Assessment of Interaction Between Cardio-Respiratory Signals Using Directed Coherence on Healthy Subjects During Postural Change

PurposeTo detect and quantify the directional interaction changes between cardio-respiratory system during postural change.MethodTraditional frequency domain analysis based on power spectrum and coherence are insufficient to quantify nonlinear structures and complexity of physiological subsystems. Recently, Granger causality is found as preferable method for evaluation of causality i.e., directional interaction. Frequency domain Granger causality based on directed coherence has been used in this study to identify directional interaction between cardiac and respiratory signal during postural change from supine to standing for healthy subjects.ResultECG and respiration signal are recorded for this study. The beat-to-beat variability series from ECG provides heart rate (RR) and the respiration amplitude corresponds to RESP time series. It was observed that respiration is responsible for the changes in ECG signal during supine position as compared to standing. The outflow of information from RESP to RR increases during supine results in stronger interaction but reduces during standing result in reduction of interaction. Similarly, the effect of RR on RESP is found significant only during standing.ConclusionThe proposed directed coherence approach detects the cardio-respiratory regulation during postural change and provide information about coupling changes during this transition.     

Gender differences in hemispheric interaction during distributed and directed attention

Gender differences in the functional hemispheric organization during memorization of dichotically presented verbal information in the situation of focused or non-focused attention were studied. Analysis of EEG coherence reactivity in six frequency bands (4-30 Hz) showed that the focused attention to stimuli presented to one ear as compared to divided attention between both ears was accompanied by an increase in the interhemispheric interaction in the thetal frequency band between the frontal cortical areas in men and between the parietoccipital areas in women. In the betal band, the focused attention was associated with a contralateral increase in the intrahemispheric coherence in men, whereas no significant difference in the intrahemispheric coherence was found in women. On the basis of coherence changes in the thetal and betal bands depending on the attention conditions together with the obtained correlation between coherence reactivity and word-recall scores, it may be suggested that verbal memorization in men is associated, predominantly, with the regulation from the anterior system of attention and from the posterior system in women.     

Correlation between the EEG coherence and recognition of emotions in speech

Analysis of the EEG in 2 extreme groups: subjects with high and low indexes of identification of emotional intonation, was carried out. The number of pairs of electrode sites with significant differences in coherence was compared at rest and during the emotion identification task in 6 standard frequency bands. The data revealed that, in general, coherence is higher in the group with low identification rates.     

Electrophysiological Correlates of Vigilance During a Continuous Performance Test in Healthy Adults

The present study evaluated patterns of electrophysiological activity associated with sustained vigilance in healthy adults. Quantitative electroencephalographs (QEEG) were recorded during the performance of a Continuous Performance Test (CPT). Participants were divided into low and high vigilance groups based upon their reaction time changes between the early and late portions of the CPT. Coherence measures were calculated from the QEEG across the baseline, early CPT, and late CPT experimental conditions. Participants in the low vigilance group had higher baseline and CPT frontal to posterior coherence in the alpha and beta bands suggestive of a less vigilant state throughout the entire study. Additionally, the low vigilance group had a significantly greater beta 1 band coherence drop from baseline to the initial portion of the CPT than the high vigilance group. The combined groups had significantly lower amounts of right hemisphere frontal to posterior coherence across a number of frequency bands throughout all of the phases of the study when compared to the homologous left hemisphere sites. These interhemispheric coherence differences are consistent with vigilance network theories that implicate the right frontal and parietal lobes in the maintenance of sustained attention (M. I. Posner & M. E. Raichle, 1994).     

Yawning as a Stereotyped Action Pattern and Releasing Stimulus

Yawning was induced by instructing subjects to “think about yawning.” Yawns were consistent in duration (X = 5.9 s), periodic (X interyawn interval = 68.3 s), and within-subject stability in yawn duration and frequency was maintained for at least several weeks. These and other characteristics qualified yawning as a stereotyped action pattern. Although visually observed yawns were potent yawn releasing stimuli, “thinking about” or reading about yawning also elicited yawning and were additional vectors for its “infectiousness.” The respiratory, stretching and “imitative” aspects of yawning were also evaluated.     

