Carl J. Ade

Anterograde and retrograde blood velocity profiles in the intact human cardiovascular system

Current assessments of the effects of shear patterns on vascular function assume that a parabolic velocity profile is always present. Any substantial deviation in the profile away from this may result in misinterpretation of the importance that shear patterns have on vascular function. The present investigation tested the hypothesis that anterograde and retrograde blood flow would have a parabolic velocity profile at rest, during cold pressor test and exercise. Eight healthy subjects completed a cold pressor test and a graded knee‐extension exercise test. Doppler ultrasound was used to determine time‐averaged mean velocity (Vmean) and time‐averaged peak velocity (Vpeak) for both anterograde and retrograde flow in the femoral artery (FA) and brachial artery (BA). The Vmean/Vpeak ratio was used to interpret the shape of the blood velocity profile (parabolic, Vmean/Vpeak= 0.5; plug‐like, Vmean/Vpeak= 1.0). At rest, BA and FA Vmean/Vpeak ratios of anterograde and retrograde flow were not significantly different from 0.5. During cold pressor test, anterograde Vmean/Vpeak in the BA (0.56 ± 0.02) and FA (0.58 ± 0.03) were significantly greater than 0.5. During peak exercise, the Vmean/Vpeak ratio of anterograde flow in the FA (0.53 ± 0.04) was not significantly different from 0.5. In all conditions, the retrograde Vmean/Vpeak ratio was lower than anterograde. These data demonstrate that blood flow through two different conduit arteries during two different physiological stressors maintains a velocity profile that resembles a slightly blunted parabolic velocity profile.

V˙o2max and Microgravity Exposure: Convective versus Diffusive O2 Transport

Exposure to a microgravity environment decreases the maximal rate of O2 uptake (VO(2max)) in healthy individuals returning to a gravitational environment. The magnitude of this decrease in VO(2max) is, in part, dependent on the duration of microgravity exposure, such that long exposure may result in up to a 38% decrease in VO(2max). This review identifies the components within the O(2) transport pathway that determine the decrease in postmicrogravity VO(2max) and highlights the potential contributing physiological mechanisms. A retrospective analysis revealed that the decline in VO(2max) is initially mediated by a decrease in convective and diffusive O(2) transport that occurs as the duration of microgravity exposure is extended. Mechanistically, the attenuation of O(2) transport is the combined result of a deconditioning across multiple organ systems including decreases in total blood volume, red blood cell mass, cardiac function and mass, vascular function, skeletal muscle mass, and, potentially, capillary hemodynamics, which become evident during exercise upon re-exposure to the head-to-foot gravitational forces of upright posture on Earth. In summary, VO(2max) is determined by the integration of central and peripheral O(2) transport mechanisms, which, if not maintained during microgravity, will have a substantial long-term detrimental impact on space mission performance and astronaut health.

The relationship between critical speed and the respiratory compensation point: Coincidence or equivalence.

Abstract It has previously been suggested that the respiratory compensation point (RCP) and critical speed (CS) parameters are equivalent and, therefore, like CS, RCP demarcates the boundary between the heavy- and severe-intensity domains. However, these findings are equivocal and therefore must be interpreted cautiously. Thus, we examined the relationship between CS and RCP across a wide range of subject fitness levels, in an attempt to determine if CS and RCP are equivalent. Forty men and 30 women (age: 23.2 ± 2.5 year, height: 174 ± 10 cm, body mass: 74.1 ± 15.7 kg) completed an incremental and four constant-speed protocols on a treadmill. RCP was determined as the point at which the minute ventilation increased disproportionately to CO2 production and the end-tidal CO2 partial pressure began to decrease. CS was determined from the constant-speed protocols using the linearized 1·time−1 model. CS and RCP, expressed as speed or metabolic rate, were not significantly different (11.7 ± 2.3 km·h−1 vs. 11.5 ± 2.3 km·h−1, p = 0.208; 2.88 ± 0.80 l·min−1 vs. 2.83 ± 0.72 l·min−1, p = 0.293) and were significantly correlated (r2 = 0.52, p < 0.0001; r2 = 0.74, p < 0.0001, respectively). However, there was a high degree of variability between the parameters. The findings of the current study indicate that, while on average CS and RCP were not different, the high degree of variability between these parameters does not permit accurate estimation of one from the other variable and suggests that these parameters may not be physiologically equivalent.

