Weak latitudinal trends in reproductive traits of Afromontane forest trees.

BACKGROUND AND AIMS: Is the increase in species diversity patterns towards lower latitudes, linked to reproductive traits? Plant reproductive organs influence reproductive isolation and hence species divergence. Abiotic differences between temperate and tropical regions can also directly impact on plant reproductive traits. Here we provide a novel overview of southern hemisphere, Afromontane forest tree taxonomical patterns and ask whether reproductive traits relate to latitude, while accounting for environmental (tree height) and evolutionary (biogeographical affinity) selective forces. METHODS: We compiled a novel dataset with a) flower colour, size and pollination syndrome and b) fruit colour, size and dispersal syndrome for 331 tree species found in six Afromontane forest regions. We categorised each species into latitudinal distribution using these six regions, spanning the southern Cape (34º S) to Mount Kenya (0º S). Additionally, we gathered maximum tree height (m) for each species and determined the global distribution of all 196 tree genera (Afrotropical, Palaeotropical or Pantropical). KEY RESULTS: Species, genera and families showed a general decrease in richness away from tropical and subtropical forests towards warm temperate forests. Southern Afrotemperate forests (the furthest south) had the highest tree endemism. There was no relationship between latitude and the reproductive traits tested here. Biogeographical affinity related to fruit colour and dispersal syndrome, with palaeotropical genera showing relative increases in black-purple fruit colour compared to pantropical genera and palaeotropical genera showing relative increases in biotic seed dispersal compared to Afrotropical genera, which showed higher relative abiotic seed dispersal. Taller trees had a higher chance to be wind or insect pollinated (compared to bird pollinated) and had larger fruits. CONCLUSIONS: Latitude explained patterns in Afromontane tree taxonomical diversity, however tree reproductive traits did not relate to latitude. We suggest that phylogenetic conservatism or convergence, or both, explain the reported patterns.

The Pathophysiology of Myocardial Ischemia and Perioperative Myocardial Infarction.

Ischemic heart disease, the leading cause of death worldwide, may result in devastating perioperative ischemia and infarction. The underlying pathophysiology, precipitating factors, and approach to prevention differ between patients presenting for noncardiac surgery, developing acute coronary syndrome versus stable angina. The first half of this article reviews the pathophysiology of acute coronary syndrome and stable angina. Acute coronary syndrome, otherwise known as Type 1 myocardial infarction, includes unstable angina, non-ST segment elevated myocardial infarction and ST segment elevated myocardial infarction. Acute coronary syndrome occurs as a result of vulnerable plaque rupture with subsequent varying degrees of thrombus formation, arterial spasm, and thus coronary occlusion. Stable angina, on the other hand, results from a myocardial oxygen delivery and demand mismatch in the setting of fixed coronary stenosis. After this discussion, the review article considers how both apply to perioperative myocardial infarctions and myocardial injury after noncardiac surgery. This article furthermore argues why myocardial oxygen delivery demand mismatch (Type 2) myocardial infarction is the most likely underlying pathophysiology responsible for perioperative myocardial infarctions. Being aware of this and knowledgeable about Type 2 infarctions may enable anesthetic providers to better predict the majority of triggers contributing to, and thus decreasing the incidence of, perioperative myocardial infarctions.

A comparison between point-of-care testing and venous glucose determination for the diagnosis of diabetes mellitus 6-12 weeks after gestational diabetes.

