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Repeatability of Cerebral Vasomotor Reactivity to Hypercapnia in Humans
Author(s) -
Nandadeva Damsara,
Patik Jordan C.,
Martin Zachary T.,
Fadel Paul J.,
Brothers R. Matthew
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.04751
Subject(s) - hypercapnia , medicine , cerebral autoregulation , cerebral blood flow , middle cerebral artery , transcranial doppler , anesthesia , blood pressure , repeatability , cardiology , autoregulation , ischemia , chemistry , chromatography , acidosis
Impaired cerebrovascular function is a risk factor for the development of various neurocognitive and cerebrovascular diseases including cognitive dysfunction, dementia, Alzheimer’s disease, and stroke. Since hypercapnia elicits a robust cerebral vasodilator response, cerebrovascular function is commonly assessed as an increase in cerebral blood flow to elevations in arterial carbon dioxide (i.e., cerebral vasomotor reactivity ‐ CVMR). Hypercapnia induced by a rebreathing protocol is one such technique used to assess cerebrovascular function. Although this technique is used to evaluate CVMR within and between subjects before and after interventions, to our knowledge, the repeatability of CVMR assessed by rebreathing has not been comprehensively investigated. Moreover, the National Institute of Health’s recent guidelines emphasize the need for rigor and reproducibility of data collection techniques. Accordingly, this study was designed to determine the within‐day repeatability of CVMR response to rebreathing‐induced hypercapnia. Eleven young healthy males (age = 24 ± 3 years, BMI = 24.3 ± 3.8 kgm −2 , mean ± SEM) reported to the laboratory following an overnight fast and performed 3 trials of rebreathing‐induced hypercapnia each separated by approximately 2 hours. Heart rate (ECG), respiration (Pneumotrace), beat‐to‐beat blood pressure (Finometer), middle cerebral artery mean blood velocity (MCAv ‐ transcranial Doppler) and breath‐by‐breath end‐tidal carbon dioxide concentration (PETCO 2 ‐ capnograph) were continuously measured. Cerebral vascular conductance index (CVCi) was calculated as MCAv divided by mean arterial pressure. CVMR was assessed as the slope of the linear regression between the increase in %MCAv and %CVCi across the range of change in PETCO 2 (ΔPETCO 2 ). The increase in %MCAv and %CVCi was also assessed at a ΔPETCO 2 of 15 mmHg which was the highest common change in magnitude of hypercapnia achieved across all rebreathing trials among all participants. Repeatability between the 3 trials was assessed using intra class correlation coefficient (ICC). The slopes of %CVCi vs. ΔPETCO 2 (3.9 ± 0.4, 3.8 ± 0.3 and 3.6 ± 0.3 %mmHg −1 for 1 st , 2 nd and 3 rd trial respectively, p = 0.82) was not different and showed very good repeatability (ICC = 0.86, p < 0.001) between the 3 rebreathing‐induced hypercapnia trials. Likewise, the % increase in CVCi at ΔPETCO 2 of 15 mmHg was not different (40 ± 4, 38 ± 4 and 36 ± 4% for 1 st , 2 nd and 3 rd trial respectively, p = 0.72) and also demonstrated very good repeatability between trials (ICC = 0.86, p < 0.001). Similar results were obtained when MCAv was used as the dependent variable. These results suggest that within‐day CVMR assessed by rebreathing‐induced hypercapnia is highly repeatable and therefore can be used as a reliable index of cerebrovascular function. Support or Funding Information Supported by UTA College of Nursing and Health Innovation