Search PubMed⌕ Search

Biomedical subjects

D C Galletly

Publications and source records attributed to D C Galletly.

At least 37 records · Page 2Linked to original sources
PubMed1999

Cardioventilatory coupling in the anaesthetised rabbit, rat and guinea-pig.

Cardioventilatory coupling is a temporal coherence of respiratory and cardiac rhythms, seen in humans at rest, and during sleep and anaesthesia. In this study we compared the cardioventilatory coupling of anaesthetised rabbits, rats and guinea-pigs. Breathing two successive anaesthetic concentrations (1 or 2% isoflurane) we compared the effect of anaesthetic depth and species on (1) heart rate, (2) heart rate variability, (3) ventilatory rate (f), (4) ventilatory variability, (5) ratio HR/f, (6) degree of coupling (Shannon entropy of the distribution of intervals between inspiration and the preceding electrocardiographic R wave - the RI interval) and (7) coupling pattern, classified into four sub-patterns (I-IV) based upon inspection of the RI interval time series. Rabbits exhibited significantly less ventilatory variability and coupling than rats or guinea-pigs. The sub-pattern of coupling also differed between the three species. Rabbits showed coupling only when HR and f were close to integer ratios whereas other species coupled at non-integer ratios. Ventilatory variability in the rat and guinea-pig differed according to the pattern of coupling observed. Of the three species studied, the rat and guinea-pig demonstrated coupling most similar to that of anaesthetised human subjects. Anaesthetic concentration did not influence the pattern or degree of coupling.

Anesthesia↗
PubMed1999

The determination of cardioventilatory coupling from heart rate and ventilatory time series.

In 35 anaesthetised human subjects, we examined the effect of cardioventilatory coupling on R-R interval and ventilatory period time series. We observed that, in the presence of coupling: (a) ventilatory period fluctuated in a quantal manner, each quantal step corresponding to a multiple (or a little less) of the heart period; (b) heart period fluctuations, associated with respiratory sinus arrythmia, were identical for consecutive ventilatory periods. The regularity of heart period variation lead to geometric patterning of raw R-R time series, R-R consecutive difference time series, the phase portrait (R-R(n) vs R-R(n+1)) and the map of R-R interval variation (DeltaR-R(n) vs DeltaR-R(n+1)). These geometric features may be useful for the determination of cardioventilatory coupling from heart rate time series.

Adult↗
PubMed1999

Cardioventilatory coupling: effects of IPPV.

Cardioventilatory coupling (CVC) is the temporal coherence of respiratory and cardiac rhythms. We have suggested that this coherence is the result of triggering of inspiratory onset by a preceding cardiovascular afferent. One implication of this triggering hypothesis is that coupling should only exist under conditions of spontaneous ventilation and not under conditions where the ventilatory period is fixed, as during intermittent positive pressure ventilation (IPPV). This study compared the degree of CVC in 20 ASA I female subjects, aged 21-50 yr, 10 of whom were breathing spontaneously and 10 were undergoing mechanical ventilation. Over 5-10 min, we recorded the timing of consecutive ECG R waves and inspiratory onsets. Coupling was demonstrated by examining these epochs for constant timing relationship between R waves and inspiration (RI intervals). Constancy of RI intervals was examined graphically (RI plot) and quantitatively using the Shannon entropy of RI interval distribution. We observed CVC in all spontaneously breathing subjects but in none of those receiving IPPV. In spontaneously breathing subjects, temporal alignment with inspiratory onset was greatest for the heart beat preceding inspiration. We conclude that although coupling has been shown to persist in the presence of electrical cardiac pacing, IPPV disrupts the coupling process, consistent with the view that in anaesthetized subjects, coupling is the triggering of inspiratory onset by a preceding heart beat and not the converse.

Adult↗
PubMed1999

Cardioventilatory coupling in atrial fibrillation.

Cardioventilatory coupling is an entrainment phenomena, distinct from respiratory sinus arrhythmia, whereby heart and breathing rhythms show temporal coherence. Coupling is commonly observed during rest, sleep and anaesthesia. Five graphical methods, each with different underlying mechanistic assumptions, have been suggested for studying this entrainment relationship: (a) time relationship between inspiration and a preceding heart beat, (b) time relationship between inspiration and a following heart beat, (c) phase of the cardiac cycle at which inspiration occurs, (d) phases of the ventilatory cycle at which heart beats occur and (e) 'relative phases' over multiple ventilatory cycles at which heart beats occur. In eight elderly human subjects with atrial fibrillation, breathing spontaneously during general anaesthesia, we recorded heart period and ventilatory time series and compared each of the graphical methods used for demonstration of coupling. We observed cardioventilatory coupling in seven of eight subjects. In each of these seven subjects, coupling was best described, both qualitatively and quantitatively, in terms of the relationship between inspiration and a preceding heart beat. The variation of the interval between inspiration and a preceding heart beat was less than for any other phase or time relationship. These data support a model of cardioventilatory coupling in which a heart beat triggers the onset of inspiration, rather than modulation of cardiac timing by ventilation or a phase relationship between the two systems.

