Attenuation of vagal noradrenergic tachycardia by naloxone

Electrical stimulation of the transected right vagus nerve in anesthetized and atropinized dogs produced tachycardia that was not attenuated by beta-adrenoceptor blockade. Naloxone in intravenous doses of 1 and 4 mg/kg antagonized the tachycardia evoked by nerve stimulation in a dose-dependent manner. However, the attenuation was maximal at approximately 55% of the control response. These results suggest that an endogenous opiate peptide(s) may have a mediator or modulator role in nonadrenergic tachycardia evoked by vagal nerve stimulation in anesthetized and atropinized dogs.

Lower oesophageal contractility: a new monitor of anaesthesia

The value of measuring lower oesophageal contractility (LOC) as a guide to the depth or adequacy of anaesthesia was investigated. Two forms of activity were recorded during light anaesthesia- nonpropulsive tertiary and provoked secondary peristalsis. Deepening anaesthesia resulted in progressive suppression of LOC. The smooth muscles of the lower oesophagus remain active despite the skeletal-muscle paralysis produced by muscle-relaxant drugs. The activity of the lower oesophagus may be a useful guide to the adequacy of anaesthesia.

Synthesis and antihypertensive activity of substituted trans-4-amino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-3-ols

A series of novel substituted trans-4-amino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-3-ols was prepared and tested for antihypertensive activity in the conscious deoxycorticosterone acetate (DOCA)/saline treated hypertensive rat. Optimum blood pressure lowering activity requires 6-substitution by a strong electron-withdrawing group, together with a pyrrolidino or piperidino group at the 4 position. Exceptions to this were the 7-nitro-4-pyrrolidine analogue and the 6-nitro-3-chloropropylamine, which retained marked antihypertensive activity. All of these compounds were direct vasodilators and had comparable antihypertensive activity to hydralazine and to the calcium antagonist, nifedipine. The synthetic route to these compounds involves cyclization of of propargyl ethers to 2H-1-benzopyrans, followed by conversion via bromohydrins to 3,4-epoxides, which were ring opened with the appropriate amines. Meta-substituted propargyl ethers gave both 5- and 7-substituted benzopyrans on thermal cyclization, the former predominating. A new route to 2,2-dimethyl-7-nitrobenzopyran is described.

Physiological interpretation of Doppler shift waveforms: the femorodistal segment in combined disease

A new method is presented for assessing the femorodistal segment in multisegmental arterial disease, using the Laplace transform technique of Doppler waveform analysis. Blood velocity/time waveforms were obtained at femoral and ankle levels in three groups of limbs--50 without arterial disease, 12 with isolated aortoiliac stenoses, and 32 with femoropopliteal occlusions, with and without proximal disease. The waveforms were analysed for Laplace transform and pulsatility index values. The omega 0 coefficients of the Laplace transform analysis at femoral and ankle levels were compared in each subject, as the omega 0 gradient (femoral/ankle omega 0): and pulsatility index damping factor (femoral/ankle P1) was also calculated. The omega 0 gradient was shown to detect femoropopliteal occlusion in the presence of multisegmental arterial disease and to give some indication of its haemodynamic significance. The diagnostic accuracy of the omega 0 gradient was superior to that of pulsatility index damping factor. When combined with its existing ability to detect aortoiliac stenosis, this new application of the Laplace transform method offers the possibility both of a system for complete localisation of significant arterial lesions, and potential for follow-up of vascular surgical procedures in the lower limb, from two simple Doppler recordings.

D-homoandrostanes. 4. The incubation of some D-homo-5 alpha-androstanes with Rhizopus nigricans

Nine dioxygenated D-homoandrostanes were incubated with Rhizopus nigricans to investigate the effect of D-ring modification on microbiological hydroxylation. Structure determination of the products by NMR spectroscopy, and in certain cases independent synthesis of their oxidised products, showed that in contrast to 5 alpha-androstanes the majority of the compounds were hydroxylated in the "reverse" mode, and only D-homo-5 alpha-androstane-3,17-dione was hydroxylated in the "normal" mode to any extent. Stereospecific ring D-hydroxylation at C(17 alpha) was observed for both D-homo-5 alpha-androstane-3,6- and 3,7-diones.

