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We aimed to validate the mathematical validity and accuracy of the respiratory components of the Nottingham Physiology Simulator (NPS), a computer simulation of physiological models. Subsequently, we aimed to assess the accuracy of the NPS in predicting the effects of a change in mechanical ventilation on patient arterial blood-gas tensions. The NPS was supplied with the following measured or calculated values from patients receiving intensive therapy: pulmonary shunt and physiological deadspace fractions, oxygen consumption, respiratory quotient, cardiac output, inspired oxygen fraction, expired minute volume, haemoglobin concentration, temperature and arterial base excess. Values calculated by the NPS for arterial oxygen tension and saturation (PaO2 and SaO2), mixed venous oxygen tension and saturation (PvO2 and SvO2), arterial and mixed venous carbon dioxide tension (PaCO2 and PvCO2) and arterial pH were accurate compared with measured values. Subsequently, arterial gas responses to changes in minute volume of FiO2 were measured in 31 patients and were compared with the NPS prediction for each response. The 95% limits of agreement in predicting the magnitude of change were: arterial oxygen tension -2.07 to 2.47 kPa; PaCO2 -0.33 to 0.67 kPa; and pH -0.023 to 0.033. This investigation has validated respiratory components of the NPS. We recommend the NPS as a clinical tool for predicting the effects of alterations in mechanical ventilation in stable patients in the intensive care unit.

We studied 10 patients undergoing laparoscopic cholecystectomy (group 1) and five control patients (group 2). We measured heart rate, arterial pressure, right atrial pressure (RAP), cardiac index (CI), systemic vascular resistance index (SVRI), intrathoracic pressure (ITP), plasma osmolality, adrenaline, noradrenaline and arginine vasopressin (aVP) concentrations, and serum renin activity (SRA), and calculated the atrial transmural pressure gradient (ATPG). We recorded significant decreases in mean arterial pressure (MAP), SVRI and CI in both groups (P < 0.05) after induction of anaesthesia. MAP and SVRI increased (P < 0.01) while CI decreased further in group 1 patients during the pneumoperitoneum. In group 1 plasma aVP concentration increased after insufflation of the pneumoperitoneum to a level sufficient to cause the recorded haemodynamic changes. ATPG decreased in group 1 patients during the pneumoperitoneum and this is a recognized trigger for aVP release.

The differences in phonation between men and women are thought to occur from anatomical differences in the larynx. However, it is not known if there are any differences in cough dynamics between the sexes. We investigated this by asking 100 healthy, non-smoking adults (50 male) to perform a voluntary cough into a tussometer. Each volunteer coughed at four different lung volumes, ranging from total lung capacity to functional residual capacity. There was a positive correlation between peak velocity time and cough peak flow rate in both males (r = 0.73, P < 0.001) and females (r = 0.78, P < 0.001). Multiple regression analysis showed that height (P < 0.05) and sex (P < 0.001) were significant determinants of the relationship between peak flow rate and peak velocity time. In a height-matched subgroup, sex differences remained significant (P < 0.05). This may be related to anatomical differences in laryngeal structure and may have implications when using tussometry to assess laryngeal function.

Tussometry is a new non-invasive technique for objectively assessing laryngeal function by analysis of the airflow waveform produced by a maximum effort voluntary cough manoeuvre. We describe the technique and present the calibration data. The tussometer has been calibrated for flows of up to 1100 litre min-1 using a flowmeter with a quoted accuracy of +/- 1.75%. The variables measured (cough peak flow rate (CPFR) and peak velocity time (PVT)) were found to be reproducible; the within-subject variability for CPFR was found to be 23.9% and for PVT 9%. There was no inter-observer variation. We found that the size of the mask used did not influence the readings obtained, providing an adequate seal was achieved.

Tussometry is a new non-invasive method of assessing laryngeal function by analysing the airflow waveform produced by a voluntary cough. Ten healthy male volunteers performed five (n = 6) or six (n = 4) voluntary cough manoeuvres at varying lung volumes from total lung capacity to functional residual capacity. During each manoeuvre, airflow (litre min-1) was plotted against time (ms) to record the peak flow generated by the cough (CPFR) and the time taken to achieve this (PVT). In addition, expired volume (CEV) was measured during each manoeuvre. Highly significant (P < 0.001) correlations existed between CPFR and PVT (r = 0.81), CPFR and CEV (r = 0.78) and PVT and CEV (r = 0.71). We conclude that PVT may vary with CPFR which in turn bears a direct relationship to expired lung volume during a cough manoeuvre. These relationships among different variables should be considered when interpreting the results of tussometry.

In a double-blind, randomized study, we have examined the influence of positive therapeutic suggestions, presented to anaesthetized patients undergoing total abdominal hysterectomy, on postoperative morbidity and duration of hospital stay. Seventy-five patients were allocated randomly to be exposed to one of three tapes containing positive therapeutic suggestions, a modified history of the Queen's Medical Centre, or no message. We found that neither therapeutic suggestions nor the presence of a voice during anaesthesia improved postoperative outcome or reduced duration of hospital stay after total abdominal hysterectomy.

