摘要:

The effects of 33% nitrous oxide on the two components of the blink reflex were studied on seven healthy volunteers. The blink responses were elicited by a supraorbital nerve stimulation and recorded from the ipsilateral orbicularis oculi muscle. The intensity of stimulation was chosen at two to three times the reflex threshold in order to obtain stable suprathreshold reflex responses as well as a tolerable pain sensation reported by the volunteers. Nitrous oxide administration resulted in a potent depression of the two components of the blink reflex. This depressive effect was more marked upon the late (R2) nociceptive component (83%) than upon the early (R1) component (41%). Simultaneously, subjects reported either a decrease in pain sensation or an indifference toward the painful stimulus. None of these effects were reversed by a double-blind intravenous naloxone (1.4 mg) injection. The analgesic effect of nitrous oxide is a nonspecific depressant action on the transmission of the nociceptive messages in central nervous structures, independent of pain-suppressive endogenous morphine-like systems.

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

An external spirometric method using a differential linear transformer was used to measure tidal volume (VT) and to determine factors influencing CO2elimination and HFJV-induced “PEEP effect” in 15 critically ill patients under HFJV. VTincreased with increasing driving pressure (DP) and decreasing frequency (f) and was influenced little by changes in I/E ratio. CO2elimination, as reflected by the measurement of PaCO2, was mainly influenced by the absolute level of VTrather than by the product VTX frequency (PaCO2= 5715/VT, r = 0.75,P< 0.05). The primary phenomenon explaining HFJV-induced “PEEP effect” was intrapulmonary gas trapping due to incomplete exhalation of the first VTadministered: the spontaneous relaxation times of these first VTwere longer than expiratory time allotted to the ventilatory settings. HFJV-induced “PEEP effect” increased with I/E ratio, DP, and f and was markedly influenced by the mechanical properties of the total respiratory system. At given ventilatory settings, HFJV-induced “PEEP effect” was greater in patients with a normal or elevated time constant of the total respiratory system (τ RS) than in patients with a low τRS. These results suggest that HFJV should not be used in patients with chronic obstructive pulmonary disease and asthma, and should be preferentially administered to patients having stiff lungs or decreased chest wall compliance.

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Morphine and meperidine distribution in the neuroaxis were studied in rats after intrathecal injection through catheters ending at the lumbar level.14C-Morphine and3H-meperidine were injected with pharmacologic doses of each drug. Radioactivity was measured in spinal cord segments at different times. At 14 min the segment with maximum morphine concentration (T11–12) contained 8.6 ± 2.4 (mean ± SD) pmol/mg, a value 215 times higher than would be observed if distribution in the body were homogeneous. The ratio between concentration in the most rostral segment (C3–4) and in the segment with maximal concentration was 0.21 ± 0.10. At 14 min the segment with maximum meperidine concentration (T9–10) contained 161.4 ± 33.9 pmol/mg wet tissue, a value 75 times higher than would be seen with even distribution in the body. The ratio (C3–4vs.T9–10) was 0.10 ± 0.04 at this time.The distribution of14C-morphine in the whole central nervous system (CNS) was studied in mice by whole body autoradiography after intrathecal injections of 5 μl at the L5–6 level. High levels of radioactivity were detected in the whole spinal cord and in brain regions close to the basal cisterns until 2 h after injection. At 4 h only the caudal part of the spinal cord had detectable levels of radioactivity.The per cent of the injected dose of morphine that was recovered from the spinal cord was 26.5 ± 4.5 at 14 min, 19.9 ± 8.8 at 44 min, and 4.5 ± 1.7 at 179 min after injection. The figure was 6.9 ± 1.8 at 14 min and 2.2 ± 0.7 at 44 min for meperidine. It could be postulated that the hydrophilic drug morphine persists for longer in the spinal cord, whereas the lipophilic meperidine is rapidly taken up and eliminated, resulting in lower recovery. The spread of morphine into the basal cisterns is consistent with the clinical risk of ventilatory depression.

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

This study was designed to evaluate a new drug delivery system. The authors undertook to determine if microdroplets prepared by encapsulating volatile anesthetics with a membrane of lecithin could be used for local anesthesia. Local anesthesia was determined by monitoring the response of the rat to tail clamping and electrical stimulation of the skin following the intradermal injection of the microdroplets. Microdroplets were prepared from isoflurane, enflurane, halothane, methoxyflurane, diethyl ether, chloroform, and heptane. Although all microdroplet preparations produced local anesthesia, only methoxyflurane microdroplets produced an ultra-long duration of local anesthesia (approximately 24 h). Further characterization of the methoxyflurane microdroplets revealed two important differences from conventional local anesthetics. First, the local anesthetic effect of methoxyflurane reached a plateau that did not change significantly for 20 h while the injection of lidocaine and bupivacaine resulted in a peak effect that returned to baseline within 1 and 3 h, respectively. Second, the anesthetic effect of methoxyflurane remained essentially localized to the site of injection, while the anesthetic effect of lidocaine and bupivacaine migrated 15 cm in less than 1 h. The toxicity and safety of methoxyflurane were evaluated. When administered over the dosage range 1–16% (v/v) intradermally, or by injections into muscle, or by repeat injections every 4 days for 16 days, all animals regained their pre-treatment response to painful stimulations, and there was no evidence of gross injury to tissue. Deliberate intravenous injection of 0.8 ml of 6.7% (v/v) methoxyflurane microdroplets had no apparent anesthetic or toxic effect. The present study demonstrates that methoxyflurane microdroplets produce an anesthetic effect that is highly localized, stable in intensity, ultra-long in duration, and reversible.

