The effect of remifentanil on respiratory variability, evaluated with dynamic modeling

The Role of fMRI in Drug Development: An Update

Functional magnetic resonance imaging (fMRI) of the brain is a technology that holds great potential for increasing the efficiency of drug development for the central nervous system (CNS). In preclinical studies and both early- and late-phase human trials, fMRI has the potential to improve cross-species translation of drug effects, help to de-risk compounds early in development, and contribute to the portfolio of evidence for a compound's efficacy and mechanism of action. However, to date, the utilization of fMRI in the CNS drug development process has been limited. The purpose of this chapter is to explore this mismatch between potential and utilization. This chapter provides introductory material related to fMRI and drug development, describes what is required of fMRI measurements for them to be useful in a drug development setting, lists current capabilities of fMRI in this setting and challenges faced in its utilization, and ends with directions for future development of capabilities in this arena. This chapter is the 5-year update of material from a previously published workshop summary (Carmichael et al., Drug DiscovToday 23(2):333-348, 2018).

A methodology to explore ventilatory chemosensitivity and opioid-induced respiratory depression risk

Our new and noteworthy methodology allows for exploration of preoperative ventilatory chemosensitivity, measured as the hypercapnic ventilatory response (HCVR), as a risk factor for postoperative opioid-induced respiratory depression (OIRD). This feasible and reliable methodology produced preliminary data that showed highly variable depression of HCVR by remifentanil, predominance of OIRD during light sleep, and potentially negative correlation between OIRD frequency generally and HCVR measurements when measured in the presence of remifentanil. Although the results are preliminary in nature, this novel methodology may guide future studies that can one day lead to effective clinical screening tools.

Opioid-Related Sleep-Disordered Breathing: An Update for Clinicians

Opioids are an effective treatment for patients with intractable pain. Long-term administration of opioids for pain relief is being delivered by an increasing number of medical providers in the United States including primary care physicians and nonspecialists. One common complication of chronic opioid use is sleep-disordered breathing which can result in various morbidities as well as an increase in all-cause mortality. It is important for providers to understand the relationship between opioids and sleep-disordered breathing as well as methods to improve diagnosis and strategies for treatment. This review aims to update clinicians on the mechanism, diagnosis, and treatment of opioid-related sleep-disordered breathing in order to improve the quality of care for patients with chronic pain.

The role of fMRI in drug development

Functional magnetic resonance imaging (fMRI) has been known for over a decade to have the potential to greatly enhance the process of developing novel therapeutic drugs for prevalent health conditions. However, the use of fMRI in drug development continues to be relatively limited because of a variety of technical, biological, and strategic barriers that continue to limit progress. Here, we briefly review the roles that fMRI can have in the drug development process and the requirements it must meet to be useful in this setting. We then provide an update on our current understanding of the strengths and limitations of fMRI as a tool for drug developers and recommend activities to enhance its utility.

Effects on breathing of agonists to μ-opioid or GABAA receptors dialyzed into the ventral respiratory column of awake and sleeping goats

Pulmonary ventilation (V̇I) in awake and sleeping goats does not change when antagonists to several excitatory G protein-coupled receptors are dialyzed unilaterally into the ventral respiratory column (VRC). Concomitant changes in excitatory neuromodulators in the effluent mock cerebral spinal fluid (mCSF) suggest neuromodulatory compensation. Herein, we studied neuromodulatory compensation during dialysis of agonists to inhibitory G protein-coupled or ionotropic receptors into the VRC. Microtubules were implanted into the VRC of goats for dialysis of mCSF mixed with agonists to either μ-opioid (DAMGO) or GABAA (muscimol) receptors. We found: (1) V̇I decreased during unilateral but increased during bilateral dialysis of DAMGO, (2) dialyses of DAMGO destabilized breathing, (3) unilateral dialysis of muscimol increased V̇I, and (4) dialysis of DAMGO decreased GABA in the effluent mCSF. We conclude: (1) neuromodulatory compensation can occur during altered inhibitory neuromodulator receptor activity, and (2) the mechanism of compensation differs between G protein-coupled excitatory and inhibitory receptors and between G protein-coupled and inotropic inhibitory receptors.