Prolactin induces yawning and the stretch-yawning syndrome in young adult male rats

Herein we report that subcutaneous injection of low doses of ovine prolactin (oPRL) induce yawning in young adult male rats. The most effective dose of oPRL in evoking yawning was 0.25 microgram/kg body weight (5.2 yawns/60 min at 1000 hr vs 0.3 in control animals). Doses of 0.025, 0.05, 2.5, 25, and 250 micrograms/kg were less effective. Interestingly, yawning in response to oPRL changes over the course of one circadian cycle with highest frequency at 1600 hr (11 yawns/80 min vs 2 yawns/80 min in animals injected with boiled oPRL). The onset of yawning in most oPRL-treated rats began approximately 40 min after oPRL injection, whereas with apomorphine the latency to the response was about 10 min. These results indicate that oPRL in addition to other hypophysial peptides such as ACTH and MSH can stimulate yawning. It is proposed that PRL after initial activation of the nigrostriatal dopamine system secondarily induces yawning by inhibition of this system via an autoreceptor-mediated negative feedback mechanism. This may explain the long latency to the response.     

Relations of the Topographic EEG Organization to Temperament Traits

EEG mapping in six frequency bands was examined in relation to Keirsey and Eysenck temperament scales in 46 males 17–20 years old at rest. An analysis of the amplitude and coherence of the EEG (16-channel recording) revealed a positive correlation between interhemispheric coherence in and bands, and neuroticism as well as sensation scales. Extraversion correlated negatively with coherence, predominantly focused in the left frontal cortex in ₂band. Combinations of these temperament traits were associated with specific patterns of EEG amplitude and coherence. The most pronounced changes in EEG were found in subjects with high sensation and judgment, which were characterized by increased amplitudes and coherence in _{1, 2}bands, as well as increased interhemispheric coherence in the frontal cortex. Such a consistent interaction of neuronal assembles within the baseline EEG suggest that certain behavioral strategies are associated with specific temperament types.     

Yawning: Relation to Sleeping and Stretching in Humans

The temporal relations among yawning, sleeping, and stretching were investigated by having undergraduate college students record the occurrences of these behaviors during a one-week period. Yawning was most frequent during the hour before sleeping and after waking. In contrast, stretching was common only during the hour after waking. Concurrent yawning and stretching were common but stretching was accompanied more often by yawning than vice-versa. The temporal proximity of yawning to sleep and waking times is probably the basis for yawning as a paralinguistic signal for drowsiness. The role of contagious yawning in synchronizing the behavior and physiological state of a group is considered.     

Impairment of space-frequency parameters of EEG coherence during cognitive performance (consequences of Chernobyl accident)

Changes in frequency and space parameters of the EEG coherence evoked by cognitive performance were analyzed in 13 healthy subjects and participants of the Chemobyl clean-up. In healthy subjects, the EEG coherences in the alpha and beta frequency bands were significantly increased during arithmetic count and during visuospatial performance. Each test was characterized by regionally-specific features. Chemobyl patients demonstrated a global decrease in the EEG coherence predominantly in the alpha and beta frequency bands, especially in the frontal cortical areas. Patients with various pathological EEG patterns demonstrated specific impairment of EEG parameters. In patients with a "flat" EEG pattern, the EEG coherence predominantly decreased in the frontal associative areas, especially during arithmetic calculation. In patients with a "hypersynchronous" EEG pattern, the decrease in the EEG coherence was most pronounced in the parietal associative areas, especially during the visuospatial performance. The revealed impairments of the EEG coherence reactivity may be a reflection of disorders of the intracortical and corticosubcortical interaction and can result from the remote postradiation brain atrophy, especially, of cortical structures.     

Analysis of nonstationarity in renal autoregulation mechanisms using time-varying transfer and coherence functions

