2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
90
ALTITUDE ATTENUATES APNEA-INDUCED INCREASE IN
HAEMOGLOBIN CONCENTRATION
Matt Richardson and Erika Schagatay
Environmental Physiology Group, Mid-Sweden University, Sundsvall, Sweden
Contact person: matt.richardson@miun.se
INTRODUCTION
During apnea at sea-level, a contraction of the spleen occurs in humans (Hurford et al
1990) causing a transient increase in hemoglobin concentration (Hb) and hematocrit
(Schagatay et al 2001). The development of these increases is progressive across 3
serial apneas, typically resulting in Hb increases of 2% (Richardson et al, 2003), and
recovery to pre-apneic values within 8-9 minutes (Schagatay et al 2005). The spleen
contraction-associated Hb increase is in part triggered by the hypoxia occurring
during apnea (Richardson et al 2005). The Hb increase leads to increased blood gas
storage capacity which facilitates prolonged apnea in humans and may be responsible
for the known prolongation of serial apneas (Schagatay et al 2001). At altitude, we
suggest that the chronic hypoxia could induce splenic contraction during eupnea in
humans, as previously observed in mice (Cook and Alafi 1956). Our aim was to
reveal whether spleen related Hb increase occurs during eupneic altitude exposure in
humans, thereby abolishing the Hb increase normally seen during apnea.
METHODS
This pilot study was conducted during an expedition to the Khumbu region in Nepal,
during which three male subjects performed 3 maximal apneas spaced by 2 minutes
rest at 1230m, 3840m, and 5100m above sea level. Apneas were performed both
during ascent and descent, each of which occurred over a period of two weeks during
the five-week expedition. Blood samples were obtained from the antecubital vein 2
minutes before the apneas (baseline), immediately following apneas (post-apnea) and
10 minutes after the final apnea (recovery), and analyzed via portable Hb analysis unit
(Hemocue, Ängelholm, Sweden). Urine flow was clear to pale yellow immediately
before each sampling session, as a gross estimate of euhydration. Apneic duration,
arterial oxygen saturation (SaO2) during eupnea and the nadir SaO2 resulting from
apnea were also recorded using a stopwatch and a portable oxygen saturation monitor
(Nonin Onyx, Nonin Medical, Minnesota USA), respectively.
RESULTS
At 1230m, SaO2 was 97%, baseline Hb was 143 g/L, SaO2 nadir after apnea was
93% and the post-apnea Hb increase from baseline was 4 g/L. As altitude increased,
baseline SaO2 decreased, baseline Hb values increased, while post-apnea changes in
Hb from baseline were smaller (Figure 1). At 5100m, SaO2 was 78%, baseline Hb
values were 181 g/L, SaO2 nadir was 74% and post-apnea Hb increases had
disappeared. This trend was reversed upon descent, and at 1230m post-apnea the
change from baseline (151g/L) was increased (6 g/L; Figure 1). Mean apneic duration
for the three apneas was negatively correlated to altitude, although mean durations
were longer during the descent trials when compared to the ascent trials (Figure 2).
An apneic duration increase across the 3-apnea series was observed at the lower
altitudes, both during ascent and descent, but at the highest altitude no increase within
the series was noted.