Oxygen transport with oscillations of inspired oxygen concentration

A theoretical model predicts that forced inspiratory oxygen concentration oscillations can be used to recover cardiorespiratory data and elicit information about the oxygen transport system (Hahn, 1996). The effects of hypoxia on the penetration of these generated oxygen oscillations into arterial and venous blood were explored in dogs exposed to a graded severity of hypoxia. Continuously recorded sinusoidal oxygen oscillations in the respired partial pressure, blood tension and mixed-venous saturation show that the transmission of forced oxygen oscillations from the lungs to the arterial blood depends on the mean arterial saturation. When mean inspired oxygen is high enough to fully saturate arterial haemoglobin, an inspired oscillation can only be transmitted in the blood as an oscillation in oxygen tension. However, in the presence of arterial hypoxaemia, oscillations in both the oxygen saturation and partial pressure of arterial blood are observed. Under these conditions, the oxygen saturation and partial pressure oscillations are also transmitted to mixed-venous blood. Our data illustrates that the link between the arterial and mixed-venous oscillations is non-linear and dependent on the sigmoidal binding relationship between oxygen and haemoglobin.

Data quality in population-based cancer registration: an assessment of the Merseyside and Cheshire Cancer Registry

Merseyside and Cheshire Cancer Registry (MCCR) data quality was assessed by applying literature-based measures to 27,942 cases diagnosed in 1990 and 1991. Registrations after death (n = 8535) were also audited (n = 917) to estimate death certificate only (DCO) case accuracy and the proportion of registrations notified by death certificate (DC). Ascertainment appeared to be high from the registration/mortality ratio for lung [1.01:1] and to be low from capture-recapture estimates (59.4%), varying significantly with site from oesophagus [92.2% (95% CI 88.5-95.9)] to breast [47.5 (95% CI 41.8-53.2)]. The estimated DC-dependent proportion was 20% (5601 out of 27 942) with successful traceback in 3533 out of 5601 (63.1%) cases. DCO flagging (2497 out of 27,942, 8.9%) overestimated true DCO cases (2068 out of 27,942, 7.4%). The proportion of cases of unknown primary site was low (1.5%), varying significantly with age [0-4.2%, (95% CI 2.5-5.9)] and district [0.8% (95% CI 0.3-1.3) to 2.2% (95% CI 1.8-2.6)]. The median diagnosis to registration interval appeared to be good (10 weeks), varying significantly with site (P < 0.0001), age (P < 0.0001) and district (P < 0.0001). The proportion with a verified diagnosis was 77.3%, varying significantly with site [lung 55.2% (95% CI 53.7-56.7) to cervix 96.9% (95% CI 96.3-97.5)], age [45.2% (95% CI 40.9-49.5) to 97.5% (95% CI 96.4-98.6)] and district [71.8% (95% CI 69.9-73.8) to 82.5% (95% CI 80.7-84.3)]. The DCO percentages varied similarly by site [non-melanoma skin 0.4% (95% CI 0.2-0.6) to lung 22.6% CI (95% 19.9-25.3)], age [0.7(95% CI 0.1-1.4) to 23.0 (95% CI 19.4-26.6)] and district [6.9% (95% CI 5.7-8.1) to 13.9% (95% CI 12.9-15.0)]. MCCR data quality varied with age, site and district - inviting action - and apparently compares favourably with elsewhere, although deficiencies in published data hampered definitive assessment. Putting quality assurance into practice identified shortcomings in the scope, definition and application of existing measures, and absent standards impeded interpretation. Cancer registry quality assurance should henceforward be within an explicit framework of agreed and standardized measures.

Prenatal administration of buprenorphine in the rat: effects on the rest-activity cycle at 22 and 30 days of age

Three doses of buprenorphine (BUP) were administered by osmotic minipump from day 8 of gestation through parturition. In addition to 0.3, 1.0, and 3.0 mg/kg/day of BUP, a vehicle control group received sterile water via minipump and a nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. BUP produced a dose response reduction in maternal water intake and reduced maternal weight gain among the two high dose groups; resorptions and birthweight were unaffected. BUP increased perinatal mortality in the two high dose groups compared with the vehicle controls and produced inconsistent effects on postnatal growth. To examine the effects of BUP on the rest-activity cycle of the offspring, groups of 3 littermates from each of the treated and control groups were tested for an 8 h observation period on electronic activity monitors at 22 and 30 days of age. Unlike previous effects described for prenatally administered methadone, a disruption in the rest-activity cycle was not observed for any of the BUP treated groups.