The extent to which renal blood flow dynamics vary in time and whether such variation contributes substantively to dynamic complexity have emerged as important questions. Data from Sprague-Dawley rats (SDR) and spontaneously hypertensive rats (SHR) were analyzed by time-varying transfer functions (TVTF) and time-varying coherence functions (TVCF). Both TVTF and TVCF allow quantification of nonstationarity in the frequency ranges associated with the autoregulatory mechanisms. TVTF analysis shows that autoregulatory gain in SDR and SHR varies in time and that SHR exhibit significantly more nonstationarity than SDR. TVTF gain in the frequency range associated with the myogenic mechanism was significantly higher in SDR than in SHR, but no statistical difference was found with tubuloglomerular (TGF) gain. Furthermore, TVCF analysis revealed that the coherence in both strains is significantly nonstationary and that low-frequency coherence was negatively correlated with autoregulatory gain. TVCF in the frequency range from 0.1 to 0.3 Hz was significantly higher in SDR (7 out of 7, >0.5) than in SHR (5 out of 6, <0.5), and consistent for all time points. For TGF frequency range (0.03-0.05 Hz), coherence exhibited substantial nonstationarity in both strains. Five of six SHR had mean coherence (<0.5), while four of seven SDR exhibited coherence (<0.5). Together, these results demonstrate substantial nonstationarity in autoregulatory dynamics in both SHR and SDR. Furthermore, they indicate that the nonstationarity accounts for most of the dynamic complexity in SDR, but that it accounts for only a part of the dynamic complexity in SHR.     

Electroencephalographic Correlates of Brain States during Verbal Learning: II. Characteristics of EEG Spatial Synchronization

Spatial EEG synchronization was studied using mean EEG coherences in 57 subjects in a resting state with the eyes open, during memorization of verbal bilingual semantic pairs (Latin and Russian), and during retrieval (monitoring) of the learned information. Statistical comparison of the EEG spectral power in the frequency bands θ, α ₁, α₂, β₁, β₂, and γ showed that induction of the states of memorization and retrieval of the verbal information resulted in multiple significant increases in the mean coherence (spatial synchronization) as compared to the state of rest. These increases were significantly higher in the state of retrieval than in the state of memorization. Such changes simultaneously occurred in different frequency bands and over the entire cortex. The highest relative augmentations of coherence with the highest significance estimates were observed in long-distance derivation pairs involving the temporal areas or combining the anterofrontal and frontal derivations with the parietal and occipital ones. The results are discussed in combination with data obtained in the same study for changes in EEG local synchronization and reported earlier. The intense rearrangements of the bioelectrical activity of the cortex may be determined both by the effect of cognitively specific mechanisms of encoding-decoding of information in the memory system and by a cognitively nonspecific modulating system of the brain.     

The Potential Regimen of Target-Controlled Infusion of Propofol in Flexible Bronchoscopy Sedation: A Randomized Controlled Trial

Objectives

Target-controlled infusion (TCI) provides precise pharmacokinetic control of propofol concentration in the effect-site (Ce), eg. brain. This pilot study aims to evaluate the feasibility and optimal TCI regimen for flexible bronchoscopy (FB) sedation.

Methods

After alfentanil bolus, initial induction Ce of propofol was targeted at 2 μg/ml. Patients were randomized into three titration groups (i.e., by 0.5, 0.2 and 0.1 μg/ml, respectively) to maintain stable sedation levels and vital signs. Adverse events, frequency of adjustments, drug doses, and induction and recovery times were recorded.

Results

The study was closed early due to significantly severe hypoxemia events (oxyhemoglobin saturation <70%) in the group titrated at 0.5 μg/ml. Forty-nine, 49 and 46 patients were enrolled into the 3 respective groups before study closure. The proportion of patients with hypoxemia events differed significantly between groups (67.3 vs. 46.9 vs. 41.3%, p = 0.027). Hypotension events, induction and recovery time and propofol doses were not different. The Ce of induction differed significantly between groups (2.4±0.5 vs. 2.1±0.4 vs. 2.1±0.3 μg/ml, p = 0.005) and the Ce of procedures was higher at 0.5 μg/ml titration (2.4±0.5 vs. 2.1±0.4 vs. 2.2±0.3 μg/ml, p = 0.006). The adjustment frequency tended to be higher for titration at 0.1 μg/ml but was not statistically significant (2 (0∼6) vs. 3 (0∼6) vs. 3 (0∼11)). Subgroup analysis revealed 14% of all patients required no further adjustment during the whole sedation. Comparing patients requiring at least one adjustment with those who did not, they were observed to have a shorter induction time (87.6±34.9 vs. 226.9±147.9 sec, p<0.001), a smaller induction dose and Ce (32.5±4.1 vs. 56.8±22.7 mg, p<0.001; 1.76±0.17 vs. 2.28 ±0.41, p<0.001, respectively), and less hypoxemia and hypotension (15.8 vs.56.9%, p = 0.001; 0 vs. 24.1%, p = 0.008, respectively).

