| | Several
lines of converging evidence support the hypothesis that the autonomic
nervous system (ANS) is involved in the development and expression
of chemotherapy-induced nausea. Many of the clinical symptoms commonly
reported by patients as associated with chemotherapy-induced nausea
are manifestations of autonomic nervous system activity. For example,
physical manifestations such as pallor, sweating, and feeling hot/cold
all over commonly precede or accompany nausea.
Following are findings
that suggest a role for the autonomic nervous system in the development
and expression of chemotherapy-induced nausea:
- Parasympathetic
changes have been related to the expression of nausea resulting
from illusory self-motion (Hu
et al., 1991; Muth
et al., 1996; Muth
et al., 1998).
- Basal ANS tone has
been shown to be related to anticipatory or conditioned nausea
induced by anti-cancer chemotherapy (Kvale
et al., 1991).
- A relationship between
autonomic dysfunction and chemotherapy-induced nausea and vomiting
has been reported (Bellg
et al., 1995; Morrow
et al., 1992).
- Studies also suggest
that that changes in parasympathetic activity may mediate symptoms
associated with nausea. For example, changes in parasympathetic
outflow may be of practical use in identifying the transition
from the prodromal phase (including nausea) to the expulsive
phase of the emetic reflex (Andrews
et al., 1993; Andrews et al.,
1995).
Figure 3.1 shows that
an increase in parasympathetic activity seems to set the stage
for the expression of nausea. Cardiac Parasympathetic (vagal)
activity as indicated by heart rate variability, measured as the
standard deviation of successive differences (SDSD) in beat-to-beat
intervals, was assessed in 24 women with ovarian cancer immediately
prior to and accompanying nausea that occurred following anti-cancer
chemotherapy. A progressive increase in SDSD followed infusion
of the chemotherapy agent, indicating a rise in cardiac parasympathetic
(vagal) activity, with onset of nausea consistently occurring
after the peak activity had been reached, at a time when SDSD
was decreasing (Morrow
et al., 1999).
| Figure
3.1: Parasympathetic Activity
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Recent research seeks
to isolate the ANS factors that are involved in nausea and vomiting
with the hope of controlling the individual factors within the
treatment environment. Yet there are a number of issues that cloud
this endeavor, not the least of which is the intimate connection
between the physiological and psychological factors that linking
these side effects.
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