Cardiovascular regulation in canines during low-frequency acceleration

Integrated, reflex, cardiovascular regulation in unanesthetized (tranquilized), chronically-instrumented dogs was studied using sinusoidal whole-body spinal-axis acceleration (+/- 2 Gz) at frequencies below 0.25 Hz. The participation of neurally mediated cardiac and vascular control mechanisms was examined by comparing the responses of the same animal in a normal (reflexive) state and ina pharmacologically blockaded (nonreflexive) state. Integrated neural mechanisms were found to be the most effective in minimizing acceleration-induced, arterial pressure disturbances for frequencies below 0.012 Hz; became progressively out of phase with the disturbances between 0.012 and 0.052 Hz, resulting in decreased effectiveness; and failed to significantly participate in the regulatory process for frequencies between 0.052 and 0.25 Hz, where "protection" was provided by the hydraulic and intrinsic biomechanical characteristics of the circulatory system. An analysis of the relative contribution of peripheral vascular and cardiac mechanisms indicated that 1) neurally mediated, systemic vascular responses were largest for frequency; 2) heart rate oscillations were large for frequencies below 0.052 Hz (corner frequency) and then decreased rapidly with increasing frequency; and 3) neurally mediated stroke volume oscillations were the largest for the lowest frequencies and decreased with increasing frequency.

A fabric pouch for maintaining transducer and catheter terminations

Management of the chronically instrumented animal is improved by enclosing the terminations of catheters and transducer wires in a subcutaneous nylon velour pouch. Six or more days after implantation, an opening is made into the pouch by removing a portion of the overlying skin; subsequent healing processes provide a satisfactory bond. Thereafter the leads can be extracted and replaced without need for anesthesia or dissection. Results in 35 animals (26 dogs and 9 monkeys) for intervals up to four months showed fibrous encapsulation was complete in 28 and partial in 7, with no mortality or significant morbidity attributable solely to the presence of the pouch. Gross and microscopic tissue examination indicated a localized foreign body reaction in response to the nylon fibers. The technique is especially useful in experimental protocols for which continuous restraint is undesirable, such as the chronically instrumented primate periodically exposed to environmental stress.

The effect of naloxone on pulsatile gonadotrophin release in normal subjects

The gonadotrophin response to naloxone infusion has been investigated in three adult males, and three adult females in the early follicular phase. The frequency of LH secretory episodes and the mean LH levels increased in both sexes. The data suggest that the pulsatile release of LH is under inhibitory opiate control.

Neural, hormonal and intrinsic mechanisms of cardiac control during acute coronary occlusion in the intact dog

Three basic mechanisms may be involved in the control of cardiac function during acute coronary occlusion: (1) neural; (2) hormonal (circulating catecholamine); and (3) intrinsic (e.g. Frank--Starling law). The response of intact, sedated (Innovar-Vet, 0.08 cc/kg), chronically instrumented dogs to a 5 min left circumflex coronary occlusion was tested to delineate the relative roles of each of the above mechanisms. First, 6 innervated and 6 cardiac denervated dogs were examined. The major difference between groups was that the occlusion-induced tachycardia was significantly smaller in the denervated dogs than in the normally innervated animals (+10 +/- 7 vs +27 +/- 4/min, respectively, (mean +/- S.D.)). Changes in the first time derivative of left ventricular pressure (d(LVP)/dt) were similar (--898 +/- 556 vs --796 +/- 274 mm Hg/sec, denervated vs innervated). Decreases in stroke volume and mean arterial pressure were also similar in the two groups. The occlusion-induced tachycardia was compared in a second group of denervated dogs (n = 5) before and after administration of propranolol to examine the role of circulating catecholamines, and, by exclusion, to observe the response of the heart per se, independently of extrinsic control factors. The heart rate response was similar in both cases (+8 +/- 4 vs +6 +/- 4/min, unblocked vs blocked). Finally, blood pressure was prevented from falling during coronary occlusion in 3 normally innervated dogs by coupling the femoral artery to a reservoir of saline suspended above the animals. Blunting the input to the baroreceptors in this manner did not significantly change the size of the occlusion-induced tachycardia. We conclude that during acute coronary occlusion in dog: (1) the major role of the cardiac nerves involves modulating changes in the chronotropic state of the heart; (2) changes in d(LVP)/dt result principally from intrinsic phenomena linked to ischemia-induced alterations in myocardial performance; (3) changes in circulating catecholamines play only a minor role in controlling the heart during acute coronary occlusion in denervated dog; and (4) receptors located within the heart figure significantly in the etiology of the occlusion-induced tachycardia.