Conclusion

Titration at 0.5 μg/ml is risky for FB sedation. A subgroup of patients required no more TCI adjustment with fewer complications. Further studies are warranted to determine the optimal regimen of TCI for FB sedation.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT01101477","term_id":"NCT01101477"}}NCT01101477     

Propofol anesthesia in loggerhead (Caretta caretta) sea turtles

Rapid, safe, and effective methods of anesthetic induction and recovery are needed for sea turtles, especially in cases eligible for immediate release. This study demonstrates that intravenous propofol provides a rapid induction of anesthesia in loggerhead (Caretta caretta) sea turtles and results in rapid recovery, allowing safe return to water shortly after the procedure. Forty-nine loggerhead sea turtles were recovered as local fishery by-catch in pound nets and transported to a surgical suite for laparoscopic sex determination. Treatment animals (n = 32) received 5 mg/kg propofol intravenously (i.v.) as a rapid bolus, whereas control animals (n = 17) received no propofol. For analgesia, all animals received a 4 ml infusion of 1% lidocaine, locally, as well as 2 mg/kg ketoprofen intramuscularly (i.m.). Physiologic data included heart and respiratory rate, temperature, and a single blood gas sample collected upon termination of the laparoscopy. Subjective data included jaw tone and ocular reflex: 3 (vigorous) to 0 (none detected). Anesthetic depth was scored from 1, no anesthesia, to 3, surgical anesthesia. Turtles receiving propofol became apneic for a minimum of 5 min with a mean time of 13.7 +/- 8.3 min to the first respiration. Limb movement returned at a mean time of 21.1 +/- 16.8 min. The treatment animals were judged to be sedated for approximately 30 min (mean anesthetic depth score > or = 1.5) when compared to controls. Median respiratory rates for treatment animals were slower compared to controls for the first 15 min, then after 35 min, they became significantly faster than the controls. Median heart rates of control animals became significantly slower than treatment animals between 40 and 45 min. Physiologic differences between groups persisted a minimum of 55 min. Possible explanations for heart rate and respiratory rate differences later in the monitoring period include a compensatory recovery of treatment animals from anesthesia-induced hypoxia and hypercapnia or, alternatively, an induced response of the nonsedated control animals. The animals induced with propofol were easier to secure to the restraint device and moved less during laparoscopy. In conclusion, propofol is a safe and effective injectable anesthetic for use in free-ranging loggerhead sea turtles that provides rapid induction and recovery.     

Reflection of the Intelligence Structure in the Spatiotemporal Features of the Baseline EEG

The EEG correlates of the verbal, numerical, and figural IQ components according to the power and coherence characteristics of the baseline EEG in six frequency bands were studied taking into account personality traits of subjects (extroversion, neuroticism, psychoticism, and anxiety). Analysis of variance and correlation showed that a decreased power of the low-frequency _{1, 2}and ₁ rhythms and increased EEG power in the ₂ band with the right-hemispheric dominance were characteristic of persons with higher intelligence. These EEG characteristics were associated with increased interhemispheric interaction according to the coherence indices and increased coherence within the right hemisphere. Each of the intelligence components (verbal, numerical, and figural) was characterized by a specific baseline frequency–spatial EEG pattern distinguished by specific interactions, predominantly, between the frontal and caudal cortical regions in the and/or ₂ frequency bands.     

Closed-Loop Control Better than Open-Loop Control of Profofol TCI Guided by BIS: A Randomized,Controlled, Multicenter Clinical Trial to Evaluate the CONCERT-CL Closed-Loop System

Background

The CONCERT-CL closed-loop infusion system designed by VERYARK Technology Co., Ltd. (Guangxi, China) is an innovation using TCI combined with closed-loop controlled intravenous anesthesia under the guide of BIS. In this study we performed a randomized, controlled, multicenter study to compare closed-loop control and open-loop control of propofol by using the CONCERT-CL closed-loop infusion system.

Methods

180 surgical patients from three medical centers undergone TCI intravenous anesthesia with propofol and remifentanil were randomly assigned to propofol closed-loop group and propofol opened-loop groups. Primary outcome was global score (GS, GS = (MDAPE+Wobble)/% of time of bispectral index (BIS) 40-60). Secondary outcomes were doses of the anesthetics and emergence time from anesthesia, such as, time to tracheal extubation.

