Hemolysis in runners as evidenced by low serum haptoglobin: Implications for preflight monitoring of astronauts

Hematological parameters and serum haptoglobin were examined in 21 male employees of the Kennedy Space Center who were at 3 levels of physical activity: 7 subjects regularly ran more than 40 km (25 miles) per week (Group I); 7 ran 13 to 24 km (8 to 15 miles) per week (II), and 7 were sedentary (III). Blood was drawn on a different day of the week for five weeks. Differences between day of the week, visit number, and activity level were examined. No differences were observed for day of week or visit number; thus mean values for each variable were calculated for each subject. Variables did not differ among groups. However, trends with level of training were observed in some critical variables. Hemoglobin (Hb) and hematocrit (Hct) conformed to a staircase effect with Group I (14.5 gm/dl and 41.3 percent) lower than Group III (15.1 gm/dl and 42.9 percent). Reticulocyte count was higher and haptoglobin levels lower in Group I (1.35% and 75.7 gm/dl) than Group III (.99 percent and 132.9 gm/dl), with haptoglobin for the high mileage Group I in the clinically abnormal range. Since haptoglobin binds free Hb following RBC destruction, these results suggest that intravascular hemolysis occurs in trained male runners. These results may have special meaning for astronauts training before long-duration spaceflights, since the further reduction in red blood cells which is reported to occur during spaceflight could become detrimental to their health and performance

Face Immersion Bradycardia: Comparison of Swimmer and Nonswimmers

Author Institution: Department of Physiology, Wright State University ; Department of Physiology, George Washington UniversityA profound bradycardia may be exhibited by waterfowl and aquatic mammals when they dive underwater in search of food. A similar response occurs in humans diving underwater or simply wetting the face while breathholding. This bradycardia is mediated by the parasympathetic nervous system (vagus). We investigated whether the extent of this apneic face immersion bradycardia, or bradycardia during dry apnea, is greater in actively training competitive swimmers than in nonswimmers. Eight competitive swimmers and eight age/sex matched nonswimmers each performed apneic face immersion and dry apneic maneuvers while prone. Resting cardiac cycle (interval) duration was not significantly different between these groups, but the swimmers had a significantly longer interval duration (lower heart rate), P<0.05, and a greater percentage decrease of interval duration during both apneic face immersion and dry apnea. Swimmers—but not nonswimmers—demonstrated cardiac arrhythmias considered to be vagally mediated during face immersion. These results indicated that competitive swimmers in active training may have a greater range of parasympathetic nervous system (vagal) control of the heart as well as the well-accepted greater resting level of vagal tone

Relationships between coronary heart disease risk factors and serum ionized calcium in Kennedy Space Center Cohort

Kennedy Space Center (KSC) employees are reported to be at high risk for coronary heart disease (CHD). Risk factors for CHD include high serum total cholesterol levels, low levels of high-density lipoprotein cholesterol (HDLC), elevated triglyceride, smoking, inactivity, high blood pressure, being male, and being older. Higher dietary and/or serum calcium Ca(++) may be related to a lower risk for CHD. Fifty men and 37 women participated. Subjects were tested in the morning after fasting 12 hours. Information relative to smoking and exercise habits was obtained; seated blood pressures were measured; and blood drawn. KCS men had higher risk values than KCS women as related to HDLC, triglycerides, systolic blood pressure, and diastolic blood pressure. Smoking and nonsmoking groups did not differ for other risk factors or for serum Ca(++) levels. Exercise and sedentary groups differed in total cholesterol and triglyceride levels. Serum Ca(++) levels were related to age, increasing with age in the sedentary group and decreasing in the exercisers, equally for men and women. It is concluded that these relationships may be significant to the risk of CHD and/or the risk of bone demineralization in an aging population

Responses to LBNP in men with varying profiles of strength and aerobic capacity: Implications for flight crews

Hemodynamic and hormonal responses to lower-body negative pressure (LBNP) were examined in 24 healthy men to test the hypothesis that responsiveness of reflex control of blood pressure during orthostatic stress is associated with strength and/or aerobic capacity. Subjects underwent treadmill tests to determine peak oxygen uptake (peak VO2) and isokinetic dynamo meter tests to determine leg strength. Based on predetermined criteria, the subjects were classified into one of four fitness profiles of six subjects each matched for age, height, and weight: (1) low strength/low aerobic fitness; (2) low strength/high aerobic fitness; (3) high strength/low aerobic fitness; and (4) high strength/high aerobic fitness. Following 90 min of 6 degree head-down tilt (HDT), each subject underwent graded LBNP through -50 mmHg or presyncope, with maximal duration 15 min. All groups exhibited typical hemodynamic, hormonal, and fluid shift responses during LBNP, with no intergroup differences except for catecholamines. Seven subjects, distributed among the four fitness profiles, became presyncopal. Subjects who showed greatest reduction in mean arterial pressure (MAP) during LBNP had greater elevations in vasopressin and lesser increases in heart rate and peripheral resistance. Peak VO2 nor leg strength were correlated with fall in MAP or with syncopal episodes. We conclude that neither aerobic nor strength fitness characteristics are good predictors of responses to LBNP stress