Maternal opinion about analgesia for labour. A controlled trial between epidural block and intramuscular pethidine combined with inhalation

In a randomised controlled trial epidural analgesia with bupivacaine 0.5% (mean dose 112.8 mg) was compared with pethidine (mean dose 200 mg) and inhalational analgesia in primipara (28 and 30 mothers) and multipara (17 and 18 mothers). Mothers who had an uneventful pregnancy and labour and agreed to have either treatment were studied during labour and followed-up at interviews for 5 months after delivery. Epidural block was rated significantly superior in respect of pain relief and comfort, there were no differences between the groups in reports of perineal discomfort. Twice as many primipara required forceps delivery after epidural block. Very few mothers, in each group, reported something missing in their experience of childbirth. Two thirds of each group would use the same method again. Epidural block can therefore be recommended to uncommitted mothers as a satisfying and effective method of pain relief for labour.

Self-administered intravenous and intramuscular pethidine. A controlled trial in labour

In a randomised controlled trial of mothers in labour intramuscular pethidine 150 mg, repeated if necessary, was compared with self-administered intravenous pethidine (0.25 mg/kg available at 10-min-intervals). Each mother agreed to have either method of pain relief and could opt for epidural block. The intramuscular group had significantly more pethidine than the intravenous group (mean differences, primipara 29 mg; multipara 16 mg). Ratings by mothers of the pain of 1st, 2nd stage and overall (analogue scores and gradings) were consistently better for the intravenous group although not significantly different. There were no differences in mean Apgar scores between the babies in the groups. In mothers who do not choose epidural block, similar pain relief is afforded by adequate intramuscular pethidine or self-demand intravenous pethidine; however, intravenous self-administration is more efficient since the pain relief is achieved with a lower dose of pethidine.

Coal liquefaction: recent findings in occupational safety and health

Some coal liquefaction materials are potentially hazardous because of similarities to materials in other related coal processes that have been associated with a high cancer risk. Limited survey data obtained by NIOSH at two coal liquefaction pilot plants have shown that workers were exposed to low concentrations of certain polynuclear aromatic hydrocarbons (PNA's) and aromatic amines, some of which are suspected carcinogens. The degree of risk incurred by such exposures cannot be determined because toxicologic data allowing for the evaluation of effects at low exposure levels are unavailable. These industrial hygiene studies are discussed as well as recent health and process aspects of this technology.

Modification of cardiac function by synchronized oscillating acceleration

The sensitivity of selected cardiovascular (CV) responses to the physical stressor of External whole-body oscillating Acceleration Synchronized with the Electrocardiogram (EASE) was analyzed in 8 chronically instrumented tranquilized dogs. A sinusoidal acceleration wave form was imposed on the supine animals along the spinal (+/- Gz) axis at a constant amplitude of +/- 0.75 G, and a frequency equal to the paced-heart frequency (2--3 Hz). When the peak force was positive in early systole, and negative in early diastole, changes in myocardial oxygen consumption (MVo2, + 8%), mean coronary flow (MCF, + 8%), stroke volume (SV, + 15%), cardiac work (CW, + 19%) and the time derivative of left ventricular pressure (dP/dt, + 18%) were minimal in comparison to nonoscillatory control values. When the peak force was positive in early diastole and negative in late diastole and early systole, changes in MVo2 (+ 41%), MCF (+ 39%), SV (+ 33%), CW (+ 50%), and dP/dt (+ 31%) were maximal. Thus the capability of EASE to produce a range of desired sustained CV responses provides a basis for its potential diagnostic/therapeutic applications.

