Barnes, Jill N.

Adults with cardiovascular disease and heart failure are at higher risk of cognitive decline. Cerebral hypoperfusion appears to be a significant contributor, which can result from vascular dysfunction and impairment of cerebral blood flow regulation. In contrast, higher cardiorespiratory fitness shows protection against brain atrophy, reductions in cerebral blood flow, and cognitive decline. Given that high intensity interval training (HIIT) has been shown to be a potent stimulus for improving cardiorespiratory fitness and peripheral vascular function, its utility for improving cognitive aging is an important area of research. This article will review the physiology related to cerebral blood flow regulation and cognitive decline in adults with cardiovascular disease and heart failure, and how HIIT may provide a more optimal stimulus for improving cognitive aging in this population.

Objective Hypercapnia, an elevated concentration of carbon dioxide (CO2) in the blood, is known to promote acute increases in cerebral blood flow (CBF). This pilot study aimed to investigate whether a novel training method involving repeated bouts of hypercapnia, would influence cerebrovascular reactivity response in healthy adults. Hypothesis Repeated bouts of hypercapnia (as interval training) may promote beneficial adaptation to increase cerebrovascular reactivity. Methods Adults over 40yrs old without known disease or cardiovascular risk factors, were recruited for a non‐randomized cross‐over design pilot study. Subjects completed a 2‐week control period followed by a 2‐week intervention. The intervention involved a progressive hypercapnia training program of six sessions, whereby subjects completed 4‐6 intervals of rebreathing oxygen until a target end‐tidal CO2 (up to 25mmHg above resting) was reached, separated by recovery intervals breathing room air. Cerebrovascular reactivity was measured during study testing visits at baseline, 2‐weeks (between control and intervention) and 4‐weeks (after intervention). During study visits subjects underwent a stepped CO2 protocol, involving 5‐min stages of inspired room air, 2% CO2, 4% CO2, and 6% CO2, while measuring middle cerebral artery velocity (CBFv) using transcranial doppler ultrasound, mean arterial pressure (MAP) by finger plethysmography, ventilation, and end‐tidal CO2. Cerebrovascular conductance (CVCi) was calculated as CBFv/MAP. The reactivity of CBFv (in cm/s/mmHg), CVCi (in cm/s/mmHg2), and MAP (in mmHg/mmHg) were calculated as the linear regression slope against end‐tidal CO2 during the stepped CO2 protocol. Chemosensitivity (in L/min/mmHg) is the linear regression slope of VE vs end‐tidal CO2. Results Six healthy adults (age: 56 ± 10; 2 females) completed the study. Study visit data are displayed in Table 1. Individual training data are presented in Table 2. Following the control period there was a large reduction from baseline in CBFv reactivity [2.81 ± 1.50 to 2.03 ± 1.03; effect size 0.9], CVCi reactivity [0.020 ± 0.015 to 0.015 ± 0.010; effect size 0.7], and MAP reactivity [0.95 ± 0.63 to 0.62 ± 0.42; effect size 0.6] with no change in chemosensitivity [0.99 ± 0.68 to 0.98 ± 0.51; effect size 0.0]. Following the intervention there was no change from the 2‐week study visit in CBFv reactivity [2.03 ± 1.03 to 2.01 ± 1.09; effect size 0.0], CVCi reactivity [0.015 ± 0.010 to 0.014 ± 0.010; effect size 0.1], and MAP reactivity [0.62 ± 0.42 to 0.72 ± 0.44; effect size 0.1] with a small increase in chemosensitivity [0.98 ± 0.51 to 1.04 ± 0.53; effect size 0.3]. Conclusion Preliminary findings suggest a very brief progressive hypercapnia training program does not increase or desensitize cerebrovascular reactivity in healthy adults. These data also suggest an exaggerated cerebrovascular reactivity response may occur to an initial exposure of a stepped CO2 protocol (without familiarization), which appears to be driven by blood pressure response not chemosensitivity. Further research, particularly in populations with impaired cerebrovascular reactivity, is of interest for CBF regulation.