AIM: To evaluate point-of-care-testing (POCT) for the diagnosis of Type 2 diabetes mellitus 6-12 weeks post-partum in women with gestational diabetes (GDM). METHODS: Post-partum glucose assessment (75-mg oral glucose tolerance test, OGTT) was performed prospectively in 122 women with GDM (1 November 2015 to 1 November 2017) at Tygerberg Hospital, Cape Town, South Africa. Individuals with known pre-existing diabetes were excluded. The accuracy and clinical utility of POCT (capillary finger-prick) were compared with laboratory plasma glucose (hexokinase and glucokinase methods). The OGTT consisted of two time points (fasting and 2 h) during which concurrent glucose samples (POCT and laboratory) were obtained. Bland-Altman plots and paired analysis were used to assess the analytical accuracy of POCT, whereas its diagnostic performance was determined using positive and negative predictive values to calculate specificity and sensitivity. RESULTS: Spearman's ranked correlation analysis indicated a strong association between POCT and laboratory glucose values at both OGTT time points (fasting, r = 0.95, P < 0.0001; 2 h, r = 0.88, P < 0.0001). Thirty-six women were diagnosed with Type 2 diabetes based on gold standard laboratory glucose levels (fasting > 7 mmol/l; 2 h > 11.1 mmol/l). POCT correctly identified Type 2 diabetes in 78% of women (28 of 36) with a positive predictive value of 89.3% and a negative predictive value of 96.7% at the fasting time point. The sensitivity and specificity of POCT to diagnose Type 2 diabetes were 89% (fasting), 85.7% (2 h) and 96.7% (fasting), 98.5% (2 h) respectively. POCT proved less sensitive to diagnose pre-diabetes (69%) but displayed satisfactory specificity (92%) at both time points assessed. CONCLUSION: POCT accurately identifies women with Type 2 diabetes 6-12 weeks after GDM.

Steroid Prophylaxis: The knowledge and practices of New Zealand General Dental Practitioners.

OBJECTIVE: To describe the knowledge and practices of New Zealand (NZ) General Dental Practitioners (GDPs) concerning the use of steroid prophylaxis. METHODS: An online survey was conducted in 2013 involving a sample of 500 NZ GDPs who met inclusion criteria and had email addresses on the Dental Council register. RESULTS: A total of 214 dentists responded, giving a 44.5% response rate after accounting for undelivered questionnaires. Nearly two-thirds (61 .7%) did not currently recommend corticosteroid prophylaxis, although nearly three-quarters (74.8%) believed that dental treatment posed a potential risk to patients with adrenal suppression. Over half (53.4%) believed that oral corticosteroids could cause adrenocortical suppression, and a similar proportion (58.3%) believed that a specific dose of oral prednisolone of 7.5 mg per day could do so. Most practitioners (79.6%) supported the formulation of steroid prophylaxis guidelines. CONCLUSION: Despite most NZ GDPs believing the dental setting to pose a risk of adrenal crisis for patients taking corticosteroids, there is some confusion among dentists identifying at-risk patients and their ability to manage if such an event was to occur in their practices. There is further confusion over whether steroid prophylaxis is warranted for perceived at-risk patients, and which regime to follow when it is. There is an associated tendency to be over-cautious when determining the need for steroid prophylaxis, and to rely on their undergraduate steroid prophylaxis guidelines when doing so. There is a need for evidence-based guidelines to be formulated by an expert panel.

Retroperitoneoscopic adrenalectomy - introducing a new surgical technique in South Africa.

BACKGROUND: Posterior retroperitoneoscopic adrenalectomy (PRA) is purported to be superior to the laparoscopic transperitoneal approach (LA) in patients with a select spectrum of benign adrenal pathologies. Advantages attributed to the technique include minimal blood loss, shortened operative times, and decreased postoperative pain, explained anatomically by the direct access to the adrenal gland. Reduced workspace is a limitation. METHODS: A retrospective review of 22 consecutive PRAs performed in a single centre between 1 September 2016 and 30 October 2020 is presented. Two experienced laparoscopic surgeons operated on all patients after acquiring the technique at international centres. Suitable candidates were carefully pre-selected. Non-benign pathology, high vascularity, body mass index (BMI) ≥ 45 kg/m2 and anatomical concerns on prior computed tomography (CT) imaging were exclusion criteria. RESULTS: Twenty-two PRAs were performed for a spectrum of benign adrenal pathologies. Twenty-one surgeries (95%) were completed. A single case of pheochromocytoma required conversion. The procedure was safe, a minor postoperative complication (pneumaturia) occurred in one case, and the mortality rate was 0%. Median operative time (80 minutes) is comparable to other reported series in the literature, with a modest linear descending tendency noted over the study period. Underlying pathology influenced operative times. Pheochromocytomas proved to be most challenging and required careful preoperative evaluation. CONCLUSION: The PRA procedures performed at Tygerberg Academic Hospital were safe and reproducible in a select group of cases with benign adrenal pathology. Endocrine surgeons proficient with laparoscopic techniques should be encouraged to use the PRA approach when encountering adrenal neoplasms that fit the criteria.

