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Dynamic blood pressure control and middle cerebral artery mean blood velocity variability at rest and during exercise in humans
Author(s) -
Ogoh S.,
Dalsgaard M. K.,
Secher N. H.,
Raven P. B.
Publication year - 2007
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2007.01708.x
Subject(s) - medicine , cardiac output , metoprolol , cardiology , baroreflex , blood pressure , cerebral blood flow , mean arterial pressure , hemodynamics , cardiac function curve , middle cerebral artery , blockade , anesthesia , heart rate , heart failure , ischemia , receptor
Aims: Cardiac failure and ischaemic heart disease patients receive standard of care cardiac β 1 ‐adrenergic blockade medication. Such medication reduces cardiac output and cerebral blood flow. It is unknown whether the β 1 ‐adrenergic blockade‐induced reduction of cardiac output in the presence of an exercise‐induced reduction in cardiac–arterial baroreflex gain affects cerebral blood flow variability. This study evaluated the influence of cardiac output variability on beat‐to‐beat middle cerebral artery mean blood velocity (MCA V mean ) during exercise with and without cardiac β 1 ‐adrenergic blockade. Methods: Eight men (22 ± 1 years; mean ± SE) performed 15 min bouts of moderate (105 ± 11 W) and heavy (162 ± 8 W) intensity cycling before and after cardio‐selective β 1 ‐adrenergic blockade (0.15 mg kg −1 metoprolol). The relationship between changes in cardiac output or mean arterial pressure (MAP) and MCA V mean as well as cardiac–arterial baroreflex gain were evaluated using transfer function analysis. Results: Both exercise intensities decreased the low frequency (LF) transfer function gain between cardiac output and MCA V mean ( P < 0.05) with no significant influence of β 1 ‐blockade. In contrast, the LF transfer function gain between MAP and MCA V mean remained stable also with no significant influence of metoprolol ( P > 0.05). The LF transfer function gain between MAP and HR, an index of cardiac–arterial baroreflex gain, decreased from rest to heavy exercise with and without β 1 ‐blockade ( P < 0.05). Conclusion: These findings suggest that the exercise intensity related reduction in cardiac–arterial baroreflex function at its operating point does not influence the dynamic control of MCA V mean , even when the ability of exercise‐induced increase in cardiac output is reduced by cardiac β 1 ‐adrenergic blockade.