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Research Containing: Stroke Volume

Pulse transit time measured by photoplethysmography improves the accuracy of heart rate as a surrogate measure of cardiac output, stroke volume and oxygen uptake in response to graded exercise

by on 22 August 2016in Biology & Biotechnology, Technology Development & Demonstration No comment

Heart rate (HR) is a valuable and widespread measure for physical training programs, although its description of conditioning is limited to the cardiac response to exercise. More comprehensive measures of exercise adaptation include cardiac output (Q), stroke volume (SV) and oxygen uptake (VO2), but these physiological parameters can be measured only with cumbersome equipment installed in clinical settings. In this work, we explore the ability of pulse transit time (PTT) to represent a valuable pairing with HR for indirectly estimating Q, SV and VO2 non-invasively. PTT was measured as the time interval between the peak of the electrocardiographic (ECG) R-wave and the onset of the photoplethysmography (PPG) waveform at the periphery (i.e. fingertip) with a portable sensor. Fifteen healthy young subjects underwent a graded incremental cycling protocol after which HR and PTT were correlated with Q, SV and VO2 using linear mixed models. The addition of PTT significantly improved the modeling of Q, SV and VO2 at the individual level ([Formula: see text] for SV, 0.548 for Q, and 0.771 for VO2) compared to predictive models based solely on HR ([Formula: see text] for SV, 0.503 for Q, and 0.745 for VO2). While challenges in sensitivity and artifact rejection exist, combining PTT with HR holds potential for development of novel wearable sensors that provide exercise assessment largely superior to HR monitors.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/25856085

The First 10 Years of Aerobic Exercise Responses to Long-Duration ISS Flights

by on 22 August 2016in Biology & Biotechnology No comment

INTRODUCTION: Aerobic deconditioning may occur during International Space Station (ISS) flights. This paper documents findings from exercise testing conducted before, during, and after ISS expeditions. METHODS: There were 30 male and 7 female astronauts on ISS missions (48 to 219 d, mean 163 d) who performed cycle exercise protocols consisting of 5-min stages eliciting 25%, 50%, and 75% peak oxygen uptake (Vo(2peak)). Tests were conducted 30 to 90 d before missions, on flight day 15 and every 30 flight days thereafter, and on recovery (R) days +5 and +30. During pre- and postflight tests, heart rate (HR) and metabolic gas exchange were measured. During flight, extrapolation of the HR and Vo2 relationship to preflight-measured peak HR provided an estimate of Vo(2peak), referred to as the aerobic capacity index (ACI). RESULTS: HR during each exercise stage was elevated (P < 0.05) and oxygen pulse was reduced (P < 0.05) on R+5 compared to preflight; however, no other metabolic gas analysis values significantly changed. Compared to preflight, the ACI declined (P < 0.001) on R+5, but recovered to levels greater than preflight by R+30 (P = 0.008). During flight, ACI decreased below preflight values, but increased with mission duration (P < 0.001). CONCLUSIONS: Aerobic deconditioning likely occurs initially during flight, but ACI recovers toward preflight levels as flight duration increases, presumably due to performance of exercise countermeasures. Elevated HR and lowered oxygen pulse on R+5 likely results from some combination of relative hypovolemia, lowered cardiac stroke volume, reduced cardiac distensibility, and anemia, but recovery occurs by R+30. Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/26630198

Orthostatic Intolerance After ISS and Space Shuttle Missions

by on 22 August 2016in Biology & Biotechnology No comment

INTRODUCTION: Cardiovascular deconditioning apparently progresses with flight duration, resulting in a greater incidence of orthostatic intolerance following long-duration missions. Therefore, we anticipated that the proportion of astronauts who could not complete an orthostatic tilt test (OTT) would be higher on landing day and the number of days to recover greater after International Space Station (ISS) than after Space Shuttle missions. METHODS: There were 20 ISS and 65 Shuttle astronauts who participated in 10-min 80 degrees head-up tilt tests 10 d before launch, on landing day (R+0), and 3 d after landing (R+3). Fisher’s Exact Test was used to compare the ability of ISS and Shuttle astronauts to complete the OTT. Cox regression was used to identify cardiovascular parameters associated with OTT completion and mixed model analysis was used to compare the change and recovery rates between groups. RESULTS: The proportion of astronauts who completed the OTT on R+0 (2 of 6) was less in ISS than in Shuttle astronauts (52 of 65). On R+3, 13 of 15 and 19 of 19 of the ISS and Shuttle astronauts, respectively, completed the OTT. An index comprised of stroke volume and diastolic blood pressure provided a good prediction of OTT completion and was altered by spaceflight similarly for both astronaut groups, but recovery was slower in ISS than in Shuttle astronauts. CONCLUSIONS: The proportion of ISS astronauts who could not complete the OTT on R+0 was greater and the recovery rate slower after ISS compared to Shuttle missions. Thus, mission planners and crew surgeons should anticipate the need to tailor scheduled activities and level of medical support to accommodate protracted recovery after long-duration microgravity exposures.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/26630196

