title: Cardiovascular and pulmonary responses to increased acceleration forces during rest and exercise.
abstract: BACKGROUND
  The reduced cardiac output (CO) secondary to increased acceleration forces (+Gz) has applicability to daily life and pathophysiology. Increased +Gz and reduced CO affect the lung, resulting in reduced oxygen transport. A variety of studies have examined tolerance to high +Gz.
  
  
  METHODS
  The present study examines the effect of +1 to +3 Gz on steady-state cardiopulmonary variables at rest and while exercising at +2 Gz and +3 Gz. This study also looks at the deterioration of steady-state cardiopulmonary variables with sustained increased +Gz and after de-training in eight male centrifuge trained subjects.
  
  
  RESULTS
  CO (-1.53 L x min(-1)/+Gz), stroke volume (-30 ml/+Gz, SV), and pulmonary diffusing capacity (-3.42 ml x mmHg(-1)/+Gz, DL(co)) decreased linearly with increased +Gz at rest while heart rate (23 bpm/+Gz, HR), total peripheral resistance (0.0095 TPRU/Gz TPR), mean arterial pressure (13.2 mmHg/+Gz, MAP), and ventilation (4.13 L x min(-1)/+Gz, V(E)) increased linearly. During graded exercise, CO and SV increased less at +2 Gz and +3 Gz while MAP and VE increased more. Failure to endure increased +Gz and the effects of de-training were primarily due to the inability to regulate MAP.
  
  
  CONCLUSIONS
  The incremental increase in increased +Gz from 1 to 3 resulted in increased MAP, which was accomplished by increasing TPR sufficiently so as to offset the reduced CO. The effects of increased +Gz and reduced CO compromised lung function and oxygen transport (-18-30%), thus compromising exercise capacity. The failure to regulate MAP at lower increased +Gz levels resulted in intolerance to higher increased +Gz.
authors.affiliation: Center for Research and Education in Special Environments, Department of Physiology and Biophysics, School of Medicine and Biomedical Sciences, University at Buffalo, 124 Sherman Hall, Buffalo, NY 14214, USA. dpenderg@buffalo.edu
authors.forename: David R
authors.initials: DR
authors.lastname: Pendergast
authors.forename: Albert
authors.initials: A
authors.lastname: Olszowka
authors.forename: Leon E
authors.initials: LE
authors.lastname: Farhi
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D001794:Blood Pressure / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology*; D002498:Centrifugation; D004562:Electrocardiography; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D006112:Gravitation; D006801:Humans; D016014:Linear Models; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology; D011674:Pulse; D012146:Rest / Q000502:physiology*; D055815:Young Adult