Biomarkers, designs, and interpretations of resting-state fMRI in translational pharmacological research: A review of state-of-the-Art, challenges, and opportunities for studying brain chemistry

A decade of research and development in resting-state functional MRI (RSfMRI) has opened new translational and clinical research frontiers. This review aims to bridge between technical and clinical researchers who seek reliable neuroimaging biomarkers for studying drug interactions with the brain. About 85 pharma-RSfMRI studies using BOLD signal (75% of all) or arterial spin labeling (ASL) were surveyed to investigate the acute effects of psychoactive drugs. Experimental designs and objectives include drug fingerprinting dose-response evaluation, biomarker validation and calibration, and translational studies. Common biomarkers in these studies include functional connectivity, graph metrics, cerebral blood flow and the amplitude and spectrum of BOLD fluctuations. Overall, RSfMRI-derived biomarkers seem to be sensitive to spatiotemporal dynamics of drug interactions with the brain. However, drugs cause both central and peripheral effects, thus exacerbate difficulties related to biological confounds, structured noise from motion and physiological confounds, as well as modeling and inference testing. Currently, these issues are not well explored, and heterogeneities in experimental design, data acquisition and preprocessing make comparative or meta-analysis of existing reports impossible. A unifying collaborative framework for data-sharing and data-mining is thus necessary for investigating the commonalities and differences in biomarker sensitivity and specificity, and establishing guidelines. Multimodal datasets including sham-placebo or active control sessions and repeated measurements of various psychometric, physiological, metabolic and neuroimaging phenotypes are essential for pharmacokinetic/pharmacodynamic modeling and interpretation of the findings. We provide a list of basic minimum and advanced options that can be considered in design and analyses of future pharma-RSfMRI studies. Hum Brain Mapp 38:2276-2325, 2017. © 2017 Wiley Periodicals, Inc.

Opioid suppression of conditioned anticipatory brain responses to breathlessness

Opioid painkillers are a promising treatment for chronic breathlessness, but are associated with potentially fatal side effects. In the treatment of breathlessness, their mechanisms of action are unclear. A better understanding might help to identify safer alternatives. Learned associations between previously neutral stimuli (e.g. stairs) and repeated breathlessness induce an anticipatory threat response that may worsen breathlessness, contributing to the downward spiral of decline seen in clinical populations. As opioids are known to influence associative learning, we hypothesized that they may interfere with the brain processes underlying a conditioned anticipatory response to breathlessness in relevant brain areas, including the amygdala and the hippocampus.

Healthy volunteers viewed visual cues (neutral stimuli) immediately before induction of experimental breathlessness with inspiratory resistive loading. Thus, an association was formed between the cue and breathlessness. Subsequently, this paradigm was repeated in two identical neuroimaging sessions with intravenous infusions of either low-dose remifentanil (0.7 ng/ml target-controlled infusion) or saline (randomised).

During saline infusion, breathlessness anticipation activated the right anterior insula and the adjacent operculum. Breathlessness was associated with activity in a network including the insula, operculum, dorsolateral prefrontal cortex, anterior cingulate cortex and the primary sensory and motor cortices.

Remifentanil reduced breathlessness unpleasantness but not breathlessness intensity. Remifentanil depressed anticipatory activity in the amygdala and the hippocampus that correlated with reductions in breathlessness unpleasantness. During breathlessness, remifentanil decreased activity in the anterior insula, anterior cingulate cortex and sensory motor cortices. Remifentanil-induced reduction in breathlessness unpleasantness was associated with increased activity in the rostral anterior cingulate cortex and nucleus accumbens, components of the endogenous opioid system known to decrease the perception of aversive stimuli.

These findings suggest that in addition to effects on brainstem respiratory control, opioids palliate breathlessness through an interplay of altered associative learning mechanisms. These mechanisms provide potential targets for novel ways to develop and assess treatments for chronic breathlessness.

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The mechanisms of how low-dose opioids relieve breathlessness are unknown.

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We tested whether low-dose opioids affect conditioned anticipation and perception of breathlessness.

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Low-dose opioids reduced unpleasantness, but not intensity of breathlessness.

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Reduced breathlessness unpleasantness was associated with activation of the endogenous opioid system.

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Breathlessness relief was predicted by decreased anticipatory activity in amygdala/hippocampus.

Effect-site concentration of remifentanil for preventing cough during emergence in elderly patients undergoing nasal surgery: a comparison with adult patients

Purpose

Prevention of cough during emergence after nasal surgery is important for avoiding surgical site bleeding. We investigated the remifentanil effect-site concentration in 50% (EC50) of the elderly patients undergoing nasal surgery for smooth emergence without cough and compared it with that of adult patients.

