title: Chronic head-down-tilt sleeping as physiological regulator of bone remodelling during diminished muscular activity in humans.
abstract: OBJECTIVE
  Head-down-tilt (HDT) sleeping with periodic fluid redistribution (PFR) assumes a significant importance by the possibility of regulating bone remodelling. We hypothesized that HDT sleeping with chronic PFR which expands fluid volume would contribute to and/or increase bone formation. Therefore, we studied the potential benefits of osteogenesis with HDT sleeping of chronic PFR during diminished muscular activity (hypokinesia; HK).
  
  
  METHODS
  Studies were conducted on 40 male healthy volunteers. They were divided into four groups: head-down-tilt sleeping control subjects (HDTSCS), head-down-tilt sleeping hypokinetic subjects (HDTSHS), active control subjects (ACS) and hypokinetic subjects (HKS). The iliac crest cancellous bone and trabecular bone volume and cortical thickness were measured during pre-experimental period of 390 days and experimental period of 360 days.
  
  
  RESULTS
  Iliac crest cancellous bone and trabecular bone volume and cortical thickness were increased (P<0·05) in the HDTSHS group compared to the HKS group. Iliac crest cancellous bone volume, cortical thickness and trabecular bone volume were reduced (P<0·05) in the HKS group compared to their pre-experimental values and the level in the other groups. In the HDTSCS group, iliac crest cancellous bone volume, cortical thickness and trabecular bone volume were increased much less than in the HDTSHS group. Bone mineral density was not affected in the ACS group compared to their pre-experimental values.
  
  
  CONCLUSIONS
  The current study shows the impact of chronic HDT sleeping with PFR on increases formation of bone demonstrating osteogenesis of bone during diminished muscular activity.
authors.affiliation: Institute of Hypokinetic Physiology, Athens, Greece.
authors.forename: Kostas K
authors.initials: KK
authors.lastname: Kakuris
authors.affiliation: Institute of Hypokinetic Biochemistry, Sofia, Bulgaria.
authors.forename: Yuri N
authors.initials: YN
authors.lastname: Yaroshenko
authors.affiliation: Institute of Hypokinetic Physiology, Athens, Greece.
authors.forename: Kirill P
authors.initials: KP
authors.lastname: Charapakhin
authors.affiliation: Institute of Hypokinetic Biochemistry, Sofia, Bulgaria.
authors.forename: Nikolay H
authors.initials: NH
authors.lastname: Neofitov
mesh_terms: D000328:Adult; D001706:Biopsy; D015519:Bone Density; D016723:Bone Remodeling; D018495:Fluid Shifts; D018475:Head-Down Tilt; D064368:Healthy Volunteers; D006801:Humans; D018476:Hypokinesia / Q000473:pathology / Q000503:physiopathology*; D007085:Ilium / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D010006:Osteoblasts / Q000473:pathology; D010010:Osteoclasts / Q000473:pathology; D012890:Sleep; D013997:Time Factors; D055815:Young Adult
keywords: bone density regulation; bone mineralization; cancellous bone; cortical thickness; periodic fluid redistribution; trabecular bone