Aged↗
PubMed1998

Artefactual episodic hypoxaemia during postoperative respiratory monitoring.

PURPOSE: To determine the reliability of continuous pulse oximetry in the detection of episodic hypoxaemia in total hip joint replacement patients. Episodic hypoxaemia has been described in postoperative patients and is associated with analgesic technique. This study compared the incidence of hypoxaemic episodes identified solely by pulse oximetry and then subsequently where additional monitoring, as indicated for sleep-related breathing disorders, was also utilised. METHODS: Eight patients were studied on the night before and for three nights after surgery. Pulse oximetry, ECG, chest impedance, nasal and oral airflow and transcutaneous CO2 were recorded. Sudden episodic hypoxaemia was defined as a decrease in oxygen saturation of > or = 5% within two minutes, for > five seconds and with a nadir of < 90%. Artefacts were identified by noise signals on the ECG and impedance recordings and by a motion annotation wave superimposed on the oximetry trace. RESULTS: Using these criteria 172 (79%) of 219 desaturation events were classified as artefactual. The median duration of genuine events was greater (P < 0.001 Mann Whitney U test) than artefactual events; 21 sec (range, 6-443) vs 11 sec (5-63). Genuine desaturations reached a median nadir of SpO2 87% (range 83-89%) compared with 81% (61-88%) for the artefactual. These differences were statistically significant (P < 0.001). CONCLUSION: Previous studies utilising unobserved pulse oximetry data alone may have overestimated the incidence of episodic hypoxaemic events in postoperative patients.

Aged↗
PubMed1998

Relationship between cardioventilatory coupling and respiratory sinus arrhythmia.

Recent studies have suggested a role for respiratory sinus arrhythmia in improving pulmonary gas transfer. However, the physiological role of cardioventilatory coupling is unknown. We have tested the hypothesis that cardioventilatory coupling aligns heart beats at positions of the ventilatory cycle where they are maximally affected by respiratory sinus arrhythmia (RSA). In 15 anaesthetized, spontaneously breathing subjects, we recorded continuously the timing of inspiration and the ECG. We then plotted the change in RR interval which occurred, as a result of RSA, after onset of inspiration (RSA plot). By comparing these RSA plots with the distribution of heart beats during the ventilatory cycle, we were able to examine the positioning of heart beats relative to acceleration of heart rate as a result of RSA. In all but two subjects we observed that during periods of strong cardioventilatory coupling, heart beats occurred at positions in the ventilatory cycle where they were maximally affected by RSA. In the presence of strong coupling, the shortest possible RR interval occurred during late inspiration, the longest possible RR interval occurred immediately before the start of inspiration. We suggest that cardioventilatory coupling may have a physiological role in optimizing RSA, perhaps to improve cardiopulmonary performance during sleep.

Adolescent↗
PubMed1997

Spectral analysis of AC and DC components of the pulse photoplethysmograph at rest and during induction of anaesthesia.

We examined spectral components of beat to beat variability in AC and DC signals of the reflectance photoplethysmograph at finger and earlobe sites in 20 resting volunteers and 20 patients during propofol, alfentanil, isoflurane, nitrous oxide anaesthesia. We observed that at rest, the majority of spectral power at both sites and in both signals was in the low 'thermoregulatory' frequency band (0.01-0.08 Hz). These fluctuations were greater in the finger than in the earlobe and in the AC signal compared to the DC. With anaesthesia, low as well as mid (0.08-0.15 Hz) frequency variability decreased at both sites and in both signals whereas high frequency 'ventilatory' power (0.15-0.45 Hz) was maintained. During anaesthesia we found no significant differences between the spectral components of the AC or DC signals or between the finger and the earlobe sites. At all frequencies, the fluctuations in the AC and DC signals were out of phase with each other.

Adult↗
PubMed1997

Coupling of spontaneous ventilation to heart beat during benzodiazepine sedation.

