Slow Recovery of Cerebral Perfusion During Hypotension in Elderly Humans




Abdali, Kulsum


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Purpose: The study sought to test the hypothesis that the function of maintaining cerebral perfusion is diminished in elderly adults due to compromised cerebral autoregulation (CA) and cardiovascular systemic mechanisms with aging. Methods: Thirteen healthy elderly (67.5±1.1 yr) and 13 young (25.8±1.0 yr) adults signed a consent form and passed a physical exam to be enrolled in the study, which was approved by the IRB at UNTHSC. Heart rate (HR), mean arterial pressure (MAP), and cerebral blood flow velocity of the middle cerebral artery (VMCA) were continuously measured during systemic hypotension induced by a rapid cuff deflation after 3-min supra-systolic occlusion with bilateral thigh cuffs. This hypotension elicited a transient decrease in VMCA i.e. ΔVMCA and a reflexive increase in HR i.e. ΔHR. Duration and rate of the recovery response from the nadir of MAP and VMCA were compared between the groups. Results: Rapid cuff deflation after 3-min supra-systolic occlusion to the legs significantly decreased MAP (ΔMAP) in both the elderly (-14.1±1.1 mmHg) and young (-16.5±1.2 mmHg) groups which were not significantly different. This hypotension elicited similar significant hypoperfusion to the brain as indicated by ΔVMCA in the elderly (-7.9±0.9 cm/s) and young (-9.5±1.0 cm/s) groups. However, the time elapsed from deflation to the nadir of MAP and VMCA (T0) and recovery time (Tr) of these variables from the nadir to return to baseline were significantly prolonged in the elderly subjects. The rates of relative changes in HR (%ΔHR/s, elderly vs young groups: 1.42±0.20 vs 4.02±0.42 %/s), MAP (%ΔMAP/sec, elderly vs young groups: 0.93±0.11 vs 1.93±0.20 %/s) and VMCA (%ΔVMCA/sec, elderly vs young groups: 1.72±0.02 vs 2.97±0.40 %/s) during recovery were diminished in elderly vs. young adults. Overall TR-ΔVMCA was significantly explained by the rates of %ΔHR, %ΔMAP, and %ΔVMCA. However, the TR-ΔVMCA/vasomotor-factor slope (-3.0±0.9) was steeper (P=0.046) than the TR-ΔVMCA/cardiac-factor slope (-1.1±0.4). The TR-ΔVMCA/CA-factor slope (-2.3±0.5) was greater (P=0.055) than the TR-ΔVMCA/cardiac-factor slope; but it did not differ from the TR-ΔVMCA/vasomotor-factor slope. Discussion: Maintenance of MAP was regulated by vasomotion and HR factors; whereas regulation of VMCA seemed to be affected by intrinsic and systemic mechanisms. Both T0 and TR were remarkably shorter for VMCA than MAP, suggesting the presence of cerebral autoregulation, which evoked an early rebound of VMCA from its nadir before MAP reached the nadir and explained a quick recovery of VMCA before MAP completed its restoration. Nonetheless, both T0 and TR were significantly longer in the elderly subjects. In addition to the response rate of VMCA, relative change rates of both MAP and HR were significantly diminished with aging, which explained a prolonged recovery of cerebral perfusion during hypotension.