Purpose: The primary purpose of this investigation is to determine whether discrete
counterpressure maneuvers (CPM; exaggerated sway, rhythmic gluteal muscle clenching) can
demonstrably improve the return of blood to the heart and the blood pressure in
paediatric patients with recurrent uncomplicated syncope (fainting), and to assess
whether these discrete CPM are more effective than those commonly recommended in the
clinic (leg crossing, crouching).
Protocol: Volunteers (n=35) will be asked to attend one testing session. Testing will
take approximately 1.5 hours. Tests will usually be conducted in the mornings. On the day
of the test volunteers will be asked to have only a light breakfast avoiding caffeine,
and should avoid strenuous exercise for at least 12 hours prior to testing. Female
participants that have reached menarche will be asked to make a note of the date of their
last period (we would prefer to schedule testing on a day when they do not have, or
expect, their period because this may influence orthostatic tolerance).
Prior to testing volunteers will be asked a brief narrative medical history including
questions regarding their syncopal diagnosis, and as to whether they have any known
cardiovascular or neurological disease, are taking any medications, and questions about
general cardiovascular risk factors such as smoking, and alcohol consumption.
Participants will also be asked to complete a short questionnaire about their fainting
spells. All participants will be asked to self-identify their stage in pubertal
development ("Tanner" stage) based on drawn images of biologically male and female bodies
at each stage. If participants to not identify with these images, have difficulty
answering the question, or do not wish to answer for any reason, they do not have to do
so (and are not required to provide this reason). Participants will then complete the
PEDS-QL (Pediatric Quality of Life Inventory) and PAQ (Physical Activity Questionnaire).
Measures of height, weight and muscle mass will be taken using a height chart and
impedance-based weighing scale. Anthropometric measurements of body composition (skinfold
thickness: bicep, tricep, thigh, medial calf; circumference: mid-upper arm, mid-thigh,
mid-calf) will also be performed. A copy of the prompt sheet used by the investigators to
facilitate taking the medical history is included with the submission. This form outlines
the medical history data collected in general terms and is used to guide a narrative
history. Participants will be asked to empty their bladder in the nearby washroom, and to
retain a sample of their urine for testing for sodium levels (a marker of salt intake and
hydration). One the urine has been tested it will be discarded. No biological samples
will be retained. A brief instruction on the different tests of nervous system function
("Valsalva maneuver") and movement patterns (see below) will occur.
Participants will then be asked to lie down on a standard hospital style examination bed.
The investigators will then attach the following CSA approved cardiovascular monitoring
(all monitors are non-invasive and painless):
A standard 3 lead electrocardiogram (ECG) will be recorded to assess heart rate and
rhythm.
Beat-to-beat blood pressure will be determined using the Finometer blood pressure
monitoring device. This consists of a small Velcro cuff placed around the middle
finger that pulses gently against the digital arteries and records and displays
blood pressure with every heartbeat.
End tidal gases will be sampled using a nasal cannula. This is to enable us to
evaluate any influence of possible hyperventilation and the associated decreases in
carbon dioxide on cerebral blood flow.
Cerebral blood flow will be determined in the middle cerebral artery using Doppler
ultrasound. An ultrasound probe will positioned on the skin overlying the temple and
held in place with a head band. Participants can move their head freely when wearing
the ultrasound probe.
Brachial blood flow will be determined using an ultrasound probe positioned
overlaying the brachial artery in the upper arm. The probe will be positioned on the
participant's arm using an adjustable holder. It will only be in place during the
initial supine period, and the Valsalva maneuver.
Once the monitors are in place, participants will be asked to perform two Valsalva
manoeuvres, which is a test of parasympathetic and sympathetic control of the circulatory
system and cardiac baroreflex function. During this test, participants will blow out
against a closed tube to produce a Valsalva strain (performed as though they were blowing
up a balloon that would not inflate, generating a pressure of 40mmHg) and sustain this
for 20 seconds. The tube will be connected to a manometer (provides a pressure reading)
so the participant can regulate their expiratory pressure. The participant will perform
one Valsalva maneuver while lying supine, and a second while sitting upright. Responses
will be monitored continuously using the equipment mentioned above.
Next, the participants will complete a 5-minute supine rest period, after which they will
be asked to rise from the supine to the standing position and stand on the force platform
while we record their cardiovascular and cerebrovascular responses for 5 minutes.
Volunteers will stand without shoes, and will be asked not to move their feet for the
duration of each standing trial. Following this, volunteers will perform four more bouts
of a 5-minute supine period, followed by a 5-minute standing period on the force
platform. During each of these trials, they will perform one of the following movements:
Exaggerated anterior-posterior sway: rocking the body in a fore-aft motion, as far
as comfortably possible without raising the heels or toes off the force platform
Gluteal clenching: rhythmic tensing of the thighs and buttocks
Crouching: lowering body to the floor in a crouched position
Leg crossing with muscle tensing: standing with legs crossed for the first 4 minutes
of the trial, clenching legs in the crossed position for the final minute.
These standing trials will be completed in a randomized order. Following their
completion, testing will be concluded. The monitoring equipment will be removed and any
residue from the ultrasound gel will be wiped away by the participant.
Testing will stop if the volunteer experiences symptoms of presyncope, decreased blood
pressure (<80mmHg systolic pressure for greater than 5 consecutive heart beats), slowing
of the heart rate (new onset bradycardia below 50bpm), or at the participant's request.
In such an instance the participant will be asked to lie flat until any symptoms or signs
of presyncope resolve. If participants meet criteria to stop testing during one of the
standing phases, but haven't yet finished all standing phases, they can decide if they
want to try the next standing phase, or stop testing all together.