Flower orientation and corolla length as reproductive barriers in the pollinator-driven divergence of Erica shannonea and Erica ampullacea.

A variety of reproductive barriers can enable reproductive isolation and stable coexistence of plant species. Differing floral traits might play an important role in reproductive isolation imposed by pollinators. Such shifts in pollinator use have been hypothesized to contribute to the radiation of Erica (Ericaceae) in the Cape Floristic Region, South Africa. The sister species Erica shannonea and Erica ampullacea co-occur and overlap in flowering phenology. Both have unscented long-tubed flowers consistent with adaptations for pollination by long-proboscid flies (LPFs), but differences in flower orientation and corolla tube length are indicative of a shift in pollinator species. We conducted controlled pollination experiments and pollinator observations to determine the breeding system and pollinators of the two species. Both species are self-incompatible and require pollinator visits for seed production, suggesting that pollinators could strongly influence flower evolution. The horizontally orientated flowers of E. shannonea were found to be pollinated by Philoliche rostrata (Tabanidae), which has a long, fixed forward-pointing proboscis, while the vertically upright orientated flowers of E. ampullacea were found to be pollinated by Prosoeca westermanni (Nemestrinidae), which has a shorter proboscis that can swivel downwards. The nemestrinid fly's proboscis is too short to access the nectar in the relative long-tubed flowers of E. shannonea and the tabanid fly's proboscis cannot swivel down to access the upright flowers of E. ampullacea. Consequently, these traits are likely to act as reproductive barriers between the two Erica species and thereby might have contributed to speciation and enable stable coexistence.

Floral colour variation of Nicotiana glauca in native and non-native ranges: Testing the role of pollinators' perception and abiotic factors.

Invasive plants displaying disparate pollination environments and abiotic conditions in native and non-native ranges provide ideal systems to test the role of different ecological factors driving flower colour variation. We quantified corolla reflectance of the ornithophilous South American Nicotiana glauca in native populations, where plants are pollinated by hummingbirds, and in populations from two invaded regions: South Africa, where plants are pollinated by sunbirds, and the Balearic island of Mallorca, where plants reproduce by selfing. Using visual modelling we examined how corolla reflectance could be perceived by floral visitors present in each region. Through Mantel tests we assessed a possible association between flower colour and different abiotic factors. Corolla reflectance variation (mainly along medium to long wavelengths, i.e. human green-yellow to red colours) was greater among studied regions than within them. Flower colour was more similar between South America and South Africa, which share birds as pollinators. Within invaded regions, corolla reflectance variation was lower in South Africa, where populations could not be distinguished from each other by sunbirds, than in Spain, where populations could be distinguished from each other by their occasional visitors. Differences in corolla colour among populations were partially associated with differences in temperature. Our findings suggest that shifts in flower colour of N. glauca across native and invaded ranges could be shaped by changes in both pollination environment and climatic factors. This is the first study on plant invasions considering visual perception of different pollinators and abiotic drivers of flower colour variation.

Evaluation of competency-driven training for facilitators delivering a psychological intervention for children in Lebanon: a proof-of-concept study.

