Cerebral Oximetry in Lower Body Negative Pressure

Overview

The study aims to describe hemodynamic effects of lower body negative pressure (LBNP). 1. If and how changes in cerebral oxygen saturation (StO2) measured by near infrared spectroscopy (NIRS) relate to changes in blood flow in the carotid arteries during progressive LBNP. 2. If and how mean systemic filling pressure (MSFP) can be measured by brief occlusion of blood flow to an arm and if this relates to LBNP-level. 3. If and how pulse pressure variations and photoplethysmographic amplitude variations during positive expiratory pressure (PEP) and continuous positive airway pressure (CPAP) relate to LBNP-level.

Full Title of Study: “Cerebral Oxygen Saturation, Mean Systemic Filling Pressure and Haemodynamic Effects of PEP and CPAP in Lower Body Negative Pressure”

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: N/A
    • Intervention Model: Single Group Assignment
    • Primary Purpose: Diagnostic
    • Masking: None (Open Label)
  • Study Primary Completion Date: March 2017

Detailed Description

20 healthy volunteers will be included. The study protocol consists of two parts. 1. LBNP is applied stepwise (20 mmHg increments). At each LBNP-level, after 2 min stabilization, blood flow in internal and external carotid arteries is measured. Thereafter, MSFP is measured. LBNP is applied to -80 mmHg, but terminated sooner if the subject experiences signs of decompensation. Changes in cerebral StO2 will be related to relative changes in blood flow in the carotid arteries. After these measurements, blood flow to one arm will be occluded for 30 s. Venous pressure measured in an antecubital vein approximates MSFP. This will be related to volume status (LBNP-level and stroke volume reduction). 2. LBNP is applied stepwise (20 mmHg increments). At each LBNP-level, after 2 min stabilization, PEP and CPAP are applied at 0, 5 and 10 cmH20. LBNP is applied to -80 mmHg, but terminated sooner if the subject experiences signs of decompensation. Flow in carotid arteries is measured by ultrasound/Doppler. Skin blood flow in the forehead measured by laser Doppler flowmetry and transcutaneous oxygen saturation. If possible, blood flow velocity in a. cerebri media will be measured by transcranial Doppler. Central venous pressure will be approximated by measuring pressure in the left subclavian vein ("half-way" catheter). Cardiac stroke volume will be measured by suprasternal Doppler. Expiratory carbon dioxide (CO2) will be measured and recorded. Acral skin photoplethysmography performed using proprietary and custom-made photoplethysmographs. Arterial blood pressure approximated by finger volume-clamp method. The measurements above will be used for analyses of possible physiological mechanisms and post-hoc analyses.

Interventions

  • Other: Lower body negative pressure
    • Model of hypovolemia: Lower body negative pressure down to -80 mmHg (maximum).
  • Device: Continuous positive airway pressure
    • CPAP of 0, 5 and 10 cm water (H2O).
  • Device: Positive expiratory pressure
    • PEP of 0, 5 and 10 cm H2O.

Arms, Groups and Cohorts

  • Experimental: Lower body negative pressure
    • Single-arm, lower body negative pressure, continuous positive airway pressure, positive expiratory pressure.

Clinical Trial Outcome Measures

Primary Measures

  • StO2 (tissue oxygen saturation).
    • Time Frame: Approximatrly 30 min: From start LBNP (lower body negative pressure) exposure to 5 min after end LBNP.
    • Association between cerebral StO2 and flow in a. carotis interna.

Secondary Measures

  • MSFP, mean systemic filling pressure (arm venous pressure during vascular occlusion).
    • Time Frame: Approximatrly 30 min: From start LBNP (lower body negative pressure) exposure to 5 min after end LBNP.
    • Association between MSFP and volume status.
  • Dynamic variables and PEP (positive expiratory pressure)/CPAP (continuous positive airway pressure)
    • Time Frame: Approximatrly 30 min: From start LBNP (lower body negative pressure) exposure to 5 min after end LBNP.
    • Association between dynamic variables during PEP/CPAP and volume status. Dynamic variables (variations in arterial pressure and photoplethysmographic waveforms with respiration) are calculated during with PEP and CPAP during hypovolemia (lower body negative pressure).

Participating in This Clinical Trial

Inclusion Criteria

  • Healthy volunteer (informed consent) Exclusion Criteria:

  • Disease/physical condition limiting normal physical activity or requiring medication (except allergies/contraceptives) – History of syncope (except with obvious vasovagal etiology) – Cardiac arrhythmia – Pregnancy – Skin infections in the elbow crease

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: N/A

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

  • Lead Sponsor
    • Oslo University Hospital
  • Provider of Information About this Clinical Study
    • Principal Investigator: Svein Aslak Landsverk, MD, PhD – Oslo University Hospital
  • Overall Official(s)
    • Svein Aslak Landsverk, M.D., PhD, Principal Investigator, Oslo University Hospital

Clinical trials entries are delivered from the US National Institutes of Health and are not reviewed separately by this site. Please see the identifier information above for retrieving further details from the government database.

At TrialBulletin.com, we keep tabs on over 200,000 clinical trials in the US and abroad, using medical data supplied directly by the US National Institutes of Health. Please see the About and Contact page for details.