We have examined in eight male volunteers the effect of midazolam sedation on the relationship between timing of spontaneous ventilations and heart beat. On 2 study days, subjects received either midazolam 0.1 mg kg-1 or saline placebo while recordings were made of ECG and ventilatory impedance pneumography. We observed in all midazolam-treated subjects clear evidence of synchronous or non-synchronous coupling between ventilation and heart beat. Non-synchronous coupling was seen in two placebo-treated subjects, one of whom had slept during the recording period. We conclude that cardioventilatory coupling is a major determinant of ventilatory timing in sedated subjects.

Adult↗
PubMed1997

Low-dose mivacurium supplementation of prilocaine i.v. regional anaesthesia.

We have compared in two groups of five healthy volunteers, the motor effect of prilocaine i.v. regional anaesthesia of the forearm with and without addition of mivacurium 0.6 mg. Although addition of mivacurium might, theoretically, provide the benefit of increased neuromuscular block with rapid plasma cholinesterase degradation in the isolated limb, we observed prolonged forearm weakness in the mivacurium group using tests of grip strength (median recovery to 90% of control, 80 min (range 60 min to > 8 h) vs control median recovery to 90% of 16 (8-24) min) and bead transfer (median recovery to 90% of control 36 (24-48) min vs control median recovery to 90% of 12 (8-16) min). This weakness was considerably in excess of that predicted by rapid systemic degradation of mivacurium. The mivacurium group experienced symptoms of local anaesthetic toxicity which did not occur in the control group and which could not be replicated by administration of mivacurium alone.

Anesthesia, Conduction↗
PubMed1997

A model of the electrocortical effects of general anaesthesia.

In an attempt to describe how reduction in synaptic efficiency by general anaesthetic agents results in loss of consciousness, we examined the behaviour of a two-dimensional (a lattice of 80 x 80 cellular elements) cellular automaton (CA) computer model as the connectivity between cellular elements was altered. The lattice was taken to represent cortical elements with variable connectivity to their neighbours. The summation of the active elements of the CA lattice was taken to represent a simulated "EEG" signal. If cellular automation elements had a high probability of connectivity, the simulated EEG showed high frequency predominance and low amplitudes, similar to the desynchronized pattern in an alert person. As connectivity was decreased, median frequency in the simulated EEG decreased and amplitude increased, similar to that in anaesthetized patients. As in our model, we believe it is possible that the human central nervous system in the conscious resting state exists above a critical threshold of synaptic efficiency; awareness is associated with an increase in synaptic efficiency and anaesthesia with a decrease that sharply reduces cortical information transfer.

Anesthetics, General↗
PubMed1997

Cardioventilatory coupling during anaesthesia.

In 20 spontaneously breathing patients undergoing minor surgical procedures under general anaesthesia, we examined the timing relationship of heart best and ventilation. Patients received propofol 2-2.5 mg kg-1 and fentanyl 1 microgram kg-1 and breathed a mixture of 1-1.5% isoflurane and 66% nitrous oxide in oxygen. We recorded ECG R wave times and the start of each inspiration. We observed that: (1) all subjects showed evidence of phase coupling in which heart beats occurred at constant phases of the ventilatory cycle; (2) there was a significant preference for whole number ratios of heart rate to ventilatory frequency; (3) phase coupling was associated frequently with quantal changes in heart rate or ventilatory frequency, or both; (4) six coupling patterns were described according to the timing relationship between the ECG R wave and start of inspiration and according to changes in the number of heart beats within each ventilatory period; (5) phase coupling was achieved primarily by transient changes in ventilatory period. Phase coupling, in concert with respiratory sinus arrhythmia, may optimize the performance of the thoracic pump, matching cardiac filling to venous return. Coupling may therefore have anaesthetic relevance in conditions of impaired cardiac performance or hypovolaemia.

Adolescent↗
PubMed1996

Periodic cardiovascular and ventilatory activity during midazolam sedation.

We have examined the effects of sedation with midazolam 0.1 mg kg-1 and reversal with flumazenil 0.5 mg on beat-to-beat heart rate (HR) variability (HRV), systolic arterial pressure (SAP), finger photoplethysmograph amplitude (PLA) and impedence pneumography in eight volunteers. With the onset of sedation there was a small decrease in SAP and increase in HR (ns). Spectral analysis of the HR time series showed reductions in the proportion of power in the high (> 0.15 Hz) frequency "ventilatory" band consistent with midazolam causing vagolysis. During sedation, low frequency (< 0.05 Hz) oscillations of PLA, HR, SAP and ventilation were observed. These were thought to be secondary to activity of coupled cardiorespiratory neurones within the brain stem and the ventilatory periodicity appeared similar to that observed during the early stages of sleep. The diminished high frequency and increased low frequency oscillations induced by midazolam sedation were reversed by administration of flumazenil.