Results

There were 89 and 86 patients in the closed-loop and opened-loop groups, respectively. GS in the closed-loop groups (22.21±8.50) were lower than that in the opened-loop group (27.19±15.26) (p=0.009). The higher proportion of time of BIS between 40 and 60 was also observed in the closed-loop group (84.11±9.50%), while that was 79.92±13.17% in the opened-loop group, (p=0.016). No significant differences in propofol dose and time of tracheal extubation were observed. The frequency of propofol regulation in the closed-loop group (31.55±9.46 times/hr) was obverse higher than that in the opened-loop group (6.84±6.21 times/hr) (p=0.000).

Conclusion

The CONCERT-CL closed-loop infusion system can automatically regulate the TCI of propofol, maintain the BIS value in an adequate range and reduce the workload of anesthesiologists better than open-loop system.

Trial Registration

ChiCTR ChiCTR-OOR-14005551     

Propofol suppresses proliferation,invasion, and migration of human melanoma cells via regulating microRNA-137 and fibroblast growth factor 9

Propofol is an intravenous anesthetic widely used in clinical surgeries, such as tumor resection. Propofol affects the growth of many cancers, though its effect on melanoma is unknown. Our study aimed to explore how propofol affects melanoma cells. Melanoma cells A2058 and WM793B were cultured with propofol for 24 hr. Propofol significantly suppressed proliferation, migration, and invasion of A2058 and WM793B cells. Lower miR-137 level was observed in A2058 and WM793B cells, compared with normal human epidermal melanocyte HEMa-LP cells. Propofol-induced miR-137 upregulation and decreased proliferation, invasive ability, and migrated ability of A2058 and WM793B cells. Transfection with the miR-137 inhibitor reversed these effects. Additionally, miR-137 was verified to target and negatively regulate fibroblast growth factor 9 (FGF9) expression. Propofol efficiently downregulated FGF9 protein expression by upregulating miR-137. Furthermore, FGF9 overexpression abrogated propofol's repressive effects on the malignant potential of A2058 and WM793B cells. These findings indicate that propofol suppressed melanoma cell proliferation, invasion, and migration by regulating miR-137 and FGF9.     

Interhemispheric EEG interrelations in recognition of masked visual images accompanied by music

Changes in the EEG depend on the style of accompanying music. Classical music produces more patterns with increased diagonal coherences in the γ frequency band, where two foci of integration are formed at points T ₄ and T ₆. During listening to rock music, a larger proportion of all changes occurred in the θ-and α₁ frequency bands; an integration focus was formed at point T ₆ in the α₁ and γ frequency bands. An increase in diagonal coherences that was observed during the recognition was especially pronounced in the Δ-, θ-and α₁ frequency bands. In addition, there was an increase in the coherence between the potentials recorded at points O ₁-P ₄ and O ₂-F ₇, and it was observed in all the frequency bands. During the recognition of masked visual images accompanied by classical or rock music, there were more patterns with an increased diagonal coherence of the currently dominant activity. Before erroneous recognition, a widely generalized increase in coherence over the brain cortex was observed in the Δ, θ, and α₁ bands, which was an informative indicator of the subsequent erroneous recognition. In tests with recognition unaccompanied by music, as well as with music, the main change in symmetrical coherences was either a decrease in or an absence of changes in this indicator versus the background value.     

The effect of preoperative suggestions on perioperative dreams and dream recalls after administration of different general anesthetic combinations: a randomized trial in maxillofacial surgery

Background

Images evoked immediately before the induction of anesthesia with the help of suggestions may influence dreaming during anesthesia.The aim of the study was to assess the incidence of evoked dreams and dream recalls by employing suggestions before induction of anesthesia while administering different general anesthetic combinations.

Methods

This is a single center, prospective randomized including 270 adult patients scheduled for maxillofacial surgical interventions. Patients were assigned to control, suggestion and dreamfilm groups according to the psychological method used. According to the anesthetic protocol there were also three subgroups: etomidate & sevoflurane, propofol & sevoflurane, propofol & propofol groups. Primary outcome measure was the incidence of postoperative dreams in the non-intervention group and in the three groups receiving different psychological interventions. Secondary endpoint was to test the effect of perioperative suggestions and dreamfilm-formation training on the occurrance of dreams and recallable dreams in different general anesthesiological techniques.