Background Prostaglandins, such as cyclooxygenase (COX), may play an important role in regulating the cerebral blood flow response to a stimulus. We have previously shown that the vasodilatory response to a chemical stimulus decreases with age, and this difference is abolished by COX inhibition. However, the effects of COX inhibition on the cerebrovascular response to an increase in metabolic demand during a cognitive challenge is unknown. This information is important due to the frequent use of COX inhibitors for pain management. Thus, the purpose of this study was to determine the effect of COX inhibition on the cerebrovascular response to a metabolic stimulus in young and older adults. Methods Seventy‐six participants, including 42 young adults (YA; 26 ± 5 y) and 34 older adults (OA; 64 ± 6 y) completed the Stroop Color Word Test, which is a test of executive function. A subset of 42 participants (n = 22 YA, n = 20 OA) also completed the N‐back Test, which is a test of working memory. Beat‐to‐beat middle cerebral artery velocity (MCAv) and mean arterial pressure (MAP) were measured at baseline and in response to each cognitive test. Cerebrovascular conductance index (CVCi) was calculated as MCAv/MAP. The response to each cognitive test was calculated as the peak percent change (%Δ) from baseline. Oral administration of the COX inhibitor Indomethacin (Indo) was given at 1.2mg/kg. Cognitive tests were then repeated after a 120‐minute wash‐in period. Results At baseline, YA had higher MCAv, CVCi, and lower MAP (p<0.01 for all) compared to OA. There were no significant differences between groups in the %Δ from baseline during the Stroop or N‐back test (p>0.05). During Indo, YA had higher MCAv (p<0.01), CVCi (p<0.01), and lower MAP (p<0.05) compared to OA. Indo decreased baseline MCAv and CVCi in both groups (p<0.01 for all) but had no effect on MAP (p>0.05). During Indo, the %Δ in MCAv during Stroop and N‐back was lower in YA (p<0.01) compared to baseline in YA. During Indo, the %Δ in MCAv was lower during Stroop in OA (p<0.01), with a trend for significance in OA during N‐back (p=0.06) compared to baseline. In YA during Indo, the %Δ in MAP was lower during Stroop (p<0.01) with a trend for significance during Nback (p=0.08) compared to baseline. In OA, the %Δ in MAP during N‐back was lower during Indo compared to baseline (p<0.05). Indo had no effect on the %Δ in CVCi (p>0.05). Importantly, there were group differences in the %Δ in MAP during Indo, such that the change was greater in OA compared with YA during Stroop (14.1 ± 1.3% vs. 10.6 ± 1.0%; p<0.05). Conclusion After administration of Indo, OA increased MAP to a greater extent during the Stroop test when compared to YA. These results suggest that OA required a larger increase in blood pressure to complete a test of executive function during COX inhibition. Because some COX inhibitors attenuate cerebral blood flow, OA may need to augment blood pressure to complete this metabolically‐challenging task. Support or Funding Information This research was funded by NIH grant HL118154. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