Measurement of respiratory parameters by using inspired oxygen sinusoidal forcing signals

A companion paper (C. E. W. Hahn. J. Appl. Physiol 81: 985-997, 1996) described a continuous-flow gas-exchange mathematical model, which predicted that forced inspired oxygen sinusoids could be used to measure respiratory parameters rapidly, in place of the inert gas argon. We therefore made simultaneous measurements of dead space volume (VD) and alveolar volume (VA) in an animal model, using argon and oxygen inspired gas concentration sinusoid forcing signals, and then compared the results. Our data confirmed the model prediction that the attenuations of the oxygen and argon sinusoid perturbations are identical in the alveolar gas space, even though there is a net uptake of oxygen by the body. Our results show that the calculated values of VD and VA, obtained by using inspired oxygen forcing signals, were independent of both the mean fractional inspired oxygen concentration (FIO2; range 0.18-0.80% vol/vol) and the oxygen forcing signal amplitude (range +/- 2-6% vol/vol). In these studies, oxygen forcing signals, with forcing periods between 1 and 2 min, were able to measure controlled changes in instrument dead space to within 16 ml and also measure positive end-expiratory pressure-induced changes in VA. Under hyperoxic conditions, intravascular oxygen sensors confirmed that the sinusoidal PO2 signal passed into the arterial blood but not into the mixed-venous blood. However, the sinusoid perturbation PO2 signal did pass into the mixed-venous blood when the mean FIO2 was mildly hypoxic (FIO2 = 0.18% vol/vol). These data show that oxygen can be used instead of argon to measure airways dead space and VA.

"Inaccuracy' in death certification--where are we now?

BACKGROUND

This review aims to document and analyse aspects of death certification that are relevant to public health.

METHODS

A literature review on death certification primarily used the computerized Index Medicus (1981 to mid-1995), and concentrated on completing death certificates, accuracy, standards, education and procedural requirements. Further sentinel publications pre-dating this were identified from the main literature base.

RESULTS

The uses of mortality data, historical and procedural context for recording death, the philosophy of Underlying Cause of Death and its relationship to the truth, the extent and impact of "inaccuracy', the certificate and the certifier, and possible ways forward are discussed. It is argued that the question "How inaccurate are cause of death data?' is harder to answer than the literature suggests. Deriving a useful estimate is difficult because of inter-study differences in (1) definition, measurement (how and by whom?) and practical importance of error, and standards used; (2) focus (e.g. death certificate or mortality data), observing everyday practice or simulation exercises, diagnostic and/or semantic issues.

CONCLUSION

The traditional perspective on improving the quality of death certification has not worked. There is a need for reorientated thinking rather than just urging more education. Evidence-based educational interventions are needed. The flaws in the theoretical framework of cause of death and the routine nature of death certification are unavoidable, but require consideration. Certifiers need practical feedback mechanisms, integral to continuing quality assurance at all levels and fostering an understanding of the construction of mortality data. Continued development should be a core public health medicine role.

Asthma deaths in Mersey region 1989-1990

BACKGROUND

We examined the circumstances surrounding death from asthma in Mersey Region and the feasibility of conducting a regional confidential enquiry, as suggested by the British Thoracic Society in response to the proposal in the Green Paper the health of the nation that asthma should be a key area for action.

METHOD

Sixty-three Mersey residents, aged 16-65 years, died in Mersey Region in 1989 and 1990 with ICD code 493. Diagnostic criteria for asthma were applied to each case. Anonymized case-note summaries were assessed by a chest physician (M.P.) for (1) severity of symptoms/disease, (2) risk of a respiratory death and (3)avoidable factors in the circumstances surrounding death.

RESULTS

Some written information was available on every patients. In 43/63 (68 percent) cases asthma was the true cause of death; 41/43 had had asthma diagnosed in life. Mean age (47 years) and median age of onset of asthma (10 years) were similar to those found in previous studies, but the proportion of men (58 percent) was higher. Only 6 (14 percent) deaths occurred after more than a few hours in hospital; for the rest, hospital contact was either too late (19 percent) or did not occur (67 percent). Of 22/43 (51 percent) patients considered at high risk of a respiratory death, 15 had poorly controlled symptoms for at least a year before their deaths. Avoidable factors were present in 29/43 (67 percent) cases; most commonly lack of assessment, inadequate doses of steroids and over-reliance on bronchodilators.

