Cerebral Circulation

Middle cerebral artery blood velocity is reduced with hyperthermia during prolonged exercise in humans

“…As a consequence of the hyperventilation, arterial P CO 2 was reduced. This is clearly one of the main reasons for the reduction in MCA V mean during exercise with hyperthermia, as arterial P CO 2 has a strong effect on the cerebral circulation, including MCA V mean (Heistad & Kontos, 1983;. When individually determined regression lines for MCA V mean and P a,CO 2 obtained during exercise were used to attribute for the differences in P a,CO 2 between the hyperthermic and control trial, it appeared that more than half of the reduction in MCA V mean was related to the decline in P a,CO 2 .…”

“…They concluded that MCA V mean depends on cardiac output rather than blood pressure, and this seems to be an acceptable conclusion since mean arterial pressure both in the present study and in their study remained well within the cerebral autoregulatory range (Paulson et al 1990). However, even within the autoregulatory range a small influence of reduced MAP on the cerebral circulation cannot be excluded (Heistad & Kontos, 1983). That blood flow to various tissue compartments can be reduced as a result of insufficient cardiac output is supported by the observations that reductions in cardiac output are accompanied by reduced leg blood flow both in dehydrated athletes (González-Alonso et al 1998) and in patients with b-adrenergic blockade (Pawelczyk et al 1992;Gullestad et al 1993).…”

“…In awake resting baboons cerebral blood flow is unaffected by hyperthermia (Hales et al 1979) and it has been suggested that cerebral blood flow in humans would also remain unaltered, except if hyperthermia-induced hyperventilation induces a drop in P a,CO 2 (Rowell, 1986). Yet, in exercising as well as resting humans, hyperthermia is often accompanied by an increase in ventilation (Haldane, 1905;Rowell et al 1969;Cabanac & White, 1995;González-Alonso et al 1998), resulting in a reduced P a,CO 2 (González-Alonso et al 1998), and as P a,CO 2 has a strong influence on the cerebral circulation (Heistad & Kontos, 1983), blood flow could be reduced during exercise with hyperthermia. Furthermore, severe hyperthermia can induce a reduction in cardiac output during exercise (Rowell et al 1966;González-Alonso et al 1999b), and an insufficient increase in systemic blood flow was found to reduce the cerebral blood velocity during exercise with a large muscle mass (Ide et al 1998).…”

Cardiomyopathy in Women: Second Heart Failure

“…Above the atrium, venous pressures become negative, venous blood readily flows back to the heart and the veins collapse. At the same time, hydrostatic forces serve to reduce arterial pressures by 40mmHg at the top of the head, and if this reduces arterial pressure below 60 mmHg, regulation of cerebral perfusion can be significantly affected [7].…”

Autorregulação encefálica na insuficiência hepática fulminante antes e após transplante hepático

“…Além disso, as tentativas de se reproduzir a curva clássica da ARE não foram bem-sucedidas, pois a obtenção de uma curva satisfatória depende de um mecanismo de feedback sensível, não representativo da fisiologia humana (Heistad, 1983). Assim, grande parte da avaliação da ARE estática consistia apenas em determinar se a autorregulação estava preservada e se havia deslocamento de sua curva.…”