Increased postflight carotid artery stiffness and inflight insulin resistance resulting from 6-mo spaceflight in male and female astronauts

by on 22 August 2016in Biology & Biotechnology No comment

Removal of the normal head-to-foot gravity vector and chronic weightlessness during spaceflight might induce cardiovascular and metabolic adaptations related to changes in arterial pressure and reduction in physical activity. We tested hypotheses that stiffness of arteries located above the heart would be increased postflight, and that blood biomarkers inflight would be consistent with changes in vascular function. Possible sex differences in responses were explored in four male and four female astronauts who lived on the International Space Station for 6 mo. Carotid artery distensibility coefficient (P = 0.005) and beta-stiffness index (P = 0.006) reflected 17-30% increases in arterial stiffness when measured within 38 h of return to Earth compared with preflight. Spaceflight-by-sex interaction effects were found with greater changes in beta-stiffness index in women (P = 0.017), but greater changes in pulse wave transit time in men (P = 0.006). Several blood biomarkers were changed from preflight to inflight, including an increase in an index of insulin resistance (P < 0.001) with a spaceflight-by-sex term suggesting greater change in men (P = 0.034). Spaceflight-by-sex interactions for renin (P = 0.016) and aldosterone (P = 0.010) indicated greater increases in women than men. Six-month spaceflight caused increased arterial stiffness. Altered hydrostatic arterial pressure gradients as well as changes in insulin resistance and other biomarkers might have contributed to alterations in arterial properties, including sex differences between male and female astronauts. Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/26747504

Midodrine prescribed to improve recurrent post-spaceflight orthostatic hypotension

by on 9 June 2015in Biology & Biotechnology No comment

Many astronauts exhibit post-spaceflight orthostatic hypotension due to inadequate norepinephrine release when in an upright posture. We hypothesized that an alpha1-adrenergic agonist, midodrine, would be an effective countermeasure. A female astronaut, who had problems with postflight orthostatic hypotension after a previous flight, consumed 10 mg midodrine after a subsequent flight, prior to her tilt test. Hemodynamic variables were compared between the two flights. Midodrine prevented severe falls in stroke volume, cardiac output and systolic pressure, and severe increases in heart rate without increasing vascular resistance, thus preventing orthostatic hypotension. This is the first report showing that midodrine has the potential to improve post-spaceflight orthostatic hypotension and suggesting that reduced venous return contributes to the etiology.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/15198285

24-hr blood pressure in HDT-bed rest and short-lasting space flight

by on 9 June 2015in Biology & Biotechnology No comment

In 2 ESA-cosmonauts we compared the 24-hr profiles in blood pressure (BP) and heart rate (HR) to those that we had observed in an earlier head-down tilted (HDT) bed rest study. In view of the lack of gravitational stress, an attenuated profile was expected, as in HDT. To obtain a full profile we measured automatic upper-arm cuff measurements in 2 cosmonauts, combined with PortapresTM recordings in one. Unlike HDT, actual microgravity did not result in attenuated circadian profiles. The levels of systolic and diastolic pressures tended to be slightly lower in flight. Only nighttime heart rate was significantly lower in Space.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/18372694

WISE-2005: adrenergic responses of women following 56-days, 6 degrees head-down bed rest with or without exercise countermeasures

by on 9 June 2015in Biology & Biotechnology No comment

We tested the hypotheses that women completing 56 days, 6 degrees head-down bed-rest (HDBR) would have changes in sensitivity of cardiovascular responses to adrenergic receptor stimulation and that frequent aerobic and resistive exercise would prevent these changes. Twenty-four women, eight controls, eight exercisers (lower body negative pressure treadmill and flywheel resistance exercise), and eight receiving nutritional supplement but no exercise were studied in baseline and during administration of the beta-agonist isoproterenol (ISO) and the alpha- and beta-agonist norepinephrine (NOR). In the control and nutrition groups, HDBR increased heart rate (HR) and reduced stroke volume (SV), and there was a significantly greater increase in HR with ISO after HDBR. In contrast, the HR and SV of the exercise group were unchanged from pre-HDBR. After HDBR, leg vascular resistance (LVR) was greater than pre-HDBR in the exercise group but reduced in control and nutrition. LVR was reduced with ISO and increased with NOR. Changes in total peripheral resistance were similar to those of LVR but of smaller magnitude, perhaps because changes in cerebrovascular resistance index were directionally opposite to those of LVR. There were no changes in sensitivity of the vascular resistance responses to adrenergic stimulation. The HR response might reflect a change in sensitivity or a necessary response to the reduction in SV after HDBR in control and nutrition groups. The reduced peripheral vascular resistance after HDBR might help to explain orthostatic intolerance in women. Exercise was an effective countermeasure to the HDBR effects.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/17928515

The Effects of Long-term Microgravity on Autonomic Regulation of Blood Circulation in Crewmembers of the International Space Station

by on 9 June 2015in Biology & Biotechnology No comment

The article presents the results of space experiment “Pneumocard”. The investigation involved all 25 Russian members of the ISS crew. The total of 226 sessions were made including 130 aboard the ISS, 50 prior to launch and 46 on return from mission. The objective was to study effects of the spaceflight factors on autonomic regulation of blood circulation, respiration and cardiac contractility during long-duration mission. The purpose was to secure new research data that would clarify our present view of adaptation mechanisms. Registered were the following signals: electrocardiogram, impedance cardiogram, seismic cardiogram, pneumotachogram, finger photoplethysmogram. A set of hardand software was used. Autonomic regulation of blood circulation by HRV analysis was investigated. It was shown that at the onset of a space mission parasympathetic involvement in regulation increases typically with subsequent mobilization of additional functional reserve. It guided the development of a functional states mathematical model incorporating the established types of autonomic regulation. Our data evidence that the combination of HRV analysis, pre-nosology diagnosis and probabilistic estimate of the pathology risk can reinforce the medical care program in space missions.

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