AIMS: The mounting evidence for effective delivery of psychological interventions by non-specialists in low- and middle-income settings has led to a rapid expansion of mental health and psychosocial support trainings globally. As such, there is a demand for strategies on how to train and implement these services to attain adequate quality. This study aims to evaluate the added value of a competency-driven approach to training of facilitators for a group intervention for children with severe emotional distress in Lebanon. METHODS: In a controlled before and after study, 24 trainees were randomly allocated to participate in either a competency-driven training (CDT) or training-as-usual (TAU) (1 : 1) for a psychological intervention for children with severe emotional distress. We assessed the change in demonstrated competencies, using standardised role-plays, before and after the training. Measures included the 13-item Working with children-Assessment of Competencies Tool (WeACT), the 15-item ENhancing Assessment of Common Therapeutic factors (ENACT) and the 6-item Group facilitation: Assessment of Competencies Tool (GroupACT). The trainer in the experimental arm used pre-training and during training competency assessment scores to make real-time adjustment to training delivery. Due to COVID-19 pandemic restrictions, all activities were done remotely. RESULTS: CDT resulted in significantly better outcomes on increasing competencies on the WeACT (repeated measures analysis of variance; F(1, 22) = 6.49, p < 0.018) and on the GroupACT (Mann-Whitney U = 22, p < 0.003), though not statistically significant on the ENACT. There is no significant between-group difference on the reduction of harmful behaviours, mainly because both forms of training appear equally successful in eliminating such behaviours. CONCLUSIONS: This proof-of-concept study demonstrates the potential of CDT, using standardised assessment of trainee competencies, to contribute to better training outcomes without extending the duration of training. CDT can result in up to 18% greater increase in adequate competency, when compared to TAU. The study also yields recommendations for further enhancing the benefits of competency-driven strategies. A fully powered trial is needed to confirm these findings.

Assessment of service provider competency for child and adolescent psychological treatments and psychosocial services in global mental health: evaluation of feasibility and reliability of the WeACT tool in Gaza, Palestine.

BACKGROUND: There is a scarcity of evaluated tools to assess whether non-specialist providers achieve minimum levels of competency to effectively and safely deliver psychological interventions in low- and middle-income countries. The objective of this study was to evaluate the reliability and utility of the newly developed Working with children - Assessment of Competencies Tool (WeACT) to assess service providers' competencies in Gaza, Palestine. METHODS: The study evaluated; (1) psychometric properties of the WeACT based on observed role-plays by trainers/supervisors (N = 8); (2) sensitivity to change among service provider competencies (N = 25) using pre-and-post training WeACT scores on standardized role-plays; (3) in-service competencies among experienced service providers (N = 64) using standardized role-plays. RESULTS: We demonstrated moderate interrater reliability [intraclass correlation coefficient, single measures, ICC = 0.68 (95% CI 0.48-0.86)] after practice, with high internal consistency (α = 0.94). WeACT assessments provided clinically relevant information on achieved levels of competencies (55% of the competencies were scored as adequate pre-training; 71% post-training; 62% in-service). Pre-post training assessment saw significant improvement in competencies (W = -3.64; p < 0.001). CONCLUSION: This study demonstrated positive results on the reliability and utility of the WeACT, with sufficient inter-rater agreement, excellent internal consistency, sensitivity to assess change, and providing insight needs for remedial training. The WeACT holds promise as a tool for monitoring quality of care when implementing evidence-based care at scale.

An audit of thyroid function testing in acutely ill patients at a South African academic hospital.

Background: Non-thyroidal illness syndrome (NTIS) can be defined as the presence of abnormal thyroid function in the absence of primary thyroid dysfunction and is associated with acute illness. Thyroid function testing is generally not advised in the critically ill patient. Thyroid-stimulating hormone (TSH) measurement is the preferred screening test for thyroid disease, but results may be misleading and variable in the setting of critical illness. Objectives: To describe the pattern of requests for TSH testing in patients admitted to the emergency department and intensive care units at Tygerberg Hospital, Cape Town, South Africa. Methods: A retrospective, descriptive (observational) study was conducted over a 6-month period to determine the number of requests for TSH testing received for patients admitted to the emergency department and intensive care units. Results: A total of 1 139 requests for TSH testing were received from the emergency department and intensive care units, of which 166 were excluded. Of the 973 requests evaluated, 14% yielded abnormal results. The majority (79.4%) of the abnormal TSH results were most likely attributed to NTIS. Follow-up TSH results after 6 - 8 weeks were available in only 18% of cases with abnormal TSH levels at initial presentation. Conclusion: We found that TSH testing was often requested in critically ill patients, but that most results were either normal or indicative of NTIS. Follow-up testing of abnormal TSH results was rarely performed. We recommend continued education of junior clinicians regarding thyroid function testing in critically ill patients. Contributions of the study: This study describes the requesting pattern for TSH tests in patients admitted to the emergency department and intensive care unit at Tygerberg Hospital, South Africa. The findings emphasise the importance of prudent thyroid function testing in critically ill patients and follow-up in suspected cases of non-thyroidal illness syndrome.