Methods

Twenty-two elderly (aged 65–80 years) and 25 adult patients (aged 20–60 years) with an American Society of Anesthesiologists physical status I/II undergoing nasal surgery were enrolled. Anesthesia was maintained with sevoflurane and remifentanil. Remifentanil EC50 and EC95 for preventing cough were determined using the modified Dixon’s up-and-down method and isotonic regression with bootstrapping approach. Recovery profiles were also recorded.

Results

With Dixon’s up-and-down method, the EC50 of remifentanil in elderly patients (2.40±0.25 ng/mL) was not significantly different from that of adults (2.33±0.30 ng/mL) (P=0.687). With isotonic regression, the EC95 of remifentanil in elderly patients (3.32 [95% confidence interval: 3.06–3.38] ng/mL) was not significantly different from that of adults (3.30 [95% confidence interval: 2.96–3.37] ng/mL). However, eye opening time (14.1±3.8 vs 12.0±2.9 seconds), extubation time (17.2±4.1 vs 14.0±3.0 seconds), and postanesthesia care unit duration (44.5±7.6 vs 38.7±3.4 minutes) in elderly patients were significantly longer than those in adults (P<0.05).

Conclusion

Remifentanil EC50 for preventing cough after nasal surgery with sevoflurane anesthesia did not differ between elderly and adult patients. However, delayed awakening and respiratory adverse events may warrant attention in elderly patients.

Model-based stability assessment of ventilatory control in overweight adolescents with obstructive sleep apnea during NREM sleep

Obstructive sleep apnea (OSA) involves the interplay of several different factors such as an unfavorable upper airway anatomy, deficiencies in pharyngeal muscle responsiveness, a low arousal threshold, and ventilatory control instability. Although the stability of ventilatory control has been extensively studied in adults, little is known about its characteristics in the pediatric population. In this study, we developed a novel experimental setup that allowed us to perturb the respiratory system during natural non-rapid eye movement (NREM) sleep conditions by manipulating the inspiratory pressure, provided by a bilevel pressure ventilator, to induce sighs after upper airway stabilization. Furthermore, we present a modeling framework that utilizes the noninvasively measured ventilatory responses to the induced sighs and spontaneous breathing data to obtain representations of the processes involved in the chemical regulation of respiration and extract their stability characteristics. After validation with simulated data, the modeling technique was applied to data collected experimentally from 11 OSA and 15 non-OSA overweight adolescents. Statistical analysis of the model-derived stability parameters revealed a significantly higher plant gain and lower controller gain in the OSA group (P = 0.046 and P = 0.007, respectively); however, no differences were found in loop gain (LG) and circulatory time delay between the groups. OSA severity and LG, within the 0.03-0.04-Hz frequency band, were significantly negatively associated (r = -0.434, P = 0.026). Contrary to what has been found in adults, our results suggest that in overweight adolescents, OSA is unlikely to be initiated through ventilatory instability resulting from elevated chemical loop gain.

Wireless non-invasive continuous respiratory monitoring with FMCW radar: a clinical validation study

Altered respiratory rate is one of the first symptoms of medical conditions that require timely intervention, e.g., sepsis or opioid-induced respiratory depression. To facilitate continuous respiratory rate monitoring on general hospital wards a contactless, non-invasive, prototype monitor was developed using frequency modulated continuous wave radar. We aimed to study whether radar can reliably measure respiratory rate in postoperative patients. In a diagnostic cross-sectional study patients were monitored with the radar and the reference monitor (pneumotachograph during mechanical ventilation and capnography during spontaneous breathing). Eight patients were included; yielding 796 min of observation time during mechanical ventilation and 521 min during spontaneous breathing. After elimination of movement artifacts the bias and 95 % limits of agreement for mechanical ventilation and spontaneous breathing were −0.12 (−1.76 to 1.51) and −0.59 (−5.82 to 4.63) breaths per minute respectively. The radar was able to accurately measure respiratory rate in mechanically ventilated patients, but the accuracy decreased during spontaneous breathing.

