, patients had 6 +/- 3 episodes of obstructive apnea/hr, an arterial oxygen saturation nadir of 85% +/- 8%, and peak end-tidal carbon dioxide tension of 52 +/- 6 mm Hg. After surgery, OSAS resolved in all patients. The standard deviation score (z score) for weight increased from -0.30 +/- 1.47 to 0.04 +/- 1.34 (p < 0.005), despite unaltered caloric intake (91 +/- 30 vs 90 +/- 27 kcal/kg per day; not significant). The initial SEE (averaged over all sleep states) was 51 +/- 6 kcal/kg per day; postoperatively, it decreased to 46 +/- 7 kcal/kg per day (p < 0.005). Although SEE decreased during all sleep stages, the greatest decrease occurred during rapid eye movement sleep. The patients with the highest SEE on initial study had the lowest z scores (r = -0.62; p < 0.05). We conclude that SEE decreases and weight improves after resolution of OSAS. We speculate that the poor growth seen in some children with OSAS is secondary to increased caloric expenditure caused by increased work of breathing during sleep.

Effects of domperidone on neonatal and adult carotid chemoreceptors in the cat

It has been postulated that the weak carotid chemoreceptor responses of neonatal mammals may be due to inhibition produced by high levels of endogenous dopamine release or exaggerated sensitivity to dopaminergic inhibition. This was studied by measuring the effect of domperidone, a selective dopamine D2-receptor antagonist, on the carotid chemoreceptor response to O2 and CO2 in anesthetized neonatal and adult cats. The animals were exposed to four levels of isocapnic O2 (arterial PO2 of approximately 35-45, 55-65, 80-90, > 300 Torr) and four levels of isoxic CO2 (end-tidal PCO2 of approximately 21, 40, 58, and 78 Torr) before and after D2-receptor blockade. Whole nerve activity was recorded from the carotid sinus nerve (CSN). Both neonatal and adult cats increase CSN activity during hypoxia and hypercapnia (P < 0.001). Domperidone caused an increase in CSN activity at all O2 levels in adults (P < 0.01) but only during hypoxia in neonates (P < 0.001). Domperidone caused an increase in CSN activity during normo- and hypercapnia in adults but only during hypercapnia in neonates (P < 0.001). Domperidone approximately doubled an index of hypoxic sensitivity in the normoxia-hypoxia range (100 to 40 Torr) in the neonatal group but had little effect on sensitivity to hypoxia in adults. We conclude that the inhibitory role of endogenous dopamine in the carotid chemoreceptors changes with postnatal development.

Afferent contributions to intermediate area of the cat ventral medullary surface during mild hypoxia

The intermediate area of the cat ventral medullary surface activates to mild hypoxia. Carotid body and vagal afferent contributions to this response were examined by recording activity levels, measured as changes in scattered 660 nm light, from the medullary surface in 7 anesthetized, spontaneously breathing cats following 12% O2 in N2 ventilatory challenge. A miniaturized video camera collected images synchronous with the peak of cardiac R wave at 1/s, from a 3.2 mm diameter area, before, and following bilateral carotid sinus denervation (CSD) and vagotomy. In intact animals, hypoxia increased activity; however, greater increases in activity levels followed CSD, while vagotomy elicited a marked reduction of the response. Thus, carotid body afferents exert inhibitory or disfacilitatory influences on intermediate area neurons, while the vagus appears to play an excitatory role.

Polysomnographic characteristics of patients with Rett syndrome

During wakefulness, patients with Rett syndrome have disordered breathing. To understand further this ventilatory control disorder, we performed polysomnography in 30 patients with Rett syndrome and 30 control subjects (female subjects with primary snoring). The median age was 7 years (range, 1 to 32 years) for Rett syndrome and 6 years (range, 1 to 17 years) for control subjects. During periods of wakefulness, 67% of patients with Rett syndrome had the characteristic pattern of disordered breathing (i.e., episodes of hyperventilation followed by central apnea and desaturation). No such events occurred during sleep. Sleep efficiency and sleep architecture were similar for both groups. During sleep, there was no difference in duration of periodic breathing, number of episodes of central apnea with desaturation, or number of episodes of obstructive apnea or end-tidal carbon dioxide tension between the two groups. Although arterial oxygen saturation during rapid eye movement (REM) sleep was slightly lower in patients with Rett syndrome (nadir, 94% +/- 2% vs 96% +/- 2%), it remained within the normal range. Parental history reflected the awake respiratory findings in most cases. We conclude that patients with Rett syndrome have normal breathing during non-rapid eye movement (NREM) sleep. We speculate that patients with Rett syndrome have normal brain-stem control of ventilation, and that the disordered breathing seen during wakefulness is due to an abnormality of the cortical influence on ventilation.