Results

Dream incidence rates measured in the control group did not differ significantly (etomidate & sevoflurane: 40%, propofol & sevoflurane: 26%, propofol & propofol: 39%). A significant increase could be observed in the incidence rate of dreams between the control and suggestion groups in the propofol & sevoflurane (26%-52%) group (p = 0.023). There was a significant difference in the incidence of dreams between the control and dreamfilm subgroup in the propofol & sevoflurane (26% vs. 57%), and in the propofol & propofol group (39% vs.70%) (p = 0.010, and p = 0.009, respectively). Similar to this, there was a significant difference in dream incidence between the dreamfilm and the suggestion subgroups (44% vs. 70%) in the propofol & propofol group (p = 0.019). Propofol as an induction agent contributed most to dream formation and recalls (χ2-test p value: 0.005). The content of images and dreams evoked using suggestions showed great agreement using all three anesthetic protocols.

Conclusion

The psychological method influenced dreaming during anesthesia. The increase of the incidence rate of dreams was dependent on the anesthetic agent used, especially the induction agent.The study was registered in ClinicalTrials.gov. Identifier: {"type":"clinical-trial","attrs":{"text":"NCT01839201","term_id":"NCT01839201"}}NCT01839201.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2253-15-11) contains supplementary material, which is available to authorized users.     

Response facilitation in the four great apes: is there a role for empathy?

Contagious yawning is a form of response facilitation found in humans and other primates in which observing a model yawning enhances the chance that the observer will also yawn. Because contagious yawning seems to be more easily triggered when models are conspecifics or have a strong social bond with the observer, it has been proposed that contagious yawning is linked to empathy. A possible way to test this hypothesis is to analyze whether individuals’ responses differ when they observe models yawning or performing different involuntary (i.e., nose wiping, scratching) and voluntary (i.e., hand closing, wrist shaking) actions that are not linked to empathy. In this study, we tested the four great ape species with two different setups by exposing them to a human experimenter repeatedly performing these actions online, and video-recorded conspecifics repeatedly performing these actions on a screen. We examined which behaviors were subject to response facilitation, whether response facilitation was triggered by both human models and video-recorded conspecifics, and whether all species showed evidence of response facilitation. Our results showed that chimpanzees yawned significantly more when and shortly after watching videos of conspecifics (but not humans) yawning than in control conditions, and they did not do so as a response to increased levels of anxiety. For all other behaviors, no species produced more target actions when being exposed to either model than under control conditions. Moreover, the individuals that were more “reactive” when watching yawning videos were not more reactive when exposed to other actions. Since, at least in chimpanzees, (1) subjects only showed response facilitation when they were exposed to yawning and (2) only if models were conspecifics, it appears that contagious yawning is triggered by unique mechanisms and might be linked to empathy.     

Comparative Responses to Propofol Anaesthesia alone and with α2-Adrenergic Medications in a Canine Model

Cardiovascular and pulmonary effects of pro-pofol, a relatively new nonbarbiturate intravenous anaesthetic, were assessed and com-pared in 22 male and female dogs. Dogs in group 1 did not receive any premedication prior to 6.6 mg/kg IV propofol, group 2 was premedicated with atropine (0.02 mg/kg IM) and the α2-agonist medetomidine (10 μg/kg IM), and group 3 received the same premedication agents as group 2, but the medetomidine effects were reversed by the α2-antagonist atipamezole (30 μg/kg IV) after 30 min of anaesthesia. Each dog in groups 2 and 3 received a propofol induction dose of 2.2 mg/kg IV The anaesthetic du-ration was shortest with propofol alone and prolonged with medetomidine as a premedication which was reversible with atipamezole. In group 1, the most prominent effects were a temporary drop in diastolic arterial blood pressure (26% and 24%) at 2 and 5 min post-propofol, respectively and a drop in respiratory frequency (41%) 2 min after pro-pofol induction. Similar respiratory depression was observed in groups 2 and 3 (20% and 48%, respectively) at the same time. Apnea was not observed. An increase in systemic arterial blood pressure was observed throughout the trial in groups 2 and 3 un-til dogs recovered or were reversed with atipamezole. Medetomidine significantly re-duces propofol dosage requirements. Safe and effective injectable anaesthesia was pro-duced by propofol in this group of dogs. The frequency of respiratory depression would suggest in clinical usage, the practitioner should be aware oxygen supplementation is the treatment of choice should apnea occur.