Acute supplementation of N‐acetylcysteine does not affect muscle blood flow and oxygenation characteristics during handgrip exercise

N‐acetylcysteine (NAC; antioxidant and thiol donor) supplementation has improved exercise performance and delayed fatigue, but the underlying mechanisms are unknown. One possibility is NAC supplementation increases limb blood flow during severe‐intensity exercise. The purpose was to determine if NAC supplementation affected exercising arm blood flow and muscle oxygenation characteristics. We hypothesized that NAC would lead to higher limb blood flow and lower muscle deoxygenation characteristics during severe‐intensity exercise. Eight healthy nonendurance trained men (21.8 ± 1.2 years) were recruited and completed two constant power handgrip exercise tests at 80% peak power until exhaustion. Subjects orally consumed either placebo (PLA) or NAC (70 mg/kg) 60 min prior to handgrip exercise. Immediately prior to exercise, venous blood samples were collected for determination of plasma redox balance. Brachial artery blood flow (BABF) was measured via Doppler ultrasound and flexor digitorum superficialis oxygenation characteristics were measured via near‐infrared spectroscopy. Following NAC supplementaiton, plasma cysteine (NAC: 47.2 ± 20.3 μmol/L vs. PLA: 9.6 ± 1.2 μmol/L; P = 0.001) and total cysteine (NAC: 156.2 ± 33.9 μmol/L vs. PLA: 132.2 ± 16.3 μmol/L; P = 0.048) increased. Time to exhaustion was not significantly different (P = 0.55) between NAC (473.0 ± 62.1 sec) and PLA (438.7 ± 58.1 sec). Resting BABF was not different (P = 0.79) with NAC (99.3 ± 31.1 mL/min) and PLA (108.3 ± 46.0 mL/min). BABF was not different (P = 0.42) during exercise or at end‐exercise (NAC: 413 ± 109 mL/min; PLA: 445 ± 147 mL/min). Deoxy‐[hemoglobin+myoglobin] and total‐[hemoglobin+myoglobin] were not significantly different (P = 0.73 and P = 0.54, respectively) at rest or during exercise between conditions. We conclude that acute NAC supplementation does not alter oxygen delivery during exercise in men.

Influence of Adjuvant Therapy in Cancer Survivors on Endothelial Function and Skeletal Muscle Deoxygenation

The cardiotoxic effects of adjuvant cancer treatments (i.e., chemotherapy and radiation treatment) have been well documented, but the effects on peripheral cardiovascular function are still unclear. We hypothesized that cancer survivors i) would have decreased resting endothelial function; and ii) altered muscle deoxygenation response during moderate intensity cycling exercise compared to cancer-free controls. A total of 8 cancer survivors (~70 months post-treatment) and 9 healthy controls completed a brachial artery FMD test, an index of endothelial-dependent dilation, followed by an incremental exercise test up to the ventilatory threshold (VT) on a cycle ergometer during which pulmonary V˙O2 and changes in near-infrared spectroscopy (NIRS)-derived microvascular tissue oxygenation (TOI), total hemoglobin concentration ([Hb]total), and muscle deoxygenation ([HHb] ≈ fractional O2 extraction) were measured. There were no significant differences in age, height, weight, and resting blood pressure between cancer survivors and control participants. Brachial artery FMD was similar between groups (P = 0.98). During exercise at the VT, TOI was similar between groups, but [Hb]total and [HHb] were significantly decreased in cancer survivors compared to controls (P < 0.01) The rate of change for TOI (ΔTOIΔ/V˙O2) and [HHb] (Δ[HHb]/ΔV˙O2) relative to ΔV˙O2 were decreased in cancer survivors compared to controls (P = 0.02 and P = 0.03 respectively). In cancer survivors, a decreased skeletal muscle microvascular function was observed during moderate intensity cycling exercise. These data suggest that adjuvant cancer therapies have an effect on the integrated relationship between O2 extraction, V˙O2 and O2 delivery during exercise.

Incidence Rate of Cardiovascular Disease End Points in the National Aeronautics and Space Administration Astronaut Corps

Background It is unknown whether the astronaut occupation or exposure to microgravity influences the risk of long‐term cardiovascular disease (CVD). This study explored the effects of being a career National Aeronautics and Space Administration (NASA) astronaut on the risk for clinical CVD end points. Methods and Results During the Longitudinal Study of Astronaut Health, data were collected on 310 NASA astronauts and 981 nonastronaut NASA employees. The nonastronauts were matched to the astronauts on age, sex, and body mass index, to evaluate acute and chronic morbidity and mortality. The primary outcomes were composites of clinical CVD end points (myocardial infarction, congestive heart failure, stroke, and coronary artery bypass surgery) or coronary artery disease (CAD) end points (myocardial infarction and coronary artery bypass surgery). Of the astronauts, 5.2% had a clinical CVD end point and 2.9% had a CAD end point compared with the nonastronaut comparisons with 4.7% and 3.1% having CVD and CAD end points, respectively. In the multivariate models adjusted for traditional risk factors, astronauts had a similar risk of CVD compared with nonastronauts (adjusted hazard ratio, 1.08; 95% CI, 0.60–1.93; P=0.80). Risk of a CAD end point was similar between groups (hazard ratio, 0.97; CI, 0.45–2.08; P=0.93). In astronauts with early spaceflight experience, the risk of CVD (hazard ratio, 0.80; CI, 0.25–2.56; P=0.71) and CAD (hazard ratio, 1.23; CI: 0.27–5.61; P=0.79) compared with astronauts with no experience were not different. Conclusions These findings suggest that being an astronaut is not associated with increased long‐term risk of CVD development.