Upper airway collapsibility in children with obstructive sleep apnea syndrome

In adults, the critical nasal pressure (Pcrit) at which the upper airway collapses is higher in patients with the obstructive sleep apnea syndrome (OSAS) than in those with primary snoring. Pediatric OSAS differs clinically from adult OSAS. We therefore compared Pcrit between prepubertal children with OSAS and primary snoring. Pcrit was determined by correlating the maximal inspiratory airflow with the level of positive or negative nasal pressure applied via a nasal mask. As in adults, we found that the maximal inspiratory airflow varied in proportion to the upstream (nasal) rather than the downstream (esophageal) pressure changes. Pcrit was 1 +/- 3 cmH2O in OSAS compared with -20 +/- 9 cmH2O in primary snorers (P < 0.002). In three OSAS patients reevaluated after tonsillectomy and adenoidectomy, Pcrit declined to -7.2 +/- 4.0 cmH2O. We conclude that the pediatric airway behaved as predicted by the Starling resistor model and that Pcrit, a measure of airway collapsibility, correlated with the degree of upper airway obstruction and was reduced postoperatively, consistent with increased upper airway stability.

Concurrent validity of the Culture-free Self-esteem Inventory and physical health in college students

55 college students received the Culture-free Self-esteem Inventory and a 13-item measure of physical health; significant Pearson correlations (generally in the .40s) were found on all but one subscale of the self-concept measure and the health measure. The results are in line with research using other measures of self-esteem and physical health and suggest that the self-esteem inventory may be useful as a research measure.

Cardiorespiratory recordings from infants dying suddenly and unexpectedly at home

OBJECTIVE

Little is known about the mechanism of death during sudden infant death. To study the mechanism, we obtained data on six infants who died while on a memory-equipped cardiorespiratory monitor.

METHODS

Waveforms of respiration and heart rate trend were available for five infants; an alarm log only was available for the sixth. These printouts were reviewed with attention to mechanism and time to death.

RESULTS

All infants were born prematurely; autopsies reported the cause of death as sudden infant death syndrome in three cases and bronchopulmonary dysplasia in the others. Bradycardia, which played a more prominent role than central apnea, was preceded by tachycardia in two deaths. Resuscitation occurred within 1 minute in four cases; no response to alarms occurred in the other two cases, apparently because the parents were desensitized by prior meaningless alarms. Five patients died within 20 minutes, whereas one death due to sudden infant death syndrome was prolonged.

CONCLUSION

Bradycardia is an important feature in all six of these infant deaths. Although its etiology is unknown, hypoxemia or obstructive apnea may precede bradycardia. Home monitors equipped to detect these possible antecedents will yield further insight into sudden infant death.

Postnatal maturation of carotid chemoreceptor responses to O2 and CO2 in the cat

This study aimed to characterize neural responses of the carotid chemoreceptors of the maturing cat to natural stimuli and to determine the time course of carotid chemoreceptor development from the neonatal period to adulthood. Carotid sinus nerve (CNS) responses to O2 and CO2 were studied in cats at 1, 4, and 8 wk of age and in adult cats (n = 6 at each age). Pentobarbital sodium-anesthetized cats were exposed to three levels of O2 (arterial PO2 = 40-45, 80-90, and > 300 Torr) at five levels of arterial PCO2 (22, 35, 48, 63, and 75 Torr) while the moving average of whole nerve output from the CSN was recorded. Ganglioglomerular nerves were sectioned. All cats at every age increased CSN activity during hypoxia. However, the CSN response to hypoxia was not sustained in some immature cats. Of the cats that sustained CSN activity during hypoxia, four of the six 1-wk-old cats showed a biphasic pattern of response, with an initial overshoot followed by a steady level of discharge. Older cats did not exhibit this pattern. CNS sensitivity to hypoxia was weakest in 1-wk-old kittens but increased to nearly adult levels by 4 wk of age. Carotid chemoreceptor responses to CO2 were also smallest in 1-wk-old kittens and increased with maturation. However, unlike hypoxia responses, CO2 sensitivity during hypoxia continued to develop between 8 wk and adulthood. O2-CO2 interaction did not become significant until after 4 wk of age. Thus, carotid chemoreceptor responses to both O2 and CO2 are weak in newborn cats and increase during postnatal development.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory compromise after adenotonsillectomy in children with obstructive sleep apnea