We have assessed postoperative pain in 50 patients who had undergone total abdominal hysterectomy, using repeated contemporaneous and single retrospective visual analogue scores. There were significant correlations between the median, mean and greatest contemporaneous scores, and the single retrospective scores, but there was a wide scatter of results among and within individual patients. We conclude that the wide variability between the two methods of assessment suggests that the two techniques should not be used interchangeably.

We have studied the effects of two discrete types of surgical stimulation on contractions in the lower oesophagus. Forty-four female patients undergoing either abdominal hysterectomy or varicose vein surgery were anaesthetized using a standard technique. The frequency of spontaneous oesophageal contractions (SLOC) and amplitude of provoked contractions (PLOC) were greater in those patients undergoing hysterectomy. The oesophageal index (OCI), a single index combining both types of contractions, was found also to relate to the nature of the surgical stimulus.

Morphine 0.125 mg kg-1 was administered i.v. to 11 normal subjects and nine patients with chronic renal failure requiring regular haemodialysis. Plasma morphine concentrations were measured using high pressure liquid chromatography (HPLC). Although there was considerable individual variation in both groups, mean plasma concentrations of morphine were significantly higher in the patients with renal failure for 15 min after administration. The decay of plasma concentration fitted a three-compartment mamillary pharmacokinetic model in all subjects. Derived values (mean +/- SEM) of T 1/2 alpha, volume of distribution of the second compartment (V2), total volume of distribution at steady state (Vss) and transfer rate constant from the first to the second compartment (k12), were significantly different between groups. Mean values of terminal elimination half-life (T 1/2 gamma) and total body clearance were similar in the two groups. It was concluded that elimination of unchanged morphine is not impaired significantly in patients with chronic renal failure, although accumulation of morphine-3-glucuronide probably occurs. Although the pharmacological effect of morphine is not related temporally to plasma morphine concentrations, the higher values in patients with renal failure may be implicated in their increased sensitivity to the drug.

Sustained-release oral morphine sulphate (MST) 20 mg was administered to 11 healthy volunteers. Mean peak plasma morphine concentration was 14.8 ng ml-1, and occurred at a mean time of 142.5 min after ingestion. Analgesia assessed by an ischaemic forearm pain test increased to a maximum approximately 40 min after the calculated peak plasma concentration of morphine had been achieved, and remained greater than control values as plasma morphine concentration decayed. However, there was not a significant correlation between analgesia and plasma morphine concentration. This may result from delay in brain penetration by morphine. The mean systemic availability of morphine in the first 7 h after administration of MST was 18.3%.

We have investigated, in volunteers, the effect of inhaling 50% nitrous oxide in oxygen on subsequent oxygenation. Subjects breathed either 50% nitrous oxide in oxygen or 50% nitrogen in oxygen during hyperventilation and normal ventilation. Arterial oxygen saturation and end-expired oxygen concentrations were lower after 50% nitrous oxide in oxygen than after the other mixture with both patterns of ventilation and were lowest after hyperventilation with 50% nitrous oxide in oxygen.

Vecuronium was used to provide muscle relaxation in a patient who subsequently developed prolonged neuromuscular blockade (8 h) after anaesthesia. The aetiology of this condition, and the possible role of vecuronium, are discussed.

In a retrospective study, 68 large bowel anastomoses carried out on patients under subarachnoid or extradural spinal nerve block with light general anaesthesia were compared with 26 anastomoses on patients receiving general anaesthesia alone. Dehiscence occurred in 7.4% of anastomoses performed under spinal nerve block compared with 23.1% in the control group. In patients receiving morphine, anastomotic dehiscence occurred after 15.2% of operations, compared with 5.9% in patients receiving pethidine. These differences are not statistically significant. However, the findings indicate the need for larger prospective studies.

In a randomized, prospective study of patients undergoing large bowel anastomosis, 47 patients received subarachnoid block and light general anaesthesia, and 51 received conventional general anaesthesia with intermittent positive pressure ventilation. Anastomotic dehiscence occurred in 17.0% of the spinal group and in 17.6% of patients anaesthetized by the conventional technique. Blood loss was significantly (P less than 0.001) lower in the spinal group than in the general anaesthesia group. Blood transfusion was required in 10.6% of patients in the spinal group and 21.6% of patients receiving general anaesthesia.

Many factors influence the outcome after surgery of the bowel. However, care in anaesthetic and postoperative management may help to reduce the frequency of complications. Such care can be directed at maintenance of or improvement in oxygen delivery to the bowel by the avoidance of hypoxia, hypocapnia and hypovolaemia, and by careful selection of drugs and techniques used during anaesthesia. Tension on anastomoses can be reduced by care in the administration of neostigmine, and possibly by the use of pethidine rather than morphine for analgesia during and after operation. Postoperative ileus may be affected by sedative and analgesic therapy.

Changes in colon blood flow in greyhounds were measured in response to acute changes in arterial PCO2, before and after spinal nerve block. Colon blood flow increased significantly after spinal nerve block, irrespective of PCO2. The findings may be of clinical importance in man.