title: Functional changes cardiovascular: normobaric activity and microgravity in young healthy human subjects.
abstract: BACKGROUND
  The cardiovascular system works to maintain homeostasis through a series of adaptive responses to physiological requirements. Different self-regulatory mechanism prevent the effects induced by hydrostatic pressure changes on oncotic pressure caused by postural changes. Gravity exerts a strong influence on the postural changes with implications on the cardiovascular system. In orbit, gravity (+Gz) is responsible of mass redistribution of circulating blood flow. The aim of this study was the evaluation of the adaptive responses of cardiovascular system to postural changes with and without the use of the Lower Body Negative Pressure (LBNP). We considered that pressure changes that occur in human body in orbit can be simulated experimentally with use of Tilt-Test (Clino/ortho; Clino/head-down; head-down/ortho). This investigation could be useful for studying the influence on astronauts of long flights.
  
  
  METHODS
  We studied in 12 months, 30 young healthy volunteers (20 males, 10 female) during postural change tests. In the first evaluation they were submitted to tilt-test for 40 minutes, remaining in head-up +60 degrees (this state corresponds to a kind of gravitational stress +Gz) and in head-down to -30 degrees (-Gz) for 20 minutes. During the second assessment (after 5 +/- 1 days) all volunteers wear a device that simulate a state of LBNP at -20 mmHg. Afterwards, they were processed to 20 minutes in Head Down -8 degrees and after 2 hours of rest to 20 minutes at -15 degrees. Volunteers were monitored measuring blood pressure, heart rate and by Transthoracic Echocardiogram (TTE).
  
  
  RESULTS
  Collected data were elaborated by a statistical analysis. We observed during orthostatic position for 40 min (+60 degrees) without LBNP, lower diameters and volumes of left and right ventricular (p < 0.05) and an increase in heart rate in comparison with the baseline conditions in clinostatism. Despite the reduction of preload volume, the mean value of cardiac output does not vary significantly. In Trendelemburg (-15 degrees) data show a non-significant variation (p > 0.05) of left and right ventricular diameters and volumes, while cardiac output and systolic blood pressure varies significantly (p < 0.05) compared to clinostatic and orthostatic position. With LBNP in head down to -8 degrees and -15 degrees, systolic and diastolic arterial pressure, ventricular volumes and cardiac output were unchanged if compared to values obtained in clinostatism with and without LBNP. If compared to -30 degrees in Trendelemburg without LBNP, data reached statistical significance (p < 0.05).
  
  
  CONCLUSIONS
  The cardiovascular system and the autonomic nervous system, respond to postural changes and to volemia alterations, maintaining the physiological cardiac output, in order to preserve the metabolic requirements of body.
authors.affiliation: Department of Heart and Great Vessels "A. Reale", School of Medicine, Sapienza University of Rome, Italy. nicola.alessandri@uniroma1.it
authors.forename: N
authors.initials: N
authors.lastname: Alessandri
authors.forename: M
authors.initials: M
authors.lastname: Petrassi
authors.forename: F
authors.initials: F
authors.lastname: Tufano
authors.forename: A
authors.initials: A
authors.lastname: Dei Giudici
authors.forename: S
authors.initials: S
authors.lastname: De Angelis
authors.forename: F
authors.initials: F
authors.lastname: Urciuoli
authors.forename: C
authors.initials: C
authors.lastname: Alessandri
authors.forename: C
authors.initials: C
authors.lastname: De Angelis
authors.forename: E
authors.initials: E
authors.lastname: Tomao
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000399:Air Pressure; D018480:Astronauts; D001794:Blood Pressure / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D004244:Dizziness; D004452:Echocardiography; D005260:Female; D018475:Head-Down Tilt; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D011187:Posture / Q000502:physiology; D014893:Weightlessness; D018544:Weightlessness Countermeasures; D055815:Young Adult