Diabetes mellitus and COVID-19: A review and management guidance for South Africa.

This article reviews the association between diabetes mellitus (DM) and COVID-19. We report on the convergence of infectious diseases such as coronavirus infections and non-communicable diseases including DM. The mechanisms for the interaction between COVID-19 and DM are explored, and suggestions for the management of DM in patients with COVID-19 in South Africa are offered.

Pulmonary artery compliance: its role in right ventricular-arterial coupling.

OBJECTIVE: The aim was to investigate the ventricular/vascular coupling of the intact right heart under conditions of normal operation and acute pulmonary hypertension. METHODS: Right ventricular contractility was obtained by calculating the end systolic pressure-volume relationship (Ees) and the effective pulmonary arterial elastance (Ea), applying the Windkessel parameters of the pulmonary arterial input impedance. Coupling between the ventricle and its load could be determined in terms of Ees and Ea. Acute pulmonary hypertension was induced by injecting glass microspheres into the pulmonary vascular bed until a mean pulmonary arterial pressure of more than 35 mm Hg had been reached. Experimental subjects were Landras/Large white pigs (n = 11), studied under general anaesthesia. Ees was obtained by normalising the right ventricle pressure-diameter equivalent of Ees to stroke volume. The lumped element parameters of the Windkessel analogue were calculated from the pulmonary artery pressure and blood flow. Stroke work was calculated from the pressure-volume loop and oxygen consumption derived from the pressure-volume area. Efficiency was taken to be the ratio between stroke work and oxygen consumption. RESULTS: Ea increased significantly as mean pulmonary artery pressure rose, while Ees remained linear and constant. Stroke work, as well as efficiency, increased, with the maximum of the stroke work curve lying to the right of the efficiency maximum. At the control step (before pulmonary artery hypertension), Ees = 1.71 Ea (n = 11). CONCLUSIONS: Under control conditions, the right ventricle operates at maximum efficiency and submaximal work output. Compliance of the pulmonary artery is a significant factor in decoupling the right ventricle from its vascular load. As the compliance decreases with acute pulmonary hypertension, the maximum stroke work against load point shifted in such a manner that the right ventricle changed its operational status from a flow to a pressure pump, resulting in a decreased stroke volume.

The effect of prostaglandin E1 on acute pulmonary artery hypertension during oleic acid-induced respiratory dysfunction.

This study examined the general effect of intravenous PGE1 on RV Ees and effective PA elastance (EA) during acute pulmonary hypertension associated with oleic acid infusion. In eight pigs, RV end-systolic elastance was quantified with the Ees and Ea was defined with reference to the Windkessel model. Oleic acid infusion increased mean PAP and Ea. Prostaglandin E1 reduced PAP and decreased Ea. Ees did not change throughout the study. Mean arterial pressure was reduced and the pulmonary shunt was increased after PGE1 infusion. The PaO2 was reduced. Data from this study suggest that although PGE1 is effective in reducing PAP, it is not as effective in reducing RV afterload. Furthermore, PGE1 does have significant side effects such as reduction of systemic arterial pressure and an increase in pulmonary shunt.

Effect of oxygenated crystalloid cardioplegia on the functional and metabolic recovery of the isolated perfused rat heart.