Activity recognition in planetary navigation field tests using classification algorithms applied to accelerometer data

Accelerometer data provide useful information about subject activity in many different application scenarios. For this study, single-accelerometer data were acquired from subjects participating in field tests that mimic tasks that astronauts might encounter in reduced gravity environments. The primary goal of this effort was to apply classification algorithms that could identify these tasks based on features present in their corresponding accelerometer data, where the end goal is to establish methods to unobtrusively gauge subject well-being based on sensors that reside in their local environment. In this initial analysis, six different activities that involve leg movement are classified. The k-Nearest Neighbors (kNN) algorithm was found to be the most effective, with an overall classification success rate of 90.8%.

Exercise-Induced Hypoalgesia Is Not Influenced by Physical Activity Type and Amount

Physical activity (PA), especially vigorous-intensity PA, has been shown to be related to pain sensitivity. The relationship among PA levels and PA types on endogenous pain inhibition after exercise, termed exercise-induced hypoalgesia (EIH), remains unclear. Purpose This studied examined the EIH response to pressure stimuli among college-age women of differing activity levels. Methods Fifty women were tested. Pressure pain threshold (PPT) values were assessed before and immediately after isometric handgrip exercise to exhaustion in the right and left forearms. Participants PA levels were assessed by wearing an accelerometer for seven consecutive days during waking hours, excluding water activities. Participants were classified into four PA groups: met the American College of Sports Medicine aerobic recommendations (AERO), met aerobic and resistance training recommendations (AERO + RT), insufficiently aerobically active but resistance trained (RT), and insufficiently active (IA) based on their measured and self-reported PA level and type. Results AERO and AERO + RT had greater vigorous (P < 0.001) and total PA (P < 0.001) compared with RT and IA. EIH was observed for PPT in both right and left arms (P < 0.001), with PPT increasing 7.7% (529 ± 236 vs 569 ± 235 kPa) and 7.0% (529 ± 299 vs 571 ± 250 kPa) in the right and left forearms, respectively. EIH did not differ among activity groups (P = 0.82). PPT values were found to be inversely related to vigorous-intensity PA (r = −0.29). Conclusions PA levels and types had no effect on endogenous pain inhibition after exercise in college-age women.

Automated hand-forearm ergometer data collection system

Handgrip contractions are a standard exercise modality to evaluate cardiovascular system performance. Most conventional ergometer systems of this nature are manually controlled, placing a burden on the researcher to guide subject activity while recording the resultant data. This paper presents updates to a hand-forearm ergometer system that automate the control and data-acquisition processes. A LabVIEW virtual instrument serves as the centerpiece for the system, providing the subject/researcher interfaces as well as coordinating data acquisition from both traditional and new sensors. Initial data indicate the viability of the system with regard to its ability to obtain consistent and physiologically meaningful data.

Effect of exercise‐induced muscle damage on vascular function and skeletal muscle microvascular deoxygenation

This paper investigated the effects of unaccustomed eccentric exercise‐induced muscle damage (EIMD) on macro‐ and microvascular function. We tested the hypotheses that resting local and systemic endothelial‐dependent flow‐mediated dilation (FMD) and microvascular reactivity would decrease, V˙O2max would be altered, and that during ramp exercise, peripheral O2 extraction, evaluated via near‐infrared‐derived spectroscopy (NIRS) derived deoxygenated hemoglobin + myoglobin ([HHb]), would be distorted following EIMD. In 13 participants, measurements were performed prior to (Pre) and 48 h after a bout of knee extensor eccentric exercise designed to elicit localized muscle damage (Post). Flow‐mediated dilation and postocclusive reactive hyperemic responses measured in the superficial femoral artery served as a measurement of local vascular function relative to the damaged tissue, while the brachial artery served as an index of nonlocal, systemic, vascular function. During ramp‐incremental exercise on a cycle ergometer, [HHb] and tissue saturation (TSI%) in the m. vastus lateralis were measured. Superficial femoral artery FMD significantly decreased following EIMD (pre 6.75 ± 3.89%; post 4.01 ± 2.90%; P < 0.05), while brachial artery FMD showed no change. The [HHb] and TSI% amplitudes were not different following EIMD ([HHb]: pre, 16.9 ± 4.7; post 17.7 ± 4.9; TSI%: pre, 71.0 ± 19.7; post 71.0 ± 19.7; all P > 0.05). At each progressive increase in workload (i.e., 0–100% peak), the [HHb] and TOI% responses were similar pre‐ and 48 h post‐EIMD (P > 0.05). Additionally, V˙O2max was similar at pre‐ (3.0 ± 0.67 L min−1) to 48 h post (2.96 ± 0.60 L min−1)‐EIMD (P > 0.05). Results suggest that moderate eccentric muscle damage leads to impaired local, but not systemic, macrovascular dysfunction.