Dynamic cerebral autoregulation is impaired during submaximal isometric handgrip in patients with heart failure.

The incidence of neurological complications, including stroke and cognitive dysfunction, is elevated in patients with heart failure (HF) with reduced ejection fraction. We hypothesized that the cerebrovascular response to isometric handgrip (iHG) is altered in patients with HF. Adults with HF and healthy volunteers were included. Cerebral blood velocity (CBV; transcranial Doppler, middle cerebral artery) and arterial blood pressure (BP; Finometer) were continuously recorded supine for 6 min, corresponding to 1 min of baseline and 3 min of iHG exercise, at 30% maximum voluntary contraction, followed by 2 min of recovery. The resistance-area product was calculated from the instantaneous BP-CBV relationship. Dynamic cerebral autoregulation (dCA) was assessed with the time-varying autoregulation index estimated from the CBV step response derived by an autoregressive moving-average time-domain model. Forty patients with HF and 23 BP-matched healthy volunteers were studied. Median left ventricular ejection fraction was 38.5% (interquartile range: 0.075%) in the HF group. Compared with control subjects, patients with HF exhibited lower time-varying autoregulation index during iHG, indicating impaired dCA ( P < 0.025). During iHG, there were steep rises in CBV, BP, and heart rate in control subjects but with different temporal patterns in HF, which, together with the temporal evolution of resistance-area product, confirmed the disturbance in dCA in HF. Patients with HF were more likely to have impaired dCA during iHG compared with age-matched control subjects. Our results also suggest an impairment of myogenic, neurogenic, and metabolic control mechanisms in HF. The relationship between impaired dCA and neurological complications in patients with HF during exercise deserves further investigation. NEW & NOTEWORTHY Our findings provide the first direct evidence that cerebral blood flow regulatory mechanisms can be affected in patients with heart failure during isometric handgrip exercise. As a consequence, eventual blood pressure modulations are buffered less efficiently and metabolic demands may not be met during common daily activities. These deficits in cerebral autoregulation are compounded by limitations of the systemic response to isometric exercise, suggesting that patients with heart failure may be at greater risk for cerebral events during exercise.

Cerebral hemodynamics with intra-aortic balloon pump: business as usual?

OBJECTIVE: Intra-aortic balloon pump (IABP) is commonly used as mechanical support after cardiac surgery or cardiac shock. Although its benefits for cardiac function have been well documented, its effects on cerebral circulation are still controversial. We hypothesized that transfer function analysis (TFA) and continuous estimates of dynamic cerebral autoregulation (CA) provide consistent results in the assessment of cerebral autoregulation in patients with IABP. APPROACH: Continuous recordings of blood pressure (BP, intra-arterial line), end-tidal CO2, heart rate and cerebral blood flow velocity (CBFV, transcranial Doppler) were obtained (i) 5 min with IABP ratio 1:3, (ii) 5 min, starting 1 min with the IABP-ON, and continuing for another 4 min without pump assistance (IABP-OFF). Autoregulation index (ARI) was estimated from the CBFV response to a step change in BP derived by TFA and as a function of time using an autoregressive moving-average model during removal of the device (ARI t ). Critical closing pressure and resistance area-product were also obtained. MAIN RESULTS: ARI with IABP-ON (4.3 ± 1.2) were not different from corresponding values at IABP-OFF (4.7 ± 1.4, p = 0.42). Removal of the balloon had no effect on ARI t , CBFV, BP, cerebral critical closing pressure or resistance area-product. SIGNIFICANCE: IABP does not disturb cerebral hemodynamics. TFA and continuous estimates of dynamic CA can be used to assess cerebral hemodynamics in patients with IABP. These findings have important implications for the design of studies of critically ill patients requiring the use of different invasive support devices.

Cerebral blood flow autoregulation in ischemic heart failure.

Patients with ischemic heart failure (iHF) have a high risk of neurological complications such as cognitive impairment and stroke. We hypothesized that iHF patients have a higher incidence of impaired dynamic cerebral autoregulation (dCA). Adult patients with iHF and healthy volunteers were included. Cerebral blood flow velocity (CBFV, transcranial Doppler, middle cerebral artery), end-tidal CO2 (capnography), and arterial blood pressure (Finometer) were continuously recorded supine for 5 min at rest. Autoregulation index (ARI) was estimated from the CBFV step response derived by transfer function analysis using standard template curves. Fifty-two iHF patients and 54 age-, gender-, and BP-matched healthy volunteers were studied. Echocardiogram ejection fraction was 40 (20-45) % in iHF group. iHF patients compared with control subjects had reduced end-tidal CO2 (34.1 ± 3.7 vs. 38.3 ± 4.0 mmHg, P < 0.001) and lower ARI values (5.1 ± 1.6 vs. 5.9 ± 1.0, P = 0.012). ARI <4, suggestive of impaired CA, was more common in iHF patients (28.8 vs. 7.4%, P = 0.004). These results confirm that iHF patients are more likely to have impaired dCA compared with age-matched controls. The relationship between impaired dCA and neurological complications in iHF patients deserves further investigation.

Unconstrained parameter estimation for assessment of dynamic cerebral autoregulation.

