Millions of people have been infected by SARS-CoV-2, or COVID-19, and recent estimates
suggest that up to 13% have developed Long COVID [1]. The World Health Organization
defines Long COVID as "the continuation or development of new symptoms 3 months after the
initial SARS-CoV-2 infection, with these symptoms lasting for at least 2 months with no
other explanation." SARS-CoV-2 is known to use angiotensin converting enzyme 2 (ACE2) to
enter cells [2], and ACE2 is located in endothelial cells throughout the cardiovascular
system contributing to significant vascular dysfunction [3]. Indeed, vascular function,
as measured by flow-mediated dilation (FMD) has been shown to be impaired in otherwise
healthy young COVID-19 survivors just 3-4 weeks after infection [4] and persists for at
least 6 months in patients who were hospitalized [5]. Recent work has shown a significant
correlation between low plasma taurine levels (a naturally occurring amino acid which can
help regulate cardiovascular and inflammation) and Long COVID symptoms, and the recovery
of taurine levels was associated with fewer adverse events [6]. Notably, twelve weeks of
taurine supplementation has been shown to improve blood pressure and vascular function in
pre-hypertension [7]. These improvements could, in turn, improve orthostatic tolerance
(i.e. lightheadedness while upright, a common symptom in Long COVID). Thus, the purpose
of the current proposal is to compare Long COVID patients who are or who are not taking
12-wks taurine supplementation, measuring vascular and orthostatic responses. We
hypothesize that those Long COVID patients taking taurine will have better vascular
function and orthostatic responses.

Participants: Drawing on the results of Sun et al. (2016) [7] to calculate a sample size,
we used an expected change in FMD of 3.2±4.7% with taurine supplementation, resulting in
a sample size of 19. To account for potential participant drop-out, we intend to recruit
30 Long COVID patients aged 18-65, including 15 males and 15 females. As this is a pilot
project, we will re-evaluate our sample sizes/statistical power when approximately 8
males and 8 females have been completed [8]. Duration and type of symptoms will be
recorded using the Symptom Burden Questionnaire for Long COVID. Autonomic function will
be assessed with the COMPASS-31 questionnaire and people with symptoms of orthostatic
intolerance and/or vasomotor impairment will be recruited. Sex and gender will be
self-identified and used as covariates. Any co-morbidities and medication use will be
recorded but not excluded.

Study Design: This will be an observational study where half of the participants will
already be taking taurine supplements and the other half will not. Each lab assessment
will take approximately 60 minutes. Participants will come to York University at baseline
and after 12 weeks of time has passed. During the first visit, they will be loaned a
Polar heart rate monitor and instructed in its use for home data collection.

1. Vascular function: Resting brachial artery FMD will be measured with Duplex
ultrasound imaging according to international guidelines [9]. Briefly, five minutes
of forearm vascular occlusion using a blood pressure cuff will be applied while
brachial artery diameter and flow are measured before, during and for 3 minutes
after cuff occlusion. Peak hyperemic brachial arterial velocity will also be
measured using Doppler ultrasound immediately after cuff release. Analysis of FMD
will be done with edge-detection software (Quipu) to expedite the analysis and
reduce measurement error [10]. Concurrently an EndoPAT device will also be used to
measure endothelial function.

2. Orthostatic responses (during supine rest and 5-min 70o head-up tilt):
Cardiovascular and respiratory measures: Heart rate will be measured by ECG, blood
pressure/cardiac output will be monitored using a beat-by-beat non-invasive blood
pressure device (NexFin), brain blood flow will be assessed with transcranial
Doppler ultrasound, and respiratory rate will be assessed using a Respitrace. Heart
Rate Variability (HRV): HRV provides an indicator of the autonomic control of heart
rate (i.e. parasympathetic and sympathetic balance [11]) and will be analyzed using
LabChart Pro 8.0 software in the supine and upright postures. Resting HRV will also
be assessed using a Polar heart rate device at home, weekly. The heart rate data
will be emailed to the students for analysis.

Analysis plan: Each variable described above will be measured before and after the 12-wks
time period. To test the study hypotheses, repeated measures analysis of variance will be
used to examine differences over time (SPSS). Sex, gender, and symptom duration will be
covariates.