Clinical Trial: Sex Hormones and Orthostatic Tolerance

Study Status: Completed
Recruit Status: Completed
Study Type: Interventional

Official Title: Sex Hormones and Orthostatic Tolerance

Brief Summary: This study is designed to determine the causes of "orthostatic intolerance" which occurs more commonly in women than in men. Orthostatic tolerance is the ability to remain standing up right for long periods of time, or to avoid dizziness when moving to standing from a seated or lying position.

Detailed Summary: In this study we are interested in determining the impact of female reproductive hormones (estrogen and progesterone) on orthostatic tolerance (described above) so we administer these hormones to participants. We also test participants' orthostatic tolerance in our laboratory and use this information to place subjects into groups.
Sponsor: Yale University

Current Primary Outcome:

• Orthostatic Tolerance [ Time Frame: 2 months ]
  We used a measure called cumulative stress index to determine orthostatic tolerance, which is the amount of time at a level of negative pressure each subject can maintain before feeling as if she is going to pass out. This is calculated by multiplying the pressure in mm Hg by the time in min.
• Baroreceptor Function [ Time Frame: 2 months ]

  This is a measure of how the body responds to changes in pressure induced by changes in position such as sitting, lying standing. The pressure changes are induced by gravity. The measurement described below to assess baroreceptor function is units of change in forearm vascular resistance for a given change in lower body negative pressure. This allows us to determine how good the body is at sending signals to the periphery to respond to postural changes.

  Baroreflex sensitivity is defined as the change in interbeat interval (IBI) in milliseconds per unit change in BP. For example, when the BP rises by 10 mmHg and IBI increases by 100 ms, BRS would be 100/10 = 10 ms/mmHg.

• Skin Microvascular Responses [ Time Frame: 2 months ]
  Changes in blood flow in the small vessel in the skin are measured in response to sequential heat and drug stimulation. It is measured in volts, and then corrected for a maximum level and expressed as "% max." This is measured with a Laser Doppler probes, which measures volts.

Original Primary Outcome:

• Orthostatic Tolerance [ Time Frame: 4 years ]
• Baroreceptor Function [ Time Frame: 4 years ]
• Skin Microvascular Responses [ Time Frame: 4 years ]

Current Secondary Outcome:

Original Secondary Outcome:

Information By: Yale University

Dates:
Date Received: June 28, 2010
Date Started: February 2006
Date Completion:
Last Updated: December 1, 2016
Last Verified: December 2016