Measurement of dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow (CBF) to changes in arterial blood pressure (ABP), has been performed with an index of autoregulation (ARI), related to the parameters of a second-order differential equation model, namely gain (K), damping factor (D) and time constant (T). Limitations of the ARI were addressed by increasing its numerical resolution and generalizing the parameter space. In 16 healthy subjects, recordings of ABP (Finapres) and CBF velocity (ultrasound Doppler) were performed at rest, before, during and after 5% CO(2) breathing, and for six repeated thigh cuff maneuvers. The unconstrained model produced lower predictive error (p < 0.001) than the original model. Unconstrained parameters (K'-D'-T') were significantly different from K-D-T but were still sensitive to different measurement conditions, such as the under-regulation induced by hypercapnia. The intra-subject variability of K' was significantly lower than that of the ARI and this parameter did not show the unexpected occurrences of zero values as observed with the ARI and the classical value of K. These results suggest that K' could be considered as a more stable and reliable index of dynamic autoregulation than ARI. Further studies are needed to validate this new index under different clinical conditions.

Objective selection of signals for assessment of cerebral blood flow autoregulation in neonates.

A number of different system identification techniques have been proposed to assess dynamic cerebral autoregulation in critically ill patients. From these methods, the response to a standard stepwise change in blood pressure can be estimated. Responses lacking physiological consistency are a common occurrence and could be the consequence of particular system identification procedures or, alternatively, caused by measurements with a poor signal-to-noise ratio. A multi-observer approach was adopted in this paper to classify cerebral blood flow velocity (CBFV) step responses to spontaneous changes in arterial blood pressure in a group of 43 neonates with a mean gestational age of 33.7 weeks (range 24-42 weeks) and a mean birthweight of 1,980 g (range 570-3,910 g). Three experienced observers independently analysed the estimated step responses in 191 recordings each lasting 100 s; for an autoregressive (ARX) model, 124 (65%) of the step responses were accepted by at least two of the three observers. Two other system identification methods, transfer function analysis and the moving average Wiener-Laguerre model, gave 90 (45%) and 98 (51%) acceptable responses, respectively. Only 54 epochs (28%) were accepted with all three methods. With 88 (46%) responses rejected by at least two methods, it can be concluded that signal quality was the main reason for nonphysiological step responses. To avoid the need for subjective visual selection, an automatic procedure for classifying step responses was implemented leading to sensitivities and specificities in the range 85-90%, with respect to the agreement with subjective evaluations. Objective selection of CBFV step responses is thus feasible and could also be adapted for other physiological measurement techniques relying on system identification methods.

An automatic selections method for cerebral blood flow autoregulation signals from neonates

Interpretation and quantification of cerebral blood flow autoregulation can be carreid out from step responses to arterial blood pressure changes estimated with various identification methods. However estimates usually need to be visually inspected to rejected some that are not physiologically acceptable...

A method for predicting the utilization of medical technology in neonatal care.

The utilization of 12 neonatal intensive care technologies was recorded in 193 patients. An index of utilization (Pu) was adopted to classify these technologies into three sub-groups corresponding to low (Pu < 15%), medium (15% < or = Pu < or = 85%), and high (Pu > 85%) intensity of use. No models were developed for technologies with high intensity of use (intravenous hydration, warming, micro-haematocrit, heart rate monitoring). Multiple linear regression was used to predict the utilization of technologies with medium intensity of use (gasometry, oxygen hood, CPAP, mechanical ventilation), and multiple logistic regression was used with the same purpose for technologies with low intensity of use (exchange transfusion, bicarbonate, adrenaline, echocardiography). Both methods yielded significant models (P < 0.05) which can be used to improve planning and management of technology in neonatal intensive care units.

Avaliaçäo de cuidados intensivos neonatais / Assessment of neonatal intensive care

Analisa o emprego de cinquenta e três tecnologias distintas em oitenta e dois pacientes de uma UCIN - Unidade de Cuidados Intensivos Neonatais, procurando caracterizar os padröes de utilizaçäo em diferentes grupos de diagnóstico e identificar a relaçäo entre a intensidade de uso de múltiplas tecnologias e indicadores de resultado

Estimating the effectiveness of perinatal care technologies by expert opinion.

The majority of technologies in use in perinatal care were organized into 45 technological functions. Forty-six experts from 19 different regions of Brazil and other Latin American countries then selected a "basic package" (BP) of 15 technological functions. Considering the 12 main causes of perinatal mortality in Brazil, the experts estimated the number of preventable deaths, assuming universal coverage by the BP and the additional reductions that could be obtained by gradually adding other technological functions to the BP. A simulation was performed for the 26 states of Brazil to identify regional priorities for the diffusion of technological functions. For most regions, the BP appears to be the most effective intervention, with the potential of reducing perinatal mortality by 33%, followed by "coordination of services and referral of pregnant women" (14%), and "treatment of respiratory conditions" (11.8%).

Utilizacao de tecnologias nos cuidados intensivos neonatais / Utilization of technology in the intensive care neonatal

Como planejar a distribuicao de Unidades de Terapia Intensiva Neonatal (UTIN) no Pais? Esta e uma questao que ainda nao dispoe de uma resposta baseada em criterios racionais, o que so podera ocorrer com o desenvolvimento de metodologia apropriada para a avaliacao das multiplas tecnologias que constituem as Utins. Este trabalho obteve informacoes quanto a utilizacao de 53 tecnologias neonatais para 82 recem-nascidos, com peso de nascimento variando de l.000 a 1999g na Utin do Instituto Fernandes Figueira, RJ. Aplicando tecnica multivariada de agrupamento foram obtidos 5 grupos de recem-nascidos com caracteristicas semelhantes de utilizacao. Estes grupos apresentaram-se correlacionados comos diagnosticos princiapis. Os resultados, aqui mostrados, abrem caminho no sen tido da aquisicao de conhecimento quanto aos possiveis padroes de uso de tecnologia em Utin e para o planejamento mais racional de sua alocacao na realidade na cional.