Cardiac responses of dogs to nonsynchronous and heart synchronous whole-body vibration

Changes in cardiac function produced by synchronizing vibration-induced forces with events in the cardiac cycle were compared to those for the nonsynchronous case in eight chronically instrumented, tranquilized dogs. The supine animals received sinusoidal, whole-body vibration (along the spinal +/- Gz axis) at a constant acceleration amplitude (+/- 0.75 G). The vibration frequency (2-3 Hz) was set equal to the paced heart frequency. Synchronization between vibration and cardiac cycles on a beat-by-beat basis produced a specific and sustained cardiovascular response; such a sustained response was not possible with nonsynchronous vibration. With synchronization, relationships could be found and sustained in which changes either exceeded or were below mean nonsynchronous levels, in some cases below previbration values. For the synchronous vs. nonsynchronous states, significant modification of cardiac function was reflected in parameters such as coronary flow (+15% to -34%) and myocardial oxygen consumption (+21% to -51%). Thus, whole-body oscillation acceleration (vibration) is a forcing function that can produce and maintain a particular cardiovascular response.

Pressor response buffering by beta-adrenergic and cholinergic vasodilation in tranquilized dogs

Buffering of alpha-receptor-mediated pressor responses by beta-adrenergic or cholinergic vasodilation in tranquilized, chronically instrumented gos was investigated. Increases in aortic pressure were produced in the same animal by intravenous injections of phenylephrine in the control state and in three successive experimental states by 1) pacing the heart to remove the reflex capability to lower heart rate, 2) pacing the heart and beta-blockade to remove beta-adrenergic vascular buffering, and 3) beta-blockade plus atropine to also remove cholinergic vascular buffering. The pressor response in each experimental state was greater than that in the state preceding it. With the combined beta-adrenergic and cholinergic blockade, the pressor response to an alpha-receptor stimulation was three times greater than that of the control state. From an analysis of the components of the pressor response, cardiac output, and peripheral resistance, it is suggested that normal buffering of an alpha-mediated pressor response may include beta-adrenergic and cholinergic vascular dilation in addition to a decrease in heart rate.

Coal gasification and occupational health

Identification and prevention of health effects due to occupational exposures in coal gasification processes requires a basic knowledge of the technological process by which gasification proceeds. This paper presents an overview of the technology and a rational approach to health hazard identification based upon the concept of the unit operation specific micro environment. A final section is devoted to summarizing current research efforts being carried out under the aegis of the National Institute for Occupational Safety and Health.

Simple and versatile method for measuring oxygen consumption in infants

A simple, rapid, and accurate method for measuring oxygen consumption in infants is described. Expired gas is entrained in a stream of air drawn through a gently applied face mask. Oxygen consumption is derived from (1) gas flow rate, measured with a flowmeter, and (2) the fall in oxygen concentration of the gas mixture, measured with a paramagnetic analyser. A measurement can be made at the bedside within 2 minutes without disturbing the infant. In 17 mature 2-day-old neonates mean oxygen consumption was 6.52 ml/kg per min, SD 0.90, similar to that previously reported using less simple methods,

Correlation of alveolar PCO2 estimated by infra-red analysis and arterial PCO2 in the human neonate and the rabbit

The performance of an infra-red analyser (Beckman LB-2) in sampling alveolar gas at ventilatory frequencies and volumes occuring in the human neonate has been examined. The optimum sampling flow rate was found to be 300 ml/min; at this flow the 90% response time of the analyser-catheter system was 140 ms. Correlation of estimated alveolar PCO2 and arterial PCO2 was performed in the rabbit which has a ventilatory rate and tidal volume similar to those of the human neonate. There was a good correlation between maximum end-expired PCO2 (PE'CO2) and arterial PCO2 over a wide range of ventilatory rates (10-100 b.p.m.); maximum PE'CO2 was a better index than mean PE'CO2 or alveolar plateau PE'CO2.

