Effect of the mode of administration of inhaled anaesthetics on the interpretation of the F(A)/F(I) curve--a GasMan simulation.

The effects of blood solubility, cardiac output and ventilation on the rise of the alveolar towards the inspired concentration, the F(A)/F(I) curve, of an inhaled anaesthetic are often thought to reflect how these factors affect wash-in of the central nervous system compartment and, therefore, speed of induction because F(A) is the partial pressure ultimately attained in the central nervous system (F(VRG)). These classical F(A)/F(I) curves assumed a constant F(I). We used GasMan to examine whether changes in solubility, cardiac output and ventilation affect the relationship between the F(A)/F(I) curve and F(VRG) differently while either F(I) or F(A) are kept constant. Using GasMan, we studied the effects of solubility (desflurane vs isoflurane), cardiac output (5 vs. 10 l x min(-1)) and minute ventilation (4 vs. 8 l x min(-1)) on F(A), F(I), F(A)/F(I) and F(VRG) with either F(I) kept constant or F(A) kept constant (at 1 minimum alveolar concentration). High fresh gas flows were used to avoid rebreathing, so that the delivered concentration matched F(I). Despite similar effects on the F(A)/F(I) curve, the effects on F(VRG) differed. With constant F(I), lower solubility or higher ventilation results in a higher F(VRG) and a higher cardiac output results in a lower F(VRG). With constant F(A), solubility has only a minimal effect on F(VRG); an increase in cardiac output hastens the rise of F(VRG) to the same plateau value; and a change in ventilation has minimal effect on F(VRG). Despite similar effects on the F(A)/F(I) curve, the effects of solubility, cardiac output and ventilation on the F(VRG) are different when either F(I) or F(A) are kept constant. With the F(I) kept constant, induction of anaesthesia is slower with a higher cardiac output, but with F(A) kept constant, induction of anaesthesia is faster with a higher cardiac output. The introduction of an end-expired closed-loop feedback administration of inhaled anaesthetics makes this distinction clinically relevant.

Derivation and prospective testing of a two-step sevoflurane-O2-N2O low fresh gas flow sequence.

Simple vaporiser setting (F(D)) and fresh gas flow (FGF) sequences make the practice of low-flow anaesthesia not only possible but also easy to achieve. We sought to derive a sevoflurane F(D) sequence that maintains the end-expired sevoflurane concentration (F(A)sevo) at 1.3% using the fewest possible number of F(D) adjustments with a previously described O2-N2O FGF sequence that allows early FGF reduction to 0.7 l min(-1). In 18 ASA physical status I to IH patients, F(D) was determined to maintain F(A)sevo at 1.3% with 2 l min(-1) O2 and 4 l min(-1) N2O FGF for three minutes, and with 0.3 and 0.4 l min(-1) thereafter. Using the same FGF sequence, the F(D) schedule that approached the 1.3% F(A)sevo pattern with the fewest possible adjustments was prospectively tested in another 18 patients. The following F(D) sequence approximated the F(D) course well: 2% from zero to three minutes, 2.6% from three to 15 minutes and 2.0% after 15 minutes. When prospectively tested, median (25th; 75th percentile) performance error was 0.8 (-2.9; 5.9)%, absolute performance error 6.7 (3.3; 10.6)%, divergence 18.2 (-5.6; 27.4)%.h(-1) and wobble 4.4 (1.7; 8.1) %. In one patient, FGF had to be temporarily increased for four minutes. One O2/N2O rotameter FGF setting change from 6 to 0.7 l min(-1) at three minutes and two sevoflurane F(D) changes at three and 15 minutes maintained predictable anaesthetic gas concentrations during the first 45 minutes in all but one patient in our study.

A new method for semiautomatic analysis of surface EMG in patients with oral parafunctions.

Sleep-related phenomena or disorders, including snoring and tooth grinding, can be investigated using polysomnography. This method, however, generates large amounts of synchronically recorded data that are often analyzed visually with subjective interpretation. The purpose of this study was to minimize the need for subjective evaluation by developing a computer program for analysis of EMG data linked with polysomnographic recordings in a standardized and semi-automatic way. The selected algorithm differs from the Root Mean Square (RMS) method by being based on the theory of "differentiated EMG" (DIFEMG), which relies on two principles. The first says that the activation of a larger number of motor units results in a greater force production. The second principle says that the force production will continue for some time after the muscle is no longer stimulated. After a visual check for artifacts in the basic EMG recordings, the computer program is used to analyze the corrected basic EMG signal. The results were that both methods yield identical results as far as the detected number of events is concerned. There is, however, a significant difference when the duration of the events is considered, because the start and end of an event can be more accurately determined with the new method presented here. The computer program described will make comparison of data from different studies easier.

Influence of a bite-plane according to Jeanmonod, on bruxism activity during sleep.

One way to look at nocturnal oral parafunction such as bruxism, is using polysomnography. Although in recent years several studies have been carried out, it is almost impossible to compare the respective results because of the lack of standardization in the methodology used. The nocturnal muscular activity of m. Masseter and m. Temporalis Anterior has been registered in 21 patients suffering from bruxism, prior and after treatment with a bite-plane made according to Jeanmonod. A group of five persons without any dental or muscular parafunction has been included as a control. A computer program based on the biomechanical principles of muscle contraction has been developed and was used to analyse the raw electromyography (EMG) signal. The data shows a significant decrease (P = 0.008) in nocturnal parafunctional muscle activity with the bite-plane in situ. The present study shows that by analysing the raw signal obtained via EMG using a specially designed computer program, it becomes possible to isolate the occurrence of parafunctional events in the EMG signal and to study the influence of a given therapy on this EMG signal.