Complex systems and the technology of variability analysis

Characteristic patterns of variation over time, namely rhythms, represent a defining feature of complex systems, one that is synonymous with life. Despite the intrinsic dynamic, interdependent and nonlinear relationships of their parts, complex biological systems exhibit robust systemic stability. Applied to critical care, it is the systemic properties of the host response to a physiological insult that manifest as health or illness and determine outcome in our patients. Variability analysis provides a novel technology with which to evaluate the overall properties of a complex system. This review highlights the means by which we scientifically measure variation, including analyses of overall variation (time domain analysis, frequency distribution, spectral power), frequency contribution (spectral analysis), scale invariant (fractal) behaviour (detrended fluctuation and power law analysis) and regularity (approximate and multiscale entropy). Each technique is presented with a definition, interpretation, clinical application, advantages, limitations and summary of its calculation. The ubiquitous association between altered variability and illness is highlighted, followed by an analysis of how variability analysis may significantly improve prognostication of severity of illness and guide therapeutic intervention in critically ill patients

Influência da cafeína na resposta pressórica ao exercício aeróbio em sujeitos hipertensos Caffeine influence on blood pressure response to aerobic exercise in hypertensive subjects

A redução da pressão arterial (PA) promovida pelo exercício físico é evidente segundo a literatura atual. Mecanismos neuro-humorais explicam essa resposta hipotensora, em que a diminuição da atividade simpática apresenta-se como um dos principais mecanismos. Porém, a ingestão de alimentos ricos em cafeína (CA) pode suprimir esta atenuação simpática. O objetivo desse estudo foi elucidar o impacto da ingestão de CA na resposta pressórica ao exercício em pessoas hipertensas. Sete hipertensos (52,3 ± 3,3 anos), sendo cinco mulheres, realizaram duas sessões de caminhada com 40 minutos de duração, em dois dias de treinamento, tendo previamente ingerido CA (4mg/kg de peso corporal) ou placebo (PL). A PA e a frequência cardíaca foram verificadas anteriormente a ingestão, após 15, 30, 45, 60 minutos da ingestão em estado de repouso e com 10, 20 e 30 minutos após o exercício. Os dados foram tratados por meio de estatística descritiva, e pelo teste não paramétrico de Wilcoxon (p < 0,05). A média da PA aumentou de 124,9/80,9mmHg antes da ingestão de CA para 129,4/84,3mmHg 60 minutos após, ainda no repouso (p < 0,05). Trinta minutos após o exercício observou-se resposta hipotensora no procedimento PL (queda da PA de 122,6/79,4mmHg para 115,7/78,6mmHg), enquanto que no procedimento com CA, a PA mostrou-se significativamente mais alta em relação aos valores de repouso (aumento de 124,9/80,9mmHg para 136,9/90,9mmHg, p < 0,05). Conclui-se que a ingestão de CA não só suprime a resposta hipotensora do exercício, como provoca uma hipertensão pós-exercício.<br>Blood pressure reduction (BP) promoted by physical exercise is evident according to the current literature. Neurohumoral mechanisms explain this hypotensive response, in which decrease of the sympathetic activity appears as one of its main mechanisms. However, the ingestion of caffeine-rich food (CA) can suppress this sympathetic attenuation. The objective of this study was to elucidate the impact of CA ingestion in BP after exercise, in hypertensive individuals. Seven hypertensive subjects (52.3 +/-3.3 years), being 5 women, accomplished two walk sessions with 40 minutes of duration, in two days of training, having previously ingested CA (4 mg/kg of body weight) or placebo (PL). BP and heart rate were verified previously to the ingestion, after 15, 30, 45, 60 minutes of the ingestion, at rest and with 10, 20 and 30 minutes after exercise. Data were treated through descriptive statistics and by the non-parametric Wilcoxon test (p<0.05). BP mean increased from 124.9/80.9 mmHg before ingestion to 129.4/84.3 mmHg 60 minutes later (p< 0.05). In the recovery period, after 30 minutes of exercise, hypotensive answer was observed in the PL procedure (decrease of 122.6/79.4 mmHg to 115.7/78.6 mmHg), while in the procedure with CA, BP was significantly higher than at rest (increase of 124.9/80.9 mmHg to 136.9/90.9 mmHg, p<0.05). It was concluded that CA not only suppresses the hypotensive response to exercise, but also provokes post-exercise hypertension