A retrospective study of pediatric patients with obstructive sleep apnea who underwent adenotonsillectomy between 1987 and 1990 was undertaken to determine the frequency of postoperative respiratory compromise and to determine if risk factors for its development could be identified. Sixty-nine patients less than 18 years old had polysomnographically documented obstructive sleep apnea and were observed postoperatively in the pediatric intensive care unit. Of these, 16 (23%) had severe respiratory compromise, defined as intermittent or continuous oxygen saturation of 70% or less, and/or hypercapnia, requiring intervention. Compared with patients without respiratory compromise, these patients were younger (3.4 +/- 4 vs 6.1 +/- 4 years) and had more obstructive events per hour of sleep on the polysomnogram (49 +/- 41 vs 19 +/- 30). They were more likely to weight less than the fifth percentile for age (odds ratio [OR], 5.1; 95% confidence interval [CI], 1.4 to 18.7), to have an abnormal electrocardiogram and/or echocardiogram (OR, 4.5; 95% CI, 1.3 to 15.1), and to have a craniofacial abnormality (OR, 6.2; 95% CI, 1.5 to 26). Multiple logistic regression analysis revealed the most significant risk factors were age below 3 years and an obstructive event index greater than 10. Children with obstructive sleep apnea are at risk for respiratory compromise following adenotonsillectomy; young age and severe sleep-related upper airway obstruction significantly increase this risk. We recommend in-hospital postoperative monitoring for children undergoing adenotonsillectomy for obstructive sleep apnea.

Correlation between humorous coping style and health

A significant correlation of -0.34 was found between scores on the Situational Humor Response Questionnaire and a measure of perceived physical health for 51 college students. Mean scores on the questionnaire were similar to those of the original standardization population.

Impotence in the elderly. Evaluation of erectile failure in men older than seventy years of age. Jefferson Sexual Function Center

A total of 102 patients over seventy years of age were evaluated in a multidisciplinary center for erectile dysfunction. The primary diagnosis was organic in 80 percent, but there were multiple associated factors. Erectile failure had persisted more than twenty-four months in 84 percent and the last successful intercourse was over one year prior to evaluation in 68 percent. There appears to be distinct differences in the pattern and etiology of erectile failure in elderly patients.

Dynamic ventilatory responses to CO2 in the awake lamb: role of the carotid chemoreceptors

In awake lambs we investigated the role of the peripheral chemoreceptors in producing dynamic ventilatory (VE) responses to CO2. The immediate VE response, within 15 s, to transient CO2 inhalation was studied in two groups: 1) five lambs before carotid denervation and 2) the same lambs after carotid denervation. The time course of VE responses during the first 60 s after a step change to 8% inspired CO2 was also studied in lambs after carotid denervation and in a group of six carotid body-intact lambs 10-11 days of age. Acute CO2 responses were assessed using step changes to various concentrations of CO2 + air and CO2 + O2, while VE was recorded breath by breath. Intact lambs exhibited a brisk VE response to step changes in CO2, beginning after 3-5 s. Hyperoxia altered but did not suppress the dynamic VE CO2 response when the carotid chemoreceptors were intact. Carotid denervation markedly reduced the VE response during the first 25 s after a CO2 step change, revealing the time delay required for the central chemoreceptors to produce an effective VE response. The residual VE response remaining after CD was thought to be mediated by the remaining aortic body chemoreceptors and was eliminated by adding O2 to the CO2 challenges. However, after carotid denervation, even with CO2 + hyperoxia, the onset of a small tidal volume response was apparent by 10-12 s.(ABSTRACT TRUNCATED AT 250 WORDS)