Quantifying the ventilatory control contribution to sleep apnoea using polysomnography

Elevated loop gain, consequent to hypersensitive ventilatory control, is a primary nonanatomical cause of obstructive sleep apnoea (OSA) but it is not possible to quantify this in the clinic. Here we provide a novel method to estimate loop gain in OSA patients using routine clinical polysomnography alone. We use the concept that spontaneous ventilatory fluctuations due to apnoeas/hypopnoeas (disturbance) result in opposing changes in ventilatory drive (response) as determined by loop gain (response/disturbance). Fitting a simple ventilatory control model (including chemical and arousal contributions to ventilatory drive) to the ventilatory pattern of OSA reveals the underlying loop gain. Following mathematical-model validation, we critically tested our method in patients with OSA by comparison with a standard (continuous positive airway pressure (CPAP) drop method), and by assessing its ability to detect the known reduction in loop gain with oxygen and acetazolamide. Our method quantified loop gain from baseline polysomnography (correlation versus CPAP-estimated loop gain: n=28; r=0.63, p<0.001), detected the known reduction in loop gain with oxygen (n=11; mean±sem change in loop gain (ΔLG) -0.23±0.08, p=0.02) and acetazolamide (n=11; ΔLG -0.20±0.06, p=0.005), and predicted the OSA response to loop gain-lowering therapy. We validated a means to quantify the ventilatory control contribution to OSA pathogenesis using clinical polysomnography, enabling identification of likely responders to therapies targeting ventilatory control.

Model-based estimation of loop gain using spontaneous breathing: a validation study

Non-invasive assessment of ventilatory control stability or loop gain (which is a key contributor in a number of sleep-related breathing disorders) has proven to be cumbersome. We present a novel multivariate autoregressive model that we hypothesize will enable us to make time-varying measurements of loop gain using nothing more than spontaneous fluctuations in ventilation and CO2. The model is adaptive to changes in the feedback control loop and therefore can account for system non-stationarities (e.g. changes in sleep state) and it is resistant to artifacts by using a signal quality measure. We tested this method by assessing its ability to detect a known increase in loop gain induced by proportional assist ventilation (PAV). Subjects were studied during sleep while breathing on continuous positive airway pressure (CPAP) alone (to stabilize the airway) or on CPAP+PAV. We show that the method tracked the PAV-induced increase in loop gain, demonstrating its time-varying capabilities, and it remained accurate in the face of measurement related artifacts. The model was able to detect a statistically significant increase in loop gain from 0.14±10 on CPAP alone to 0.21±0.13 on CPAP+PAV (p<0.05). Furthermore, our method correctly detected that the PAV-induced increase in loop gain was predominantly driven by an increase in controller gain. Taken together, these data provide compelling evidence for the validity of this technique.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Assessing the effects of pharmacological agents on respiratory dynamics using time-series modeling

Developing quantitative descriptions of how stimulant and depressant drugs affect the respiratory system is an important focus in medical research. Respiratory variables-respiratory rate, tidal volume, and end tidal carbon dioxide-have prominent temporal dynamics that make it inappropriate to use standard hypothesis-testing methods that assume independent observations to assess the effects of these pharmacological agents. We present a polynomial signal plus autoregressive noise model for analysis of continuously recorded respiratory variables. We use a cyclic descent algorithm to maximize the conditional log likelihood of the parameters and the corrected Akaike's information criterion to choose simultaneously the orders of the polynomial and the autoregressive models. In an analysis of respiratory rates recorded from anesthetized rats before and after administration of the respiratory stimulant methylphenidate, we use the model to construct within-animal z-tests of the drug effect that take account of the time-varying nature of the mean respiratory rate and the serial dependence in rate measurements. We correct for the effect of model lack-of-fit on our inferences by also computing bootstrap confidence intervals for the average difference in respiratory rate pre- and postmethylphenidate treatment. Our time-series modeling quantifies within each animal the substantial increase in mean respiratory rate and respiratory dynamics following methylphenidate administration. This paradigm can be readily adapted to analyze the dynamics of other respiratory variables before and after pharmacologic treatments.

Temporal dynamics of lactate concentration in the human brain during acute inspiratory hypoxia

PURPOSE

To demonstrate the feasibility of measuring the temporal dynamics of cerebral lactate concentration and examine these dynamics in human subjects using magnetic resonance spectroscopy (MRS) during hypoxia.