A history of preeclampsia (PE) places women at higher risk for future cardiovascular disease and cognitive decline. We have previously shown that postmenopausal women with a history of PE demonstrated a reduced cerebral blood flow response to hypercapnia compared with postmenopausal women with a history of a normotensive pregnancy (NP). These findings suggest cerebrovascular effects of PE 30+ years postpartum. In addition, we have reported that women with a history of PE did not have an exaggerated pressor response to a sympathoexcitatory stimulus. However, it is possible that women with a history of PE may have an altered cerebral blood flow response to a sympathoexcitatory stimulus. In this study, middle cerebral artery blood velocity (MCAv) and beat‐to‐beat mean arterial blood pressure (MAP) were measured during isometric handgrip to fatigue (IHG) at 30% of maximal voluntary contraction followed by post‐exercise ischemia (PEI) for 90 seconds and a two minute recovery period (REC). Participants were postmenopausal women with a history of PE (n = 21; age at study = 58±5 y; years since last pregnancy = 35±3 y) and NP (n = 27; age at study = 58±5 y; years since last pregnancy = 35±3 y). Baseline MAP and MAP responses to IHG and PEI were similar between groups (p>0.05). PE women demonstrated lower MCAv at baseline (NP: 72±3 cm/s vs. PE: 57±4 cm/s), IHG (NP: 78±4 cm/s vs. PE: 63±4 cm/s), PEI (NP: 74±4 cm/s vs. PE: 60±4 cm/s), and REC (NP: 70±3 cm/s vs. PE: 58±4 cm/s) compared with NP women (p<0.05 for all). MCAv, when calculated as a percent change from baseline, was elevated during IHG in both PE and NP women as expected (p<0.05); however, PE women had an augmented MCAv response during the last third of IHG compared with NP women (NP: 9±2 % vs. PE: 13±2 %; p<0.05). PE women also had a higher MCAv response during REC compared with NP women (NP:−2±2% vs. PE: 3±2%; p<0.05). Importantly, these elevated MCAv responses occurred despite the fact that MAP was not different between groups. In summary, PE women demonstrated a lower basal cerebral blood velocity but an elevated cerebrovascular response to a sympathoexcitatory stimulus compared with NP women. This suggests that in postmenopausal women, there is an effect of pregnancy history on the sensitivity of the cerebral blood flow response to a sympathoexcitatory stimulus. Support or Funding Information NIH: AG 044170. This investigation was supported by the National Institutes of Health, under Ruth L. Kirschstein National Research Service Award T32 HL 007936 from the National Heart Lung and Blood Institute to the University of Wisconsin‐Madison Cardiovascular Research Center. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Hypertensive pregnancy (HP) is considered a risk factor for cardiovascular disease. Blood pressure (BP) response to physical stressor is an independent marker of cardiovascular risk. However, there is limited data regarding the pressor response to acute physical stress in women with a history of HP. Hence, the aim of the study was to compare BP responses in women with a history of HP to age and parity matched controls. Beat to beat BP was recorded in postmenopausal women (age = 59 ± 1 yrs, BMI = 31 ± 2 kg/m2) with and without a history of HP at baseline and during isometric handgrip (HG) exercise (30% of MVC) to fatigue. Isometric handgrip exercise was followed by 90 seconds of supra‐systolic cuff occlusion on the exercising arm. In both groups combined (N=31), systolic blood pressure (SBP) increased significantly from baseline to HG to cuff inflation (143 ± 3 to 161 ± 3 to 167 ± 4 mmHg). Similarly, mean arterial pressure (MAP) increased significantly from baseline to HG to cuff inflation (106 ± 2 to 119 ± 2 to 122 ± 2 mmHg). Diastolic pressure (DBP) increased significantly only from baseline to HG (80 ± 1 to 88 ± 1 mmHg) and baseline to cuff inflation (89 ± 2 mmHg). However, there were no significant differences in SBP, DBP and MAP between women with and without a history of HP (p>0.05). Even though both groups had an increase in BP variables in response to HG and cuff occlusion, there was no difference in the BP response to acute physical stressors in women with a history of HP as compared to control participants. Funding: National Institute of Aging 1P50AG044170‐01 and CTSA UL1 TR000135 and HL 118154 (JNB)

Evidence suggests that increased sympathetic tone but no change of blood pressure (BP) via lower body negative pressure (LBNP) reduces indices of aortic wave reflection in young adults. The aim of this study was to examine whether aging affects central artery hemodynamics and indices of wave reflection during LBNP. In 12 young (27 ± 2 years, 5F/7M) and 10 older (70 ± 2 years 5F/5M) subjects, noninvasive aortic pressure waveforms were synthesized from high‐fidelity radial pressure waveforms via applanation tonometry before and during 10 minutes of LBNP (‐20mmHg). Aortic BP and indices of aortic wave reflection (i.e. Augmentation index; AIx) were calculated from the generated aortic pressure waveform. Aortic systolic BP decreased during LBNP in the young (110 ± 3 vs. 106 ± 3 mmHg, P<0.05), but not the older adults (139 ± 3 vs. 136 ± 3 mmHg, P=0.15). Aortic diastolic BP did not change in either group (P=0.56). Since heart rate (HR) changed in the young (P<0.05) but not in the older adults (P=0.33) during LBNP, we used the AIx normalized to a HR of 75bpm as an index of wave reflection. AIx@75bpm decreased in young adults (‐6 ± 3 vs. ‐13 ± 3%, P<0.001), whereas no change was observed in older adults (26 ± 3 vs. 25 ± 3%, P=0.39). Our data suggest that reductions in aortic systolic blood pressure and wave reflection during lower body negative pressure are attenuated in older compared to young adults. Funded by NIH HL‐105467