The use of an oxygenated crystalloid cardioplegic solution to improve myocardial preservation during elective cardiac arrest was evaluated with the isolated perfused rat heart used as a model. Experiments were conducted at 4 degrees C and 20 degrees C. The oxygen tension of the nonoxygenated and oxygenated cardioplegic solutions averaged 117 and 440 mm Hg, respectively. At 4 degrees C, the adenosine triphosphate content of hearts subjected to 120 minutes of oxygenated cardioplegia was significantly higher than that of the nonoxygenated cardioplegia group. However, functional recovery during reperfusion was similar for both groups. At 20 degrees C, the myocardial adenosine triphosphate concentration decreased at a significantly faster rate during ischemia in the group receiving nonoxygenated cardioplegia compared with the oxygenated cardioplegia group. Hearts subjected to 180 minutes of ischemia with oxygenated cardioplegia had a normal ultrastructural appearance whereas hearts subjected to 120 minutes of nonoxygenated cardioplegia showed severe ischemic damage. Myocardial functional recovery in the group receiving oxygenated cardioplegia exceeded that of the group receiving nonoxygenated cardioplegia. The use of myocardial adenosine triphosphate concentration at the end of the ischemic period to predict subsequent cardiac output, peak systolic pressure, and total myocardial work showed significant positive correlations.

Oxygen requirements of the isolated rat heart during hypothermic cardioplegia. Effect of oxygenation on metabolic and functional recovery after five hours of arrest.

Previous studies from this laboratory demonstrated that the use of an oxygenated cardioplegic solution in the hypothermic arrested rat heart resulted in improved preservation of high-energy phosphate stores (adenosine triphosphate and creatine phosphate), mechanical recovery during reperfusion, and preservation of myocardial ultrastructure. In the current study the effect of cardioplegic solutions oxygenated with 30%, 60%, and 95% oxygen was evaluated in the isolated rat heart with reference to the maintenance of adenosine triphosphate, creatine phosphate, oxygen consumption, functional recovery, and mitochondrial oxidative phosphorylation in vitro. Results indicate that the hearts receiving cardioplegic solutions supplemented with 95% oxygen and 5% carbon dioxide maintained adenosine triphosphate and creatine phosphate at control values for at least 5 hours. The oxygen consumption during elective cardiac arrest, mechanical performance during reperfusion, and in vitro mitochondrial oxygen uptake and phosphorylation rate were highest in the hearts receiving cardioplegic solutions supplemented with 95% oxygen when compared to solutions with 30% and 60% oxygen. Addition of glucose and insulin to the cardioplegic solution (95% oxygen) increased the adenosine triphosphate levels but failed to improve function after reperfusion. Although myocardial adenosine triphosphate and creatine phosphate were well preserved by the oxygenated cardioplegic solution, there was a discrepancy between the adenosine triphosphate levels at the end of the arrest period, which represents the potential for mechanical function, and the actual function of the hearts after 5 hours.

Oxygenation of cardioplegic solutions: a note of caution.

The merits of oxygenated crystalloid cardioplegic solutions have been well established in experimental animals. The positive effects of oxygenation of Plasmalyte B (Sabax Ltd) and St. Thomas Hospital solution (Plegisol) were achieved by gassing with 95% O2/5% CO2 and 100% O2, respectively. In view of the marked pH differences induced by these gas mixtures, we evaluated the effect of mode of oxygenation on myocardial recovery during reperfusion after hypothermic cardioplegic arrest. Oxygenation with 100% O2 of Plasmalyte B containing high K+ levels caused marked deterioration in myocardial recovery, whereas the mode of oxygenation did not affect recovery after arrest with St. Thomas Hospital solution. Because the major differences between these solutions reside in their respective K+, Mg2+, and HCO3- contents, the effects of variations in the levels of these ions were investigated. The results showed that oxygenation with 100% O2 was deleterious only in the presence of high K+ (29 mmol/L), low Mg2+ (3 mmol/L), and high NaHCO3 (28 mmol/L) levels. The marked decline in mechanical recovery during reperfusion was associated with significant changes in myocardial adenosine triphosphate and intracellular Ca2+ levels. Although an explanation for these findings is not readily available, it is suggested that complex ionic interactions and possibly oxygen free radical generation may lead to intracellular Ca2+ overload, depression in mitochondrial adenosine triphosphate generation, and, hence, deterioration in mechanical recovery.

Preservation of myocardial function and biochemistry after blood and oxygenated crystalloid cardioplegia during cardiac arrest.