MATERIALS AND METHODS

A respiratory protocol consisting of 10-minute baseline normoxia, 20-minute inspiratory hypoxia, and ending with 10-minute normoxic recovery was used, throughout which lactate-edited MRS was performed. This was repeated four times in three subjects. A separate session was performed to measure blood lactate. Impulse response functions using end-tidal oxygen and blood lactate as system inputs and cerebral lactate as the system output were examined to describe the dynamics of the cerebral lactate response to a hypoxic challenge.

RESULTS

The average lactate increase was 20% ± 15% during the last half of the hypoxic challenge. Significant changes in cerebral lactate concentration were observed after 400 seconds. The average relative increase in blood lactate was 188% ± 95%. The temporal dynamics of cerebral lactate concentration was reproducibly demonstrated with 200-second time bins of MRS data (coefficient of variation 0.063 ± 0.035 between time bins in normoxia). The across-subject coefficient of variation was 0.333.

CONCLUSION

The methods for measuring the dynamics of the cerebral lactate response developed here would be useful to further investigate the brain's response to hypoxia.

Abdominal relaxation during emergence from general anesthesia with propofol and remifentanil

STUDY OBJECTIVE

To characterize respiratory dynamics during emergence from propofol-remifentanil anesthesia using noninvasive respiratory inductance plethysmography (RIP).

DESIGN

Observational pilot study.

SETTING

Operating room in a university-affiliated teaching hospital.

PATIENTS

50 ASA physical status 1, 2, and 3 patients scheduled for microdirect laryngoscopy or bronchoscopy using total intravenous anesthesia (TIVA) with high-frequency jet ventilation.

INTERVENTIONS

Patients were fitted with plethysmography bands around the chest and abdomen prior to induction. Following completion of surgery in patients undergoing brief airway procedures using propofol-remifentanil general anesthesia, the anesthetic infusions were stopped and ventilation suspended until resumption of spontaneous ventilation or desaturation below 90%. During this period of apnea, abdominal and thoracic girth was assessed with noninvasive RIP.

MEASUREMENTS

Cross-sectional area of the thorax and abdomen during emergence were measured.

MAIN RESULTS

Useful data were obtained from 41 patients, with stable apnea lasting 404 ± 193.1 seconds; of these, 34 exhibited a slow and significant decrease in abdominal girth over a period of 267.8 ± 128.5 seconds. Resumption of spontaneous ventilation generally coincided with the end of this abdominal relaxation.

CONCLUSION

Slow expiration is the initial step in the resumption of spontaneous ventilation during apnea induced with TIVA using propofol-remifentanil.

Model-based characterization of ventilatory stability using spontaneous breathing

Cyclic ventilatory instabilities are widely attributed to an increase in the sensitivity or loop gain of the chemoreflex feedback loop controlling ventilation. A major limitation in the conventional characterization of this feedback loop is the need for labor-intensive methodologies. To overcome this limitation, we developed a method based on trivariate autoregressive modeling using ventilation, end-tidal Pco(2) and Po(2); this method provides for estimation of the overall "loop gain" of the respiratory control system and its components, chemoreflex gain and plant gain. Our method was applied to recordings of spontaneous breathing in 15 anesthetized, tracheostomized, newborn lambs before and after administration of domperidone (a dopamine D(2)-receptor antagonist that increases carotid body sensitivity). We quantified the known increase in hypoxic ventilatory sensitivity in response to domperidone; controller gain for O(2) increased from 0.06 (0.03, 0.09) l·min(-1)·mmHg(-1) to 0.09 (0.08, 0.13) l·min(-1)·mmHg(-1); median (interquartile-range). We also report that domperidone increased the loop gain of the control system more than twofold [0.14 (0.12, 0.22) to 0.40 (0.15, 0.57)]. We observed no significant changes in CO(2) controller gain, or plant gains for O(2) and CO(2). Furthermore, our estimate of the cycle duration of periodic breathing compared favorably with that observed experimentally [measured: 7.5 (7.2, 9.1) vs. predicted: 7.9 (7.0, 9.2) breaths]. Our results demonstrate that model-based analysis of spontaneous breathing can 1) characterize the dynamics of the respiratory control system, and 2) provide a simple tool for elucidating an individual's propensity for ventilatory instability, in turn allowing potential therapies to be directed at the underlying mechanisms.