Adult↗
PubMed1994

Endogenous opioid modulation of hypercapnic-stimulated respiration in the rat.

The role of endogenous opioids in respiratory control in the pentobarbital anaesthetised rat was investigated using a rebreathing technique to generate a progressively increasing hypercapnic stimulus to the respiratory centers following administration of an opioid antagonist or agonist. Respiratory output was measured by intraesophageal pressure (IEP) changes, and a ventilatory equivalent (VEq) was calculated by multiplying IEP by respiratory rate (mmHg.min-1). A non-selective opioid antagonist, naloxone (0.4 mg/kg i.v.), significantly enhanced the slope of the CO2 response curve for VEq (20 +/- 3 mmHg.min-1.%CO2-1) compared with the control (14 +/- 2 mmHg.min-1.%CO2(-1)) (P < 0.05; n = 14). A similar enhancement of the hypercapnic response by naloxone was found in rats anaesthetised with urethane (n = 5). The mu receptor agonist dermorphin (1 mg/kg i.v.) significantly depressed the slope of the CO2 response curve for IEP (-0.01 +/- 0.03) compared with the control (0.10 +/- 0.03) in pentobarbital anaesthetised rats (P < 0.05; n = 5) but had no significant effect on respiratory rate. These results suggest a role of endogenous opioids in the modulation of respiration during hypercapnia.

Amino Acid Sequence↗
PubMed1994

Effect of halothane, isoflurane and fentanyl on spectral components of heart rate variability.

We have examined the effect of isoflurane, halothane and fentanyl on heart rate variability (HRV) using power spectral analysis (PSA). Forty patients were allocated randomly to receive one of four anaesthetic techniques. Anaesthesia was induced with propofol 2 mg kg-1 and all patients breathed a mixture of 66% nitrous oxide in oxygen. Twenty of these spontaneously breathing patients received 1.5% isoflurane and 20 received 0.75% halothane. Ten patients in each of these groups received fentanyl 1 microgram kg-1 before induction. PSA was performed on 5-min segments of beat-to-beat R-R interval data taken before and 5 min after induction. No significant difference was observed in time domain or spectral HRV measures between inhalation agents. Fentanyl was associated with significantly slower heart rates, although no difference was observed in the power spectrum of those receiving fentanyl. Analysis of pooled data from the 40 subjects showed that mean heart rate was unchanged and heart rate SD was decreased, as were total and individual powers in three frequency bands of the HRV spectrum (low 0.02-0.08 Hz, mid 0.08-0.15 Hz and high 0.15-0.45 Hz). A significant decrease in the ratio of high power to (low + mid) power indicated a shift towards sympatholysis with anaesthesia. However, a significantly greater depression of mid frequency components in comparison with low or high frequencies suggests that anaesthesia selectively depressed components of the HRV mechanism, independent of a general effect on autonomic tone.

Adult↗
PubMed1994

Heart rate variability during propofol anaesthesia.

We have examined the effect of i.v. propofol anaesthesia on beat-to-beat heart rate variability. The power in all frequency bands (0.02-0.08, 0.08-0.15, 0.15-0.45 Hz) decreased, although the reduction in lower power was significantly less than that for mid (P = 0.001) and high (P = 0.04) power.

Adult↗
PubMed1994

Effect of propofol on heart rate, arterial pressure and digital plethysmograph variability.

We have investigated the effects of propofol on beat-to-beat fluctuations in heart rate, arterial pressure (continuous arterial tonometry) and infrared finger plethysmography in 10 healthy male patients undergoing elective surgery. Administration of Diprivan (propofol 10 mg ml-1) 0.2 ml kg-1, followed by an infusion of 1 ml kg-1 h-1, was associated with transient tachycardia and a reduction in arterial pressure that preceded an increase in plethysmograph amplitude. The temporal sequence of these cardiovascular changes suggests that the initial tachycardia was not a reflex response to hypotension and that cutaneous changes in adrenergic tone were not responsible for the decrease in arterial pressure. The observation that the hypotensive action of propofol preceded the increase in plethysmographic amplitude suggests that multiple mechanisms were implicated in the hypotensive action of propofol and the relative importance of these mechanisms may vary according to the time of measurement. Compared with preanaesthetic control values, spectral analysis of heart rate variability, arterial pressure and plethysmograph variability showed reduction in variability and total spectral power. Spectral power in low (< 0.08 Hz) and mid (0.08-0.15 Hz) frequency bands decreased for each variable, while high (> 0.15 Hz) frequency "ventilatory" power decreased for heart rate and possibly diastolic pressure and increased for systolic pressure and plethysmograph variability.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