Osmoregulatory bicarbonate secretion exploits H(+)-sensitive haemoglobins to autoregulate intestinal O2 delivery in euryhaline teleosts.

Marine teleost fish secrete bicarbonate (HCO3 (-)) into the intestine to aid osmoregulation and limit Ca(2+) uptake by carbonate precipitation. Intestinal HCO3 (-) secretion is associated with an equimolar transport of protons (H(+)) into the blood, both being proportional to environmental salinity. We hypothesized that the H(+)-sensitive haemoglobin (Hb) system of seawater teleosts could be exploited via the Bohr and/or Root effects (reduced Hb-O2 affinity and/or capacity with decreasing pH) to improve O2 delivery to intestinal cells during high metabolic demand associated with osmoregulation. To test this, we characterized H(+) equilibria and gas exchange properties of European flounder (Platichthys flesus) haemoglobin and constructed a model incorporating these values, intestinal blood flow rates and arterial-venous acidification at three different environmental salinities (33, 60 and 90). The model suggested red blood cell pH (pHi) during passage through intestinal capillaries could be reduced by 0.14-0.33 units (depending on external salinity) which is sufficient to activate the Bohr effect (Bohr coefficient of -0.63), and perhaps even the Root effect, and enhance tissue O2 delivery by up to 42 % without changing blood flow. In vivo measurements of intestinal venous blood pH were not possible in flounder but were in seawater-acclimated rainbow trout which confirmed a blood acidification of no less than 0.2 units (equivalent to -0.12 for pHi). When using trout-specific values for the model variables, predicted values were consistent with measured in vivo values, further supporting the model. Thus this system is an elegant example of autoregulation: as the need for costly osmoregulatory processes (including HCO3 (-) secretion) increases at higher environmental salinity, so does the enhancement of O2 delivery to the intestine via a localized acidosis and the Bohr (and possibly Root) effect.

[Postoperative mortality in infective endocarditis: determinant factors]. / Fatores determinantes da letalidade após cirurgia para endocardite infecciosa.

The factors leading to high postoperative mortality in active infectious endocarditis (IE) are poorly defined. We studied patients operated at an University Hospital between March 1978 and April 1992. We hypothesized that the summation of potential adverse factors would strongly increase mortality after surgery. We studied 39 patients (28 men), age range 13-70 years (mean +/- SD = 32 +/- 16) operated during active IE (time from onset 52 +/- 48 days). Predisposing factor: rheumatic valvar disease in 14 cases, intravenous drug use in 5. Affected valves: aortic in 14, mitral in 10, tricuspid in 8, multiple structures in 7. In most cases, S aureus (12) or Streptococcus sp (10) was isolated in blood cultures. Surgery was indicated in most patients because of heart failure (30), multiple embolic complications (17) or treatment failure (14). The possible adverse influence of specific demographic characteristics, clinical features and surgical variables was assessed by the Student t test or the chi 2 test. Also, multiple regression analysis was performed in order to identify independent adverse factors for increased mortality. Positive correlations were further investigated with the chi 2 test to assess whether an increasing number of adverse factors could identify a special subset of patients with markedly elevated death risk. Fourteen patients (36%) died after surgery. Emergency surgery (p = 0.001), the presence of coma 6 hours after surgery (p = 0.0015) and S. aureus infection (p = 0.023) were all associated with increased mortality. The presence of neurological complications was correlated with a high mortality (54% vs. 27%). However this increase was of dubious statistical significance (p = 0.097). Multiple regression analysis confirmed S. aureus and emergency surgery as independent adverse factors for increased mortality. When put together, an increasing number of adverse factors was highly predictive of a fatal outcome, even after exclusion of that evaluated after surgery (level of consciousness). Patients with two or three adverse factors had a very high mortality rate (> 76.9%). Mortality following surgery for active IE is increased in patients operated on an emergency basis especially if the infection is caused by S. aureus. The presence of neurological complications may also be associated with worse outcome. Early consideration of surgery should reduce the high mortality in patients with active IE.

Alterações da ultra-estrutura miocárdica durante cirurgia cardíaca / Ultrastructural changes of the myocardium during cardiac surgery

Os autores fazem uma revisao da ultra-estrutura miocardica normal e alterada por isquemia cardiaca e circulacao extracorporea, analisando a quantificacao das alteracoes encontradas. Admiten que o estudo da ultra-estrutura miocardica e um bom metodo para estudar a protecao miocardica durante cirurgia cardiaca

Proteção miocárdica por cardiologia sanguínea durante circulação extracorpórea. Avaliação ultra-estrutural miocárdica no cão / Myocardial protection by blood cardioplegia during extracorporeal circulation. Ultrastructural myocardial evaluation in the dog

Os autores desenvolveram metodo simplificado para infusao de cardioplegia sanguinea durante circulacao extracorporea. Fizeram estudo experimental, em caes, para averiguar a eficiencia do metodo. Dois grupos de 5 caes foram submetidos a 60 min de esquemia cardiaca, seguidos de 60 min de reperfusao coronaria. A protecao miocardica, durante isquemia cardiaca, foi obtida com o metodo de cardioplegia sanguinea no grupo I e com cardioplegia acelular gelada no grupo II. Para comparar os dois metodos empregados, foram feitas quatro biopsias de ventriculo esquerdo, para estudo ultra-estrutural: antes da isquemia cardiaca; ao fim de 60 min de isquemia cardiaca; com 30 mim de reperfusao coronaria e com 60 min de reperfusao coronaria.Nas tres primeiras biopsias houve apenas alteracoes ultra-estruturais miocardicas discretas, sem diferencas entre os dois grupos. Nas ultimas, as alteracoes ultraestruturais foram mais severas no grupo II do que no grupo I. Conclui-se que o metodo de protecao miocardica com cardioplegia sanguinea e eficaz para 60 min de isquemia cardiaca, sendo inclusive superior a cardioplegia acelular gelada

Veia axilar - acesso alternativo do implante de marca-passo definitivo. / Axillary vein - alternative access in definitive pacemaker implantation

Os autores apresentam sua experiencia em pacientes portadores de alteracoes do ritmo cardiaco, que necessitaram de marca-passo definitivo, nos quais, por impossibilidade do uso da veia cefalica como acesso eletivo, utilizaram a veia axilar como alternativa. Comentam detalhes da tecnica e analisam o acompanhamento clinico destes pacientes, com 4 a 24 meses de evolucao

Isquemia medular por deprivacao sanguinea temporaria - estudo experimental em caes. / Spinal cord ischemia following temporary blood flow oclusion - experimental study in dogs

Os autores apresentam estudo experimental em caes, em que procuram demonstrar o papel do tempo de pincamento aortico no aparecimento da lesao medular. Estudam tambem a possibilidade de lesao, quando o suprimento sanguineo ofertado a medula ocorre em regime de hipotensao arterial