Take a deep breath: the relief effect of spontaneous and instructed sighs

Spontaneous sighing is related to subjective relief of negative emotional states. Whether this also applies to instructed sighing is not known. The present study aimed to investigate sEMG and respiratory variability (1) during recovery from mental stress with and without an instructed sigh; (2) before and after spontaneous sighs throughout the experiment. A spontaneous sigh was preceded by increasing sEMG and increasing random respiratory variability, and followed by decreasing sEMG and increased structured correlated respiratory variability. Following an instructed sigh, a smaller reduction in sEMG and an increase in random respiratory variability during recovery from mental stress were observed. Thus, a spontaneous sigh seemed to induce relief. An instructed sigh appeared to inhibit recovery from mental stress.

Nonlinear, data-driven modeling of cardiorespiratory control mechanisms

We present applications of recently developed algorithms for data-driven nonlinear systems identification to the study of cardiovascular and respiratory control mechanisms on an integrated systems level, utilizing experimental data obtained during resting conditions. Specifically, we consider cerebrovascular regulation during normal conditions, orthostatic stress and autonomic blockade in a two-input context, as well as respiratory control during a model opioid drug (remifentanil) infusion in a closed-loop context. The results illustrate the potential of using data-driven modeling approaches, which do not rely on prior assumptions about model structure, for modeling physiological systems, as they are well-suited to their complexity. They also illustrate the potential of utilizing spontaneous physiological variability, which can be monitored noninvasively and does not require experimental interventions, to extract rich information about the function of the underlying mechanisms. We also discuss some important practical issues, such as the presence of nonstationarities and model order selection, related to the application of similar approaches to the analysis of physiological systems.

Isoflurane-induced changes in righting response and breathing are modulated by RGS proteins

BACKGROUND

Recent evidence suggests that G protein-coupled receptors, especially those linked to G(alpha)(i), contribute to the mechanisms of anesthetic action. Regulator of G protein signaling (RGS) proteins bind to activated G(alpha)(i) and inhibit signal transduction. Genomic knock-in mice with an RGS-insensitive G(alpha)(i2) G184S (G(alpha)(i2) GS) allele exhibit enhanced G(alpha)(i2) signaling and provide a novel approach for investigating the role of G(alpha)(i2) signaling and RGS proteins in general anesthesia.

METHODS

We anesthetized homozygous G(alpha)(i2) GS/GS and wild-type (WT) mice with isoflurane and quantified time (in seconds) to loss and resumption of righting response. During recovery from isoflurane anesthesia, breathing was quantified in a plethysmography chamber for both lines of mice.

RESULTS

G(alpha)(i2) GS/GS mice required significantly less time for loss of righting and significantly more time for resumption of righting than WT mice. During recovery from isoflurane anesthesia, G(alpha)(i2) GS/GS mice exhibited significantly greater respiratory depression. Poincaré analyses show that GS/GS mice have diminished respiratory variability compared with WT mice.

CONCLUSION

Modulation of G(alpha)(i2) signaling by RGS proteins alters loss and resumption of wakefulness and state-dependent changes in breathing.

Opioids depress cortical centers responsible for the volitional control of respiration

Respiratory depression limits provision of safe opioid analgesia and is the main cause of death in drug addicts. Although opioids are known to inhibit brainstem respiratory activity, their effects on cortical areas that mediate respiration are less well understood. Here, functional magnetic resonance imaging was used to examine how brainstem and cortical activity related to a short breath hold is modulated by the opioid remifentanil. We hypothesized that remifentanil would differentially depress brain areas that mediate sensory-affective components of respiration over those that mediate volitional motor control. Quantitative measures of cerebral blood flow were used to control for hypercapnia-induced changes in blood oxygen level-dependent (BOLD) signal. Awareness of respiration, reflected by an urge-to-breathe score, was profoundly reduced with remifentanil. Urge to breathe was associated with activity in the bilateral insula, frontal operculum, and secondary somatosensory cortex. Localized remifentanil-induced decreases in breath hold-related activity were observed in the left anterior insula and operculum. We also observed remifentanil-induced decreases in the BOLD response to breath holding in the left dorsolateral prefrontal cortex, anterior cingulate, the cerebellum, and periaqueductal gray, brain areas that mediate task performance. Activity in areas mediating motor control (putamen, motor cortex) and sensory-motor integration (supramarginal gyrus) were unaffected by remifentanil. Breath hold-related activity was observed in the medulla. These findings highlight the importance of higher cortical centers in providing contextual awareness of respiration that leads to appropriate modulation of respiratory control. Opioids have profound effects on the cortical centers that control breathing, which potentiates their actions in the brainstem.