Measurement of carbon dioxide output, alveolar carbon dioxide concentration and alveolar ventilation in the neonate

A system is described for measuring carbon dioxide output and alveolar carbon dioxide concentration in the neonate and for deriving the volume of alveolar ventilation. Air is drawn through a soft rubber face mask applied loosely to the face so that all expired gas is entrained. A fraction of the flow is sampled by an infra-red analyser, the signal from which is integrated to provide a measure of carbon dioxide output. Alveolar carbon dioxide concentration is measured by continuous sampling of expired gas through a nasal catheter. The response time of the catheter-analyser system is 140 ms. In 20 healthy 1-day-old neonates the mean carbon dioxide excretion was 5.86 ml/min. kg-1 (STPD) and the mean alveolar PCO2 was 4.85 kPa. From these measurements mean alveolar ventilation 147 ml/min. kg-1 (BTPS) was calculated. These results are similar to those obtained by other methods.

Frequency of HLA antigen in asbestos workers with and without pulmonary fibrosis

HLA antigens were determined in 37 patients with asbestosis and 37 matched controls with equivalent asbestos exposure but no pulmonary fibrosis. All had worked in the same textile factory. No significant differences in the prevalence of antigens were found between the two groups or between either group and controls who had not been exposed to asbestos. When the data were combined with findings from other pilot studies the previously suggested association between asbestosis and HLA-B27 was not confirmed. Subjects who were positive for HLA-B12 tended also to have advanced radiographic fibrosis. Asbestos workers without pulmonary fibrosis had an unexpectedly high frequency of HLA-BW5, which might indicate that this antigen protects against the development of pulmonary fibrosis.

Reversal of narcotic depression in the neonate by nalozone

Naloxone 40 mug was administered intravenously one minute after birth to 20 out of 44 neonates whose mother had been given pethidine in labour. These neonates were compared with 20 others whose mothers had had only lumbar epidural block. Alveolar PCO2, alveolar ventilation, and ventilatory rate were measured 10 and 30 minutes after birth. The untreated neonates of mothers who had had pethidine showed significant ventilatory depression compared with infants in the epidural and naloxone-treated groups. The naloxone-treated neonates were comparable with the epidural group, although the effects of naloxone were diminishing at 30 minutes. Naloxone is an effective narcotic antagonist which should be considered to be the drug of choice for treating narcotic depression in the neonate.

Apparatus for patient-controlled administration of intravenous narcotics during labour

The intermittent intravenous administration of narcotic analgesics had advantages over intramuscular administration, but is often impracticable. The design of a prototype apparatus is described, from which analgesic, pethidine, can be self-administered intravenously during labour. The apparatus consists of a syringe pump and control system from which the patient can demand an increment of analgesic. The minimum interval between increments and the dose of the increment are preset. A demand for analgesia is only successful when the patient passes a reaction-time test, subsequently modified. The apparatus has been used by forty-two mothers in labour. The mean total dose self-administered (2.2 mg/kg) was well within the prescribed limits, suggesting that mothers regulated their demand. The apparatus appears acceptable and safe in labour. The apparatus will probably be of value in comparative studies of analgesics.

Horner's syndrome as a complication of lumbar epidural block

Two cases of Horner's syndrome complicating lumbar epidural block in pregnant women in labour are described. The aetiology of the complication is discussed and it is suggested that epidural injections should not be made while the patient is in the lithotomy position.