CONCLUSION

These findings resemble those of previous studies, showing that little has changed. Asthma deaths occur mostly outside hospital; thus to replace deaths, resources should be directed at the community to improve the recognition of asthma by patients, their families and the primary care team. A regional confidential enquiry is feasible and could be an effective mechanism for proving management.

Measurement of tidal flow using a transit-time ultrasonic breath analyser

The ability of the Transit-time Ultrasonic Breath Analyser (TUBA, GHG Medical Electronics GMBH, Zürich, Switzerland) to measure peak flow and tidal volume in the laboratory was tested using a variety of flow and pressure conditions, chosen to simulate the respiratory patterns of patients receiving mechanical ventilatory support. A stable zero baseline was achieved by acoustic damping of the TUBA flow sensor head. A piston pump was used to generate sinusoidal flow pattern, with a peak flow range from 0.1 to 1.51.s-1. The calculated peak flow matched the peak flow measured by the TUBA. The TUBA accurately measured tidal volumes (+/- 10%) delivered using three different flow patterns over a range of volumes from 0.25 to 11. We conclude, that once modified, the TUBA can provide an accurate measurement of peak flow and tidal volume over a range of values likely to be encountered during mechanical ventilation of the lungs.

Neuroendoscopic laser-assisted ventriculostomy of the third ventricle

Hydrocephalus is caused by an imbalance between the production and absorption of cerebrospinal fluid. Ventriculostomy of the third ventricle now is an acceptable treatment alternative for this problem. This procedure reduces costs over the course of the illness because the patient does not require subsequent shunt revisions throughout his or her life. The specialized care and the fear associated with the dependency on mechanical hardware also are eliminated if shunt placement is avoided. Postoperative complications may include increased intracranial pressure, bleeding, infection, and pain.

A regional survey of intravenous therapy practices

In this article, the authors share the results of a survey developed by a group of nurses in a 400-bed community hospital and distributed to 25 health care agencies throughout the northeastern New York region. The survey is comprised of six major categories, with questions pertaining to flushing and dressing protocols, types of vascular access devices used, and the availability of equipment and resources. Sixty percent of the agencies responded, including hospital, home care, hospice, and physician office settings. Major findings identified a lack of consistency in flushing and dressing protocols and in the types of equipment used. Implications for future practice will be presented along with the results of the survey.

Assessment of cardiorespiratory function using oscillating inert gas forcing signals

A theoretical model (Hahn et al. J. Appl. Physiol. 75: 1863-1876, 1993) predicts that the amplitudes of the argon and nitrous oxide inspired, end-expired, and mixed expired sinusoids at forcing periods in the range of 2-3 min (frequency 0.3-0.5 min-1) can be used directly to measure airway dead space, lung alveolar volume, and pulmonary blood flow. We tested the ability of this procedure to measure these parameters continuously by feeding monosinusoidal argon and nitrous oxide forcing signals (6 +/- 4% vol/vol) into the inspired airstream of nine anesthetized ventilated dogs. Close agreement was found between single-breath and sinusoid airway dead space measurements (mean difference 15 +/- 6%, 95% confidence limit), N2 washout and sinusoid alveolar volume (mean difference 4 +/- 6%, 95% confidence limit), and thermal dilution and sinusoid pulmonary blood flow (mean difference 12 +/- 11%, 95% confidence limit). The application of 1 kPa positive end-expiratory pressure increased airway dead space by 12% and alveolar volume from 0.8 to 1.1 liters but did not alter pulmonary blood flow, as measured by both the sinusoid and comparator techniques. Our findings show that the noninvasive sinusoid technique can be used to measure cardiorespiratory lung function and allows changes in function to be resolved in 2 min.

Self-esteem, social support, and satisfaction differences in women with adequate and inadequate prenatal care

This descriptive, retrospective study examined levels of self-esteem, social support, and satisfaction with prenatal care in 193 low-risk postpartal women who obtained adequate and inadequate care. The participants were drawn from a regional medical center and university teaching hospital in New Mexico. A demographic questionnaire, the Coopersmith self-esteem inventory, the personal resource questionnaire part 2, and the prenatal care satisfaction inventory were used for data collection. Significant differences were found in the level of education, income, insurance, and ethnicity between women who received adequate prenatal care and those who received inadequate care. Women who were likely to seek either adequate or inadequate prenatal care were those whose total family income was $10,000 to $19,999 per year and high school graduates. Statistically significant differences were found in self-esteem, social support, and satisfaction between the two groups of women. Strategies to enhance self-esteem and social support have to be developed to reach women at risk for receiving inadequate prenatal care.