We compared the ability of blood cardioplegia and oxygenated crystalloid cardioplegic solutions to maintain regional left ventricle contractility and adenosine triphosphate levels after cardiopulmonary bypass. Ten baboons were subjected to 90-minute cardiopulmonary bypass conducted at 28 degrees C. Hemodynamic measurements were made before and after the bypass procedure, and biopsies for high-energy phosphate determinations were performed at different time intervals during and after bypass. The results showed improved maintenance of myocardial contractility (measured with the regional end-systolic pressure-length relationship) with the oxygenated crystalloid solution. Expressed as a percentage of values before bypass, contractility after bypass averaged 81.69% +/- 4.81% and 80.47% +/- 10.05%, respectively, after 10 and 20 minutes using the oxygenated crystalloid cardioplegia. For blood cardioplegia, the corresponding values were 71.9% +/- 8.73% and 64.99% +/- 8.60% (mean +/- standard error of the mean). The 10- and 20-minute postbypass values between the two groups differed significantly (t test, Welch modification: p = 0.0464 and p = 0.0342). Myocardial adenosine triphosphate level was higher immediately after induction of cardiac arrest when blood cardioplegia was used (blood cardioplegia, 6.82 mol.g wet wt-1; crystalloid cardioplegia, 4.95 mol.g wet wt-1; p = 0.0314), but values subsequently equalized.

Effect of compliance on a time-domain estimate of the characteristic impedance of the pulmonary artery during acute pulmonary hypertension.

In 11 pigs under general endotracheal anaesthesia, the time-domain method of determining the pulmonary arterial input impedance was compared with the frequency-domain equivalent under normal conditions as well as acute pulmonary hypertension induced by glass microspheres. The time-domain methods of determining the pulmonary arterial compliance C and pulmonary vascular bed resistance Rp compared favourably with the frequency-domain equivalents (r = 0.774, n = 60, p < 0.001 and r = 0.906, n = 60, p < 0.001, respectively), even at mean pulmonary artery pressures (MPAP) of 35 mmHg and above. A consistent and ever-increasing difference between characteristic impedance Zo(omega), estimated by averaging input impedance modulus values over a selected frequency range, and its time domain equivalent Ro with increasing MPAP was shown to be the cause of the poor fit between the measured and remodelled pulmonary blood flow. By analysing a time-domain estimate of the pulmonary characteristic impedance Ro(C, Rp, t), it was demonstrated that the characteristic impedance was dependent on C. Ro is therefore not an accurate representation of the characteristic impedance, especially under conditions of acute pulmonary hypertension. Ro(C, Rp, t) should therefore be calculated instead.

The oxyhemoglobin dissociation curve before, during and after cardiac surgery.

The oxyhemoglobin dissociation curve was quantified in 15 patients subjected to hypothermic cardiopulmonary bypass under opiate-benzodiazepine anesthesia using the alpha-stat approach to control blood acid-base status. The P50 was calculated from a single measurement of oxygen tension and hemoglobin saturation in blood obtained from the pulmonary artery or the venous line from the cardiopulmonary bypass circuit. In addition, the P50 was directly determined at the registered patient temperature. The P50 decreased from 3.87(+/- 0.15) kPa (mean, SEM) before anesthesia to 1.55(+/- 0.16) kPa during hypothermic (25.43 +/- 1.99 degrees C) cardiopulmonary bypass (p less than 0.001). On rewarming, the P50 increased to 4.89 +/- 0.27 kPa (at 36.14 +/- 0.14 degrees C, p less than 0.001 compared to the preinduction and hypothermic values). Eight hours after cardiopulmonary bypass the P50 returned to the preinduction value (3.72 +/- 0.22 kPa). The relationship between temperature and P50 is described by the regression equation: P50 = 0.22(+/- 0.02).Temperature--3.78(+/- 0.62). The correlation was 0.78 (p less than 0.001). It is concluded that (1) the leftward shift of the oxyhemoglobin dissociation curve during hypothermia may be detrimental to oxygen delivery and (2) the oxygen saturation of the venous blood should not be used indiscriminately to evaluate cellular oxygen status.