<a name=“OLE_LINK2”></a><a name=“OLE_LINK1”>Hypertensive pregnancy (HP) disorders have been linked to a four‐fold increased risk for development of future cardiovascular diseases. We examined whether history of HP in postmenopausal women (N=20, 59±5 yr) influenced the risk factors for cardiovascular disease as assessed by aortic pulse wave characteristics, compared to age and parity matched controls (N=18, 60±4 yr). Non‐invasive aortic pressure waveforms were synthesized from high‐fidelity pressure waveforms obtained from SphygmoCor applanation tonometry using the radial artery. Aortic systolic and diastolic blood pressure (ASBP, ADBP), aortic augmentation index (AI x ), augmented pressure (AP), aortic pulse pressure (APP), and left ventricular wasted energy (E w ) were calculated from the generated aortic pressure waveform. There were no differences in ASBP (125±4 vs. 129±4 mmHg), ADBP (79±2 vs. 81±2 mmHg), AP (17±2 vs. 17±2 mmHg), AI x (35±2 vs. 29±1%), AI x @75BPM (31±2 vs. 29±1%), E w (3313±338 vs. 3364±432 dynes/cm 2 /s), between women with a history of HP vs. matched controls, respectively (P>0.05 for all). Body mass index was significantly higher in women with a history of HP (30.6±1 vs. 26.7±1 kg/m 2 , P<0.05), however it did not statistically influence any of the indices (P>0.05 for all). Our results suggest that postmenopausal women with a history of HP do not demonstrate elevated aortic blood pressure or altered aortic pulse wave characteristics in comparison to matched controls. </a> Supported by: National Institute of Aging 1P50AG044170‐01 and CTSA UL1 TR000135 and HL 118154

Cerebrovascular reactivity to hypercapnia is higher in women receiving menopausal hormone therapy (MHT) compared with controls, and this may persist after cessation of MHT. We hypothesized that the effect of MHT may be influenced by mean arterial pressure (MAP). Therefore, we examined both middle cerebral artery velocity (MCAv) and MAP responses to stepped hypercapnia in 60 postmenopausal women who were previously randomized to receive oral conjugated equine estrogen (oCEE, n=15), transdermal 17β estradiol (tE2, n=22), or placebo (PLA, n=23) for 4 years. After a 3 year washout period, reactivity was calculated from the slope of the relationship between MCAv or MAP and end‐tidal CO 2 . MCAv reactivity was higher in the oCEE group compared with the PLA group (1.6±0.2 vs. 1.1±0.1 cm/s/mmHg; oCEE vs. PLA, respectively, p<0.05), but similar between the tE2 and PLA group (1.3±0.2 vs. 1.1±0.1 cm/s/mmHg; tE2 vs. PLA, respectively, p>0.05). There were no significant differences in MAP reactivity (1.0±0.2, 0.6±0.1, 0.7±0.2 mmHg/mmHg of CO 2 , oCEE vs. tE2 vs. PLA, respectively, p>0.05) among the groups. However, in the combined MHT group, MAP reactivity was positively correlated with MCAv reactivity (r=0.58, p<0.001), such that women with higher MAP responses demonstrate greater MCAv responses to hypercapnia. In conclusion, there were no differences in MAP reactivity 3 years after cessation of MHT. In addition, our results suggest that greater cerebrovascular reactivity in postmenopausal women who received MHT may be driven by augmented blood pressure responses to hypercapnia. Funding: K99 HL 118164, AG 044170 and HL 83947.

Cerebral blood flow velocity responses to hypercapnia are blunted by the cyclooxygenase inhibitor indomethacin (INDO). We hypothesized that INDO would also attenuate middle cerebral artery blood flow velocity (MCAv) responses to an acute cognitive challenge. We evaluated the MCAv responses to an acute cognitive challenge in 20 healthy young (20‐35 yrs) and older (56‐76 yrs) healthy adults, including 10 men and 10 women before and 90 minutes after INDO administration. The cognitive challenge consisted of 2 blocks of the Stroop color word test: easy (3 colors) and difficult (8 colors). Mean arterial pressure (MAP), end‐tidal CO 2 , and MCAv were monitored throughout the protocol. There were no differences in MAP or end tidal CO 2 between trials. Indeed, MCAv was lower during INDO than baseline for both the easy (50±4 vs. 68±4 cm/s; p<0.01) and difficult (49±3 vs. 66±3 cm/s; p<0.001) cognitive challenges. Additionally, there was an Age x Sex interaction for the increase in MCAv during the easy cognitive task, with older men having a greater increase than older women (15±5 vs. ‐1±5%, respectively; p<0.05). This interaction was not statistically significant for the difficult cognitive task or during the INDO trial. In conclusion, similar to hypercapnia, the cyclooxygenase inhibitor INDO blunts cerebral blood flow velocity responses to an acute cognitive challenge. Funded by NIH grant HL 118154