Measurement of dead-space in a model lung using an oscillating inspired argon signal

In a model lung, airways dead-space can be accurately measured using a forced inspired oscillating argon signal, which varies sinusoidally about a mean concentration of 6% v/v with an amplitude of +/- 4% v/v. With sinusoid forcing periods longer than 120 seconds, and at a breathing rate of 13.4 breaths minute-1, the mean airways dead-space can be measured with a standard error of less than 5%. Sinusoid forcing periods shorter than 120 s provided inaccurate estimates of dead-space and so should not be used with this technique.

Development of a concentric water-displacement model lung

Simulation of lung ventilation using a model lung can provide a means of evaluating lung function tests, mathematical models and computer algorithms. We describe a new water-displacement lung model, which can simulate lung volumes up to 3.8 l and tidal volumes up to 1 l. Gas mixing is ensured by using a ring of venturi devices. Model compliance and airways resistance are described.

Death certification by house officers and general practitioners--practice and performance

The objective of this study was to assess the knowledge, attitudes and behaviour of House Officers and General Practitioners (GPs) in relation to death certification, to determine the scope for future intervention. A postal questionnaire was used to survey all House Officers (174) and a 10 per cent random sample of GPs (131) in Mersey Region. The main outcome measures were: death certification experience; knowledge, attitudes and behaviour in relation to data uses and coding; and acceptability of Cause of Death statements. Response rates were comparable-119/174 House Officers (68.4 per cent) and 95/131 GPs (72.5 per cent). Most House Officers (78.8 per cent) and GPs (85.3 per cent) reported that they made the best possible Cause of Death statement but, respectively, 62.4 per cent and 59.3 per cent of these might modify a statement in some circumstances. Significantly more House Officers (70.3 per cent) than GPs (44.2 per cent) acknowledge room for improvement and were amenable to more training (86.6 per cent versus 52.5 per cent), but significantly fewer felt sufficiently instructed (23.7 per cent versus 52.6 per cent). Most respondents (> 90 per cent) considered accurate death certification important, but 46.2 per cent of House Officers had not read the death certificate book instructions. Knowledge was variable, especially concerning Underlying Cause of Death. Written Cause of Death statements were broadly similar in style and standard between groups. Experience did not appear to improve death certification practice. Better and co-ordinated undergraduate and early post-graduate education (which should be continuing and audited), and practical accessible guidance on death certificate completion, might improve standards of practice and performance within the existing framework. Alternative methods of presenting guidance on death certificate completion should be explored.

Effect of bicarbonate administration on skeletal muscle intracellular pH in the rat: implications for acute administration of bicarbonate in man

1. The effect of bicarbonate administration on the intracellular pH of rat skeletal muscle was examined by using 31P n.m.r. 2. Bicarbonate administered intraperitoneally caused a significant intracellular acidosis in rat skeletal muscle in vivo. When the bicarbonate was administered intravenously there was no such change in the pH of the skeletal muscle. 3. Bicarbonate administration by either route resulted in an elevated mixed venous partial pressure of carbon dioxide and an elevated arterial pH, but no significant change in the arterial partial pressure of carbon dioxide. The increase in arterial bicarbonate concentration after intraperitoneal injection of bicarbonate was delayed when compared with that after intravenous injection. 4. The administration of hypertonic solutions intravenously caused a transient 40-50% fall in blood pressure, which had resolved within 1 min. 5. The data suggest that the effect of bicarbonate administration on intracellular pH in vivo is related not only to carbon dioxide loading of the cell but also to the rate of change in the extracellular bicarbonate concentration.

Na+/H+ and HCO3-/Cl- exchange in the control of intracellular pH in vivo in the spontaneously hypertensive rat

