Eat, drink and be merry--and protect the brain.

Abstract

Cerebral blood flow is sensitive to even minor changes in the arterial carbon dioxide tension (), with the ‘reactivity’ being ∼4% for a 1 mmHg change in . That is the case at a normal of ∼40 mmHg (5.3 kPa), but the reactivity becomes lower at low or high levels (e.g. Hurr et al. 2015a,b). Also, the cerebral CO2 reactivity differs between the parts of the brain served by the internal carotic artery, including the middle cerebral artery and those parts of the brain supplied by the vertebral artery (Sato et al. 2012). Accepting anatomical differences and that the CO2 reactivity of the brain depends on the , there remains variation in responses, i.e. the CO2 reactivity of the brain is reported with a substantial SD of ∼30% of the mean (e.g. Sato et al. 2012). Such variation in results may be taken to reflect how accurately the variable can be determined by the method chosen, or the SD may reflect that the measured varible is not entirely stable, e.g. heart rate and blood pressure vary through the respiratory cycle. Yet, there may also be genuine differences among subjects and circumstanses. For example, the CO2 reactivity for the brain circulation is reported to increase during exercise (Rasmussen et al. 2006), while CO2 reactivity does not explain the reduction in cerebral blood flow when people are upright (Immink et al. 2009). Among subjects, it may not be appreciated that there can be sex differences in the determined variable(s), dependence on the size of the individual or variation related to physical fitness besides age. Such influences are then addressed in separate evaluations, and it should be considered whether difference in results may also relate to genetics. An important physiological variable, cardiac output, differs according to Arg16Gly polymorphism, both at rest and during exercise (Snyder et al. 2006; Rokamp et al. 2013). Considering a genetic influence on the circulation, Hurr et al. (2015b) provided the observation that the increase in middle cerebral artery mean flow velocity as an indication for cerebral blood flow in response to (expressed by the end-tidal value) is smaller at college age for African Americans than for Causian Americans. A comparison of the CO2 reactivity of the brain between different ethnic groups is of interest because African Americans are known to suffer from cardiovascular diseases related to the so-called metabolic syndrome/diabetes type II, including hypertension, coronary artery disease and, notably, stroke. To prevent such calamaties, focus has been on, e.g. control of diet, antihypertensive medication and prescription of exercise, all of which typically are not attractive to the patient, who is likely not to be experiencing symptoms when the advise/therapy is instituted. Thus, type II diabetics suffer from fatigue (Kim et al. 2015), limiting their enthusiasm for exericse. Advice may be obtained in the Bible: And I commend joy, for man has nothing better under the sun but to eat and drink and be joyful, for this will go with him in his toil through the days of his life that God has given him under the sun (Ecclesiastes 8:15). One or several interventions can be proved beneficial, but the patient's adherence to the intervention is limited if it is not associated with some joy. Obviously, taking pills is no fun and medication is often not taken because the patient experiences side-effects. Likewise, prescription of exercise results in increased activity, but only for as long as the study lasts if it is not felt to be interesting. For example, Ottesen et al. (2010) found that among inactive women (fun) football creates more ‘social capital’ than (dull) running. Also it is well known that whatever diet is applied and however successful it is in reducing weight, the weight is regained shortly after the end of the diet. In a follow-up paper in this isssue of Experimental Physiology, Hurr et al. (2015a) demonstrate that the ∼20% reduced CO2 reactivity for young African Americans is normalized following administration of flavanol. As mentioned by the authors, flavanol is an ingredient of, for example, chocolate, black tea and red wine. Obviously, it needs to be established to what extent the reactivity of the brain early in life is coupled to later development of stroke, but before that relationship is established we and, especially, people of African orgin can be advised not to be restricted but to enjoy the pleasure of, for example, chocolate, tea and red wine. Cheers!