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Reflex circulatory responses are chiefly governed by the integrated functions of both sympathetic and parasympathetic nervous systems at any moment. To examine how sympathetic denervation of the important effector organ, the heart, modifies such reflex responses, the authors compared circulatory responses to arterial baroreflexes, the Valsalva maneuver (VM), coughing (C), swallowing (S), and nasal stimulation (NS) before and after cervical epidural blockade using 10 ml of 1.5% lidocaine in awake, healthy humans.The cervico-thoracic sympathetic denervation (sensory block of C4-T7) caused a slight suppression of the baroreflex sensitivity assessed by increases in RR intervals to increased systolic blood pressure with a pressor test (phenylephrine) in all eight subjects studied; the mean slopes of the regression lines were 29.1 ± 9.8 ms · mmHg−1before the blockade and 17.2 ± 6.3 ms · mmHg−1after the blockade (P< 0.05). However, the baroreflex sensitivity to a depressor test (nitroglycerin) remained unchanged following the blockade. Furthermore, the responses in heart rate and blood pressure to VM (Phases II and IV) and the responses in heart rate to C, S, and NS were partially suppressed after the blockade (P< 0.05). Despite these suppressions, the overall responses to VM, C, S, and NS remained unchanged after the blockade. No predominant parasympathetic responses such as profound hypotension and bradycardia were observed during any maneuver after the blockade.Since the vagus nerves were kept intact, these results indicate that acute sympathetic denervation of the central organs appears to preserve reflex circulatory responses to physical maneuvers such as producing high intrathoracic pressure, moderate changes in blood pressure or swallowing, though with some suppression of the cardiac acceleratory response. The results suggest that sympathetic control of heart rate functions as an inhibitor of the vagus rather than an active cardiac accelerator.

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

During normovolemia, nitrous oxide causes mild sympathetic stimulation and direct mycardial depression; these effects offset each other, resulting in only minimal cardiovascular changes. To test the hypothesis that during hypovolemia this balance would change and depression predominate, 10 swine were made hypovolemic (30% blood loss) and then were given 70% N2O (0.25 MAC in swine) or an equipotent concentration of halothane, an agent that does not cause sympathetic stimulation. The alternate anesthetic was given to the same hypovolemic swine on another day. Five minutes after induction of anesthesia during hypovolemia, both N2O and halothane caused significant, physiologically important deterioration of compensation for hemorrhage. Halothane decreased systemic vascular resistance (SVR); N2O was more variable in its action, and SVR did not decrease significantly. Both agents caused similar decreases in cardiac output, mean aortic blood pressure, stroke volume, oxygen consumption, and left ventricular minute work, despite increases in plasma epinephrine concentration and plasma renin activity. No differences were found between groups for any of these variables (P> 0.05). Plasma norepinephrine concentration increased only in the N2O group and was greater in that group than in the halothane group. The deterioration of cardiovascular compensation for hemorrhage was expressed metabolically by similar decreases in the two groups in partial pressure of oxygen of mixed venous blood and by increases in blood lactate concentration. Thirty minutes after induction of anesthesia, with stable end-tidal anesthetic concentrations, both groups had some cardiovascular, but no metabolic, recovery. Oxygen tension of mixed venous blood and blood lactate concentrations continued to be similar in the two groups. The authors conclude that administration of N2O in hypovolemic swine results in cardiovascular depression that is not different from that caused by halothane, an anesthetic having no sympathetic properties.

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Adenosine triphosphate (ATP) has been reported to be a hypotensive agent similar in effect to sodium nitroprusside (SNP). The purpose of this study was to examine and compare the effects of both SNP and ATP on general coronary hemodynamics, myocardial O2consumption, and circulating catecholamines. Twelve dogs were anesthetized with 1.0% halothane and given either SNP or ATP by controlled infusion to reduce their systemic blood pressure by 50% for a 2-h period followed by a (blood pressure) recovery period. The ATP-induced hypotension was rapid, easily controlled, not accompanied by tachyphylaxis over the 120 min studied, and resulted in an increase in coronary sinus blood flow (CSBF), which plateaued at 260% above control. The increase in CSBF was almost immediate and remained at this elevated level for the duration of the induced hypotension. During the ATP-induced hypotension, there was no change in heart rate or circulating catecholamines. A 60% reduction in myocardial O2uptake was observed, presumably from the cardiac unloading. In contrast, SNP-induced hypotension required a marked increase in dose over time, did not significantly increase CSBF, did increase heart rate, and resulted in large increases in circulating plasma catecholamines. Neither agent affected cardiac output. ATP-induced hypotension resulted in no change in cardiac lactic acid uptake, while SNP caused lactic acid production, indicating possible cardiac ischemia or cyanide toxicity.

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1985

数据来源: OVID