1. We have previously shown that the cytosolic acid concentration changes in skeletal muscle during contraction in spontaneously hypertensive rats and normotensive Wistar-Kyoto rats in vivo. We have now found that this change was unaffected by 20% inhaled CO2 or by 4,4'-di-isothiocyanostilbene-2,2'-disulphonate. This is evidence that HCO3- exchange in vivo is not important in the control of cytosolic acid concentration during skeletal muscle contraction in either spontaneously hypertensive or Wistar-Kyoto rats. 2. We have also previously shown that the difference in cytosolic acid response during contraction between spontaneously hypertensive and Wistar-Kyoto rats is due to increased Na+/H+ antiporter activity in the spontaneously hypertensive rats. Our current findings suggest that this increase in Na+/H+ antiporter activity is more likely to be due to a change in the Km of the antiporter than to a change in the Vmax. We estimate that the Km of the antiporter changes in hypertension from pH 7.16 to 7.33. 3. We did not find any differences between adult spontaneously hypertensive and Wistar-Kyoto rats with regard to resting intracellular and extracellular pH and resting intracellular and extracellular HCO3- concentrations. In addition, we did not find any evidence of a difference in skeletal muscle HCO3-/Cl- exchange between adult spontaneously hypertensive and Wistar-Kyoto rats. 4. At rest, skeletal muscles of the spontaneously hypertensive and Wistar-Kyoto rats have the same lactate production, HCO3-/Cl- exchange and arterial partial pressure of CO2. In addition, we can also calculate that at a resting intracellular pH of 7.05 in the spontaneously hypertensive rats, the antiporter is 66% saturated.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA triple-helix formation at physiologic pH and temperature

Oligonucleotides that form a triple helix with duplex DNA offer a novel way to site specifically regulate gene expression in vivo. Triple helices formed by homopyrimidine oligomers containing both cytosine and thymine are stabilized by acid pH and low temperature, and there is little information about triplex formation with these oligomers at both pH 7.5 and 37 degrees C. Therefore, we examined the effect of changing various conditions on triplex formation at pH 7.5. A 30-mer oligonucleotide (composed of T and 5-methyl C) at submicromolar concentrations formed a triplex with its target duplex at pH 7.5 and 37 degrees C. Association of the 30-mer oligomer with the duplex was slow, with complete association requiring about 1 h. At 37 degrees C, a 21-mer oligomer bound weakly to the target duplex but both a 25-mer and the 30-mer readily formed a triplex. This relationship of triplex formation with length was temperature dependent, as at 25 degrees C the 21-mer behaved similarly to the longer oligomers. Increasing spermine concentrations (from 0.2 to 1 mM) increased the amount of triplex formed. Spermine may be important only for the association of the oligomer to the duplex, since decreasing the spermine concentration after the triplex formed did not reduce the amount of triplex detected. At 1 mM spermine, formation of the triple-helical complex was very dependent on the concentration of KCl; increasing the KCl from 50 to 100 mM prevented triplex formation. However, the inhibitory effect of KCl could be abrogated by raising the spermine concentration to 2 mM. Our observations indicate that a triple helix can form under physiologic conditions but its formation is affected by several competing interactions.

Anti-Sc1 in pregnancy

Anti-Sc1 was detected in a gravida-2 patient at 12 weeks' gestation. At 29 weeks, the antibody was found to be of the IgG3 subclass with a titer of 16, score 36, by the indirect antiglobulin test, and it produced 7 percent lysis by antibody-dependent cellular cytotoxicity (ADCC) assay, a finding that suggested an unaffected fetus. The titer remained constant throughout the pregnancy, as did the IgG subclass and activity in the ADCC assay. At delivery of the full-term infant, the cord hemoglobin was 13.5 g per dL and the direct antiglobulin test was positive (3+) with anti-IgG. The infant did not require transfusion. A sample taken 9 weeks after delivery showed 44 percent lysis in the ADCC assay. The anti-Sc1 titer was 32, score 65.

Compliance with breast cancer screening achieved by the Aylesbury Vale mobile service (1984-1988)

The uptake of breast cancer screening in women aged 45-64 years, living in Aylesbury Vale district, was determined between 1984 and 1988. During this period, self-referral gave way to invitation as the method of gaining access to the service. In the initial period of open access the estimated uptake was 27.9 per cent. A pilot study of response to invitation (and reminder) in two general practices resulted in a compliance of 80.6 per cent. Extended to 20 general practices in Aylesbury Vale, overall compliance with invitation was 73.7 per cent. The response amongst previously screened volunteers was higher (91.5 per cent) than amongst unscreened women (67.6 per cent). There was no significant trend in compliance with age although the oldest women had the lowest uptake. Second round compliance in the two pilot practices reduced to 77 per cent, with 86.1 per cent of a cohort of screened women responding to a second offer of screening. The implications of these results for the national breast cancer screening programme are discussed together with the difficulties associated with the routine derivation of uptake. It is concluded that not only must the accuracy of population registers be improved, but also standard definitions of uptake measurements should be agreed and adopted.