Interpretation
Wearing a mask can create a
hard-to-ventilate space providing low oxygen environment that can have
physiologic consequences. As an example, hypoxia may stimulate
erythropoietin secretion, which in turn increases reticulocytes
production4. The reticulocytes will eventually mature
to red blood cells, manifested as elevated hemoglobin levels. A study
conducted by
Vij
et al., investigated the effect of chronic hypoxia on hematologic
parameters. The study followed 40 healthy men’s hemoglobin, fibrinogen,
platelets and white blood cells concentration at sea level and at the
following 3- and 13-months sojourn at high altitude. The study’s results
suggest that prolonged stay at high altitude leads to elevated
hemoglobin and fibrinogen levels and a lower platelet and white blood
cells levels3. Due to the function of hemoglobin as an
oxygen carrier throughout the cardiovascular system, higher levels of
hemoglobin lead to greater Vo2-max capacity, enabling
better physical performance. A common practice in the elite athletes’
field is training in high altitude, in an intent of utilizing this
phenomenon5. Due to geographical limitations, not all
athletes are able to train in high altitude, possibly preventing them
from gaining high-altitude training advantages. For this reason,
elevation-masks were developed in a purpose of imitating the oxygen
deprivation conditions present in high-altitude. Theses masks use a
valve system to reduce the amount of airflow to the lungs. In this study
we report the same results as did
Vij
et al. Hemoglobin and fibrinogen levels increase while platelets and
white blood cells levels decrease. A possible explanation is that
wearing a mask throughout the day during the COVID-19 pandemic has the
same hematologic effect as does the elevation-masks.
We have found higher post-partum hemorrhage rates during the
mask-wearing period, and a lower platelet count. The American College of
Obstetricians and Gynecologists classifies platelet count less than 70
k/microliter as a risk factor for post-partum hemorrhage. Nevertheless,
Shravya et al. reported a twofold greater likelihood of post-partum
hemorrhage among women with mild thrombocytopenia (platelet count
100–149 k/microliter)6. Our results may reflect the
same consequences of mild thrombocytopenia on post-partum hemorrhage
rates.
The elevated hemoglobin levels may be a plausible explanation to our
reported lower rates of preterm birth and composite neonatal outcome.
Hemoglobin concentrations greater than 14.6 g/dL at prenatal visits were
previously associated with increased risk of preterm birth, stillbirth
and growth restriction7,8. Conversely, relative
elevations of hemoglobin levels can protect against anemia during
pregnancy, previously associated with adverse obstetrical outcomes
including preterm birth, low birth weight, stillbirth and neonatal
mortality9,10. These results can potentially reflect
an effect of anemia correction due to hemoglobin elevation.
Additionally,
A proposed underlying mechanism for the pregnancy outcomes is the
induction of heme oxygenase-1 (HO-1) during hypoxia11.
HO-1 induction has been shown to improve pregnancy outcome, reduce the
rate of placental mediated complications12 and of
spontaneous preterm birth13.
Reported preterm birth rates during the COVID-19 pandemic are scarce,
and mainly include women infected with COVID-1914. A
previous report regarding preterm births during the pandemia among women
who were mostly not infected with COVID-19 did not find a difference in
preterm birth rates15. A possible explanation for the
difference between the two studies are different populations studied and
different sample sizes.
Mask wearing may also have significant impact on high risk populations
such as elderlies, patients suffering from cardiac and hematologic
diseases, as well as patients with lung diseases such as chronic
obstructive pulmonary disease and asthma. First and foremost, these
populations may bare increased sensitivity to altered blood composition,
as described, and consequent cardiac activity. Additionally, though not
evaluated in our study, the presence of a mask may also increase
air-flow resistance, thereby deteriorating spirometric measurements.